PRACTICAL THRESHOLDS FOR SEPARATING EROSIVE AND NONEROSIVE STORMS

Abstract

Determination of a practical threshold for separating erosive and nonerosive rainfall events can reduce theamount of work necessary to read rainfall charts and to calculate rainfall erosivity. The objective of this study was to developa method of determining practical thresholds for erosive rainfall events and to evaluate its effectiveness for calculation oferosivity. Rainfall and runoff data measured for three plots and a small watershed from 1961 to 1969 at the Zizhouexperimental station of the Yellow River Basin in China were used. Three thresholds for separating erosive events were givenby using different types of rainfall data: (1) 12 mm for storm rainfall amount, (2) 2.4 mm h1 for average rainfall intensity,and (3) 13.3 mm h1 for the maximum 30minute rainfall intensity. All methods had less than 0.1% overall error in theprediction of the erosivity value. Peak intensity provided the greatest accuracy for separating erosive rains, followed byrainfall intensity and then rainfall amount. A total of 79%, 77%, and 88% of the total number of events were omitted fromthe calculations using rainfall amount, average rainfall intensity, and 30minute peak intensity, respectively. Any of the abovethree thresholds may be used according to data availability and desired accuracy of the erosivity estimation.