• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Table of Contents
 List of Figures
 List of Tables
 Introduction
 Environmental conditions and...
 Geology
 History of human impacts on...
 Changes due to beach nourishment...
 Summary of Perdido Key monitor...
 Plans for future interpretatio...
 References






Group Title: UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 91/009
Title: Perdido Key historical summary and interpretation of monitoring programs
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 Material Information
Title: Perdido Key historical summary and interpretation of monitoring programs
Series Title: UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 91/009
Physical Description: Book
Language: English
Creator: Work, Paul
Publisher: Coastal and Oceanographic engineering Department, University of Florida
Publication Date: 1991
 Subjects
Subject: Perdido Key (Fla)
 Notes
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
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Table of Contents
    Front Cover
        Front Cover
    Title Page
        Page i
    Table of Contents
        Page ii
        Page iii
    List of Figures
        Page iv
    List of Tables
        Page v
    Introduction
        Page 1
        Page 2
        Page 3
    Environmental conditions and history
        Page 4
        Page 3
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Geology
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    History of human impacts on area
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    Changes due to beach nourishment project
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    Summary of Perdido Key monitoring
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
    Plans for future interpretation/prediciton
        Page 45
    References
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
Full Text



UFL/COEL-91/009


PERDIDO KEY
HISTORICAL SUMMARY AND INTERPRETATION OF
MONITORING PROGRAMS






by


Paul Work
Lynda Charles
and
Robert G. Dean


June, 1991




Submitted to:

Department of the Navy
Southern Division
Naval Facilities Engineering Command
Charleston, SC 29411-0068








UFL/COEL-91/009


PERDIDO KEY

HISTORICAL SUMMARY AND INTERPRETATION OF

MONITORING PROGRAMS




Submitted to:

Department of the Navy

Southern Division

Naval Facilities Engineering Command

Charleston, SC 29411-0068




Prepared by:

Paul Work

Lynda Charles

and

Robert G. Dean

Coastal and Oceanographic Engineering Department

University of Florida

Gainesville, FL 32611


June, 1991








TABLE OF CONTENTS


LIST OF FIGURES


LIST OF TABLES


1 Introduction


2 Environmental Conditions

2.1 Wave Climate ......

2.2 Winds ..........

2.3 Tides ...........

2.4 Major Storms ......

2.4.1 Camille .....

2.4.2 Eloise ......

2.4.3 Frederic .....

2.4.4 Elena .......

2.5 Return Periods .....


and History















. .. .

. . ,


3 Geology


4 History of Human Impacts on Area

4.1 Tidal Inlets and Barrier Islands ....................

4.2 Pensacola Pass/Perdido Key . . . . . .

4.3 Historical Shoreline Changes . . . . . .


5 Changes Due to Beach Nourishment Project

5.1 Cross-Shore Changes ...........................

5.2 Equilibrium Beach Profiles ........................







Evolution of Perdido Key Beach Profiles ...............


5.4 Planform Changes .............

6 Summary of Perdido Key Monitoring
6.1 Macroinvertebrate Communities ......
6.2 Vegetation Monitoring ...........
6.3 Perdido Key Beach Mouse . . .
6.4 Physical Monitoring . . .

7 Plans for Future Interpretation/Prediction


REFERENCES


...............


. . .








LIST OF FIGURES


FIGURE PAGE

1 Location map ................................ 2

2 Geologic column of formations in western panhandle of Florida (Marsh,

1966). ..................................... 13

3 Geologic cross-section through western Florida's Gulf coast (Marsh,

1966). ................. .................. 14

4 Geologic profiles through Pensacola Bay area (Marsh, 1966). . 16

5 Locations of Florida DNR survey monuments along Perdido Key. 20

6 Equilibrium throat area vs. tidal prism (O'Brien, 1969). ...... ..23

7 Perdido Key shoreline history, 1858-1902 . . . ... 28

8 Perdido Key shoreline history, 1920-1978. . . . ... 29

9 Perdido Key shoreline history, 1858-1978. . . . ... 30

10 Perdido Key shoreline changes, 1858-1978. . . . ... 31

11 Pre- and post- nourishment beach profiles for range R-45, Perdido

Key, Florida.. .. .. .. ... .. .. . .. . .. .. 33

12 Profile scaling parameter, A, vs. sediment size, D, and fall velocity, w

(Dean, 1987). ................... ........... 35

13 Effect of sediment size on equilibrium beach profiles (Dean, 1991). .. 36

14 a) Commonly idealized form for post-nourishment beach planform; b)

Actual planform changes at Perdido Key. . . . ... 38

15 Evolution of idealized beach nourishment project. Wave direction Ob

= 0 (normally incident waves; Hb=0.5 m). . . . .. 39








LIST OF TABLES


TABLE PAGE

1 Wave data for Perdido Key area. ..................... 6

2 Wind data for Perdido Key area. ... ................ 6

3 Storms making landfall in Perdido Key/Pensacola area, 1889-1990.

H=hurricane, TS=Tropical Storm. ................... 8

4 Combined Total Storm Tide vs. Return Period for Escambia County.

From Dean and Chiu, 1986. ........................ 11

5 History of maintenance dredging at Pensacola Pass (from Hine, et al.,

1986, and Dean, 1988a; Dean 1988b) . . . ..... 25

6 Channel Dimension History (from Dean, 1988a; Dean, 1988b). .... 26

7 Average Grain Size Characteristics at Various Profile Locations 37










PERDIDO KEY
HISTORICAL SUMMARY AND INTERPRETATION OF
MONITORING PROGRAMS

June, 1991




1 Introduction


A monitoring study of Perdido Key, Florida was initiated in 1989 to document

conditions prior to construction of a major beach nourishment project. Plans

call for the study to span a five-year period. The study is divided into several

components, with a research team devoted to each aspect. The Coastal and

Oceanographic Engineering Department of the University of Florida is responsible

for documentation of physical conditions at the site; the Institute for Coastal and

Estuarine Research at the University of West Florida is conducting the biological

study of the island; the Gulf Coast Research Laboratory is responsible for the

benthic study; and the Alabama Cooperative Fish and Wildlife Research Unit

is monitoring the status of the Perdido Key beach mouse. The primary focus

of this report will be on historical and expected future changes relevant to the

physical study; summaries of the other components of the monitoring study are

presented in Section 6.

Perdido Key is a relatively narrow, linear barrier island located in Escambia

County, in the western "Panhandle" of Florida (Figure 1). It trends east-west,

so that its southern shore faces the Gulf of Mexico; its northern coast abuts

Big Lagoon and Old River. Perdido Pass (the entrance to Perdido Bay) forms

the western boundary of Perdido Key, and the island is bordered on the east by

Pensacola Pass. A major U.S. Naval facility is located in Pensacola, requiring that

Pensacola Pass be maintained to a navigable depth at all times. Pensacola Pass

has been dredged for over a century for navigation purposes, with the required

1


j





































0 5 km


Figure 1.


Location map










depth increasing with time. Recent requirements to increase the depth further

have provided a large quantity of sediment for beach nourishment on Perdido

Key.

The eastern 10.5 km of Perdido Key is part of the Gulf Islands National

Seashore, administered by the National Park Service. The beach nourishment

project lies wholly within the National Seashore boundaries. Much of the dredge

spoil available for beach nourishment has already been placed on the beach,

initially increasing its width by approximately 150 m over a distance of 8 km.

Approximately 3.4 million m3 of the remaining suitable material will be placed

in the littoral zone just offshore of Perdido Key.

The physical monitoring study involves the collection of a large amount of
data that should assist in the prediction of future changes at Perdido Key. Hy-

drographic and topographic surveys are to be conducted annually, and sediment

samples collected simultaneously throughout the project area. Wave, tide, and

current data are being collected essentially continuously by an offshore wave gage

and current meter. Atmospheric data are recorded by a weather station at the

Perdido Key Ranger Station. These data sets will provide information necessary
for calibration of numerical simulation techniques for prediction of changes at

Perdido Key. Detailed analysis and prediction of changes will require a more

substantial data base; only one post-nourishment survey is presently available.

Based upon experience from other similar sites, however, some general expecta-

tions will be discussed.


2 Environmental Conditions and History

Very little environmental data exist for the immediate vicinity of Perdido Key.

The ongoing data collection efforts of the University of Florida's Coastal and

Oceanographic Engineering Department (Work et al., 1991a) and a previous










study by Psuty (1987) are the only known studies where in-situ data were col-

lected. Oceanographic data collected by the University of Florida include: wave

height, period, and direction; tidal stage; and magnitude and direction of mean

currents. All data are collected by one instrument, located in approximately 7

m of water. The gage is located offshore of the Perdido Key Ranger Station. An

additional tide gage is located on the Fort Pickens pier on the Sound side of Santa

Rosa Island. A weather station is located at the Perdido Key Ranger Station,

collecting air temperature, wind direction, wind speed, rainfall, and wetness data.

Data collection for both units commenced in January, 1990.

The study by Psuty (1987) included collection of nearshore pressure and ve-

locity records at several locations along Perdido Key. Only five days of data were

collected, however, so the information is not of significant help in an historical

study.

The remaining available data for the area typically offer very coarse spatial or

temporal resolution, or were obtained using very crude data collection methods

(e.g. visual observations of wave heights). The review provided here is not in-

tended to be exhaustive, but rather to provide an overview of the environmental

conditions to which the study area is exposed.


2.1 Wave Climate

Weather and sea state observations obtained from ships offshore of the north-

western coast of Florida are available for the period 1859-1971, with eighty per-

cent of the records between 1952 and 1971 (U.S. Naval Weather Service Com-

mand, 1975). The spatial resolution is so coarse, however (grid size is approxi-

mately 2.50 of latitude by 2.50 of longitude), that the data are of little value for

investigation of shoreline changes along Perdido Key. The fact that ships tend

to avoid severe weather also tends to bias this data source.










depth increasing with time. Recent requirements to increase the depth further

have provided a large quantity of sediment for beach nourishment on Perdido

Key.

The eastern 10.5 km of Perdido Key is part of the Gulf Islands National

Seashore, administered by the National Park Service. The beach nourishment

project lies wholly within the National Seashore boundaries. Much of the dredge

spoil available for beach nourishment has already been placed on the beach,

initially increasing its width by approximately 150 m over a distance of 8 km.

Approximately 3.4 million m3 of the remaining suitable material will be placed

in the littoral zone just offshore of Perdido Key.

The physical monitoring study involves the collection of a large amount of
data that should assist in the prediction of future changes at Perdido Key. Hy-

drographic and topographic surveys are to be conducted annually, and sediment

samples collected simultaneously throughout the project area. Wave, tide, and

current data are being collected essentially continuously by an offshore wave gage

and current meter. Atmospheric data are recorded by a weather station at the

Perdido Key Ranger Station. These data sets will provide information necessary
for calibration of numerical simulation techniques for prediction of changes at

Perdido Key. Detailed analysis and prediction of changes will require a more

substantial data base; only one post-nourishment survey is presently available.

Based upon experience from other similar sites, however, some general expecta-

tions will be discussed.


2 Environmental Conditions and History

Very little environmental data exist for the immediate vicinity of Perdido Key.

The ongoing data collection efforts of the University of Florida's Coastal and

Oceanographic Engineering Department (Work et al., 1991a) and a previous










Additional visual observations are documented by Balsillie (1975). These

observations differ in that they were obtained at a number of nearshore sites.

Wave height, direction, and period were all measured visually by an observer on

the beach or a pier, and longshore currents were measured by visual observation

of the movement of a cloud of dye placed in the surf zone. Beach profiles were

surveyed in some cases. The data collection site nearest Perdido Key was located

at Fort Pickens State Park (now part of the Gulf Islands National Seashore), on

the western end of Santa Rosa Island. Eight months of data (September-October,

1969, and March-August, 1970) are available, with typically 20 to 30 readings

per month. While quite useful for the identification of trends, visual observations

cannot be relied upon for accurate, quantitative values describing the nearshore

wave climate.

Hindcast data are also available for the area. Hindcast studies typically begin

with maps of the atmospheric pressure throughout the area of interest. The

pressure field is used to compute the wind field, and a wave generation model

is used to compute the wave climate. The usefulness of the resulting data is

dependent on the accuracy of the maps and the methods by which the wind and

wave climates are computed, as well as the spatial and temporal resolution of the

results.

Hubertz and Brooks (1989) present the results of a hindcast study for the

Gulf of Mexico, spanning 20 years (1956-1975). Data are reported at three-hour

intervals, using a 55 km grid. Since one grid cell is larger than Perdido Key,

this hindcast data could not be used directly for modelling of coastal processes

along the island, but could be used as input to a model having finer resolution.

Additionally, this data set does not include tropical storms or hurricanes.

Table 1 presents representative wave data from the sources cited above.












Table 1: Wave data for Perdido Key area.


Data Source Location Technique Period of Ha, m Period, sec
Record Max. Avg. Max Avg.
USNWSC (1975) Area 26 (Pensacola) Visual 1949-1971 8-10 1.1 >13
Balsillie (1975) Ft. Pickens St. Pk. Visual 9/69-8/70 0.66 (Hb) 5.78
Hubertz/Brooks (1989) Sta. 29 (Pensacola) Hindcast 1956-1975 3.7 1.0 9.6-10.5 5.2
Work et al. (1991a) Perdido Key In-situ 1/90-10/90 1.7 0.41 11.6 5.8



2.2 Winds

Wind data are available from several of the same sources discussed above.

The measured wind speeds, directions, and air temperatures at Perdido Key

were compared to values from the National Weather Service weather station at

Pensacola, with favorable agreement (Work et al., 1991a). Table 2 below summa-

rizes wind conditions in the study area. March is generally the windiest month

of the year, with August having the least wind (U.S. Dept. of Commerce, 1981).

Wind directions are the compass heading from which the wind originates.



Table 2: Wind data for Perdido Key area.

Data Source Location Period of Record Wind Speed, m/s (mph) Wind Direction
Max. Avg. Avg.
USNWSC (1975) Area 26 (Pensacola) 1950-1971 25+ (55) 6.0 (13.5) 1290
Balsillie (1975) Ft. Pickens St. Pk. 9/69-8/70 10+ (22) ~1400
Hubertz/Brooks (1989) Sta. 29 (Pensacola) 1956-1975 10-13 (23-29) 1340
NOS (1981) Pensacola 24 yrs 4.5 (10) (1300 hrs) ~90
Work et al. (1991a) Perdido Key 1/90-4/91 11.2 (25.0) 3.4 (7.6) 1510


2.3 Tides

The tides in the vicinity of Perdido Key are diurnal. The mean range at the

entrance to Pensacola Bay is 0.34 m (U.S. Dept. of Commerce, 1990).



2.4 Major Storms

Information regarding storms generally consists of qualitative descriptions of

damages incurred or hindcast data. Reported and computed wave heights, wind

speeds, storm tides, etc., are often only approximate, and spatial gradients are

6










often strong, meaning that knowledge of a parameter at one location does not
imply that conditions at a nearby site are known with much certainty. In recent
years, however, there have been a number of storms that have passed directly over

moored, offshore data buoys, providing some rare in- -situ data of wave climate

during a hurricane.

The hurricane season in the Perdido Key area generally extends from July
through October. The earliest recorded hurricane was that of September, 1559,
which is said to have caused severe damage in the Pensacola area (Ludlum, 1963).
At least eight other major hurricanes struck the same area in the next 200 years

(Dunn et al., 1967). A number of severe storms that have impacted the area since
1889 are shown in Table 3. Landfalling tropical storms and hurricanes are fairly

common along the Florida panhandle, and can be expected between Pensacola
and Panama City at least once every five years, on average (NOAA, 1984). This

claim is also supported by the table below.
Hindcast results for the period 1956-1975 (Abel et al., 1989) yielded the fol-
lowing return period/significant wave height combinations (for station 29, closest
to Pensacola): 5 years/5.6 m; 10 years/7.4 m; 20 years/9.7 m; 50 years/15.7 m.

These values include only hurricane waves; tropical storms were not hindcast. A
discussion of some of the more noteworthy storms follows. Only a brief discussion

is given; future reports will attempt to quantify storm-induced changes further.


2.4.1 Camille

Hurricane Camille was the most severe to strike the U.S. Gulf Coast in recent
history. It made landfall August 17, 1969, near Bay St. Louis, MS, with winds

estimated at over 90 m/s (>200 mph). In Pensacola, gusts to 32 m/s (71 mph)
were recorded, and storm tides reached 1.8 m, but no records of severe local

damage were found (U.S. Dept. of Commerce, 1969).

























Table 3: Storms making landfall in Perdido
H=hurricane, TS=Tropical Storm.


Key/Pensacola area, 1889-1990.


Landfall Name Max. Wind m/s (mph) H, m Storm Tide, m (MSL)
Sept. 23, 1889 H
July 7, 1896 H
Aug. 2, 1898 H
Aug., 1901 H 40 (90P)
Sept. 13, 1903 H
Sept. 27, 1906 H 37-45 (83-100P)
Sept. 20, 1909 29 (64P)
Aug. 11, 1911 H 36 (80P)
Sept. 14, 1912 H 33 (74P)
July 5, 1916 H 46 (104P)
Oct. 18, 1916 H 54 (120P)
Sept. 28, 1917 H 56 (125P)
July 4, 1919 TS
Sept. 15, 1924 H
Sept. 21, 1926 H 68 (152P) 3.2
Sept. 30, 1929 31 (70P)
Aug. 31, 1932 H 40 (90P)
July 31, 1936 H
Aug. 13, 1939 H 26 (59)
Aug. 30, 1950 Baker (H) 32 (72) 1.7
Sept. 26, 1953 Florence (H)
Sept. 25, 1956 Flossy (H) 39 (88)
Sept. 8, 1957 Debbie (TS)
Oct. 8, 1959 Irene (TS)
Sept. 26, 1960 Florence (TS)
Aug. 17, 1969 Camille (H) 32 (71P) 13.2 (offshore; Hmax=22) 1.8
June 19, 1972 Agnes (H)
Sept. 23, 1975 Eloise (H) 57 (125) 8.8 (offshore)
Sept. 12, 1979 Frederic (H) 43 (96P) 8.9 (offshore) 3.3-4.6?
Sept. 2, 1985 Elena (H) 38 (84P) 4.1 (offshore) 0.9
Aug. 15, 1987 TS


INote: ouperscript


"r aenotes value for lerdido Key/'ensacola area, not necessarily maximum for entire
storm system.










Wave data were recorded at several offshore oil platforms, one close to the
path followed by Camille. The gage on this platform recorded a peak significant
wave height of 13.1 m, with a corresponding period of 11.5 seconds (water depth
100 m). The maximum wave height recorded was 22 m, and maximum period 18
seconds (Hamilton and Steere, 1969). Camille resulted in much coastal damage,
but the most severe damage was found west of the Perdido Key area.


2.4.2 Eloise
Hurricane Eloise struck (primarily) Bay, Walton, and Okaloosa Counties in

Florida on September 23, 1975. Winds up to 24 m/s (53 mph) were recorded in
Pensacola during the storm, but there is no record of significant damage to the
Perdido Key area.


2.4.3 Frederic

Hurricane Frederic made landfall at Dauphin Island, AL, on September 12,
1979, with winds gusting to 65 m/s (145 mph). Wind gusts up to 43 m/s (96
mph) were recorded at the Pensacola Naval Air Station. Damage was most severe

on Dauphin Island and in Gulf Shores, AL, but Perdido Key was also severely
damaged. The history and effects of the storm are detailed in U.S. Army Corps

of Engineers, Mobile District (1981).
Storm tides along Perdido Key were estimated at 3.3-4.6 m, causing erosion
of the beaches and dunes, and breaches in the dune line in several places, but no
permanent breakthrough occurred. Large washover fans of sediment transported
across the island by this storm are still evident on the north side of Perdido Key.
It was estimated that 243,000 m3 of sand were eroded from 9.8 km of Perdido
Key beaches. Three beach profiles on Perdido Key were surveyed by the Florida
Department of Natural Resources subsequent to the storm.










A wave height (exclusive of runup) of 4.8 m was reported along Perdido Key,
although it is not known how this value was obtained. The storm passed over a
data buoy moored offshore, where a maximum wind speed of 34 m/s (76 mph)
and maximum significant wave height of 8.9 m were recorded.
The road running the length of the island was seriously damaged by the storm
tide. Chunks of asphalt ripped from the roadbed can be found in several places.
A U.S. Air Force target vessel, the U.S.S. ex-Ozark, went aground 60 m offshore
of Perdido Key after its anchor broke loose. It was later refloated and removed.
Although not the strongest storm to hit the Gulf Coast in recent history, Frederic
may be the most significant storm in terms of its impact on Perdido Key.


2.4.4 Elena
Hurricane Elena threatened a large section of the Gulf Coast, due to its cir-
cuitous path prior to landfall on September 2, 1985, at Biloxi, MS. Winds to 38
m/s (84 mph) were recorded at the Pensacola Naval Air Station (NRC, 1991).
Unofficial weather service estimates of windspeed on Perdido Key were 40 m/s
(90 mph). Storm surges in Florida were greatest in the Cedar Key and Alligator
Point areas, but the most heavily damaged area in Florida was Pinellas County
(Bodge and Kriebel, 1985).


2.5 Return Periods
Return periods for storm tides have been calculated for Escambia County as
part of the State of Florida's Coastal Construction Control Line program, which
establishes requirements for new construction along the Florida coast (Dean and
Chiu, 1986). Estimates were obtained through application of a numerical model
of hurricane-induced forces on the Gulf coastal waters. Results are given for two
locations in Escambia County situated, respectively, east and west of the Perdido
Key section of the Gulf Islands National Seashore. The water level/return period
combinations are shown in Table 4.










Table 4: Combined Total Storm Tide vs. Return Period for Escambia County.
From Dean and Chiu, 1986.


3 Geology

Escambia County lies in the Gulf Coastal Plain physiographic province which
extends along the entire gulf coast of the United States. Coastal plain sediments,
most of which were deposited during higher stands of the sea, consist of unconsol-

idated sands, limestones, silts and clays of Cretaceous, Tertiary, and Quaternary
age. The coastal plain is approximately 200 miles wide (in the N-S direction)
along the Florida panhandle. Cooke (1939) subdivides the coastal plain in this
area into two topographic regions: the Western Highlands, consisting of a south-
westward sloping plateau whose surface has been incised by numerous streams;
and the Coastal Lowlands, consisting of relatively undissected, nearly level plains
lying less than 100 feet above present sea level. The Coastal Lowlands occupy a
narrow strip 10 to 12 miles wide along the coast and it is within this region that
Perdido Key lies.
The coastal plain is bounded to the north by the Piedmont Plateau phys-
iographic province where igneous and metamorphic rocks ranging in age from
Precambrian to Paleozoic are exposed at the surface. These ancient rocks extend
to great but unknown depths beneath the coastal plain region and are uncon-
formably overlain by the unconsolidated coastal plain sediments which form a
southward thickening wedge.


Return Period Storm Tide, m (NGVD)
(yrs) West East
500 4.7 4.4
200 3.9 3.8
100 3.5 3.4
50 3.0 3.0
20 2.2 2.2
10 1.3 1.3










The subsurface geology of Escambia County is more similar to that of the
north-central Gulf Coast comprised of Alabama, Mississippi, and Louisiana to
the west rather than the geology of peninsular Florida to the east. A detailed
description of the geology is given by Marsh (1966) and Coe (1979). The general-
ized stratigraphic column for the western Florida panhandle is shown in Figure 2.
Escambia County lies on the north flank of the Gulf Coast geosyncline (Barton
et al., 1934; Howe, 1936) and the east flank of the Mississippi Embayment. These
structures contribute to the southwestward dip which is characteristic of all the
formations in the area at least as far down as the base of the Cretaceous deposits
(Figure 3). Faulting has occurred to the northeast of Escambia County where
a west-northwestward-trending graben, the Pollard graben, extends southward
from Alabama. The major fault lines in this area are the Jay, Pollard, and Foshee
faults which extend downward through the Upper Cretaceous sediments.
The most distinctive feature of coastal plain topography is the Pleistocene
marine "terraces" which have been traced by previous workers along the Gulf

Coast and along much of the Atlantic coast. For the state of Florida, the findings
of these previous workers are summarized in map form (see Florida Geological
Survey map series no. 71, 1975). These terraces represent ancient shorelines,
deposited during major stillstands or slight transgressions of the sea, during the
Pleistocene as sea level fluctuated with the glacial and interglacial periods which

characterized this epoch. During these major stillstands or slight transgressions
of the sea and similar to the depositional processes going on at present-day coast-
lines, formation of a barrier island chain occurred with associated lagoonal/marsh
sediments being deposited on the landward side of the barrier island sequence.
Inlet deposits, estuarine and channel sediments, and a seaward thinning wedge of
offshore sediments were also deposited and are therefore also associated with the
terrace deposits. Thus, each terrace is basically an ancient barrier island complex,

preservation of which has occurred as a result of each subsequent fluctuation in
sea level being less than the previous sea level rise.
















GENERALIZED GEOLOGIC COLUMN
OF FORMATIONS IN THE WESTERN FLORIDA PANHANDLE
GRAPHIC
SERIES SECTION FORMATION
PLEISTOCENE MARINE TERRACE DEPOSITS: Sand, light tan, fine to coarse

CITRONELLE FORMATION: Sand with lenses of clay and gravel. Sand, light-
PLEISTOCENE (?) *. yellowish-brown to reddish-brown, very fine to very coarse and
poorly sorted. Hardpan layers in upper part. Logs and carbonace-
ous zones present in places. Fossils extremely scarce except near
S the coast where shell beds may be the marine equivalent of the
fluvial faces of the Citronelle.


,.< MIOCENE COARSE CLASTICS: Fossiliferous sand with lenses of clay and
S gravel. Sand is light-gray to light-brown, very fine to very coarse
and poorly sorted. Fossils abundant, mostly minute mollusks.
S Contains a few zones of carbonaceous material. Lower part of
coarse clastics present only in northern part of area, interfingering
UPPER MIOCENE
UPPER MIOCENE with Pensacola Clay In the central part.

SPENSACOLA CLAY: Formation consists of an Upper Member and Lower
Member of dark-to-light-gray, tough, sandy clay; separated by the
Escambia Sand Member of gray, fine to coarse, quartz sand. Con-
tains carbonized plant fragments, and abundant mollusks and fora-
__' _' minifers. Pensacola Clay Is present only in southern half of area,
UPPER MIDDLE TO -0---- interfingering with the Miocene coarse clastics in the central part.
LOWER UPPER MIOCENE '


LOWER MIOCENE AND CHICKASAWHAY LIMESTONE AND TAMPA FORMATION UNDIFFERENTIATED
UPPER OLIGOCENE Tampa: Limestone, light-gray to grayish-white, hard, with several beds
of clay; Chickasawhav: Dolomitic limestone, gray, vesicular.
MIDDLE OLIGOCENE .--..- BUCATUNNA CLAY MEMBER OF BYRAM FORMATION: Clay, dark-gray soft, silty
MIDDLE OLIGCENE --to sandvy, foraminiferal. carbonaceous.

UPPER EOCENE OCALA GROUP: Limestone, light-gray to chalky-white foraminifers extremely
abundant, esp. Lepidocvclina: corals, echinoids, mollusks, bryozoans


LISBON EQUIVALENT: Shaly limestone, dark-gray to grayish cream; hard,
compact; glauconitic; with thick intervals of dense, light gray shale.
MIDDLE EOCENE


( TALLAHATTA FORMATION: Shale and siltstone, light-gray, hard, with numer-
Sous interbeds of gray limestone and very fine to very coarse, pebbly
sand. Foraminifers locally abundant

SHATCHETIGBEE FORMATION: Clay, gray to dark-gray, micaceous, silty, with
LOWER EOCENE -:-- beds of glauconitic shale, siltstone, and shaly limestone. Mollusks,
foraminifers, corals echinoids. Bashi Marl Member (about 10 feet
thick) at base.


Figure 2. Geologic column of.formations in western panhandle of
Florida (Marsh, 1966)























West E cO. >e o Ual E




1200 .s c:, ,,,
Mean Sea i j2. 0: g =. (3z M Ch O IMI Ni B"
Level ==^ ^ ^ ^ ^





2000 ,c "O J ?-": o; We ho

2400 cj::-_ of 1 g projected along strike Into
42800.-. -6 oN 0 5F 10 16 20 miles
3200 UPr-- S-




Figure 3. Geologic cross-section through western Florida's Gulf coast
(Marsh, 1966)










In Escambia County remnants of these terraces are preserved as upland pla-
teaus, flat-topped hills, low coastal plains, and benches along the rivers and
bays. Three marine surfaces of Pleistocene age may be recognized in topographic
profiles across the area (Figure 4). These surfaces may be associated with the
Pamlico shoreline (8 m above present mean sea level) which developed during
the late Pleistocene, the Penholloway shoreline (21 m) which developed during
early Pleistocene, and a seaward-sloping upland surface whose elevation ranges
from approximately 30 to 800 m which is probably a composite of Cooke's Hazel-
hurst (formerly Brandywine) terrace (Cooke, 1945) and MacNeil's "high terrace"

(MacNeil, 1949).
Presently, the bulk of the northwest Florida coast is eroding with eroded
material being deposited at spit termini rather than being lost offshore. The
48 km stretch of Santa Rosa Island between Pensacola Beach and Fort Walton
Beach is the only coastal stretch prograding seaward along this area (between
1934 and 1965/69 seaward growth average rate of 0.6 m/yr).
From his study of the beach ridge plains between Pensacola, FL and Mobile
Point, AL, Stapor (1973) concludes that there has been a complex history of

interrupted deposition rather than constant, continuous construction along this
stretch of coastline. Stapor (1973) observes that in this area: (1) net coastal
erosion has replaced net seaward growth of beach ridge plains, (2) relatively
young, high coastal dunes presently migrate over older beach ridge plains, and
(3) heavy mineral concentrations found along present eroding beaches are absent
in beach ridge plains. From these observations, Stapor (1973) suggests there
has been a shift from an economy of abundant sand (promoting beach ridge
construction) to one of a shortage of sand (net coastal erosion) where exact timing
of this shift for individual regions depends on the depletion of local sand supplies.

Stapor (1973) suggests that a series of longshore drift cells, rather than one

well-integrated longshore drift system, characterize the northwest Florida coast,
























Vr ldexagger2on aut106 bn iw
S1 2 3 S 6 I g mi.ea


S..


'nC Y2A 1ty


ma- ^ /:


Figure 4. Geologic profiles through Pensacola Bay area
(Marsh, 1966)










with some of these drift cells appearing to be interconnected, but many apparently

experiencing little net exchange of sand with either adjacent cells or offshore

regions. He proposes that shoreline changes from records going back to 1871

indicate that Santa Rosa Island was probably composed of several longshore drift

cells, possibly experiencing net communication, but not a single, well integrated

system, with Perdido Key appearing to have also been characterized by similar

cellular transport.

In the north-central Gulf coast, core data (Otvos, 1979) provide supporting

evidence that shoal-bar aggradation (Otvos, 1981), rather than spit segmentation

(Gilbert, 1885) or mainland dune-ridge engulfment (Hoyt, 1967), has been the

predominant mechanism of barrier island formation. In contrast with the trans-

gressive Atlantic coast where barrier island evolution is typically associated with

landward migration (de Beaumont, 1845), the barrier islands of the Gulf coast

between Gulfport and Pensacola seem to have emerged from shoals practically

"in place" and have shifted only laterally to the west in the general direction of

littoral drift (Otvos, 1979).

Another barrier island type also recognized along the north central gulf coast

is the secondary "composite" barrier island. This type of island is characterized

by the presence of a shallow pre-Holocene (usually Pleistocene) core extending

near or above present sea level which is veneered by Holocene shoreface, beach

and dune deposits. During island formation the pre-Holocene core acts as a

stabilizer while further seaward and longshore progradation take place. This

island development pattern has been observed at eastern Dauphin Island (Otvos,

1976, 1979), central Santa Rosa Island (Otvos, 1982), Deer and Round Islands,

as well as at several South Carolina, Georgia, and northern Florida islands (e.g.,

Hilton Head, Sapelo, Ossabaw, St. Catherines, and Wassaw Islands).










4 History of Human Impacts on Area

Since the beach nourishment project motivating this study represents a major
human modification to the natural environment, it is useful to investigate the
history of human impacts on Perdido Key. Due to the dynamic nature of such
a site, evidence of small-scale, man-made changes to the island will be quickly
erased. The focus will be on the eastern portion of Perdido Key, land which is
now part of the Gulf Islands National Seashore.
Several factors combined to make Perdido Key an unlikely spot for early set-
tlements. Its lack of freshwater, terrestrial food sources, and soil suitable for
agriculture; vulnerability to storms and the accompanying flooding; and the re-
mote location are the most obvious deterrents to the establishment of a long-term
settlement. An archeological survey of Perdido Key (Prokopetz, 1974) presents
a partial history of man on the island. A Fort Walton period (1400-1750 A.D.)
aboriginal site was discovered, and it was suggested that several other sites from
this and other periods may have existed, but sites such as this had minimal lasting
impact on the physical nature of the island.
The Spanish, French, and British all claimed the Pensacola Bay area at various
times from the mid-16th century until the United States took possession from
the Spanish in 1821. There is no record of any settlement or activity on Perdido
Key during this time, however.
The initiation of construction of Fort McRee on the eastern end of Perdido
Key in 1831 appears to have been the first significant modification to the nat-
ural condition of the island. Fort McRee was destroyed during the Civil War
and abandoned afterwards. The land upon which the fort sat has been eroded;
remains of the fort are thought to be in or adjacent to Pensacola Pass. A de-
fense battery was constructed during World War I roughly 600 m from the former
location of Fort McRee. Ruins of this structure are still visible.










In recent decades Perdido Key has emerged as a beach resort area. The

intracoastal waterway through Big Lagoon was authorized in 1933 and dredged

in the early 1940's to a depth of 3.6 m (12 ft) and a width of 38 m (125 ft).

Condominiums and other housing units have been constructed along with service

industry facilities (restaurants, gas stations, etc.). Because of its incorporation

into the Gulf Islands National Seashore in 1971, the eastern half of Perdido Key

has not been developed in this manner, but has been affected by man. Aerial

photos from 1987 show two short rock groins in the vicinity of Florida Department

of Natural Resources (DNR) survey monument R67. (See Figure 5 for locations

of survey monuments). These groins are approximately 100 m long and extend 15

m into Pensacola Pass. These groins are presently still visible, but deteriorating.

No other hard structures for erosion control are visible in the 1973 photos or have

been built within the National Seashore boundaries since that time.

Several construction projects have been completed for use by visitors to the

National Seashore. A visitor center and parking lot were constructed near mon-

ument R34. A paved road leads from this area north to a boat launching ramp

on Big Lagoon. The access road to the park and leading east as far as monument

R44 was paved prior to National Park Service acquisition of the land. Major

storms (such as Hurricane Frederic in 1979) have damaged the road. Blocks of

asphalt ripped up from the roadbed during storms can be found immediately

north of the road in several places. A lighted Coast Guard navigation tower is

located near monument R67 on the eastern end of the island.

Off-road vehicles formerly resulted in significant impacts to Perdido Key

(Shabica and Cousens, 1983). Aerial photos from 1973 reveal multiple vehicle

tracks along the length of the National Seashore, with typically one track along

each coast and another down the center of the island. The destruction of vegeta-

tion that occurred resulted in a National Park Service decision to ban recreational

















//


/ 01


Meteorological


2 3 4 5km
I- I ]


ill I I
Ii1 I II


Approximate
Westerly Park
Boundary


Wave Gage


SI I I
Beach Nourishment


NOTE:
R-40 Is Florida Department of Natural
Resources Monumented "Range 40"


Figure 5. Locations of Florida DNR survey monuments along Perdido Key


R-30


Tide Gage










off-road vehicle use on Perdido Key in 1979. Following recovery of the vegetation,

off-road vehicle use was again permitted in August, 1981. Since the mid-1980's,

only National Park Service and research vehicles have been allowed on the beaches

of the Perdido Key section of the Gulf Islands National Seashore.

Beach nourishment represents the most obvious human impact on Perdido

Key. In July, 1985, approximately 1.86 million m3 of sand was placed on the

south shore of Perdido Key for beach nourishment, between monuments R59 and

R65 (Hine et al., 1986). The 1989-90 beach nourishment project motiviating this

study is much larger in scope, nourishing the region from monument R41 to R64

and involving up to 8 million m3 of material by the time it is completed. The

description of the effects of a change of this magnitude will follow the discussion

of inlet/barrier island dynamics presented in the next section.


4.1 Tidal Inlets and Barrier Islands

Dredging of a tidal inlet for navigation improvement often disrupts the re-

lationship between the inlet and adjacent barrier islands. Because of the long

history of dredging at Pensacola Pass, it is plausible to suggest that this may

have significantly affected Perdido Key. A general discussion of the interaction

between a tidal inlet and the adjacent lands is therefore appropriate.

Tidal current velocities through an inlet are a function of the tidal range,

the surface area of the bay behind the inlet that is subject to tides, and the

cross-sectional area of the inlet throat. The tidal range and the area of the

bay are generally fixed by nature; man typically increases the inlet throat area

by increasing the depth for navigation purposes. Since the volumetric flowrate

through the inlet remains unchanged and the cross-sectional area is increased,

the velocity must decrease unless the width is decreased correspondingly.










O'Brien (1931; 1969) found that for a natural tidal inlet, there is generally an

equilibrium cross-sectional area that is a function of the volume of flow, or tidal

prism, that must enter and leave the inlet during each tidal cycle (Figure 6). If

the throat area is increased, the velocity through the inlet is reduced, allowing

deposition of sediment in the channel. Conversely, if the throat area is decreased

(typically by a storm forcing sediment into the inlet), the increased velocities will

tend to scour material out until the inlet returns to its equilibrium condition.

O'Brien found that the peak spring tide velocity associated with equilibrium is

approximately one meter per second. Unfortunately the equilibrium configuration

rarely provides adequate depth for safe navigation of modern vessels.

In its natural state, flood (bayward) and ebb (seaward) tidal flows will tend

to flush sediments in and out of a tidal inlet to maintain its equilibrium geometry.

The sediment carried out of the inlet will be transported until the flow velocity

decreases below some threshold required for sediment motion. Since sediment

is transported in this manner during both flood and ebb tides, large deposits

of sand are typically found both seaward and bayward of the inlet throat. The

depth of water over these shoals is generally less than that in the inlet, making

them a serious impediment to navigation.

The offshore wave climate generally limits the size of the ebb tidal shoal.

Larger waves tend to force material from the shoal back onshore, until a dynamic

equilibrium is reached between the onshore stress exerted by the waves and the

offshore stress exerted by the ebb tidal flow.

The local wave climate is also important to the inlet/barrier island "sediment

budget". At most sites, the dominant waves tend to come from some direc-

tion other than shore-normal, driving a longshore current which carries sediment

along the beach. Neglecting changes in the cross-shore direction, it can be said

that as long as there is no spatial variation in this longshore sediment trans-













































A MINIMUM FLOW AREA (ft2)


Figure 6.


Equilibrium throat area vs. prism (O'Brien,
1969)


V)

W
z
C)"

z
a->

C'
z
cc
0
C,


a-
z
0
EE



IL



I-
CL


10










port rate, there will be no change in the planform of the beach. Maintenance of

the inlet/barrier island equilibrium condition therefore requires that sediment be

passed from the updrift barrier island across the ebb tidal shoal to the downdrift

barrier island. Stabilization of an inlet with jetties and/or dredging through the

ebb tidal shoal effectively interrupts this longshore transport of sediment, typi-

cally resulting in accretion updrift and erosion downdrift of the inlet.


4.2 Pensacola Pass/Perdido Key

The above discussion is relevant to the case of Pensacola Pass, a natural tidal

entrance which has been dredged for over a century. The longshore sediment

transport rate in the area has been estimated at 200,000 m3/yr, from east to

west (Dean, 1988a). Thus in its natural condition, sediment should be passed

from Santa Rosa Island onto the ebb tidal shoal and over to Perdido Key west

of the inlet, the ebb shoal acting as a "bridge" to carry the sediment across the

inlet. Dredging of Pensacola Pass has effectively cut through the ebb tidal shoal,

leaving Middle Ground and East Bank shoals east of the pass and Caucus Shoal

to the west. Because the deepened channel effectively interrupts the longshore

transport of sediment across the inlet, erosion of Perdido Key should be expected.

This has been found to be the case.

Erosion downdrift of a deepened tidal inlet is often mitigated by sand by-

passing, where sediment accreting updrift of the inlet and filling the channel is

dredged and placed on the downdrift beaches. At Pensacola Pass, however, most

dredged material has been disposed of offshore, removing material from the sed-

iment budget. Table 5 provides the available data regarding dredging quantities

and disposal areas. As shown in the table, historical records indicate that approx-

imately 28 million m3 of material has been dredged from Pensacola Pass (prior to

initiation of the ongoing project); all but 7.2 million m3 of this material has been


















Table 5: History of maintenance dredging
1986, and Dean, 1988a; Dean 1988b).


at Pensacola Pass (from Hine, et al.


Date Source Disposal Area Quantity, mr


1883 4/30-6/30
1885 5/25-6/30
1885 7/1-8/9
1886
1891 7/1-7/28
1893 6/14-6/30
1894 7/1-8/15
1896
1897 4/20-7/19
1897 7/1-7/12
1898 2/8-7/27
1899 2/8-6/30
1900
1901
1902
1905
1906
1907
1908
1909
1910 7/1-10/7
1911
1914
1915
1917
1921
1922
1927
1930
1932 4/24-6/30
1933 7/1-10/5
1934 1/23-4/16
1934 9/16-10/31
1935 8/22-9/22
1937 8/22-9/18
1938 8/14-9/17
1939
1940 7/1-7/22
1940 9/9-10/10
1946
1947 4/30-6/30
1947 10/14-10/31
1948
1950 6/1-6/30
1951 7/1-7/15
1953 11/2-11/22
1955 11/9-11/19
1958 11/13-11/19
1959 7/7-8/9
1959 7/12-9/4
1959 9/30-11/30
1964 9/28-12/12 E
1967
1968


Entrance Uh.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance Ch.
Entrance and Harbor
Entrance Ch.
Entrance Ch.
Entrance Ch.
entrance and Turning
Entrance Ch.
Entrance Ch.


Upen Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Open Water
Santa Rosa Pt.
Santa Rosa Pt.
Santa Rosa Pt.
Open Water
Open Water
Open Water


Continued


6400
28,300
12,500
42,400
10,800
21,300
70,800
300,000
230,000
5700
195,000
226,000
367,000
248,000
141,000
153,000
453,000
219,000
654,000
235,000
292,000
731,000
295,000
14,500
187,000
105,000
189,000
602,000
707,000
516,000
588,000
447,000
529,000
284,000
356,000
392,000
86,300
232,000
504,000
165,000
647,000
92,800
361,000
303,000
176,000
418,000
202,000
208,000
743,000
3,019,000
1,538,000
1,898,000
937,000
720,000


r` ; ii "~ -'--


Continued


















Table 5: Continued


Table 6: Channel Dimension History (from Dean, 1988a; Dean, 1988b).


Date Source Disposal Area Quantity, mn
1969 1/4-1/10 Entrance Ch. Open Water 167,000
1970 Entrance and Turning Open Water 183,000
1971 9/1-10/19 Entrance Ch. Open Water 1,195,000
1971 1/15-1/22 Entrance Ch. Open Water 131,000
1975 1/31-2/14 Entrance Ch. Open Water 840,000
1981 2/8-2/19 Entrance Ch. Open Water 500,000
1983 12/13-12/23 Entrance Ch. Open Water 87,000
1984 Entrance Ch. Open Water 700,000
1985 6/20-7/31 Entrance Ch. Perdido Key 1,860,000
1987 Entrance Ch. Open Water 150,000
1989-91 Entrance Ch. Perdido Key Ongoing


Year Depth (m) Width (m) Authorized or Actual
1881 7.3 24 Authorized
1885 6.9 24 Actual
1890 7.3 37 Actual
1896 9.1 91 Authorized
1902 9.1 152 Authorized
1935 9.8 152 Authorized
1959 11.3 244 Actual
1988 13.4 244 Authorized
1989 14.6 244 Authorized










removed from the local sediment budget by offshore disposal. Table 6 presents

channel dimensions.

In general, the more the depth of a channel is increased beyond its "natural"

depth, the greater the dredging rate required to maintain its depth. Part of this

is due to the reduced tidal velocities as described earlier, but the increased slopes

of the channel walls also lead to slumping of material into the channel. This

could lead to erosion of both islands adjacent to the inlet.


4.3 Historical Shoreline Changes

Historical shoreline change data are often useful for calibration of numerical

models of shoreline change that can in turn be used to predict future changes.

Digitized shoreline position data were obtained from the Florida Department of

Natural Resources (DNR). Figures 7 through 10 show shoreline changes at Per-

dido Key, spanning over a century. The data obtained from the Florida DNR

provide shoreline positions in a cartesian state plane coordinate system. A co-

ordinate transformation was used to generate the referenced figures. The new

coordinate system was defined so that its origin is near the center of Pensacola

Pass, and the direction of the y-axis approximates the average shore-normal

azimuth of 167.80, measured from North. The x-axis therefore corresponds to

distance from Pensacola Pass. Shoreline changes are simply defined as the change

in the y-coordinate between the two surveys.

Inspection of the figures reveals that the most significant erosion on Per-

dido Key has been within the Gulf Islands National Seashore, corresponding to

0< x <10,500 m in the figures. West of this region (x >10,500 m), a net ac-

cretion is evident. The eroded and accreted volumes approximately balance; one

possible interpretation is that material eroded from the eastern end of Perdido

Key has been transported westward and deposited west of the National Seashore.






PERDIDO KEY SHORELINE HISTORY


800.0



700.0



600.0



S500.0
CT
a:

400.0

rr3
CD

C_ 300.0
cj


LL-
O C 200.0

CO
LL_
S100.0
CD


0.0



-100.0



-200.0


4000.0 6000.0 8000.0 10000.0 12000.0 14000.0 16000.0

DIST. FROM PENSACOLA PRSS, M

Figure 7. Perdido Key shoreline history, 1858-1902






PERDIDO KEY SHORELINE HISTORY


DIST. FROM PENSACOLR PASS, M


Figure 8. Perdido Key shoreline history, 1920-1978


800.0



700.0



S600.0


CE



CD
U
H-






C)




U-
I-
CDi



LL_
Ll_
0


500.0



400.0



300.0



200.0



100.0



0.0



-100.0



-200.0






PERDIDO KEY SHORELINE HISTORY

800.0
1858
...................... 1890/95
700.0 ---1934
----------1978


600.0 /


500.0 \
r.-





300.0-
200.0 "'",
X "I "' ..... ... . ,X ".-"
\\ / "" '","" \\




(c



100.0

:1


-100.0 -







-200.0 I I I I I I I I I
0.0 2000.0 4000.0 6000.0 8000.0 10000.0 12000.0 14000.0 16000.0 18000.0 20000.0 22000.0

DIST. FROM PENSACOLA PASS, M
-2 0 0 ------------------------------------------
0. 2000 iOOO 60. 000 1000 100. 40. 60. 80. 00. 20.
DrT FRMPNROL RS


Figure 9. Perdido Key shoreline history, 1858-1978






PERDIDO KEY SHORELINE CHANGES


250.0



200.0



150.0



100.0
LLJ
C3

S50.0


5 -
IT
(_J


oA Z 0.0

_J

C- -50.0 -
I
CO
-100.0



-150.0 -


1858-90/95
..-...-..-.......---- 1890/95-1934
_-_-_.__- 1934-1978
______-- -1890/95-1978


I \


.1 'i-


/


I


i'
!,4


I I
2000.0 4000.0


I
6000.0

DIST.


8000.0

FROM


I I
-4


I I
10000.0 12000.0

PENSACOLA


14000.0

PASS


I I I I
16000.0 18000.0 20000.0 22000.0

, M


Figure 10. Perdido Key shoreline history, 1858-1978


-200.0










Data collected as part of the ongoing monitoring of the nourished beach will help

clarify the sediment transport processes affecting Perdido Key. Future work will

hopefully add to the available historical database and allow a more detailed anal-

ysis.


5 Changes Due to Beach Nourishment Project

A beach nourishment project can change the character of a beach in a number

of ways. The focus here will be on physical changes, primarily the shape and size

of the beach. Because of the complex nature of most shoreline change problems,

sediment transport is generally divided into components: cross-shore (perpen-

dicular to the beach) and longshore (shore-parallel) transport. Both modes are

important subsequent to a beach nourishment project. Cross-shore changes will

be discussed first.


5.1 Cross-Shore Changes

Figure 11 provides a representative example of conditions immediately before

and after the beach nourishment project. The horizontal axis denotes distance

from the survey monument, and the vertical indicates elevation. Common traits

of the pre-nourishment profiles sampled, including this example, are a sequence

of dunes reaching 3-5 m in elevation, seaward of which a relatively narrow, un-

vegetated beach is present. The subaqueous portion of the profile is characterized

by a planar slope in the swash zone, a distinct breakpoint bar, and a very mild
slope beyond the -5 m contour.

The pre-nourishment condition can be considered representative of an "equi-

librium" beach profile. With this in mind, the profile immediately after comple-

tion of the beach nourishment is clearly oversteepened and thus out of equilib-

rium. The dry beach width has increased roughly 150 m, the nearshore slope is



















IU ...-...-...- ... .... . .. . > ...;.... ..... -.-. .. .; .... .... ... :...-\ ...... .. ... ... .. .. ,.... ... ... ..... ...*. -.....
........ .. ..... ..... ........... .......... ....... -.... .. ..... .. ....-.... ...- ...-.... .... ..... ..... ....;.-.............-- .... .........
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...................... ....... ... ........7 ... .... ......... ...... .. ..... ...........;....... ........... ....... .. O...... ..s...... ........
-.- -' .... ......... -- ... .... ....... ..... ..... ........ .... ... ........... ..... -- ...;.... ... ----... .. --.... .... ........j .--- --...
....---.--3- *.. .............-J-- *-... ...--.- .. -----t... ..- --- ---- -. ... --- -- --- -- -- -- ----- ---







---- *.---.--- --- --+-* ---- -- -- -- --.-- --- --- - ---- -.... *.*-.-...--- ----------
-~- i---- --~---3-1---------- t-~------:- t( ---:----- --:1-6-- --1-->-1-- ....i--0-



. .... .L ... ................. ... .... .... ...... ....I.. ...... .... ..i.^.^ .......^ ;.---.. :: .-:::;:: ....i--- ..j.: .



.....- .. .... ........ ....... ---. .- Post-Nourishment .
- *.,* **. *.*.,-. -. ... .*.. -. .--,.... ..... .. ....... -re-ou r -s n m e n. ,---,---{..^ .-.. -, :--^ ---^ -......... -... .


..-....^*. *^... ... ... ... ... ... ..... .. .......
~-- --- .{...- ... .. .. ---4..... ... ...- --....---..- ..... --- ..^.. ...... .- ;- ---.... .... .... --- .--- --- ---....-.-.... -...--..... ....
--- ------------ ------------------~--







"" '".... ... .. -.............. ... ... ... ................. ........ ; ... ..........-.... .... .... ....
:::::::::::::::::::::1---:::::::::::::::::::::::::::::::::: -----~-l-::::::::::::::::::::-:::::::::::--: :::::::::::::::::::::::::::::::::::::::::::
0 : : ... .- -. ..... .- .. ..... .. ... .......... ........ ........



---.. -..-.--.... ..... ... ....... ........ ........ ............ ;..... ... ... .... ... .... ; ........ -.... ... ..... .. ;.........
... .o""ro.--* ... ... -- 1 ---. -.. ...-. .... .. .. .... .. .. ... ..... ... .-.... ..... ..- ...-- ...
...... .... ........ ...-- -- )--..-- -- --- ------ --- --. ......-- ..---- -------




--- .. ..... ..... ..--- --- -..-.- ........ --.... --- -- .. ---. - --- --. --- --- --- -- -------- ----- ----
... .... ....... .. ................ ............. ...... .. ..... ..... .... ... .




.... ... ... ........... .. ... ........ ................. ........ .... .. ,'.... ..............'.... ....... .......... ........ ...; .... ...............
-- ------ ----. . .............. -- --c-~'-- --- ----- ----------
-------t-- ..L..~.-".. --~-rC--l-- -:- .I-------:---:--!-- -----~--- L- 1 -----J-- ...........--!--~--
. . - - - ---- L-- i- -

--------------- --- ---------------- --- . - .

----:-----l--'--I--:-- --- ---- --------- --------- ------------
....... ............ i-- ------ ----------- .. ..... -- ----------------------- ....... ---- ---


-----r-................ --~-- --- --- ----:------------I-- -------- --- --- .. . .. ...
(-----t-- -~----0----?-.............. J ---:--t--- --1--'----1------- L ... .... f . ........


-400


-300


-200


-100


GULFWARO DISTANCE FROM MONUMENT (METERS)


500


SEPTEMBER, 1990
- MEASURED PROFILE
----CONSTRUCTED PROFILE


OCTOBER, 1989
- MEASURED PROFILE
---CONSTRUCTED PROFILE


RANGE:R-45 1/2
SURVEY BEARMHAG.N):1600

PROJECT:PERD IDO KEY


Figure 11. Pre- and post-nourishment beach profiles for range R-45, Perdido Key,
Florida










much steeper, and no bar exists. With time, it is anticipated that the nourished

beach will also evolve toward an equilibrium condition.


5.2 Equilibrium Beach Profiles

Bruun (1954) first proposed the simple relationship describing equilibrium

beach profiles, based on data from the Danish North Sea coast and Mission Bay,

California:


h(y) = Ay2/3 (1)

where h is the water depth at some distance y offshore of the still water line,

and A is a scaling parameter dependent primarily on sediment characteristics.

Later studies by Dean (1977) and Moore (1982) helped establish the relationship

between sediment size and the scaling parameter, A, shown in Figure 12.

The equilibrium beach profile theory predicts an unrealistic infinite slope at

the shoreline, and monotonically increasing depths offshore, thus ruling out off-

shore bars, but has been found to be of use in many situations. Dean (1991)

discusses many applications of the theory.
As indicated in Figure 12, larger sediment sizes correspond to larger values

of the A parameter, and therefore steeper beach slopes. If two beaches can each

be characterized by a single sediment size, one having coarse sediment and the

other fine, the resulting profiles are as shown in Figure 13.


5.3 Evolution of Perdido Key Beach Profiles

The previous discussion has emphasized the importance of sediment size on

beach profiles. Table 7 illustrates the sediment sizes at the various sampling

depths at Perdido Key before and after nourishment of the beach. Note that

these values have been obtained by averaging values from each beach profile,

34















SEDIMENT FALL VELOCITY, w (cm/s)


10.0


100.0


0.01
1.0





F
F
C
0.10 -







0.01 -
0.01


SEDIMENT SIZE, D (mm)


Figure 12.


Profile scaling parameter, A, vs. sediment size, D, and fall velocity,
w (Dean, 1987).


0.1 1.0 10.0 100.0

















DISTANCE OFFSHORE (m)
0 100
0








I-
= D 0.




SOD = 0.6 mm

LU





10


Effect of sediment size on equilibrium beach profiles (Dean, 1991)


Figure 13.










so there is more variation than indicated here, but little variation is evident ei-

ther spatially or temporally. Since the nourishment operation did not markedly

change the sediment sizes, the nourished beach should be expected to evolve

to an equilibrium profile that differs little from the pre-nourishment condition.

Equilibrium beach profile theory holds that if there is no change in sea level or

sediment size, the effect of a beach nourishment project is to simply displace the

profile seaward with no change in form. The time required for equilibration of a

nourished beach profile is not well-known; one benefit of the ongoing monitoring

study will be the acquisition of data defining this time scale.



Table 7: Average Grain Size Characteristics at Various Profile Locations

Gulf Side
Location Pre-Nourishment Post-Nourishment
Average D50 (mm) Average Ds0 (mm)
Dune 0.36 0.35
Berm 0.37 0.38
Beachface 0.38 0.39
-1 m 0.36 0.28
-2 m 0.30 0.34
-5 m 0.32 0.32
-8 m/End of Line 0.32 0.32



5.4 Planform Changes

A beach nourishment project generally increases the beach width by nearly a

constant amount over a fixed length of beach. With an initially straight beach,

the post-nourishment planform can then be idealized as shown in Figure 14a.
The simple planform change idealized in Figure 14a lends itself well to ana-
lytical solutions describing the shoreline evolution in time. With the additional
assumption of a spatially and temporally uniform wave climate (often a very re-

strictive assumption), the shoreline evolution is as shown in Figure 15. Numerical








Idealized Beachfil



i ..................................


0 1 2 3 4 5 6 7 8 10
Longshore Distance, km


Perdido Key Beachfill


1
1
1
E 1

C.
0



U,


30 35 40 45 50 55 60 65
Range Number


Figure 14. a) Commonly idealized form for post-nourishment
beach planform; b) Actual planform changes at
Perdido Key

38


.. .. .. .. .. .. .. .. .. .. .. .. .


















Initial Condition

T = 1 year

T = 3 years

T = 5 years

T= 10 years


Longshore Distance, km


Figure 15.


Evolution of idealized beach nourishment project. Wave
direction eb = 00 (normally incident waves; Hb = 0.5 m)










(computer-based) solutions of the governing equations for this beach nourishment
problem are often employed to allow simulation of more realistic geometries and
wave climates.

The planform changes described above result totally from longshore gradients
in the longshore sediment transport rate. The local wave climate and shoreline
orientation are the key variables in determining the magnitude of this transport.
An accurate prediction of the expected changes at Perdido Key would require
application of a refraction model to determine the wave climate throughout the
project domain. A realistic forecast of the offshore wave climate would also be

required. Future work will discuss further the anticipated planform changes at
Perdido Key.


6 Summary of Perdido Key Monitoring

This section provides an overall summary of all of the monitoring components

that are underway on Perdido Key. The purpose is to attempt to integrate
results into a comprehensive framework to characterize the effects of the beach
nourishment project and to identify any unexpected impacts of the nourishment.
The main information available to date is that available in the progress reports
for the first year by the various investigators. These progress reports describe

experimental techniques and design, and pre-nourishment conditions, but to date
do not encompass nourishment conditions.
A brief review is provided below of each of the study components.


6.1 Macroinvertebrate Communities

This study is being conducted by Heard et al. (Rakocinski, 1990) at the
Gulf Coast Research Laboratory in Ocean Springs, Mississippi. Experimental
design includes an extensive field sampling program, laboratory analysis and
characterization of the macroinvertebrate samples.










Four transects oriented approximately perpendicular to shore have been es-

tablished. Along each of these transects, nine sampling stations were located at

the following distances in meters from the shoreline: 0, 25, 50, 75, 100, 150, 300,

500 and 800. These 36 stations were complemented by eleven swash zone sam-

ples ranging from DNR Monuments 34 to 67. In addition, four lagoon stations

were established. Sampling methods included use of box-core, yabby pump, berm

trawl and kicknet equipment. Water quality data included temperature, dissolved

oxygen, salinity and pH. Sediment samples were collected at the various stations.

The samples have been analyzed and the results and additional data stored

in databases. Analysis of biota includes presentation, as a function of distance

offshore, of the following variables: species richness, total density, and diversity.

Also, for the four transects, the following sediment characteristics were plotted

as a function of offshore distances: median grain diameter, percent silt/clay and

the standard deviation of the sediment size.

The "level of disturbance" was identified as the most significant factor in the

distribution and other characteristics of the macroinvertebrates. This "level of

disturbance" is believed to be due to turbulence, primarily wave-induced. It is

hypothesized that the nearshore communities which, by their presence, are well-

suited to an energetic region will recover quickly following beach nourishment.

However, the offshore communities will be slower to adapt.

Various advanced statistical tests are reviewed as to their appropriateness

in identifying a causal relationship between beach nourishment and changes in

macroinvertebrate density or other characteristics.









41










6.2 Vegetation Monitoring

This component of the study is being conducted by Gibson et al. at the

University of West Florida. The general objectives of the study include char-

acterization of the types, densities and distributions of vegetation prior to and

following nourishment and, identifying differences and quantifying rates of colo-

nization.

The first annual report (Gibson and Looney, 1990) presents monitoring results

of Autumn, 1989 and Spring and Summer, 1990, prior to and during nourishment,

respectively. Permanent plots along thirteen cross-island transects were estab-

lished and monitored. The plots are located at specified distances along each

transect and extend from the mean high water (MHW) line on the Gulf side to

the waterline on the Lagoon side. Thus the number of plots per transect depends

on the island width, varying from 10 to 39. Monitoring includes the vegetative

cover within each plot and the buildup of sand within each plot. Specific at-

tention was focused on Uniola Paneculata (sea oats) to determine the number of

seedlings and total number per quadrate. Sampling in four macroplots was con-

tinued. These 15 m x 25 m plots include: pioneer beach, swale marsh and woods

and have been monitored regularly since 1983. Plans are to conduct monitoring

during the Fall, Spring and Summer seasons. The data collected during the Au-

tumn, 1989 and Spring, 1990 monitoring have been analyzed and developed into

a data base. Special statistical analysis techniques have been applied to classify

the "statistical and ecological relevance" of the various vegetation types.

Analysis results include the identification of 79 new plant species in the Gulf

Islands National Seashore of Perdido Key. Statistical procedures identified nine

basic vegetation types in Autumn, 1989 and again in Spring, 1990. Species

abundance and distribution of vegetation types was established.










It is anticipated that the vegetation data base formed before and during nour-

ishment coupled with the statistical methods employed will provide a good basis

for evaluating post-nourishment data and thus identifying effects.


6.3 Perdido Key Beach Mouse

The study of the Perdido Key Beach Mouse is being carried out under the

direction of Dr. Nicholas Holler, Unit Leader of the Alabama Cooperative Fish

and Wildlife Research Unit at Auburn University. The overall purpose of this

study is to identify any impact on the mouse population and patterns of concen-

tration. Methodology used is primarily live trapping and observation of tracks

and droppings. Also vegetation data is being collected as a possible correlative

parameter with mice density.

In conjunction with this project, four trapping efforts have been documented:

October, 1989, and January, April and July, 1990; however, earlier trapping data

are available for July and December, 1988 and June, 1989. The trapping transect

encompassed from DNR Monument 65 near the eastern end of Perdido Key to

approximately 7 km west. Live traps were located at nominal spacings of 10 m

except in those interdunal areas lacking vegetation. The results available to date,

expressed in terms of total individuals trapped, show fluctuations but no negative

effects which seem to be related to the dredging which commenced in Fall, 1989.

The numbers trapped ranged from 19 in December, 1988 to 90 in April, 1990. To

attempt to remove any seasonal fluctuations, the numbers trapped in July, 1988,

June, 1989 and July, 1990 are 55, 67 and 73 which shows an increasing trend.

These are preliminary data and interpretation of cause and effect is probably

premature.

Plans are to continue trapping at 50 selected stations. In addition to trapping,

plans are to collect fecal pellets from 30 animals per trapping sequence. Sea oat










and beach grass density will be noted at each of the 50 stations in Fall, 1990,

Spring, 1991 and seed production will be documented in the Fall season. Each

season, 30 Santa Rosa beach mice will be taken and a stomach contents analysis

conducted.

This program promises to provide valuable data on the impact/non-impact

and adaptability of the Perdido Key Beach Mouse. Of considerable interest will

be the rate at which the mouse population migrates gulfward as the vegetation

propagates onto the now relatively barren "new" beach.


6.4 Physical Monitoring

The physical monitoring is being conducted by the University of Florida and

includes upland, lagoon and offshore profiling, sand sampling, wave and tide mea-

surements, meteorological measurements and ground photographic documenta-

tion. The data are to be interpreted to provide a basis for predicting the physical

performance of the project. A historical substudy is underway to characterize

the geological history of the area and quantify as well as possible anthropogenic

effects. The rate of sand deposition by the sand fencing will also be documented.

Field studies have been carried out in August-November, 1989 and August-

November, 1990. An in-situ recording wave gage and weather station were in-

stalled in January, 1990 and a shore-connected wave gage was installed in early

1991.

Analysis of the survey data has identified a total of 4.3 million m3 (5.6 million

yd3) of sand added as contrasted to the pay quantity of 5.4 million m3. The

difference is interpreted, at least in part, as due to significant erosion of material

placed in the vicinity of the western end of the project. The stability of this

area is poor due to the proximity of the deepened channel and this sand was

placed first, thereby having a greater time to evolve before the post-nourishment










survey. Comparison of the pre- and post-nourishment sediments demonstrates
the material to be of generally good quality. However, the 5 m contour sam-

ples contained greater fines (silts and clays) from the post-nourishment sampling

compared to the pre-nourishment. This is believed to be fine material that has

been washed out from the nourishment and concentrated in the nearshore area.

The weather data have been compared to results from the Pensacola Naval Air

Station and generally good results were found. Plans include the correlation of
wave data with profile and planform evolution results to compare expected and

actual project performance.


7 Plans for Future Interpretation/Prediction

The data collected as part of the beach nourishment physical monitoring study

will allow investigation of a number of physical processes. Both cross-shore and

longshore sediment transport rates will be known, allowing calibration, and hope-

fully improvement, of numerical models for prediction of beach changes over time.
Prediction of project lifetimes and the degree and rate of sediment compaction

and overwash are also of interest during the feasibility study stage of a beach

nourishment project. Any sorting of the newly-placed sediment that occurs will

influence the resulting shape of the beach profile, thus the cross-shore distribution

of grain sizes is also an important relation. The effects of the deepened channel on

both Perdido Key and on the dredging rate required for channel maintenance will

be important when determining the feasibility of other, similar projects including
channel maintenance.


8 References

Abel, C.E., Tracy, B.A., Vincent, C.L., and Jensen, R.E. (1989). Hurricane
Hindcast Methodology and Wave Statistics for Atlantic and Gulf Coast
Hurricanes from 1956-1975. WIS Report 19, U.S. Army Corps of Engineers,
Coastal Engineering Research Center, Vicksburg, MS.










survey. Comparison of the pre- and post-nourishment sediments demonstrates
the material to be of generally good quality. However, the 5 m contour sam-

ples contained greater fines (silts and clays) from the post-nourishment sampling

compared to the pre-nourishment. This is believed to be fine material that has

been washed out from the nourishment and concentrated in the nearshore area.

The weather data have been compared to results from the Pensacola Naval Air

Station and generally good results were found. Plans include the correlation of
wave data with profile and planform evolution results to compare expected and

actual project performance.


7 Plans for Future Interpretation/Prediction

The data collected as part of the beach nourishment physical monitoring study

will allow investigation of a number of physical processes. Both cross-shore and

longshore sediment transport rates will be known, allowing calibration, and hope-

fully improvement, of numerical models for prediction of beach changes over time.
Prediction of project lifetimes and the degree and rate of sediment compaction

and overwash are also of interest during the feasibility study stage of a beach

nourishment project. Any sorting of the newly-placed sediment that occurs will

influence the resulting shape of the beach profile, thus the cross-shore distribution

of grain sizes is also an important relation. The effects of the deepened channel on

both Perdido Key and on the dredging rate required for channel maintenance will

be important when determining the feasibility of other, similar projects including
channel maintenance.


8 References

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