Coastal Engineering 60 (2012) 84–94

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Coastal Engineering

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Observations and simulation of winds, surge, and currents on Florida's east coastduring hurricane Jeanne (2004)

Peter Bacopoulos a,⁎, William R. Dally b, Scott C. Hagen a, Andrew T. Cox c

a University of Central Florida, 4000 Central Florida Blvd., Orlando, FL, 32816, USAb Surfbreak Engineering Sciences, Inc., Winter Park, FL, 32792, USAc Oceanweather Inc., 5 River Road, Suite 1, Cos Cob, CT, 06807, USA

⁎ Corresponding author. Tel.: +1 407 823 1176; fax:E-mail address: peter.bacopoulos@ucf.edu (P. Bacop

0378-3839/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.coastaleng.2011.08.010

a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 May 2010Received in revised form 8 July 2011Accepted 30 August 2011Available online 29 September 2011

Keywords:WindsSurgeCurrentsFlorida's east coastObservationsModeling

A novel set of measurements of winds, water levels, and currents recorded in September of 2004 capturedthe landfall of Hurricane Jeanne. The dataset provides a full picture of the meteorology and hydrodynamics asso-ciated with Hurricane Jeanne and are used to test the state-of-the-art in numerical modeling of storm surge. Ashallow water equations model (ADCIRC) is driven by rigorously modeled winds and astronomic tides to repli-cate continuous hydrodynamic records at two stations, one inMelbourne Beach (Spessard) and the other insidePort Canaveral (Trident Pier), where instrumentationwas located by happenstance. Simulation results representthe time-series of water surface elevations measured in the open coast off Melbourne Beach (Spessard) within0.05 m root mean square error and within 12% of observed maximum surge elevation (1.35 m simulated vs.1.52 mmeasured) and exhibit details induced by a ‘loop’ performed by the hurricane before itmade landfall. Pre-diction of water levels inside Port Canaveral (Trident Pier) is to within 0.06 m root mean square error and in-cludes the observed forerunner and peak surge of the hurricane. In regard to nearshore currents offMelbourne Beach (Spessard), the timing of a sudden switch in the direction of themeasured (longshore) currentis replicatedwell with themagnitude of the peak current simulated towithin 14% of observation (0.96 m/smod-eled vs. 1.11 m/smeasured). The capability to accurately simulate the tidal and storm surge hydrodynamics dur-ing Hurricane Jeanne provides confidence in using this class of shallow water equations models in coastalengineering practice.

+1 407 823 3315.oulos).

rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Simulation of a unique set of measurements of the winds,storm surge, and nearshore currents generated by Hurricane Jeanne(Lawrence and Cobb 2005) is presented. As shown in Fig. 1, after un-expectedly making a loop in the open Atlantic, Jeanne made landfallon the east coast of Florida around 0400 h (UTC) on September 26,2004 with maximum sustained winds approaching 125 km/h. Landfallwas over St. Lucie Inlet.Measurements taken in the right-front quadrantduring landfall are available from two stations: Spessard Holland NorthBeach Park (Spessard) located in Melbourne Beach; and at the TridentSubmarine Pier (Trident Pier) inside Port Canaveral located about38 km to the north, as shown in Fig. 1.

2. Observations

2.1. FCFP Station Spessard

By happenstance, measurements from Spessard Holland NorthBeach Park were being collected as part of an ongoing effort to devel-op long-term nearshore wave and wind information for the state ofFlorida. As part of the ‘Florida Coastal Florida Project’ (FCFP), a Tele-dyne RD Instruments Sentinel® Acoustic Doppler Current Profiler(ADCP) was permanently installed approximately 610 m from thebeach, at a mean water depth of ~8.5 m. The ADCP was mounted ona stainless steel pipe that was jetted into the sea floor, and its sur-veyed elevation was −7.844 m NAVD88 (North American VerticalDatum of 1988). Directional wind data were collected using an R.M.Young® anemometer. The instrument was attached to the top of a10-m-tall tower, installed on the crest of the dune bluff at the site.The shoreline in the vicinity has an orientation nominally 20° counter-clockwise from north–south. A complete description of the SpessardStation is provided in Dally and Osiecki (2005).

Data measured at Spessard are presented in Fig. 2 (wind speedsand directions) Fig. 3 (water levels), and Fig. 4 (current speeds and

Fig. 1. Hurricane Jeanne (12-hourly storm track: September 14–29, 2004) in western North Atlantic Ocean with eventual landfall on Florida's east coast. Inset shows landfall onSeptember 26, 0400 hours (UTC) over St. Lucie Inlet with modeled winds (in right-front quadrant of hurricane) approaching 125 km/hr and locations of two observation stations(Spessard and Trident Pier).

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directions). Data are shown for September 13–October 1 to includethe storm event itself and, for contrast, the time periods before andafter the storm. Herein, wind directions are reported as the direction

Fig. 2. Wind measurements at Spessard in comparison to modeled wind input for ADCIRC asarg(Uw,Vw).

from which the wind blows, in° measured clockwise from true north.During Hurricane Jeanne's loop in the open Atlantic (September 20–24), the winds were steady at about 9 m/s, gradually transitioned

interpolated to mesh node nearest Spessard: (a) speed mod(Uw,Vw); and (b) direction

Fig. 3.Water level measurements at Spessard compared to (a) predicted astronomic tides and (b) fully simulated (tides+surge) elevations. Predicted astronomic tides are obtainedby resynthesis of tidal constituents known for Trident Pier. (c) Plot of difference, Δ, of measured water levels minus predicted astronomic tides. (d) Plot of difference, Δ, of measuredwater levels minus fully simulated (tides+surge) elevations.

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from east-northeast (~60°) to north. Winds then increased to almost15 m/s as landfall approached (September 26), but unfortunately, theanemometer system failed during landfall.

Water level data were provided by the ADCP's pressure transducer.These data have been adjusted for variation in barometric pressureusing simulated pressure-field data (detailed later). Fig. 3a plots themeasurements against a resynthesis of 37 tidal constituents correspond-ing to a National Ocean Service (NOS) observation station at Trident Pier(detailed later). The predicted tide oscillates about NAVD88 withamplitude around 0.6 m. Starting on September 20th and continuingthrough the 25th, the increase in onshore winds caused a distinct risein the mean water level which persisted as the storm performed itsloop in the open Atlantic. Landfall on the morning of the 26th wasmanifested by the almost complete masking of low tide, after whichthe tide fluctuation and mean water level returned to normal. Thesurge peaked during times of high tide with the initial surge peakbeing 1.52 m and the second surge peak being 1.39 m.

Currents measured by the ADCP tend to follow the winds (Fig. 4 vs.Fig. 2) but clearly are constrained in direction by the close proximity ofthe shoreline. During the time when Hurricane Jeanne made its loop inthe open Atlantic (September 20–24), currents were directed to

the south-southeast (~160°) at speeds of 0.1–0.3 m/s. However, uponlandfall (September 26), currents switched abruptly from being direct-ed towards the south-southeast (peak magnitude of 0.86 m/s) to thenorth-northwest (peak magnitude of 1.11 m/s). After landfall, the cur-rents subsided quickly.

2.2. Trident Pier

A second set of wind measurements (Fig. 5) and water levels(Fig. 6) is available from an NOS observation station #8721604(Trident Pier) in the Trident Submarine basin located inside PortCanaveral. Wind speeds and directions are obtained from NOS'sCenter for Operational Oceanographic Products and Services (websitehttp://tidesandcurrents.noaa.gov/ accessed on March 26, 2010) athourly intervals for September 13–October 1. Note that Trident Pieris not in a marine exposure, so the observed wind speeds have beenmodified for land exposure using the directional roughness coeffi-cients andmethodology described in Powell et al. (2004). At this loca-tion, winds fluctuated around 5 m/s during Hurricane Jeanne's loop inthe open Atlantic (September 20–24) and then increased to almost25 m/s around the time of landfall. The wind record also shows, in

Fig. 4. Currents measured at Spessard versus simulated currents: (a) speed mod(Uc,Vc); and (b) direction arg(Uc,Vc). Plots of (c) difference, Δ, of measured minus simulated currentspeed and (d) significant wave heights Hs measured at Spessard.

Fig. 5.Winds measured at Trident Pier versus modeled wind input for ADCIRC as interpolated to mesh node nearest Trident Pier: (a) speed mod(Uw,Vw); and (b) direction arg(Uw,Vw).

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Fig. 6. ADCIRC finite element mesh for Western North Atlantic Tidal model domain including South Atlantic Bight coast (Florida, Georgia, and Carolinas). Inset shows details aroundlocal region of interest, including St. Lucie Inlet and two observation stations (Spessard and Trident Pier).

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general, that the winds came from the north before landfall and fromthe south after landfall, as would be expected in this situation.

A tide gauge was also located at the south end of the Trident Pier.This gauge was an Aquatrak® acoustic sensor installed inside a 4-inch-diameter protective well (National Oceanic and AtmosphericAdministration/NOS 1998). The tide gauge has provided water leveldata since 1994, fromwhich a set of 37 tidal constituents has been de-rived by NOS. A resynthesis of these constituents is shown in Fig. 6aanalogous to that presented in Fig. 3a. Trends generally mimickedthose observed at Spessard; however, the behavior of the surgelevel during landfall was notably different between the two observa-tion stations with the high tides being higher at Trident Pier than atSpessard and the low tide on the morning of Hurricane Jeanne's land-fall being more evident in the Trident Pier record than in the Spessardrecord (detailed later).

3. Atmospheric modeling

Wind (30-minute sustained) and pressure information used to drivethe ADCIRC model (detailed later) were obtained from the MORPHOSproject (Hanson et al. 2007). Wind and pressure fields were computedusing the Interactive Objective Kinematic Analysis (IOKA) system (Cox

et al. 1995) where tropical storm winds from a reanalysis performedusing the H⁎Wind system (Powell et al. 1998) and local measurementswere blended into a synoptic-scale wind and pressure field providedby the National Center for Environmental Protection Global ForecastSystem (NCEP GFS). A tropical model, herein referred to as TC96(Thompson and Cardone 1996), governed by vertically integratedequations of motion that describe horizontal airflow through theplanetary boundary layer (Cardone et al. 1994), was applied to eachtropical system within the computational domain to provide pressurefields complementary to the IOKA/H⁎Wind wind fields. TC96, whichcalculates snapshots (in time) that represent distinct phases of thestorm's evolution, was driven by the National Hurricane Center/TropicalPrediction Center track and intensity information as well as by dataobtained from hurricane hunter aircraft and analyzed by the HurricaneResearch Division Wind Analysis System (Powell et al. 1998).

Localwindmeasurements including buoys, coastalmanned stations,and coastal land stations were assimilated into the IOKA system to pro-vide local-scale wind response over the impacted area. Fig. 7 displaysavailable marine data with a hand-drawn analysis of the wind speedisotachs where the core of the wind field within Hurricane Jeanne isprovided by the H⁎Wind solution. Source H⁎Wind wind fields withinthe core of the storm range in resolution from 1.5 to 2 km.

Fig. 7. Wind field analysis during Hurricane Jeanne for 0600 hours (UTC) on September 26, 2004. Isotachs (knots, 30-minute average, 10 meters above the surface) blended fromH*Wind snapshot and IOKA background field.

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4. Hydrodynamic model description and setup

ADCIRC-2DDI is the depth-integrated version of the hydrodynamiccode ADCIRC (Kolar et al. 1994a; Luettich and Westerink 2006b;Westerink et al. 2008). ADCIRC solves the shallow water equationsin the form of the Generalized Wave Continuity Equation (GWCE)(Kinnmark 1985; Kolar et al. 1994b; Lynch and Gray 1979) using a con-tinuous Galerkin finite element method applied over linear triangles.Time discretization uses a three-level implicit scheme.

4.1. Finite element mesh

The Western North Atlantic Tidal (WNAT) model domain de-scribes the Caribbean Sea, the Gulf of Mexico, and the westernNorth Atlantic Ocean found west of the 60° west meridian (Hagenet al. 2006). A high-resolution (10–100 m, in general) representationof the full estuarine waterbody environment of the South AtlanticBight coast (Florida, Georgia, and the Carolinas) is incorporated intothe WNAT model domain (Bacopoulos et al., 2011). Locally, thispermits for the inclusion of St. Lucie Inlet as well as of all of theother inlets along the South Atlantic Bight coast (64 in total). Fig. 8presents the finite element mesh along with a detailed inset of thelocal region of interest. Mesh resolution at Spessard is ~500 m andat Trident Pier is ~100 m. Certainly, there are regions of meshwhere the nodal spacing is finer than the resolution of the wind andpressure fields, but in such areas the resolution of the mesh is dictatedby factors other than meteorological forcing, such as complexities incoastal configuration and variations in bathymetric depths.

4.2. Initial conditions and boundary conditions

The model begins from a cold start (still water condition and equi-potential surface at NAVD88). Boundary conditions are ramped overthe first 0.5 d and include tidal elevation forcing on the open bound-ary and no-normal flow constraints (with free tangential slip) along

all coastlines. Seven principal tidal constituents (K1, O1, M2, S2, N2,K2, and Q1), interpolated from the global ocean model of Le Provostet al. (1998), constitute the tidal elevation forcing. Tidal potentialforcings for these same seven constituents are applied over the inte-rior of the model domain. Wind and pressure forcing are also appliedover the model domain interior temporally interpolated between 30-minute snapshots of the modeled winds and pressures.

4.3. Atmospheric forcing

Wind forcing is applied as a surface stress using the quadratic draglaw proposed by Garratt (1977) to convert wind speeds to windstresses:

τs=ρw ¼ ρaCDV210=ρw and CD ¼ μ 0:75þ 0:067V10ð Þ=1000

ð1aÞ and ð1bÞ

where τs=wind stress; V10=10-minute sustained wind speed acting10 m above the surface [in units of m·s–1]; ρw=density of seawater;ρa=density of air; CD=wind speed-dependent drag coefficient;and μ=user-specified multiplier. The drag coefficient is capped atCD≤0.0035. The 30-minute sustained winds are converted to 10-minute sustained winds by multiplying by a factor of 1.09 to accountfor the expected higher wind speed variability at shorter time scales(Powell et al., 1996). As a result, in Eq. (1b) the multiplier μ is set to1.3, i.e., 1.093.

Pressure forcing is applied as an inverted barometer effect whichtransforms atmospheric pressure deficit (in stress units) into equiva-lent water column heights (in length units):

ζp ¼ pamb−pð Þ=ρwg ð2Þ

where ζp=equivalent water column height; pamb=ambient atmo-spheric pressure (1013.25 hPa); p=local atmospheric pressure;ρw=density of seawater; and g=acceleration due to gravity.

Fig. 8. ccb.

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4.4. Bottom friction

Bottom friction is represented in ADCIRC using a quadratic rela-tionship and a depth-dependent drag coefficient (Luettich et al.1992):

τb;x ¼ ρwCf

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiU2 þ V2

pU ; τb;y ¼ ρwCf

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiU2 þ V2

pV

and

Cf ¼ Cfmin1þ Hbreak=Hð Þθh iγ=θ

ð3a and 3bÞ

where τb,x and τb,y=bottom stress in the x (longitudinal) and y (lat-itudinal) directions; Cf=bottom friction coefficient; U and V=depth-integrated velocities in the x (longitudinal) and y (latitudinal) direc-tions; Cf,min=0.0025=minimum bottom friction coefficient; Hbreak=break depth (=10m); H=total height of the water column, i.e.,CfbCf,minwhenHbHbreak and Cf=Cf,min whenH≥Hbreak; θ=dimension-less parameter controlling how rapidly Cf approaches its upper andlower limits (=10); and γ=dimensionless parameter controllinghow quickly Cf increases as H decreases (=⅓). These parametervalues have been used in prior tidal simulations for this model domain(Bacopoulos et al., 2011). As examples, Spessard is located in a waterdepth of ~8.5 m, and thus Cf=0.0027 at Spessard, and Trident Pier is

located in a water depth of ~5.0 m, and thus Cf=0.0032 at TridentPier. Cf can be related to Manning's roughness n using the relation(Atkinson et al. 2011):

Cf ¼ gn2=H1=3 ⇔|{z}algebra

n ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiCf H

1=3=gq

ð4Þ

where n=Manning's roughness. At Spessard, Cf=0.0027 and H=8.5 m which yields n=0.024 s/mF, and at Trident Pier, Cf=0.0032and H=5.0 m which yields n=0.024 s/mF. Manning's n value of0.024 s/mF is in the middle of the range for open water (Arcementand Schneider 1989): nlower=0.020 s/mF and nupper=0.030 s/mF.

4.5. Other settings

ADCIRC is configured to run in fully nonlinear mode by enablingthe nonlinear bottom friction detailed above, nonlinear finite ampli-tude effects (Luettich et al., 1992), and nonlinear advective accelera-tion terms. A wetting and drying algorithm within ADCIRC (Dietrichet al. 2006) is enabled. Minimum wetted bathymetric depth is set to0.01 m, i.e., computational nodes and the accompanying elementswith water depths less than the minimum wetted bathymetricdepth are considered to be dry. The minimum velocity which willpermit flow to propagate into a dry element is set equal to 0.01 m/s.Note that very few nodes in the computational mesh are above

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NAVD88, and wetting and drying becomes activated only in the lim-ited cases where local water level is greater than local bathymetricdepth. Horizontal eddy viscosity in the depth-integrated momentumdispersion (Luettich and Westerink 2006b) is set to a constant anduniform value of 5.0 m2/s, an appropriate setting for open water(Bunya et al. 2010). The GWCE weighting parameter τ0, whichweights the relative contributions of the primitive-continuity andpure-wave forms of the GWCE (Kolar et al. 1994b; Lynch and Gray1979), is set equal to 0.005 when the water column height H ≥10 m and 0.020 when the water column height Hb10 m (Luettichand Westerink 2006a). The model simulates shallow water flow(solving for water surface elevation and depth-integrated velocities)for 18 d (September 13–October 1, 2004) using a time step of 0.25 s.Model setup is summarized in Table 1.

5. Results and discussion

5.1. Winds

Figs. 2 and 5 show time-series of modeled winds that are input forADCIRC as interpolated to the mesh nodes nearest Spessard (locatedwithin 500 m) and Trident Pier (located within 100 m), respectively.At Spessard, modeled wind speed and direction track the measure-ments well but with slight under-prediction in speed as the storm be-gins to make landfall. At Trident Pier, peak wind speeds (~25 m/s) areslightly lower than at Spessard due to the greater distance from thehurricane's core. For both of the available wind records, there is excel-lent agreement to the data, including during the peak of the hurricaneat Trident Pier, which is exemplary of the quality of the wind forcing.

Table 1Hydrodynamic model setup.

Name Notation Setting

Wind drag multiplier μ 1.3Run length – 18 dTime step Δt 0.25 sInitial conditions – Still water condition and

equipotential surface at NAVD88Boundary conditions(open)

– Tidal elevation (K1, O1, M2, S2,N2, K2, Q1)

Boundary conditions(closed)

– No-normal flow with freetangential slip

Boundary conditions(interior)

– Tidal potential (K1, O1, M2, S2, N2,K2, Q1) and winds+pressures

Forcing ramp – 0.5 dMinimum bottom frictioncoefficient

Cf,min 0.0025

Break depth (control) Hbreak 10 mBreak depth (sensitivity) Hbreak 1 m and 15 mDimensionless bottomfriction parameter

θ 10

Dimensionless bottomfriction parameter

γ F

Nonlinear bottom friction – EnabledNonlinear finite amplitudeeffects

– Enabled

Nonlinear advective terms – EnabledMinimum wettedbathymetric depth

h0 0.01 m

Minimum wetting velocity Vmin 0.01 m/sHorizontal eddy viscosity(control)

νT 5 m2/s

Horizontal eddy viscosity(sensitivity)

νT 0 m2/s and 50 m2/s

Generalized wavecontinuity equation

τ0 0.005 (if H ≥ 10 m)

weighting parameter 0.020 (if H b 10 m)

5.2. Water levels

Water levels measured at Spessard are adjusted for variation inbarometric pressure. The simulated pressure-field data are interpolat-ed to the mesh node nearest Spessard (located within 500 m) andused for adjustment, which is applied using the inverted barometereffect provided by Eq. (2). For pbpamb, i.e., positive pressure deficits,the adjustment ζp is positive, and vice versa. Over most of the data re-cord, the adjustment ζp is on the order of ±1 cm but does reach up-wards of +30 cm during landfall.

Simulatedwater levels are compared to observations at both Spessardand Trident Pier (Figs. 3 and 6). Added to the simulatedwater levels is aresynthesis of the two seasonal constituents, SA=solar annual andSSA=solar semi-annual, which is done to account for seasonal effects(baroclinic processes and radiational heating) that are not directly in-cluded in the model. The amplitude of the SA constituent is 9.7 cmand the amplitude of the SSA constituent is 6.2 cm. At landfall, the SAand SSA constituents were in a phase such that they contributed a com-bined 7.9 cm of increase in water surface elevation.

Simulated water levels show excellent agreement to the measure-ments at Spessard (Fig. 3b). The tidal signature is well-recognizedand describes most of the water level variability during non-meteorologically active periods, but is still evident even during thestrongest effect of the hurricane. With respect to meteorologicallyactive periods, the model captures: 1) the ‘superelevation,’ i.e., the in-creased steady water level, of about 0.4 m from September 20ththrough the 25th; and 2) the double peak in surge. The initial peak insurge was replicated to within 12% of its observation (1.35 m simulatedvs. 1.52 mmeasured), with the second peak replicated to within 12% ofthe observation (1.23 m simulated vs. 1.39 m measured). When calcu-lated over the entire data record, root mean square error is 0.05 m.

Fig. 3c shows a plot of the difference Δ equal to measured waterlevels minus predicted astronomic tides and Fig. 3 d shows a plot ofthe difference Δ equal to measured water levels minus fully simulated(tides+surge) elevations. The oscillatory behavior of the Δ curves isdue the tendency of the model to produce tides that are lower thanthose measured, as well as slight phase difference, and will beinvestigated below. Nevertheless, the consistent difference of ~0.4 mbetween measured water levels and predicted astronomic tides fromSeptember 20th through the 25th,which is the ‘superelevation’ referredto earlier. This is followed by a difference of approximately 1.9 maround the time of landfall, which represents the true storm surge.The mean difference between measured and simulated water levels issmall but with a slightly positive bias that is associatedwith themodel'sdiscrepancy at low tides.

At Trident Pier, fully simulated (tides+surge) elevations agreewell with the measured water levels (Fig. 6b) and tend to display be-havior similar to that from Spessard (Fig. 6 vs. Fig. 3). When calculat-ed over the entire data record, root mean square error is 0.06 m. Thesame double peak in surge occurs at Trident Pier; however, it was inopposite fashion as it occurred at Spessard where the initial peakwas lower than the second peak: the model replicates this to within28% on the initial peak (1.37 m simulated vs. 1.89 m measured) andto within 14% on the second peak (1.23 m simulated vs. 1.43 m mea-sured). Fig. 6c shows a plot of the difference Δ equal to measuredwater levels minus predicted astronomic tides and Fig. 6 d shows aplot of the difference Δ equal to measured water levels minus fullysimulated (tides+surge) elevations. Trends at Trident Pier are simi-lar trends as to those found at Spessard.

Tidal behavior during landfall is notably different at the two obser-vation stations, with the high tides being higher at Trident Pier thanat Spessard. Surge elevation initially peaks at Spessard at 1.52 mwith a second peak at 1.39 m, whereas at Trident Pier, first at1.43 m and then at 1.89 m. Also, the low tide on the morning of Hur-ricane Jeanne's landfall is more evident in the Trident Pier record, incontrast to the near complete masking of low tide at Spessard.

Table 2Harmonic analysis of observed and simulated records for Spessard and Trident Pier. i=count; Ci= ith constituent; Ai= ith amplitude; φi= ith phase; obs=observation; mod=sim-ulation; diff=difference; Σ5=summation of M2, N2, S2, K1, and O1 observed amplitudes; Σ=summation of all 35 observed amplitudes; and Ai,obs,%= ith observed amplitude ÷summed observed amplitudes.

i Ci σi Spessard Trident Pier φi,diffb

Ai,obs Ai,obs,% φi,obs Ai,sim φi,sim Ai,diffa φi,diff

a Ai,obs Ai,obs,% φi,obs Ai,sim φi,sim Ai,diffa φi,diff

a

°/h m % ° m ° m ° m % ° m ° m ° °

1 O1 13.94 0.07 7 202 0.08 212 0.01 10 0.08 8 207 0.08 209 0.00 2 3572 K1 15.04 0.10 10 214 0.10 198 0.00 344 0.10 10 200 0.10 196 0.00 356 3583 N2 28.44 0.10 10 333 0.11 349 0.01 16 0.12 13 346 0.12 348 0.00 2 3594 M2 28.98 0.50 47 359 0.49 4 0.01 5 0.51 53 7 0.50 3 0.01 356 3595 S2 30.00 0.09 9 39 0.08 11 0.01 332 0.08 8 27 0.09 10 0.01 343 359Σ5 0.90 82 0.90 91Σ 1.05 100 0.98 100

a Difference: for amplitude=−simulated – observed|; and for phase=simulated – observed.b Difference=simulated phase (Trident Pier) – simulated phase (Spessard).

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Measured low tide during landfall at Spessard was 0.76 m with themodel estimating 0.65 m. At Trident Pier, measured low tide duringlandfall was 0.6 m whereas the model estimated 0.3 m.

5.3. Harmonic analysis

Harmonic analysis reveals the source of at least some of the dis-crepancy in predicting low tide and tidal phase at both Spessardand Trident Pier. Table 2 presents the amplitudes and phases for 35tidal constituents extracted from both the observed and simulated re-cords at Spessard and the simulated record at Trident Pier usingT_TIDE (Pawlowicz et al. 2002). Observed tidal constituents for Tri-dent Pier are taken from those published by NOS's Center for Opera-tional Oceanographic Products and Services (website http://tidesandcurrents.noaa.gov/ accessed on June 10, 2011). The NOStidal constituent dataset (total of 37) is different from the T_TIDEtidal constituent dataset with respect to tidal frequency; however,many of the NOS tidal frequencies (24 of them) are the same as theT_TIDE tidal frequencies. Focus is on the M2, N2, S2, K1, and O1tidal constituents since together they constitute the majority of theoverall signal in terms of cumulative amplitude vs. overall amplitude:82% at Spessard and 91% at Trident Pier. For these top five constitu-ents, the greatest difference between observed amplitude and simu-lated amplitude is only 1 cm (true for both Spessard and TridentPier). This is confirmed in Figs. 3b and 6b in that the tidal ranges ofthe observed signals are very near the tidal ranges of the simulatedsignals. There is some disparity between the observed and simulatedphases. At Spessard, phase difference equals 10 and 344 [−16]° forthe diurnal constituents (O1 and K1) and phase difference equals 5,16, and 332 [−28]° for the semi-diurnal constituents (M2, N2, andS2). In contrast, at Trident Pier, phase difference is within 4° for thesame constituents except for S2 which has a phase difference of 17°.The magnitude of the phase difference of M2 (with tidal frequencyσ equal to 28.98° per hour) is φ=5° which calculates to a time differ-ence T(=φ ÷ σ) of 10 min.

Fig. 9. Bottom friction coefficient Cf versus bathymetric d

5.4. Currents

Fig. 4 shows plots of simulated currents as compared to measure-ments at Spessard. Comparisons are not performed for Trident Piersince no record of currents is available for that station. At Spessard,simulated current speeds were 0.1–0.3 m/s for September 20–24(when Hurricane Jeanne performed its loop in the open Atlantic)and follow the observations closely, both in overall magnitude andfluctuations. Upon landfall, the model captures the observed direc-tional switch in currents within the two-hour resolution of the mea-surements. Peak velocities before and after the directional switch incurrents are slightly under-predicted: initial peak at 0.81 m/s simula-tion versus 0.86 m/s measurement (6% error) and second peak at0.96 m/s simulation versus 1.11 m/s measurement (14% error). Simu-lated current directions match the observations quite well, whichare constrained to either 160 or 340° because of the close proximityto the shoreline which is oriented ~20° counterclockwise of duenorth.

When calculated over the entire 13 d of the data record, root meansquare error is only 0.05 m/s. Fig. 4c shows a plot the difference Δequal to measured minus simulated current speeds, which showsthe largest positive difference of ~0.3 m/s occurring around the timeof landfall and the largest negative difference of ~0.2 m/s occurringduring the recession of the surge event. The under-prediction ofpeak velocities correlates with the largest significant wave heights(~4.2 m) recorded at Spessard (Fig. 4d). It is plausible that duringthe peak of the storm, when the waves were at their largest, theADCP was actually in the tail of the wave-driven longshore current,which would explain the under-prediction of the peak currents.

5.5. Sensitivity tests

Sensitivity tests are performed with respect to the settings of thebreak depth Hbreak used in the bottom friction formulation (Eq. 3b)and the horizontal eddy viscosity νT used in the depth-integrated mo-mentum dispersion (Luettich and Westerink 2006b). As a reference,

epth h for different values of break depth (Hbreak).

Fig. 10. Simulated current speeds mod(Uc,Vc) for different break depth (Hbreak) values.

93P. Bacopoulos et al. / Coastal Engineering 60 (2012) 84–94

Hbreak of 10 m is used, and for sensitivity, Hbreak of 1 m and 15 m areused. For eddy viscosity, a reference value νT of 5 m2/s is used, andfor sensitivity, νT of 0 m2/s and 50 m2/s are used (Table 1).

Fig. 9 shows a plot of the bottom friction coefficient Cf as a functionof the bathymetric depth h (proxy for the total height of the watercolumn H) for different values of the break depth Hbreak (Eq. 3b).Note the increase in Cf for decreasing h values below the controlvalue of Hbreak. Cf is at its minimum value (0.0025) for h values greaterthan the respective value of Hbreak and Spessard is located in waterdepth of ~8.5 m.

Fig. 10 shows a plot of simulated currents at Spessard using differ-ent Hbreak values (1, 10, and 15 m). The curves lie nearly on top of oneanother. Sensitivity to break depth is slight. For horizontal eddyviscosity, there is virtually no sensitivity (not shown, but tested fordifferent νT values: 0, 5, and 50 m2/s). This suggests that the currentsat Spessard are not controlled by either Hbreak or νT and that tides andmeteorology are dominating the local flow, as should be expectedgiven the open-coast location of the Spessard site. Future work shouldlook into quantifying the momentum balance and its components,including bottom friction and horizontal eddy viscosity [turbulenceclosure], to further understand the physics of the flow.

6. Summary and conclusions

The present state-of-the-art in modeling of hurricane-inducedwinds, surge, and nearshore currents has been rigorously testedusing unique data collected during the landfall of Hurricane Jeanneon Florida's central Atlantic coast in September 2004. The IOKAwind fields developed for the storm replicate the anemometer re-cords available from both Spessard and Trident Pier reasonably well(Figs. 2 and 5), and when used to drive ADCIRC result in faithful esti-mates of 1) surge level at both locations (Figs. 3 and 6), and 2) near-shore currents measured by the ADCP at Spessard (Fig. 4).

Given the complex behavior of the storm, e.g., the loop it madeprior to landfall, and the number of detailed steps required by themodeling progression, the overall results are remarkable and encour-aging. The fact that all parameters used in ADCIRC were standard, de-fault values and that no additional calibration was required isnoteworthy. Small differences between measured and modeledwater levels at Spessard (Fig. 3d) are attributed more to the modelingof astronomic tides than to modeling the storm-induced surge. Basedupon prior experience with ADCIRC, some additional improvement inthe storm surge prediction at Trident Pier (Fig. 6d) might be gainedby refinement of the mesh inside Port Canaveral.

Comparison of the IOKA-driven ADCIRC results to the nearshorecurrents measured during Jeanne (Fig. 4) is believed to be trulyunique, and is made possible only by the deliberate use of an acousticcurrent profiler at the Spessard station. Although the model compar-ison to the observed currents is generally satisfactory, improvementduring the very peak of the storm might be possible if wave-induced

forcing were to be included. This, as well as modeling the nearshorewaves themselves (Fig. 4 d), are likely topics for future work.

Acknowledgements

The authors acknowledge the many agencies and individuals thatsupported various components of this study. Data collection at FCFPStation Spessard in Melbourne Beach was conducted by Mr. DanielOsiecki (formerly of Surfbreak Engineering Sciences, Inc.) and wassponsored by the Florida Department of Environmental Protection(FDEP), Bureau of Beaches and Coastal Systems. Wind and pressureforcing for Hurricane Jeanne was developed under the MORPHOS pro-gram, established by the U.S. Army Corps of Engineers (USACE). W. R.Dally wishes to thank the Program for the Study of Developed Shore-lines, Western Carolina University, for its support during the develop-ment of this paper. The Institute of Simulation and Training at theUniversity of Central Florida (UCF) contributed computer time to per-form the hydrodynamic simulations. The statements, findings, con-clusions, and recommendations are those of the authors and do notnecessarily reflect the views of FDEP, USACE, UCF, or their affiliates.

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