A Risk-Based Decision Support System for Flood Operations of Lake Mendocino in Water Year 2019

In November 2018 the United States Army Corps of Engineers (USACE) approved a request to incorporate forecasts into the flood operations of Lake Mendocino for water year (WY) 2019. This deviation from operations would allow water to be pre-released from storage in advance of storm events based on weather and flow forecast information. Lake Mendocino is a 111,000 acre-foot reservoir located near Ukiah, California, which is owned and operated for flood control by the USACE and is operated for water supply by the Sonoma Water. Lake Mendocino has been selected as the first pilot project for the Forecast Informed Reservoir Operations (FIRO) program, a multi-agency effort to incorporate precipitation and flow forecasts to inform the operations of reservoirs. To support Lake Mendocino operations for WY 2019, a decision support system (DSS) was developed based on the framework developed for the Yuba and Feather Rivers by the California Department of Water Resources. The Lake Mendocino DSS also includes a risk-based management tool called Ensemble Forecast Operations (EFO) that utilizes 15-day ensemble streamflow predictions issued by NOAA’s California-Nevada River Forecast Center (CNRFC). The outcomes for WY 2019 support the findings of previous studies completed for Lake Mendocino, which demonstrated that FIRO can improve water supply reliability without increasing flood risk to downstream communities. Further efforts are being planned for implementation of FIRO for WY 2020, and studies are currently underway to support modification of the Lake Mendocino Water Control Manual for permanent implementation of FIRO.