Application of a stochastic precipitation model to estimate the inflow frequency of extreme floods to Folsom Dam on the American River Basin, near Sacramento, California

The Hydrologic Engineering Center, Corps of Engineers (Davis, CA) together with MGS, Inc. (Olympia, WA) are developing a stochastic precipitation model for estimating the inflow frequency of large floods into Folsom Dam on the American River. The impetus for this study is the critical, and somewhat controversial problem, of estimating the frequency of regulated flows below the dam. These estimates will help form the basis for flood plain development below the dam; and, has implications for mitigating the flood hazard below the dam and evaluation of the adequacy of the dams outlet structures. The stochastic precipitation model is based on combing the results of a regional precipitation frequency analysis for Northern California with a storm re-sampling algorithm. The model produces realizations of possible future storms by generating possible future storm depths from depth-duration frequency curves. The storm depths are distributed basin wide by using a storm pattern obtained from a sample catalogue of historic events. The generated storms are combined with an American River Basin watershed model to derive the inflow frequency curve to the dam.