DTIC ADA595762: Tidal Motion in a Complex Inlet and Bay System, Ponce de Leon Inlet, Florida

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YIP·'3 VOL. 16, NO.3 'CERF SUMMER2000
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An International Forum for the Littoral Sciences
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1. REPORT DATE 2. REPORT TYPE 3. DATES COVERED
2000 N/A -
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Tidal Motion in a Complex Inlet and Bay System, Ponce de Leon Inlet,
5b. GRANT NUMBER
Florida
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
Militello, Adele, and Zarillo, Gary A.
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
USAE Waterways Experiment Station, Coastal and Hydraulics REPORT NUMBER
Laboratory, Vicksburg, MS; Division of marine and Envuronmental
Systems, Florida Institute of Technology, Melbourne, FL
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release, distribution unlimited
13. SUPPLEMENTARY NOTES
14. ABSTRACT
Tidal motion and inlet processes were investigated in Ponce de Leon (Ponce) Inlet, Florida, and its bay
channels through a 10-week data-collection campaign and two-dimensional numerical simulation
modeling. Water level and current were measured at six locations spanning the ebb shoal, inlet, and bay
channels. Measurements revealed that the inlet was flood dominated during the data-collection period. The
flood dominance may have been enhanced by a net influx of water during the measurement period, which
was captured at two measurement stations in the bay channels located 5 km away from the inlet. Scour,
erosion, and sedimentation are problems faced at Ponce Inlet, and calculations suggest tide-related
circulation patterns contribute to problematic hot spots. Tidal attenuation was calculated along a 7 km
transect from the ebb shoal, through the inlet, and south along the Indian River North.
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF
ABSTRACT OF PAGES RESPONSIBLE PERSON

a. REPORT b. ABSTRACT c. THIS PAGE UU 14
unclassified unclassified unclassified
Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
Journal of Coastal Research
840-852 West Palm Beach, Florida Summer 2000
I, Tidal Motion in a Complex Inlet and Bay System,
Ponce de Leon Inlet, Florida
Adele Militellot and Gary A. Zarillo:j:
t USAE Waterways +D ivision of Marine and
Experiment Station, Coastal Environmental Systems,
and Hydraulics Laboratory, Florida Institute of
3909 Halls Ferry Road, Technology, 150 W.
Vicksburg, MS 39180, University Blvd.,
U.S.A. Melbourne, FL 32901,
U.S.A.
ABSTRACT ............................................... .
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AtidDe DmmeaOsNurAemLe InNt.D EX WORDS: Tidal inlet, inlet hydraulics, tidal attenuation, flood dominance, circulation modeling,
INTRODUCTION estuary or bay. Attenuation is strong in systems containing
Tidal inlets and the associated bays behind them are sub significant tidal fiats, shoals, and shallow water. Sediment
ject to a wide range of driving forces that create unique hy transport is linked to tidal attenuation by two general means:
drodynamic conditions for each inlet and bay system accord 1) damping of the tide alters the strength of the current,
ing to its geometry and bottom topography. Understanding which induces scour and deposition, and 2) as the tide atten
of sedimentation and scour patterns within inlets and navi uates with distance from an inlet, other processes such as
gation channels can be improved by resolving circulation pat wind or river inflow can become dominant, resulting in cir
terns controlled by the acting physical processes. For in culation patterns that may be different from those produced
stance, in the direct vicinity of an inlet, tidal motion domi by the tide. Additionally, modification of the bottom topog
nates the flow. However, in distant reaches of a bay, other raphy influences the tidal propagation. Thus, a feedback
processes such as river flow or wind may dominate. The pres mechanism can occur between the tidal hydrodynamics and
ence ofhydraulics structures, such as bridges, can disrupt the sediment transport through bottom topography change.
pattern of tidal flow, modifYing the tidal amplitude and cur Bridges can significantly modifY tidal propagation through
rents. This study identifies the circulation patterns and in a channel or bay because these structures behave as point
vestigates tidal propagation and attenuation in a complex in sources of tidal-amplitude reduction. The upstream side of a
let and bay system with hydraulic structures. bridge can possess significantly smaller tidal amplitude as
Tidal wave propagation is accompanied by attenuation. compared to the downstream side. Thus, bridges can define
Bottom friction works to both modif'y the spectra of the water the boundaries between hydraulic regimes, or compartments,
motion and reduce the tidal amplitude with distance into an that have different circulation patterns (SURAK, 1994,
BROWN et al., 1995). However, little work has been conducted
98266 received 30 November 1998; accepted in revision 15 May 1999. on the resistance that bridges impose on tidal flows, and
Tidal Motion, Ponce de Leon Inlet, Florida 841
~
-N-
~ GULF
OflriEXICO
LOCATION MAP
AT LANT/C OCEAN
Pones de Leon
Inlet
Indian River
North
Coronado
Beach
Bridge
~
0 1MI
0 ....
Figure 1. Location map of the Ponce de Leon Inlet study site. Measurement station locations are shown as filled circles.
MEHTA (1996) has identified this topic as having high pri The area of study includes the inlet, ebb shoal, and back bay
ority for inlet-related research. and associated channels. Stabilization of the inlet was initi
Tidal motion at Ponce de Leon (Ponce) Inlet, Florida and ated in 1968 and completed in 1971. Two jetties were con
its adjacent bay channels is examined here by field measure structed and as part of a sand bypassing system, the north
ments and application of a two-dimensional, depth-integrated jetty was constructed with a weir section. The weir did not
hydrodynamic numerical model. Circulation patterns in the function as anticipated, and scour occurred in the northern
inlet are identified and discussed in relation to localized scour inlet throat while the south spit migrated into the inlet (PAR
and deposition. Attenuation of the M2 tidal constituent is in THENAIDES and PURPURA, 1972; PURPURA, 1977; JONES and
vestigated along a reach of the inlet and bay system and MEHTA, 1978). The weir was closed in 1984, but scour at the
quantified in terms of an amplitude reduction per unit length north jetty and encroachment of the south spit into the inlet
ionfc clhuadnende als. Tphaert cohfa tnhgise iinnv teisdtaigl aatmiopnl iotfu tdhee aflto aw bartid ag ceo ims pallesxo has continued (TAYLOR et al., 1996, HARKINS et al., 1997).
Erosion of the north interior spit, west of the north jetty,
inlet and back-bay system.
increased upon weir closure (IiARKINS et al.~ 1997). Presently,
the south jetty is almost entirely buried by sand.
STUDY SITE
Ponce Inlet is hydraulically linked northward to the Hali
Ponce Inlet is located on the east coast of Florida and lies fax River and southward to the Mosquito Lagoon via the In
approximately 92 km north of Canaveral Harbor (Figure 1). dian River North. In this area of the Central Florida Coast,
Journal of Coastal Research, Vol. 16, No. 3, 2000
842 Militello and Zarillo
Figure 2. Aerial photograph taken March 21, 1996, showing the flood shoal west of Ponce de Leon Inlet. Rockhouse Creek splits the shoal into two
lobes.
the mean tidal range in the ocean is approximately 1 m, and (Figure 1). The IWW traverses the length of the study site
the mean spring range reaches 1.3 m. The tide is semi-diur and is the major channel within the Halifax River/Mosquito
nal, with the M amplitude dominating other constituents by Lagoon complex away from the inlet. Design dimensions of
2
an order of magnitude or more. The barrier island systems the IWW are 90 m width and 3.7 m depth. The confluence of
to the north of Cape Canaveral typically possess a narrow the IWW and the Halifax River lies 3.5 km north ofthe inlet,
and low-profile structure, well-developed flood shoals, and and the IWW joins the Indian River North 2 km south of the
ebb shoals of smaller volume that are largely submerged inlet.
(HAYES, 1979, ZAlULLO et al., 1982). Although the bay di West of the inlet, the flood shoal occupies a significant
rectly west of the inlet throat retains its natural configura amount of the bay area, as shown in Figure 2. Rockhouse
tion, a navigation channel was dredged west of the bay in the creek is a tidal channel that bifurcates the shoal and provides
1950's as part of the Intracoastal Waterway (IWW) system direct exchange between the inlet and the IWW. The flood
Journal ofCoaslal Research, VoL 16, No.3, 2000
Tidal Motion, Ponce de Leon Inlet, Florida 843
shoal is exposed during much of the tidal cycle so that flow National Ocean Service (NOS) standard harmonic analysis
is commonly restricted to the main channel and Rockhouse methods were applied to all water-level data from stations
Creek. Other natural features in the area include Rose Bay having continuous records of 29 days or longer to calculate
and Turnbill Bay and numerous small channels that provide tidal constituents. Where possible, harmonic analysis of over
water exchange for marsh and mangrove habitats of the area. lapping 29-day segments of water-level data were conducted,
These channels and bays act as storage for water flowing into and the results were vector averaged to provide a more stable
and out of the Ponce Inlet system. estimate of tidal constituents. Shortened time series at Sta
The Coronado Beach Bridge is one of eight bridges that tions A and F allowed harmonic analysis on a single 29-day
span the Halifax River/Mosquito Lagoon complex. This bridge record in each case.
crosses the Indian River North approximately 4 km south of
Ponce Inlet and is the closest bridge to the inlet. The circuM CffiCULATION MODEL SETUP AND
lation model is applied to estimate the tidal amplitude atten CAUBRATION
uation at the bridge.
Hydrodynamic modeling of the study site was conducted by
MEASUREMENTS application of the two-dimensional, depth-integrated, finite
element model ADCIRC (LUETTICH et al., 1992). The numer
Synoptic measurements of water level and current velocity ical grid encompassed Florida's east coast and contains the
were collected at six locations in the Ponce Inlet system (Fig entire Halifax River and Mosquito Lagoon complex within
ure 1) from August 21 through November 1, 1997 (ZARILLO the computational domain (Figure 3). Details of the grid in
and MILITELLO, 1999). The measurement strategy was aimed the inlet and limited back-bay area are shown in Figure 4.
at collecting data for calibration of the circulation model and High resolution was specified in the inlet and back bay re
a wave-propagation model (SMITH and SMITH, 1999) and to gions to calculate water level and current over the complex
augment long-term_ data collection at the site (KING et al., bottom topography. The grid was constructed using National
1999). Station A was located on the ebb shoal, whereas Sta Oceanic and Atmospheric Administration bottom topography
tions B and C were located in the main inlet conveyance in the Atlantic Ocean. SHOALS data were applied to define
channel. Station D was located west of the main inlet channel the bottom topography in the vicinity of Ponce Inlet, includ
and east of the flood shoal. Station E was located approxi ing the inlet, ebb shoal, and limited back-bay channels. Flood
mately 5 km south of the inlet in the Indian River North (0.8 shoal elevations were estimated from aerial photographs. In
km south of the Coronado Beach Bridge), and Station F was the remaining interior regions, bottom elevations were ap
located on the Halifax River approximately 5 km north of the plied from NOS charts. All bottom topographic data were con
inlet. Stations D, E, and F were leveled with respect to the verted to Mean Sea Level (MSL). Figure 5 shows the bottom
National G<lodetic Vertical Datum (NGVD). topography specified in the model in the vicinity of the inlet.
Instrument packages for fixedMstation monitoring each con The inlet gorge and ebb and flood shoals are well defined by
sisted of a 2-axis Marsh-McBirney electromagnetic current the bottom topographic data.
meter combined with a high-resolution pressure transducer The model was forced at its ocean boundaries with four
(puv-type sensors). Current velocity and water-level mea semi-diurnal tidal constituents M2, N2, ~. 82, and four di
surements were calculated from a 1-min average of samples urnal constituents K P Q and 0 developed from a pre
11 11 11 1
taken at 1 Hz. The sampling interval was one hour. All sen vious ADCIRC modeling effort (WESTERINKel al., 1993). Sim
sors were calibrated before and after field deployment. ulations were conducted with the finite-amplitude and ad
Bottom topography at the study site was acqnlred by the vective terms included in the computations. Wind fields were
SHOALS lidar system (LILLYCROP et al., 1996) during Sep obtained from the National Center for Environmental Pre
tember and October 1996 surveys. Data were collected at 4 diction and applied over the model domain. Wind information
m X 4 m horizontal resolution. The area of survey coverage was specified at a spatial resolution of 0.25 deg and temporal
included the inlet, ebb shoal, nearshore zone north and south resolution of 6 hr. Resolution of the wind field was sufficient
of the inlet, and limited reaches of the Halifax River and In for simulating large-scale meteorological forcing, but not me
dian River North. Maximum depth of the survey was 9 m, soscale motions such as sea breeze. Thus, water motion in
and elevations were referenced to the NGVD. The dense duced by mesoscale wind processes was not simulated. The
SHOALS data were reduced to 7 m X 7 m resolution by ap specified time interval for the simulation was from August
plication of the minimum curvature gridding method. The 22, 1997 (Julian Day (JD) 234) to October 24, 1997 (JD 297).
processed bottom topography was output to a rectangular During the simulation period, no storms passed through the
grid. study area.
Comparisons of current speed, current direction, and wa The Coronado Beach Bridge was represented in the com
ter-elevation time series were made among the six stations putational grid by modification of the bottom topography. At
to determine if water level, tidal phase, tidal amplitude, and the bridge site, depths were reduced over much of the width
current magnitude were consistent with respect to station po of the Indian River North, leaving a narrow region of chan
sition and inlet geometry. This review resulted in the elimi nelized flow. The depths were adjusted until the calculated
nation of short segments of data from Stations A and F that M amplitude at Station E was close to that of the measure
2
may have been contaminated by low battery power or elec ments.
tronic noise. Tidal constituents contained in the database from which
Journal of Coastal Research, VoL 16, No. 3, 2000
844 Militello and Zarillo
River
Ponce
de Leon
Inlet
Mosquito
Lagoon
Figure 3. Regional view of finite-element grid showing Halifax River and Mosquito Lagoon complex.
the model ocean forcings were extracted are overpredicted in wave over the ebb shoal. Bathymetry data applied in the
the northern region of the grid applied for this study (WES model for the ebb shoal were collected approximately one
TERINK et al., 1993). Calibration of the model was conducted year before the simulation time. Because of the dynamic na
by reduction of tidal amplitudes at the ocean boundary until ture of the ebb shoal, sand movement may have locally mod
calculated water levels were in agreement with measure Hied the bottom between 1996 and 1997, which would cor
ments. Phases at the ocean boundaries were not modified. A respondingly change the tidal shoaling properties in this
spatially-constant drag coefficient was specified over the area.
model domain and not modified during the calibration pro M, water-level amplitude and phase calculated by standard
cess. NOS harmonic analysis are given in Table 1 for measure
Representative plots of water level from each of the six ments and model output. Within the inlet and at Station E,
gauge locations are shown in Figure 6. Measured and calcu the difference in M amplitude is 5 em or less. The 9-cm am
2
lated water levels are presented for comparison. Time series plitude difference at Station A may owe to inaccuracies in
for Stations B, C, D, and E are presented for August 25, 1997 representation of the ebb shoal bottom topography, insuffi
(JD 237) through September 1, 1997 (JD 244). Because of cient resolution over the shoal, or non-tidal processes active
equipment problems at Stations A and F, the time series for in the area that were not included in the circulation model.
those stations are presented for different dates than Stations The 8-cm difference at Station F most likely owes to the pres
B, C, D, and E. Time series for Stations A and F are shown ence of shoals in the Halifax River that are not represented
for October 13, 1997 (JD 286) through October 20, 1997 (JD in the model (detailed and recent bottom topographic data
293). Calculated water levels generally compare well to mea were not available away from the inlet). The difference in
surements. Station A shows the largest discrepancy, with the phase between the measurements and model calculations is
model consistently underpredicting the tidal peaks and typically about 30 deg, or approximately 1 hr for an M, tide.
troughs by 2 to 4 em. The source of this underprediction is Minimum phase difference is 6 deg (0.2 hr) at Station E and
thought to be inaccurate calculation of shoaling of the tidal maximum phase difference is 40 deg (1.4 hr) at Station F.
Journal of Coastal Research, Vol. 16, No. 3, 2000
Tidal Motion, Ponce de Leon Inlet, Florida 845
Figure 4. Detail of computational finite-element grid within the study area.
Depth in meters
Contour interval = 1 m
Figure 5. Bottom topography for the study area, relative to MSL.
Journal of Coastal Research, Vol. 16, No. 3, 2000
846 Militello and Zarillo
1.5 E 1.5 Measured Station D
Ec: Measured Station A " 1.0 Modeled
0 1.0 Modeled ~
~ 0.5 m0 0.5
m0
0 0.0 00 0.0
•0 ~
t" ·0.5 ("/) -0.5
(/) ~
*~ -1.0 ~ -1.0
~ -1.5
-1.5
286 287 288 289 290 291 292 293 294 237 238 239 240 241 242 243 244 245
Julian Day, 1997 Julian Day, 1997
E 1.5 E 1.5 Measured Station E
c: Station 8 "
~ 1.0 .~., 1.0 Modeled
m>0 0.5 w> 0.5
•00 0.0 •00 0.0
t t
("/) -0.5 ("/) -0.5
•0~ -1.0 •~ -1.0
~
~
-1.5 -1.5
237 238 239 240 241 242 243 244 245 237 238 239 240 241 242 243 244 245
Julian Day, 1997 Julian Day, 1997
"E 1.5 Measured Station C E 1.5 Measured Station F
0 1.0 " 1.0 Modeled
~ ~
ill 0.5 0.5
m0
•00 0.0 0 0.0
t •0
("/) -0.5 t" -0.5
~ (/)
* -1.0 0~ -1.0
~ ~
-1.5 -1.5
237 238 239 240 241 242 243 244 245 286 287 288 289 290 291 292 293 294
Julian Day, 1997 Julian Day, 1997
Figure 6. Representative measured and calculated water level (MSL) at instrument locations.
Phase errors may also be caused by inaccuracies in the bot current speed is underpredicted at Station A, particularly on
tom topography. flood flow. Error in the calculations may owe to the same
Measurements at Stations A, B, and C show flow domi sources as discussed for water-level calculations at Station A.
nance along the E-W alignment, owing to the orientation of Another source of error is comparison of velocity from a point
the inlet. Comparison of measured and calculated E-W cur current meter to a depth-integrated calculation. A significant
rent speed at these three stations is shown in Figure 7. Pos difference in the tidal phase is evident between the measure
itive values indicate flow toward the east. Calculated E-W ments and calculated current. Because this phase error is
greater at Station A as compared to Stations B and C, the
increased error is thought to be caused by localized circula
Table 1. Comparison of measured and modeled M tidal constituents at
gauge locations. 2 tion that may not be well represented by the model. The E
W current calculated at Station B compares well to measure
Measured Modeled ments. Generally, the current is over-predicted mainly during
Station Amplitude, em Phase, deg Amplitude, em Phase, deg ebb tide. Contributing factors to the error at Station B are
general over-prediction of the current, difference between
A 59 102 50 69
B 51 91 49 70 measured and calculated tidal phase, and inexact replication
c 53 105 48 71 of tidal asymmetry. At Station C, the E-W current matches
D 45 100 47 72 well for ebb tide, but underpredicts significantly on flood tide.
E 30 90 33 84 The following section includes discussion of a flood bias of the
F 31 123 39 83
current present in the measurements that persisted for the
Journal of Coastal Research, Vol. 16, No. 3, 2000
Tidal Motion, Ponce de Leon Inlet, Florida 847
1.0 Station A 0.2 --EW Station E
"E 0.5 ,, E00 0.0 --------· NS
"' "'
w w
w w
<~n 0.0 <~n -0.2
c c
-0.5
~ ~
;(0;.:) -1.0 MMeoadseulerde d (0.) -0.4
w
-0.6
-1.5
286 287 288 289 290 291 292 293 294
Julian Day, 1997 Julian Day, 1997
0.8
" 1.0 Station 8 " r· /\ ('. /\ Station F
E ' E 0.4 .. :\
"' 0.5 "'
ww ww
Uc~) 0.0 Uc~) 0.0
~ ~
(0.) 00 -0.4 -- EW
~ -1.0 --------· NS
-0.8
-1.5 286 287 288 289 290 291 292 293 294
237 238 239 240 241 242 243 244 245
Julian Day, 1997
Julian Day, 1997
Figure 8. Representative measured current at Stations E and F. EW
"E 1.0 Station C and NS denote flow parallel to the east-west and north-south axes, re
"' spectively. Positive values indicate flow toward the east and north.
w 0.5
w
U~)
c 0.0
~
(.) -0.5 with the duration of the ebb portion of the tidal cycle exceed
;;:
w -1.0 ing that of the flood. These properties indicate that the inlet
was flood dominated during the period of measurement.
-1.5 Representative measured currents at Stations E and F are
237 238 239 240 241 242 243 244 245 shown in Fig. 8. The current at Station E flowed toward the
Julian Day, 1997 southwest throughout the duration of the data collection.
This flow direction is along the principal axis of the Indian
Fatig Sutraet i7o.n s RAe, pBr,e saenndt aCt.i vPeo msiteiavseu vraeldu easn din cdaiclcautela ftleodw Eto-Wwa crdu rtrheen te asspte. ed River North. The tidal flow is manifested as a strengthening
of the southwest flow on flood tide and reduction of the flow
to near zero at ebb tide. Peak flood current was typically
about 0.5 m/s. Because the flow was directed upstream for
duration of the data record. This bias was not simulated by the entire length of the record, there was a net influx of water
the model and contributes to error in calculation of the cur into the Indian River Lagoon North and Mosquito Lagoon
rent. system.
Station F exhibited strongly asymmetric current motion
INLET CURRENTS AND CIRCULATION PATfERNS with respect to flood and ebb tidal currents (Figure 8). Peak
Station A was located in a region of expanding and con flood current was stronger and longer in duration than peak
tracting flow as water moves out of and into the inlet and ebb current, and directed toward the northeast. The gauge
has currents that typically peak at approximately 0.5 m/s. was located in a section of the Halifax River that trends
Currents at Station B are stronger than at Station A, owing northwest and southeast, and where flow into and out of Rose
to Station B being located further into the inlet throat. Peak Bay meets the Halifax River. The easterly flow component
currents at Stations B are approximately 0.8 m/s and those during flood tide and the westerly component during ebb tide
at Station C exceed 1 m/s. Previous measurements within the may owe to a localized circulation resulting from the conflu
inlet throat have shown that the peak current is approxi ence of Rose Bay and the Halifax River. Reduction in the
mately 1 m/s (TAYLOR et al., 1996, KING et al., 1998) and the east-west flow component magnitude during peak flood rep
present measurements agree with those collected in the past. resents turning of the current. Similar to the current record
A maximum current speed of approximately 1 m/s is required at Station E, the flow is largely directed upstream, indicating
to maintain an inlet (O'BRIEN, 1969), and speeds in Ponce a net inflow of water into the Halifax River during the mea
Inlet are sufficient for maintaining the inlet. Stations A, B, · surement period.
and C have stronger flood tidal currents than ebb current The process controlling the net influx of water at Stations
Journal of Coastal Research, Vol. 16, No. 3, 2000