Abstract
In this paper, we attempted to review the erosion in the Ouergha watershed by applying two spatial approaches. The Ouergha watershed has an area of around 7300 km² representing approximately 18.2% of the Sebou basin of which it is the main tributary. In order to develop the erosion map using the SWAT model, it was important to prepare a large spatial database describing basin proprieties, furthermore, the daily hydro-climatic data. This model integrates MUSLE equation for the estimation of specific degradation. In addition, the estimation of erosion through SWAT was consolidated by constructing an erosion mapping through RUSLE method. This method was applied following an approach based on the use of remote sensing data and GIS tools to produce the major factors involved in the erosive process and their integration into RUSLE. The results obtained, in cartographic form, make it possible to target areas that require priority action for a larger-scale analysis, with a view to finding appropriate solutions to fight against erosion and protect the natural environment. Soil degradation in the Ouergha watershed is around 27 ton/ha/year (SWAT_MUSLE) and 25 ton/ha/year (RUSLE). Average sediment yield was estimated for Al Wahda dam of 10.4 Million tons.
Highlights
IntroductionThe climate is first sub-humid semi-arid or arid, in the south it has a Saharan character
Soil and Water Assessment Tool (SWAT) Model has made it possible to reproduce the flow rates observed in calibration and validation, as shown by the performance factors presented in Table 2, which it is noted that the performance is generally good
The relatively poor performance observed at these two stations can partly be justified by the low accuracy of the release records data of the upstream reservoirs or the unmastered irrigation water withdrawal. 3.2 Spatial distribution of soil loss 3.2.1 Soil loss map by SWAT-Modified Universal Soil Loss Equation (MUSLE) The SWAT erosion simulations show that the range of sediment yield delivered by the different spatial units of the Ouergha watershed varies from negligible erosion to more than 37 ton/ha/year
Summary
The climate is first sub-humid semi-arid or arid, in the south it has a Saharan character. In the Ouergha Watershed, precipitation has inherited this diverse climate. This gives it a strong spatiotemporal irregularity of precipitation, from 1300 mm in the extreme north and center to about 600 mm in the south. The construction and monitoring of dams against drought is necessary for better management of water resources. The durability of these needed constructions rest on the problem of siltation. This natural phenomenon caused by water erosion is related to watershed characteristics in relations with topography, pedology, lithology, hydrology, vegetation cover, and human activities. Water erosion is increasing aggressively due to climate change effects and torrential rains during extreme events
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