Supporting Folsom Dam Water Control Manual Update through the Use of the National Weather Service Hydrologic Ensemble Forecast Service (HEFS) Hindcasts (Invited Presentation)

The California-Nevada River Forecast Center (CNRFC) uses the Hydrologic Ensemble Forecasting Service (HEFS) to issue short and long range streamflow ensemble forecasts every day. These forecasts are used by a wide variety of users, including water managers, to assist in reservoir release decisions. The HEFS utilizes weather forecast information from the CNRFC quantitative precipitation forecast (QPF) and the Global Ensemble Forecast System (GEFS) to help describe short term streamflow forecasts uncertainty. Reservoir managers are able to use this information help make better informed release decisions during flood events.

Folsom Dam was able to formalize the use of HEFS forecasts by analyzing 25 years of reforecasts (hindcasts), and develop rules that have been incorporated into a new Water Control Manual. This process was a joint effort between state, local, and federal agencies including the U.S. Army Corps of Engineers, U.S. Bureau of Reclamation, the Sacramento Area Flood Control Agency, California Department of Water Resources, and the National Weather Service. This presentation will discuss the concepts of the HEFS along with results from the CNRFC’s hindcast efforts that were used by the multi-agency team to derive new flood release rules for Folsom Dam.