Tests on Arizona's New Flood Estimates

Abstract

A method for estimating regional flood frequency was prepared by R. H. Roeske of the U.S. Geological Survey (USGS) in 1978 for the Arizona Department of Transportation. Hydrologists may wish to use these regression equations for estimating flood peaks or for other purposes in development or flood control engineering. Many of those needs are for watersheds smaller than 10 sq. mi., however, for which USGS measurements are scarce. Records from two groups of small experimental watersheds near Tombstone and Flagstaff, one gaged by the U.S. Department of Agriculture's (USDA) Science and Education Administration and the other by the Forest Service, were used to independently evaluate the generalized Arizona relationships in specific applications to small watershed work. The new design floods for each experimental watershed were compared with estimates made using the USGS equation for two of the six flood frequency regions (FFR) in Arizona. The study showed that use of the generalized regional curve may underestimate flood peaks. Deviations from the curve can be caused by land use changes, differences in analytical methods, and use of short records.