A Modeling Approach to Soil Erosion Control and Management Using PAP/RAC Model and GIS: A Case Study of Boufekrane Watershed, Morocco

Abstract

Erosion by water remains the predominant form of land degradation in the world and accounts for 84% of affected areas. More particularly, the Mediterranean costal region is recognized to be of extreme fragility to erosion. Studies estimated that Morocco agriculture represents almost 20% of its annual GDP, which makes it more concerned with the issue of soil erosion which is recognized to significantly affect crop productivity. The area under study, Boufekrane, is an agricultural area where cultivations (including cereals and tree crops) and other activities such as grazing and livestock account for more than 80% of the total watershed area. The overall purpose of this study was to evaluate soil erosion in Boufekrane watershed located in the eastern part of the plain of Sais (Morocco). Prioritization of the watershed in terms of erosion risk magnitude and expansion trends was made using ArcGIS and qualitative approach called PAP / RAC. It consisted to integrate major causative factors recognized to influence water erosion. In this study, slope, lithology, pedology, vegetation cover and land use were used to assess soil erosion risks. Mapping and overlaying of thematic maps were performed by using ArcGIS software. The assessment of water erosion in this study was carried out in three phases based on PAP/RAC guidelines. The first approach called predictive was aimed at providing preliminary hypotheses for development of erosion risk. It consisted of analysis of natural factors influencing water erosion. The second phase called descriptive consisted to identify current on-site erosion forms that develop in Boufekrane. The consolidation phase, which was the last step, exhibited spatial distribution of erosion risk in Boufekrane by integration and combination of results obtained from the two previous phases. Results indicated that 55.61% of the watershed is affected by sheet erosion, 12.42% is affected by solifluction /sheet erosion. Gully and rills only accounts for 17% of the total surface area of the watershed and are found in areas where slopes and soils are highly sensitive to erosion. The results also showed that cultivation practices, crop types and vegetation cover are found to influence erosion processes in Boufekrane. Effects of slope in water-induced erosion process were found to be of minor degree. The final output map provides a valuable insight for soil conservation planning in Boufekrane and contributes to a more standardized framework of soil erosion control by making findings more applicable and comparable to other watersheds where decision to address soil erosion has been made based on PAP/RAC. In addition, the study can enable the local authorities to prevent from a premature and quick sedimentation of El Gaada dam. However, the model did not consider important data such as rainfall and other climatic data which taints its accuracy in evaluating soil erosion water. Therefore, there is a high recognition to improve PAP/RAC model if one wants it to be an efficient and effective tool for decision-making in soil erosion control and management projects.