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Ivan-like hurricane storm surge
simulations for Tampa Bay, FL
with 3-D and 2-D models
R.H. Weisberg and L. Zheng
Storm Surge Workshop
St. Pete Beach
2/11/09
Inundation based on uniform sea level rise of:
5 ft 20 ft
Potential for Tampa Bay area inundation is
large due to land elevation and geometry
A house on the Waveland, MS coastline
water-gutted from below.
Rte 90 bridge across Bay St. Louis, MS. All
spans were knocked from their supports.
Destroyed homes in South Diamondhead, MS.
Hurricane Storm Surge Simulation
Requirements
1. A high resolution, physics-based circulation model with
flooding and drying capabilities.
2. A high resolution water depth (bathymetry) and land
elevation data set on which to overlay the model.
3. Accurate enough wind and pressure fields to drive the
model.
Here we use the Finite Volume Coastal Ocean
Model (FVCOM) of Chen et al. (2003).
Overall Model Domain and Grid
The Ivan track (red dots) and the tracks (black dots) used in
this study (with landfalls as Sarasota, Indian Rocks Beach,
Tarpon Springs, Bayport, and Cedar Keys.
Ivan Winds on approach and at Landfall
While Ivan reached category 5 in the Caribbean it was a 4
upon approach and a 3 at landfall.Category mph knots m/s
1 74-95 64-82 33-43
2 96-110 83-95 44-49
3 111-130 96-113 50-59
4 131-155 113-135 60-70
5 >155 >135 >70
Surge elevation relative to mean sea level (left) and land elevation
(middle), plus wind vectors on wind speed contours (right) 3 hours before
and at IRB landfall (hrs. 27 and 30, respectively).
Maximum IRB landfall surge relative to land at sub-domains emphasizing
St. Pete Be. (left), Old Tampa Bay (middle), and Hillsborough Bay (right).
Time series of surge height sampled at selected locations
where:
ζ is the sea level,
H=h+ζ is the total water depth,
is the surface wind stress,
is the bottom friction stress, and
is the sum of the local and Coriolis accelerations,
the advective accelerations, and the horizontal diffusion,
each calculated separately before summation.
Rρ
τ
ρ
τζgH-
0
b
0
s
bτ sτ
R
Vertically Integrated Momentum Balance
Stress Parameterizations
wwads VVρCτ
1-
w
1-
w
1-
w
-1
w
3
d
ms25.0V250.0650.49
ms25.0Vms11.0V0.0650.49
ms11.0V1.2
10C
bbwzb VVρCτ
,0.0025])H/zσ[ln(1
kmaxC
2
01kb
2
z
-3
wd 10)V067.075.0(C
H
HC b
f 1C minf
Wind Stress
3-D FVCOM Cd
2-D IPET Cd
Bottom Stress
3-D FVCOM Cz
2-D IPET Cf
Parameter Examples
Wind Stress
For 50 ms-1 wind Cd (3-D) is 2.11x10-3, whereas Cd (IPET 2-D) is 4.1x10-3
Bottom Stress
For the 3-D FVCOM used here, Cz is capped at 0.005
For IPET Katrina ADCIRC Cf (2-D) is 0.003 at 2 m depth, 0.007 at 1m
depth, and larger for shallower depths.
Hence,
The IPET 2-D ADCIRC compensates for larger bottom stress by using
larger wind stress.
Absolute (black) and percent (red) differences between 3-D and 2-D
surges at four positions from the mouth to the head of the bay.
Conclusions
1. Local:
Tampa Bay, FL is as vulnerable to hurricane storm surge
inundation as was coastal Mississippi for H. Katrina.
2. General:
A. Storm surge simulation is sensitive to model
construction: i.e., 3-D, versus 2-D. The explanation is
bottom stress. A 2-D model overestimates bottom stress,
and hence underestimates surge.
B. Calibration can mitigate this (e.g., the IPET, Katrina
analyses are excellent), but forecasts without calibration
data may be in significant error.
C. Agencies (NOAA, FEMA, USACE) employ 2-D models. Our
findings suggest the importance of 3-D.
D. Studies are necessary to improve surface and bottom
stress parameterizations.
Acknowledgments
This work began with support by ONR, grant #s
N00014-05-1-0483 and N00014-02-1-0972, and it
continues with support from NOAA, grant #
NA07NOS4730211. The second of these was for the
Southeast Atlantic Coastal Ocean Observing System
(SEACOOS), and the third is related to the Southeast
Atlantic Coastal Ocean Observing Regional
Association (SECOORA). Changsheng Chen
(UMassD) kindly shared the FVCOM code.
Coupled Wave Effects
To investigate the effects of waves on the combined surge
and waves we (with Yong Huang) coupled an unstructured
version of SWAN to the FVCOM and repeated the
experiments. The following figures show: 1) significant wave
height, radiation stress and wind stress at several times
during the simulation, 2) surge heights with and without the
wave coupling by radiation stress, and 3) surge height
differences with and without the wave coupling. To the surge
heights with wave coupling must also be added the wave
amplitude (between approximately 0.5 to 0.7 times the wave
height) to get the total vertical reach of water over the
evolution of the storm.
Surge height with/without wave radiation stress.
Surge height difference with/without wave radiation stress.
Significant wave height, radiation stress, and wind stress
Significant wave height, radiation stress, and wind stress