Runoff and Soil Erosion Under Different Soil Surface Roughness

Full Presentation Abstract
Soil erosion is a result of detachment of particles or small aggregates from the soil surface followed by transport of the detached material. One factor that affects surface runoff and soil erosion is the soil surface roughness (SSR). Engineered slopes are often left with a soil surface ‘finish’ to control runoff and erosion. Previous research shows that an increased roughness causes a decrease in runoff and soil loss, whilst other studies point towards the opposite.

To date there have been no studies into the effect of both magnitude and orientation of SSR on runoff, infiltration and soil erosion (i.e. by raindrop splash, overland flow and wind), occurring simultaneously. In this study, we compared the effects of up-down-slope oriented roughness, across-slope oriented roughness and random roughness, along with a smooth surface. We used a moderate slope gradient of 10%, a simulated rainfall intensity of 90 mm hr-1 and storm durations of 15 and 30 minutes. SSR was measured using the chain method before and after the rainfall event. Images of the soil surface were taken using a hand-held laser scanner to monitor the effect of rainfall and overland flow on the morphology. The outcome of this study shows that rainfall erosivity increases roughness of the initially smooth surface and decreases SSR of the initially rough surfaces. In the random roughness treatment, this decrease was 64% of the pre-rainfall condition. This treatment generated significantly more runoff and soil loss and less infiltration than the other treatments (p < 0.001). Contrary to expectations, the across-slope oriented roughness did not always reduce runoff and soil erosion compared to the up-down-slope orientation and the smooth surface.