Rainfall simulation for the study of the effects of efficient factors on run-off rate

Depending upon the watershed characteristics and weather conditions, a substantial part of the precipitation may be changed into run-off. Knowledge about the discharge and volume of the run-off generated by rainfall, especially in ungauged catchments, plays an important role in water resources management planning. In the absence of sufficient data recorded from the real rainfall events, use of rainfall simulators in the field and laboratory may be recommended to simulate run-off in different conditions of soil, vegetation cover, slope and rainfall. In this study, a rainfall simulator (a portable non-pressurized type) was used to examine the effects of slope steepness, vegetation cover, clay, sand, silt and antecedent soil moisture content on run-off amount. Two sets of simulated rainfall events with 24.5 and 32 mm/h intensity were applied on 145 experimental plots with dimensions 1.2 m × 0.89 m in Taleghan watershed, Iran, and the relevant run-off amounts were measured in each experimental plot. Based on the results obtained from the correlation matrix, the most influential factors on run-off were vegetation cover, antecedent soil moisture content, clay, sand, silt and slope, for rainfall intensity of 24.5 mm/h. While for the rainfall intensity of 32 mm/h, vegetation cover, sand, antecedent soil moisture content, silt, clay and slope were the most influential factors. Two regression equations were also developed for predicting surface run-off with different field and rainfall conditions.