Simulation of Hydrology, Stream Flow, and Reservoir Levels in the Upper Russian River Watershed In Support of Forecast Informed Reservoir Operations at Lake Mendocino

Abstract:

The physics based, fully-distributed Gridded Surface Subsurface Hydrologic Analysis (GSSHA) watershed model was used to simulate hydrology and lake levels in the Upper Russian River watershed as part of a multi-agency effort to develop Forecast Informed Reservoir Operations (FIRO) for Lake Mendocino.

Coupled surface/groundwater models were developed from point and spatially distributed data sets and were driven by precipitation and meteorological forcings from various data sources including the RHONET gauge network, the California/Nevada River Forecast Center (CNRFC) gage derived data and meteorological forecasts from the Scripps Institute Center for Western Weather and Water Extremes' West-WRF model, a version of the mesoscale Weather Research and Forecast (WRF) model, set up specifically to provide forecasts for atmospheric rivers in the western United States. GSSHA models of various grid resolutions were calibrated to historical data sets and then verified to independent data.

The calibrated models were capable of reproducing US Geological Survey gauging station flows in the Upper Russian River watershed. Applying the calibrated model parameters to validation periods showed that these models are good predictors of the river flows and lake levels when compared to historical observations. The models were also useful for understanding hydrology in the basin as well as determining an annual water budget for the watershed and the reservoir. A West-WRF driven GSSHA model was capable of reproducing flows and lake levels for a 1 day forecast lead time but using forecast lead times longer than 1 day resulted in departures from the historical data sets. Physics based hydrology models are sensitive to precipitation and analysis of the West-WRF total seasonal precipitation indicated that the rainfall decreased as the forecast lead time increased, resulting in under prediction of flows to Lake Mendocino. The results indicate that an operational West-WRF/GSSHA application may be beneficial in providing information and guidance in a FIRO setting. Improvements to the West-WRF longer lead forecasts of precipitation as well as calibration of GSSHA to the different West-WRF lead time precipitation forecasts could improve the utility of such a system. These are active research topics in the FIRO program.