Estimation of sediment deposits in the Ghézala reservoir in northern Tunisia

Abstract

Abstract. The control of sedimentation in a reservoir provides a global evaluation of the process of erosion and transportation of sediment. Knowledge of sedimentation is useful for reservoir management. Bathymetric surveys can be used to assess the silting volume of dams. The results of two surveys of the Ghézala dam reservoir in northern Tunisia are available. The measurements provide initial information about the quantity and variability of silting and the mechanism of sediment deposition. According to the results of measurements, the average annual specific sediment yield of the Ghézala dam watershed is estimated at 1851 tkm-2yr-1. The annual average sediment volume trapped varies from 23 000 m3 in 1993 to 66 692 m3 in 2011. The sedimentation rates increases from 0.20 to 0.57 % overtime. The results indicate interdependence between the specific erosion rates and the occurrence of soils on steep slopes. The pressure exerted on the soil by plowing as well as overgrazing to meet the needs of the population of this area has exposed the soil to continued deterioration manifested by increased erosion endangering the only source of revenue for the area.