1. 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

2. 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

3. 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

4. Grid Structure
Water depth

5. 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

6. Model Grids
Surface element
=121338
Surface element
=239541

7. Grid layout at York and James Rivers

8. 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.

9. Tidal Simulation (M2 tide)

10. Tidal Simulation (K1)

11. Observation Stations

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

13. Tidal Constituents Comparison (phase)
Phase is in degree

14. Isabel Simulation Results

15. Comparison of Model Results (with and without inundation)

16. Comparison of Model Results (with and without inundation)

17. Influence of Open Boundary Condition
Inverse Pressure Adjustment

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

19. Comparison with ADCIRC

20. 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