Analyses of hydrologic forecasts from the US National Oceanic and Atmospheric Administration (NOAA), National Weather Service (NWS) (NOAA/NWS) Ohio River Community Hydrologic Engineering Center River Analysis System (HEC-RAS) Model for an approximate 12-month hindcast model validation period using observed precipitation and an independent five-month operational, real-time forecast period using quantitative precipitation forecast (QPF) are presented. The significant role the model played during forecast operations over the major April-May 2011 flooding period along the lower Ohio River and Mississippi River is also discussed. The model is one of many models used within the flood early warning system (FEWS)-based NWS community hydrologic prediction system (CHPS) at the NWS Ohio River Forecast Center (OHRFC). The model was developed as a cooperative effort involving the OHRFC, USGS, and USACE. The physical scope of the model, which is unique in real-time hydrologic forecasting, includes 23 locks and dams on the Ohio River and tributaries, with numerous bridges, off-channel storage areas, and lateral structures, such as levees. The model comprises over 3,100 cross sections, spanning approximately 3,200km of continuous modeled reach. HEC-RAS model-based hydrologic forecasts show improvement in terms of reduced peak stage bias, mean absolute error, and root mean square error when compared to observed USGS river stages over lumped-parameter hydrologic routing methods that are currently used operationally. Overall, verification of forecast river stages, spanning a broad range of river levels, including the timing of hydrograph peaks, is comparable between the HEC-RAS and legacy model-based routings. Validation analyses indicate improvement over a previous model implementation following the inclusion of several additional tributary inflows within the 1D hydrodynamic model framework and recalibration. Operational complications are also discussed, such as problems related to handling real-time gate operations on the Ohio River mainstem, major tributary inflows that are insufficiently modeled, and use of lateral inflows from uncalibrated Sacramento Soil Moisture Accounting (SAC-SMA) hydrologic model subbasins that flow directly into the Ohio River mainstem.
