California StreamStats

California StreamStats provides peak-flow statistics with annual exceedance probabilities of 50, 20, 10, 4, 2, 1, 0.5, and 0.2 percent. These peak flows have recurrence intervals of 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year floods. Two reports document the regression equations used in StreamStats for estimating peak flows. The report by Gotvald and others (2012) presents equations applicable throughout California except for the southern desert region. Equations from the report by Thomas and others (1997) are available for southern desert region of California. These reports present the regression equations used to estimate peak flows, document the errors associated with the estimates, and describe the methods used to develop the equations and to measure the basin characteristics used in the equations.

• Gotvald, A.J., Barth, N.A., Veilleux, A.G., and Parrett, Charles, 2012, Methods for determining magnitude and frequency of floods in California, based on data through water year 2006: U.S. Geological Survey Scientific Investigations Report 2012–5113, 38 p., 1 pl.
• Thomas, B.E., Hjalmarson, H.W., and Waltemeyer, S.D., 1997, Methods for Estimating Magnitude and Frequency of Floods in the Southwestern United States: U.S. Geological Survey Water-Supply Paper 2433, 195 p.

Thomas and others (1997) did not develop a regression equation for the 0.2 percent probability peak flow. In areas where these equations are used, the 0.2 percent probability peak flow is determined by extrapolating the frequency curve based on a method described on page 14 in the report:

• Ries, K.G., III, 2006, The National Streamflow Statistics Program: A computer program for estimating streamflow statistics for ungaged sites: U.S. Geological Techniques and Methods Report TM Book 5, Chapter A6, 45 p.

Click on this link to obtain general information on the California application, as well as specific sources and computation methods for basin characteristics.