how, and how effectively, can vegetation dissipate storm surge, wave, and flooding?
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8/10/2019 How, and How Effectively, can Vegetation Dissipate Storm Surge, Wave, and Flooding?
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The Big Pictureafter Sandy in NYC
Tremendous interest in the role ofcoastal wetlands in reducingstorm surge and inundation
But, how well does coastal wetlands reduce storm surge?
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8/10/2019 How, and How Effectively, can Vegetation Dissipate Storm Surge, Wave, and Flooding?
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What role does Piermont Marsh play in reducing flooding? What are the relative roles of various species?
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Can Ecosystem Service (Healthy Marshes and Mangroves)be used to dissipate storm surge and coastal flooding?
Yes. It depends on many things:
Vegetation type, height, density, and distributionLocal bathymetry and topography
Local climate and weather wind and pressure deficitLocal hydrodynamic condition waves and currentsLocal salinity and temperature and water quality
Sediment supply Is rate of SLR ~ rate of sediment accretion? Available space for vegetation migration
Will seawalls and other structures block vegetation migration?
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Vegetation-Resolving Hydrodynamic Modeling
Improves modeling of the influence of vegetation onstorm surge, without using the empirical Manningscoefficient
Quantifies the influence of vegetation on storm surgeInvestigates vegetations performance during real storms
Some example publications:
1. Sheng, Y.P., A. Lapetina, and G. Ma (2012). The reduction of storm surge by vegetationcanopies: Three-dimensional simulations, Geophysical Research Letters , 2012.
2. Lapetina, A. and Y.P. Sheng (2014). Three-Dimensional Modeling of Storm Surge andInundation including the Effects of Coastal Vegetation, Estuaries and Coasts , 2014.
3. Lapetina, A. and Y.P. Sheng. The Influence of Vegetation on Storm Surge and CoastalInundation in the Northern Gulf of Mexico, Submitted, JGR-Oceans .
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How does vegetation affect surge & wave?
Vegetation plays a major role in coastal circulation and waveprocessesSource of drag in the water column from profile drag andskin friction, reducing mean flow and dissipate wave energy
and wave heightProfile drag and skin friction drag depend on flow speed as well as Frontal Area and Wetted Area of vegetationSource of turbulence from wake production and shear,affecting turbulent kinetic energy Sink of turbulence through dissipation
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Incorporation of vegetation processes into a 3D modelCH3D-SSMS (Sheng et al.2010, Sheng and Liu 2011,Sheng et al. 2012), alreadyincludes bottom stress, windeffects, wave effects,radiation stresses, and vortexforces
Permits the inclusion of vegetation effects such asprofile drag, skin frictiondrag, and vertical Reynoldsstresses
Includes wave effects of vegetation through two-waycoupling to SWAN (Booij etal. 1999; Suzuki et al. 2012)
How does this 3Dmodel compare tosimpler 2D model tosimulate the effects of vegetation? Ref. #2
How can the influenceof vegetation bequantified? Ref. #1 What is the effect of vegetation during a realhurricane? Ref. #3
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Y(cm)
TKE Data (cm/s)
0 0.5 1 1.5 2 2.50102030
0
0.1
0.2
X (m)
Y(cm)
TKE Model Results (cm/s)
0 0.5 1 1.5 2 2.50
102030
0
0.1
0.2
Vegetation Model Validation (Ref. #1)
Neumeier (2007) experimentReal Spartina anglica
32 cm deep water19 cm tall canopy 1200 stems/m 2
0 0.5 1 1.5 2 2.50
102030
Y(cm)
Velocity Data (cm/s)
05
1015
Y(cm)
Velocity Model Results (cm/s)
0 0.5 1 1.5 2 2.50
102030
051015
r2=0.98, rms error=0.59 cm/s
r2= 0.95, rms error=0.015 cm/s
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How well does coastal vegetation reduce storm surge?Likely varies with:
-Canopy height (cm)-Canopy width (km)-Canopy density (stems/m 2)
Consider a storm: Cat. 2, 6.71 m/s (15 mph) forward speedConsider the following canopy conditions:
Height (50, 75, 100, 125 cm)
Width (0.5, 1, 1.5 km)Density (100, 200, 300 stems/m 2)
Run the vegetation-resolving modeling system and compare the resulting TIV (TInundation Volume) and Vegetation Dissipation Potential (VDP) for various
vegetation conditions in a square basin with the following transect
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Vegetation Dissipation Potential (VDP)
= 1
0= 1
0
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Do storm characteristics affect dissipation rates? Yes, likely depends upon
-Storm forward speed -Storm intensity
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Vegetation reduced flooding during H. Ike
VegetationFree
VegetatioResolving
Domain wideRMSE
60.6 36.0Domain Wide
Average% Error
11.9% 7.6%
ChambersCountyRMSE
108.4 61.2
ChambersCounty
Average% Error
17.9% 9.6%
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Vegetation Free Mangroves Case 1:300 stems/m2, 150 cm
Vegetation reduces flooding in Miami-Dade County(maximum inundation map during Hurricane Andrew)
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Case Name Vegetation Type Vegetation Height(cm)
Vegetation Density( / )
Case 1 Mangrove 150 300
Case 2 Mangrove 300 300
Case 3 Mangrove 150 600
Case 4 Mangrove 300 600
Increasing density and height further reduces flooding
Case 1- Case 2 Case 1 Case 3 Case 1 Case 4
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What Happened to Piermont during Sandy (2012)
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Assuming 25 m/sec wind from the East
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How can we use the vegetation resolvingmodeling to predict the effectiveness of
Piermont Marsh in protecting people fromfuture flooding risk?
Conduct a forensic study of H. Sandy to assess therole of Piermont Marsh;
Conduct modeling in conjunction with the USGSSWATH field program in Piermont Marsh;
Calculate the flooding risk under current climateand future climate, using ensembles of storms
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