Changeability of soil erosion variables in small field plots from different rainfall durations with constant intensity

Rainfall duration is among the most effective characteristics of erosivity factor on runoff, splash and soil loss, especially when a rainfall duration is selected for laboratory or field plot studies. Selecting the appropriate rainfall duration particularly in laboratory studies (because of higher relative changes in lower durations), may lead to decrease the errors in the studied treatments. The rainfall duration must be well considered before any experiments exploring the effect of rainfall as one of the main factors. Therefore, the present study was conducted in field plots with area of 1 m2 located in an 18% slope, loamy-clay, under rainfall simulation with the intensity of 40 mm h−1. Total and net splashes, sediment concentration, soil loss, sheet erosion and sediment delivery ratio were measured and evaluated in 6 levels of rainfall duration (5, 10, 15, 20, 25 and 30 min), with 3 replications. The results showed that, although the runoff volume increased with increasing rainfall duration generally, there was insufficient capacity for runoff to transport the considerable amounts of the splashed and eroded soil to the plot outlet. The translocation of soil surface particles and sheet erosion were therefore increased due to more duration of rainfall and runoff, while a significant portion of the eroded soil, even after 30 min rainfall duration was not transported to the plot outlet. Based on the results, the sensitivity and efficiency of Generalized Linear Model (GLM) and Generalized Additive Model (GAM) in the evaluation of the differences between hydrological responses in various rainfall durations were different. According to the results, there was a change in the average ratio of sediment delivery in studied treatments from 0.41 to 13.03% for 5 and 30 min respectively. The results clearly showed that the duration corresponding to the intensity is the best choice to adopt soil erosion studies at plot and experimental conditions.