Regional modelling with flood-duration-frequency approach in the middle Cheliff watershed

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.