A Flood Warning Model for Virginia

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Moses Carter
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1 A Flood Warning Model for Virginia Murari Paudel, Ph.D. Aquaveo LLC & Gamal Hassan, P.E. PLC

2 Summary Flood Modeling Overview Methodology Model Building Results Post Processing Information dissemination Flood Forecast Tool Challenges Model Improvement

3 Virginia Flood Model VDOT - Hampton Roads district Determine which bridge is at higher risk of flooding Total watershed area ~ 4,240 sq miles 498 bridges/culverts, 8 meteorological stations, 5 counties

4 Flood Modeling Estimating the timing and depth of flood wave Computer Simulation 1D modeling approach Solution at the cross sections 2D modeling approach Solution at each node within the active domain

5 Flood Modeling Steady State Transient Modeling

6 Flood Modeling Hydrologic and Hydraulic Integration Flow Change Locations Inflow Hydrographs Hydrology and Hydraulics in the same model

7 Flood Modeling 2D Transient Models Previously Data unavailability and limited computation resources were set backs for such models Large number of online data repositories Powerful computers at considerably low price

8 Tools Watershed Modeling System (WMS) Surfacewater Modeling System (SMS) TUFLOW Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) HEC-HMS

9 Tools WMS Geo processing of terrain, land cover and soil data Watershed delineation Raingage data preparation (Thiessen Polygons and IDW rasters) Composite CN computation HEC-HMS model parameterization and input file generation HEC-HMS Hydrologic Model SMS Hydraulic model discretization TUFLOW input parameters and model file generation TUFLOW results visualization and processing TUFLOW Hydraulic Model MS Excel Macro for some post processing Web based interactive mapping tool

10 Methodology Input Data Topography Climatology Hydrography Hydrologic Model Hydraulic Model Model Results Post-processing Software/Interface/Tools Improvements Flood Depth Time Duration Extent Web Based Interactive Flood Visualization Tool

11 Input Data VDOT Bridge Data USGS 10m DEM Data USGS Soil Maps WMS GIS Data Terrain (Tin) Rivers & Streams Watersheds Combined Watershed, Bridges, & Rainfall Distribution USGS Stream Gage Data Output Data Post Processing USGS Land Use NOAA Point Rainfall Data NOAA Forecast Rainfall Time Series Transformation Sub-Watersheds and Terrain Data HEC-HMS Sub-Watersheds Hydrographs Rainfall Data SMS TUFLOW 2-D Hydrodynamic 10 Second Time Step Web-based Interactive Bridge Flooding

12 Virginia Flood Model Hydrology basins (HEC-HMS) 2D Domain (TUFLOW)

13 Virginia Flood Model HEC-HMS Models 11 sub basins Curve Number method for losses Thiessen Polygons for rainfall distribution Clark Unit Hydrograph for transformation Calibrated to USGS stream gage data

14 Virginia Flood Model TUFLOW Model (~2220 sq mi) 50m grid cells 2.3 million cells Channel cross sections at each bridge site Roadway profile on both side of each bridge IDW rainfall grid derived from NOAA rain gage data Hydrograph inflow from 11 hydrologic basins Spatially varying overland roughness

15 Model Results The hydraulic model writes out solution datasets at each node of the grid/mesh Overland flow depth Water Surface Elevation Flow Velocity Flow Direction etc

16 Model Calibration Model Run Both the Hydrologic and Hydraulic Models were run several times to calibrate the hydraulic model to USGS stream gage data

17 Post Processing

18 Post Processing

19 Post Processing Results Processing TUFLOW gridded solution - each specified dataset - each output time interval The solution data is often huge (~4.75 GB for this model) SMS can create: Contour maps at each time step Flood extent polygons Animation showing how flooding the flooding sequence Export rasters and shapefiles to use in other GIS tools Export images and tables Developed MS Excel based macro to develop bridge flooding scenarios

20 Post Processing Uses WSE time series at each bridge site (from SMS) Compares with the bridge deck elevation Can export to Google Earth or send , plot and print time series

21 Post Processing

22 Post Processing Bridge Inundation Mapping (Online Tool)

23 Change of Plan CPU version of TUFLOW MS Windows 7 64 bit, Intel Core i7 CPU 3.6 GHz, 32 GB RAM 1 Processor 8 cores The 24 hour storm runs for ~120 hrs GPU Version of TUFLOW NVIDIA GeForce GTX CUDA cores The 24 hours storm runs for ~9 hrs CPU fewer cores optimized for serial processing GPU 1000s of smaller cores designed for parallel processing

24 Flood Forecast Tool Rainfall Forecast Hydrology Hydrographs Hydraulics Results Water Surface Elevation over Time at each bridge Location Processing Bridge inundation scenarios Processing Bridge closure schedule Calibrated Models 9 hrs 2 hrs 2 hrs 1 hr 14 hrs

25 Flood Forecast Tool NOAA forecast ~ 48 hrs Min time of concentration (depends on the location of the bridge) ~ 2 hrs ~ 50 hrs Flood forecast Model run and post processing ~ 13 hrs QA/QC ~ 2hrs Information ~ 1 hrs dissemination ~ 16 hrs Model tells if a bridge is likely to flood ~ 30+ hrs in advance

26 Challenges Large Domain Terrain Representation Available Terrain data resolution Model grid resolution Capturing channels, roads and embankments Capturing proper conveyance Computation Time and Resources To simulate a 24 hour storm event, in a descent computer the model runs for about 120 hrs Data handling Model building and geo processing Model results and post processing Linkage and Automation All-in-One magical tool not available Interaction between hydrology and hydraulic model Information dissemination Processing the results in a format usable by the emergency responders From rainfall data to bridge closure schedule

27 Future Improvements Going higher resolution (smaller grid size) Use 1D-2D coupling Use higher end GPU processors Automation Use web services to harness NOAA rainfall forecast automatically Run HMS automatically based on some rainfall threshold Fetch HMS results and feed into TUFLOW Feed rainfall into TUFLOW Run TUFLOW and extract results Post process the results and generate bridge inundation scenario Inform ( /text) about the new results for necessary QA/QC Publish the inundation and closure schedules

28 Thank You Questions??

Quality Assurance Reviews of Hydraulic Models Developed for the Central Valley Floodplain Evaluation and Delineation Program

Quality Assurance Reviews of Hydraulic Models Developed for the Central Valley Floodplain Evaluation and Delineation Program Techniques Applied and Lessons Learned Seth Ahrens, P.E., CFM Selena Forman,