Virginia Institute of Marine Sciences College of William and Mary Improved Storm Surge Model Prediction Using a High Resolution Unstructured Grid Jian Shen Virginia Institute of Marine Sciences College of William and Mary

Unstructured 3D Model (UnTRIM) “UnTRIM” incorporates an Unstructured grid into TRIM model (Tidal, Residual, Intertidal Mudflat), originally developed by Vincenzo Casulli It simulates three-dimensional hydrodynamic and transport processes It uses an orthogonal unstructured grid It conserves mass locally as well as globally It uses Eulerian-Langangian transport scheme It employs semi-implicit finite difference and finite volume method- very efficient computationally It is capable of simulating wet-dry processes

Orthogonal Grid Structure Use polygons to represent a prototype estuary (3-, 4-, 5-sides) Better fitting complicated geometry in estuarine and coastal environment Using orthogonal grid simplifies the numerical algorithm

Grid Structure Water depth

Isabel Simulation Studies Study the accuracy of model prediction of Isabel forced by a stationary, circular wind model Compare model prediction with and without simulating inundation Study influence of open boundary condition specification on surge simulation still boundary condition vs. inverse pressure adjust boundary condition

Model Grids Surface element =121338 Surface element =239541

Grid layout at York and James Rivers

Model Calibration Calibrate model for tide forced by 9 tidal constituents M2, S2, K1, O1, Q1, K2, N2, M4, and M6 Model was run for 3 months and the results of the last 29 days were used for computing tidal harmonics Timestep = 5 min.

Tidal Simulation (M2 tide)

Tidal Simulation (K1)

Observation Stations

Tidal Constituents Comparison (Amplitude) Amplitude is in m Observations are based on 1992 data

Tidal Constituents Comparison (phase) Phase is in degree

Isabel Simulation Results

Comparison of Model Results (with and without inundation)

Comparison of Model Results (with and without inundation)

Influence of Open Boundary Condition Inverse Pressure Adjustment

Comparison with ADCIRC UnTrim With inverse pressure adjustment Timestep =5 minutes ADCIRC Without inverse pressure adjustment Timestep =5 sec

Comparison with ADCIRC

Conclusions Grid resolution is crucial for accurately simulating surge and inundation Wind filed is critical in accurately simulation storm surge Unstructured model is a robust tool for simulating tide and storm surge