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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 flows—recorded by the gauging station (1105 km2) since September 1969—have been regulated by the Hammam Debagh Dam, located immediately upstream of the station (1070 km2). 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−2year−1), but high inter-annual variability characterizes the specific suspended sediment (TSS = 0.5 and 1396 t km−2year−1in 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 hm3year−1) does not represent the entire volume of silting of the dam (0.98 hm3year−1on average), identified using bathymetry. This second method includes bedload and other inputs of sediment that are very difficult to measure. [ABSTRACT FROM AUTHOR]

Climate variability, non-optimal water resources management and increase of human pressure are three possible factors influencing runoff and water resources in semi-arid Algerian catchments, such as the Tafna catchment (western Algeria). This catchment is subject to a semi-arid climate. In addition to rainfall impact, we examine the influence of other factors, such as geology, topography and human activity, on the runoff variability in the Tafna catchment. For this purpose, to complement the rainfall and discharge series analysis, we considered baseflow and the baseflow index (BFI). The analysis was conducted for five sub-catchments of the Tafna basin, where daily rainfall and discharge series were available for the 1976–2006 period. In the analysis, we distinguished two domains defined from the topography: a high-altitude area and a plain area. According to their geological setting, the hydrological regime is different. High-altitude catchments have a larger baseflow and BFI than catchments in the plain. This may be related to the differences in lithology, as high-altitude catchments have a large area of karstic geological formations. No significant trends or step changes were found in the annual rainfall for the 1976–2006 period. We found a decrease in the mean annual discharge of two high-altitude discharge stations (significant at the 1% and 10% levels, respectively). A decreasing trend was also found for two high-altitude catchments and a plain catchment (significant at both the 1% and 5% level). The BFI decrease is only significant for one high-altitude catchment. This is evidence of a decrease in storage within high-altitude catchments. Runoff change in the Tafna catchment could therefore be related to other factors, such as human impact, rather than to rainfall change. [ABSTRACT FROM AUTHOR]