Transitioning NWS Operational Hydraulics Models from FLDWAV to HEC-RAS

The NOAA National Weather Service (NWS) Office of Hydrologic Development (OHD) is investigating two approaches to transition NWS operational hydraulic models from FLDWAV to HEC-RAS: (1) transform existing FLDWAV and DWOPER models into HEC-RAS and (2) modify and calibrate existing HEC-RAS models created for a purpose other than real-time forecasting. We evaluated these two approaches in the lower part of the Tar River, NC, and the lower Columbia River, OR. We also developed procedures and utility programs to assist with model conversions. The results are mixed. For the relatively simple Tar River, direct duplication of FLDWAV cross-sections and Manning's roughness specifications within HEC-RAS resulted in similar simulations. Also, a model built with more detailed cross-sections but the same roughness parameters from FLDWAV model could produce comparable simulation with some simple Manning's n adjustments. For the lower Columbia, approximate duplication of geometry requires more Manning's n adjustments, but still offers a viable pathway toward model conversion. Further work on the lower Columbia model is needed to see whether more precise representation of storage areas will improve results.