Soil erosion in gully catchments affected by land-levelling measures in the Souss Basin, Morocco, analysed by rainfall simulation and UAV remote sensing data

Abstract

Land-levelling measures are widely used in the Souss valley, South Morocco, for the implementation of land use change. However, their impact on soil erosion in this region is unclear. This paper presents the approach of combining punctual process analysis through experimental rainfall simulation and gully mapping as well as volume quantification analysing on a local scale using unmanned aerial vehicle (UAV) remote sensing data. Thus, the influence of the impacts of land levelling in the catchment area on the linear soil erosion by gullies can be elucidated. Soil surface characteristics, modified by land levelling, lead to higher runoff generation and sediment production. Mean runoff coefficients from 54% to 58% are found in levelled study sites, and 38% to 47% are found in undisturbed areas. Mean sediment loads reach 48.6gm−2 to 81gm−2 under the influence of levelling, but only 9.3gm−2 to 23.7gm−2 without it. Quantification of soil erosion by UAV data showed that a gully in a levelled study site eroded about 720m3 of soil within only one rain period. The surface of the catchment area was lowered 0.054m on average due to land levelling, whereas in study sites without land levelling, the monitoring did not show significant differences of shape and extent of the gullies at two different points in time. The strong influence of land levelling can be documented with the connection of these two methods. A clear amplification of soil erosion is induced by land-levelling measures.