Water Erosion in the Watershed of Oued Tlacht (Kebdana Massif, North-East Morocco)

Abstract

Water erosion is one of the major risks that destabilize fragile environments all over the world. The loss of fertile soils and the deterioration of agricultural production are two aspects illustrating the impact of this risk on the food security of populations. In north-eastern Morocco, the watersheds along the northern foothills of the Kebdana massif are the site of soil loss triggered by sheet runoff, concentrated runoff and gullying. This phenomenon of degradation is governed by the steepness of the slope, the extensive destruction of the plant cover (steppe and matorral) and the presence of silty and sandy formations. To highlight this problem, we chose the Oued Tlacht sub-basin located east of the northern foothills of the Kebdana to carry out rain simulation measurements (intensity 80 mm / 1 hour for 20 minutes) over six plots using a ramp simulator. The problem covered by this note is to describe the manifestations of this risk and try to relate the results obtained to the factors responsible for this risk. The procedure used to tackle this problem consists in analyzing the hydrodynamic properties, the states of the soil surfaces (roughness, compactness, texture, structure, porosity, impact effect), the modes of occupation of the soil (fallow, bare soil, covered soil, worked soil, uncultivated soil), and the effect of the slope (soils plowed in the direction of the slope or not). The results obtained from the watering tests show that the runoff coefficient increases in the soils of the plots which are both unprotected by the plant-cover and unworked. The soils of these two types of land spread over enormous areas.