Data Error Effects in Unit Hydrograph Derivation

Abstract

Errors in rainfall and streamflow data cause errors in unit hydrographs derived therefrom. The effects of various types of data error on unit hydrographs derived by various methods have been examined. The data errors studied were those in the loss-rate assumption, total rainfall measurement, the discharge rating curve, base-flow separation, and time synchronization of rain gages and streamflow recorder. The methods of derivation were the harmonic, Laguerre, least squares, and gamma distribution methods. Effects of hyetograph and unit hydrograph shapes were also investigated. It was concluded that unit hydrograph shape had little effect, and that hyetograph shape had little effect except in combination with the Laguerre method, when it was of critical importance. No single method of derivation could be recommended in preference to the others. Synchronization-type data errors and the uniform loss-rate assumption tend to produce significant errors in the unit hydrograph, but the other error types caused surprisingly low errors.