Estimating peak rates of runoff and design hydrographs from rainfall in the state of Oklahoma

Abstract

A simple method is presented for the determination of the peak rate of runoff and design hydrograph from small watersheds of drainage area up to five square miles. The principle of this study is to describe flood hydrographs observed on small watersheds by a Pearson Type III function, which has three parameters. These hydrograph parameters are then correlated to other numerical variables which describe rain storms causing the flood, topographic characteristics, soil type, and vegetation on the watershed. Three simple empirical equations from regression analysis are presented for determination of the three hydrograph parameters, peak rate of runoff, total runoff, time to mass center of area of the hydrograph from peak, which describe the complete hydrograph. The design hydrograph may be determined from the physiographic conditions and measurements obtained from topographic maps, design rainfall intensity, and total rainfall. The method is suitable for use in the design of small hydraulic structures. All the data that could be collected from the U.S.S.C.S. and the U.S.G.S. at the time of the study was utilized for the statistical analysis. The estimate of accuracy is discussed in the text. An actual hydrograph design procedure is explained step by step with a design example. The proposed method may be improved and brought up to date when new data become available, from the many hydrologic projects which have been started recently in Oklahoma. Some suggestions are given for future studies of this problem.