Streamflow Simulation Using Deterministic Model

Abstract

The National Weather Service River Forecast System (NWSRFS) model is used to generate 30 years of sequential streamflows for Laguna de Santa Rosa in northern California. The model is calibrated by simulating 11 years of daily streamflows for a 12.5 sq mi subwatershed in the upper portion of the Laguna de Santa Rosa watershed. Daily streamflow data for this subwatershed are available at a USGS gauging station. Daily precipitation values are obtained as weighted average of precipitation data at two stations in the vicinity. These are converted into a six‐hourly time series using average distribution patterns for six‐hourly precipitation. Daily lake evaporation values are estimated using regression analyses with monthly pan evaporation data for nearby stations, daily average distribution patterns, and applicable pan coefficients. These values are converted into evapo‐transpiration demand by the model using specified evapotranspiration adjustment factors. In spite of these approximations and adjustments, the calibration is satisfactory. The calibrated model is used to generate and combine daily streamflows for three tributaries of the Laguna de Santa Rosa.