Contact:  Lynn Johnson

HMT Helps Design of Russian River Hydrologic Index

Management of water stored in reservoirs requires rules to guide decisions on release amounts and timing for downstream water uses. The Sonoma County Water Agency in California has embarked on an effort to redefine the rules by which the reservoirs in the Russian River basin are operated.

The reservoir decision rules need to be redesigned due to changes in permits for diversions and requirements for maintain flows for endangered fisheries.

A hydrologic index characterizes the hydrologic conditions within a watershed, e.g., normal, dry, or critical. The hydrologic index will be used to determine reservoir releases from Lake Sonoma and Lake Mendocino to meet minimum biological stream flows and water demands within the Russian River watershed.

The HMT-West is involved in an advisory role in the development of the hydrologic index. A multi-agency advisory comprised of representatives from the SCWA, US Army Corps of Engineers, US Geological Survey, California-Nevada River Forecast Center and California Department of Water Resources are helping guide the development of the RR hydrologic index.

A computer simulation model – the HEC-ResSim model – is being used to evaluate alternative hydrologic indices using a historic record (1910 – 2009) of reservoir inflow, local runoff hydrographs, and water demand. Since the river inflows and local runoff are a result of precipitation, there is the prospect that the hydrologic index and reservoir release decisions would be informed by high resolution precipitation estimations and forecasts being developed by the HMT-West project. Efforts to install advanced gap-filling rainfall-radar and other sensors in the vicinity of the Russian River basin can help reservoir operators better schedule the reservoir releases to minimize flood risks and conserve water supply.