This study describes a statistical approach of watercourses hydrological regimes in flood, taking into account the latter duration d and return period T. The choice of Middle Cheliff watershed as study area is linked to disasters strong return period in the western region of Algeria. The Midlle Cheliff catchment basin, located in northwest Algeria, has particularly experienced severe floods over the last years. In view of the recurrence of these unusual events, the estimation and the predetermination of floods extreme quantiles are a strategic axis for prevention against floods in this region. The a curves are first of all locally determined, directly from a statistical analysis of flow continuously exceeded during a duration d (QCXd) on different durations from available data of the study region. Then, these curves are compared to those obtained by application of different regional models VFS (Vandenesse, Florac and Soyans) in which two indices of the watershed characteristic flood are taken into account, a descriptive duration of the flood dynamics (D) and the instantaneous maximal annual flow of 10 year return period (QIXA10). The final choice of the model is based on verification of certain criteria, such as: Nash and the root mean squared error (RMSE). The closest regional models to the local ones are Florac’s for low duration and return periods, and Vandenesse’s for large return periods, for different durations. These results could be used to build regional Q-d-F curves on ungauged or partially gauged Algerian basins.

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The rapid demographic evolution wields a big pressure on water resources potentialities; in addition, the climate change effects have influenced the natural renovation rate of water resources around the world. Starting from a previous published model, a sensitive analysis was established after introducing three parameters as watershed topography, stream network density and geology index to illustrate the impact of each of these parameters on the rate of groundwater recharge. This modified model has been improved by in-site experiment (soil chloride mass balance) tested in some selected sites in Sidi Slimane River located in the region of Djelfa at 300 km from Algiers (Algeria). The results obtained show that the parameters like geology, topography and the amount of rainfall and the drainage density influence the velocity of groundwater recharge. By introducing the chloride concentration in soil, the model becomes most independent and gives good results that can be used in water resources planning in semiarid land.