Effects of Rainfall Duration on Hydrological Response of Field Plots under Rainfall Simulation

By increasing the intensity of rainfall, runoff, which is considered as a very important factor in soil erosion process, occurs. Climate, geometrical characteristics of watershed, geological formations, soil, vegetation and land use are among factors affecting runoff generation. Although in plots under rainfall simulation, the experiment time is more limited and the effect of rainfall duration on the results is more tangible, this effect has been less considered. The present study was therefore conducted to evaluate the effect of rainfall duration in 6 levels of 5, 10, 15, 20, 25 and 30 minutes with 3 replications under constant rainfall intensity of 40 millimeter per hour on runoff parameters including commencement time, volume, coefficient and end time and sediment concentration. The field plots under rainfall simulation located in an eastern highland slope of Kojour Watershed were selected to achieve the study purposes. The Results indicated that the runoff parameters were significantly increased (p≥0.05) with increasing rainfall duration while the rate of increase was not the same in different rainfall duration levels. In other words, under the present study conditions, the turning point of hydrological response to rainfall duration was occurred between 25-30 minutes, where the gradient of runoff parameters with rainfall duration was considerably increased. The results also showed that the sediment concentration decreased with increasing rainfall duration.