Surface roughness effects on soil loss rate in complex hillslopes under laboratory conditions

Factors involved in hillslope geometry and soil erosion are still under discussion by the scientific community- and one of these factors is microtopography. In this research, the effect of surface roughness (SR) on the soil loss was investigated for different complex hillslope (CHS) systems in terms of plan shapes (convergent, parallel, and divergent) and profile curvatures (convex, concave, and straight), considering representative surface conditions of the arid steep slope region of Tahoneh Watershed, located close to the city of Yazd, Iran. The current research was conducted under laboratory conditions on three different soil types with an SR of 0.015, 0.016, and 0.018 and using a rainfall simulator under a rainfall intensity of 26 +/- 3 mm/h with a duration of 15 min. The results showed that the soil loss, as well as the sediment's arrival time into the outlet of each complex hillslope, varied with SR changes. S, oil loss decreased in each CHS, and the sediment's arrival time into the outlet was delayed with increased SR in the soil types. A significant difference (F = 51.648, P = 0.001) was obtained in the interaction between the SR and CHSs on the soil loss, as well as the sediment's arrival time into the outlet. The results of this study using these specific soils indicate that the highest soil loss reduction due to the SR can be observed in straight parallel hillslopes. We conclude that our results can give new key insights about complex geomorphological processes related to sediment mobilization at the pedon scale in arid watersheds to mitigate the negative impacts of human activities on non-straight parallel hillslopes.