The effect of slope and rainfall intensity on runoff and soil erosion using a rainfall simulator

Soil erosion due to rainfall is influenced by various factors such as rainfall characteristics, slope, soil properties, land use, and other related factors. The aim of this study was to evaluate the effects of different levels of slope and rainfall intensity on runoff and sediment characteristics by using a rainfall simulator in the laboratory.

In this study, changes in parameters of runoff volume, runoff coefficient, sediment concentration, and soil erosion due to changes in two slope factors at three levels of 1, 3, and 5% and rainfall intensity factor at five levels of 45, 37.5, 30, 22.5 and 15 mm hr-1 were measured using a rainfall simulator. Analysis of variance of the parameters measured in the experiments was performed with three replications in a factorial design in a completely randomized design using SPSS 23 software. Duncan's mean comparison test was also used to evaluate the significance of the difference between the means at the level of 5%.

The results of the analysis of variance indicated the significant effects of different levels of slope and rainfall intensity on the values of the measured parameters including runoff volume, runoff coefficient, sediment concentration, and soil erosion at the level of one percent. The results of the Duncan test also showed a significant difference at the level of one percent for all measurement parameters, so that the highest and lowest increase in mean values for increasing the slope from 1 to 5 percent related to soil erosion and runoff coefficient which were equal to 182 and 5 percent, respectively. Also, the greatest change among the measurement parameters occurred in the average amount of soil erosion (116% increase) from a slope of 1 to 3% with a 41.75 gr increase in soil erosion. With increasing rainfall intensity from 15 to 45 mm hr-1, the average of all measured parameters including runoff volume, runoff coefficient, sediment concentration, and soil erosion increased by 341, 20, 635, and 446%, respectively. The highest difference between the measured parameters occurred in changing the rainfall intensity from 15 to 22.5 mm hr-1 to the extent that runoff volume, runoff coefficient, sediment concentration, and soil erosion have increased 587 ml, 7%, 2 g lit-1, and 36 g with change in rainfall intensity from 15 to 22.5 mm hr-1.

The results of the present study showed a significant difference between the mean parameters of runoff volume, runoff coefficient, sediment concentration, and soil erosion at different levels of slope and rainfall intensity treatments at the level of one percent. The highest and lowest increases in mean values for increasing slope from 1 to 5% were related to soil loss and runoff coefficient and were equal to 182 and 5% increase in their mean values, respectively. With an increase in rainfall and its intensity from 15 to 45 mm hr-1, the values of all studied variables, namely, runoff volume, runoff coefficient, sediment concentration, and soil erosion increased by 341, 20, 635, and 446%, respectively. The highest soil erosion was measured at a slope of 5% with a rainfall intensity of 45 mm hr-1, equal to 160.1 gr, and the lowest at a slope of 1% with a rainfall intensity of 15 mm hr-1 and equal to 18.2 gr.