Advances in Coastal Inundation Simulation Using Unstructured-Grid Coastal Ocean Models

Transcription

1 Advances in Coastal Inundation Simulation Using Unstructured-Grid Coastal Ocean Models Bob Beardsley (WHOI) Changsheng Chen (UMass-Dartmouth) Bob Weisberg (U. South Florida) Joannes Westerink (U. Notre Dame) MARICOOS Coastal Inundation Module Design Workshop September 14-15, 2006

2 Basic Requirements for Inundation Simulation (coastal flooding caused by river discharge, tides, storm surge, and tsunami processes) 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 river discharge, tidal forcing, and surface wind and pressure fields to drive the model.

3 Basic Classes of Ocean Model Grids: 1. Structured cartesian (rectangular), orthogonal curvilinear, spherical 2. Unstructured triangular, trapezoidal (geometric flexibility) Two U.S. Unstructured-Grid Ocean Models: 1. ADCIRC (finite-element) coastal ocean model (J. Westerink, R. Luettich, et al, 1992) 2. Finite-Volume Coastal Ocean Model (FVCOM) (C. Chen, H. Liu, and R Beardsley, 2003)

4 Example of ADCIRC applied to Hurricane Surge Simulation Westerink, et al, A Basin to Channel Scale Unstructured Grid Hurricane Storm Surge Model Applied to Southern Louisiana, Monthly Weather Review (in review)

5 Land BC s: 1. Upriver Tidal Propagation 2. River Discharge OBC s: 1. Tides 2. Inverted Barometer Surface Forcing: 1. Wind Stress 2. Atmospheric Pressure (Large domain approach simplifies boundary conditions, avoids tidal resonance problems in GoM, at the cost of ~ 5-10% additional grid cells/computational effort)

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8 Hurricane Betsy track and 10 minute averaged maximum marine wind speed contours from H*WIND (m/s)

9 Hurricane Betsy modeled peak storm surge elevation, with error in peak storm surge height (m) at stations. Positive error values indicate model over-prediction and negative values indicate under-prediction. Dry areas are shown in gray and levee structures are shown as brown lines.

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11 Steps taken to obtain accurate model simulation 1. Very careful adjustment of bathymetry and elevation data from different sources to common surface (steric effects). 2. Different methods used for flooding and drying of grid cells, barriers (impervious and porous), spillways. 3. Used two hurricane models to produce surface wind and pressure fields to drive model. 4. Modification of wind field over land and in land-water zone due to spatial change in surface roughness (z o ) caused by land canopy, buildings, etc. 5. Adjusted grid resolution, bathymetry/topography detail as suggested by model results and model/data comparisons. 6. Wind-wave effects on ocean roughness z o, surge elevation, and sediment/structure change TO BE ADDED.

12 FVCOM: Finite-Volume Coastal Ocean Model Key Features: An unstructured triangle grid for representing complex coastal geometry 3D primitive equations, with flow dependent turbulence closure Finite-volume (differences of fluxes) for mass, momentum, heat, and salt conservation, plus computational efficiency Provision for flooding and drying land Examples: 1. Hurricane surge simulation 2. NE regional model system for inundation simulation

13 Example of FVCOM applied to Hurricane Surge Simulation Weisberg and Zheng, What May Have Occurred Had Hurricane Ivan Made Landfall Within the Tampa Bay Region?

14 A Zoom View of the Tampa Bay Region Longitude

15 Merged Bathymetry and Topography

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17 Schematic of UMassD Regional NE Model System for Inundation Simulation/Prediction BC s NCEP North American Weather Model (NAM) Satellite SST Buoy Winds Insolation Regional Mesoscale Model (MM5,WRF) Global Wave Model BC s BC s Ocean GCM Heat Flux Wind Stress P-E U,V Form Drag Surface Wave Model SWAN U,V, Waves, Langmuir Cells Global Tidal Model Freshwater Input Local Inundation Models (FVCOM, ADCIRC,...) FVCOM Bottom Stress Satellite SST, U,V Buoy T,S,U,V,P BC s Sediment Transport Model (USGS) KEY In Development Existing Models Core Models Data

18 The Gulf of Maine/Georges Bank MM5 Weather Forecast Model System Song Hu and Zhongxiang Wu ETA/NAM Nested Region domain MM5 (resolution: 30 km) Non-hydrostatic Assimilation Air stations Buoy data Satellite data Local network Local domain Nested Local domain MM5 (resolution: 10 km) Assimilation SST (9 km) Local buoys Sites of Surface Buoys Regional domain Wind stress, heat flux, air pressure, precipitation - evaporation On-going modifications: 1. Convert the MM5 to 4 km resolution over the Gulf of Maine and 1 km resolution over Georges Bank, Mass Bay and New England Shelf 2. Convert to WRF mesoscale model

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20 256 Processors (Intel 3.4 GHz Pentium 4) 256 Gigabytes RAM, Infiniband High Speed Network 7 Terabytes disk space Third Generation Gulf of Maine FVCOM

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23 M2 tidal currents

24 Summary ADCIRC and FVCOM both use unstructured triangular grids to represent complex coastal geometries - allowing river to basin grids with sufficient horizontal resolution to capture key physical processes ADCIRC and FVCOM both feature flooding and drying - allowing them to simulate inundation associated with river, tidal, storm surge, and tsunami processes FVCOM uses finite-volume approach providing excellent local mass, momentum, heat, salt conservation FVCOM is an open community model system with support by a UMassD/WHOI development team lead by C. Chen, G. Cowles, and R. Beardsley. UMassD NE regional coupled atmosphere/ocean FVCOM system exists - which could provide starting point for regional inundation prediction system.