The Effect of Check Dams and the Use of Semi-Arid slopes on Runoff and Soil Loss, at Some Valleys of the South of Al-Jabal Al-Akhdar, Libya

Abstract

This limited study highlights the impact of some patterns of human use and activity within fragile and marginal environments that require implementation of appropriate plans to conserve soil and water resources. The study conducted some morphometric and field measurements related to soil erosion in some valleys and streams of the Samalus Basin, south of Al-Jabal Al Akhdar. The semi-arid area suffers from degradation and erosion in which the cultivation of grain crops and intensive pastoral activity on fragile lands are dominant. The study also monitored and evaluated the efficiency of some soil conservation methods such as contour tillage and rock check dams built in the region, where the depth of soil deposits behind the dams was measured. The study results confirmed the dominance of shallow and very shallow soils with the presence of important areas of open stone lands, in addition to the spread of alluvial soils, which indicates the continued loss of the soft clay layer due to erosion. Field estimates of erosion and surface run-off showed significant differences in the amount of soil loss between the valleys that are of different use, as the amount of soil loss in Bouarikat valley exceeded that transferred in El-Eish valley by more than ten times. The noticeable difference in the pattern of land management could explain this significant difference in soil losses, as Wadi El-Eish was characterized by the cultivation of grain crops in fields protected by rock check dams, as well as the presence of controlled grazing, which maintain a vegetation cover capable of protecting the soil from erosion. On the other hand, it was found that the quarrying-related activities in Wadi Bouiraikat have played a large role in disaggregating soil particles and making it ready for transport by runoff. The study showed the success of rock check dams built on the degraded slopes in conserving soil and moisture required for plant growth, which contributed to a qualitative and quantitative improvement in the natural environment behind the dams. Some dams managed to hold more than 50 cm of soil above the original depth, and most of the dams succeeded in reserving soil with a depth of 10 to 30 cm added to the depth of the original soil. Contour plowing on slopes also had an important role in reducing the yield of sediments coming towards the dams. The findings of the current study opens the door to more upcoming studies that are more detailed and specific to reach the best sustainable management methods for degraded semi-arid and arid slope lands.