干旱区生态环境知识资源中心

In the semi-arid Mediterranean climate of the Maghreb region, Algeria, the intensity and high variability of rainfall contribute to soil erosion that feeds the sediment load of the wadis, which, in turn, is a factor in the rapid silting-up of reservoirs. The temporal variability of solid and liquid flows, an important characteristic in Mediterranean regions, is the subject of this research, which focuses on the Wadi Bouhamdane in eastern Algeria. Since December 1987, the wadi flowsrecorded by the gauging station (1105 km(2)) since September 1969have been regulated by the Hammam Debagh Dam, located immediately upstream of the station (1070 km(2)). The study involved the treatment of a long time series of suspended sediment concentration and water flow data, together with daily water discharge data recorded at the dam site. A power function describing the relationship between the instantaneous suspended sediment loads and the instantaneous water flow was used to estimate daily suspended sediment discharge of two series (1969-1987 and 1995-2010), recorded, respectively, at the outlet of the basin (gauging station) and at the dam site. The results show a moderate mean annual specific suspended sediment flux (257 t km(-2) year(-1)), but high inter-annual variability characterizes the specific suspended sediment (TSS = 0.5 and 1396 t km(-2) year(-1) in 1996/97 and 2004/05, respectively), which increases significantly in the season of high streamflow. Thus, floods generate large quantities of sediment that represent a significant proportion of the annual total and monthly specific degradation throughout the basin. The comparative approach shows that the sediment flux estimated by concentration measurements at the wadi gauging station (0.22-0.29 hm(3) year(-1)) does not represent the entire volume of silting of the dam (0.98 hm(3) year(-1) on average), identified using bathymetry. This second method includes bedload and other inputs of sediment that are very difficult to measure.