Citation
Coastal engineering study of proposed Navarre Pass

Material Information

Title:
Coastal engineering study of proposed Navarre Pass
Series Title:
UFLCOEL
Creator:
University of Florida -- Coastal and Oceanographic Engineering Laboratory ( Originator )
University of Florida -- Engineering and Industrial Experiment Station
Florida -- Santa Rosa County Beach Administration ( Funder )
Place of Publication:
Gainesville Fla
Publisher:
University of Florida
Publication Date:
Language:
English
Physical Description:
xv, 132 leaves, 3 plates of maps (folded) in envelope : ill, maps, photos. ; 28 cm.

Subjects

Subjects / Keywords:
Coastal engineering -- Florida ( lcsh )
Littoral drift -- Florida ( lcsh )
Inlets -- Planning -- Florida ( lcsh )
Santa Rosa Sound (Fla.) ( lcsh )
Models -- Navarre Pass Inlet (Fla.) ( lcsh )
Coastal and Oceanographic Engineering thesis M.S
Coastal and Oceanographic Engineering -- Dissertations, Academic -- UF
Genre:
bibliography ( marcgt )
technical report ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 76-77).
Funding:
Sponsored by Santa Rosa County Beach Administration.
General Note:
"February 1973."
Statement of Responsibility:
by Coastal and Oceanographic Engineering Laboratory, Florida Engineering and Industrial Experiment Station.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida
Resource Identifier:
09958161 ( OCLC )

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Full Text
COASTAL ENGINEERING STUDY

OF
PROPOSED NAVARRE PASS
-7,3-00,6
Sponsor:
Santa Rosa County Beach Administration
Submitted by: Coastal and Oceanographic Engineering Laboratory
Florida Engineering and Industrial Experiment Station
University of Florida
Gainesville, Florida February, 1973




ABSTRACT

This report describes the results of a coastal engineering field and numerical study of the proposed Navarre Pass. The field measurements are based on three field trips during which bathymetry and tides and currents were measured. The numerical model simulates the tides and flows in Santa Rosa Sound and is capable of including the effects of Navarre Pass. Littoral drift direction and magnitude are of considerable importance in planning the inlet; calculations were carried out using shore-based observations obtained in a program of the Coastal Engineering Research Center.
The results of the study indicate that:
1. Navarre Pass would only reduce slightly the
equilibrium cross-sectional flow areas into
Pensacola (1.8%) and Choctawhatchee (0.1%)
Bays.
2. The velocities through Navarre Pass would
be well within the limits considered safe
for small craft navigation.
3. Planning for artificial transfer of sand
should be based on an annual rate of
200,000 cubic yards to the west. Initial disposition of dredged material should be as a feeder beach on the west side of the
Pass.
4. The Pass would cause a localized moderation
of Sound salinities in the vicinity of the Pass.




5. The tide and geometric characteristics are
such that Navarre Pass will always tend to
close unless maintained open by jetties.
Based on these results, it is concluded that if proper financial provision is made for construction and maintenance of the inlet, there should be no significant adverse effects to the stability of the Santa Rosa Island Beaches, nor to the adjacent waters.

iii




TABLE OF CONTENTS
Page
ABSTRACT .. ......................................... 1.
LIST OF TABLES ..................................... vii
LIST OF FIGURES .................................... viii
LIST OF SYMBOLS .................................... xii
ACKNOWLEDGEMENTS ................................... xiv
I. INTRODUCTION ............................... 1
II. PURPOSES OF STUDY .............................. 3
Impact of Pass on Natural
Processes ..............................3
Conceptual Design Features
of Navarre Pass .......................4
III. BRIEF HISTORY OF NAVARRE PASS ..................5
IV. METEOROLOGY AND HYDROGRAPHY OF AREA .......... 12
General Description ..................... 12
Winds ................................ 13
Sea ..................................13
Swell ................................ 17
Tides ................................ 17
Offshore Currents ....................... 19
Santa Rosa Sound Currents .............. 22
V. FIELD STUDIES AND RESULTS ...................... 25
Field Trip No. 1,
May 13-18, 1970 ....................... 25
Field Trip No. 2,
December 7-12, 1970 .................. 32
Field Trip No. 3,
July 19-23, 1971 ...................... 38




TABLE OF CONTENTS-Continued

Page
VI. LITTORAL DRIFT ............................. 42
Introduction ............................ 42
Littoral Drift Estimates ............. 43
Experimental Groin at Navarre ........ 51
Summary and Recommendations ............. 61
VII. SUMMARY OF NUMERICAL MODEL CALCULATIONS ............................ 62
Introduction ............................ 62
Results Obtained Using the
Numerical Model ...................... 63
Effect of Navarre Pass on Entrances
to Pensacola and Choctawhatchee
Bays .............................. 63
Maximum Velocities Through
Navarre Pass ...................... 64
Relative Stability of
Navarre Pass ...................... 64
VIII. RECOMMENDED DESIGN OF NAVARRE
PASS INLET .............................. 65
Functional Design .................... 65
Recommended Layout of Navarre Pass ... 65
Disposition of Initially
Dredged Material .................. 73
Alternate Designs .................... 74
IX. SUMMARY AND CONCLUSION ..................... 75
Summary ................................. 75
Conclusion .............................. 75
X. REFERENCES ................................. 76
APPENDIX
I. NUMERICAL MODEL OF THE BAY SYSTEM
AFFECTING NAVARRE PASS .................. 78
Introduction ............................ 78
Derivation of the Numerical Model ....... 79




TABLE OF CONTENTS-Continued

Page
Governing Differential Equations ... 79
Finite Difference Equations..............82
Boundary Conditions.................... 83
Application of the Numerical
Model................................... 86
Assessment/Calibration of the
Numerical Model..................... 87
Use of Numerical Model to Evaluate
Effect of Navarre Pass................98
Maximum Velocities Through
Navarre Pass......................... 101
II. STABILITY OF NAVARRE PASS..................... 103
Introduction.............................. 103
Method.................................... 103
Numerical Model......................... 105
Sedimentary Stability................... 105
Equilibrium Cross-Sectional
Area................................ 109
Application of Stability Equilibrium
Concepts to Navarre and
Rollover Passes......................... 112
Navarre Pass........................... 115
Rollover Pass.......................... 123
Conclusion Regarding Relative
Stability of Navarre and
Rollover Passes......................... 123
III. GLOSSARY OF TERMS............................. 130
Introduction.............................. 130




LIST OF TABLES

Table Page
I Summary of Field Trip Activities
and Information Obtained.......................26
II Summary of Median Diameters of
Sand Samples Analyzed (Field
Trip of May 1970)............................. 31
III Summary of Calculated Littoral Drift Using LEO Data......................... 50
1-1 Characteristics of Schematized Bay/Inlet System.............................. 88
1-2 Summary of Measured Tidal Characteristics............................... 89
1-3 Dimensions Used in Flow Calculations at Navarre Bridge............................. 94
1-4 Predicted Effect of Navarre Pass on Flows in and out of Pensacola and
Choctawhatchee Bays........................... 99
I-5 Calculated Maximum Discharges and Velocities Through Navarre Pass
for Various Tidal Ranges...................... 102
11-1 Ratio i, R, of Maximum to Minimum
Tidal Ranges During the Period
January 1 to February 9, 1970.................116

vii




LIST OF FIGURES

Figure Page
1 Location Map of Santa Rosa
Island Region .............................. 2
2 Aerial Photograph Prior to Navarre
Pass Cut (Date of Photograph:
February 14, 1963) ......................... 6
3 Oblique View of Gulf Terminus of
Navarre Pass (Date: Unknown,
but Probably August, 1965) ................. 7
4 Aerial Photograph of Navarre Pass
Showing Effect of Westerly Littoral
Drift (Date of Photograph: On or
About September 1, 1965) ................ 8
5 Oblique View of Navarre Pass Shortly
After Closure (Date of Photograph:
September 1965) .......... o ......... 9
6 Aerial Photograph Showing Filling of
Pass by Air and Water Transported
Sand (Date of Photograph: June 1970) ..... 11
7 Data Squares in Gulf of Mexico and
Caribbean Sea ....... o..o ................... 14
8 Monthly Wind Roses at Data Square
Off Navarre Pass Area .... o .... o ............ 15
9 Monthly "Sea" Roses at Data Square
Off Navarre Pass Area .................... 16
10 Monthly Swell Roses at Data Square
Off Navarre Pass Area ...................... 18
11 Predicted Tides at Galveston, Pensacola and
Miami Harbor Entrances ........ o ............ 20

viii




LIST OF FIGURES-Continued

Figure Page
12 Example of Measured Tides in Gulf
of Mexico and Santa Rosa Sound ............. 21
13 Measured Currents Offshore Navarre
Beach, Florida. May 15-16, 1970 ........... 23
14 Currents Measured at Navarre
Bridge, December 9-11, 1970 ................ 24
15 Measured Tides in Gulf of Mexico
and in Santa Rosa Sound During
Field Trip of May 13-18, 1970 .............. 27
16 Locations of Principal Measurements
Conducted During Field Trips ............... 28
17 Location of Tidal Division Line
at 1545 on May 16, 1970 .................... 30
18 Beach Profiles, December 9, 1970 ........... 33
19 Measured Tides in Gulf of Mexico and
in Santa Rosa Sound During Field Trip
of December 7-12, 1970 ..................... 37
20 Measured Tides in Gulf of Mexico and
in Santa Rosa Sound During Field Trip
of July 19-23, 1971 ........................ 39
21 Experimental Groin Under Construction ...... 41
22 Coastal Sector Method Used by Coastal.
Engineering Research Center in
Reporting Wave Direction ................... 48
23 Locations of CERC LEO Data Used in
Littoral Drift Calculations. Drift
Directions and Net Annual Rates
Also Shown ................................. 49
24 Photographic History of Navarre Experimental
Groin ...................................... 52-59




LIST OF FIGURES-Continued
Figure Page
25 Weir Jetty System at Hillsboro
Inlet, Florida................................ 68
26 St. George Island Cut. Note Erosion
Where Bank Protection is Not
Provided...................................... 71
1-1 Bay System Represented in Numerical Model............................... 80
1-2 Illustration of Bay Segment Representation................................ 84
1-3 Schematization of Pensacola Bay/ Choctawhatchee Bay/Santa Rosa Sound/
Gulf of Mexico System........ ................ 85
1-4 Comparison of Measured and Calculated Ratios of Sound to Gulf Tidal Ranges
Versus Gulf Tidal Range...................... 91
1-5 Comparison of Measured and Calculated Phase Lags Between Gulf and Sound
Tidal Extremes................................ 92
1-6 Comparison of measured and Computed Santa Rosa Sound Tides and
Discharges.................................... 95
11-1 Schematic Illustrating Stability Analysis
for Single and Multiple Inlets................104
11-2 Illustration of Escoffier's Stability
Concept...................................... 107
11-3 Equilibrium Cross-Sectional Area and
Tidal Prism Relationship (From O'Brien) .... 111
11-4 Variation of Maximum Inlet Velocity with
Cross-Sectional Area for Equilibrium
Conditions................................... 113
11-5 Variation of Maximum Velocity with Inlet
Cross-Sectional Area and Tidal Range.
Navarre Pass, Florida.............. ........... 114




LIST OF FIGURES-Continued

Figure Page
11-6 Predicted Tides at Galveston, Pensacola and Miami Harbor Entrances. Note Differences in Tidal Range Variations ............ 117
11-7 Cumulative Probability Distributions for Predicted Gulf Tidal Ranges at
Navarre and Rollover Passes ................ 119
11-8 Auxiliary Diagram for Determination of Tidal Range Corresponding to
Sedimentary Equilibrium (Example
Shown for AC = 5000 ft2) ................... 120
11-9 Stability Analysis for Navarre Pass, Florida .............................. 122
II-10 Area Map Showing Location of Rollover Fish Pass ......................... 124
II-11 Numerical Model Representation of Galveston Bay .............................. 125
11-12 Variation of Maximum Velocity with Inlet Cross-Sectional Area and Tidal
Range Rollover Fish Pass, Texas .......... 126
11-13 Stability Analysis for Rollover
Fish Pass, Texas ........................... 127




LIST OF SYMBOLS

Symbol Description
A,, A2 Flow areas through Navarre Bridge
Ac Cross-sectional flow area of inlet
ACE Equilibrium cross-sectional flow area
A* Critical cross-sectional flow area
C
A Plan area of bay segment
P
Cf Wind stress coefficient
D Total depth = h + n
f Darcy-Weisbach friction factor
g Gravitational constant
-G Subscript referring to "Gulf" variable
h Depth below mean sea level
K Entrance loss coefficient
en
K Exit loss coefficient
ex
z Length of bay segment or inlet
n Exponent of velocity in sediment transport
relationship
n Subscript referring to nth bay segment
p Tidal prism
P Probability in percent
q Discharge per unit width in the x-direction
q R Runoff in cubic ft/sec per foot of bay
length

xii




LIST OF SYMBOLS-Continued

Symnbol1 Description
Q Total discharge across bay segment or through
inlet
R Ratio of maximum to minimum tidal ranges
R Hydraulic radius, also tide range
S Subscript referring to "Sound" variable or
"Spring" tidal range
t Time
T Tidal period
U Wind speed at 30 ft reference elevation
V Water velocity, in bay segment or through
inlet
w Width of bay segment considered .x Horizontal distance coordinate aligned with
bay axis
y Horizontal distance coordinate perpendicular
to bay axis
Angle of wind vector relative to bay axis
'n Water surface displacement from mean sea
level, positive upwards
7r Numerical constant, 3.14159 ...
P mass density of water
Pa Mass density of air
a Angular frequency of tide
T Wind stress on water surface
1
T b Frictional stress on bottom of water column

xiii




ACKNOWLEDGEMENTS

Many individuals have contributed in a variety of ways to the study reported herein. The efforts of the Staff of the Department of Coastal and Oceanographic Engineering who participated in the field program are appreciated.
The cooperation of the Santa Rosa County Beach
Administration was most helpful, and the interaction and discussions with Messrs. Baskerville and Escoffier of Baskerville-Donovan Engineers, Inc., contributed to the final design presented in this report. Captain R. W. Slye kindly photographed the experimental groin and provided comments regarding its performance. Mr. W. J. Wells was instrumental in implementing this study and maintained an interest throughout the investigation.
Mr. Walter Burdin of the Mobile District of the U. S. Army Corps of Engineers provided several aerial photographs and a continuing interest in this project.
The Coastal Engineering Research Center willingly provided their Littoral Environmental Observation (LEO) data which included observations of wave height, period and direction. Mr. Curtis Baskette, a Graduate Student, became interested in and developed a computer program to compute littoral drift from the LEO data.

xiv




The study was under the general direction of R. G. Dean, Professor of Coastal and Oceanographic Engineering.




I. INTRODUCTION

In May, 1970, the Santa Rosa County Beach
Administration contracted with the Coastal and Oceanographic Engineering (COE) Department of the University of Florida to carry out a coastal engineering study of the proposed Navarre Pass through Santa Rosa Island. Santa Rosa Island is a narrow barrier island with an east-west axis paralleling the mainland; the island is separated from the mainland by Santa Rosa Sound, see Figure 1. The proposed site for Navarre Pass is approximately at the mid-point of the Island and several thousand feet east of the Navarre Bridge; the approximate latitude and longitude of the Pass Site are: 30*231 N and 86151'10" W, respectively.
The Pass was first cut through the Island in July, 1965, however by September, 1965, the cut had widened and shoaled and was impassable to small craft. Since closing, the Pass reportedly has been reopened at least twice by a hurricane (Camille, 1969) and a severe winter storm. In December, 1970, the berm elevation across the original cut had been built up to an elevation of approximately +6 ft MSL.

- 1 -




Pensacola Bay -

Boy

'East Bay

Choctawhatchee

Navarre Snta .Pass osnta Location
Rosa
Island

GULF

OF

MEXICO

MAP OF SANTA ROSA ISLAND REGION

Bay

Destin (East) Pass

FIGURE I LOCATION




II. PURPOSES OF STUDY

The two primary purposes of the study include:
(1) The impact of the Pass on natural processes, and (2)
Recommendations relative to the conceptual design of the
Pass.
Impact of Pass on Natural Process
The various natural processes of interest in this
study are discussed in the following paragraphs.
1. Beach stability.--The possible effect of the Pass
on the adjacent beaches was the consideration of greatest concern. Santa Rosa Island beaches are
presently some of the finest in the State, are
unencumbered by groin and seawall structures and
are relatively stable. The deleterious effects
on beach stability of inlet excavation and/or modification along the Florida East Coast has justifiably caused concern relative to future
inlet modification. The littoral drift*
characteristics in the area are particularly
relevant to the matter of beach stability. The quantities and directions of littoral drift are
also of interest in the configuration of the
jetties, design of bypassing features and
financial provision to mechanically transfer
the sand interrupted by the presence of the Pass
and jetties.
2. Stability of neighboring passes.-T1he passes to
the east and west (East Pass and Pensacola Bay Entrance, respectively) would be influenced to
some extent by the proposed Navarre Pass. It is
conceivable that the water flowing through the
Pass could "capture" a significant amount of the
flow presently occurring through East Pass and
Pensacola Bay Entrance, thereby causing these
*Glossary of terms is provided as Appendix III.

-3 -




passes to shoal and a resulting increased
dredging requirement or a decreased equilibrium
cross-sectional area.
Conceptual Design Features of Navarre Pass
Based on the results of the study, recommendations
will be presented relating to the following conceptual
design features of the Pass:
1. inlet dimensions and layout.--TEhe primary factors
considered in the inlet dimensions and layout will be: safe navigation, minimum effects on
adjacent beaches, effect on neighboring passes,
and maintenance costs.
2. Sand transfer and disposition of initial
excavation material.-'I'he initial and maintenance
sand disposition including quantities will be
recommended so as to result in a minimum
interruption of the natural sand transport
processes and beach stability.
3. Channel protection. -Unless provided with
adequate protection against erosion, the banks
of the cut and dunes will erode due to water
and wind forces and tend to deposit in the Pass.
The resulting deposition of material can interfere
with navigation and cause an added dredging
cost. Rip-rap or vertical sheet piling will
represent the best form of bank protection in
the cut whereas vegetation, if properly maintained
could provide good protection against erosion
by wind of the dunes and portions of the cut
above water.

-4 -




III. BRIEF HISTORY OF NAVARRE PASS

Navarre Pass was originally cut in July, 1965, by a pipe-line dredge at a cost of $30,000. The original dimensions were 100 ft wide by 9 ft deep. The primary purposes of the Pass included a more direct access to Snapper grounds and to provide a general economic stimulus to this portion of the Santa Rosa Island area.
Figures 2 and 3 are aerial photographs prior to the Pass dredging and shortly after the dredging, respectively. The date of the photograph in Figure 3 is not known, but was probably taken in August, 1965. Note that some narrowing of the mouth of the Pass has occurred on the east side indicating the effect of westerly littoral drift. The photograph presented in Figure 4 was taken on or about September 1, 1965, and presents a more advanced case of deposition against the near-Gulf portion of the east side of the cut. The shoaling is not apparent from this photograph, but probably has reached an advanced stage. Figure 5 represents a photograph taken in September, 1965, after complete closure of the Pass. Again the effects of the westerly littoral drift in displacing the channel to the west are evident. Hurricane Betsy occurred during September 8-11, 1965, and presumably

-5 -




f2 I
~N

2 AERIAL PHOTOGRAPH
NAVARRE PASS CUT
PHOTOGRAPH: FEBRUARY

PRIOR (DATE
14,

-6-

4L41
41k 0

FIGURE

TO OF 1963)

w




v* '.4-*,low

'~ ~

FIGURE 3

OBLIQUE VIEW OF OF NAVARRE PASS PROBABLY AUGUST,

GULF TERMINUS (DATE: UNKNOWN,
1965)

-7-

~.

.7 u~ ~




41

FIGURE 4 AERIAL PHOTOGRAPH OF NAVARRE
PASS SHOWING EFFECT OF WESTERLY
LITTORAL DRIFT (DATE OF
PHOTOGRAPH ON OR ABOUT
SEPTEMBER I 1 1965)




FIGURE 5 OBLIQUE VIEW OF NAVARRE PASS
SHORTLY AFTER CLOSURE (DATE OF
PHOTOGRAPH:. SEPTEMBER 1965)

-9




was instrumental in the rapid development of the final closure stages.
As shown in Figure 6, by June, 1970, the Pass
had filled substantially so that the only remnants of the channel remaining below water are at the Sound side of the Pass.
According to R. Bruno (1), the Pass has been opened naturally on at least two occasions since 1965. One of these occurred during Hurricane Camille in August, 1969 and the other opening resulted from a winter storm. No information is available concerning the extent of these openings nor of the magnitudes of the resulting flows through the Pass Site. Presumably the Pass closed fairly rapidly after each opening.

- 10 -




FIGURE 6 AERIAL PHOTOGRAPH SHOWING
FILLING OF PASS BY AIR
AND WATER TRANSPORTED
SAND (DATE OF PHOTOGRAPH:
JUNE 1970)

- 11 -




IV. METEOROLOGY AND HYDROGRAPHY OF AREA

General Description
The general offshore region near Santa Rosa Island is characterized by prevailing easterly winds with strong northerly winter winds. The easterly winds result in predominately southeasterly waves occurring in the nearshore region. These waves are responsible for the predominately westerly littoral drift. Tides in this area are predominately diurnal (i.e., a period of 24 hours) with the diurnal tidal range at Pensacola listed at 1.3 ft. During the field trips conducted in conjunction with this study, Gulf tides were measured from the Navarre Pier with tidal ranges in excess of 2 ft. Concurrent measurements of the tides in Santa Rosa Sound demonstrated that the tidal lag between the Gulf and the Sound generally varies between
2 to 3 1 hours and there is little if any reduction in tidal range (at Navarre Bridge, where the Sound tidal measurements were conducted). The Gulf nearshore currents were not studied extensively, however during one field trip an easterly current greater than 1 ft/second was measured fairly near shore. On later field trips, existing near shore currents were observed to be much weaker and were not measured.

- 12 -




Winds

Data representing the offshore winds in the Gulf of Mexico are available in Reference 2. These data are the results of observations and measurements obtained
from ships; the data are presented as average monthly conditions by the 5 degree latitude and longitude data squares shown in Figure 7. For the square off the Navarre Pass site, the monthly data are presented in Figure 8. The most persistent winds are seen to be from the east (easterly winds), with easterly winds of 11 to 16 knots occurring 8% of the time and easterly winds of 17-27 knots occurring 4% of the time. Calms occur about 11% of the time. With the predominant easterly winds, it is clear that the resulting predominant waves and littoral drift will be directed toward the west.
During the period December through June, there are
reasonably strong southeast winds and during October through March, fairly strong north and northeast winds occur.
Sea
The average distribution of sea (i.e., locally
generated waves, generally of short period) obtained from Reference 2 are presented in Figure 9. Because sea results from the local winds, there is a strong resemblance between the wind roses presented in Figure .8 and the sea roses. It should be stressed that these sea roses pertain

- 13 -




-4-

--V

_ I I
- - II I I I I I

--1-

950 900 850

800

FIGUE 7 DATASQURESIN GULF OF MEXICO AND CARIBBEAN SE

a0

750

700

FIGURE 7 DATA SQUARES

SEA




9475

0 0 20 3040 50 60.70 To 90 00
January

9778
2 CI 0 1020 3040 50 60 TO 80 9 o
May

11886
0 o 20 040 50 60 70 TO 90 100
September

February March

11666
19
0 ioJ20 n 4 e 5 60 70 80 90 1oo
June

0 Qo20 -O 40 50 60 70 to 90
October

July

10554

0 102003040 5060 70 8090o100
November

0 10 20 30 ,40 50 6) ;7o 80 9CITOo
April
12412 24
0 10 2 30 4 50O 60 ro 8o 01000
August

0 10 20 30 40 5060 70 80 90 OO
December

FIGURE 8 MONTHLY WIND ROSES AT DATA SQUARE OFF NAVARRE PASS AREA

(SEE FIGURE 7) DATA FROM REFERENCE 2

- "15 -

LEGEND
NUMBER or -315
OBSERVATIONS KNOTS
,NA-10I1-16l727 T28
BEAUFORT
% BEAUFORT 0-1 PERCENT FREQUENCY
ROSE SCALE (PERCENT FREQUENCY)
IT 0 10 20 30 AO
DOUBLE CIRCLE INDICATES THEORETICAL WIND ROSE.
WIND SPEED SUMMARY (ALL DIRECTIONS)
BEAUFORT FORCE
CALM 2-3 4 5-6 7-12
0 10 20 30 40 50 60 70 T 80 90 10
PERCENT




0
0 o 20 30 40 5060 TO8090-00
January
7274
0
0 10 20 0 040 50 60 T8090 100
May

I I"f l r......I..I...I..
0 to02030 40 50 60 7080 90 100
September

February March

. 0 ;0 20 30 40 50 60 70 8090 100
June
9523
4 0
0 '0Q20 30040 50 60 7080 90i00
October

8543

0 10 20 50040 50 60 7080 90 100
July

7621

0 o v m 20 30 40 5 e6 ro190rMo
November

6481

16.11 .s.I T i I I I . .. . ... I... .I. .
0 10 20 30 40 50 60 7080 90 100
April
9129
0 0 C
0 1020 30 4C 50 60 70 8009010
August

7344

III"Il ... I I .. II o I ...1I' I III 1
0 11 20 30 40 5060 70 8090 100
December

FIGURE 9 MONTHLY AT DATA
NAVARRE

"SEA" ROSES SQUARE OFF PASS AREA

(SEE FIGURE 7) DATA FROM REFERENCE 2

LEGEND-SEA
203--OBSERVATIONS
% CALM
I 3-- CONFUSED i 0 SLIGHT(<3FT.)
U MODERATE (3--5 FT.) lo i ROUGH (5-8 FT.)
069 IROUGH (012 FT.)
HIGH ( :Q FT.

C j- 20 30
-40

Al.
0 O 20 50 40 50 60 7080 90 100(%)
SUMMARY SCALE (ALL DIRECTIONS)

- 16 -

................ I




to the data square off Santa Rosa Island as shown in Figure 7 and the sea indicated as originating from the north is not of concern in considering nearshore processes. For this data square, 80% of the sea has a characteristic (significant) wave height less than 12 ft.
Swell
The average monthly swell roses, determined from Reference 2 are presented in Figure 10. As for the case of the sea roses, the predominant swell affecting the Santa Rosa Island shoreline would propagate from the southeast, again contributing to a net westerly littoral drift.
Tides
The tides are of particular importance in
maintaining an inlet open under the action of littoral drift which, unopposed, would result in the closing of an inlet. It is valid to regard the tidal "forces" and littoral drift "forces" in opposition, with the tidal forces being more or less predictable and periodic and the littoral drift forces only predictable on an average seasonal basis. Because periods of high littoral drift could result in the closure of an inlet, the most effective tidal characteristics for maintaining an inlet open would be a constant tidal range. The "forces" to maintain an inlet open would then

- 17 -




5150

0 10 20 30 4050 60 70 80 90 to0
January

4694
37 0
0 10 20 30 40 50 60 70 80 90100

Moy

February

June

4741

0 10 20 3040 50 60 70 80 90 100

March

6591 53 0
i ....0I... 20 .... 4 .. 0 6p r 0,0 9... 0 00
0 10 20 30 40 50 60 TO 80 90 100

July

0 10 20 30 40 50 60 7080 90 100
April

6860
51 0
0 1020530 420500 009C 1(o

August

6260
35
0

September

* 7141
32
0 10 20 3040 50 60708090o100
October

5281
25 0
I gill 9# ,= = 10 20 3040 50 60 70809010t
November

5206
I 111111.. tl I I l .. .1.i'"'.
0 10 20 30 40 50 60 TO80 90 100

December

FIGURE 10 MONTHLY SWELL

ROSES

AT DATA SQUARE OFF

NAVARRE

PASS AREA

LEGEND-SWELL
203-OBSERVATIONS 5 % NO SWELL
3 % Y CONFUSED
- LOW (1-6 FEET)
MODERATE (6-12 Fl.)
tOJ HIGH 1>12 FT.)
c -20
30
-40 ," ,,
0 1020 '040 50 60 70 80 902100(%)
SUMMARY SCALE (ALL DIRECTIONS)

- 18 -

(SEE FIGURE 7) DATA FROM REFERENCE 2

4402




always be operating at an effective level to counteract any unusually heavy littoral drift occurrence. Unfortunately, the tidal range in the Santa Rosa Island area of the Gulf of Mexico is not nearly constant, but varies greatly from spring to neap conditions. The tidal ranges encountered during the different field trips varied from a low value of 0.36 ft (4 inches) to an upper range of
2.2 ft. The tide tables indicate a ratio of maximum to minimum tidal range of approximately a factor of 18. Figure 11 presents a plot of the predicted tides for the month of January and a portion of February, 1971 for Pensacola, Galveston Entrance and Miami Harbor Entrance. The low tidal range periods are indicated when an inlet would be highly susceptible to deposition. An example of the measured Gulf and Sound tides obtained during the July 1971 field trip is presented in Figure 12.. Offshore Currents
During two of the field tripsattempts were made to install a recording current meter in a water depth of approximately 16 ft at a location about 900 ft offshore of the Pass Site. The first attempt was successful and resulted in a recording of approximately 24 hours duration, however the current meter malfunctioned during the second attempt and no data were obtained. The data obtained during the first field trip were quite

- 19 -




1.0
> 0
0

GALVESTON ENTRANCE

I
U

January, 1971

February, 1971

FIGURE I I PREDICTED TIDES AT GALVESTON, PENSACOLA AND
MIAMI HARBOR ENTRANCES. NOTE DIFFERENCES
IN TIDAL RANGE VARIATIONS

- 20 -

Period of Period
Low Relative of High
Susceptibility Relative
to Deposition Susceptibility
to Deposition
PENSACOLA

m




Note In This Figure, The Gulf And
Sound Tides Are Not Referenced To A Common Elevation Datum

FIGURE 12

EXAMPLE OF, MEASURED TIDES IN GULF OF MEXICO SANTA ROSA SOUND'

AND




surprising and showed a strong easterly current (1.3 ft/sec) at the time of installation which decreased to approximately
0.5 ft/second during the 24 hour recording period. These data are presented in Figure 13. During the second field trip, the divers noted while installing and recovering the current meter that there was no appreciable current. It is believed that the current measured during the first field trip was perhaps due to some effect of the Gulf Stream which does form a general clockwise circulation pattern in the Gulf of Mexico. Because the information pertaining to this current is very limited, it is not possible to conclude whether the effect on littoral drift is significant, however it is noted that if the prevailing current direction is easterly, and if the current is significant in the surf zone area, then the effect would be to reduce the net westerly littoral drift. Santa Rosa Sound Currents
During one of the field trips, currents were
measured from the Navarre Bridge over a 40-hour period. These measurements were conducted with a nonrecording current meter and therefore were taken intermittently. The measurements are presented in Figure 14 where it is seen that the maximum velocities are on the order of
1 ft/sec.

- 22 -




NOTE CURRENT METER LOCATED APPROXIMATELY
900 FT. OFFSHORE OF PROPOSED INLET
SITE WATER DEPTH = 15 FT. DISTANCE,
OF METER ABOVE BOTTOM 6 FT.

- 2000 TIME (hours)

2400

0400

0800

1200

MAY 16

FIGURE 13

MEASURED

CURRENTS

OFFSHORE

NAVARRE

FLORIDA. MAY 15 16, 1970

2.0

1.0 -

1200

1600

MAY 15

BEACH,

I I I I

I I I I

ED




Smoothed Curve Drawn
Through Measurements
9 000600 1200 1800 000 0600
Dec. 9, 1970 Dec. 10, 1970 c. 11, 1970
_ _ _ 1. i

0
0

Note: See Figure '16
For Location of
Current Measurements

_ I II

MEASURED AT NAVARRE BRIDGE, DECEMBER

I-

9-11I, 1970

FIGURE 14 CURRENTS




V. FIELD STUDIES AND RESULTS

Three separate field studies were carried out during the study. The dates and programs carried out during these three studies are presented in Table I.
A brief description of each of the field studies is presented below.
Field Trip No. 1, May 13-18., 1970
During this field trip a baseline was established
which ranged approximately 1000 feet east of the centerline of the proposed inlet to 2000 feet west of the centerline. The baseline was located shoreward of the active beach profile on the foredunes to reduce losses of the stakes. Beach profiles and offshore soundings were conducted and the contoured results are presented as Plate I in the report cover jacket. Two tide gages were installed: one was located in the Sound in the vicinity of the south bridge section of the Navarre Bridge; the second was installed on the Navarre Pier near its seaward end. The tides during this period were quite small. The predicted tides at Pensacola, Florida ranged from 0.3 to 0.7 feet. The recorded tides are presented in Figure 15 and Figure 16 shows the locations of the tide gages and other field measurements. From the tide records, very little difference in Bay and Gulf tidal

- 25 -




Data Obtained
Dates Encompassed Gulf Sound Beach Offshore Additional Activities and
by Field Trip Tides Tides Profiles Soundings Data Obtained
May 13-18, 1970 Yes Yes Yes Yes 1. Baseline Established
(36 Hour (36 Hour 2. Offshore Currents
Duration) Duration) Measured (24 Hours)
3. Sand Samples Collected
4. Sound "Tidal Division
Line" Established
Dec. 7-12, 1970 Yes Yes Yes No 1. Sound Currents
(36 Hour (36 Hour Measured From Navarre
Duration) Duration) Bridge (40 Hour
Duration)
July 20-25, 1971 Yes Yes Yes Yes 1. Experimental "Sand Bag
(24 Hour (24 Hour Groin" for Littoral
Duration) Duration) Drift observations
Constructed

TABLE I
Summary of Field Trip Activities and Information obtained




- +0.5 E 0
-0.5
2 +0.5
0
0
, .8-0.5
+0.5
-0.5
p-

0900

1200

1500

1800

2100

0000

0300

0600

FIGURE 15

MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF MAY 13-18, 1970

Santa Rosa Sound Tides May 14, 1970 May 1970
L.;;_k ,_-:_____-___"- - i5 197i0 L-

Gulf of Mexico Tides

I I III I I I I I I I III III I I Iii 11 1 Iii 1 1 11

w V J '0%-%,




I I I I I I
0 5000
Scale (ft)

Navarre Bridge Sound Tide

ound Current Measurements
Sound
n Site of Orig

I -,Extent

Tide Gage

16 LOCATIONS

of Gulf Bathym

Pier

OF PRINCIPAL

MEASUREMENTS

etric Survey CONDUCTED

FIELD TRIPS

eco

Guki

FIGURE

.--

DURING




amplitudes could be determined. An attempt was made to determine the location of the "tidal division line" in the Sound. This is a somewhat hypothetical separation line of the area (to the West) which is served (alternately filled and drained) by Pensacola Bay Entrance and the area (to the East) which is served by the East Pass to Choctawhatchee Bay. This line is affected greatly by winds and under conditions of very high winds may not exist at all. The location shown in Figure 17 was determined on May 16 by searching until the velocity some distance to the west of that location was toward the east and the velocity some distance to the east of that location was directed toward the west. Computations using the numerical model described in Appendix I indicates that the position of the "tidal division line" varies during a tidal period from approximately 15 miles east to 20 miles west of the Navarre Pass Site.
Offshore currents were determined by installing a current meter approximately 900 feet offshore of the location of the proposed pass. The current flowed to the east during the two day period the meter was installed, see Figure 13. The peak current was approximately
1.3 ft/sec. Thirteen nearshore sand samples were collected and later analyzed for grain size distribution. Table II summarizes the results of the analysis of median diameters

- 29 -




i i I
0 I 2
Scale (Statute Miles) ..... .
-l vrre Bridge
-d DiSanti Rosa Sound
I \ ~~~~~r-Tidal Division Line ........

FIGURE 17 LOCATION OF TIDAL DIVISION LINE AT 1545 ON
MAY 16, 1970




TABLE II

Summary of Median Diameters of Sand Samples
Analyzed (Field Trip of May 1970)

Sample Collected Sample Location on Sample Median
at Station Beach Profile Diameter (mm)

2 ft Below Mean Sea Level Base of Small Scarp Midshore Between Waterline and Berm
2 ft Below Mean Sea Level Limit of Wave Uprush
Foredune Midway Between Berm and Scarp Base of Scarp
2 ft Below Mean Sea Level Midway Between Berm and Scarp 2 ft Below Mean Sea Level Limit of Wave Uprush
Base of Scarp

________________________ J I

0.42 0.35 0.50 0.51 0.37 0.45 0.46 0.36 0.50 0.40 0.33 0.47 0.37

- 31 -

10+00 E 10+00 E 10+00 E 0+00 0+00 0+00 10+00 W 10+00 W 10+00 W 20+00 W 20+00 W 20+00 W 20+00 W




of the samples. It is seen that the median diameter ranges from 0.33 mm to 0.51 mm. This represents a relatively coarse beach sand for the State of Florida.
FieZd Trip No. 2, December 7-12, 1970
During this field trip, the waves became quite high on the morning of December 8, thereby precluding the possibility of launching a boat through the surf to conduct offshore soundings. Beach profile measurements were conducted and are shown in Figure 18.
It is of interest to note that, in places, the sand accumulation in the former Navarre Pass "cut" was 18" from May 1970 to December 1970 as determined by noting the burial of the stake at Station 0+00. It is not known whether this accumulation was primarily due to wind-blown sand or sand transported over the berm by combinations of high tides and waves.
Two tide gages were installed at the same locations described for the previous field trip. The predicted tides at Pensacola Bay during this trip ranged from 1.2 feet to
2.1 feet. The tide records for the period December 8-11 are shown in Figure 19. It was found again that there was little difference in tidal amplitude between the Sound and Gulf and also that the tidal lag was between 3 and 4 hours.

- 32 -




-Station 20+00 W

100

Distance From Baseline (ft)

200

-Station 18+00 W
Or 100 200
Distance From Baseline (ft)
-|_

100

-Station 16+00 W
0 '

200

Distance From Baseline (ft)
Station 14+00 W isn 100r Baseline J20 Distance From Baseline (t) ----..

FIGURE 18 BEACH PROFILES, DECEMBER
- 33 -

9, 1970

-J4

r

-

4_j
0

-(

-J
W<




.4p. IF I

0
> L.25

Distance From Baseline (ft)
Station 8+00W
0

Distance From Baseline (ft) Station 6+00 W
2^3O

Distance From Baseline (ft)

18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970
- 34 -

-Station 12+00 W
01
0 00 200
Distance From Baseline (ft)
Station 10+00 W
o

J
C,<

4-~J to
C
0
a'.c I1J'~

+10

4
S- .
0--!?

FIGURE

200

I%"

ir.w

100




00%,

-Station 4+00 W

200

0 wc

FIGURE 18 (CONTINUED)

BEACH P DECEMBER

- 35 -

PROFILES,
9, 1970

Distance From Baseline (ft)
-Station 2+00 W 100 200
Distance From Baseline (ft)
Station 0+00
100 200
Distance From Baseline (ft)
Station 2+OO E
o ooo200
Distance From Baseline (ft)


U,
0
Lu<

_j
C
0
>
_.0.
.J,-

+I1

+I10




_________I I I

IU
Station 8+00 E
OO10 200
Distance From Baseline (ft)
0
- Station 10+00 E
0 istance 10om Bowline 200O
Distance From Baseline (ft)

18 (CONTINUED)

BEACH Pf
DECEMBER

PROFILES,
9, 1970

- 36 -

-Sttion 4+00 E
01
0 ) 200
Distance From Baseline (ft)

-u)
0
co

-C
0
.4
W<

0j
0

+1

-J
Wl<

FIGURE




.. +1.0
E + 0.5 520
0o
-0.5
w-
-I 1.0
+1.0
+ +0.5
0.
o
0
W
+ 1.0
6 .+0.5
E
.00O
,- 0
>
4)
-0.5
S'

0900 1200 1500 1800 2100
4
N- ote: December 10, 1970
Gulf and Sound Tides
Not Referenced to Same Datum

Sound
I I I I

\ 0300 0600
ecember II, 1970

FIGURE 19

MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF DECEMBER 7-12, 1970

- 37 -

\Gulf
II I I I I I

L

D-




A current meter was also installed offshore, however the high wave activity caused a mechanical failure and no data were obtained. It was noted during installation and retrieval of the current meter, that net currents were relatively small.
Sound currents were measured over a 40-hour period. The results of these measurements have been presented as Figure 14. The maximum velocities were in excess of 1 ft/sec. The significance of the Sound currents and their relationship to the tides will be discussed later when the calibration of the numerical model is presented.
Field Trip No. 3, July 19-23, 1971
In addition to the type of information collected on previous field trips, a temporary sand bag groin was installed to act as a partial littoral drift barrier. The hydrographic information collected during this field trip included beach and offshore soundings and Gulf and Sound tide records.
The Gulf tidal range measured was approximately 2 ft and the tidal lag between Gulf and Sound was in the range 3h 20m to 4h 20m. See Figure 20 for the tide records which were measured during a 48-hour period.
The contoured results of the beach profiles and offshore soundings are presented as Plate II in the cover

- 38 -




1 1_ _

July 21, 1971 Sound
I I I Gull f I

July 22 71 I
1 i 1 l I I I

0900 1200 1 0 18 2100 030
Time (Hours)

+1.0
July 22, 1971 July 23, 1971
ai
~Sound
-Gulf
o0 I I i I I I I i ] I I Ii ,
Note Gulf and Sound Tides
Not Referenced to Sme
Datum
-I_0

FIGURE 20 MEASURED TIDES IN GULF OF MEXICO AND IN SANTA
ROSA SOUND DURING FIELD TRIP OF JULY 19-23 1971

- 39 -

E
.._3
Il>
ti
2

TI II




jacket of this report. In order to carry out these surveys, it was necessary to reestablish much of the baseline which had been destroyed by four-wheel vehicles and other extraneous activities.
An experimental sand bag-groin was constructed
at the site of the planned Navarre Pass. The purpose of this groin was to perform as a partial littoral drift barrier and through observations of the impoundment, to provide a qualitative indication of the direction and persistence of the nearshore littoral drift. Two photographs of the groin under construction are shown in Figure 21. Unfortunately, due to settlement, the groin was only effective for a period of 2 months and the groin was not maintained because the required sand bags were not available for a period of 4 to 6 months. The performance of the groin will be discussed in "Section VI Littoral Drift" and photographs (kindly taken by R. W. Slye) will be presented.

- 40 -




July 1971 Groin Under Construction

July 1971 Groin Nearing Completion
Extreme Low Tide

FIGURE 21. EXPERIMENTAL GROIN UNDER CONSTRUCTION




VI. LITTORAL DRIFT

Introduction
In considering the establishment of a new inlet, the magnitude and direction of sand transported in the nearshore region (littoral drift) by waves and possibly currents are most important factors and also the most difficult to establish accurately.
Jetties act to block sand from entering inlets, thereby rendering them more suitable for navigation. In performing this function, jetties interrupt the natural flow of sand (littoral drift) along the shore with the resulting accumulation of sand on the updrift side of the jetties. Since the waves maintain their sand-transporting capacity downdrift of the jetties, serious erosion can occur with long-term degradation of the downdrift beaches.
In addition to interrupting the natural flow of
sand along a beach, the interaction of inlet currents and sediment causes bars to be built offshore and in the inner bay. The material comprising these bars is derived from the natural sand system and therefore represents a loss to that system. Of course, once these bars have been established to near-capacity then subsequent annual losses are reduced.

- 42 -




In considering the establishment of a new inlet, the sand must be recognized as a valuable resource and the sand transfer as a natural process. Interruption of the sand transfer or the net loss of a significant amount of sand from the active system will definitely lead to a significant adverse effect on the downdrift beaches. In recognizing the significance of these processes and the necessity of maintaining the stability of the Santa Rosa Island beaches, the cutting and stabilizing of a new inlet should be planned to minimize any net loss of sand to the system and also to provide for the mechanical transfer of the sand interrupted by the presence of the jetties. A number of attempts have been made to design jettied inlets such that sand is prevented from interfering with.navigation, yet the currents and waves still provide for the natural transfer of sand. A survey of jettied inlets will demonstrate that this approach has not proven successful and that the only effective concept is to provide for the artificial bypassing of sand.
Littoral Drift Estimates
Littoral drift estimates can be based on field
measurements or on calculation procedures using wave data. Each of these approaches has advantages and disadvantages.
Good accuracy in field measurements of littoral drift requires a near-complete trap (e.g. a long jetty)

- 43 -




and reasonably long records in which the trap impoundment history is documented and/or records are kept of the amount of material removed or added to maintain stability of the downdrift shoreline. Littoral drift calculations are based on wave measurements and/or observations; to date (1972) the calculation procedures have not been developed and verified to the degree that a high degree of confidence is warranted. The most often applied calculation procedure
(3) does not account for many presumably important parameters, including
(1) sand size
(2) sand specific gravity
(3) beach slope
(4) beach roughness
In attempting to develop the best estimate of littoral drift, all sources of information should be reviewed with relative confidence based on the particular circumstances attending each measurement or calculation.
Field Measurements.-rhe available field
measurements in the Navarre Pass area are generally based on the westward rate of growth of the western ends of barrier islands and on the accretion behind the eastern jetty at Perdido Pass.
Based on the rate of growth of the western end
of Santa Rosa Island, and the dredged quanititie-s in the

- 44 -




Bay Entrance and on the shoals, the U. S. Army Corps of Engineers (4) has concluded that the average annual
westward and eastward drif tare 130, 000 and 65, 000 cubic yards, respectively, resulting in an annual net westward drift of 65,000 cubic yards.
In 1938, F. F. Escoffier (5) analyzed the westward growth rates of the eastern shore of East Pass (entrance to Choctawhatchee Bay), the results available at that time indicated an annual deposition rate of 26,300 cubic yards, although Escoffier noted that this quantity is undoubtedly smaller than the net littoral drift due to some bypassing of material past the inlet.
The Corps of Engineers (4) estimates the westerly and easterly drift components at Perdido Pass to be 130,000 and 65,000 cubic yards per year resulting in a net westerly drift of 65,000 cubic yards per year. During the period May 1969 to March 1970, the Corps measured the deposition inside the Perdido Pass weir jetty to be 146,000 cubic yards. Hurricane Camille occurred within this period and may account for the higher than anticipated impounded quantities. For the period 1934-1953 (before the weir jetty system was constructed), J. W. Johnson (6) analyzed accretion at the eastern bank of Perdido Pass and concluded the annual deposition to be 200,000 cubic yards; presumably this would correspond approximately to the net westerly littoral drift.

- 45 -




Calculations of Littoral Drift. -D. S. Gorsline (7) conducted a one-year study of Gulf beaches extending from Keaton Beach, Florida to Gulf Shores, Alabama. His study included monthly surveys of fifteen beaches in the study area and wave observations. Gorsline carried out calculations which indicated the gross drift rates at Pensacola to be approximately 200,000 cubic yards per year with--a net westerly drift of 78,500 cubic yards/year. It should be stressed that Gorsline's calculations at each location were based on only one observation per month over a period of one year. There is a good likelihood, therefore that his results are not representative of average annual conditions.
T. L. Walton (8) has carried out computations
of littoral drift along all of the sandy beach segments of the State of Florida. The calculations are based on long-term wave observations collected by military and commercial ships. The wave characteristics are transformed to shore using standard procedures and drift is calculated based on the usual relationship (3). In comparing his predictions with other estimates for the Florida East Coast, Walton found generally good agreement for portions of the northern Florida east coast, however his calculated values were much higher than estimates based on impounded quantities along the lower Florida east coast. This difference was attributed, at least in part, to the

- 46 -




proximity of the Gulf Stream and its effect in causing an increase in height of waves propagating from the northeast. This would qualitatively explain the differences noted. In the Navarre Pass area, Walton's calculated annual westward and eastward drifts are approximately 400,000 and 100,000 cubic yards, respectively, resulting in a net westward littoral drift of 300,000 cubic yards per year.
The Coastal Engineering Research Center (CERC) collects shore-based observations in a program entitled "Littoral Environmental Observations" (LEO) The LEO data are generally taken daily and include visual estimates of breaking wave height and breaking wave direction in terms of a coastal sector method, see Figure 22. These data provide an alternate basis of estimating littoral drift, using the usual calculation procedure and assuming that the wave conditions reported are representative for the entire 24-hour period. Data were provided by C. J. Galvin and A. De Wall of CERC for four locations: Navarre Beach, Grayton Beach, Beasley Park and Crystal Pier. The period over which data were available ranged from 8 months at Navarre Beach to 24 months at Beasley Park and Crystal Pier. See Figure 23 for a map of the four observation
locations. Table III summarizes the littoral drift values calculated from the LEO data.

- 47 -




OCEAN

If No Waves, Fill in Zero

0
Observer

Shoreline

LAND
WAVE DIRECTION CODE FOR WAVES AT BREAKING

FIGURE 22 COASTAL SECTOR METHOD USED
ENGINEERING RESEARCH CENTER
REPORTING WAVE DIRECTION

BY IN

COASTAL

- 48 -




Pensacola Bay

thatchee Bay

GULF OF MEXICO

Note: Arrows and Numbers Indicate
Calculated Directions and
Net Annual "'Littoral Drift
(in Cubic Yards/Year) Using
Leo Data

FIGURE 23

LOCATIONS OF CERC LEO DATA USED IN LITTORAL DRIFT CALCULATIONS. DRIFT DIRECTIONS AND NET ANNUAL RATES ALSO SHOWN




TABLE III

Summary of Calculated Littoral Drift Using LEO Data

Results Averaged Annual
Duration of Data Calculated Littoral Drift Net Drift
Location Available Interval (Cubic Yards) (Cubic Yards/Year)
Navarre Beach 8 months Jan. 1, 1970 to
Sept. 1, 1970 158,000(W)* 237,000(W)
Grayton Beach 24 months Dec. 1, 1970 to
Dec. 1, 1971 53,345(W) 52,100(W)
Dec. 1, 1971 to
Dec. 1, 1972 50,776(W)
Beasley Park 24 months Jan. 1, 1971 to
Jan. 1, 1972 30,064(W) 45,200(W
Jan. 1, 1971 to
Nov. 1, 1971 50,321(W)
Crystal Pier 12 months July 1, 1971 to
July 1, 1972 253,331 253,331(W)

*(W) denotes drift from East to West.




Experimental Groin at Navarre
An experimental sand bag groin was constructed at the site of the original Pass. The purpose of the groin was to obtain information regarding the variability and (hopefully) magnitudes of littoral drift. The groin was constructed on July 22, 1971 and extended 100 ft seaward of the mean high water line. The groin was about 3 ft high by 8 ft wide; two photographs showing the groin under construction have been presented as Figure 2i.
The groin was reasonably effective in trapping
the nearshore portion of drift for a period of approximately
2 months, after which the portion of the groin traversing the beach face was undermined and settled significantly (about 4-6 ft). At that time, it was planned to rebuild the groin by adding more sand bags. Unfortunately the sand bags were not available* for a period of 4 to 6 months and the experiment was discontinued.
A brief photographic history of the groin is
presented in Figure 24. ** During the period August 5 to August 8, 1971, impoundment occurred on the west side of the groin. On the morning of August 9, impoundment was evident on the east side of the groin which remained the
*The factory had experienced a fire.
*Captain R. W. Slye of the Santa Rosa County Beach Administration kindly offered to photograph The groin.

- 51 -




August 5, 1971 Note Slight Build-up 0800 From West

August 8, 1971 Continued Accretion 0800 on West Side of Groin

FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (Photographs Taken by Captain R. W. Slye)

(;I




August 9, 1971 0900

- Accretion is Now Apparent on
East Side of Groin. Some
Transport of Sand Over Groin is Evident

August 20, 1971 -

Some Evidence of Lessened Easterly Drift Compared to Photograph of August 9, 1971

FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued)
(Photographs Taken by R. W. Slye)

C, wA




August 28, 1971 0800

- Accretion on Western
Side of Groin Compare
With Photographs of August 9 and 20, 1971

September 2, 1971 0830

-Evidence of Drift Reversal Compared to August 28, 1971 Photograph. Also Note Lowering of Middle Portion
of Groin Due to Undermining

FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued)
(Photographs Taken by R. W. Slye)

(n




September 8, 1971 1200

- Same General Accretion
Situation as Shown on
September 2 Photograph

September 13, 1971 0900

Groin Has Been Flanked With Scarping to East (Also See Following Photograph of Same Date)

FIGURE 24.

PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued)
(Photographs Taken by R. W. Slye)

cn,




September 13, 1971 Showing Effect of High 0900 Tides and Easterly Drift
and Escarpment

September 22, 1971 1130

- Drift Accumulation on
East Side of Groin Indicates Reversal From September 13
Photograph

FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken By R. W. Slye)




October 1, 1971 0830

-Groin Profile Has Been Lowered Significantly Due to Undermining. Groin is Now Generally Ineffective for Drift Impoundment

October 7, 1971 Drift Passes Over 0800 Groin i*'n Beach Face
Region

FIGURE 24.

PHOTOGRAPHIC HISTORY OF EXPERIMENTAL GROIN (continued)
(Photographs Taken by R. W. Slye)

01




. .. .. .. ..

m, 00

October 14, 1971 0900

-Beach Accretion Has November 30, 1971
Nearly Completely 0800
Buried Shoreward One-Third of Groin

- Groin Ineffective as
Littoral Drift Impediment.
Photograph Taken at Low
Tide

FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued)
(Photographs Taken by R. W. Slye)




December 16, 1971 M Final Photograph of 0800 Experimental Groin
FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued)
(Photographs Taken By R. W. Slye)




dominant side through August 20. By August 28, the drift had reversed again and the impoundment was on the west side of the groin. On September 2, 1971, impoundment had occurred on the east side and the first groin subsidence is evident. By September 13, 1971, the groin had been flanked by high waves and tides and the impoundment was on the west side of the groin. By September 22, the drift evidence was from the east. The photographs on October 1, 1971, and thereafter show that the upper one-third of the groin had subsided to such an extent that it would no longer be effective in impounding littoral drift.
Although it is clear that the groin installation was not effective to obtain quantitative evidence regarding the littoral drift, it is of interest that during the two month period over which it was effective, the impoundment indicated nearshore drift reversal at least six times. Furthermore, because the nominal interval between photographs is one week but was as great as eleven days, it is likely that more reversals than noted had taken place. It is noted that the months of August and September are not expected to be the months of heaviest nor most persistent drift. The sea and swell charts for this period, however, do indicate that for average August and September months, net drifts to the west are to be expected.

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Although it is not possible to draw strong
conclusions from the experimental groin due to the short period over which it was effective, it does appear that drift rates based on the ship data would yield drift rates to the west that would be unrealistically high.
Summary and Recommendations
Several littoral drift estimates in the Navarre Pass area have been presented. These estimates.all indicate a net westward drift with net magnitudes ranging from 65,000 to 300,000 cubic yards per year. This range represents a factor of 4.6 which is not too surprising considering the present state of knowledge of littoral drift quantities.
Considering the estimates available, it is
believed that the net annual littoral drift is something less than 200,000 cubic yards to the west. It will be recommended that the inlet maintenance be planned to provide transfer of 200,000 cubic yards per year with the understanding that the actual amount required is expected to be less than this value. This represents a responsible approach to the problem of maintaining the littoral drift and it is realistic to reduce the amount of sand transfer below that planned, however, the financial and equipment problems attendant with increasing the sand transfer above that originally planned argue against arranging for a lesser amount.

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VII. SUMMARY OF NUMERICAL.MODEL CALCULATIONS

Introduction
In order to represent the behavior of Navarre Pass and its interaction with adjacent entrances a computer method which simulated the flows into and through the Santa Rosa Sound system was developed and applied. This method is called a "numerical model" as opposed to a hydraulic model and has the advantage of rationally incorporating the interaction of Navarre Pass with the tides and flows in Santa Rosa Sound and also with the flows through the entrances to Choctawhatchee and Pensacola Bays.
The basis for and evaluation of the numerical
model are described fully in Appendix I "Numerical Model of the Bay System Affecting Navarre Pass." After evaluation for the present situation in which no flows occur through Navarre Pass, the model was modified and used to evaluate the effect of Navarre Pass on flows through neighboring inlets and also to calculate the expected velocities through Navarre Pass. Appendix II "Stability of Navarre Pass" presents an evaluation of the tendency of Navarre Pass to close by comparing the sedimentary stability

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with Rollover Pass, Texas which is an artificial inlet which grew rapidly after opening. The results of applying the numerical model are described in detail in Appendixes I and II and are presented briefly in the following sections.
Results Obtained Using the Numerical Model
Effect of Navarre Pass on Entrances to Pensacola and
Choctawhatchee Bays
The percentage changes in flows through Pensacola and Choctawhatchee Bays due to the influence of Navarre Pass were evaluated for various Gulf tidal ranges. These results are tabulated in Table 1-4 (Appendix I). It was found that, as expected, the presence of Navarre Pass would decrease the total inflows and outflows through the entrances to Pensacola and Choctawhatchee Bay Entrances. The largest percentage effect was on Pensacola Bay Entrance due to the Sound being of greater width between Navarre Pass and Pensacola Bay than between Navarre Pass and Choctawhatchee Bay.
For a tidal range of 1.5 ft (approximate average), the percentage reductions in the maximum flows in and out of Pensacola and Choctawhatchee Bays are 2.0% and 0.1%, respectively. For a more complete summary refer to Table 1-4 in Appendix I. The reduction in tidal flows

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into Pensacola Bay will result in an associated reduction of 1.8% in equilibrium cross-sectional flow area into this Bay. For Choctawhatchee Bay the equilibrium flow area will be reduced by 0.1%.
Maximum Velocities Through Navarre Pass
The peak velocities averaged over the Pass crosssection are calculated to vary from 1.27 ft/sec to 3.54 ft/sec for Gulf tidal ranges varying from 0.5 to 2.0 ft, respectively. This range of velocities is well within acceptable limits for small craft navigational safety. A more complete summary of maximum velocities is presented in Table 1-5 of Appendix I.
Relative Stability of Navarre Pass
Computations were carried out in Appendix II to compare the tendency of Navarre and Rollover (Texas) Passes to remain open. These two passes have respective histories of closure and growth following their initial openings. The calculations showed that the geometric and tidal conditions at Navarre Pass are much less conducive to remaining open without jetties than at Rollover Pass. These calculations simply reinforce the known requirement for jetties at Navarre Pass.

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VIII. RECOMMENDED DESIGN OF NAVARRE PASS INLET

Functional Design
In developing a functional design of Navarre Pass, the primary factors considered were: (1) minimum adverse effects on adjacent beach stability through effective sand by-passing and placement of initial sand dredged, (2) navigational safety for craft using the Pass, (3) improvement of water quality within the Sound adjacent to the Pass, and
(4) a minimum of required costs associated with the periodic maintenance of the Pass.
Some of the factors noted above conflict, for
example the effective by-passing of sand will be fairly expensive. In the recommendations pertaining to the layout and planning for the Pass, the highest priority will be given to beach stability and navigational safety.
Recommended Layout of Navarre Pass
Prior to discussing the recommended layout of
Navarre Pass, it is emphasized that it is not intended to present a final detailed design, but rather a workable conceptual design which is in accordance with the objectives presented in the preceding section. The Santa Rosa
County Beach Administration and their engineers, will make a,

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detailed engineering design and will make modifications to the recommended layout which facilitate or reduce the cost of construction. These modifications, however, should not significantly impair the performance of the design.
The recommended layout of Navarre Pass is presented as Plate III in the jacket in the back cover of this report. The main components of the Pass include: (1) a weir jetty and deposition basin for the trapping and retention of sand until by-passed to the downdrift (west) side of the Pass, (2) a training wall on the Pass sides to provide lateral stability of the cut, (3) a navigational channel, 12 feet deep by 150 feet wide extending through the Island to the 12 feet contour on the Gulf side and to the Intercoastal Waterway on the Sound side, and two jetties extending into the Gulf, and (4) either mechanical or vegetative control of wind drift of sand. Each of these features is discussed separately below.
1. Weir Jetty and Deposition Basin-A weir jetty and deposition basin (sand trap) are recommended with the weir section 400 ft long, oriented parallel to shore and with the weir crest elevation at the approximate present mean sea level contour. The design and construction of the weir are to be such that minor required increases in weir elevation can be accomplished by the addition of stone. In considerations of weir stability, the design should account for the expected variations in sand

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elevations on both sides of the weir. The weir design recommended is similar to that at Hillsboro Inlet, see Figure 25. The weir section at Hillsboro Inlet is 200 ft long and the elevation of the weir crest is at MSL. The eastern end of the weir should be tied into the natural dune system in order to prevent flanking and a short adjustable groin should be located at the eastern end of the weir in order to provide a control on the stability of the updrift (eastern) beaches.
The expected performance of the weir/deposition basin is as follows. After initial or maintenance dredging of the basin, the predominately westward littoral drift will deposit in the basin at the eastern end of the basin. If the tides and waves are low during this period, a spit will grow toward the west and will be located on
the Gulfward side of the weir. During periods of high tides and/or high waves, the sand forming this spit will be carried further into the deposition basin and the weir will be re-exposed. For the dimensions of the basin shown, the volumetric storages below MSL are 48,000 and 64,000 cubic yards based on a 1:3 side slope and maximum basin depths of 12 and 18 ft below MSL respectively. Depending on the quantities of net westerly littoral drift, the basin would require maintenance dredging and by-passing to the west side of the inlet on a frequency ranging from 1 to 3 times a year if carried out on a

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FIGURE 25 WEIR JETTY SYSTEM AT
HILLSBORO INLET, FLORIDA
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demand basis. Because the heaviest littoral drift is expected during the winter, the required dredging may be more frequent during this season. Due to the present uncertainties in net littoral drift magnitudes, it will be difficult to realistically address the problem of maintenance dredging and by-passing to the west if this is planned to be done on a contract basis. An alternate concept providing flexibility would be a relatively small custom dredge built for and operated under the direction of an agency established for the overseeing of the Pass operation and maintenance. This would also allow any small amount of maintenance dredging required in the channel or at the tips of the jetty to be carried out during relatively calm wave conditions which would be difficult to schedule in advance on a contract basis. The Hillsboro Inlet District has successfully operated their small custom dredge for by-passing and minor maintenance dredging in the channel and marin a- for over eight years.
The possibility of the northern portion of the
deposition basin providing a recreational facility could be considered. The wave energy at this point will be reduced and the beach slope could be controlled. A marina occupying a portion of the basin is another possibility, but would be reduced in value due to land access problems, especially if a bridge spanning the Pass is not constructed.

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2. Training Wall on Sides of Cut--rhe banks of the cut should be stabilized with sheet piling or rubble protection to prevent sloughing and erosion of the sides. The consequences of not providing a means for bank stabilization will be a widening and shoaling crosssection, and increased maintenance and possibly a migrating interior channel which would also result in the need for increased maintenance. There are advantages of reduced reflection of boat waves if a rubble mound bank protection is chosen. The cut through St. George Island (Figure 26) is an example of erosion if no training walls are provided.
3. Navigational Channel and Jetties-It is
understood that the Navarre Pass Committee desires a 12 ft deep channel to match the depth of the Intercoastal Waterway through Santa Rosa Sound. The desired width of the 12 ft depth portion is 150 ft with a somewhat greater width of the remaining portion of the cut. Some of these features are flexible and can be varied within limits of safe navigational consideration. The channel shown in Plate III is 12 ft deep for a width of 150 ft and is a reduced depth, say 6 ft, over the remainder of the 400 ft width. The reduced depth portion of the channel will serve as a fishing area for small boats, or as a safe area for boats experiencing engine trouble, etc. Also, a wider inlet, immediately past the tips of the jetties, is

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26 ST. GEORGE ISLAND CUT. NOTE
EROSION WHERE BANK PROTECTION
IS NOT PROVIDED
- 71 -

FIGURE

I




favorable psychologically to operators of entering craft. The Sound Side of the channel could be provided with short (30 ft) rubble mound structures to keep drift out of the channel. An alternate and reasonable approach would simply be to accept some minor dredging of the Pass in this area.
The jetties should extend to approximately the 12 ft Gulf contour and a design entrance width of approximately 170 ft is recommended. The jetties should be provided with a core so that the possibility for sand being carried through the jetties is minimal. The eastern jetty is extended further seaward than the west jetty because the predominant wave action is from the east and entering craft can first "duck behind" the protection of the east jetty and can then contend with the presence of jetties on both sides in comparatively protected waters.
4. Stabilization of Sand Against Wind DriftInspection of the dune system in the Navarre Beach area indicates that wind drift is an effective agent for sand transport. In the interest of reducing the maintenance dredging in the Pass and in preventing erosion of the land features, it is important that the areas near the Pass be provided with mechanical (sand fences) or natural (vegetative) control against wind erosion. This is particularly important along the boundary of the Pass

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where presently-existing vegetation will necessarily be removed by the excavation activity. Disposition of-Initially Dredged Material
The initial dredging of the Pass and deposition
basin will result in approximately 400,000 cubic yards of beach quality sand. It is recommended that at least 90% of this material be placed on the western side of the inlet to be used as "feeder sand" for the down drift beaches while the near Pass bathymetry is adjusting to the presence of the Pass system and while the deposition basin is filling. The material should be placed so as to cause a seaward extension and an increase in elevation of the existing down drift shores. If the material is distributed over 2000 ft of beach on the down drift side of the Pass, approximately 200,000 cubic yards of sand will be required to advance the shoreline seaward a distance of 100 ft. The remaining 160,000 (or so) cubic yards could be used to raise the elevation of this section of the beach. This remaining portion placed on the newly-established beach
would thereby raisee its elevation and not damage the existing vegetation. This amount of material would result in a new dune approximately 16 ft high by 150 ft wide and 2000 ft long.

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Alternate Designs
only one design for Navarre Pass has been
presented. This design is considered to be the best choice from a functional standpoint, however it is recognized that the present design will be somewhat more expensive to construct than others. One alternate design which could be less expensive would be one similar to that at Perdido Pass, Alabama. This design incorporates a weir section as part of the eastern jetty and the interior region adjacent to the eastern jetty serves as the deposition basin. Apparent drawbacks to this design would appear to include the possibility of undesirable wave conditions inside the jetties during periods of high tides and waves, and the possible difficulty of sand encroaching on and causing shifting of the navigational cut.

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IX. SUMMARY AND CONCLUSION

Summary
The results of this study have indicated that:
1. Navarre Pass would only reduce slightly the
equilibrium cross-sectional flow areas into
Pensacola (1.8%) and Choctawhatchee (0.1%)
Bays.
2. The velocities through Navarre Pass would be
well within the limits considered safe for small
craft navigation.
3. Planning for the artificial transfer of sand
should be based on an annual rate of 200,000
cubic yards to the west. Initial disposition of
sand dredged should be as a feeder beach on the
west side of the Pass.
4. The Pass would cause a localized moderation of
salinities and increased flushing in the waters
adjacent to the Pass.
5. The tide and geometric characteristics are such
that Navarre Pass will always tend to close;
jetties are therefore essential to the stability
of the Pass.
Conclusion
Based on the results of this study, it is concluded
that if proper financial provision is made for the
construction and maintenance of the inlet, there should
be no significant adverse hydrographic effects to the
stability of the Santa Rosa Island Beaches, nor to the
adjacent waters.

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X. REFERENCES

1. Bruno, R., Personal Communication.
2. Oceanographic Atlas of the North Atlantic Ocean, U. S.Navy Oceanographic Office, Publication No. 700,
Section IV, Sea and Swell, 1963.
3. Shore Protection, Planning and Design, Technical Report No. 4, Coastal Engineering Research Center, U. S. Army Corps of Engineers, Third Edition, June
1966.
4. National Shoreline Study, Regional Inventory Report, South Atlantic-Gulf Region, Puerto Rico and the
Virgin Islands, U. S. Army Corps of Engineers,
South Atlantic Division, Atlanta, Georgia, August 1971.
5. Escoffier, F. F., "Study of East Pass Channel, Choctawhatchee Bay, Florida," United States Engineers
Office, Mobile District, Mobile, Alabama, 1938.
6. Johnson, J. W., "Nearshore Sediment Movement,"
Bulletin, American Association of Petroleum Geologists,
Vol. 40, 1956, pp. 2211-2232.
7. Gorsline, D. S., "Dynamic Characteristics of West Florida Gulf Beaches," Vol. 4, Marine Geology, 1966,
pp. 187-206.
8. Walton, T. L., "Littoral Drift Computations Along
the Coast of Florida by Use of Ship Wave Observations,"
M.S. Thesis, Coastal and Oceanographic Engineering
Department, University of Florida, 1972.
9. O'Brien, M. P., "Estuary Tidal Prisms Related to Entrance Areas," Civil Engineering, Vol. 1, No. 8,
pp. 738-739, 1931.
10. Escoffier, F. F., "The Stability of Tidal Inlets,"
Shore and Beach, Vol. 8, No. 4, pp. 114-115, 1940.

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11. Keulegan, G. H., "Tidal Flows in Entrances. Water
Level Fluctuations of Basins in Communication with
Seas," Third Progress Report, National Bureau of
Standards Report, No. 1146, 1951.
12. O'Brien, M. P., "Equilibrium Flow Areas of Inlets on
Sandy Coasts," Journal, Waterways and Harbors Division,
ASCE, Vol. 95, No. WW1, pp. 43-52, Feb. 1969.
13. Rouse, H., "Elementary Mechanics of Fluids," John Wiley
and Sons, Inc., 1956.

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APPENDIX I
NUMERICAL MODEL OF THE BAY SYSTEM AFFECTING NAVARRE PASS
Introduction
The purpose of the numerical model is to provide a means of realistically representing the hydraulics of the system and any changes that would occur due to the opening of Navarre Pass. Because of the extreme length (approximately 50 miles) of Santa Rosa Sound, the construction of a hydraulic (physical) model was ruled out during the conduct of the project.
In the following sections of the Appendix, the governing differential equations will be presented and cast into finite difference form for numerical solution; this provides the basis for simulating the tides and currents that would occur at any locality in the system represented. Two representations of the numerical model will then be discussed: (1) In the calibration phase, data collected during the study will be used to assess the validity of and/or modify the numerical model, and (2) With the validity established, the Pass will be introduced into the numerical model and the hydraulics of the inlet and/or

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the effect of the Inlet on the tide in Santa Rosa Sound and on the hydraulics of the Pensacola Bay Entrance and East Pass will be investigated. Figure I-1 presents the geographic area represented in the numerical model.
Derivation of the Numerical Model Governing Differential Equations
The differential equations governing the flow in bay systems are the depth-integrated equations of motion and continuity.
Equation of Motion.--The vertically integrated differential equation of motion can be written for the x-direction in a semi-linearized form as
atTb) (I-l)
in which
q = discharge per unit width in the x-direction
t = time
g = gravitational constant
D = total depth = h + n
h = depth referred to mean sea level
n = tide displacement above mean sea level due
to astronomical, wind and barometric tides
x = horizontal distance coordinate aligned with
bay axis

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GULF

0 F

System Model

, .o .......
" "Limits Encompassing Bay ast .- ,Represented in Numerical
say.
wBay*S f* *
r.. .. .
"r -~ *.. . . :.
t
0. und
a a i . '..
' .. "" "..,-

M E X-IC 0

Z-! BAY SYSTEM REPRESENTED IN NUMERICAL

MODEL

FIGURE

* .. .

#-'n fro,,
Ce
- ___1




p = mass density of water
T = wind stress in x-direction on air-water
Interface
T = frictional stress on bottom of water column
b
The quantities T'n and Tb can be expressed as T = CfPaU2 cos 5 (I-2)
S=pf qjqj (1-3)
b 28D2
8D
in which
C = wind stress coefficient
0.0013, U < 23.6 ft/sec (I-4)
23.6) 2
0.0013 + 0.00295 1.0 26 U > 23.6 ft/sec
Pa = mass density of air
U = wind speed at 30 ft reference elevation
S = angle of wind vector relative to the bay axis
f = Darcy-Weisbach friction factor (Reference 13, page 201)
Equation of Continuity.-The equation of continuity in one dimension is expressed as
ii + @q R (-5)
at ax w
in which the righthand side represents the effect of runoff,

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q= runoff in cubic ft/sec per foot of bay
length
w = width of segment considered
it is noted that in the present application of the model, the wind stress, T 1, and direct precipitation and runoff will be taken as zero, however they have been included here for completeness.
Finite Difference Equations
In order to employ Equations (I-1) and (1-5) for realistic geometries and Gulf tides, it is necessary to cast these equations into finite difference form. The time- and space-staggered procedure is used in which the equation of motion is applied between midpoints of adjacent segments (i.e., across a segment boundary) at full time steps, At, and the equation of continuity is applied for each segment at half time step increments.
Finite Difference Form of the Equation of Motion. -Equation (I-1) can be expressed in finite difference form for the total flow, Q n, onto the nth segment, as:
Q +AtF 'r w D g~ -1 T
Q nlL [p T1n n-j (1-6)
n 1+ w At f I 1n'
8 (5w)2

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in which the over-barred quantities represent averages based on the nth and (n-l)th segments. The prime indicates the value at time t + At whereas unprimed quantities are known from calculation at time t, and w is the width of the bay segment, see Figure 1-2 for the variable representations and Figure 1-3 for the numerical model representation of the area of concern.
Finite Difference Equation of Continuity. -Equation
(1-5) can be written in finite difference form as
q R At
= n + Q + n (1-7)
n n Ax w n n+1J w
where the primes indicate the unknown quantities as before and the terms on the right hand side are known from calculations at previous times. Boundary Conditions
The boundary conditions for this problem are the
flows through the inlets and may be expressed, for example, for Destin Pass as:
Ac V2gjnjo qGI sign(ln0 T- G)/Ken + Kex + ft/4R
in which

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Variables Represented
at Segment Midpoints:

Variables Represented
at Segment Junctions
Q

7/ / ////

Qnf l *n, hn
. I .t ..

n -Segment i

* "n.+i, hn

+ x

FIGURE I-2

ILLUSTRATION
REPRESENTATION

OF BAY SEGMENT

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n-I
n-l

Qn+l




Pensacola Boy Segment

I_- I I I ~

---Pensacola Boy Entrance -Novarre Pass Destin Pass( Site
GULF OF MEXICO
FIGURE I-3 SCHEMATIZATION OF PENSACOLA BAY/ CHOCTAWHATCHEE BAY / SANTA ROSA SOUND /
GULF OF MEXICO SYSTEM

V 7l7 7ll7-7i7l
II




Full Text

PAGE 1

COASTAL ENGINEERING STUDY OF PROPOSED NAVARRE PASS 73 -o0 Sponsor: Santa Rosa County Beach Administration Submitted by: Coastal and Oceanographic Engineering Laboratory Florida Engineering and Industrial Experiment Station University of Florida Gainesville, Florida February, 1973

PAGE 2

ABSTRACT This report describes the results of a coastal engineering field and numerical study of the proposed Navarre Pass. The field measurements are based on three field trips during which bathymetry and tides and currents were measured. The numerical model simulates the tides and flows in Santa Rosa Sound and is capable of including the effects of Navarre Pass. Littoral drift direction and magnitude are of considerable importance in planning the inlet; calculations were carried out using shore-based observations obtained in a program of the Coastal Engineering Research Center. The results of the study indicate that: 1. Navarre Pass would only reduce slightly the equilibrium cross-sectional flow areas into Pensacola (1.8%) and Choctawhatchee (0.1%) Bays. 2. The velocities through Navarre Pass would be well within the limits considered safe for small craft navigation. 3. Planning for artificial transfer of sand should be based on an annual rate of 200,000 cubic yards to the west. Initial disposition of dredged material should be as a feeder beach on the west side of the Pass. 4. The Pass would cause a localized moderation of Sound salinities in the vicinity of the Pass. ii

PAGE 3

5. The tide and geometric characteristics are such that Navarre Pass will always tend to close unless maintained open by jetties. Based on these results, it is concluded that if proper financial provision is made for construction and maintenance of the inlet, there should be no significant adverse effects to the stability of the Santa Rosa Island Beaches, nor to the adjacent waters. iii

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TABLE OF CONTENTS Page ABSTRACT ............................................ ii LIST OF TABLES ..... ............................... vii LIST OF FIGURES .................................... viii LIST OF SYMBOLS ..................................... xii ACKNOWLEDGEMENTS ................................... xiv I. INTRODUCTION ............................... 1 II. PURPOSES OF STUDY .......................... 3 Impact of Pass on Natural Processes ............ ............. 3 Conceptual Design Features of Navarre Pass ....... ............. 4 III. BRIEF HISTORY OF NAVARRE PASS .............. 5 IV. METEOROLOGY AND HYDROGRAPHY OF AREA ........ 12 General Description ..................... 12 Winds ................................ 13 Sea ........... ...................... 13 Swell .... ............................ 17 Tides ..................... ........... .. 17 Offshore Currents ............... ..... 19 Santa Rosa Sound Currents ............ 22 V. FIELD STUDIES AND RESULTS .................. 25 Field Trip No. 1, May 13-18, 1970 ...... ............. 25 Field Trip No. 2, December 7-12, 1970 ............... 32 Field Trip No. 3, July 19-23, 1971 ..... ............. 38 iv

PAGE 5

TABLE OF CONTENTS-Continued Page VI. LITTORAL DRIFT ............................. 42 Introduction ............................ 42 Littoral Drift Estimates ............. 43 Experimental Groin at Navarre ........ 51 Summary and Recommendations ............. 61 VII. SUMMARY OF NUMERICAL MODEL CALCULATIONS ............................ 62 Introduction ............................ 62 Results Obtained Using the Numerical Model ...................... 63 Effect of Navarre Pass on Entrances to Pensacola and Choctawhatchee Bays .............................. 63 Maximum Velocities Through Navarre Pass ...................... 64 Relative Stability of Navarre Pass ...................... 64 VIII. RECOMMENDED DESIGN OF NAVARRE PASS INLET .................... .. ... .... 65 Functional Design .................... 65 Recommended Layout of Navarre Pass ... 65 Disposition of Initially Dredged Material .................. 73 Alternate Designs ................... 74 IX. SUMMARY AND CONCLUSION ..................... 75 Summary ................................ 75 Conclusion .............................. 75 X. REFERENCES .............. .................. .76 APPENDIX I. NUMERICAL MODEL OF THE BAY SYSTEM AFFECTING NAVARRE PASS .................. 78 Introduction ............................ 78 Derivation of the Numerical Model ....... 79 v

PAGE 6

TABLE OF CONTENTS-Continued Page Governing Differential Equations ..... 79 Finite Difference Equations .......... 82 Boundary Conditions ................. 83 Application of the Numerical Model ................................ 86 Assessment/Calibration of the Numerical Model .................. 87 Use of Numerical Model to Evaluate Effect of Navarre Pass ............ 98 Maximum Velocities Through Navarre Pass ...................... 101 II. STABILITY OF NAVARRE PASS .................. 103 Introduction ........................... 103 Method .................................. 103 Numerical Model ...................... 105 Sedimentary Stability ................ 105 Equilibrium Cross-Sectional Area .............................. 109 Application of Stability Equilibrium Concepts to Navarre and Rollover Passes ..................... 112 Navarre Pass ......................... 115 Rollover Pass ........................ 123 Conclusion Regarding Relative Stability of Navarre and Rollover Passes ...................... 123 III. GLOSSARY OF TERMS .......................... 130 Introduction ............................ 130 vi

PAGE 7

LIST OF TABLES Table Page I Summary of Field Trip Activities and Information Obtained ................... 26 II Summary of Median Diameters of Sand Samples Analyzed (Field Trip of May 1970) .......................... 31 III Summary of Calculated Littoral Drift Using LEO Data ....................... 50 I-1 Characteristics of Schematized Bay/Inlet System ........................... 88 I-2 Summary of Measured Tidal Characteristics ............................ 89 I-3 Dimensions Used in Flow Calculations at Navarre Bridge .......................... 94 I-4 Predicted Effect of Navarre Pass on Flows in and out of Pensacola and Choctawhatchee Bays ........................ 99 I-5 Calculated Maximum Discharges and Velocities Through Navarre Pass for Various Tidal Ranges .................. 102 II-1 Ratio R, of Maximum to Minimum Tidal Ranges During the Period January 1 to February 9, 1970 .............. 116 vii

PAGE 8

LIST OF FIGURES Figure Page 1 Location Map of Santa Rosa Island Region .............................. 2 2 Aerial Photograph Prior to Navarre Pass Cut (Date of Photograph: February 14, 1963) ......................... 6 3 Oblique View of Gulf Terminus of Navarre Pass (Date: Unknown, but Probably August, 1965) ................. 7 4 Aerial Photograph of Navarre Pass Showing Effect of Westerly Littoral Drift (Date of Photograph: On or About September 1, 1965) ................... 8 5 Oblique View of Navarre Pass Shortly After Closure (Date of Photograph: September 1965) ............................ 9 6 Aerial Photograph Showing Filling of Pass by Air and Water Transported Sand (Date of Photograph: June 1970) ...... 11 7 Data Squares in Gulf of Mexico and Caribbean Sea .............................. 14 8 Monthly Wind Roses at Data Square Off Navarre Pass Area ...................... 15 9 Monthly "Sea" Roses at Data Square Off Navarre Pass Area ..................... 16 10 Monthly Swell Roses at Data Square Off Navarre Pass Area ...................... 18 11 Predicted Tides at Galveston, Pensacola and Miami Harbor Entrances ...................... 20 viii

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LIST OF FIGURES-Continued Figure Page 12 Example of Measured Tides in Gulf of Mexico and Santa Rosa Sound ............. 21 13 Measured Currents Offshore Navarre Beach, Florida. May 15-16, 1970 ........... 23 14 Currents Measured at Navarre Bridge, December 9-11, 1970 ............... 24 15 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of May 13-18, 1970 .............. 27 16 Locations of Principal Measurements Conducted During Field Trips .............. .28 17 Location of Tidal Division Line at 1545 on May 16, 1970 ............. ..... 30 18 Beach Profiles, December 9, 1970 ........... 33 19 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of December 7-12, 1970 .................... 37 20 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of July 19-23, 1971 ........................ 39 21 Experimental Groin Under Construction ...... 41 22 Coastal Sector Method Used by Coastal Engineering Research Center in Reporting Wave Direction .................. 48 23 Locations of CERC LEO Data Used in Littoral Drift Calculations. Drift Directions and Net Annual Rates Also Shown ................................. 49 24 Photographic History of Navarre Experimental Groin .......................................... 52-59 ix

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LIST OF FIGURES-Continued Figure Page 25 Weir Jetty System at Hillsboro Inlet, Florida ............................... 68 26 St. George Island Cut. Note Erosion Where Bank Protection is Not Provided .......... ......................... 71 I-1 Bay System Represented in Numerical Model ............................ 80 I-2 Illustration of Bay Segment Representation ............................. 84 I-3 Schematization of Pensacola Bay/ Choctawhatchee Bay/Santa Rosa Sound/ Gulf of Mexico System ...................... 85 I-4 Comparison of Measured and Calculated Ratios of Sound to Gulf Tidal Ranges Versus Gulf Tidal Range ................... 91 I-5 Comparison of Measured and Calculated Phase Lags Between Gulf and Sound Tidal Extremes ............................. 92 I-6 Comparison of Measured and Computed Santa Rosa Sound Tides and Discharges .......... .... ................... 95 II-1 Schematic Illustrating Stability Analysis for Single and Multiple Inlets ............. 104 II-2 Illustration of Escoffier's Stability Concept .................................... 107 II-3 Equilibrium Cross-Sectional Area and Tidal Prism Relationship (From O'Brien) .... 111 II-4 Variation of Maximum Inlet Velocity with Cross-Sectional Area for Equilibrium Conditions ................................. 113 II-5 Variation of Maximum Velocity with Inlet Cross-Sectional Area and Tidal Range. Navarre Pass, Florida ..................... 114 x

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LIST OF FIGURES-Continued Figure Page II-6 Predicted Tides at Galveston, Pensacola and Miami Harbor Entrances. Note Differences in Tidal Range Variations ............ 117 II-7 Cumulative Probability Distributions for Predicted Gulf Tidal Ranges at Navarre and Rollover Passes ................ 119 II-8 Auxiliary Diagram for Determination of Tidal Range Corresponding to Sedimentary Equilibrium (Example Shown for AC = 5000 ft2) ................... 120 II-9 Stability Analysis for Navarre Pass, Florida .............................. 122 II-10 Area Map Showing Location of Rollover Fish Pass ......................... 124 II-11 Numerical Model Representation of Galveston Bay .............................. 125 II-12 Variation of Maximum Velocity with Inlet Cross-Sectional Area and Tidal Range -Rollover Fish Pass, Texas .......... 126 II-13 Stability Analysis for Rollover Fish Pass, Texas .......................... 127 xi

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LIST OF SYMBOLS Symbol Description A,, A2 Flow areas through Navarre Bridge Ac Cross-sectional flow area of inlet ACE Equilibrium cross-sectional flow area A* Critical cross-sectional flow area C A Plan area of bay segment Cf Wind stress coefficient D Total depth = h + n f Darcy-Weisbach friction factor g Gravitational constant -G Subscript referring to "Gulf" variable h Depth below mean sea level K Entrance loss coefficient en K Exit loss coefficient ex L Length of bay segment or inlet n Exponent of velocity in sediment transport relationship n Subscript referring to nth bay segment p Tidal prism P Probability in percent q Discharge per unit width in the x-direction qR Runoff in cubic ft/sec per foot of bay length xii

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LIST OF SYMBOLS-Continued Symbol Description Q Total discharge across bay segment or through inlet R Ratio of maximum to minimum tidal ranges R Hydraulic radius, also tide range -S Subscript referring to "Sound" variable or "Spring" tidal range t Time T Tidal period U Wind speed at 30 ft reference elevation V Water velocity, in bay segment or through inlet w Width of bay segment considered x Horizontal distance coordinate aligned with bay axis y Horizontal distance coordinate perpendicular to bay axis B Angle of wind vector relative to bay axis n Water surface displacement from mean sea level, positive upwards 7T Numerical constant, 3.14159 .... p Mass density of water Pa Mass density of air a Angular frequency of tide T Wind stress on water surface Tb Frictional stress on bottom of water column xiii

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ACKNOWLEDGEMENTS Many individuals have contributed in a variety of ways to the study reported herein. The efforts of the Staff of the Department of Coastal and Oceanographic Engineering who participated in the field program are appreciated. The cooperation of the Santa Rosa County Beach Administration was most helpful, and the interaction and discussions with Messrs. Baskerville and Escoffier of Baskerville-Donovan Engineers, Inc., contributed to the final design presented in this report. Captain R. W. Slye kindly photographed the experimental groin and provided comments regarding its performance. Mr. W. J. Wells was instrumental in implementing this study and maintained an interest throughout the investigation. Mr. Walter Burdin of the Mobile District of the U. S. Army Corps of Engineers provided several aerial photographs and a continuing interest in this project. The Coastal Engineering Research Center willingly provided their Littoral Environmental Observation (LEO) data which included observations of wave height, period and direction. Mr. Curtis Baskette, a Graduate Student, became interested in and developed a computer program to compute littoral drift from the LEO data. xiv

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The study was under the general direction of R. G. Dean, Professor of Coastal and Oceanographic Engineering. xv

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I. INTRODUCTION In May, 1970, the Santa Rosa County Beach Administration contracted with the Coastal and Oceanographic Engineering (COE) Department of the University of Florida to carry out a coastal engineering study of the proposed Navarre Pass through Santa Rosa Island. Santa Rosa Island is a narrow barrier island with an east-west axis paralleling the mainland; the island is separated from the mainland by Santa Rosa Sound, see Figure 1. The proposed site for Navarre Pass is approximately at the mid-point of the Island and several thousand feet east of the Navarre Bridge; the approximate latitude and longitude of the Pass Site are: 30023' N and 86051'10" W, respectively. The Pass was first cut through the Island in July, 1965, however by September, 1965, the cut had widened and shoaled and was impassable to small craft. Since closing, the Pass reportedly has been reopened at least twice by a hurricane (Camille, 1969) and a severe winter storm. In December, 1970, the berm elevation across the original cut had been built up to an elevation of approximately +6 ft MSL. -1

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Escambia Bay Pensacola Bay East Bay Big Lagoon Choctawhatchee Bay -" Destin S _Santa (East) Location Rosa Pass Island GULF OF MEXICO FIGURE I LOCATION MAP OF SANTA ROSA ISLAND REGION

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II. PURPOSES OF STUDY The two primary purposes of the study include: (1) The impact of the Pass on natural processes, and (2) Recommendations relative to the conceptual design of the Pass. Impact of Pass on Natural Process The various natural processes of interest in this study are discussed in the following paragraphs. 1. Beach stability.--The possible effect of the Pass on the adjacent beaches was the consideration of greatest concern. Santa Rosa Island beaches are presently some of the finest in the State, are unencumbered by groin and seawall structures and are relatively stable. The deleterious effects on beach stability of inlet excavation and/or modification along the Florida East Coast has justifiably caused concern relative to future inlet modification. The littoral drift* characteristics in the area are particularly relevant to the matter of beach stability. The quantities and directions of littoral drift are also of interest in the configuration of the jetties, design of bypassing features and financial provision to mechanically transfer the sand interrupted by the presence of the Pass and jetties. 2. Stability of neighboring passes.--The passes to the east and west (East Pass and Pensacola Bay Entrance, respectively) would be influenced to some extent by the proposed Navarre Pass. It is conceivable that the water flowing through the Pass could "capture" a significant amount of the flow presently occurring through East Pass and Pensacola Bay Entrance, thereby causing these *Glossary of terms is provided as Appendix III. -3

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passes to shoal and a resulting increased dredging requirement or a decreased equilibrium cross-sectional area. Conceptual Design Features of Navarre Pass Based on the results of the study, recommendations will be presented relating to the following conceptual design features of the Pass: 1. Inlet dimensions and layout.--The primary factors considered in the inlet dimensions and layout will be: safe navigation, minimum effects on adjacent beaches, effect on neighboring passes, and maintenance costs. 2. Sand transfer and disposition of initial excavation material.--The initial and maintenance sand disposition including quantities will be recommended so as to result in a minimum interruption of the natural sand transport processes and beach stability. 3. Channel protection.--Unless provided with adequate protection against erosion, the banks of the cut and dunes will erode due to water and wind forces and tend to deposit in the Pass. The resulting deposition of material can interfere with navigation and cause an added dredging cost. Rip-rap or vertical sheet piling will represent the best form of bank protection in the cut whereas vegetation, if properly maintained could provide good protection against erosion by wind of the dunes and portions of the cut above water. -4

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III. BRIEF HISTORY OF NAVARRE PASS Navarre Pass was originally cut in July, 1965, by a pipe-line dredge at a cost of $30,000. The original dimensions were 100 ft wide by 9 ft deep. The primary purposes of the Pass included a more direct access to Snapper grounds and to provide a general economic stimulus to this portion of the Santa Rosa Island area. Figures 2 and 3 are aerial photographs prior to the Pass dredging and shortly after the dredging, respectively. The date of the photograph in Figure 3 is not known, but was probably taken in August, 1965. Note that some narrowing of the mouth of the Pass has occurred on the east side indicating the effect of westerly littoral drift. The photograph presented in Figure 4 was taken on or about September 1, 1965, and presents a more advanced case of deposition against the near-Gulf portion of the east side of the cut. The shoaling is not apparent from this photograph, but probably has reached an advanced stage. Figure 5 represents a photograph taken in September, 1965, after complete closure of the Pass. Again the effects of the westerly littoral drift in displacing the channel to the west are evident. Hurricane Betsy occurred during September 8-11, 1965, and presumably -5

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.rrP NAVARRE PASS CUT (DATE OF PHOTOGRAPH: FEBRUARY 14, 1963) -6-

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4dr 0410 ro rllaw ~3 ON dkv

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FIGURE 4 AERIAL PHOTOGRAPH OF NAVARRE PASS SHOWING EFFECT OF WESTERLY LITTORAL DRIFT (DATE OF PHOTOGRAPH : ON OR ABOUT SEPTEMBER 1, 1965) -8-W

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FIGURE 5 OBLIQUE VIEW OF NAVARRE PASS SHORTLY AFTER CLOSURE (DATE OF PHOTOGRAPH : SEPTEMBER 1965) -9

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was instrumental in the rapid development of the final closure stages. As shown in Figure 6, by June, 1970, the Pass had filled substantially so that the only remnants of the channel remaining below water are at the Sound side of the Pass. According to R. Bruno (1), the Pass has been opened naturally on at least two occasions since 1965. One of these occurred during Hurricane Camille in August, 1969 and the other opening resulted from a winter storm. No information is available concerning the extent of these openings nor of the magnitudes of the resulting flows through the Pass Site. Presumably the Pass closed fairly rapidly after each opening. -10

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FIGURE 6 AERIAL PHOTOGRAPH SHOWING FILLING OF PASS BY AIR AND WATER TRANSPORTED SAND (DATE OF PHOTOGRAPH: JUNE 1970) -11

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IV. METEOROLOGY AND HYDROGRAPHY OF AREA General Description The general offshore region near Santa Rosa Island is characterized by prevailing easterly winds with strong northerly winter winds. The easterly winds result in predominately southeasterly waves occurring in the nearshore region. These waves are responsible for the predominately westerly littoral drift. Tides in this area are predominately diurnal (i.e., a period of 24 hours) with the diurnal tidal range at Pensacola listed at 1.3 ft. During the field trips conducted in conjunction with this study, Gulf tides were measured from the Navarre Pier with tidal ranges in excess of 2 ft. Concurrent measurements of the tides in Santa Rosa Sound demonstrated that the tidal lag between the Gulf and the Sound generally varies between 2 to 32 hours and there is little if any reduction in tidal range (at Navarre Bridge, where the Sound tidal measurements were conducted). The Gulf nearshore currents were not studied extensively, however during one field trip an easterly current greater than 1 ft/second was measured fairly near shore. On later field trips, existing near shore currents were observed to be much weaker and were not measured. -12

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\'I Winds Data representing the offshore winds in the Gulf of Mexico are available in Reference 2. These data are the results of observations and measurements obtained from ships; the data are presented as average monthly conditions by the 5 degree latitude and longitude data squares shown in Figure 7. For the square off the Navarre Pass site, the monthly data are presented in Figure 8. The most persistent winds are seen to be from the east (easterly winds), with easterly winds of 11 to 16 knots occurring 8% of the time and easterly winds of 17-27 knots occurring 4% of the time. Calms occur about 11% of the time. With the predominant easterly winds, it is clear that the resulting predominant waves and littoral drift will be directed toward the west. During the period December through June, there are reasonably strong southeast winds and during October through March, fairly strong north and northeast winds occur. Sea The average distribution of sea (i.e., locally generated waves, generally of short period) obtained from Reference 2 are presented in Figure 9. Because sea results from the local winds, there is a strong resemblance between the wind roses presented in Figure 8 and the sea roses. It should be stressed that these sea roses pertain -13

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300 -1. :, .' ..j oo. Nov rre .Pass Site Data Square / U I VUsed For /, 1 Navarre Pass/ A S200 --. -/ stuÂŽ Z/Z .-I :5 -I I --/I I 1 I-. .1 1 II, 1 950 90 85 800 750 70 FIGURE 7 DATA SQUARES IN GULF OF MEXICO AND CARIBBEAN SEA

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9475 8576 1013 9681 6 656 00 10 20 00 40 50 60 70 80 90 100 10 20 3040 50 60.70 80 90 100 uI ]O 1 00 40 50 6) To 80 9C_ too January February March April 11666 9778 12099 12412 r1920 ? ^ i -^ )---a r--^T 12 C---[ '21 24 0 10 20 30 40 50 60 TO 80 9 00 0 0 10 20 0 40 150 60 17 0 O 90 0000 S 20 40 506 0 90o 20 30 40 So 60 r0 8o90 100 May June July August 10554 11886 12789 10449 I 5. i i 6 0 10 20 0 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 September October November December LEGEND NUMBER Or ___ 3, OBSERVATIONS -KNOTS FIGURE 8 MONTHLY WIND ROSES I 008 B R 0BEAUFORT AT DATA SQUARE OFF % BEAUFORT 01--ROSE SCALE (PERCENT FREQUENCY) NAVARRE PASS AREA ,O ,o20 30 o DOUBLE CIRCLE INDICATES THEORETICAL WIND ROSE. (SEE FIGURE 7) WIND SPEED SUMMARY (ALL DIRECTIONS) DATA FROM REFERENCE 2 BEAUFORT ORC CALM 2-3 4 5-6 7-12 0 10 20 30 40 30 60 70 80 100 PERCENT -"15

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5916 7298 7511 7 6481 January February March April 724 7414 8543 9129 I1161111111111 1 1 PIT 0 10 20 00 40 50 0 TO 80 90 r 00 0 ;O 20 30 40 50 60 70 80 90 100 I c 10 30 4 5S 61 71 80 90 0 10 20 30 4C 50 60 70 0O 90 100 May June July August 7621 j 7344 8461 9523 004 0 0 0 10 20 30 40 50 60 70 80 90 100 20 30 40 )' 60 70 80 90 100 'i i 0 1 20 0 40 50 60 70 80 90 100 i o.--:.09 ._ ___ 'i-_--' ....... September October November December LEGEND SEA 0 6203 -OBSERVATIONS FIGURE 9 MONTHLY "SEA" ROSES 20( OsRO AT DATA SQUARE OFF RGH, (5T. VERY ROUGH (8-12 FT.) NAVARRE PASS AREA" (SEE FIGURE 7) 30 / 404 (ALL DIRECTIONS) -16-

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to the data square off Santa Rosa Island as shown in Figure 7 and the sea indicated as originating from the north is not of concern in considering nearshore processes. For this data square, 80% of the sea has a characteristic (significant) wave height less than 12 ft. Swell The average monthly swell roses, determined from Reference 2 are presented in Figure 10. As for the case of the sea roses, the predominant swell affecting the Santa Rosa Island shoreline would propagate from the southeast, again contributing to a net westerly littoral drift. Tides The tides are of particular importance in maintaining an inlet open under the action of littoral drift which, unopposed, would result in the closing of an inlet. It is valid to regard the tidal "forces" and littoral drift "forces" in opposition, with the tidal forces being more or less predictable and periodic and the littoral drift forces only predictable on an average seasonal basis. Because periods of high littoral drift could result in the closure of an inlet, the most effective tidal characteristics for maintaining an inlet open would be a constant tidal range. The "forces" to maintain an inlet open would then -17

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4433 4741 4402 5150 0 0 020 30 4050 60000 TO 0820 39000000 0 010 20o 0 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0J 10 20 30 40 50 60 70 80 90 100 January February March April 5329 6591 4694 44 6860 0 53 0 51 37 0 0 ""i""1" ""1""i'1"" "1 1' "1 1 1"1.... o ,oo 2o 0 0 0to eoo i0 h0iom T 0 10 20 30 40 50 60 70 80 90100 0 10 10 '0 40 10 60 10 10 90100 0 10 20 30 40 5o 60 to 80 90 00 0 10 20 40 50 60 9O 70 80 90 100 May June July August 7141 5206 6260 5281 32 0 25 -T 0 o 0l I0l O 10 20 3030 40 50 60 70 80 90 100 100 S70 t 0 10 0 30 40 50 60 70 80 900100 September October November December LEGEND-SWELL FIGURE 10 MONTHLY SWELL ROSES 3% NO SWELL %_ CONFUSED AT DATA SQUARE OFF o ODERATE (6-12FT) ; HIGH (>12 FT.) NAVARRE PASS AREA I2 I (SEE FIGURE 7) |^ J DATA FROM REFERENCE 2 _.,, .. 0 t10 20 30 40 50 60 70 o80 90 I00(%) SUMMARY SCALE (ALL DIRECTIONS) -18

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always be operating at an effective level to counteract any unusually heavy littoral drift occurrence. Unfortunately, the tidal range in the Santa Rosa Island area of the Gulf of Mexico is not nearly constant, but varies greatly from spring to neap conditions. The tidal ranges encountered during the different field trips varied from a low value of 0.36 ft (4 inches) to an upper range of 2.2 ft. The tide tables indicate a ratio of maximum to minimum tidal range of approximately a factor of 18. Figure 11 presents a plot of the predicted tides for the month of January and a portion of February, 1971 for Pensacola, Galveston Entrance and Miami Harbor Entrance. The low tidal range periods are indicated when an inlet would be highly susceptible to deposition. An example of the measured Gulf and Sound tides obtained during the July 1971 field trip is presented in Figure 12. Offshore Currents During two of the field trips, attempts were made to install a recording current meter in a water depth of approximately 16 ft at a location about 900 ft offshore of the Pass Site. The first attempt was successful and resulted in a recording of approximately 24 hours duration, however the current meter malfunctioned during the second attempt and no data were obtained. The data obtained during the first field trip were quite -19

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1.0 -I.0GALVESTON ENTRANCE Period of Period Low Relative of High Susceptibility Relative to Deposition Susceptibility 10 to Deposition rp 1.0 ) IUI )| I UIU u V u --1.0 PENSACOLA January, 1971 February, 1971 5 10 15 20 25 30 5 1i l l l l l I i I iI I I I I l i l I i 1 1 1 1 1 1 I III I i 2.03: 1.0-1.0MIAMI HARBOR ENTRANCE FIGURE II PREDICTED TIDES AT GALVESTON, PENSACOLA AND MIAMI HARBOR ENTRANCES. NOTE DIFFERENCES IN TIDAL RANGE VARIATIONS -20

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Note In This Figure, The Gulf And Sound Tides Are Not Referenced Gulf of Mexico To A Common Elevation Datum Santa Rosa Tide 0 12 15 18 0 9 12. 15 0 3 6 9 oHours SJuly 21, 1971 .July 22, 1971 --July 23, 1971 -2 FIGURE 12 EXAMPLE OF MEASURED TIDES IN GULF OF MEXICO AND SANTA ROSA SOUND

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surprising and showed a strong easterly current (1.3 ft/sec) at the time of installation which decreased to approximately 0.5 ft/second during the 24 hour recording period. These data are presented in Figure 13. During the second field trip, the divers noted while installing and recovering the current meter that there was no appreciable current. It is believed that the current measured during the first field trip was perhaps due to some effect of the Gulf Stream which does form a general clockwise circulation pattern in the Gulf of Mexico. Because the information pertaining to this current is very limited, it is not possible to conclude whether the effect on littoral drift is significant, however it is noted that if the prevailing current direction is easterly, and if the current is significant in the surf zone area, then the effect would be to reduce the net westerly littoral drift. Santa Rosa Sound Currents During one of the field trips, currents were measured from the Navarre Bridge over a 40-hour period. These measurements were conducted with a nonrecording current meter and therefore were taken intermittently. The measurements are presented in Figure 14 where it is seen that the maximum velocities are on the order of 1 ft/sec. -22

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2.0 NOTE: CURRENT METER LOCATED APPROXIMATELY 900 FT. OFFSHORE OF PROPOSED INLET SITE WATER DEPTH = 15 FT. DISTANCE. o OF METER ABOVE BOTTOM = 6 FT. 4z 1.0w -o 1200 1600 2000 2400 0400 0800 1200 TIME (hours) MAY 15 MAY 16 IFIGURE 13 MEASURED CURRENTS OFFSHORE NAVARRE BEACH, FLORIDA. MAY 15 -16, 1970

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1.0 I Smoothed Curve Drawn Through Measurements 0 o I , I, \ l l i l l l ll 1 1 l 4,-O 1800 0000 0600 1200 1800 0000 0600 -Dec. 9, 1970 Dec. 10, 1970 Dec. II, 1970 \ e Note: See Figure 16 SFor Location of Current Measurements 1.0 FIGURE 14 CURRENTS MEASURED AT NAVARRE BRIDGE, DECEMBER 9-11, 1970

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V. FIELD STUDIES AND RESULTS Three separate field studies were carried out during the study. The dates and programs carried out during these three studies are presented in Table I. A brief description of each of the field studies is presented below. Field Trip No. 1, May 13-18, 1970 During this field trip a baseline was established which ranged approximately 1000 feet east of the centerline of the proposed inlet to 2000 feet west of the centerline. The baseline was located shoreward of the active beach profile on the foredunes to reduce losses of the stakes. Beach profiles and offshore soundings were conducted and the contoured results are presented as Plate I in the report cover jacket. Two tide gages were installed: one was located in the Sound in the vicinity of the south bridge section of the Navarre Bridge; the second was installed on the Navarre Pier near its seaward end. The tides during this period were quite small. The predicted tides at Pensacola, Florida ranged from 0.3 to 0.7 feet. The recorded tides are presented in Figure 15 and Figure 16 shows the locations of the tide gages and other field measurements. From the tide records, very little difference in Bay and Gulf tidal -25

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TABLE I Summary of Field Trip Activities and Information Obtained Data Obtained Dates Encompassed Gulf Sound Beach Offshore Additional Activities and by Field Trip Tides Tides Profiles Soundings Data Obtained May 13-18, 1970 Yes Yes Yes Yes 1. Baseline Established (36 Hour (36 Hour 2. Offshore Currents Duration) Duration) Measured (24 Hours) 3. Sand Samples Collected 4. Sound "Tidal Division Line" Established Dec. 7-12, 1970 Yes Yes Yes No 1. Sound Currents (36 Hour (36 Hour Measured From Navarre Duration) Duration) Bridge (40 Hour Duration) July 20-25, 1971 Yes Yes Yes Yes 1. Experimental "Sand Bag (24 Hour (24 Hour Groin" for Littoral Duration) Duration) Drift Observations Constructed

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+0.5 +0.5 Santo Rosa Sound Tides May 14, 1970 May 15, 1970 E 0 -0r Gulf of Mexico Tides _--0.5 2 +0.5 May -15, 1970 May 16, 1970 -. .... .. ....-S0 1.0.5 +0.5 c May 16, 1970 May 17, 1970 0 0 -____ -0. ----------------------------------------------------------------------0.5 rI j1 II I I I I I I I 1 1 1 1 0900 1200 1500 1800 2100 0000 0300 0600 FIGURE 15 MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF MAY 13-18, 1970

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N 0 5000 ..'. Scale (ft) Sound S on 0o Site of Original -Navarre Bridge Navarre Pass Cut Navarre Bridge Sound Tide Gageu M.a : sS .."s ......... s...-d.. Sant of Su'f" i Gage Extent of Gulf Bothymetric Survey N--" Gulf Tide Gage.' Pier FIGURE 16 LOCATIONS OF PRINCIPAL MEASUREMENTS CONDUCTED DURING FIELD TRIPS

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amplitudes could be determined. An attempt was made to determine the location of the "tidal division line" in the Sound. This is a somewhat hypothetical separation line of the area (to the West) which is served (alternately filled and drained) by Pensacola Bay Entrance and the area (to the East) which is served by the East Pass to Choctawhatchee Bay. This line is affected greatly by winds and under conditions of very high winds may not exist at all. The location shown in Figure 17 was determined on May 16 by searching until the velocity some distance to the west of that location was toward the east and the velocity some distance to the east of that location was directed toward the west. Computations using the numerical model described in Appendix I indicates that the position of the "tidal division line" varies during a tidal period from approximately 15 miles east to 20 miles west of the Navarre Pass Site. Offshore currents were determined by installing a current meter approximately 900 feet offshore of the location of the proposed pass. The current flowed to the east during the two day period the meter was installed, see Figure 13. The peak current was approximately 1.3 ft/sec. Thirteen nearshore sand samples were collected and later analyzed for grain size distribution. Table II summarizes the results of the analysis of median diameters -29

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I IN 0 I 2 Scale (Statute Miles) re Bridge Iw Santa Rosa Sound "~--Tidal Division Line Santa FIGURE 17 LOCATION OF TIDAL DIVISION LINE AT 1545 ON MAY 16, 1970

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TABLE II Summary of Median Diameters of Sand Samples Analyzed (Field Trip of May 1970) Sample Collected Sample Location on Sample Median at Station Beach Profile Diameter (mm) 10+00 E 2 ft Below Mean 0.42 Sea Level 10+00 E Base of Small Scarp 0.35 10+00 E Midshore Between 0.50 Waterline and Berm 0+00 2 ft Below Mean 0.51 Sea Level 0+00 Limit of Wave 0.37 Uprush 0+00 Foredune 0.45 10+00 W Midway Between 0.46 Berm and Scarp 10+00 W Base of Scarp 0.36 10+00 W 2 ft Below Mean 0.50 Sea Level 20+00 W Midway Between 0.40 Berm and Scarp 20+00 W 2 ft Below Mean 0.33 Sea Level 20+00 W Limit of Wave 0.47 Uprush 20+00 W Base of Scarp 0.37 -31

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of the samples. It is seen that the median diameter ranges from 0.33 mm to 0.51 mm. This represents a relatively coarse beach sand for the State of Florida. Field Trip No. 2, December 7-12, 1970 During this field trip, the waves became quite high on the morning of December 8, thereby precluding the possibility of launching a boat through the surf to conduct offshore soundings. Beach profile measurements were conducted and are shown in Figure 18. It is of interest to note that, in places, the sand accumulation in the former Navarre Pass "cut" was 18" from May 1970 to December 1970 as determined by noting the burial of the stake at Station 0+00. It is not known whether this accumulation was primarily due to wind-blown sand or sand transported over the berm by combinations of high tides and waves. Two tide gages were installed at the same locations described for the previous field trip. The predicted tides at Pensacola Bay during this trip ranged from 1.2 feet to 2.1 feet. The tide records for the period December 8-11 are shown in Figure 19. It was found again that there was little difference in tidal amplitude between the Sound and Gulf and also that the tidal lag was between 3 and 4 hours. -32

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+ 10 --,* ^ ^ ---------------Station 20+00 W 0 Is---^ ---_0 100 200 Distance From Baseline (ft) I 10 -" Station 18+00 W 100 200 Distance From Baseline (ft) 2 +10 Cj Station 16+00 W 0 100 200 Distance From Baseline (ft) +10 s^ -----_I --Station 14+00 W 4.S ( __ O100 2300 Distance From Baseline (ft) FIGURE 18 BEACH PROFILES, DECEMBER 9, 1970 -33

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J --Station 12+00 W 0 _0 o100 200 Distance From Baseline (ft) +10 -.--Station 10+00 W 0 _0oo \ .200 t Distance From Baseline (ft) +10 _J --Station 8+00 W 0 |> 0O 100 __ 200 ,i,< Distance From Baseline (ft) +10 S) \-Station 6+00 W £B 6 100 1 200 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -34

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cJ -Station 4+00 W 20 Distance From Baseline (ft) +10 o----Station .:2+00 W o oo 100 200 S Distance From Baseline (ft) +10 -, = ----S---Station 0+00 1 0_ 100 _200 Distance From Baseline (ft) +10 _-Station 2+00 E S100 200 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -35

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+10 -) -Station 4+00 E > 1 Distance From Baseline (ft) +10 S-Station 6+00 E S_____ _____0 200 Distance From Baseline (ft) +10 _J Station 8+00 E 4S,'___ 100 200 < Distance From Baseline (ft) +10 -J --Station 10+00 E S0,36 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -36

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... +1.0 -__ SSound + 0.5 -Gulf § o 1I I I II I I 1, S0900 1200 1500 1800 2100 06 W I Time (hours) CST -0.5 I b ._ December 8, 1970 December 9, 1970 -1.0 +1.0 Gulfound +0.5 0 01200 1500 1800 2100 0600 0 December 9, 1970 1December 10, 1970 -0.5 -1.0 +1.0 '8 ^ -/Sound < +0.5 -\Gulf 900 1200 1500 1800 2100 0300 06 S n *; "y <~~~-------------' ----^ -o.Note: December 10, 1970 ecember II, 1970 .' SGulf and Sound Tides -1.0 Not Referenced to Some Datum FIGURE 19 MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF DECEMBER 7-12, 1970 -37

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A current meter was also installed offshore, however the high wave activity caused a mechanical failure and no data were obtained. It was noted during installation and retrieval of the current meter, that net currents were relatively small. Sound currents were measured over a 40-hour period. The results of these measurements have been presented as Figure 14. The maximum velocities were in excess of 1 ft/sec. The significance of the Sound currents and their relationship to the tides will be discussed later when the calibration of the numerical model is presented. Field Trip No. 3, July 19-23, 1971 In addition to the type of information collected on previous field trips, a temporary sand bag groin was installed to act as a partial littoral drift barrier. The hydrographic information collected during this field trip included beach and offshore soundings and Gulf and Sound tide records. The Gulf tidal range measured was approximately 2 ft and the tidal lag between Gulf and Sound was in the range 3h 20m to 4h 20m. See Figure 20 for the tide records which were measured during a 48-hour period. The contoured results of the beach profiles and offshore soundings are presented as Plate II in the cover -38

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S 0900 1200 15o0 180 .2100 03 WL > Time (Hours) -+1.0 *..).. -------1.0 15 I -July 22, 1971 July 23, 1971 __ -^ ~ S o u n d E --Gulf .o0 -1.0 +10, +. ROSA SOUND DURING FIELD TRIP OF JULY 19-23 1971 -39

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jacket of this report. In order to carry out these surveys, it was necessary to reestablish much of the baseline which had been destroyed by four-wheel vehicles and other extraneous activities. An experimental sand bag-groin was constructed at the site of the planned Navarre Pass. The purpose of this groin was to perform as a partial littoral drift barrier and through observations of the impoundment, to provide a qualitative indication of the direction and persistence of the nearshore littoral drift. Two photographs of the groin under construction are shown in Figure 21. Unfortunately, due to settlement, the groin was only effective for a period of 2 months and the groin was not maintained because the required sand bags were not available for a period of 4 to 6 months. The performance of the groin will be discussed in "Section VI -Littoral Drift" and photographs (kindly taken by R. W. Slye) will be presented. -40

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July 1971 -Groin Under Construction July 1971 -Groin Nearing Completion Extreme Low Tide FIGURE 21. EXPERIMENTAL GROIN UNDER CONSTRUCTION

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VI. LITTORAL DRIFT Introduction In considering the establishment of a new inlet, the magnitude and direction of sand transported in the nearshore region (littoral drift) by waves and possibly currents are most important factors and also the most difficult to establish accurately. Jetties act to block sand from entering inlets, thereby rendering them more suitable for navigation. In performing this function, jetties interrupt the natural flow of sand (littoral drift) along the shore with the resulting accumulation of sand on the updrift side of the jetties. Since the waves maintain their sand-transporting capacity downdrift of the jetties, serious erosion can occur with long-term degradation of the downdrift beaches. In addition to interrupting the natural flow of sand along a beach, the interaction of inlet currents and sediment causes bars to be built offshore and in the inner bay. The material comprising these bars is derived from the natural sand system and therefore represents a loss to that system. Of course, once these bars have been established to near-capacity, then subsequent annual losses are reduced. -42

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In considering the establishment of a new inlet, the sand must be recognized as a valuable resource and the sand transfer as a natural process. Interruption of the sand transfer or the net loss of a significant amount of sand from the active system will definitely lead to a significant adverse effect On the downdrift beaches. In recognizing the significance of these processes and the necessity of maintaining the stability of the Santa Rosa Island beaches, the cutting and stabilizing of a new inlet should be planned to minimize any net loss of sand to the system and also to provide for the mechanical transfer of the sand interrupted by the presence of the jetties. A number of attempts have been made to design jettied inlets such that sand is prevented from interfering with.: navigation, yet the currents and waves still provide for the natural transfer of sand. A survey of jettied inlets will demonstrate that this approach has not proven successful and that the only effective concept is to provide for the artificial bypassing of sand. Littoral Drift Estimates Littoral drift estimates can be based on field measurements or on calculation procedures using wave data. Each of these approaches has advantages and disadvantages. Good accuracy in field measurements of littoral drift requires a near-complete trap (e.g. a long jetty) -43

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and reasonably long records in which the trap impoundment history is documented and/or records are kept of the amount of material removed or added to maintain stability of the downdrift shoreline. Littoral drift calculations are based on wave measurements and/or observations; to date (1972) the calculation procedures have not been developed and verified to the degree that a high degree of confidence is warranted. The most often applied calculation procedure (3) does not account for many presumably important parameters, including (1) sand size (2) sand specific gravity (3) beach slope (4) beach roughness In attempting to develop the best estimate of littoral drift, all sources of information should be reviewed with relative confidence based on the particular circumstances attending each measurement or calculation. Field Measurements.--The available field measurements in the Navarre Pass area are generally based on the westward rate of growth of the western ends of barrier islands and on the accretion behind the eastern jetty at Perdido Pass. Based on the rate of growth of the western end of Santa Rosa Island, and the dredged quaritities in the -44

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Bay Entrance and on the shoals, the U. S. Army Corps of Engineers (4) has concluded that the average annual westward and eastward drift are 130,000 and 65,000 cubic yards, respectively, resulting in an annual net westward drift of 65,000 cubic yards. In 1938, F. F. Escoffier (5) analyzed the westward growth rates of the eastern shore of East Pass (entrance to Choctawhatchee Bay), the results available at that time indicated an annual deposition rate of 26,300 cubic yards, although Escoffier noted that this quantity is undoubtedly smaller than the net littoral drift due to some bypassing of material past the inlet. The Corps of Engineers (4) estimates the westerly and easterly drift components at Perdido Pass to be 130,000 and 65,000 cubic yards per year resulting in a net westerly drift of 65,000 cubic yards per year. During the period May 1969 to March 1970, the Corps measured the deposition inside the Perdido Pass weir jetty to be 146,000 cubic yards. Hurricane Camille occurred within this period and may account for the higher than anticipated impounded quantities. For the period 1934-1953 (before the weir jetty system was constructed), J. W. Johnson (6) analyzed accretion at the eastern bank of Perdido Pass and concluded the annual deposition to be 200,000 cubic yards; presumably this would correspond approximately to the net westerly littoral drift. -45

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Calculations of Littoral Drift.--D. S. Gorsline (7) conducted a one-year study of Gulf beaches extending from Keaton Beach, Florida to Gulf Shores, Alabama. His study included monthly surveys of fifteen beaches in the study area and wave observations. Gorsline carried out calculations which indicated the gross drift rates at Pensacola to be approximately 200,000 cubic yards per year with a net westerly drift of 78,500 cubic yards/year. It should be stressed that Gorsline's calculations at each location were based on only one observation per month over a period of one year. There is a good likelihood, therefore that his results are not representative of average annual conditions. T. L. Walton (8) has carried out computations of littoral drift along all of the sandy beach segments of the State of Florida. The calculations are based on long-term wave observations collected by military and commercial ships. The wave characteristics are transformed to shore using standard procedures and drift is calculated based on the usual relationship (3). In comparing his predictions with other estimates for the Florida East Coast, Walton found generally good agreement for portions of the northern Florida east coast, however his calculated values were much higher than estimates based on impounded quantities along the lower Florida east coast. This difference was attributed, at least in part, to the -46

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proximity of the Gulf Stream and its effect in causing an increase in height of waves propagating from the northeast. This would qualitatively explain the differences noted. In the Navarre Pass area, Walton's calculated annual westward and eastward drifts are approximately 400,000 and 100,000 cubic yards, respectively, resulting in a net westward littoral drift of 300,000 cubic yards per year. The Coastal Engineering Research Center (CERC) collects shore-based observations in a program entitled "Littoral Environmental Observations" (LEO). The LEO data are generally taken daily and include visual estimates of breaking wave height and breaking wave direction in terms of a coastal sector method, see Figure 22. These data provide an alternate basis of estimating littoral drift, using the usual calculation procedure and assuming that the wave conditions reported are representative for the entire 24-hour period. Data were provided by C. J. Galvin and A. De Wall of CERC for four locations: Navarre Beach, Grayton Beach, Beasley Park and Crystal Pier. The period over which data were available ranged from 8 months at Navarre Beach to 24 months at Beasley Park and Crystal Pier. See Figure 23 for a map of the four observation locations. Table III summarizes the littoral drift values calculated from the LEO data. -47

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OCEAN If No Waves, Fill in Zero 3 2 4 S\ /o 100 250 250 600 600 Shoreline Observer LAND WAVE DIRECTION CODE FOR WAVES AT BREAKING FIGURE 22 COASTAL SECTOR METHOD USED BY COASTAL ENGINEERING RESEARCH CENTER IN REPORTING WAVE DIRECTION -48

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S Pensacola Bay Pens a By / Choctawhatchee Bay 5"i',Oo( e (Beasley ., tat ,o Park) Cry ,^^ GULF OF MEXICO Note: Arrows and Numbers Indicate Calculated Directions and Net Annual Littoral Drift (in Cubic Yards/Year) Using Leo Data FIGURE 23 LOCATIONS OF CERC LEO DATA USED IN LITTORAL DRIFT CALCULATIONS. DRIFT DIRECTIONS AND NET ANNUAL RATES ALSO SHOWN

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TABLE III Summary of Calculated Littoral Drift Using LEO Data Results Averaged Annual Duration of Data Calculated Littoral Drift Net Drift Location Available Interval (Cubic Yards) (Cubic Yards/Year) Navarre Beach 8 months Jan. 1, 1970 to Sept. 1, 1970 158,000(W)* 237,000(W) Grayton Beach 24 months Dec. 1, 1970 to Dec. 1, 1971 53,345(W) 52,100(W) Dec. 1, 1971 to Dec. 1, 1972 50,776(W) Beasley Park 24 months Jan. 1, 1971 to Jan. 1, 1972 30,064(W) 45,200(W) Jan. 1, 1971 to Nov. 1, 1971 50,321(W) Crystal Pier 12 months July 1, 1971 to July 1, 1972 253,331 253,331(W) *(W) denotes drift from East to West.

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Experimental Groin at Navarre An experimental sand bag groin was constructed at the site of the original Pass. The purpose of the groin was to obtain information regarding the variability and (hopefully) magnitudes of littoral drift. The groin was constructed on July 22, 1971 and extended 100 ft seaward of the mean high water line. The groin was about 3 ft high by 8 ft wide; two photographs showing the groin under construction have been presented as Figure 21. The groin was reasonably effective in trapping the nearshore portion of drift for a period of approximately 2 months, after which the portion of the groin traversing the beach face was undermined and settled significantly (about 4-6 ft). At that time, it was planned to rebuild the groin by adding more sand bags. Unfortunately the sand bags were not available* for a period of 4 to 6 months and the experiment was discontinued. A brief photographic history of the groin is presented in Figure 24.** During the period August 5 to August 8, 1971, impoundment occurred on the west side of the groin. On the morning of August 9, impoundment was evident on the east side of the groin which remained the *The factory had experienced a fire. **Captain R. W. Slye of the Santa Rosa County Beach Administration kindly offered to photograph the groin. -51

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August 5, 1971 -Note Slight Build-up August 8, 1971 -Continued Accretion 0800 From West 0800 on West Side of Groin FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (Photographs Taken by Captain R. W. Slye)

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4pf .. 0"" W-August 9, 1971 -Accretion is Now Apparent on August 20, 1971 -Some Evidence of Lessened 0900 East Side of Groin. Some Easterly Drift Compared to Transport of Sand Over Groin Photograph of August 9, 1971 is Evident FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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August 28, 1971 -Accretion on Western September 2, 1971 -Evidence of Drift Reversal 0800 Side of Groin -Compare 0830 Compared to August 28, 1971 With Photographs of Photograph. Also Note August 9 and 20, 1971 Lowering of Middle Portion of Groin Due to Undermining FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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September 8, 1971 -Same General Accretion September 13, 1971 -Groin Has Been Flanked 1200 Situation as Shown on 0900 With Scarping to East September 2 Photograph (Also See Following Photograph of Same Date) FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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September 13, 1971 -Showing Effect of High September 22, 1971 -Drift Accumulation on 0900 Tides and Easterly Drift 1130 East Side of Groin and Escarpment Indicates Reversal From September 13 Photograph FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken By R. W. Slye)

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October 1, 1971 -Groin Profile Has Been October 7, 1971 -Drift Passes Over 0830 Lowered Significantly 0800 Groin in Beach Face Due to Undermining. Region Groin is Now Generally Ineffective for Drift Impoundment FIGURE 24. PHOTOGRAPHIC HISTORY OF EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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October 14, 1971 -Beach Accretion Has November 30, 1971 -Groin Ineffective as 0900 Nearly Completely 0800 Littoral Drift Impediment. Buried Shoreward Photograph Taken at Low One-Third of Groin Tide FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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December 16, 1971 Final Photograph of 0800 Experimental Groin FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken By R. W. Slye)

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dominant side through August 20. By August 28, the drift had reversed again and the impoundment was on the west side of the groin. On September 2, 1971, impoundment had occurred on the east side and the first groin subsidence is evident. By September 13, 1971, the groin had been flanked by high waves and tides and the impoundment was on the west side of the groin. By September 22, the drift evidence was from the east. The photographs on October 1, 1971, and thereafter show that the upper one-third of the groin had subsided to such an extent that it would no longer be effective in impounding littoral drift. Although it is clear that the groin installation was not effective to obtain quantitative evidence regarding the littoral drift, it is of interest that during the two month period over which it was effective, the impoundment indicated nearshore drift reversal at least six times. Furthermore, because the nominal interval between photographs is one week but was as great as eleven days, it is likely that more reversals than noted had taken place. It is noted that the months of August and September are not expected to be the months of heaviest nor most persistent drift. The sea and swell charts for this period, however, do indicate that for average August and September months, net drifts to the west are to be expected. -60

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Although it is not possible to draw strong conclusions from the experimental groin due to the short period over which it was effective, it does appear that drift rates based on the ship data would yield drift rates to the west that would be unrealistically high. Summary and Recommendations Several littoral drift estimates in the Navarre Pass area have been presented. These estimates all indicate a net westward drift with net magnitudes ranging from 65,000 to 300,000 cubic yards per year. This range represents a factor of 4.6 which is not too surprising considering the present state of knowledge of littoral drift quantities. Considering the estimates available, it is believed that the net annual littoral drift is something less than 200,000 cubic yards to the west. It will be recommended that the inlet maintenance be planned to provide transfer of 200,000 cubic yards per year with the understanding that the actual amount required is expected to be less than this value. This represents a responsible approach to the problem of maintaining the littoral drift and it is realistic to reduce the amount of sand transfer below that planned, however, the financial and equipment problems attendant with increasing the sand transfer above that originally planned argue against arranging for a lesser amount. -61

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VII. SUMMARY OF NUMERICAL MODEL CALCULATIONS Introduction In order to represent the behavior of Navarre Pass and its interaction with adjacent entrances a computer method which simulated the flows into and through the Santa Rosa Sound system was developed and applied. This method is called a "numerical model" as opposed to a hydraulic model and has the advantage of rationally incorporating the interaction of Navarre Pass with the tides and flows in Santa Rosa Sound and also with the flows through the entrances to Choctawhatchee and Pensacola Bays. The basis for and evaluation of the numerical model are described fully in Appendix I -"Numerical Model of the Bay System Affecting Navarre Pass." After evaluation for the present situation in which no flows occur through Navarre Pass, the model was modified and used to evaluate the effect of Navarre Pass on flows through neighboring inlets and also to calculate the expected velocities through Navarre Pass. Appendix II -"Stability of Navarre Pass" presents an evaluation of the tendency of Navarre Pass to close by comparing the sedimentary stability -62

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with Rollover Pass, Texas which is an artificial inlet which grew rapidly after opening. The results of applying the numerical model are described in detail in Appendixes I and II and are presented briefly in the following sections. Results Obtained Using the Numerical Model Effect of Navarre Pass on Entrances to Pensacola and Choctawhatchee Bays The percentage changes in flows through Pensacola and Choctawhatchee Bays due to the influence of Navarre Pass were evaluated for various Gulf tidal ranges. These results are tabulated in Table I-4 (Appendix I). It was found that, as expected, the presence of Navarre Pass would decrease the total inflows and outflows through the entrances to Pensacola and Choctawhatchee Bay Entrances. The largest percentage effect was on Pensacola Bay Entrance due to the Sound being of greater width between Navarre Pass and Pensacola Bay than between Navarre Pass and Choctawhatchee Bay. For a tidal range of 1.5 ft (approximate average), the percentage reductions in the maximum flows in and out of Pensacola and Choctawhatchee Bays are 2.0% and 0.1%, respectively. For a more complete summary refer to Table I-4 in Appendix I. The reduction in tidal flows -63

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into Pensacola Bay will result in an associated reduction of 1.8% in equilibrium cross-sectional flow area into this Bay. For Choctawhatchee Bay the equilibrium flow area will be reduced by 0.1%. Maximum Velocities Through Navarre Pass The peak velocities averaged over the Pass crosssection are calculated to vary from 1.27 ft/sec to 3.54 ft/sec for Gulf tidal ranges varying from 0.5 to 2.0 ft, respectively. This range of velocities is well within acceptable limits for small craft navigational safety. A more complete summary of maximum velocities is presented in Table I-5 of Appendix I. Relative Stability of Navarre Pass Computations were carried out in Appendix II to compare the tendency of Navarre and Rollover (Texas) Passes to remain open. These two passes have respective histories of closure and growth following their initial openings. The calculations showed that the geometric and tidal conditions at Navarre Pass are much less conducive to remaining open without jetties than at Rollover Pass. These calculations simply reinforce the known requirement for jetties at Navarre Pass. -64

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VIII. RECOMMENDED DESIGN OF NAVARRE PASS INLET Functional Design In developing a functional design of Navarre Pass, the primary factors considered were: (1) minimum adverse effects on adjacent beach stability through effective sand by-passing and placement of initial sand dredged, (2) navigational safety for craft using the Pass, (3) improvement of water quality within the Sound adjacent to the Pass, and (4) a minimum of required costs associated with the periodic maintenance of the Pass. Some of the factors noted above conflict, for example the effective by-passing of sand will be fairly expensive. In the recommendations pertaining to the layout and planning for the Pass, the highest priority will be given to beach stability and navigational safety. Recommended Layout of Navarre Pass Prior to discussing the recommended layout of Navarre Pass, it is emphasized that it is not intended to present a final detailed design, but rather a workable conceptual design which is in accordance with the objectives presented in the preceding section. The Santa Rosa County Beach Administration and their engineers will make a -65

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detailed engineering design and will make modifications to the recommended layout which facilitate or reduce the cost of construction. These modifications, however, should not significantly impair the performance of the design. The recommended layout of Navarre Pass is presented as Plate III in the jacket in the back cover of this report. The main components of the Pass include: (1) a weir jetty and deposition basin for the trapping and retention of sand until by-passed to the downdrift (west) side of the Pass, (2) a training wall on the Pass sides to provide lateral stability of the cut, (3) a navigational channel, 12 feet deep by 150 feet wide extending through the Island to the 12 feet contour on the Gulf side and to the Intercoastal Waterway on the Sound side, and two jetties extending into the Gulf, and (4) either mechanical or vegetative control of wind drift of sand. Each of these features is discussed separately below. 1. Weir Jetty and Deposition Basin-A weir jetty and deposition basin (sand trap) are recommended with the weir section 400 ft long, oriented parallel to shore and with the weir crest elevation at the approximate present mean sea level contour. The design and construction of the weir are to be such that minor required increases in weir elevation can be accomplished by the addition of stone. In considerations of weir stability, the design should account for the expected variations in sand -66

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elevations on both sides of the weir. The weir design recommended is similar to that at Hillsboro Inlet, see Figure 25. The weir section at Hillsboro Inlet is 200 ft long and the elevation of the weir crest is at MSL. The eastern end of the weir should be tied into the natural dune system in order to prevent flanking and a short adjustable groin should be located at the eastern end of the weir in order to provide a control on the stability of the updrift (eastern) beaches. The expected performance of the weir/deposition basin is as follows. After initial or maintenance dredging of the basin, the predominately westward littoral drift will deposit in the basin at the eastern end of the basin. If the tides and waves are low during this period, a spit will grow toward the west and will be located on the Gulfward side of the weir. During periods of high tides and/or high waves, the sand forming this spit will be carried further into the deposition basin and the weir will be re-exposed. For the dimensions of the basin shown, the volumetric storages below MSL are 48,000 and 64,000 cubic yards based on a 1:3 side slope and maximum basin depths of 12 and 18 ft below MSL respectively. Depending on the quantities of net westerly littoral drift, the basin would require maintenance dredging and by-passing to the west side of the inlet on a frequency ranging from 1 to 3 times a year if carried out on a -67

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FIGURE 25 WEIR JETTY SYSTEM AT HILLSBORO INLET, FLORIDA -68

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demand basis. Because the heaviest littoral drift is expected during the winter, the required dredging may be more frequent during this season. Due to the present uncertainties in net littoral drift magnitudes, it will be difficult to realistically address the problem of maintenance dredging and by-passing to the west if this is planned to be done on a contract basis. An alternate concept providing flexibility would be a relatively small custom dredge built for and operated under the direction of an agency established for the overseeing of the Pass operation and maintenance. This would also allow any small amount of maintenance dredging required in the channel or at the tips of the jetty to be carried out during relatively calm wave conditions which would be difficult to schedule in advance on a contract basis. The Hillsboro Inlet District has successfully operated their small custom dredge for by-passing and minor maintenance dredging in the channel and marina for over eight years. The possibility of the northern portion of the deposition basin providing a recreational facility could be considered. The wave energy at this point will be reduced and the beach slope could be controlled. A marina occupying a portion of the basin is another possibility, but would be reduced in value due to land access problems, especially if a bridge spanning the Pass is not constructed. -69

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2. Training Wall on Sides of Cut--The banks of the cut should be stabilized with sheet piling or rubble protection to prevent sloughing and erosion of the sides. The consequences of not providing a means for bank stabilization will be a widening and shoaling crosssection, and increased maintenance and possibly a migrating interior channel which would also result in the need for increased maintenance. There are advantages of reduced reflection of boat waves if a rubble mound bank protection is chosen. The cut through St. George Island (Figure 26) is an example of erosion if no training walls are provided. 3. Navigational Channel and Jetties-It is understood that the Navarre Pass Committee desires a 12 ft deep channel to match the depth of the Intercoastal Waterway through Santa Rosa Sound. The desired width of the 12 ft depth portion is 150 ft with a somewhat greater width of the remaining portion of the cut. Some of these features are flexible and can be varied within limits of safe navigational consideration. The channel shown in Plate III is 12 ft deep for a width of 150 ft and is a reduced depth, say 6 ft, over the remainder of the 400 ft width. The reduced depth portion of the channel will serve as a fishing area for small boats, or as a safe area for boats experiencing engine trouble, etc. Also, a wider inlet, immediately past the tips of the jetties, is -70

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FIGURE 26 ST. GEORGE ISLAND CUT. NOTE EROSION WHERE BANK PROTECTION IS NOT PROVIDED -71

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favorable psychologically to operators of entering craft. The Sound Side of the channel could be provided with short (30 ft) rubble mound structures to keep drift out of the channel. An alternate and reasonable approach would simply be to accept some minor dredging of the Pass in this area. The jetties should extend to approximately the 12 ft Gulf contour and a design entrance width of approximately 170 ft is recommended. The jetties should be provided with a core so that the possibility for sand being carried through the jetties is minimal. The eastern jetty is extended further seaward than the west jetty because the predominant wave action is from the east and entering craft can first "duck behind" the protection of the east jetty and can then contend with the presence of jetties on both sides in comparatively protected waters. 4. Stabilization of Sand Against Wind DriftInspection of the dune system in the Navarre Beach area indicates that wind drift is an effective agent for sand transport. In the interest of reducing the maintenance dredging in the Pass and in preventing erosion of the land features, it is important that the areas near the Pass be provided with mechanical (sand fences) or natural (vegetative) control against wind erosion. This is particularly important along the boundary of the Pass -72

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where presently-existing vegetation will necessarily be removed by the excavation activity. Disposition of Initially Dredged Material The initial dredging of the Pass and deposition basin will result in approximately 400,000 cubic yards of beach quality sand. It is recommended that at least 90% of this material be placed on the western side of the inlet to be used as "feeder sand" for the down drift beaches while the near Pass bathymetry is adjusting to the presence of the Pass system and while the deposition basin is filling. The material should be placed so as to cause a seaward extension and an increase in elevation of the existing down drift shores. If the material is distributed over 2000 ft of beach on the down drift side of the Pass, approximately 200,000 cubic yards of sand will be required to advance the shoreline seaward a distance of 100 ft. The remaining 160,000 (or so) cubic yards could be used to raise the elevation of this section of the beach. This remaining portion placed on the newly-established beach would thereby : raise its elevation and not damage the existing vegetation. This amount of material would result in a new dune approximately 16 ft high by 150 ft wide and 2000 ft long. -73

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Alternate Designs Only one design for Navarre Pass has been presented. This design is considered to be the best choice from a functional standpoint, however it is recognized that the present design will be somewhat more expensive to construct than others. One alternate design which could be less expensive would be one similar to that at Perdido Pass, Alabama. This design incorporates a weir section as part of the eastern jetty and the interior region adjacent to the eastern jetty serves as the deposition basin. Apparent drawbacks to this design would appear to include the possibility of undesirable wave conditions inside the jetties during periods of high tides and waves, and the possible difficulty of sand encroaching on and causing shifting of the navigational cut. -74

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IX. SUMMARY AND CONCLUSION Summary The results of this study have indicated that: 1. Navarre Pass would only reduce slightly the equilibrium cross-sectional flow areas into Pensacola (1.8%) and Choctawhatchee (0.1%) Bays. 2. The velocities through Navarre Pass would be well within the limits considered safe for small craft navigation. 3. Planning for the artificial transfer of sand should be based on an annual rate of 200,000 cubic yards to the west. Initial disposition of sand dredged should be as a feeder beach on the west side of the Pass. 4. The Pass would cause a localized moderation of salinities and increased flushing in the waters adjacent to the Pass. 5. The tide and geometric characteristics are such that Navarre Pass will always tend to close; jetties are therefore essential to the stability of the Pass. Conclusion Based on the results of this study, it is concluded that if proper financial provision is made for the construction and maintenance of the inlet, there should be no significant adverse hydrographic effects to the stability of the Santa Rosa Island Beaches, nor to the adjacent waters. -75

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X. REFERENCES 1. Bruno, R., Personal Communication. 2. Oceanographic Atlas of the North Atlantic Ocean, U. S.Navy Oceanographic Office, Publication No. 700, Section IV, Sea and Swell, 1963. 3. Shore Protection, Planning and Design, Technical Report No. 4, Coastal Engineering Research Center, U. S. Army Corps of Engineers, Third Edition, June 1966. 4. National Shoreline Study, Regional Inventory Report, South Atlantic-Gulf Region, Puerto Rico and the Virgin Islands, U. S. Army Corps of Engineers, South Atlantic Division, Atlanta, Georgia, August 1971. 5. Escoffier, F. F., "Study of East Pass Channel, Choctawhatchee Bay, Florida," United States Engineers Office, Mobile District, Mobile, Alabama, 1938. 6. Johnson, J. W., "Nearshore Sediment Movement," Bulletin, American Association of Petroleum Geologists, Vol. 40, 1956, pp. 2211-2232. 7. Gorsline, D. S., "Dynamic Characteristics of West Florida Gulf Beaches," Vol. 4, Marine Geology, 1966, pp. 187-206. 8. Walton, T. L., "Littoral Drift Computations Along the Coast of Florida by Use of Ship Wave Observations," M.S. Thesis, Coastal and Oceanographic Engineering Department, University of Florida, 1972. 9. O'Brien, M. P., "Estuary Tidal Prisms Related to Entrance Areas," Civil Engineering, Vol. 1, No. 8, pp. 738-739, 1931. 10. Escoffier, F. F., "The Stability of Tidal Inlets," Shore and Beach, Vol. 8, No. 4, pp. 114-115, 1940. -76

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11. Keulegan, G. H., "Tidal Flows in Entrances. Water Level Fluctuations of Basins in Communication with Seas," Third Progress Report, National Bureau of Standards Report, No. 1146, 1951. 12. O'Brien, M. P., "Equilibrium Flow Areas of Inlets on Sandy Coasts," Journal, Waterways and Harbors Division, ASCE, Vol. 95, No. WW1, pp. 43-52, Feb. 1969. 13. Rouse, H., "Elementary Mechanics of Fluids," John Wiley and Sons, Inc., 1956. -77

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APPENDIX I NUMERICAL MODEL OF THE BAY SYSTEM AFFECTING NAVARRE PASS Introduction The purpose of the numerical model is to provide a means of realistically representing the hydraulics of the system and any changes that would occur due to the opening of Navarre Pass. Because of the extreme length (approximately 50 miles) of Santa Rosa Sound, the construction of a hydraulic (physical) model was ruled out during the conduct of the project. In the following sections of the Appendix, the governing differential equations will be presented and cast into finite difference form for numerical solution; this provides the basis for simulating the tides and currents that would occur at any locality in the system represented. Two representations of the numerical model will then be discussed: (1) In the calibration phase, data collected during the study will be used to assess the validity of and/or modify the numerical model, and (2) With the validity established, the Pass will be introduced into the numerical model and the hydraulics of the inlet and/or -78

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the effect of the Inlet on the tide in Santa Rosa Sound and on the hydraulics of the Pensacola Bay Entrance and East Pass will be investigated. Figure I-1 presents the geographic area represented in the numerical model. Derivation of the Numerical Model Governing Differential Equations The differential equations governing the flow in bay systems are the depth-integrated equations of motion and continuity. Equation of Motion.--The vertically integrated differential equation of motion can be written for the x-direction in a semi-linearized form as = -D + -Tb) (I-1) at ax p ( b in which q = discharge per unit width in the x-direction t = time g = gravitational constant D = total depth = h + n h = depth referred to mean sea level n = tide displacement above mean sea level due to astronomical, wind and barometric tides x = horizontal distance coordinate aligned with bay axis -79

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:. ., /Limits Encompassing Bay System .. ... Represented in Numerical Model .' -.. "" ay j Pensacola Bay .. .. .' '" ... co/ S. .". Choctawhatche. e : Say G U L F 0 F M E X -LC 0 (esti ast) FIGURE X-I BAY SYSTEM REPRESENTED IN NUMERICAL MODEL

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p = mass density of water T = wind stress in x-direction on air-water Sinterface Tb = frictional stress on bottom of water column b The quantities T and Tb can be expressed as T = CfPaU2 cos B (1-2) Pf qjlq (1-3) b -8D2 in which Cf = wind stress coefficient 0.0013, U < 23.6 ft/sec (1-4) 0.0013 + 0.00295 1.0 -2j U > 23.6 ft/sec Pa = mass density of air U = wind speed at 30 ft reference elevation S = angle of wind vector relative to the bay axis f = Darcy-Weisbach friction factor (Reference 13, page 201) Equation of Continuity.-The equation of continuity in one dimension is expressed as i + q R (1-5) at ax w in which the righthand side represents the effect of runoff, -81

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q = runoff in cubic ft/sec per foot of bay length w = width of segment considered It is noted that in the present application of the model, the wind stress, T and direct precipitation and runoff will be taken as zero, however they have been included here for completeness. Finite Difference Equations In order to employ Equations (I-1) and (1-5) for realistic geometries and Gulf tides, it is necessary to cast these equations into finite difference form. The timeand space-staggered procedure is used in which the equation of motion is applied between midpoints of adjacent segments (i.e., across a segment boundary) at full time steps, At, and the equation of continuity is applied for each segment at half time step increments. Finite Difference Form of the Equation of Motion.--Equation (I-1) can be expressed in finite difference form for the total flow, Qn' onto the nth segment, as: Q +At T -wD g n -n 1 Q n p nl n n-1 (1-6) n w At f IQn 1 + 8(Dw)2 -82

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in which the over-barred quantities represent averages based on the nth and (n-l)th segments. The prime indicates the value at time t + At whereas unprimed quantities are known from calculation at time t, and w is the width of the bay segment, see Figure I-2 for the variable representations and Figure I-3 for the numerical model representation of the area of concern. Finite Difference Equation of Continuity.-Equation (1-5) can be written in finite difference form as qR At n' = + Q -Q + n (1-7) n n Ax w n n+1j w n n where the primes indicate the unknown quantities as before and the terms on the right hand side are known from calculations at previous times. Boundary Conditions The boundary conditions for this problem are the flows through the inlets and may be expressed, for example, for Destin Pass as: Ac /2g nTo -qGI sign(nlo -IG) /Ken + Ke + ft/4R in which -83

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Variabtes Represented Variobles Represented at Segment Midpoints: at Segment Junctions 7*, hn hn ,, *n+l h Q n-I I nth Segment 10 + x FIGURE 1-2 ILLUSTRATION OF BAY SEGMENT REPRESENTATION S84

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SChoctowPensacol Bay / hatchee Segment Bay Segment -T-_ -' --t----H---------Cx0 7 9 1/ / 7/ / / / ,/ / / / / / / / / / / Sant Roso Island/ / / / // / / / / / i-Pensacola Bay Entrance Navarre Pass Destin Pass ( Site GULF OF MEXICO FIGURE 1-3 SCHEMATIZATION OF PENSACOLA BAY / CHOCTAWHATCHEE BAY / SANTA ROSA SOUND / GULF OF MEXICO SYSTEM

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AC = cross-sectional flow area of Destin Pass Qii = flow from Choctawhatchee Bay into the Gulf of Mexico o10 = Choctawhatchee Bay Tide nG = Gulf tide (specified) K = entrance loss coefficient = 0.3 en K = exit loss coefficient = 1.0 ex AC R = hydraulic radius of inlet = + w + 2h + nio + 0G w = effective width of Destin Pass h = effective depth of Destin Pass (relative to mean sea level) An expression similar to Equation (1-8) applies for Pensacola Bay Entrance and Navarre Pass. Application of the Numerical Model In this section the application of the numerical model will be presented in two different phases. The first phase is the assessment of the numerical model by judging how well the model represents the existing situation in the Santa Rosa Sound area. The second phase considers the system with Navarre Pass open and presents an evaluation of the flows to be expected through Navarre Pass and also evaluates the effect of Navarre Pass on the Entrance to Pensacola Bay and on East Pass. In Appendix II, the numerical model is employed using recently developed procedures to evaluate the sedimentary stability of the Pass. -86

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Assessment/Calibration of the Numerical Model In order to evaluate the validity of the numerical model, the ability of the numerical model to represent the tides and flows in Santa Rosa Sound with measured data was assessed. The characteristics of the one-dimensional numerical model are shown in Figure I-3 and the characteristics of the various elements used in the model are summarized in Table I-1. The Gulf tide, nG, was represented by RG =G -sin(7.27 x 10-5 t) (1-9) in which RG and t are the Gulf tidal range and time, respectively. The measured data included: open coast tides measured from the Navarre Pass Pier, Santa Rosa Sound Tides as measured from the Navarre Bridge and, for one field trip, currents measured from the Navarre Bridge. The tidal data collected during the three field trips are summarized in Table 1-2. Measured Tidal Ranges and Lags.--The three field trips occurred during periods of different average Gulf tidal ranges varying from 0.37 ft to 2.01 ft,cf Table 1-2. From the measured data, it was noted that the ratio of -87

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TABLE I-i Characteristics of Schematized Bay/Inlet System (see Figure I-3) TABLE I-A Inlets Characteristics £(ft) h(ft) w(ft) K + K f INLET en ex Pensacola Bay Entrance 12,000 32.0 2400 1.3 0.03 Destin Pass 12,000 12.0 2170 1.3 0.03 TABLE I-B Bay System Segments 00 Characteristics Segment x (ft) y*(ft) R (ft) h (ft) w (ft) A (ft2) f No. n n n n n n Pn 2 0 960,000 50,000 29.8 88,890 4.0 x 109 0.03 3 60,000 600,000 27,000 15.0 9,170 2.4 x 108 0.03 4 87,000 600,000 27,000 13.0 9,730 2.64 x 108 0.03 5 114,000 600,000 27,000 12.0 9,170 2.48 x 108 0.03 6 141,000 600,000 27,000 8.0 7,000 2.00 x 108 0.03 7 168,000 600,000 27,000 14.0 4,500 1.40 x 108 0.03 8 195,000 600,000 27,000 9.0 1,460 3.94 x 107 0.03 9 222,000 600,000 27,000 10.0 1,480 4.00 x 107 0.03 10 307,120 780,000 24,000 25.0 180,000 3.60 x 109 0.03 *Note: The origin of yn is arbitrary.

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TABLE I-2 Summary of Measured Tidal Characteristics Tidal Range (ft) Tidal Lag *(hours, min) Average Average Average of Average Average High High Low Low Low and Date Gulf Gulf Sound Sound Water Water Water Water High Water May 14, 1970 0.39 0.59 3h 15m 3h 20m May 15, 1970 0.36 0.37 0.43 0.50 2h 15m 2h 25m 3h 35m 3h 23m 2h 55m May 16, 1970 0.36 0.49 lh 45m 3h 15m Dec. 8, 1970 1.08 .1.38 1.79 3h 15m 3h 15m 3h 30m 3h 23m 1 >1.64 3h 15m 3h 30m 3h 23m Dec. 9, 1970 2.20 2.20 3h 15m 3h 45m July 21, 1971 2.17 .1.97 5 3h 20m 3 4h 20m 4h 07m 3h 52m 2.01 1.85 3h 37m 4h 07m 3h 52m July 22, 1971 1.84 1.72 3h 53m 3h 53m *Measured from preceding corresponding occurrence (high or low water) in Gulf.

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Sound to Gulf tidal ranges and the lags depended on the Gulf tidal range. Averages of these quantities were determined for each field trip and are presented in Table I-2 and plotted as the points in Figures I-4 and 1-5. The numerical model was run for Gulf tidal ranges, RG, of 0.5, 1.0 and 2.0 ft, respectively. For each of these runs, the Gulf tide was assumed to be sinusoidal and given by Equation (1-9). The runs of the numerical model demonstrated that the calculated ratio of Sound to Gulf tidal ranges and tidal lags also varied with Gulf tidal range. The calculated results for ratios of ranges are presented in Figure 1-4. Examination of this figure will show that the numerical model predicts values of the tidal range which are approximately 18% too low, however the correct trend of increasing ratio RS/RG with decreasing tidal range is accurately represented. The reason for the 18% discrepancy is not known. Only one tide gage was available in Santa Rosa Sound and attempts to adjust the numerical model further without additional data would be somewhat arbitrary. The effect of the Navarre Bridge causeway was not represented in the model and reflection of the tides from this feature could conceivably account for an effect of this magnitude. The measured tidal lags, presented in Figure I-5 indicate an increasing lag with increasing Gulf tidal range. -90

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, LAverages Based on d Field Trip of. May 1970 \ -Dec 1970 .^July 1971, 1.0 Calculations From Numerical Model 0.5 0 0 1.0 2.0 Gulf Tidal Range, RG, (ft.) FIGURE 1-4 COMPARISON OF MEASURED AND CALCULATED RATIOS OF SOUND TO GULF TIDAL RANGES VERSUS GULF TIDAL RANGE -91

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0 4.0 C Calculations From Numerical Model wI / uly, 1971 S Dec, 1970 I / / o / -/ Note: Circles and Vertical S/ Lines Represent / Average and Extreme / Tidal Lags Measured 2.0 / on Three Field co Trips a May 1970 -j Field Trip 1.0 00 1.0 2.0 Gulf Tidal Range, RG, (ft) FIGURE 1-5 COMPARISON OF MEASURED AND CALCULATED PHASE LAGS BETWEEN GULF AND SOUND TIDAL EXTREMES -92

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It should be noted that, due to the extremely small tidal variations during the May, 1970 field trips, it was difficult to measure these tidal lags with confidence. The numerical model correctly predicts the increasing tidal lag with Gulf tidal range and agrees with the averages of the measured lags within 30 minutes, except for the data taken for the small Gulf tidal range, in which case there is a difference slightly in excess of one hour. Measured currents.-During the December, 1970, field trip, currents were measured in the Santa Rosa Sound using a Savonius Current meter suspended from the main span of the bridge, see Figures 16 and 14 for the location of the measurements and results obtained. The maximum velocities were on the order of 1 ft/sec and the Gulf tidal range varied from 1.38 to 2.20 ft, see Figure 19. In order to assess the approximate validity of the numerical model in representing the flows in the Santa Rosa Sound, system, the measured velocities were converted to discharges (in cfs) by the following equation Q (cfs) = 15,390 V(ft/sec) (I-10) Equation (I-10) is based upon the areas and velocities through the two openings in the Navarre Bridge causeway. The measurements were conducted in the main (navigational) span. Considering that the slope of the water surface -93

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causing the flow through the two spans is the same, it can be shown that 2/3 Q = AIVI + A2V2 = (A + A2) V (I-) in which the Manning equation has been used and for our case, the dimensions shown in Table I-3 were used. Equation (I-10) follows using these data and Equation (1-11l). TABLE I-3 Dimensions Used in Flow Calculations at Navarre Bridge Flow Area Width Depth Cross-Sectional Area Main Opening (Navigational) 1350 ft 10 ft 13,500 ft2 Secondary Opening (Southerly) 600 ft 5 ft 3,000 ft2 In order to compare the flows determined from the measured velocities and those calculated using the numerical model, the model was run using a Gulf tidal range of 2 ft, and plotted with the measured data for the period December 9-11, 1970, see Figure 1-6. With regard to the tides, it is evident that the numerical model predicts good phase lags of the Sound tides, although the predicted -94

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S-----Measured Gulf Tide d -I0 1= 1500 1800 2100 0300 0600 1200 1500 1800 2100 0 0300 0600 -1.0 Decemlyr 9, 1970 December 10, 1970 Decymber I0. 19701 Decemrer II. 1970 20,O Note: Points Represent Discharges ,Determined From Measured Velocities / o oYo ----^--^------------7'" \ ~-s----S10,00 -Soune d Tide n (Bsed n f 2ft. Gulf Tidl RRange) C 1200 0001500 1800 2100 0000 0300 0600 .-1.0 Decemr 91970 December K, 1970 December 10. 1970 December 11. 81970 2 0,000 -Q --\ G Determined From Measured Velocities / I= 2 ft. Gulf Tidd Rang) m 1200 1500 1800 2100 G\ 0000 0300 0600 0900 / 1200 1500 1800 2100 \0000 0300 0600 K%00000900-----------' ---/--------\--"-M20000 FIGURE 1-6 COMPARISON OF MEASURED AND COMPUTED SANTA ROSA SOUND TIDES AND DISCHARGES

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Sound Range is too low. This also follows from Figure 1-4. Reflection of tides from the Navarre Bridge causeway was not included in the model and has been mentioned as a possible reason for this difference. Considering that a Gulf tidal range slightly greater than 2 feet would have been more appropriate, the Sound tidal range is approximately 20% lower than measured. The discharge (flow) comparison is available from 1500 December 9 to 0700 December 11, 1970. Because the measurements were conducted at discrete times, it is difficult to assess the agreement with a high degree of confidence. It is possible to state that the predicted and measured maxima do occur at approximately the same time. It appears that the calculated discharges are about 40% to 60% higher than those measured; this difference depends on the flow areas presented in Table 1-3, which are considered known only with 20%. The shorter period oscillations present in the calculated discharges in Figure I-6 are believed to be an artificial result of the numerical model, although the measurements were not sufficiently detailed to determine whether these features were present in nature. Measured nodal line.--On May 16, 1970, during the first field trip, an attempt was made to locate a nodal line, i.e., a line in Santa Rosa Sound which is -96

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characterized by zero velocity and flows on both sides directed toward that point or away from that point. With considerable difficulty a point of zero velocity was located about seven miles west of Navarre Bridge, however the tides during this field trip were very weak (average Gulf range = 0.37 ft) and wind therefore could be a dominating factor. Furthermore, on examining the predictions of the numerical model, it was found that the stationary nodal line concept is not really valid. According to the numerical model, the nodal line varies with the stage of the tide and in the case of Santa Rosa Sound ranges from 15 miles west of Navarre Bridge, nearly to the junction of Santa Rosa Sound with Choctawhatchee Bay. For these reasons, attempts to utilize the nodal line concept in verifying the numerical model were discontinued. Conclusions regarding the numerical model assessment.-Some differences exist between the available data and predictions of the model. In particular the predicted Sound tidal range (at Navarre Bridge) is low by about 20% and for the low Gulf tidal ranges, the calculated Sound lags appear to be small by about one hour, although accurate determinations from the field data are difficult due to the low tides. The proper trends with Gulf tidal range are predicted for ranges -97

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and lags. Predictions of total flows at the Navarre Bridge appear to be in good phasing, but high by about 40%. In summary of the numerical model assessment, it is regarded that the numerical model provides a reasonably good calculation procedure for evaluating the effects of modifications of the bay system, such as the opening of Navarre Pass. Use of Numerical Model to Evaluate Effect of Navarre Pass In this section, the numerical model was employed to represent the bay system including the effect of Navarre Pass. The characteristics of Navarre Pass included are: Width = 300 ft (Including effect of jetties) Length = 3200 ft (Including effect of jetties) Depth (average) = 10 ft K = 0.3 en K = 1.0 ex f = 0.03 Effect on entrances to Pensacola and Choctawhatchee Bays.-The calculated maximum inflow and outflow discharges through the Gulf entrances to Pensacola Bay and Choctawhatchee Bays are presented in Table I-4 for the -98

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TABLE I-4 Predicted Effect of Navarre Pass on Flows in and out of Pensacola and Choctawhatchee Bays Maximum Flows Without Maximum Flows With Navarre Pass (cfs) Navarre Pass (cfs) Percent Change Inflow Gulf Tidal or Pensacola Choctawhatchee Pensacola Choctawhatchee Pensacola Choctawhatchee Range (ft) Outflow Bay Bay Bay Bay Bay Bay Inflow 85,820 34,110 83,330 34,030 -2.9% -0.2% 0.50 Outflow 85,040 33,560 82,660 33,490 -2.8% -0.2% 1.0 Inflow 152,600 49,350 149,000 49,290 -2.4% -0.1% 1.0 Outflow 150,200 48,510 146,500 48,450 -2.5% -0.1% Inflow 253,200 71,560 249,900 71,500 -1.3% -0.1% 2.0utflow 246,300 68,460 242,200 68,430 -1.7% -0.1% Outflow 246,300 68,460 242,200 68,430 -1.7% -0.1%

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cases of Navarre Pass closed and open. The percentage changes are summarized in the last two columns. As expected, it is seen that the result of opening Navarre Pass would be to decrease slightly the flows through the other two entrances to the Bay system. The reason that the effect is so small is that the tidal lag between the Gulf and Sound in the vicinity of the Pass site is fairly large (-3 hours). Therefore the effect of modifying the Sound tide near Navarre has only a slight effect on the Pensacola and Choctawhatchee Bay tides and hence causes only minor changes in flows into these bays from the Gulf. The percentage effect on Pensacola Bay Entrance is greater (up to 2.9%) than for Destin Pass (up to 0.2%). It is noted that these larger percentage values are associated with the smaller tidal ranges. The average Gulf tidal range is about 1.5 ft and the associated percentage changes for Pensacola Entrance and Destin Pass are about 2.0% and 0.1%, respectively. It is worthwhile to examine the effect of reductions of this magnitude on cross-sectional flow area from the Gulf to the Bay system. The results of O'Brien indicate a relationship (to be described more completely in Appendix II) between the tidal prism, P, and channel equilibrium cross-sectional area, AC. Using O'Brien's relationship, it can be shown -100

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that the percentage change in equilibrium area is related to the percentage change in maximum discharge by: Percentage Change in AE = 0.9 x (Percentage Change in Qmax) For our case, the indicated results for an average Gulf tidal range of 1.5 ft are that the cross-sectional flow areas into Pensacola and Choctawhatchee Bays would be reduced by 1.8% and 0.1%, respectively. Maximum Velocities Through Navarre Pass The flow characteristics predicted by the numerical model are discharges and therefore the velocities presented below are the cross-sectional averages. The maximum velocities over the cross-section could range up to 30-40% higher than the values presented. The maximum (over time) discharges and velocities occurring as a result of different tidal ranges are presented in Table 1-5. From navigational considerations, the velocities presented in Table I-5 are very acceptable. Within the State of Florida,maximum inlet velocities up to 4-6 ft/sec exist in small inlets that are used extensively by small pleasure boats, e.g., Boynton Beach Inlet and Bakers Haulover. Conclusions resulting from application of numerical model.-Based on the results obtained by -101

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TABLE I-5 Calculated Maximum Discharges and Velocities Through Navarre Pass for Various Tidal Ranges Maximum Discharge Maximum Velocity (cfs) (ft/sec) Gulf Tidal Range (ft) Flood Ebb Flood Ebb 0.5 4494 4410 1.27 1.27 1.0 7768 7421 2.17 2.16 2.0 12800 11,910 3.47 3.54 applying the numerical model, it is concluded that: (1) the reduction in cross-sectional flow areas from the Gulf of Mexico to Pensacola and Choctawhatchee Bays will be slight (approximatelyl.8%and 0.1%, respectively) and (2). the maximum velocities in Navarre Pass would be well within the acceptable limits for small boat traffic. -102

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APPENDIX II STABILITY OF NAVARRE PASS Introduction In this appendix, the sedimentary stability of Navarre Pass will be examined. Sedimentary stability, used in the context of this report refers to the capability of the Pass to remain open naturally without artificial structures. From experience gained following the original opening of the Pass it is known that the Pass is not stable, however it is worthwhile to: (1) examine the cause of the instability and to determine whether it is predictable, and (2) to incorporate information regarding the natural stability characteristics of the Pass into the design of the inlet system. Method The method employed in the stability analysis combines earlier work by O'Brien (9) and Escoffier (10) and uses the numerical model to determine the hydraulics of the inlet/bay system. The elements of the method are presented in Figure II-1. In the following subsections, the three elements comprising the method will be discussed briefly. -103

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SINGLE INLET ANALYSIS MULTIPLE INLET ANALYSIS HYDRAULIC ANALYSIS HYDRAULIC ANALYSIS Inlet Velocity: Inlet Velocity: Response to changes Response to changes In Flow Area and In Flow Area and Tidal Range Tidal Range (Keulegan or (Numerical Modeling) Numerical Modeling) A Hydraulics I Hydraulics Sedimentary fSedimentary 0u" 0 S-edi Flow Area Flow Area Conditions for Conditions for Sedimentary Equilibrium Sedimentary Equilibrium (O'Brien) (O Brien) FIGURE "I-I SCHEMATIC ILLUSTRATING STABILITY ANALYSIS FOR SINGLE AND MULTIPLE INLETS -104

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Numerical Model For a simple inlet/bay system such as shown in Figure II-1-a, the hydraulics could be represented by the Keulegan method (11) or an equivalent. In the present case, it is necessary to represent the hydraulics by a numerical modeling procedure because the Santa Rosa Sound system is quite complex and the Sound tides and discharge values depend on the flows through Pensacola Bay Entrance, East Pass and also on Navarre Pass if it were open, and also depend in a complicated way on the travel time of a long wave from the various Sound entrances to any point of concern. The basis for and calibration of the numerical model used to represent the Santa Rosa Sound has been described in Appendix I. Sedimentary Stability The criterion for sedimentary stability of an inlet was first investigated by Escoffier (10). This criterion is best understood by considering a single inlet connecting a bay to a tidal body of water. The relationship of importance is the variation of the maximum inlet velocity which occurs during a tidal cycle, Vmax, with the inlet cross-sectional area Ac. First, consider a very small inlet cross-sectional area AC in which friction dominates. As AC approaches zero, it is clear that the velocity will approach zero. Second, -105

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consider a large cross-sectional area. In this case, the tidal range inside the inlet is the same as that in the ocean and if the area were increased further, the tidal prism could not increase and the maximum velocity would necessarily decrease. From the preceding discussion, it is evident that for very small and large cross-sectional flow areas the maximum inlet velocity approaches zero; it therefore follows that V must max exhibit a maximum value at some inlet cross-sectional area, AC, see Figure II-2 for an idealized situation. In the following discussion, it will be shown that cross-sectional areas less than A* (Region 1) are unstable with respect to forces that would tend to cause changes in cross-sectional areas, whereas cross-sectional areas greater than A* (Region 2) are stable and an equilibrium area tends to prevail. Region 1 -Unstable Conditions.-Consider some particular inlet/bay system and a cross-sectional area, A < A* Suppose that the cross-sectional area is in C C. equilibrium with the prevailing forces on the inlet such that sediment transported into the inlet is exactly balanced by transport from the inlet by the tidal flows. Next consider a period of increased sediment transport into the inlet resulting in deposition and a reduction in AC' -106

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SII Region 1 Region 2 Unstable Areas Stable Areas Note: Change in Channel CrossNote: Change in Channel Cross5 Sectional Area Results in "Sectional Area Results in Changes Which Further Changes Which Tend to Accentuate Change / Restore Original Area SVm/ oax vs A 0 010 -Critical Area, Ac 2 I II Example I: Example 2: i I AA=-IO ft2 i\ AA =-I0,000 ft2 I. AV = -0.3 ft/sec. I \ ,AV = +0.6 ft./sec. Result: Deposition Tendency, \ I Result: Scour Tendency 10 102 104 Inlet Channel Cross-Sectioncil Flow Area, Ac, (ft2) FIGURE 3T-2 ILLUSTRATION OF ESCOFFIER'S STABILITY CONCEPT

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The Vmax resulting from a reduction in A is a max C smaller Vmax and a reduced capability to maintain the max inlet open. The changes, then tend to perpetuate (and accelerate) the deviation from the equilibrium. To complete the discussion of Region 1, consider some increase in the forces which would increase the inlet area to a value above the equilibrium value. The increased area results in an increased velocity thereby increasing the scouring capability, etc. In summary of considerations of Region 1, it has been shown that any changes from an equilibrium condition will tend to perpetuate these changes. Because in a natural environment, the "forces" are changeable, it can be concluded that Region 1 conditions could not be expected to occur over a long period of time. The cross-sectional area would either enlarge into Region 2 or the inlet would close. Region 2 -Stable Conditions.-If a similar type of argument is followed for Region 2 as was presented for Region 1, it will be found that a change in forces from equilibrium cause changes in these forces which tend to return conditions to equilibrium. Suppose that an anomalous littoral drift resulted in a deposition in the inlet cross-section such that the area is decreased below some equilibrium value. This reduction in area is seen from Figure II-2 to cause an increase in maximum -108

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velocity, thereby increasing the scouring capability which would tend to restore equilibrium. Conversely an increase in cross-sectional area, is seen to cause a reduced velocity and scouring capability and, again a tendency toward restored equilibrium results. Based on the preceding considerations, it may be concluded that for A < A*, the inlet cross-sectional C C areas are unstable with respect to forces causing changes from equilibrium, whereas for A > A, the inlet is stable around some equilibrium value A .Although the inlet stability concepts presented here are highly idealized, they are essential to a conceptual understanding of inlet behavior. In a realistic case, the tidal range is not constant but varies between neap and spring ranges and an inlet may function in the unstable region for periods of times sufficiently short that a long-term equilibrium is maintained through a balance by the scouring action while the inlet system is in Region 2, stable conditions. In the following subsection, the equilibrium area concepts developed by O'Brien will be discussed. Equilibrium Cross-Sectional Area The relationship between inlet equilibrium cross-sectional area and tidal prism was first presented -109

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by O'Brien (9), and he has later (12) augmented the original results. His results are summarized in Figure II-3 for a semi-diurnal tide. Very briefly, there is a relationship between the spring tidal prism of an inlet and the minimum cross-sectional flow area measured at mean sea level conditions. This relationship may be interpreted in terms of the equilibrium shear stress or maximum velocity that can be sustained by erodible materials which comprise inlet beds. It will be more convenient to transform the relationship shown in Figure II-3 into a Vmax vs AE relationship. This max CE transformation also removes the limitation of Figure II-3 being applicable only to semi-diurnal tides (the tide at Santa Rosa Island is diurnal, i.e., of 24-hour period). To determine the Vmax vs AE relationship, it will be max CE assumed that the discharge through an inlet varies in a sinusoidal manner Q = Qmax cos at The tidal prism, P, is therefore T/4 P = 2 Qmax cos at dt or -110

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1012 0 0 8 S10 Co i.10. 1 EE FIGURE 11-3 EQUILIBRIUM CROSS -SECTIONAL AREA AND TIDAL PRISM RELATIONSHIP (FROM O'BRIEN) -111

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T P = -Q Tr max and since Qma = AC V we have P = A V (II-l) IT C max ( or, in order to determine the desired relationship from Figure 11-3, Equation (II-1) is written as PIT V max ACT (11-2) The relationship Vmax vs AC is presented in maox C Figure 11-4. The stability relationship and equilibrium cross-sectional area are combined in Figure II-5 for various tidal ranges for Navarre Pass where it is seen that for each tidal range for which a portion of the stability curve lies above the equilibrium curve, there is one equilibrium area. For tidal ranges for which the stability curve completely lies below the equilibrium curve, the inlet would be unstable for all cross-sectional areas and would always close if larger tidal ranges did not occur. Application of Stability/Equilibrium Concepts to Navarre and Rollover Passes In order to evaluate the stability/equilibrium relationships and their applicability to real inlets, the -112

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4>E I Q O'Brien's Sedimentary U) Equilibrium Relationship o1 E S.S0 E I 0 I I I I I I I I I I 4 6 8 1000 2 4 6 8 10000 2 4 Equilibrium Cross Sectional Area (ft2) FIGURE lE4 VARIATION OF MAXIMUM INLET VELOCITY WITH CROSS -SECTIONAL AREA FOR EQUILIBRIUM CONDITIONS

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Tidol Range = 2.0> 4 O' Brien's Sedimentary //Equilibrium E Relationship > o I I [ I I I I I I 01.0' 4 6 8 1000 2 4 6 8 10000 2 4 CrossSectional Area (ft2) FIGURE 11-5 VARIATION OF MAXIMUM VELOCITY WITH INLET CROSSSECTIONAL AREA AND TIDAL RANGE. NAVARRE PASS, FLORIDA

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method was applied to two real inlet situations: (1) Navarre Pass, with a history of closure after being dredged, and (2) Rollover Pass cut through Bolivar Peninsula in Texas and with a history of growth until the cross-sectional area was limited artificially by lining with steel sheet piling on the sides and a concrete sill on the bottom. In the following presentations for the two inlets, the one-dimensional numerical model is used to represent the hydraulics and the actual variations in tidal range are realistically included. Navarre Pass In previous sections, the basic stability and equilibrium concepts have been reviewed. In the application of these concepts to an actual situation, it is necessary to represent the variations in tidal range which prevail in the area of interest. The method of accounting for variations in tidal range is illustrated by application to Navarre Pass in the following sections. Using the numerical model, the relationship for maximum velocity, V versus cross-sectional area, AC, was established for several tidal ranges spanning the ranges occurring at the area of interest. Figure II-5 represents this relationship for Navarre Pass for Gulf tidal ranges of 0.5 ft, 1.0 ft and 2.0 ft. The results presented in Figure II-5 are based on 18 individual computer runs of the numerical model program. In these -115

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computations, it is necessary to make some assumptions regarding the relative width to depth of the flow area; for the calculations on which Figure II-5 is based, it was assumed that the inlet width was 35 times the depth. As an example, for an inlet depth of 12 ft, the associated width would be 420 ft. The variation in tidal range differs considerably with locale and relates very strongly to the stability of an inlet. For example, the tides for three locations as determined from the Tide Tables for the period January 1, 1970 to February 9, 1970, are presented in Figure II-6 and the ratio of maximum to minimum ranges are summarized in Table II-1. TABLE II-1 Ratio, R, of Maximum to Minimum Tidal Ranges During the Period January 1 to February 9, 1970 Location Ratio, R Pensacola Bay Entrance 19 Galveston Bay Entrance 4.4 Miami Harbor Entrance 2.3 In the procedure employed herein, the tidal range is determined for a representative period -116

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.0 I O -1.0-GALVESTON ENTRANCE Period of Period Low Relative of High Susceptibility Relative to Deposition Susceptibility to Deposition 1.0 0-----1.0PENSACOLA January, 1971 February, 1971 5 10 15 0 25 5 I1tI 51 11 1t I 1111111 111111 I lI I Ii II I il[ 2.0 N-1.0-I I -1.0MIAMI HARBOR ENTRANCE FIGURE 31-6 PREDICTED TIDES AT GALVESTON, PENSACOLA AND MIAMI HARBOR ENTRANCES. NOTE DIFFERENCES IN TIDAL RANGE VARIATIONS -117

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(approximately 4 weeks) from the Tide Tables and represented as a cumulative probability distribution, see Figure II-7 for the Pensacola (Navarre Pass) and Galveston (Rollover Pass) Entrance distributions as determined from the Tide Tables for the interval: January 7 to February 3, 1970. Stability in regions previously described as "unstable" (Region 1) and "stable" (Region 2) must be interpreted separately. For Region 1, consider a crosssectional area of 5000 ft2.An auxiliary diagram is first prepared from Figure II-5 of maximum velocity, Vmax versus Gulf tidal range, RG, see Figure 11-8. In addition,the velocity determined from O'Brien's equilibrium relationship is indicated on this auxiliary plot. From Figure 11-8, it is seen that Gulf tidal ranges in excess of 1.25 ft will exceed the "equilibrium" velocity. From Figure II-7a, this required tidal range will be exceeded a percentage P = 68% of the time. The procedure is then repeated for other cross-sectional areas and the results plotted versus AC. The interpretation of P in Region 1 is that this is a measure of the percent of time favorable for growth in this unstable region. For example, for the example cross-sectional area of 5000 ft2, conditions favorable toward cross-sectional increase would occur 68% of the time. A stability diagram -118

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I o 2 3 s -/ E .0 Gulf Tidal Range (ft) FIGURE I -7a PENSACOLA BAY ENTRANCE (NAVARRE PASS) 100 S50 I Oo I I I I I I I I I 7|50 4 a) 0 0 I 2 3 Gulf Tidal Range (ft) FIGURE TI -7b GALVESTON BAY ENTRANCE (ROLLOVER PASS) FIGURE IE -7 CUMULATIVE PROBABILITY DISTRIBUTIONS FOR PREDICTED GULF TIDAL RANGES AT NAVARRE AND ROLLOVER PASSES -119

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3 S-Vmx For Sedimentary u Equilibrium = 2.7 ftec 2 >E / y Tidal Range Corresponding to Sedimentary I Equilibrium = 1.25 ft 0 II O I 1.25 2 Gulf Tidal Range (ft) FIGURE E -8 AUXILIARY DIAGRAM FOR DETERMINATION OF TIDAL RANGE CORRESPONDING TO SEDIMENTARY EQUILIBRIUM (EXAMPLE SHOWN FOR Ac=5000 ft ) -120

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comprising the results of the same calculations for other areas, AC, is presented in Figure II-9 for Navarre Pass. Note that it is of considerable interest that, for Navarre Pass, the percent of time for favorable growth decreases markedly near the larger unstable areas. In Region 2, the same calculation and plotting representation procedure is followed, however the interpretation differs. The percentage value continues to decrease for the larger areas because the "equilibrium" velocity increases whereas Vmax decreases with increasing cross-sectional area. The interpretation is that, if the inlet is stable, the cross-sectional area will occur such that the percentage, P, is in the range 10-20%. This is due to the fact that O'Brien's relationship was based on spring tide conditions, and normally tidal ranges exceed the spring tide range on the order of 10 to 20% of the time. For Navarre Pass and cross-sectional areas-near the midpoint of the transition region, conditions for favorable growth only exist some 42% of the time. In the stable region, tidal conditions above those required for equilibrium occur a maximum of 34% of the time. An interpretation of these stability results can only be carried out on a comparative basis, for example with the results for Rollover Pass presented in the following section. -121

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80 Transition I .2 Percent of TimeReion ;60Tidal Conditions Are c Favorable for Growth Unstable/ / Stable g -Percent of z 40 I Time Tidal .Conditions are o Above Those Required for c2 Equilibrium S20-/ o I I I I I I / 4 6 8 1000 2 4 6 8 10000 2 4 Cross -Sectional Area, Ac (ft2) FIGURE 3r1-9 STABILITY ANALYSIS FOR NAVARRE PASS, FLORIDA

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Rollover Pass For comparison purposes, the treatment first presented for Navarre Pass is carried out for Rollover Pass. Figure II-10 shows the location of Rollover Pass relative to Galveston Bay and Figure II-11 presents a schematic of the simplified one-dimensional model used to represent Galveston Bay and the associated entrances to the Bay. The Vmax vs. A relationship as determined for Rollover Pass is presented in Figure II-12 for tidal ranges of 0.5, 1.0 and 2.0 ft. It is noted that the basic difference between Navarre and Rollover Passes is evident by comparison of Figures II-5 and II-12; for the smaller cross-sectional areas and the same tidal ranges, Rollover Pass is characterized by larger velocities. For example, a cross-sectional area of 4000 ft2 and a tidal range of 1 ft will cause maximum velocities of 2 and 3.3 ft/sec in Navarre and Rollover Passes, respectively. The cumulative probability distribution for Gulf tidal ranges at Galveston Bay Entrance has been presented as Figure II-7-b. Figure II-13 is a presentation of the stability analysis, P vs AC. Conclusion Regarding Relative Stability of Navarre and Rollover Passes Comparison of Figures II-9 and II-13 shows that Rollover Pass presents a much more favorable situation than -123

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MATAGORDA BAY Z GULF oF OV OF MEXICO LAG UNA ." MADRE -. BAy WEST BAY ENTRANCE ROLL.VER FISH PASS SAN LUIS PASS FIGURE I-10AREA MAP SHOWING LOCATION OF ROLLOVER FISH PASS

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FIGURE I1 -II NUMERICAL MODEL REPRESENTATION OF GALVESTON BAY / ROLLOVER PASS SAN LUIS GALVESTON PASS ENTRANCE GULF OF MEX ICO

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S5.^ TIDAL RANGE 2.0' 4H OBRIEN'S SEDIMENTARY SEQUILIBRIU 0.5 RELATIONSHIP 2 *o 4 6 8 1000 2 46 8 10000 2 .4 CROSS-SECTIONAL AREA (ft2) FIGURE 1-12 VARIATION OF MAXIMUM VELOCITYWIT}_ INLET CROSSSECTIONAL AREA AND TIDAL RANGE -ROLLOVER FISH PASS,TEXAS

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100 I I P e o Percent of Time 80 -/ /I / Tidal Conditions Tidal Conditions are I Ae Above Those < I Are Above Those F Favorable for Growth Required For S0 I Equilibrium II ICU \ CrossSectional Area, Ac (ft2) FI3 Unstable I R Stable F S1TEXAS I I I A I I I 4 6 8 1000 2 4 6 8 10000 2 4 Cross -Sectional Area, Ac (ft2) FIGURE 1 -13 STABILITY ANALYSIS FOR ROLLOVER FISH PASS, TEXAS

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Navarre Pass for initial growth and achieving an eventual equilibrium stable area. At the midpoints of the two transition regions, the percentages of time that conditions are favorable for growth are 45% and 95% for Navarre and Rollover Passes, respectively. At the lower areas within the "stable region," the percentage of time that tidal conditions are above those required for equilibrium are 35% and 94%, respectively. The lower value for Navarre Pass would indicate it to be more susceptible to closure due to heavy littoral drift resulting from an extreme storm, whereas during 94% of the time, the velocities in Rollover Pass would be above those required for equilibrium and the Pass would likely recover from deposition. A second factor favoring Rollover Pass pertains to the velocity Vmax at the stable max side of the transition region. The sediment transporting capacity of a flow is proportional to velocity V raised to some power n (3 < n < 5). The ability of an inlet to enlarge or maintain a cross-sectional area after or during heavy littoral drift therefore is strongly dependent on the maximum velocity. The corresponding velocities for Navarre and Rollover Passes for a two foot tidal range are 3.9 and 5.1 ft/sec, respectively. It is noted that if the equilibrium cross-sectional area is associated with tidal conditions which exceed those required for equilibrium 15% of the time, then Rollover Pass would have stabilized at a -128

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cross-sectional area of 18,000 ft2.The inlet was cut with a cross-sectional area of 640 ft2 and grew until it was artificially stabilized at a cross-sectional area in excess of 3000 ft2. Finally, it should be noted that there are a number of assumptions made in the stability analysis presented here which should be considered in evaluating the stability method and results. One of the most questionable assumptions is the fixed ratio of width to depth for the inlet cross-section. Although the ratio of 35 used is a realistic value for many existing inlets, in some cases the inlet depth is limited by the depth of the bay adjacent to the inlet. -129

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APPENDIX III GLOSSARY OF TERMS Introduction Presented below are definitions of terms which may not be familiar to all readers in the context used in this report. Bar A depositional feature which may result from decreasing velocities near the Gulf or Sound terminus of the Pass. Beach face The relatively steeply sloping portion of the beach on which wave uprush and downrush occurs. Berm The mildly sloping (or flat) portion of the beach located at the approximate limits of maximum wave uprush. Deposition basin An excavation area to serve for the temporary detention of littoral drift until bypassed. Diurnal tide A tide having a period of approximately 24 hours, e.g., the tide in Santa Rosa Sound area. Downdrift The direction along the beach corresponding to the net littoral drift. Foredune The small dune-like features at the toe of the major dunes. Usually these are dunes in the process of development. Hydraulic model A reduced-sized version of a natural feature or area. Designed to simulate hydraulic phenomena in a scaled-down representation. -130

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Hydraulic radius A parameter used in hydraulic analysis. For a given cross-sectional flow area, indicates the efficiency of the particular cross-sectional shape. Littoral drift That sand and shell material which moves parallel to the beach due to the action of waves and winds. Longshore Pertains to the direction parallel to the beach. For example longshore current is thatcomponent parallel to the local beach alignment. Median diameter The diameter of sand below and above which fifty percent of the sample lies. Neap tide The astronomical tides occurring with near-minimum tidal ranges. Numerical model A computer simulation of a particular feature or bay system. Based on the governing equations. Phase lag The time in hours and minutes, between occurrence of Gulf maximum (or minimum) tides and the resulting event occurring at any location in the Sound. Sea Waves generated locally, of short period, and present a "confused" picture. Scarp An erosional feature, evident as a steep near-vertical face on the beach. Semi-diurnal tide A tide with a period of approximately 12.4 hours. Spring tide The astronomical tides occurring with the near-maximum tidal ranges. Stability Pertains to the tendency of a beach to exhibit only minor seasonal fluctuations or to an inlet to exhibit neither a net growth nor reduction in size. -131

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Swell Water waves of relatively long period generated by a distant storm. Appear as long-crested waves. Tidal prism The total volume of water which flows in (or out) of an inlet on a flood (or ebb) cycle. Tidal range The vertical distance between a successive maximum and a following minimum or a minimum and a following maximum of a tidal oscillation. Updrift The direction along the beach opposite to the direction of net littoral drift. Uprush The rapid excursion of a broken water wave up the beach face. Weir jetty A type of jetty system which incorporates a low section in the updrift jetty to allow sand to pass over the weir and settle in a planned deposition area. -132



PAGE 1

COASTAL ENGINEERING STUDY OF PROPOSED NAVARRE PASS 73 -o0 Sponsor: Santa Rosa County Beach Administration Submitted by: Coastal and Oceanographic Engineering Laboratory Florida Engineering and Industrial Experiment Station University of Florida Gainesville, Florida February, 1973

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ABSTRACT This report describes the results of a coastal engineering field and numerical study of the proposed Navarre Pass. The field measurements are based on three field trips during which bathymetry and tides and currents were measured. The numerical model simulates the tides and flows in Santa Rosa Sound and is capable of including the effects of Navarre Pass. Littoral drift direction and magnitude are of considerable importance in planning the inlet; calculations were carried out using shore-based observations obtained in a program of the Coastal Engineering Research Center. The results of the study indicate that: 1. Navarre Pass would only reduce slightly the equilibrium cross-sectional flow areas into Pensacola (1.8%) and Choctawhatchee (0.1%) Bays. 2. The velocities through Navarre Pass would be well within the limits considered safe for small craft navigation. 3. Planning for artificial transfer of sand should be based on an annual rate of 200,000 cubic yards to the west. Initial disposition of dredged material should be as a feeder beach on the west side of the Pass. 4. The Pass would cause a localized moderation of Sound salinities in the vicinity of the Pass. ii

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5. The tide and geometric characteristics are such that Navarre Pass will always tend to close unless maintained open by jetties. Based on these results, it is concluded that if proper financial provision is made for construction and maintenance of the inlet, there should be no significant adverse effects to the stability of the Santa Rosa Island Beaches, nor to the adjacent waters. iii

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TABLE OF CONTENTS Page ABSTRACT ............................................ ii LIST OF TABLES ..... ............................... vii LIST OF FIGURES .................................... viii LIST OF SYMBOLS ..................................... xii ACKNOWLEDGEMENTS ................................... xiv I. INTRODUCTION ............................... 1 II. PURPOSES OF STUDY .......................... 3 Impact of Pass on Natural Processes ............ ............. 3 Conceptual Design Features of Navarre Pass ....... ............. 4 III. BRIEF HISTORY OF NAVARRE PASS .............. 5 IV. METEOROLOGY AND HYDROGRAPHY OF AREA ........ 12 General Description ..................... 12 Winds ................................ 13 Sea ........... ...................... 13 Swell .... ............................ 17 Tides ..................... ........... .. 17 Offshore Currents ............... ..... 19 Santa Rosa Sound Currents ............ 22 V. FIELD STUDIES AND RESULTS .................. 25 Field Trip No. 1, May 13-18, 1970 ...... ............. 25 Field Trip No. 2, December 7-12, 1970 ............... 32 Field Trip No. 3, July 19-23, 1971 ..... ............. 38 iv

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TABLE OF CONTENTS-Continued Page VI. LITTORAL DRIFT ............................. 42 Introduction ............................ 42 Littoral Drift Estimates ............. 43 Experimental Groin at Navarre ........ 51 Summary and Recommendations ............. 61 VII. SUMMARY OF NUMERICAL MODEL CALCULATIONS ............................ 62 Introduction ............................ 62 Results Obtained Using the Numerical Model ...................... 63 Effect of Navarre Pass on Entrances to Pensacola and Choctawhatchee Bays .............................. 63 Maximum Velocities Through Navarre Pass ...................... 64 Relative Stability of Navarre Pass ...................... 64 VIII. RECOMMENDED DESIGN OF NAVARRE PASS INLET .................... .. ... .... 65 Functional Design .................... 65 Recommended Layout of Navarre Pass ... 65 Disposition of Initially Dredged Material .................. 73 Alternate Designs ................... 74 IX. SUMMARY AND CONCLUSION ..................... 75 Summary ................................ 75 Conclusion .............................. 75 X. REFERENCES .............. .................. .76 APPENDIX I. NUMERICAL MODEL OF THE BAY SYSTEM AFFECTING NAVARRE PASS .................. 78 Introduction ............................ 78 Derivation of the Numerical Model ....... 79 v

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TABLE OF CONTENTS-Continued Page Governing Differential Equations ..... 79 Finite Difference Equations .......... 82 Boundary Conditions ................. 83 Application of the Numerical Model ................................ 86 Assessment/Calibration of the Numerical Model .................. 87 Use of Numerical Model to Evaluate Effect of Navarre Pass ............ 98 Maximum Velocities Through Navarre Pass ...................... 101 II. STABILITY OF NAVARRE PASS .................. 103 Introduction ........................... 103 Method .................................. 103 Numerical Model ...................... 105 Sedimentary Stability ................ 105 Equilibrium Cross-Sectional Area .............................. 109 Application of Stability Equilibrium Concepts to Navarre and Rollover Passes ..................... 112 Navarre Pass ......................... 115 Rollover Pass ........................ 123 Conclusion Regarding Relative Stability of Navarre and Rollover Passes ...................... 123 III. GLOSSARY OF TERMS .......................... 130 Introduction ............................ 130 vi

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LIST OF TABLES Table Page I Summary of Field Trip Activities and Information Obtained ................... 26 II Summary of Median Diameters of Sand Samples Analyzed (Field Trip of May 1970) .......................... 31 III Summary of Calculated Littoral Drift Using LEO Data ....................... 50 I-1 Characteristics of Schematized Bay/Inlet System ........................... 88 I-2 Summary of Measured Tidal Characteristics ............................ 89 I-3 Dimensions Used in Flow Calculations at Navarre Bridge .......................... 94 I-4 Predicted Effect of Navarre Pass on Flows in and out of Pensacola and Choctawhatchee Bays ........................ 99 I-5 Calculated Maximum Discharges and Velocities Through Navarre Pass for Various Tidal Ranges .................. 102 II-1 Ratio R, of Maximum to Minimum Tidal Ranges During the Period January 1 to February 9, 1970 .............. 116 vii

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LIST OF FIGURES Figure Page 1 Location Map of Santa Rosa Island Region .............................. 2 2 Aerial Photograph Prior to Navarre Pass Cut (Date of Photograph: February 14, 1963) ......................... 6 3 Oblique View of Gulf Terminus of Navarre Pass (Date: Unknown, but Probably August, 1965) ................. 7 4 Aerial Photograph of Navarre Pass Showing Effect of Westerly Littoral Drift (Date of Photograph: On or About September 1, 1965) ................... 8 5 Oblique View of Navarre Pass Shortly After Closure (Date of Photograph: September 1965) ............................ 9 6 Aerial Photograph Showing Filling of Pass by Air and Water Transported Sand (Date of Photograph: June 1970) ...... 11 7 Data Squares in Gulf of Mexico and Caribbean Sea .............................. 14 8 Monthly Wind Roses at Data Square Off Navarre Pass Area ...................... 15 9 Monthly "Sea" Roses at Data Square Off Navarre Pass Area ..................... 16 10 Monthly Swell Roses at Data Square Off Navarre Pass Area ...................... 18 11 Predicted Tides at Galveston, Pensacola and Miami Harbor Entrances ...................... 20 viii

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LIST OF FIGURES-Continued Figure Page 12 Example of Measured Tides in Gulf of Mexico and Santa Rosa Sound ............. 21 13 Measured Currents Offshore Navarre Beach, Florida. May 15-16, 1970 ........... 23 14 Currents Measured at Navarre Bridge, December 9-11, 1970 ............... 24 15 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of May 13-18, 1970 .............. 27 16 Locations of Principal Measurements Conducted During Field Trips .............. .28 17 Location of Tidal Division Line at 1545 on May 16, 1970 ............. ..... 30 18 Beach Profiles, December 9, 1970 ........... 33 19 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of December 7-12, 1970 .................... 37 20 Measured Tides in Gulf of Mexico and in Santa Rosa Sound During Field Trip of July 19-23, 1971 ........................ 39 21 Experimental Groin Under Construction ...... 41 22 Coastal Sector Method Used by Coastal Engineering Research Center in Reporting Wave Direction .................. 48 23 Locations of CERC LEO Data Used in Littoral Drift Calculations. Drift Directions and Net Annual Rates Also Shown ................................. 49 24 Photographic History of Navarre Experimental Groin .......................................... 52-59 ix

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LIST OF FIGURES-Continued Figure Page 25 Weir Jetty System at Hillsboro Inlet, Florida ............................... 68 26 St. George Island Cut. Note Erosion Where Bank Protection is Not Provided .......... ......................... 71 I-1 Bay System Represented in Numerical Model ............................ 80 I-2 Illustration of Bay Segment Representation ............................. 84 I-3 Schematization of Pensacola Bay/ Choctawhatchee Bay/Santa Rosa Sound/ Gulf of Mexico System ...................... 85 I-4 Comparison of Measured and Calculated Ratios of Sound to Gulf Tidal Ranges Versus Gulf Tidal Range ................... 91 I-5 Comparison of Measured and Calculated Phase Lags Between Gulf and Sound Tidal Extremes ............................. 92 I-6 Comparison of Measured and Computed Santa Rosa Sound Tides and Discharges .......... .... ................... 95 II-1 Schematic Illustrating Stability Analysis for Single and Multiple Inlets ............. 104 II-2 Illustration of Escoffier's Stability Concept .................................... 107 II-3 Equilibrium Cross-Sectional Area and Tidal Prism Relationship (From O'Brien) .... 111 II-4 Variation of Maximum Inlet Velocity with Cross-Sectional Area for Equilibrium Conditions ................................. 113 II-5 Variation of Maximum Velocity with Inlet Cross-Sectional Area and Tidal Range. Navarre Pass, Florida ..................... 114 x

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LIST OF FIGURES-Continued Figure Page II-6 Predicted Tides at Galveston, Pensacola and Miami Harbor Entrances. Note Differences in Tidal Range Variations ............ 117 II-7 Cumulative Probability Distributions for Predicted Gulf Tidal Ranges at Navarre and Rollover Passes ................ 119 II-8 Auxiliary Diagram for Determination of Tidal Range Corresponding to Sedimentary Equilibrium (Example Shown for AC = 5000 ft2) ................... 120 II-9 Stability Analysis for Navarre Pass, Florida .............................. 122 II-10 Area Map Showing Location of Rollover Fish Pass ......................... 124 II-11 Numerical Model Representation of Galveston Bay .............................. 125 II-12 Variation of Maximum Velocity with Inlet Cross-Sectional Area and Tidal Range -Rollover Fish Pass, Texas .......... 126 II-13 Stability Analysis for Rollover Fish Pass, Texas .......................... 127 xi

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LIST OF SYMBOLS Symbol Description A,, A2 Flow areas through Navarre Bridge Ac Cross-sectional flow area of inlet ACE Equilibrium cross-sectional flow area A* Critical cross-sectional flow area C A Plan area of bay segment Cf Wind stress coefficient D Total depth = h + n f Darcy-Weisbach friction factor g Gravitational constant -G Subscript referring to "Gulf" variable h Depth below mean sea level K Entrance loss coefficient en K Exit loss coefficient ex L Length of bay segment or inlet n Exponent of velocity in sediment transport relationship n Subscript referring to nth bay segment p Tidal prism P Probability in percent q Discharge per unit width in the x-direction qR Runoff in cubic ft/sec per foot of bay length xii

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LIST OF SYMBOLS-Continued Symbol Description Q Total discharge across bay segment or through inlet R Ratio of maximum to minimum tidal ranges R Hydraulic radius, also tide range -S Subscript referring to "Sound" variable or "Spring" tidal range t Time T Tidal period U Wind speed at 30 ft reference elevation V Water velocity, in bay segment or through inlet w Width of bay segment considered x Horizontal distance coordinate aligned with bay axis y Horizontal distance coordinate perpendicular to bay axis B Angle of wind vector relative to bay axis n Water surface displacement from mean sea level, positive upwards 7T Numerical constant, 3.14159 .... p Mass density of water Pa Mass density of air a Angular frequency of tide T Wind stress on water surface Tb Frictional stress on bottom of water column xiii

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ACKNOWLEDGEMENTS Many individuals have contributed in a variety of ways to the study reported herein. The efforts of the Staff of the Department of Coastal and Oceanographic Engineering who participated in the field program are appreciated. The cooperation of the Santa Rosa County Beach Administration was most helpful, and the interaction and discussions with Messrs. Baskerville and Escoffier of Baskerville-Donovan Engineers, Inc., contributed to the final design presented in this report. Captain R. W. Slye kindly photographed the experimental groin and provided comments regarding its performance. Mr. W. J. Wells was instrumental in implementing this study and maintained an interest throughout the investigation. Mr. Walter Burdin of the Mobile District of the U. S. Army Corps of Engineers provided several aerial photographs and a continuing interest in this project. The Coastal Engineering Research Center willingly provided their Littoral Environmental Observation (LEO) data which included observations of wave height, period and direction. Mr. Curtis Baskette, a Graduate Student, became interested in and developed a computer program to compute littoral drift from the LEO data. xiv

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The study was under the general direction of R. G. Dean, Professor of Coastal and Oceanographic Engineering. xv

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I. INTRODUCTION In May, 1970, the Santa Rosa County Beach Administration contracted with the Coastal and Oceanographic Engineering (COE) Department of the University of Florida to carry out a coastal engineering study of the proposed Navarre Pass through Santa Rosa Island. Santa Rosa Island is a narrow barrier island with an east-west axis paralleling the mainland; the island is separated from the mainland by Santa Rosa Sound, see Figure 1. The proposed site for Navarre Pass is approximately at the mid-point of the Island and several thousand feet east of the Navarre Bridge; the approximate latitude and longitude of the Pass Site are: 30023' N and 86051'10" W, respectively. The Pass was first cut through the Island in July, 1965, however by September, 1965, the cut had widened and shoaled and was impassable to small craft. Since closing, the Pass reportedly has been reopened at least twice by a hurricane (Camille, 1969) and a severe winter storm. In December, 1970, the berm elevation across the original cut had been built up to an elevation of approximately +6 ft MSL. -1

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Escambia Bay Pensacola Bay East Bay Big Lagoon Choctawhatchee Bay -" Destin S _Santa (East) Location Rosa Pass Island GULF OF MEXICO FIGURE I LOCATION MAP OF SANTA ROSA ISLAND REGION

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II. PURPOSES OF STUDY The two primary purposes of the study include: (1) The impact of the Pass on natural processes, and (2) Recommendations relative to the conceptual design of the Pass. Impact of Pass on Natural Process The various natural processes of interest in this study are discussed in the following paragraphs. 1. Beach stability.--The possible effect of the Pass on the adjacent beaches was the consideration of greatest concern. Santa Rosa Island beaches are presently some of the finest in the State, are unencumbered by groin and seawall structures and are relatively stable. The deleterious effects on beach stability of inlet excavation and/or modification along the Florida East Coast has justifiably caused concern relative to future inlet modification. The littoral drift* characteristics in the area are particularly relevant to the matter of beach stability. The quantities and directions of littoral drift are also of interest in the configuration of the jetties, design of bypassing features and financial provision to mechanically transfer the sand interrupted by the presence of the Pass and jetties. 2. Stability of neighboring passes.--The passes to the east and west (East Pass and Pensacola Bay Entrance, respectively) would be influenced to some extent by the proposed Navarre Pass. It is conceivable that the water flowing through the Pass could "capture" a significant amount of the flow presently occurring through East Pass and Pensacola Bay Entrance, thereby causing these *Glossary of terms is provided as Appendix III. -3

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passes to shoal and a resulting increased dredging requirement or a decreased equilibrium cross-sectional area. Conceptual Design Features of Navarre Pass Based on the results of the study, recommendations will be presented relating to the following conceptual design features of the Pass: 1. Inlet dimensions and layout.--The primary factors considered in the inlet dimensions and layout will be: safe navigation, minimum effects on adjacent beaches, effect on neighboring passes, and maintenance costs. 2. Sand transfer and disposition of initial excavation material.--The initial and maintenance sand disposition including quantities will be recommended so as to result in a minimum interruption of the natural sand transport processes and beach stability. 3. Channel protection.--Unless provided with adequate protection against erosion, the banks of the cut and dunes will erode due to water and wind forces and tend to deposit in the Pass. The resulting deposition of material can interfere with navigation and cause an added dredging cost. Rip-rap or vertical sheet piling will represent the best form of bank protection in the cut whereas vegetation, if properly maintained could provide good protection against erosion by wind of the dunes and portions of the cut above water. -4

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III. BRIEF HISTORY OF NAVARRE PASS Navarre Pass was originally cut in July, 1965, by a pipe-line dredge at a cost of $30,000. The original dimensions were 100 ft wide by 9 ft deep. The primary purposes of the Pass included a more direct access to Snapper grounds and to provide a general economic stimulus to this portion of the Santa Rosa Island area. Figures 2 and 3 are aerial photographs prior to the Pass dredging and shortly after the dredging, respectively. The date of the photograph in Figure 3 is not known, but was probably taken in August, 1965. Note that some narrowing of the mouth of the Pass has occurred on the east side indicating the effect of westerly littoral drift. The photograph presented in Figure 4 was taken on or about September 1, 1965, and presents a more advanced case of deposition against the near-Gulf portion of the east side of the cut. The shoaling is not apparent from this photograph, but probably has reached an advanced stage. Figure 5 represents a photograph taken in September, 1965, after complete closure of the Pass. Again the effects of the westerly littoral drift in displacing the channel to the west are evident. Hurricane Betsy occurred during September 8-11, 1965, and presumably -5

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.rrP NAVARRE PASS CUT (DATE OF PHOTOGRAPH: FEBRUARY 14, 1963) -6-

PAGE 22

4dr 0410 ro rllaw ~3 ON dkv

PAGE 23

FIGURE 4 AERIAL PHOTOGRAPH OF NAVARRE PASS SHOWING EFFECT OF WESTERLY LITTORAL DRIFT (DATE OF PHOTOGRAPH : ON OR ABOUT SEPTEMBER 1, 1965) -8-W

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FIGURE 5 OBLIQUE VIEW OF NAVARRE PASS SHORTLY AFTER CLOSURE (DATE OF PHOTOGRAPH : SEPTEMBER 1965) -9

PAGE 25

was instrumental in the rapid development of the final closure stages. As shown in Figure 6, by June, 1970, the Pass had filled substantially so that the only remnants of the channel remaining below water are at the Sound side of the Pass. According to R. Bruno (1), the Pass has been opened naturally on at least two occasions since 1965. One of these occurred during Hurricane Camille in August, 1969 and the other opening resulted from a winter storm. No information is available concerning the extent of these openings nor of the magnitudes of the resulting flows through the Pass Site. Presumably the Pass closed fairly rapidly after each opening. -10

PAGE 26

FIGURE 6 AERIAL PHOTOGRAPH SHOWING FILLING OF PASS BY AIR AND WATER TRANSPORTED SAND (DATE OF PHOTOGRAPH: JUNE 1970) -11

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IV. METEOROLOGY AND HYDROGRAPHY OF AREA General Description The general offshore region near Santa Rosa Island is characterized by prevailing easterly winds with strong northerly winter winds. The easterly winds result in predominately southeasterly waves occurring in the nearshore region. These waves are responsible for the predominately westerly littoral drift. Tides in this area are predominately diurnal (i.e., a period of 24 hours) with the diurnal tidal range at Pensacola listed at 1.3 ft. During the field trips conducted in conjunction with this study, Gulf tides were measured from the Navarre Pier with tidal ranges in excess of 2 ft. Concurrent measurements of the tides in Santa Rosa Sound demonstrated that the tidal lag between the Gulf and the Sound generally varies between 2 to 32 hours and there is little if any reduction in tidal range (at Navarre Bridge, where the Sound tidal measurements were conducted). The Gulf nearshore currents were not studied extensively, however during one field trip an easterly current greater than 1 ft/second was measured fairly near shore. On later field trips, existing near shore currents were observed to be much weaker and were not measured. -12

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\'I Winds Data representing the offshore winds in the Gulf of Mexico are available in Reference 2. These data are the results of observations and measurements obtained from ships; the data are presented as average monthly conditions by the 5 degree latitude and longitude data squares shown in Figure 7. For the square off the Navarre Pass site, the monthly data are presented in Figure 8. The most persistent winds are seen to be from the east (easterly winds), with easterly winds of 11 to 16 knots occurring 8% of the time and easterly winds of 17-27 knots occurring 4% of the time. Calms occur about 11% of the time. With the predominant easterly winds, it is clear that the resulting predominant waves and littoral drift will be directed toward the west. During the period December through June, there are reasonably strong southeast winds and during October through March, fairly strong north and northeast winds occur. Sea The average distribution of sea (i.e., locally generated waves, generally of short period) obtained from Reference 2 are presented in Figure 9. Because sea results from the local winds, there is a strong resemblance between the wind roses presented in Figure 8 and the sea roses. It should be stressed that these sea roses pertain -13

PAGE 29

300 -1. :, .' ..j oo. Nov rre .Pass Site Data Square / U I VUsed For /, 1 Navarre Pass/ A S200 --. -/ stuÂŽ Z/Z .-I :5 -I I --/I I 1 I-. .1 1 II, 1 950 90 85 800 750 70 FIGURE 7 DATA SQUARES IN GULF OF MEXICO AND CARIBBEAN SEA

PAGE 30

9475 8576 1013 9681 6 656 00 10 20 00 40 50 60 70 80 90 100 10 20 3040 50 60.70 80 90 100 uI ]O 1 00 40 50 6) To 80 9C_ too January February March April 11666 9778 12099 12412 r1920 ? ^ i -^ )---a r--^T 12 C---[ '21 24 0 10 20 30 40 50 60 TO 80 9 00 0 0 10 20 0 40 150 60 17 0 O 90 0000 S 20 40 506 0 90o 20 30 40 So 60 r0 8o90 100 May June July August 10554 11886 12789 10449 I 5. i i 6 0 10 20 0 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 September October November December LEGEND NUMBER Or ___ 3, OBSERVATIONS -KNOTS FIGURE 8 MONTHLY WIND ROSES I 008 B R 0BEAUFORT AT DATA SQUARE OFF % BEAUFORT 01--ROSE SCALE (PERCENT FREQUENCY) NAVARRE PASS AREA ,O ,o20 30 o DOUBLE CIRCLE INDICATES THEORETICAL WIND ROSE. (SEE FIGURE 7) WIND SPEED SUMMARY (ALL DIRECTIONS) DATA FROM REFERENCE 2 BEAUFORT ORC CALM 2-3 4 5-6 7-12 0 10 20 30 40 30 60 70 80 100 PERCENT -"15

PAGE 31

5916 7298 7511 7 6481 January February March April 724 7414 8543 9129 I1161111111111 1 1 PIT 0 10 20 00 40 50 0 TO 80 90 r 00 0 ;O 20 30 40 50 60 70 80 90 100 I c 10 30 4 5S 61 71 80 90 0 10 20 30 4C 50 60 70 0O 90 100 May June July August 7621 j 7344 8461 9523 004 0 0 0 10 20 30 40 50 60 70 80 90 100 20 30 40 )' 60 70 80 90 100 'i i 0 1 20 0 40 50 60 70 80 90 100 i o.--:.09 ._ ___ 'i-_--' ....... September October November December LEGEND SEA 0 6203 -OBSERVATIONS FIGURE 9 MONTHLY "SEA" ROSES 20( OsRO AT DATA SQUARE OFF RGH, (5T. VERY ROUGH (8-12 FT.) NAVARRE PASS AREA" (SEE FIGURE 7) 30 / 404 (ALL DIRECTIONS) -16-

PAGE 32

to the data square off Santa Rosa Island as shown in Figure 7 and the sea indicated as originating from the north is not of concern in considering nearshore processes. For this data square, 80% of the sea has a characteristic (significant) wave height less than 12 ft. Swell The average monthly swell roses, determined from Reference 2 are presented in Figure 10. As for the case of the sea roses, the predominant swell affecting the Santa Rosa Island shoreline would propagate from the southeast, again contributing to a net westerly littoral drift. Tides The tides are of particular importance in maintaining an inlet open under the action of littoral drift which, unopposed, would result in the closing of an inlet. It is valid to regard the tidal "forces" and littoral drift "forces" in opposition, with the tidal forces being more or less predictable and periodic and the littoral drift forces only predictable on an average seasonal basis. Because periods of high littoral drift could result in the closure of an inlet, the most effective tidal characteristics for maintaining an inlet open would be a constant tidal range. The "forces" to maintain an inlet open would then -17

PAGE 33

4433 4741 4402 5150 0 0 020 30 4050 60000 TO 0820 39000000 0 010 20o 0 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0J 10 20 30 40 50 60 70 80 90 100 January February March April 5329 6591 4694 44 6860 0 53 0 51 37 0 0 ""i""1" ""1""i'1"" "1 1' "1 1 1"1.... o ,oo 2o 0 0 0to eoo i0 h0iom T 0 10 20 30 40 50 60 70 80 90100 0 10 10 '0 40 10 60 10 10 90100 0 10 20 30 40 5o 60 to 80 90 00 0 10 20 40 50 60 9O 70 80 90 100 May June July August 7141 5206 6260 5281 32 0 25 -T 0 o 0l I0l O 10 20 3030 40 50 60 70 80 90 100 100 S70 t 0 10 0 30 40 50 60 70 80 900100 September October November December LEGEND-SWELL FIGURE 10 MONTHLY SWELL ROSES 3% NO SWELL %_ CONFUSED AT DATA SQUARE OFF o ODERATE (6-12FT) ; HIGH (>12 FT.) NAVARRE PASS AREA I2 I (SEE FIGURE 7) |^ J DATA FROM REFERENCE 2 _.,, .. 0 t10 20 30 40 50 60 70 o80 90 I00(%) SUMMARY SCALE (ALL DIRECTIONS) -18

PAGE 34

always be operating at an effective level to counteract any unusually heavy littoral drift occurrence. Unfortunately, the tidal range in the Santa Rosa Island area of the Gulf of Mexico is not nearly constant, but varies greatly from spring to neap conditions. The tidal ranges encountered during the different field trips varied from a low value of 0.36 ft (4 inches) to an upper range of 2.2 ft. The tide tables indicate a ratio of maximum to minimum tidal range of approximately a factor of 18. Figure 11 presents a plot of the predicted tides for the month of January and a portion of February, 1971 for Pensacola, Galveston Entrance and Miami Harbor Entrance. The low tidal range periods are indicated when an inlet would be highly susceptible to deposition. An example of the measured Gulf and Sound tides obtained during the July 1971 field trip is presented in Figure 12. Offshore Currents During two of the field trips, attempts were made to install a recording current meter in a water depth of approximately 16 ft at a location about 900 ft offshore of the Pass Site. The first attempt was successful and resulted in a recording of approximately 24 hours duration, however the current meter malfunctioned during the second attempt and no data were obtained. The data obtained during the first field trip were quite -19

PAGE 35

1.0 -I.0GALVESTON ENTRANCE Period of Period Low Relative of High Susceptibility Relative to Deposition Susceptibility 10 to Deposition rp 1.0 ) IUI )| I UIU u V u --1.0 PENSACOLA January, 1971 February, 1971 5 10 15 20 25 30 5 1i l l l l l I i I iI I I I I l i l I i 1 1 1 1 1 1 I III I i 2.03: 1.0-1.0MIAMI HARBOR ENTRANCE FIGURE II PREDICTED TIDES AT GALVESTON, PENSACOLA AND MIAMI HARBOR ENTRANCES. NOTE DIFFERENCES IN TIDAL RANGE VARIATIONS -20

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Note In This Figure, The Gulf And Sound Tides Are Not Referenced Gulf of Mexico To A Common Elevation Datum Santa Rosa Tide 0 12 15 18 0 9 12. 15 0 3 6 9 oHours SJuly 21, 1971 .July 22, 1971 --July 23, 1971 -2 FIGURE 12 EXAMPLE OF MEASURED TIDES IN GULF OF MEXICO AND SANTA ROSA SOUND

PAGE 37

surprising and showed a strong easterly current (1.3 ft/sec) at the time of installation which decreased to approximately 0.5 ft/second during the 24 hour recording period. These data are presented in Figure 13. During the second field trip, the divers noted while installing and recovering the current meter that there was no appreciable current. It is believed that the current measured during the first field trip was perhaps due to some effect of the Gulf Stream which does form a general clockwise circulation pattern in the Gulf of Mexico. Because the information pertaining to this current is very limited, it is not possible to conclude whether the effect on littoral drift is significant, however it is noted that if the prevailing current direction is easterly, and if the current is significant in the surf zone area, then the effect would be to reduce the net westerly littoral drift. Santa Rosa Sound Currents During one of the field trips, currents were measured from the Navarre Bridge over a 40-hour period. These measurements were conducted with a nonrecording current meter and therefore were taken intermittently. The measurements are presented in Figure 14 where it is seen that the maximum velocities are on the order of 1 ft/sec. -22

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2.0 NOTE: CURRENT METER LOCATED APPROXIMATELY 900 FT. OFFSHORE OF PROPOSED INLET SITE WATER DEPTH = 15 FT. DISTANCE. o OF METER ABOVE BOTTOM = 6 FT. 4z 1.0w -o 1200 1600 2000 2400 0400 0800 1200 TIME (hours) MAY 15 MAY 16 IFIGURE 13 MEASURED CURRENTS OFFSHORE NAVARRE BEACH, FLORIDA. MAY 15 -16, 1970

PAGE 39

1.0 I Smoothed Curve Drawn Through Measurements 0 o I , I, \ l l i l l l ll 1 1 l 4,-O 1800 0000 0600 1200 1800 0000 0600 -Dec. 9, 1970 Dec. 10, 1970 Dec. II, 1970 \ e Note: See Figure 16 SFor Location of Current Measurements 1.0 FIGURE 14 CURRENTS MEASURED AT NAVARRE BRIDGE, DECEMBER 9-11, 1970

PAGE 40

V. FIELD STUDIES AND RESULTS Three separate field studies were carried out during the study. The dates and programs carried out during these three studies are presented in Table I. A brief description of each of the field studies is presented below. Field Trip No. 1, May 13-18, 1970 During this field trip a baseline was established which ranged approximately 1000 feet east of the centerline of the proposed inlet to 2000 feet west of the centerline. The baseline was located shoreward of the active beach profile on the foredunes to reduce losses of the stakes. Beach profiles and offshore soundings were conducted and the contoured results are presented as Plate I in the report cover jacket. Two tide gages were installed: one was located in the Sound in the vicinity of the south bridge section of the Navarre Bridge; the second was installed on the Navarre Pier near its seaward end. The tides during this period were quite small. The predicted tides at Pensacola, Florida ranged from 0.3 to 0.7 feet. The recorded tides are presented in Figure 15 and Figure 16 shows the locations of the tide gages and other field measurements. From the tide records, very little difference in Bay and Gulf tidal -25

PAGE 41

TABLE I Summary of Field Trip Activities and Information Obtained Data Obtained Dates Encompassed Gulf Sound Beach Offshore Additional Activities and by Field Trip Tides Tides Profiles Soundings Data Obtained May 13-18, 1970 Yes Yes Yes Yes 1. Baseline Established (36 Hour (36 Hour 2. Offshore Currents Duration) Duration) Measured (24 Hours) 3. Sand Samples Collected 4. Sound "Tidal Division Line" Established Dec. 7-12, 1970 Yes Yes Yes No 1. Sound Currents (36 Hour (36 Hour Measured From Navarre Duration) Duration) Bridge (40 Hour Duration) July 20-25, 1971 Yes Yes Yes Yes 1. Experimental "Sand Bag (24 Hour (24 Hour Groin" for Littoral Duration) Duration) Drift Observations Constructed

PAGE 42

+0.5 +0.5 Santo Rosa Sound Tides May 14, 1970 May 15, 1970 E 0 -0r Gulf of Mexico Tides _--0.5 2 +0.5 May -15, 1970 May 16, 1970 -. .... .. ....-S0 1.0.5 +0.5 c May 16, 1970 May 17, 1970 0 0 -____ -0. ----------------------------------------------------------------------0.5 rI j1 II I I I I I I I 1 1 1 1 0900 1200 1500 1800 2100 0000 0300 0600 FIGURE 15 MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF MAY 13-18, 1970

PAGE 43

N 0 5000 ..'. Scale (ft) Sound S on 0o Site of Original -Navarre Bridge Navarre Pass Cut Navarre Bridge Sound Tide Gageu M.a : sS .."s ......... s...-d.. Sant of Su'f" i Gage Extent of Gulf Bothymetric Survey N--" Gulf Tide Gage.' Pier FIGURE 16 LOCATIONS OF PRINCIPAL MEASUREMENTS CONDUCTED DURING FIELD TRIPS

PAGE 44

amplitudes could be determined. An attempt was made to determine the location of the "tidal division line" in the Sound. This is a somewhat hypothetical separation line of the area (to the West) which is served (alternately filled and drained) by Pensacola Bay Entrance and the area (to the East) which is served by the East Pass to Choctawhatchee Bay. This line is affected greatly by winds and under conditions of very high winds may not exist at all. The location shown in Figure 17 was determined on May 16 by searching until the velocity some distance to the west of that location was toward the east and the velocity some distance to the east of that location was directed toward the west. Computations using the numerical model described in Appendix I indicates that the position of the "tidal division line" varies during a tidal period from approximately 15 miles east to 20 miles west of the Navarre Pass Site. Offshore currents were determined by installing a current meter approximately 900 feet offshore of the location of the proposed pass. The current flowed to the east during the two day period the meter was installed, see Figure 13. The peak current was approximately 1.3 ft/sec. Thirteen nearshore sand samples were collected and later analyzed for grain size distribution. Table II summarizes the results of the analysis of median diameters -29

PAGE 45

I IN 0 I 2 Scale (Statute Miles) re Bridge Iw Santa Rosa Sound "~--Tidal Division Line Santa FIGURE 17 LOCATION OF TIDAL DIVISION LINE AT 1545 ON MAY 16, 1970

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TABLE II Summary of Median Diameters of Sand Samples Analyzed (Field Trip of May 1970) Sample Collected Sample Location on Sample Median at Station Beach Profile Diameter (mm) 10+00 E 2 ft Below Mean 0.42 Sea Level 10+00 E Base of Small Scarp 0.35 10+00 E Midshore Between 0.50 Waterline and Berm 0+00 2 ft Below Mean 0.51 Sea Level 0+00 Limit of Wave 0.37 Uprush 0+00 Foredune 0.45 10+00 W Midway Between 0.46 Berm and Scarp 10+00 W Base of Scarp 0.36 10+00 W 2 ft Below Mean 0.50 Sea Level 20+00 W Midway Between 0.40 Berm and Scarp 20+00 W 2 ft Below Mean 0.33 Sea Level 20+00 W Limit of Wave 0.47 Uprush 20+00 W Base of Scarp 0.37 -31

PAGE 47

of the samples. It is seen that the median diameter ranges from 0.33 mm to 0.51 mm. This represents a relatively coarse beach sand for the State of Florida. Field Trip No. 2, December 7-12, 1970 During this field trip, the waves became quite high on the morning of December 8, thereby precluding the possibility of launching a boat through the surf to conduct offshore soundings. Beach profile measurements were conducted and are shown in Figure 18. It is of interest to note that, in places, the sand accumulation in the former Navarre Pass "cut" was 18" from May 1970 to December 1970 as determined by noting the burial of the stake at Station 0+00. It is not known whether this accumulation was primarily due to wind-blown sand or sand transported over the berm by combinations of high tides and waves. Two tide gages were installed at the same locations described for the previous field trip. The predicted tides at Pensacola Bay during this trip ranged from 1.2 feet to 2.1 feet. The tide records for the period December 8-11 are shown in Figure 19. It was found again that there was little difference in tidal amplitude between the Sound and Gulf and also that the tidal lag was between 3 and 4 hours. -32

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+ 10 --,* ^ ^ ---------------Station 20+00 W 0 Is---^ ---_0 100 200 Distance From Baseline (ft) I 10 -" Station 18+00 W 100 200 Distance From Baseline (ft) 2 +10 Cj Station 16+00 W 0 100 200 Distance From Baseline (ft) +10 s^ -----_I --Station 14+00 W 4.S ( __ O100 2300 Distance From Baseline (ft) FIGURE 18 BEACH PROFILES, DECEMBER 9, 1970 -33

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J --Station 12+00 W 0 _0 o100 200 Distance From Baseline (ft) +10 -.--Station 10+00 W 0 _0oo \ .200 t Distance From Baseline (ft) +10 _J --Station 8+00 W 0 |> 0O 100 __ 200 ,i,< Distance From Baseline (ft) +10 S) \-Station 6+00 W £B 6 100 1 200 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -34

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cJ -Station 4+00 W 20 Distance From Baseline (ft) +10 o----Station .:2+00 W o oo 100 200 S Distance From Baseline (ft) +10 -, = ----S---Station 0+00 1 0_ 100 _200 Distance From Baseline (ft) +10 _-Station 2+00 E S100 200 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -35

PAGE 51

+10 -) -Station 4+00 E > 1 Distance From Baseline (ft) +10 S-Station 6+00 E S_____ _____0 200 Distance From Baseline (ft) +10 _J Station 8+00 E 4S,'___ 100 200 < Distance From Baseline (ft) +10 -J --Station 10+00 E S0,36 Distance From Baseline (ft) FIGURE 18 (CONTINUED) BEACH PROFILES, DECEMBER 9, 1970 -36

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... +1.0 -__ SSound + 0.5 -Gulf § o 1I I I II I I 1, S0900 1200 1500 1800 2100 06 W I Time (hours) CST -0.5 I b ._ December 8, 1970 December 9, 1970 -1.0 +1.0 Gulfound +0.5 0 01200 1500 1800 2100 0600 0 December 9, 1970 1December 10, 1970 -0.5 -1.0 +1.0 '8 ^ -/Sound < +0.5 -\Gulf 900 1200 1500 1800 2100 0300 06 S n *; "y <~~~-------------' ----^ -o.Note: December 10, 1970 ecember II, 1970 .' SGulf and Sound Tides -1.0 Not Referenced to Some Datum FIGURE 19 MEASURED TIDES IN GULF OF MEXICO AND IN SANTA ROSA SOUND DURING FIELD TRIP OF DECEMBER 7-12, 1970 -37

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A current meter was also installed offshore, however the high wave activity caused a mechanical failure and no data were obtained. It was noted during installation and retrieval of the current meter, that net currents were relatively small. Sound currents were measured over a 40-hour period. The results of these measurements have been presented as Figure 14. The maximum velocities were in excess of 1 ft/sec. The significance of the Sound currents and their relationship to the tides will be discussed later when the calibration of the numerical model is presented. Field Trip No. 3, July 19-23, 1971 In addition to the type of information collected on previous field trips, a temporary sand bag groin was installed to act as a partial littoral drift barrier. The hydrographic information collected during this field trip included beach and offshore soundings and Gulf and Sound tide records. The Gulf tidal range measured was approximately 2 ft and the tidal lag between Gulf and Sound was in the range 3h 20m to 4h 20m. See Figure 20 for the tide records which were measured during a 48-hour period. The contoured results of the beach profiles and offshore soundings are presented as Plate II in the cover -38

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S 0900 1200 15o0 180 .2100 03 WL > Time (Hours) -+1.0 *..).. -------1.0 15 I -July 22, 1971 July 23, 1971 __ -^ ~ S o u n d E --Gulf .o0 -1.0 +10, +. ROSA SOUND DURING FIELD TRIP OF JULY 19-23 1971 -39

PAGE 55

jacket of this report. In order to carry out these surveys, it was necessary to reestablish much of the baseline which had been destroyed by four-wheel vehicles and other extraneous activities. An experimental sand bag-groin was constructed at the site of the planned Navarre Pass. The purpose of this groin was to perform as a partial littoral drift barrier and through observations of the impoundment, to provide a qualitative indication of the direction and persistence of the nearshore littoral drift. Two photographs of the groin under construction are shown in Figure 21. Unfortunately, due to settlement, the groin was only effective for a period of 2 months and the groin was not maintained because the required sand bags were not available for a period of 4 to 6 months. The performance of the groin will be discussed in "Section VI -Littoral Drift" and photographs (kindly taken by R. W. Slye) will be presented. -40

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July 1971 -Groin Under Construction July 1971 -Groin Nearing Completion Extreme Low Tide FIGURE 21. EXPERIMENTAL GROIN UNDER CONSTRUCTION

PAGE 57

VI. LITTORAL DRIFT Introduction In considering the establishment of a new inlet, the magnitude and direction of sand transported in the nearshore region (littoral drift) by waves and possibly currents are most important factors and also the most difficult to establish accurately. Jetties act to block sand from entering inlets, thereby rendering them more suitable for navigation. In performing this function, jetties interrupt the natural flow of sand (littoral drift) along the shore with the resulting accumulation of sand on the updrift side of the jetties. Since the waves maintain their sand-transporting capacity downdrift of the jetties, serious erosion can occur with long-term degradation of the downdrift beaches. In addition to interrupting the natural flow of sand along a beach, the interaction of inlet currents and sediment causes bars to be built offshore and in the inner bay. The material comprising these bars is derived from the natural sand system and therefore represents a loss to that system. Of course, once these bars have been established to near-capacity, then subsequent annual losses are reduced. -42

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In considering the establishment of a new inlet, the sand must be recognized as a valuable resource and the sand transfer as a natural process. Interruption of the sand transfer or the net loss of a significant amount of sand from the active system will definitely lead to a significant adverse effect On the downdrift beaches. In recognizing the significance of these processes and the necessity of maintaining the stability of the Santa Rosa Island beaches, the cutting and stabilizing of a new inlet should be planned to minimize any net loss of sand to the system and also to provide for the mechanical transfer of the sand interrupted by the presence of the jetties. A number of attempts have been made to design jettied inlets such that sand is prevented from interfering with.: navigation, yet the currents and waves still provide for the natural transfer of sand. A survey of jettied inlets will demonstrate that this approach has not proven successful and that the only effective concept is to provide for the artificial bypassing of sand. Littoral Drift Estimates Littoral drift estimates can be based on field measurements or on calculation procedures using wave data. Each of these approaches has advantages and disadvantages. Good accuracy in field measurements of littoral drift requires a near-complete trap (e.g. a long jetty) -43

PAGE 59

and reasonably long records in which the trap impoundment history is documented and/or records are kept of the amount of material removed or added to maintain stability of the downdrift shoreline. Littoral drift calculations are based on wave measurements and/or observations; to date (1972) the calculation procedures have not been developed and verified to the degree that a high degree of confidence is warranted. The most often applied calculation procedure (3) does not account for many presumably important parameters, including (1) sand size (2) sand specific gravity (3) beach slope (4) beach roughness In attempting to develop the best estimate of littoral drift, all sources of information should be reviewed with relative confidence based on the particular circumstances attending each measurement or calculation. Field Measurements.--The available field measurements in the Navarre Pass area are generally based on the westward rate of growth of the western ends of barrier islands and on the accretion behind the eastern jetty at Perdido Pass. Based on the rate of growth of the western end of Santa Rosa Island, and the dredged quaritities in the -44

PAGE 60

Bay Entrance and on the shoals, the U. S. Army Corps of Engineers (4) has concluded that the average annual westward and eastward drift are 130,000 and 65,000 cubic yards, respectively, resulting in an annual net westward drift of 65,000 cubic yards. In 1938, F. F. Escoffier (5) analyzed the westward growth rates of the eastern shore of East Pass (entrance to Choctawhatchee Bay), the results available at that time indicated an annual deposition rate of 26,300 cubic yards, although Escoffier noted that this quantity is undoubtedly smaller than the net littoral drift due to some bypassing of material past the inlet. The Corps of Engineers (4) estimates the westerly and easterly drift components at Perdido Pass to be 130,000 and 65,000 cubic yards per year resulting in a net westerly drift of 65,000 cubic yards per year. During the period May 1969 to March 1970, the Corps measured the deposition inside the Perdido Pass weir jetty to be 146,000 cubic yards. Hurricane Camille occurred within this period and may account for the higher than anticipated impounded quantities. For the period 1934-1953 (before the weir jetty system was constructed), J. W. Johnson (6) analyzed accretion at the eastern bank of Perdido Pass and concluded the annual deposition to be 200,000 cubic yards; presumably this would correspond approximately to the net westerly littoral drift. -45

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Calculations of Littoral Drift.--D. S. Gorsline (7) conducted a one-year study of Gulf beaches extending from Keaton Beach, Florida to Gulf Shores, Alabama. His study included monthly surveys of fifteen beaches in the study area and wave observations. Gorsline carried out calculations which indicated the gross drift rates at Pensacola to be approximately 200,000 cubic yards per year with a net westerly drift of 78,500 cubic yards/year. It should be stressed that Gorsline's calculations at each location were based on only one observation per month over a period of one year. There is a good likelihood, therefore that his results are not representative of average annual conditions. T. L. Walton (8) has carried out computations of littoral drift along all of the sandy beach segments of the State of Florida. The calculations are based on long-term wave observations collected by military and commercial ships. The wave characteristics are transformed to shore using standard procedures and drift is calculated based on the usual relationship (3). In comparing his predictions with other estimates for the Florida East Coast, Walton found generally good agreement for portions of the northern Florida east coast, however his calculated values were much higher than estimates based on impounded quantities along the lower Florida east coast. This difference was attributed, at least in part, to the -46

PAGE 62

proximity of the Gulf Stream and its effect in causing an increase in height of waves propagating from the northeast. This would qualitatively explain the differences noted. In the Navarre Pass area, Walton's calculated annual westward and eastward drifts are approximately 400,000 and 100,000 cubic yards, respectively, resulting in a net westward littoral drift of 300,000 cubic yards per year. The Coastal Engineering Research Center (CERC) collects shore-based observations in a program entitled "Littoral Environmental Observations" (LEO). The LEO data are generally taken daily and include visual estimates of breaking wave height and breaking wave direction in terms of a coastal sector method, see Figure 22. These data provide an alternate basis of estimating littoral drift, using the usual calculation procedure and assuming that the wave conditions reported are representative for the entire 24-hour period. Data were provided by C. J. Galvin and A. De Wall of CERC for four locations: Navarre Beach, Grayton Beach, Beasley Park and Crystal Pier. The period over which data were available ranged from 8 months at Navarre Beach to 24 months at Beasley Park and Crystal Pier. See Figure 23 for a map of the four observation locations. Table III summarizes the littoral drift values calculated from the LEO data. -47

PAGE 63

OCEAN If No Waves, Fill in Zero 3 2 4 S\ /o 100 250 250 600 600 Shoreline Observer LAND WAVE DIRECTION CODE FOR WAVES AT BREAKING FIGURE 22 COASTAL SECTOR METHOD USED BY COASTAL ENGINEERING RESEARCH CENTER IN REPORTING WAVE DIRECTION -48

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S Pensacola Bay Pens a By / Choctawhatchee Bay 5"i',Oo( e (Beasley ., tat ,o Park) Cry ,^^ GULF OF MEXICO Note: Arrows and Numbers Indicate Calculated Directions and Net Annual Littoral Drift (in Cubic Yards/Year) Using Leo Data FIGURE 23 LOCATIONS OF CERC LEO DATA USED IN LITTORAL DRIFT CALCULATIONS. DRIFT DIRECTIONS AND NET ANNUAL RATES ALSO SHOWN

PAGE 65

TABLE III Summary of Calculated Littoral Drift Using LEO Data Results Averaged Annual Duration of Data Calculated Littoral Drift Net Drift Location Available Interval (Cubic Yards) (Cubic Yards/Year) Navarre Beach 8 months Jan. 1, 1970 to Sept. 1, 1970 158,000(W)* 237,000(W) Grayton Beach 24 months Dec. 1, 1970 to Dec. 1, 1971 53,345(W) 52,100(W) Dec. 1, 1971 to Dec. 1, 1972 50,776(W) Beasley Park 24 months Jan. 1, 1971 to Jan. 1, 1972 30,064(W) 45,200(W) Jan. 1, 1971 to Nov. 1, 1971 50,321(W) Crystal Pier 12 months July 1, 1971 to July 1, 1972 253,331 253,331(W) *(W) denotes drift from East to West.

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Experimental Groin at Navarre An experimental sand bag groin was constructed at the site of the original Pass. The purpose of the groin was to obtain information regarding the variability and (hopefully) magnitudes of littoral drift. The groin was constructed on July 22, 1971 and extended 100 ft seaward of the mean high water line. The groin was about 3 ft high by 8 ft wide; two photographs showing the groin under construction have been presented as Figure 21. The groin was reasonably effective in trapping the nearshore portion of drift for a period of approximately 2 months, after which the portion of the groin traversing the beach face was undermined and settled significantly (about 4-6 ft). At that time, it was planned to rebuild the groin by adding more sand bags. Unfortunately the sand bags were not available* for a period of 4 to 6 months and the experiment was discontinued. A brief photographic history of the groin is presented in Figure 24.** During the period August 5 to August 8, 1971, impoundment occurred on the west side of the groin. On the morning of August 9, impoundment was evident on the east side of the groin which remained the *The factory had experienced a fire. **Captain R. W. Slye of the Santa Rosa County Beach Administration kindly offered to photograph the groin. -51

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August 5, 1971 -Note Slight Build-up August 8, 1971 -Continued Accretion 0800 From West 0800 on West Side of Groin FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (Photographs Taken by Captain R. W. Slye)

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4pf .. 0"" W-August 9, 1971 -Accretion is Now Apparent on August 20, 1971 -Some Evidence of Lessened 0900 East Side of Groin. Some Easterly Drift Compared to Transport of Sand Over Groin Photograph of August 9, 1971 is Evident FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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August 28, 1971 -Accretion on Western September 2, 1971 -Evidence of Drift Reversal 0800 Side of Groin -Compare 0830 Compared to August 28, 1971 With Photographs of Photograph. Also Note August 9 and 20, 1971 Lowering of Middle Portion of Groin Due to Undermining FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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September 8, 1971 -Same General Accretion September 13, 1971 -Groin Has Been Flanked 1200 Situation as Shown on 0900 With Scarping to East September 2 Photograph (Also See Following Photograph of Same Date) FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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September 13, 1971 -Showing Effect of High September 22, 1971 -Drift Accumulation on 0900 Tides and Easterly Drift 1130 East Side of Groin and Escarpment Indicates Reversal From September 13 Photograph FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken By R. W. Slye)

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October 1, 1971 -Groin Profile Has Been October 7, 1971 -Drift Passes Over 0830 Lowered Significantly 0800 Groin in Beach Face Due to Undermining. Region Groin is Now Generally Ineffective for Drift Impoundment FIGURE 24. PHOTOGRAPHIC HISTORY OF EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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October 14, 1971 -Beach Accretion Has November 30, 1971 -Groin Ineffective as 0900 Nearly Completely 0800 Littoral Drift Impediment. Buried Shoreward Photograph Taken at Low One-Third of Groin Tide FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken by R. W. Slye)

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December 16, 1971 Final Photograph of 0800 Experimental Groin FIGURE 24. PHOTOGRAPHIC HISTORY OF NAVARRE EXPERIMENTAL GROIN (continued) (Photographs Taken By R. W. Slye)

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dominant side through August 20. By August 28, the drift had reversed again and the impoundment was on the west side of the groin. On September 2, 1971, impoundment had occurred on the east side and the first groin subsidence is evident. By September 13, 1971, the groin had been flanked by high waves and tides and the impoundment was on the west side of the groin. By September 22, the drift evidence was from the east. The photographs on October 1, 1971, and thereafter show that the upper one-third of the groin had subsided to such an extent that it would no longer be effective in impounding littoral drift. Although it is clear that the groin installation was not effective to obtain quantitative evidence regarding the littoral drift, it is of interest that during the two month period over which it was effective, the impoundment indicated nearshore drift reversal at least six times. Furthermore, because the nominal interval between photographs is one week but was as great as eleven days, it is likely that more reversals than noted had taken place. It is noted that the months of August and September are not expected to be the months of heaviest nor most persistent drift. The sea and swell charts for this period, however, do indicate that for average August and September months, net drifts to the west are to be expected. -60

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Although it is not possible to draw strong conclusions from the experimental groin due to the short period over which it was effective, it does appear that drift rates based on the ship data would yield drift rates to the west that would be unrealistically high. Summary and Recommendations Several littoral drift estimates in the Navarre Pass area have been presented. These estimates all indicate a net westward drift with net magnitudes ranging from 65,000 to 300,000 cubic yards per year. This range represents a factor of 4.6 which is not too surprising considering the present state of knowledge of littoral drift quantities. Considering the estimates available, it is believed that the net annual littoral drift is something less than 200,000 cubic yards to the west. It will be recommended that the inlet maintenance be planned to provide transfer of 200,000 cubic yards per year with the understanding that the actual amount required is expected to be less than this value. This represents a responsible approach to the problem of maintaining the littoral drift and it is realistic to reduce the amount of sand transfer below that planned, however, the financial and equipment problems attendant with increasing the sand transfer above that originally planned argue against arranging for a lesser amount. -61

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VII. SUMMARY OF NUMERICAL MODEL CALCULATIONS Introduction In order to represent the behavior of Navarre Pass and its interaction with adjacent entrances a computer method which simulated the flows into and through the Santa Rosa Sound system was developed and applied. This method is called a "numerical model" as opposed to a hydraulic model and has the advantage of rationally incorporating the interaction of Navarre Pass with the tides and flows in Santa Rosa Sound and also with the flows through the entrances to Choctawhatchee and Pensacola Bays. The basis for and evaluation of the numerical model are described fully in Appendix I -"Numerical Model of the Bay System Affecting Navarre Pass." After evaluation for the present situation in which no flows occur through Navarre Pass, the model was modified and used to evaluate the effect of Navarre Pass on flows through neighboring inlets and also to calculate the expected velocities through Navarre Pass. Appendix II -"Stability of Navarre Pass" presents an evaluation of the tendency of Navarre Pass to close by comparing the sedimentary stability -62

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with Rollover Pass, Texas which is an artificial inlet which grew rapidly after opening. The results of applying the numerical model are described in detail in Appendixes I and II and are presented briefly in the following sections. Results Obtained Using the Numerical Model Effect of Navarre Pass on Entrances to Pensacola and Choctawhatchee Bays The percentage changes in flows through Pensacola and Choctawhatchee Bays due to the influence of Navarre Pass were evaluated for various Gulf tidal ranges. These results are tabulated in Table I-4 (Appendix I). It was found that, as expected, the presence of Navarre Pass would decrease the total inflows and outflows through the entrances to Pensacola and Choctawhatchee Bay Entrances. The largest percentage effect was on Pensacola Bay Entrance due to the Sound being of greater width between Navarre Pass and Pensacola Bay than between Navarre Pass and Choctawhatchee Bay. For a tidal range of 1.5 ft (approximate average), the percentage reductions in the maximum flows in and out of Pensacola and Choctawhatchee Bays are 2.0% and 0.1%, respectively. For a more complete summary refer to Table I-4 in Appendix I. The reduction in tidal flows -63

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into Pensacola Bay will result in an associated reduction of 1.8% in equilibrium cross-sectional flow area into this Bay. For Choctawhatchee Bay the equilibrium flow area will be reduced by 0.1%. Maximum Velocities Through Navarre Pass The peak velocities averaged over the Pass crosssection are calculated to vary from 1.27 ft/sec to 3.54 ft/sec for Gulf tidal ranges varying from 0.5 to 2.0 ft, respectively. This range of velocities is well within acceptable limits for small craft navigational safety. A more complete summary of maximum velocities is presented in Table I-5 of Appendix I. Relative Stability of Navarre Pass Computations were carried out in Appendix II to compare the tendency of Navarre and Rollover (Texas) Passes to remain open. These two passes have respective histories of closure and growth following their initial openings. The calculations showed that the geometric and tidal conditions at Navarre Pass are much less conducive to remaining open without jetties than at Rollover Pass. These calculations simply reinforce the known requirement for jetties at Navarre Pass. -64

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VIII. RECOMMENDED DESIGN OF NAVARRE PASS INLET Functional Design In developing a functional design of Navarre Pass, the primary factors considered were: (1) minimum adverse effects on adjacent beach stability through effective sand by-passing and placement of initial sand dredged, (2) navigational safety for craft using the Pass, (3) improvement of water quality within the Sound adjacent to the Pass, and (4) a minimum of required costs associated with the periodic maintenance of the Pass. Some of the factors noted above conflict, for example the effective by-passing of sand will be fairly expensive. In the recommendations pertaining to the layout and planning for the Pass, the highest priority will be given to beach stability and navigational safety. Recommended Layout of Navarre Pass Prior to discussing the recommended layout of Navarre Pass, it is emphasized that it is not intended to present a final detailed design, but rather a workable conceptual design which is in accordance with the objectives presented in the preceding section. The Santa Rosa County Beach Administration and their engineers will make a -65

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detailed engineering design and will make modifications to the recommended layout which facilitate or reduce the cost of construction. These modifications, however, should not significantly impair the performance of the design. The recommended layout of Navarre Pass is presented as Plate III in the jacket in the back cover of this report. The main components of the Pass include: (1) a weir jetty and deposition basin for the trapping and retention of sand until by-passed to the downdrift (west) side of the Pass, (2) a training wall on the Pass sides to provide lateral stability of the cut, (3) a navigational channel, 12 feet deep by 150 feet wide extending through the Island to the 12 feet contour on the Gulf side and to the Intercoastal Waterway on the Sound side, and two jetties extending into the Gulf, and (4) either mechanical or vegetative control of wind drift of sand. Each of these features is discussed separately below. 1. Weir Jetty and Deposition Basin-A weir jetty and deposition basin (sand trap) are recommended with the weir section 400 ft long, oriented parallel to shore and with the weir crest elevation at the approximate present mean sea level contour. The design and construction of the weir are to be such that minor required increases in weir elevation can be accomplished by the addition of stone. In considerations of weir stability, the design should account for the expected variations in sand -66

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elevations on both sides of the weir. The weir design recommended is similar to that at Hillsboro Inlet, see Figure 25. The weir section at Hillsboro Inlet is 200 ft long and the elevation of the weir crest is at MSL. The eastern end of the weir should be tied into the natural dune system in order to prevent flanking and a short adjustable groin should be located at the eastern end of the weir in order to provide a control on the stability of the updrift (eastern) beaches. The expected performance of the weir/deposition basin is as follows. After initial or maintenance dredging of the basin, the predominately westward littoral drift will deposit in the basin at the eastern end of the basin. If the tides and waves are low during this period, a spit will grow toward the west and will be located on the Gulfward side of the weir. During periods of high tides and/or high waves, the sand forming this spit will be carried further into the deposition basin and the weir will be re-exposed. For the dimensions of the basin shown, the volumetric storages below MSL are 48,000 and 64,000 cubic yards based on a 1:3 side slope and maximum basin depths of 12 and 18 ft below MSL respectively. Depending on the quantities of net westerly littoral drift, the basin would require maintenance dredging and by-passing to the west side of the inlet on a frequency ranging from 1 to 3 times a year if carried out on a -67

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FIGURE 25 WEIR JETTY SYSTEM AT HILLSBORO INLET, FLORIDA -68

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demand basis. Because the heaviest littoral drift is expected during the winter, the required dredging may be more frequent during this season. Due to the present uncertainties in net littoral drift magnitudes, it will be difficult to realistically address the problem of maintenance dredging and by-passing to the west if this is planned to be done on a contract basis. An alternate concept providing flexibility would be a relatively small custom dredge built for and operated under the direction of an agency established for the overseeing of the Pass operation and maintenance. This would also allow any small amount of maintenance dredging required in the channel or at the tips of the jetty to be carried out during relatively calm wave conditions which would be difficult to schedule in advance on a contract basis. The Hillsboro Inlet District has successfully operated their small custom dredge for by-passing and minor maintenance dredging in the channel and marina for over eight years. The possibility of the northern portion of the deposition basin providing a recreational facility could be considered. The wave energy at this point will be reduced and the beach slope could be controlled. A marina occupying a portion of the basin is another possibility, but would be reduced in value due to land access problems, especially if a bridge spanning the Pass is not constructed. -69

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2. Training Wall on Sides of Cut--The banks of the cut should be stabilized with sheet piling or rubble protection to prevent sloughing and erosion of the sides. The consequences of not providing a means for bank stabilization will be a widening and shoaling crosssection, and increased maintenance and possibly a migrating interior channel which would also result in the need for increased maintenance. There are advantages of reduced reflection of boat waves if a rubble mound bank protection is chosen. The cut through St. George Island (Figure 26) is an example of erosion if no training walls are provided. 3. Navigational Channel and Jetties-It is understood that the Navarre Pass Committee desires a 12 ft deep channel to match the depth of the Intercoastal Waterway through Santa Rosa Sound. The desired width of the 12 ft depth portion is 150 ft with a somewhat greater width of the remaining portion of the cut. Some of these features are flexible and can be varied within limits of safe navigational consideration. The channel shown in Plate III is 12 ft deep for a width of 150 ft and is a reduced depth, say 6 ft, over the remainder of the 400 ft width. The reduced depth portion of the channel will serve as a fishing area for small boats, or as a safe area for boats experiencing engine trouble, etc. Also, a wider inlet, immediately past the tips of the jetties, is -70

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FIGURE 26 ST. GEORGE ISLAND CUT. NOTE EROSION WHERE BANK PROTECTION IS NOT PROVIDED -71

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favorable psychologically to operators of entering craft. The Sound Side of the channel could be provided with short (30 ft) rubble mound structures to keep drift out of the channel. An alternate and reasonable approach would simply be to accept some minor dredging of the Pass in this area. The jetties should extend to approximately the 12 ft Gulf contour and a design entrance width of approximately 170 ft is recommended. The jetties should be provided with a core so that the possibility for sand being carried through the jetties is minimal. The eastern jetty is extended further seaward than the west jetty because the predominant wave action is from the east and entering craft can first "duck behind" the protection of the east jetty and can then contend with the presence of jetties on both sides in comparatively protected waters. 4. Stabilization of Sand Against Wind DriftInspection of the dune system in the Navarre Beach area indicates that wind drift is an effective agent for sand transport. In the interest of reducing the maintenance dredging in the Pass and in preventing erosion of the land features, it is important that the areas near the Pass be provided with mechanical (sand fences) or natural (vegetative) control against wind erosion. This is particularly important along the boundary of the Pass -72

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where presently-existing vegetation will necessarily be removed by the excavation activity. Disposition of Initially Dredged Material The initial dredging of the Pass and deposition basin will result in approximately 400,000 cubic yards of beach quality sand. It is recommended that at least 90% of this material be placed on the western side of the inlet to be used as "feeder sand" for the down drift beaches while the near Pass bathymetry is adjusting to the presence of the Pass system and while the deposition basin is filling. The material should be placed so as to cause a seaward extension and an increase in elevation of the existing down drift shores. If the material is distributed over 2000 ft of beach on the down drift side of the Pass, approximately 200,000 cubic yards of sand will be required to advance the shoreline seaward a distance of 100 ft. The remaining 160,000 (or so) cubic yards could be used to raise the elevation of this section of the beach. This remaining portion placed on the newly-established beach would thereby : raise its elevation and not damage the existing vegetation. This amount of material would result in a new dune approximately 16 ft high by 150 ft wide and 2000 ft long. -73

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Alternate Designs Only one design for Navarre Pass has been presented. This design is considered to be the best choice from a functional standpoint, however it is recognized that the present design will be somewhat more expensive to construct than others. One alternate design which could be less expensive would be one similar to that at Perdido Pass, Alabama. This design incorporates a weir section as part of the eastern jetty and the interior region adjacent to the eastern jetty serves as the deposition basin. Apparent drawbacks to this design would appear to include the possibility of undesirable wave conditions inside the jetties during periods of high tides and waves, and the possible difficulty of sand encroaching on and causing shifting of the navigational cut. -74

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IX. SUMMARY AND CONCLUSION Summary The results of this study have indicated that: 1. Navarre Pass would only reduce slightly the equilibrium cross-sectional flow areas into Pensacola (1.8%) and Choctawhatchee (0.1%) Bays. 2. The velocities through Navarre Pass would be well within the limits considered safe for small craft navigation. 3. Planning for the artificial transfer of sand should be based on an annual rate of 200,000 cubic yards to the west. Initial disposition of sand dredged should be as a feeder beach on the west side of the Pass. 4. The Pass would cause a localized moderation of salinities and increased flushing in the waters adjacent to the Pass. 5. The tide and geometric characteristics are such that Navarre Pass will always tend to close; jetties are therefore essential to the stability of the Pass. Conclusion Based on the results of this study, it is concluded that if proper financial provision is made for the construction and maintenance of the inlet, there should be no significant adverse hydrographic effects to the stability of the Santa Rosa Island Beaches, nor to the adjacent waters. -75

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X. REFERENCES 1. Bruno, R., Personal Communication. 2. Oceanographic Atlas of the North Atlantic Ocean, U. S.Navy Oceanographic Office, Publication No. 700, Section IV, Sea and Swell, 1963. 3. Shore Protection, Planning and Design, Technical Report No. 4, Coastal Engineering Research Center, U. S. Army Corps of Engineers, Third Edition, June 1966. 4. National Shoreline Study, Regional Inventory Report, South Atlantic-Gulf Region, Puerto Rico and the Virgin Islands, U. S. Army Corps of Engineers, South Atlantic Division, Atlanta, Georgia, August 1971. 5. Escoffier, F. F., "Study of East Pass Channel, Choctawhatchee Bay, Florida," United States Engineers Office, Mobile District, Mobile, Alabama, 1938. 6. Johnson, J. W., "Nearshore Sediment Movement," Bulletin, American Association of Petroleum Geologists, Vol. 40, 1956, pp. 2211-2232. 7. Gorsline, D. S., "Dynamic Characteristics of West Florida Gulf Beaches," Vol. 4, Marine Geology, 1966, pp. 187-206. 8. Walton, T. L., "Littoral Drift Computations Along the Coast of Florida by Use of Ship Wave Observations," M.S. Thesis, Coastal and Oceanographic Engineering Department, University of Florida, 1972. 9. O'Brien, M. P., "Estuary Tidal Prisms Related to Entrance Areas," Civil Engineering, Vol. 1, No. 8, pp. 738-739, 1931. 10. Escoffier, F. F., "The Stability of Tidal Inlets," Shore and Beach, Vol. 8, No. 4, pp. 114-115, 1940. -76

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11. Keulegan, G. H., "Tidal Flows in Entrances. Water Level Fluctuations of Basins in Communication with Seas," Third Progress Report, National Bureau of Standards Report, No. 1146, 1951. 12. O'Brien, M. P., "Equilibrium Flow Areas of Inlets on Sandy Coasts," Journal, Waterways and Harbors Division, ASCE, Vol. 95, No. WW1, pp. 43-52, Feb. 1969. 13. Rouse, H., "Elementary Mechanics of Fluids," John Wiley and Sons, Inc., 1956. -77

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APPENDIX I NUMERICAL MODEL OF THE BAY SYSTEM AFFECTING NAVARRE PASS Introduction The purpose of the numerical model is to provide a means of realistically representing the hydraulics of the system and any changes that would occur due to the opening of Navarre Pass. Because of the extreme length (approximately 50 miles) of Santa Rosa Sound, the construction of a hydraulic (physical) model was ruled out during the conduct of the project. In the following sections of the Appendix, the governing differential equations will be presented and cast into finite difference form for numerical solution; this provides the basis for simulating the tides and currents that would occur at any locality in the system represented. Two representations of the numerical model will then be discussed: (1) In the calibration phase, data collected during the study will be used to assess the validity of and/or modify the numerical model, and (2) With the validity established, the Pass will be introduced into the numerical model and the hydraulics of the inlet and/or -78

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the effect of the Inlet on the tide in Santa Rosa Sound and on the hydraulics of the Pensacola Bay Entrance and East Pass will be investigated. Figure I-1 presents the geographic area represented in the numerical model. Derivation of the Numerical Model Governing Differential Equations The differential equations governing the flow in bay systems are the depth-integrated equations of motion and continuity. Equation of Motion.--The vertically integrated differential equation of motion can be written for the x-direction in a semi-linearized form as = -D + -Tb) (I-1) at ax p ( b in which q = discharge per unit width in the x-direction t = time g = gravitational constant D = total depth = h + n h = depth referred to mean sea level n = tide displacement above mean sea level due to astronomical, wind and barometric tides x = horizontal distance coordinate aligned with bay axis -79

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:. ., /Limits Encompassing Bay System .. ... Represented in Numerical Model .' -.. "" ay j Pensacola Bay .. .. .' '" ... co/ S. .". Choctawhatche. e : Say G U L F 0 F M E X -LC 0 (esti ast) FIGURE X-I BAY SYSTEM REPRESENTED IN NUMERICAL MODEL

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p = mass density of water T = wind stress in x-direction on air-water Sinterface Tb = frictional stress on bottom of water column b The quantities T and Tb can be expressed as T = CfPaU2 cos B (1-2) Pf qjlq (1-3) b -8D2 in which Cf = wind stress coefficient 0.0013, U < 23.6 ft/sec (1-4) 0.0013 + 0.00295 1.0 -2j U > 23.6 ft/sec Pa = mass density of air U = wind speed at 30 ft reference elevation S = angle of wind vector relative to the bay axis f = Darcy-Weisbach friction factor (Reference 13, page 201) Equation of Continuity.-The equation of continuity in one dimension is expressed as i + q R (1-5) at ax w in which the righthand side represents the effect of runoff, -81

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q = runoff in cubic ft/sec per foot of bay length w = width of segment considered It is noted that in the present application of the model, the wind stress, T and direct precipitation and runoff will be taken as zero, however they have been included here for completeness. Finite Difference Equations In order to employ Equations (I-1) and (1-5) for realistic geometries and Gulf tides, it is necessary to cast these equations into finite difference form. The timeand space-staggered procedure is used in which the equation of motion is applied between midpoints of adjacent segments (i.e., across a segment boundary) at full time steps, At, and the equation of continuity is applied for each segment at half time step increments. Finite Difference Form of the Equation of Motion.--Equation (I-1) can be expressed in finite difference form for the total flow, Qn' onto the nth segment, as: Q +At T -wD g n -n 1 Q n p nl n n-1 (1-6) n w At f IQn 1 + 8(Dw)2 -82

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in which the over-barred quantities represent averages based on the nth and (n-l)th segments. The prime indicates the value at time t + At whereas unprimed quantities are known from calculation at time t, and w is the width of the bay segment, see Figure I-2 for the variable representations and Figure I-3 for the numerical model representation of the area of concern. Finite Difference Equation of Continuity.-Equation (1-5) can be written in finite difference form as qR At n' = + Q -Q + n (1-7) n n Ax w n n+1j w n n where the primes indicate the unknown quantities as before and the terms on the right hand side are known from calculations at previous times. Boundary Conditions The boundary conditions for this problem are the flows through the inlets and may be expressed, for example, for Destin Pass as: Ac /2g nTo -qGI sign(nlo -IG) /Ken + Ke + ft/4R in which -83

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Variabtes Represented Variobles Represented at Segment Midpoints: at Segment Junctions 7*, hn hn ,, *n+l h Q n-I I nth Segment 10 + x FIGURE 1-2 ILLUSTRATION OF BAY SEGMENT REPRESENTATION S84

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SChoctowPensacol Bay / hatchee Segment Bay Segment -T-_ -' --t----H---------Cx0 7 9 1/ / 7/ / / / ,/ / / / / / / / / / / Sant Roso Island/ / / / // / / / / / i-Pensacola Bay Entrance Navarre Pass Destin Pass ( Site GULF OF MEXICO FIGURE 1-3 SCHEMATIZATION OF PENSACOLA BAY / CHOCTAWHATCHEE BAY / SANTA ROSA SOUND / GULF OF MEXICO SYSTEM

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AC = cross-sectional flow area of Destin Pass Qii = flow from Choctawhatchee Bay into the Gulf of Mexico o10 = Choctawhatchee Bay Tide nG = Gulf tide (specified) K = entrance loss coefficient = 0.3 en K = exit loss coefficient = 1.0 ex AC R = hydraulic radius of inlet = + w + 2h + nio + 0G w = effective width of Destin Pass h = effective depth of Destin Pass (relative to mean sea level) An expression similar to Equation (1-8) applies for Pensacola Bay Entrance and Navarre Pass. Application of the Numerical Model In this section the application of the numerical model will be presented in two different phases. The first phase is the assessment of the numerical model by judging how well the model represents the existing situation in the Santa Rosa Sound area. The second phase considers the system with Navarre Pass open and presents an evaluation of the flows to be expected through Navarre Pass and also evaluates the effect of Navarre Pass on the Entrance to Pensacola Bay and on East Pass. In Appendix II, the numerical model is employed using recently developed procedures to evaluate the sedimentary stability of the Pass. -86

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Assessment/Calibration of the Numerical Model In order to evaluate the validity of the numerical model, the ability of the numerical model to represent the tides and flows in Santa Rosa Sound with measured data was assessed. The characteristics of the one-dimensional numerical model are shown in Figure I-3 and the characteristics of the various elements used in the model are summarized in Table I-1. The Gulf tide, nG, was represented by RG =G -sin(7.27 x 10-5 t) (1-9) in which RG and t are the Gulf tidal range and time, respectively. The measured data included: open coast tides measured from the Navarre Pass Pier, Santa Rosa Sound Tides as measured from the Navarre Bridge and, for one field trip, currents measured from the Navarre Bridge. The tidal data collected during the three field trips are summarized in Table 1-2. Measured Tidal Ranges and Lags.--The three field trips occurred during periods of different average Gulf tidal ranges varying from 0.37 ft to 2.01 ft,cf Table 1-2. From the measured data, it was noted that the ratio of -87

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TABLE I-i Characteristics of Schematized Bay/Inlet System (see Figure I-3) TABLE I-A Inlets Characteristics £(ft) h(ft) w(ft) K + K f INLET en ex Pensacola Bay Entrance 12,000 32.0 2400 1.3 0.03 Destin Pass 12,000 12.0 2170 1.3 0.03 TABLE I-B Bay System Segments 00 Characteristics Segment x (ft) y*(ft) R (ft) h (ft) w (ft) A (ft2) f No. n n n n n n Pn 2 0 960,000 50,000 29.8 88,890 4.0 x 109 0.03 3 60,000 600,000 27,000 15.0 9,170 2.4 x 108 0.03 4 87,000 600,000 27,000 13.0 9,730 2.64 x 108 0.03 5 114,000 600,000 27,000 12.0 9,170 2.48 x 108 0.03 6 141,000 600,000 27,000 8.0 7,000 2.00 x 108 0.03 7 168,000 600,000 27,000 14.0 4,500 1.40 x 108 0.03 8 195,000 600,000 27,000 9.0 1,460 3.94 x 107 0.03 9 222,000 600,000 27,000 10.0 1,480 4.00 x 107 0.03 10 307,120 780,000 24,000 25.0 180,000 3.60 x 109 0.03 *Note: The origin of yn is arbitrary.

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TABLE I-2 Summary of Measured Tidal Characteristics Tidal Range (ft) Tidal Lag *(hours, min) Average Average Average of Average Average High High Low Low Low and Date Gulf Gulf Sound Sound Water Water Water Water High Water May 14, 1970 0.39 0.59 3h 15m 3h 20m May 15, 1970 0.36 0.37 0.43 0.50 2h 15m 2h 25m 3h 35m 3h 23m 2h 55m May 16, 1970 0.36 0.49 lh 45m 3h 15m Dec. 8, 1970 1.08 .1.38 1.79 3h 15m 3h 15m 3h 30m 3h 23m 1 >1.64 3h 15m 3h 30m 3h 23m Dec. 9, 1970 2.20 2.20 3h 15m 3h 45m July 21, 1971 2.17 .1.97 5 3h 20m 3 4h 20m 4h 07m 3h 52m 2.01 1.85 3h 37m 4h 07m 3h 52m July 22, 1971 1.84 1.72 3h 53m 3h 53m *Measured from preceding corresponding occurrence (high or low water) in Gulf.

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Sound to Gulf tidal ranges and the lags depended on the Gulf tidal range. Averages of these quantities were determined for each field trip and are presented in Table I-2 and plotted as the points in Figures I-4 and 1-5. The numerical model was run for Gulf tidal ranges, RG, of 0.5, 1.0 and 2.0 ft, respectively. For each of these runs, the Gulf tide was assumed to be sinusoidal and given by Equation (1-9). The runs of the numerical model demonstrated that the calculated ratio of Sound to Gulf tidal ranges and tidal lags also varied with Gulf tidal range. The calculated results for ratios of ranges are presented in Figure 1-4. Examination of this figure will show that the numerical model predicts values of the tidal range which are approximately 18% too low, however the correct trend of increasing ratio RS/RG with decreasing tidal range is accurately represented. The reason for the 18% discrepancy is not known. Only one tide gage was available in Santa Rosa Sound and attempts to adjust the numerical model further without additional data would be somewhat arbitrary. The effect of the Navarre Bridge causeway was not represented in the model and reflection of the tides from this feature could conceivably account for an effect of this magnitude. The measured tidal lags, presented in Figure I-5 indicate an increasing lag with increasing Gulf tidal range. -90

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, LAverages Based on d Field Trip of. May 1970 \ -Dec 1970 .^July 1971, 1.0 Calculations From Numerical Model 0.5 0 0 1.0 2.0 Gulf Tidal Range, RG, (ft.) FIGURE 1-4 COMPARISON OF MEASURED AND CALCULATED RATIOS OF SOUND TO GULF TIDAL RANGES VERSUS GULF TIDAL RANGE -91

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0 4.0 C Calculations From Numerical Model wI / uly, 1971 S Dec, 1970 I / / o / -/ Note: Circles and Vertical S/ Lines Represent / Average and Extreme / Tidal Lags Measured 2.0 / on Three Field co Trips a May 1970 -j Field Trip 1.0 00 1.0 2.0 Gulf Tidal Range, RG, (ft) FIGURE 1-5 COMPARISON OF MEASURED AND CALCULATED PHASE LAGS BETWEEN GULF AND SOUND TIDAL EXTREMES -92

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It should be noted that, due to the extremely small tidal variations during the May, 1970 field trips, it was difficult to measure these tidal lags with confidence. The numerical model correctly predicts the increasing tidal lag with Gulf tidal range and agrees with the averages of the measured lags within 30 minutes, except for the data taken for the small Gulf tidal range, in which case there is a difference slightly in excess of one hour. Measured currents.-During the December, 1970, field trip, currents were measured in the Santa Rosa Sound using a Savonius Current meter suspended from the main span of the bridge, see Figures 16 and 14 for the location of the measurements and results obtained. The maximum velocities were on the order of 1 ft/sec and the Gulf tidal range varied from 1.38 to 2.20 ft, see Figure 19. In order to assess the approximate validity of the numerical model in representing the flows in the Santa Rosa Sound, system, the measured velocities were converted to discharges (in cfs) by the following equation Q (cfs) = 15,390 V(ft/sec) (I-10) Equation (I-10) is based upon the areas and velocities through the two openings in the Navarre Bridge causeway. The measurements were conducted in the main (navigational) span. Considering that the slope of the water surface -93

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causing the flow through the two spans is the same, it can be shown that 2/3 Q = AIVI + A2V2 = (A + A2) V (I-) in which the Manning equation has been used and for our case, the dimensions shown in Table I-3 were used. Equation (I-10) follows using these data and Equation (1-11l). TABLE I-3 Dimensions Used in Flow Calculations at Navarre Bridge Flow Area Width Depth Cross-Sectional Area Main Opening (Navigational) 1350 ft 10 ft 13,500 ft2 Secondary Opening (Southerly) 600 ft 5 ft 3,000 ft2 In order to compare the flows determined from the measured velocities and those calculated using the numerical model, the model was run using a Gulf tidal range of 2 ft, and plotted with the measured data for the period December 9-11, 1970, see Figure 1-6. With regard to the tides, it is evident that the numerical model predicts good phase lags of the Sound tides, although the predicted -94

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S-----Measured Gulf Tide d -I0 1= 1500 1800 2100 0300 0600 1200 1500 1800 2100 0 0300 0600 -1.0 Decemlyr 9, 1970 December 10, 1970 Decymber I0. 19701 Decemrer II. 1970 20,O Note: Points Represent Discharges ,Determined From Measured Velocities / o oYo ----^--^------------7'" \ ~-s----S10,00 -Soune d Tide n (Bsed n f 2ft. Gulf Tidl RRange) C 1200 0001500 1800 2100 0000 0300 0600 .-1.0 Decemr 91970 December K, 1970 December 10. 1970 December 11. 81970 2 0,000 -Q --\ G Determined From Measured Velocities / I= 2 ft. Gulf Tidd Rang) m 1200 1500 1800 2100 G\ 0000 0300 0600 0900 / 1200 1500 1800 2100 \0000 0300 0600 K%00000900-----------' ---/--------\--"-M20000 FIGURE 1-6 COMPARISON OF MEASURED AND COMPUTED SANTA ROSA SOUND TIDES AND DISCHARGES

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Sound Range is too low. This also follows from Figure 1-4. Reflection of tides from the Navarre Bridge causeway was not included in the model and has been mentioned as a possible reason for this difference. Considering that a Gulf tidal range slightly greater than 2 feet would have been more appropriate, the Sound tidal range is approximately 20% lower than measured. The discharge (flow) comparison is available from 1500 December 9 to 0700 December 11, 1970. Because the measurements were conducted at discrete times, it is difficult to assess the agreement with a high degree of confidence. It is possible to state that the predicted and measured maxima do occur at approximately the same time. It appears that the calculated discharges are about 40% to 60% higher than those measured; this difference depends on the flow areas presented in Table 1-3, which are considered known only with 20%. The shorter period oscillations present in the calculated discharges in Figure I-6 are believed to be an artificial result of the numerical model, although the measurements were not sufficiently detailed to determine whether these features were present in nature. Measured nodal line.--On May 16, 1970, during the first field trip, an attempt was made to locate a nodal line, i.e., a line in Santa Rosa Sound which is -96

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characterized by zero velocity and flows on both sides directed toward that point or away from that point. With considerable difficulty a point of zero velocity was located about seven miles west of Navarre Bridge, however the tides during this field trip were very weak (average Gulf range = 0.37 ft) and wind therefore could be a dominating factor. Furthermore, on examining the predictions of the numerical model, it was found that the stationary nodal line concept is not really valid. According to the numerical model, the nodal line varies with the stage of the tide and in the case of Santa Rosa Sound ranges from 15 miles west of Navarre Bridge, nearly to the junction of Santa Rosa Sound with Choctawhatchee Bay. For these reasons, attempts to utilize the nodal line concept in verifying the numerical model were discontinued. Conclusions regarding the numerical model assessment.-Some differences exist between the available data and predictions of the model. In particular the predicted Sound tidal range (at Navarre Bridge) is low by about 20% and for the low Gulf tidal ranges, the calculated Sound lags appear to be small by about one hour, although accurate determinations from the field data are difficult due to the low tides. The proper trends with Gulf tidal range are predicted for ranges -97

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and lags. Predictions of total flows at the Navarre Bridge appear to be in good phasing, but high by about 40%. In summary of the numerical model assessment, it is regarded that the numerical model provides a reasonably good calculation procedure for evaluating the effects of modifications of the bay system, such as the opening of Navarre Pass. Use of Numerical Model to Evaluate Effect of Navarre Pass In this section, the numerical model was employed to represent the bay system including the effect of Navarre Pass. The characteristics of Navarre Pass included are: Width = 300 ft (Including effect of jetties) Length = 3200 ft (Including effect of jetties) Depth (average) = 10 ft K = 0.3 en K = 1.0 ex f = 0.03 Effect on entrances to Pensacola and Choctawhatchee Bays.-The calculated maximum inflow and outflow discharges through the Gulf entrances to Pensacola Bay and Choctawhatchee Bays are presented in Table I-4 for the -98

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TABLE I-4 Predicted Effect of Navarre Pass on Flows in and out of Pensacola and Choctawhatchee Bays Maximum Flows Without Maximum Flows With Navarre Pass (cfs) Navarre Pass (cfs) Percent Change Inflow Gulf Tidal or Pensacola Choctawhatchee Pensacola Choctawhatchee Pensacola Choctawhatchee Range (ft) Outflow Bay Bay Bay Bay Bay Bay Inflow 85,820 34,110 83,330 34,030 -2.9% -0.2% 0.50 Outflow 85,040 33,560 82,660 33,490 -2.8% -0.2% 1.0 Inflow 152,600 49,350 149,000 49,290 -2.4% -0.1% 1.0 Outflow 150,200 48,510 146,500 48,450 -2.5% -0.1% Inflow 253,200 71,560 249,900 71,500 -1.3% -0.1% 2.0utflow 246,300 68,460 242,200 68,430 -1.7% -0.1% Outflow 246,300 68,460 242,200 68,430 -1.7% -0.1%

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cases of Navarre Pass closed and open. The percentage changes are summarized in the last two columns. As expected, it is seen that the result of opening Navarre Pass would be to decrease slightly the flows through the other two entrances to the Bay system. The reason that the effect is so small is that the tidal lag between the Gulf and Sound in the vicinity of the Pass site is fairly large (-3 hours). Therefore the effect of modifying the Sound tide near Navarre has only a slight effect on the Pensacola and Choctawhatchee Bay tides and hence causes only minor changes in flows into these bays from the Gulf. The percentage effect on Pensacola Bay Entrance is greater (up to 2.9%) than for Destin Pass (up to 0.2%). It is noted that these larger percentage values are associated with the smaller tidal ranges. The average Gulf tidal range is about 1.5 ft and the associated percentage changes for Pensacola Entrance and Destin Pass are about 2.0% and 0.1%, respectively. It is worthwhile to examine the effect of reductions of this magnitude on cross-sectional flow area from the Gulf to the Bay system. The results of O'Brien indicate a relationship (to be described more completely in Appendix II) between the tidal prism, P, and channel equilibrium cross-sectional area, AC. Using O'Brien's relationship, it can be shown -100

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that the percentage change in equilibrium area is related to the percentage change in maximum discharge by: Percentage Change in AE = 0.9 x (Percentage Change in Qmax) For our case, the indicated results for an average Gulf tidal range of 1.5 ft are that the cross-sectional flow areas into Pensacola and Choctawhatchee Bays would be reduced by 1.8% and 0.1%, respectively. Maximum Velocities Through Navarre Pass The flow characteristics predicted by the numerical model are discharges and therefore the velocities presented below are the cross-sectional averages. The maximum velocities over the cross-section could range up to 30-40% higher than the values presented. The maximum (over time) discharges and velocities occurring as a result of different tidal ranges are presented in Table 1-5. From navigational considerations, the velocities presented in Table I-5 are very acceptable. Within the State of Florida,maximum inlet velocities up to 4-6 ft/sec exist in small inlets that are used extensively by small pleasure boats, e.g., Boynton Beach Inlet and Bakers Haulover. Conclusions resulting from application of numerical model.-Based on the results obtained by -101

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TABLE I-5 Calculated Maximum Discharges and Velocities Through Navarre Pass for Various Tidal Ranges Maximum Discharge Maximum Velocity (cfs) (ft/sec) Gulf Tidal Range (ft) Flood Ebb Flood Ebb 0.5 4494 4410 1.27 1.27 1.0 7768 7421 2.17 2.16 2.0 12800 11,910 3.47 3.54 applying the numerical model, it is concluded that: (1) the reduction in cross-sectional flow areas from the Gulf of Mexico to Pensacola and Choctawhatchee Bays will be slight (approximatelyl.8%and 0.1%, respectively) and (2). the maximum velocities in Navarre Pass would be well within the acceptable limits for small boat traffic. -102

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APPENDIX II STABILITY OF NAVARRE PASS Introduction In this appendix, the sedimentary stability of Navarre Pass will be examined. Sedimentary stability, used in the context of this report refers to the capability of the Pass to remain open naturally without artificial structures. From experience gained following the original opening of the Pass it is known that the Pass is not stable, however it is worthwhile to: (1) examine the cause of the instability and to determine whether it is predictable, and (2) to incorporate information regarding the natural stability characteristics of the Pass into the design of the inlet system. Method The method employed in the stability analysis combines earlier work by O'Brien (9) and Escoffier (10) and uses the numerical model to determine the hydraulics of the inlet/bay system. The elements of the method are presented in Figure II-1. In the following subsections, the three elements comprising the method will be discussed briefly. -103

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SINGLE INLET ANALYSIS MULTIPLE INLET ANALYSIS HYDRAULIC ANALYSIS HYDRAULIC ANALYSIS Inlet Velocity: Inlet Velocity: Response to changes Response to changes In Flow Area and In Flow Area and Tidal Range Tidal Range (Keulegan or (Numerical Modeling) Numerical Modeling) A Hydraulics I Hydraulics Sedimentary fSedimentary 0u" 0 S-edi Flow Area Flow Area Conditions for Conditions for Sedimentary Equilibrium Sedimentary Equilibrium (O'Brien) (O Brien) FIGURE "I-I SCHEMATIC ILLUSTRATING STABILITY ANALYSIS FOR SINGLE AND MULTIPLE INLETS -104

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Numerical Model For a simple inlet/bay system such as shown in Figure II-1-a, the hydraulics could be represented by the Keulegan method (11) or an equivalent. In the present case, it is necessary to represent the hydraulics by a numerical modeling procedure because the Santa Rosa Sound system is quite complex and the Sound tides and discharge values depend on the flows through Pensacola Bay Entrance, East Pass and also on Navarre Pass if it were open, and also depend in a complicated way on the travel time of a long wave from the various Sound entrances to any point of concern. The basis for and calibration of the numerical model used to represent the Santa Rosa Sound has been described in Appendix I. Sedimentary Stability The criterion for sedimentary stability of an inlet was first investigated by Escoffier (10). This criterion is best understood by considering a single inlet connecting a bay to a tidal body of water. The relationship of importance is the variation of the maximum inlet velocity which occurs during a tidal cycle, Vmax, with the inlet cross-sectional area Ac. First, consider a very small inlet cross-sectional area AC in which friction dominates. As AC approaches zero, it is clear that the velocity will approach zero. Second, -105

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consider a large cross-sectional area. In this case, the tidal range inside the inlet is the same as that in the ocean and if the area were increased further, the tidal prism could not increase and the maximum velocity would necessarily decrease. From the preceding discussion, it is evident that for very small and large cross-sectional flow areas the maximum inlet velocity approaches zero; it therefore follows that V must max exhibit a maximum value at some inlet cross-sectional area, AC, see Figure II-2 for an idealized situation. In the following discussion, it will be shown that cross-sectional areas less than A* (Region 1) are unstable with respect to forces that would tend to cause changes in cross-sectional areas, whereas cross-sectional areas greater than A* (Region 2) are stable and an equilibrium area tends to prevail. Region 1 -Unstable Conditions.-Consider some particular inlet/bay system and a cross-sectional area, A < A* Suppose that the cross-sectional area is in C C. equilibrium with the prevailing forces on the inlet such that sediment transported into the inlet is exactly balanced by transport from the inlet by the tidal flows. Next consider a period of increased sediment transport into the inlet resulting in deposition and a reduction in AC' -106

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SII Region 1 Region 2 Unstable Areas Stable Areas Note: Change in Channel CrossNote: Change in Channel Cross5 Sectional Area Results in "Sectional Area Results in Changes Which Further Changes Which Tend to Accentuate Change / Restore Original Area SVm/ oax vs A 0 010 -Critical Area, Ac 2 I II Example I: Example 2: i I AA=-IO ft2 i\ AA =-I0,000 ft2 I. AV = -0.3 ft/sec. I \ ,AV = +0.6 ft./sec. Result: Deposition Tendency, \ I Result: Scour Tendency 10 102 104 Inlet Channel Cross-Sectioncil Flow Area, Ac, (ft2) FIGURE 3T-2 ILLUSTRATION OF ESCOFFIER'S STABILITY CONCEPT

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The Vmax resulting from a reduction in A is a max C smaller Vmax and a reduced capability to maintain the max inlet open. The changes, then tend to perpetuate (and accelerate) the deviation from the equilibrium. To complete the discussion of Region 1, consider some increase in the forces which would increase the inlet area to a value above the equilibrium value. The increased area results in an increased velocity thereby increasing the scouring capability, etc. In summary of considerations of Region 1, it has been shown that any changes from an equilibrium condition will tend to perpetuate these changes. Because in a natural environment, the "forces" are changeable, it can be concluded that Region 1 conditions could not be expected to occur over a long period of time. The cross-sectional area would either enlarge into Region 2 or the inlet would close. Region 2 -Stable Conditions.-If a similar type of argument is followed for Region 2 as was presented for Region 1, it will be found that a change in forces from equilibrium cause changes in these forces which tend to return conditions to equilibrium. Suppose that an anomalous littoral drift resulted in a deposition in the inlet cross-section such that the area is decreased below some equilibrium value. This reduction in area is seen from Figure II-2 to cause an increase in maximum -108

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velocity, thereby increasing the scouring capability which would tend to restore equilibrium. Conversely an increase in cross-sectional area, is seen to cause a reduced velocity and scouring capability and, again a tendency toward restored equilibrium results. Based on the preceding considerations, it may be concluded that for A < A*, the inlet cross-sectional C C areas are unstable with respect to forces causing changes from equilibrium, whereas for A > A, the inlet is stable around some equilibrium value A .Although the inlet stability concepts presented here are highly idealized, they are essential to a conceptual understanding of inlet behavior. In a realistic case, the tidal range is not constant but varies between neap and spring ranges and an inlet may function in the unstable region for periods of times sufficiently short that a long-term equilibrium is maintained through a balance by the scouring action while the inlet system is in Region 2, stable conditions. In the following subsection, the equilibrium area concepts developed by O'Brien will be discussed. Equilibrium Cross-Sectional Area The relationship between inlet equilibrium cross-sectional area and tidal prism was first presented -109

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by O'Brien (9), and he has later (12) augmented the original results. His results are summarized in Figure II-3 for a semi-diurnal tide. Very briefly, there is a relationship between the spring tidal prism of an inlet and the minimum cross-sectional flow area measured at mean sea level conditions. This relationship may be interpreted in terms of the equilibrium shear stress or maximum velocity that can be sustained by erodible materials which comprise inlet beds. It will be more convenient to transform the relationship shown in Figure II-3 into a Vmax vs AE relationship. This max CE transformation also removes the limitation of Figure II-3 being applicable only to semi-diurnal tides (the tide at Santa Rosa Island is diurnal, i.e., of 24-hour period). To determine the Vmax vs AE relationship, it will be max CE assumed that the discharge through an inlet varies in a sinusoidal manner Q = Qmax cos at The tidal prism, P, is therefore T/4 P = 2 Qmax cos at dt or -110

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1012 0 0 8 S10 Co i.10. 1 EE FIGURE 11-3 EQUILIBRIUM CROSS -SECTIONAL AREA AND TIDAL PRISM RELATIONSHIP (FROM O'BRIEN) -111

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T P = -Q Tr max and since Qma = AC V we have P = A V (II-l) IT C max ( or, in order to determine the desired relationship from Figure 11-3, Equation (II-1) is written as PIT V max ACT (11-2) The relationship Vmax vs AC is presented in maox C Figure 11-4. The stability relationship and equilibrium cross-sectional area are combined in Figure II-5 for various tidal ranges for Navarre Pass where it is seen that for each tidal range for which a portion of the stability curve lies above the equilibrium curve, there is one equilibrium area. For tidal ranges for which the stability curve completely lies below the equilibrium curve, the inlet would be unstable for all cross-sectional areas and would always close if larger tidal ranges did not occur. Application of Stability/Equilibrium Concepts to Navarre and Rollover Passes In order to evaluate the stability/equilibrium relationships and their applicability to real inlets, the -112

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4>E I Q O'Brien's Sedimentary U) Equilibrium Relationship o1 E S.S0 E I 0 I I I I I I I I I I 4 6 8 1000 2 4 6 8 10000 2 4 Equilibrium Cross Sectional Area (ft2) FIGURE lE4 VARIATION OF MAXIMUM INLET VELOCITY WITH CROSS -SECTIONAL AREA FOR EQUILIBRIUM CONDITIONS

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Tidol Range = 2.0> 4 O' Brien's Sedimentary //Equilibrium E Relationship > o I I [ I I I I I I 01.0' 4 6 8 1000 2 4 6 8 10000 2 4 CrossSectional Area (ft2) FIGURE 11-5 VARIATION OF MAXIMUM VELOCITY WITH INLET CROSSSECTIONAL AREA AND TIDAL RANGE. NAVARRE PASS, FLORIDA

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method was applied to two real inlet situations: (1) Navarre Pass, with a history of closure after being dredged, and (2) Rollover Pass cut through Bolivar Peninsula in Texas and with a history of growth until the cross-sectional area was limited artificially by lining with steel sheet piling on the sides and a concrete sill on the bottom. In the following presentations for the two inlets, the one-dimensional numerical model is used to represent the hydraulics and the actual variations in tidal range are realistically included. Navarre Pass In previous sections, the basic stability and equilibrium concepts have been reviewed. In the application of these concepts to an actual situation, it is necessary to represent the variations in tidal range which prevail in the area of interest. The method of accounting for variations in tidal range is illustrated by application to Navarre Pass in the following sections. Using the numerical model, the relationship for maximum velocity, V versus cross-sectional area, AC, was established for several tidal ranges spanning the ranges occurring at the area of interest. Figure II-5 represents this relationship for Navarre Pass for Gulf tidal ranges of 0.5 ft, 1.0 ft and 2.0 ft. The results presented in Figure II-5 are based on 18 individual computer runs of the numerical model program. In these -115

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computations, it is necessary to make some assumptions regarding the relative width to depth of the flow area; for the calculations on which Figure II-5 is based, it was assumed that the inlet width was 35 times the depth. As an example, for an inlet depth of 12 ft, the associated width would be 420 ft. The variation in tidal range differs considerably with locale and relates very strongly to the stability of an inlet. For example, the tides for three locations as determined from the Tide Tables for the period January 1, 1970 to February 9, 1970, are presented in Figure II-6 and the ratio of maximum to minimum ranges are summarized in Table II-1. TABLE II-1 Ratio, R, of Maximum to Minimum Tidal Ranges During the Period January 1 to February 9, 1970 Location Ratio, R Pensacola Bay Entrance 19 Galveston Bay Entrance 4.4 Miami Harbor Entrance 2.3 In the procedure employed herein, the tidal range is determined for a representative period -116

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.0 I O -1.0-GALVESTON ENTRANCE Period of Period Low Relative of High Susceptibility Relative to Deposition Susceptibility to Deposition 1.0 0-----1.0PENSACOLA January, 1971 February, 1971 5 10 15 0 25 5 I1tI 51 11 1t I 1111111 111111 I lI I Ii II I il[ 2.0 N-1.0-I I -1.0MIAMI HARBOR ENTRANCE FIGURE 31-6 PREDICTED TIDES AT GALVESTON, PENSACOLA AND MIAMI HARBOR ENTRANCES. NOTE DIFFERENCES IN TIDAL RANGE VARIATIONS -117

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(approximately 4 weeks) from the Tide Tables and represented as a cumulative probability distribution, see Figure II-7 for the Pensacola (Navarre Pass) and Galveston (Rollover Pass) Entrance distributions as determined from the Tide Tables for the interval: January 7 to February 3, 1970. Stability in regions previously described as "unstable" (Region 1) and "stable" (Region 2) must be interpreted separately. For Region 1, consider a crosssectional area of 5000 ft2.An auxiliary diagram is first prepared from Figure II-5 of maximum velocity, Vmax versus Gulf tidal range, RG, see Figure 11-8. In addition,the velocity determined from O'Brien's equilibrium relationship is indicated on this auxiliary plot. From Figure 11-8, it is seen that Gulf tidal ranges in excess of 1.25 ft will exceed the "equilibrium" velocity. From Figure II-7a, this required tidal range will be exceeded a percentage P = 68% of the time. The procedure is then repeated for other cross-sectional areas and the results plotted versus AC. The interpretation of P in Region 1 is that this is a measure of the percent of time favorable for growth in this unstable region. For example, for the example cross-sectional area of 5000 ft2, conditions favorable toward cross-sectional increase would occur 68% of the time. A stability diagram -118

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I o 2 3 s -/ E .0 Gulf Tidal Range (ft) FIGURE I -7a PENSACOLA BAY ENTRANCE (NAVARRE PASS) 100 S50 I Oo I I I I I I I I I 7|50 4 a) 0 0 I 2 3 Gulf Tidal Range (ft) FIGURE TI -7b GALVESTON BAY ENTRANCE (ROLLOVER PASS) FIGURE IE -7 CUMULATIVE PROBABILITY DISTRIBUTIONS FOR PREDICTED GULF TIDAL RANGES AT NAVARRE AND ROLLOVER PASSES -119

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3 S-Vmx For Sedimentary u Equilibrium = 2.7 ftec 2 >E / y Tidal Range Corresponding to Sedimentary I Equilibrium = 1.25 ft 0 II O I 1.25 2 Gulf Tidal Range (ft) FIGURE E -8 AUXILIARY DIAGRAM FOR DETERMINATION OF TIDAL RANGE CORRESPONDING TO SEDIMENTARY EQUILIBRIUM (EXAMPLE SHOWN FOR Ac=5000 ft ) -120

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comprising the results of the same calculations for other areas, AC, is presented in Figure II-9 for Navarre Pass. Note that it is of considerable interest that, for Navarre Pass, the percent of time for favorable growth decreases markedly near the larger unstable areas. In Region 2, the same calculation and plotting representation procedure is followed, however the interpretation differs. The percentage value continues to decrease for the larger areas because the "equilibrium" velocity increases whereas Vmax decreases with increasing cross-sectional area. The interpretation is that, if the inlet is stable, the cross-sectional area will occur such that the percentage, P, is in the range 10-20%. This is due to the fact that O'Brien's relationship was based on spring tide conditions, and normally tidal ranges exceed the spring tide range on the order of 10 to 20% of the time. For Navarre Pass and cross-sectional areas-near the midpoint of the transition region, conditions for favorable growth only exist some 42% of the time. In the stable region, tidal conditions above those required for equilibrium occur a maximum of 34% of the time. An interpretation of these stability results can only be carried out on a comparative basis, for example with the results for Rollover Pass presented in the following section. -121

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80 Transition I .2 Percent of TimeReion ;60Tidal Conditions Are c Favorable for Growth Unstable/ / Stable g -Percent of z 40 I Time Tidal .Conditions are o Above Those Required for c2 Equilibrium S20-/ o I I I I I I / 4 6 8 1000 2 4 6 8 10000 2 4 Cross -Sectional Area, Ac (ft2) FIGURE 3r1-9 STABILITY ANALYSIS FOR NAVARRE PASS, FLORIDA

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Rollover Pass For comparison purposes, the treatment first presented for Navarre Pass is carried out for Rollover Pass. Figure II-10 shows the location of Rollover Pass relative to Galveston Bay and Figure II-11 presents a schematic of the simplified one-dimensional model used to represent Galveston Bay and the associated entrances to the Bay. The Vmax vs. A relationship as determined for Rollover Pass is presented in Figure II-12 for tidal ranges of 0.5, 1.0 and 2.0 ft. It is noted that the basic difference between Navarre and Rollover Passes is evident by comparison of Figures II-5 and II-12; for the smaller cross-sectional areas and the same tidal ranges, Rollover Pass is characterized by larger velocities. For example, a cross-sectional area of 4000 ft2 and a tidal range of 1 ft will cause maximum velocities of 2 and 3.3 ft/sec in Navarre and Rollover Passes, respectively. The cumulative probability distribution for Gulf tidal ranges at Galveston Bay Entrance has been presented as Figure II-7-b. Figure II-13 is a presentation of the stability analysis, P vs AC. Conclusion Regarding Relative Stability of Navarre and Rollover Passes Comparison of Figures II-9 and II-13 shows that Rollover Pass presents a much more favorable situation than -123

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MATAGORDA BAY Z GULF oF OV OF MEXICO LAG UNA ." MADRE -. BAy WEST BAY ENTRANCE ROLL.VER FISH PASS SAN LUIS PASS FIGURE I-10AREA MAP SHOWING LOCATION OF ROLLOVER FISH PASS

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FIGURE I1 -II NUMERICAL MODEL REPRESENTATION OF GALVESTON BAY / ROLLOVER PASS SAN LUIS GALVESTON PASS ENTRANCE GULF OF MEX ICO

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S5.^ TIDAL RANGE 2.0' 4H OBRIEN'S SEDIMENTARY SEQUILIBRIU 0.5 RELATIONSHIP 2 *o 4 6 8 1000 2 46 8 10000 2 .4 CROSS-SECTIONAL AREA (ft2) FIGURE 1-12 VARIATION OF MAXIMUM VELOCITYWIT}_ INLET CROSSSECTIONAL AREA AND TIDAL RANGE -ROLLOVER FISH PASS,TEXAS

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100 I I P e o Percent of Time 80 -/ /I / Tidal Conditions Tidal Conditions are I Ae Above Those < I Are Above Those F Favorable for Growth Required For S0 I Equilibrium II ICU \ CrossSectional Area, Ac (ft2) FI3 Unstable I R Stable F S1TEXAS I I I A I I I 4 6 8 1000 2 4 6 8 10000 2 4 Cross -Sectional Area, Ac (ft2) FIGURE 1 -13 STABILITY ANALYSIS FOR ROLLOVER FISH PASS, TEXAS

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Navarre Pass for initial growth and achieving an eventual equilibrium stable area. At the midpoints of the two transition regions, the percentages of time that conditions are favorable for growth are 45% and 95% for Navarre and Rollover Passes, respectively. At the lower areas within the "stable region," the percentage of time that tidal conditions are above those required for equilibrium are 35% and 94%, respectively. The lower value for Navarre Pass would indicate it to be more susceptible to closure due to heavy littoral drift resulting from an extreme storm, whereas during 94% of the time, the velocities in Rollover Pass would be above those required for equilibrium and the Pass would likely recover from deposition. A second factor favoring Rollover Pass pertains to the velocity Vmax at the stable max side of the transition region. The sediment transporting capacity of a flow is proportional to velocity V raised to some power n (3 < n < 5). The ability of an inlet to enlarge or maintain a cross-sectional area after or during heavy littoral drift therefore is strongly dependent on the maximum velocity. The corresponding velocities for Navarre and Rollover Passes for a two foot tidal range are 3.9 and 5.1 ft/sec, respectively. It is noted that if the equilibrium cross-sectional area is associated with tidal conditions which exceed those required for equilibrium 15% of the time, then Rollover Pass would have stabilized at a -128

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cross-sectional area of 18,000 ft2.The inlet was cut with a cross-sectional area of 640 ft2 and grew until it was artificially stabilized at a cross-sectional area in excess of 3000 ft2. Finally, it should be noted that there are a number of assumptions made in the stability analysis presented here which should be considered in evaluating the stability method and results. One of the most questionable assumptions is the fixed ratio of width to depth for the inlet cross-section. Although the ratio of 35 used is a realistic value for many existing inlets, in some cases the inlet depth is limited by the depth of the bay adjacent to the inlet. -129

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APPENDIX III GLOSSARY OF TERMS Introduction Presented below are definitions of terms which may not be familiar to all readers in the context used in this report. Bar A depositional feature which may result from decreasing velocities near the Gulf or Sound terminus of the Pass. Beach face The relatively steeply sloping portion of the beach on which wave uprush and downrush occurs. Berm The mildly sloping (or flat) portion of the beach located at the approximate limits of maximum wave uprush. Deposition basin An excavation area to serve for the temporary detention of littoral drift until bypassed. Diurnal tide A tide having a period of approximately 24 hours, e.g., the tide in Santa Rosa Sound area. Downdrift The direction along the beach corresponding to the net littoral drift. Foredune The small dune-like features at the toe of the major dunes. Usually these are dunes in the process of development. Hydraulic model A reduced-sized version of a natural feature or area. Designed to simulate hydraulic phenomena in a scaled-down representation. -130

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Hydraulic radius A parameter used in hydraulic analysis. For a given cross-sectional flow area, indicates the efficiency of the particular cross-sectional shape. Littoral drift That sand and shell material which moves parallel to the beach due to the action of waves and winds. Longshore Pertains to the direction parallel to the beach. For example longshore current is thatcomponent parallel to the local beach alignment. Median diameter The diameter of sand below and above which fifty percent of the sample lies. Neap tide The astronomical tides occurring with near-minimum tidal ranges. Numerical model A computer simulation of a particular feature or bay system. Based on the governing equations. Phase lag The time in hours and minutes, between occurrence of Gulf maximum (or minimum) tides and the resulting event occurring at any location in the Sound. Sea Waves generated locally, of short period, and present a "confused" picture. Scarp An erosional feature, evident as a steep near-vertical face on the beach. Semi-diurnal tide A tide with a period of approximately 12.4 hours. Spring tide The astronomical tides occurring with the near-maximum tidal ranges. Stability Pertains to the tendency of a beach to exhibit only minor seasonal fluctuations or to an inlet to exhibit neither a net growth nor reduction in size. -131

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Swell Water waves of relatively long period generated by a distant storm. Appear as long-crested waves. Tidal prism The total volume of water which flows in (or out) of an inlet on a flood (or ebb) cycle. Tidal range The vertical distance between a successive maximum and a following minimum or a minimum and a following maximum of a tidal oscillation. Updrift The direction along the beach opposite to the direction of net littoral drift. Uprush The rapid excursion of a broken water wave up the beach face. Weir jetty A type of jetty system which incorporates a low section in the updrift jetty to allow sand to pass over the weir and settle in a planned deposition area. -132