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Interim Report

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Title:
Interim Report
Series Title:
Hydrographic measurements at St. Andrew Bay entrance, Florida
Creator:
Jain, Mamta
Place of Publication:
Gainesville, Fla.
Publisher:
Coastal & Oceanographic Engineering Dept. of Civil & Coastal Engineering, University of Florida
Publication Date:
Language:
English

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University of Florida
Holding Location:
University of Florida
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All applicable rights reserved by the source institution and holding location.

Full Text
UFL/COEL-2001/014

HYDROGRAPHIC MEASUREMENTS AT ST. ANDREW BAY ENTRANCE, FLORIDA
by
Mamta Jain and
Ashish J. Mehta
Submitted to: Coastal Technology Corporation Destin, FL 32541

December 2001




UFL/COEL-2001/014

HYDROGRAPHIC MEASUREMENTS AT ST. ANDREW BAY ENTRANCE, FLORIDA By
Mamta Jain and Ashish J. Mehta

Submitted to:
Coastal Technology Corporation
Destin, FL 32541
Coastal and Oceanographic Engineering Program Department of Civil and Coastal Engineering University of Florida Gainesville, FL 32611

December 2001




SUMMARY
Hydrographic measurements were carried out in St. Andrew Bay Entrance (also known as Panama City Harbor Entrance) connecting St Andrew Bay to the Gulf of Mexico, Florida between 09/18/2001 and 09/19/2001. The measurement included: 1) Two flow cross-sectional surveys one being in the entrance channel vicinity of the throat where the jetties are located and the other towards St. Andrew Bay, 2) vertical profiles of flow velocity across these two cross-sections and 3) 2-day record of tidal variation in the channel. These data were used to determine the corresponding time variation of flow discharge in the channel. The discharge was in turn used to calculate the flood and ebb tidal prism through the throat cross-section.
We report the following approximate values: tidal prism 7.0x 107 M3 (from peak discharge), tidal range 0. 17 m, representative cross-section (mid-tide) 6,365 M2 and peak (cross-sectional mean) flood/ebb velocity 0.63 m/s.




TABLE OF CONTENTS
S U M M A R Y ........................................................................................ 2
TABLE OF CONTENTS ........................................................................ 3
LIST OF FIGURES .............................................................................. 4
LIST OF TABLES ................................................................................ 5
ACKNOWLEDGMENT ......................................................................... 6
1. INTRODUCTION ............................................................................ 7
2. MEASUREMENTS ........................................................................... 10
2.1 C ross-S ections ............................................................................. 10
2.2 T ide L evel .................................................................................. 11
2.3 Current and Discharge .................................................................. 13
3. T ID A L P R ISM ................................................................................. 18
3.1 Calculation of Tidal Prism .............................................................. 18
3.2 Comparison with O'Brien Relationship ............................................... 18
4. CONCLUDING COMMENTS ............................................................. 20
R E F E R E N C E S ..................................................................................... 22
3




LIST OF FIGURES

Fig 1. 1 St. Andrew Bay Entrance, Florida in 1993. Jetties are -430 m apart............ 8
Fig. 1.2 St. Andrew Bay Entrance bathymetry and current measurement cross-sections. The tide level recorder was located northward of the area shown....................... 9
Fig 2.1 a Cross-section A: measured and compared with 2000 bathymetry. Distance is measured from point A-I ........................................................... 10
Fig 2.1b Cross-section B: measured and compared with 2000 bathymetry. Distance is measured from point B -I..........................................................i1
Fig. 2.2a Measured tide in the channel vicinity on September 18-19, 2001. The datum is MLLW ............................................................................ 12
Fig. 2.2b NOS Predicted tide at the entrance on September 18-19, 2001. The datum is MLLW ............................................................................ 12
Fig. 2.3a Cross-sectional mean current variation at cross-section A on September 18, 2001............................................................................... 13
Fig. 2.3b Cross-sectional mean current variation at cross-section B on September19, 2001............................................................................... 14
Fig. 2.4a. Discharge variation at cross-section A on September 18, 2001 .............14
Fig. 2.4b. Discharge variation at cross-section B on September 19, 2001 .............15
Fig. 2.5a. Flood velocity structure at cross-section A on September 18, 2001 at 09:25. Vertical axis represents current speed in mis. Depth and width axes are in meters. Origin of width is point A-lI............................................................... 16
Fig. 2.5b. Flood velocity structure at cross-section A on September 18, 2001 at 17:18. Vertical axis represents current speed in miLs. Depth and width axes are in meters. Origin of width is point A- I................................................................16
Fig. 2.5c. Ebb velocity structure at cross-section A on September 18, 2001 at 15:55. Vertical axis represents current speed in rn/s. Depth and width axes are in meters. Origin of width is point A-2 ............................................................... 17
Fig. 2.5d. Flood velocity structure at cross-section A on September 18, 2001 at 20:48. Vertical axis represents current speed in rn/s. Depth and width axes are in meters. Origin of width is point A-1 ............................................................... 17




LIST OF TABLES
Table 1. 1 Locations of channel cross-sections .................................................. 7
Table 2.1 ADCP measurement sequence ....................................................... 13
Table 2.2 Characteristic peak velocity and discharge values at cross-sections A and B. 15 Table 3.1 Flood and ebb tidal prism s ............................................................ 18




ACKNOWLEDGMENT

This study was carried out for Coastal Technology Corporation, Destin, Florida. Assistance provided by Michael Dombrowski of Coastal Tech is sincerely acknowledged. Field work was performed by Sidney Schofield and Vic Adams, both of the Coastal and Oceanographic Engineering Laboratory of the Department of Civil and Coastal Engineering, University of Florida.




HYDROGRAPHIC MEASUREMENTS AT ST. ANDREW BAY ENTRANCE, FLORIDA
1. INTRODUCTION
Hydrographic measurements were carried out in St. Andrew Bay Entrance (also known as Panama City Harbor Entrance) connecting St Andrew Bay to the Gulf of Mexico in Bay County, Florida between 09/18/2001 and 09/19/2001. The measurements included: 1) Two flow cross-sectional surveys one being in the entrance channel vicinity of the throat where the jetties are located and the other towards St. Andrew Bay, 2) vertical profiles of flow velocity across these two cross-sections and 3) 2-day record of tidal variation in the channel. Results and analysis based on these measurements are described in this report.
Figure 1. 1 is an aerial view of the St. Andrew Bay Entrance channel and Fig. 1.2 is a bathymetric survey based largely on measurements carried out in 2000. The two cross-sections (A & B) where currents were measured with a vessel mounted Acoustic Doppler Current Profiler, or ADCP (Workhorse 1200 kHz, RD Instruments, San Diego, CA) and the location of an ultrasonic tide level recorder (Model #220, Infinities USA, Daytona Beach, FL) are as marked. The coordinates of end-points A-1, A-2, B- I and B-2 are given in Table 1. 1. The tide gage was located in waters (Grand Lagoon) close to the entrance channel, at Lat: 30 07.9667, Long: -85 43.6667. Table 1. 1 Locations of channel cross-sections Section Side Latitude Longitude Northing Basting
A A-1 30 07.7086 -85 43.3667 412452.6240 1613441.9000
A A-2 30.07.4492 -85 43.2846 410875.8000 1613857.6000
B B-I 3007.3508 -8543.9159 410315.8300 1610524.0000
B B-2 3007.1753 -8543.7126 409240.0000 1611584.6000




Fig 1. 1 St. Andrew Bay Entrance, Florida in 1993. Jetties are -430 m apart.




412000.00 1
..$fO' i -55,00
411000.00
410000.00
409000,00, 4
1610000.00 1611000.00 1612000.00 1613000.00 1614000.00 1615000.00
Fig. 1.2 St. Andrew Bay Entrance bathymetry and current measurement cross-sections A and B. The tide level recorder was located northward of the area shown. The datum is
MLLW.




2. MEASUREMENTS

2.1 Cross-Sections
Cross-sections A and B measured by the ADCP are shown in Figs. 2.1a,b. These
have been compared with the bathymetric survey of 2000. The trends in the two sets of
depths are qualitatively (although not entirely) comparable. As far the velocity
measurements given later are concerned, the ADCP based values must be treated as
having a good degree of accuracy because they were measured at the precise times and
locations of acoustic profiling for current data. On the other hand, the bathymetric data
are likely to be less accurate, given that they were not synchronous.
Batymetry side-A Side-A-1 Side- A-2
0
100 200 300 400 500 600
-2
-4
-6
E -8
a) -10
0
-12 -14 -16
-18
-- ADCP ---- Bathymetry chart Distance (m)
Fig 2.1 a Cross-section A: measured and compared with 2000 bathymetry. Distance is measured from point A-1. The datum is MLLW.




Batymetry side-B
Side-B1 Side-B-2
0
-2 100 150 200 250 300 350 400 450 500
-4
-6
--10
0
-12
-14 -16 -18
--ADCP ---- Bathymetry chart Distance (m)
Fig 2.1b Cross-section B: measured and compared with 2000 bathymetry. Distance is measured from point B-1. The datum is MLLW.
2.2 Tide Level
Tidal variation in the channel was measured and compared with the predicted National Ocean Service (NOS) tide at St Andrew Bay Entrance channel based on reference station at Pensacola. The measured tide is shown in Fig. 2.2a and the corresponding NOS tide in Fig. 2.2b. Both show general similarities, although the measured one should be deemed more accurate. The record began on 09/18/01 at 9:00:00 and ended on 09/19/01 at 20:15:00. The measured data indicate a weak semi-diurnal signature with a range variation of 0.11 to 0.17 m.




Tide at St Andrew Bay Entrance
-Tide at St Andrew Bay Entrance

0 0
oo 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 M 0 O 0
0 N 0000 00 0

Time (hrs)

u~-,, i~iu I

09/18/01
L Y

Fig. 2.2a Measured tide in the channel vicinity on Septemberl8-19, 2001. The datum is MLLW.

NOS Tides

0.45 0.4 0.35 S0.3 > 0.25
0.2 S 0.15
0.1
0.05
0

r- n 00 00 a, 8f "1000 15 q 0R In In 7 0R C I N In
09/18/01 Time (hr:min 09/19/01

Fig. 2.2b NOS predicted tide at the entrance on Septemberl8-19, 2001. The datum is MLLW.

-Tides

.i 1 1 1 . 1 T1 . . . . . . . . . . . . . . . . . . . . . .I.. . I . .I.. . . . . .

nml 1' I,




2.3 Current and Discharge
The sequence of ADCP measurements is as given in Table 2.1.
Table 2.1 ADCP measurement sequence
Cross Date Time Date Time No. of transects
Section starting starting ending ending
A 09/18/2001 09:25 09/18/2001 09:02 84
B 09/19/2001 09:10 09/19/2001 20:05 70
The time-variation of the cross-sectional mean current variation at A and B is plotted in Figs. 2.3a,b, respectively. The corresponding discharges are given in Figs.
2.4a,b.
Velocity Profile side-A
0.80
0.60 0.40
" 0.20
2!, 0.00
C.,, O T
- L 0 CO N1 (0 0 LO IO
-0.40.
-0.60
-0.80
-velocity Profile on side A Time (hrs)
Fig. 2.3a Cross-sectional mean current variation at A on September 18, 2001.




Velocity profile side B

IR
c o
-0.1 o -

,- 0
o co
CO

-0.4
--Velocity profile side B Time (hrs)

Fig. 2.3b Cross-sectional mean current variation at B on September 19, 2001.
Discharge Profile side A 5000
4000 3000 2000
0Y)
1000
. 0_ .c. .... .,. ., . .. ... .. .. . . .. . . ,
LO CO O 0 0 CO CO r- ON C N LO ( CD 0
o c cNl e c) m o '- 0 o o N cl I LO CO Ln C') LO

-2000
-3000
-4000

~- C') 0 N ~ 0 C') U) C') C)00r--NC')C~t

'- C') 0 N U) COON............

-- Total discharge Time (hrs)

Fig. 2.4a. Discharge variation at cross-section A on September 18, 2001.
14

o (0 (0 0 o M N 0 LO LO C1t M o0~-~ o(
-oC)o(




Discharge profile side B

4000 3000 2000
Co)
E 1000
00
-1000 In 6 9 n n IN it (n LP c
-2000 -3000
Time (hrs)
--M- "Total discharge "]
Fig. 2.4b. Discharge variation at cross-section B on September 19, 2001.
Based on the data in Figs. 2.3a,b and 2.4a,b, Table 2.2 provides characteristic velocity and discharge related times and magnitudes. Table 2.2 Characteristic peak velocity and discharge values at cross-sections A and B.
Cross-section A Cross-section B
Quantity Peak Time Peak Time Peak Time Peak Time
flood Ebb flood ebb
Velocity (mi/s) 0.63 09:25 -0.62 17:18 0.45 10:37 -0.34 18:32 Discharge (m3/s) 4200 09:25 -3620 17:18 2980 10:37 -2250 18:32
Lillycrop et al. (1989) measured 0.70 m/s peak flood velocity and -0.84 m/s at ebb close to cross-section A. Ichiye and Jones (1961) reported 0.52 m/s and 0.61 m/s, respectively. During both studies East Pass, a second entrance to the bay, was open. During the present study it was closed.
Examples of measured flood and ebb velocity structures over cross-section A are shown in Figs. 2.5a,b,c,d for illustrative purposes. From Table 2.2 we note that at each section, peak (cross-sectional mean) flood and ebb velocities were of comparable magnitude. On the other hand, the ebb discharge was lower than flood, at A by 14% and




at B by 24%. Assuming the validity of the data, one must attribute this difference between flood and ebb prisms to the temporary storage of water in St. Andrew Bay, in the absence of any other openings.
-2
00
250
15 0
Fig. 2.5a. Flood velocity structure at cross-section A on September 18, 2001 at 09:25. Vertical axis represents current speed in m/s. Depth and width axes are in meters. Origin of width is point A-1.
2 02 -2, 0
Fig. 2.5b. Ebb velocity structure at cross-section A on September 18, 2001 at 17:18. Vertical axis represents current speed in mis. Depth and width axes are in meters. Origin of width is point A-i1.




0
5
300
1250 10 20 0
1515
155 100
20 0
Fig. 2.5c. Ebb velocity structure at cross-section A on September 18, 2001 at 15:55. Vertical axis represents current speed in m/s. Depth and width axes are in meters. Origin of width is point A-2.
01
5250
125
0 200
150
15 100
20 0
Fig. 2.5d. Flood velocity structure at cross-section A on September 18, 2001 at 20:48. Vertical axis represents current speed in m/s. Depth and width axes are in meters. Origin of width is point A-1.




3. TIDAL PRISM

3.1 Calculation of Tidal Prism
The flood and ebb tidal prisms were estimated as follows. Referring to Fig. 2.4a, the flood tidal prism was estimated by extrapolation of the starting point of the discharge curve, as measurement did not run over the entire flood cycle. However, from Fig. 2.2a we note that the tide is measurably semi-diurnal (M2), so the tidal period is 12.42 h. Hence, by extending the flood tide curve (to a comparatively minor extent, on the order of 1 hour) to the previous slack water, the flood tidal prism (equal to volume of water entering the channel) is found to be 9.2x 107 in3. In Table 3.1 flood and ebb prisms obtained from Figs. 2.4a,b are given.
When a complete discharge curve for that purpose is not available, the following formula yields an approximate value of the prism, P:
QT
M (A-3. 1)
)zCK
where Q,, is the peak discharge (Table A-2.2), T is the (semi-diurnal, M2) tidal period (12.42 h) and the coefficient CK = 0.86 (Keulegan, 1967). Values are given in Table 3. 1. Table 3.1 Flood and ebb tidal prisms
Cross-section A (09/18/0 1) Cross-section B (09/19/01)
Method Flood Ebb Tide range Flood Ebb Tide range
(m 3) (m 3) (in) (m 3) (m 3) (in)
Area 9.2x 107 3.4x 107 0.17 7.7 X107 1.7 X107 0.16
Peak 7.0x 107 6.0x 107 0.17 4.9x 10' 3.7x 107 0.16
3.2 Comparison with O'Brien Relationship The O'Brien (1969) relationship between the throat area A, and the tidal prism P on the spring range for sandy inlets in equilibrium is:




For inlets with two jetties, a = 7.49xlO-4 and b = 0.86 (Jarrett, 1976). Now, considering cross-section A to represent the throat section, Ac = 6,365 m 2 at mid-tide level. Thus, from Eq. 3.1 we obtain P = 11 .x 107 in3, which may be compared with the measured 9.2x 107 Mn3. The latter value is 19% less than the former; however it is uncertain if this difference is has significance in relation to the stability of the channel, since Eq. 3.1 merely provides an estimate. Overall we may surmise that the measured value is a reasonable estimate of the prism, given that the value obtained from Eq. 3.1 is not drastically different.




4. CONCLUDING COMMENTS
We note that the discharge measurements by the ADCP model used are constrained by the acoustic black zones at the top and the bottom, as well as the inability of the vessel (make, draft) to traverse near-bank depths less than the vessel draft plus required underkeel clearance. The blank zone limitations led to the need to the need to extrapolate the velocity data in order to calculate the cross-sectional mean velocities and corresponding discharges.
Built-in routines in the instrument calculate the measured discharge and convert to total discharge. At sections A and B the total discharge was typically greater than the measured discharge by 13% and 23%, respectively.
No correction was applied for the loss of data due to vessel limitation close to channel banks. One may expect that, typically, the discharge not accounted for in this way would be less than -5% at this entrance as a result of this limitation.
Finally, we note that the backscatter signals were not corrected for any effects due to salinity induced stratification in the channel, instrument. During the study period at this entrance, the error from this source is likely to have been secondary to that due to above-mentioned limitations.
By definition, the tidal prism characteristic of an entrance is that during flood flow (at spring tide). Accordingly, and based on the reported measurements, we report the
3
following approximate values for St. Andrew Entrance: tidal prism 7.0 m tidal range 0. 17 m, representative cross-section (mid-tide) 6,365 M2 and peak (cross-sectional mean) flood/ebb velocity 0.63 m/s.




While the tidal prism is seemingly reasonable, an unquantified degree of uncertainty in its value exists due to: 1) lack of full coverage of the flood cycle and 2) the inevitable presence of acoustic blank zones with the device used. It is our recommendation that if available resources allow for monitoring only two tidal cycles, monitoring should be carried out across a single cross-section over two tidal cycles, as opposed to one cycle at two sections. Presently, more efficient devices are being developed to reduce the blank zone. These should find considerable use in Florida's shallow coastal environment.




REFERENCES

Ichiye, T., and Jones, M. L., 1961. On the hydrology of the St. Andrew Bay system, Florida. Limnology and Oceanography, 6(3), 302-311.
Jarrett, J. T. Prism-inlet area relationships. G.IT.I Report No. 3, U.S. Army Engineering Coastal Engineering Research Center, Ft. Belvoir, VA.
Lillycrop, W. J., Rosati, J. D., and McGehee, D. D., 1989. A study of sand waves in the Panama City, Florida, entrance channel. Technical Report CERC-89-7, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
O'Brien, M. P., 1969. Equilibrium flow areas of inlets on sandy coasts. Journal of the Waterways and Harbors Division of ASCE, 95(1), 43-52.