Impact de l'érosion sur l'envasement des barrages, la recharge des nappes phréatiques côtières et les intrusions marines dans la zone semi-aride méditerranéenne : cas du barrage de Boukourdane (Algérie)
Impact of erosion on the silting of dams, on the recharging groundwater and on coastal marine intrusion in the Mediterranean semi-arid area: Case of Boukourdane dam (Algeria). Description of the subject. Water erosion is a particularly important issue, especially in the Mediterranean and semi-arid zone. This zone is characterized by irregular rainfall patterns, which have a considerable influence on soil loss. In mountainous areas, water erosion phenomena are accentuated by steep slopes and low ground cover. The dams draining these areas undergo siltation linked to significant erosion. The silting of the dams drastically limits their capacity and thus their operating life. When used for recharging aquifers, the resuspension of fine particles may accumulate in the recharge areas and reduce infiltration capacity by clogging soil porosity. This leads to a significant reduction of groundwater levels. Additionally, groundwater situated in the coastal zone is submitted to intensive pumping. These two phenomena make groundwater particularly sensitive to marine intrusions. Objectives. This article aims, on the one hand to quantify the rate of siltation in the case of the Boukourdane dam (northern Algeria), which is used to recharge groundwater. On the other hand, the article also shows the reduction in permeability in the capturing field with the current management of releases. Method. Solid rates were set in relation to the liquid flow and sediment concentration occasionally taken from the wadi. The relation established made it possible to evaluate the solid contributions to the dam of Boukourdane. The impact of the releases on recharging the well field was evaluated by grouping wells and the well field mushrooms using heuristic k-means. Regressions were applied to the piezometric variations of each group. Results. This dam is fed by a catchment area of 156 km². Sediment transport was estimated from empirical formulas. The specific degradation rate was estimated at 366 t·km-2·year-1 during the 1993 to 2005 period. The increase in the frequency of extreme rainfall resulted in an increase in the soil erosion rate to 446 t·km-2·year-1 during the 1993 to 2013 period. The volume of sediments accumulated in the dam reached 8·104 m³·year-1 and 11·104 m³·year-1 respectively during these two periods. Conclusions. A change in the management of current releases has a positive impact on the partial restoration of the hydraulic conductivity and de facto, on the fight against marine intrusion
