Evaluation of Erosion and Deposition Process of Soil by Using RUSLE and GIS on Wadi El Malleh Watershed, Morocco
Nasser Mohamed Eid, Asmaa
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Soil erosion by water considered as serious problem in the Mediterranean region due to the aggressive characteristics of the Mediterranean climate, the mountainous terrain, the traditional farming and other anthropogenic pressure on its land and soil. In Morocco, food security is one of the major problems which face numerous challenges including climatic uncertainties and growing population. Demand for food is increasing rapidly at the same time that available natural resources are increasingly degraded. Huge land areas are used for agriculture purposes daily which lead to deforestation. Deforestation, poor land use such as construction of buildings on agricultural land and uncontrolled techniques for cultivation are the main factors of soil erosion. Erosion affects about 13 million ha of cultivated land in Morocco and lead to huge loss of water storage capacity, about 50 million cubic meters annually. These challenges increased the need to better understand how to control soil erosion through assessment and mapping of the areas of level of risk and use soil erosion models to highlight the need of soil coverage by active green vegetation and residue and enhance watershed management. The present study was scheduled to assess soil erosion in Wadi El Malleh watershed using Geographical Information System (GIS) and the Revised Universal Soil Loss Equation (RUSLE) together with the SEDIMENTATION model to evaluate the annual average soil loss and sedimentation rate from Wadi El Malleh watershed which located in the Northern-Fez city (Morocco), and covers an approximate area of 34m2. First of all, the RUSLE and SEDIMENTATION models were combined with GIS technologies to predict the spatiotemporal distribution of erosion and deposition rates under different land uses. The different land uses were assessed using the Google Earth image, which has taken in 2013. The image was first georeferenced and projected into (Datum: Merchich North Morocco); the Moroccan coordinates system and classified by Idrisi Selva software. The use of static RUSLE model allowed the estimation of soil loss. Then the results applied in the deposition modelling calculations to assess the spread loss of soil downstream by Sedimentation model. By comparing the static and dynamic soil losses, the resulted annual average soil loss rates related to land cover type is between (0.760 to 294.41 t/ha/y) which consider a minimum annual average soil loss value in the urban areas followed by (5.726 t/ha/y) in the irrigated agriculture areas and a maximum annual soil loss value reported at the bad land. The watershed topographically characterizes by steep slopes which resulted in vulnerability to severe erosion at most of the watershed areas and caused sediment deposition. The values of the annual soil deposition rates resulted from the SEDIMENTATION model are (81.86 t/ha/y) in bad land and (-19.19 t/ha/y) in irrigated agriculture areas and (-13.66 t/ha/y) in reforestation land (the negative values means deposition). Taking into consideration the erosion and deposition processes at the same time, the low values of soil erosion calculated by the RUSLE model can be obtained. The results of this study recommends that further studies should be undertaken to identify the suitable soil and water conservation measures to eliminate soil degradation process for the whole region.