Assessment of the hydrological response of the watershed through a distributed physically-based modeling for extreme events: Application in the Raghay catchment (Medjerda) (Northern Tunisia)

This research study consists on the validation of the physically and distributed hydrological model, throw the application of the ATHYS platform for hydrological modeling, for the case study of a catchment area situated in the left bank of the high valley of the Medjerda basin, the catchment area of the Raghay wadi having an area of approximately 322 km². This watershed is characterized by a very important morphological, climatic and physical variability in time and space, often presenting very important floods because of the not measured flow coming from the Algerian frontier part instead of the large difference of atitude from 165 to 1180 in the Tunisian part. The choice is fixed on six events distributed over three different seasons, recorded on the level of two pluviographic stations for an hour time-step and which control the flow in the discharge system of the catchment area. The parameters of entry of the GREEN and AMPT production function are maps having the variability of the physical parameters of the soil as well as the variation of altitude and of the directions of drainage. The advantage of this function is related on its physical base, and the theoretical possibility to estimate and optimize the parameters starting from data of grounds or “in situ” measurements. The evaluated criteria for optimization are the Nash criteria which is varying between 0.73 and 0.98 for the calibration phase, and between 0.62 and 0.75 for the validation for the three seasons, instead of the Arithmetic Mean Error for the volume and the peak flow giving very good errors for the Wintry season, good errors for the Autumnal season and medium errors for the Springer season. The results of simulations show that the selected model is well validated for the Raghay catchment than, its performance in the comprehension of the hydrological answer of a Mediterranean watershed, which provide important information for decision makers in order of protection again- t floods of the area.