Modifications to the ADCIRC hydrodynamic model to incorporate precipitation and inland hydrology

Flooding due to precipitation and overland runoff can significantly increase coastal water levels during a hurricane or other extreme event. To enable a “total water level” approach where these sources are included along with the more typical tidal, wind, wave, and storm surge forcings, an accumulation (source) term has been added to the Advanced CIRCulation model (ADCIRC). This term allows both distributed (precipitation) and point sources to be easily incorporated in an ADCIRC simulation. Multiple file formats can be supported for distributed rainfall over the wetted ADCIRC domain. Point sources are used to add upland, rainfall-induced streamflow by extracting streamflows from the National Water Model (NWM) and applying them at the end point of any NWM feature that terminates within the wetted ADCIRC domain. Simple test problems are used to validate that both sources conserve mass locally and result in accurate final water levels. Next, a previously vetted model, which includes high refinement of four water bodies within the Tar and Neuse watersheds, and has been used extensively in studies along the North Carolina coast, was used to compare the new methodology to the standard river flux boundary implementation during Hurricane Isabel. Results indicate that the new methodology is consistent with the flux boundary approach. Further tests with the new 120m mesh during Hurricanes Isabel and Irene allow the addition of NWM point sources and indicate that the addition of precipitation and overland runoff do improve the model performance and result in higher flood levels in the coastal regions as well as inland.