Etude des évenement extremes et leur impact sur l'écoulement solide : cas du bassin versant du Mazafran.

Abstract

The rainfall series of the Mazafran watershed and their modeling using the annual maximum series (AMS) and the partial duration series (PDS) are carried out by the classic method onthree stations taken for an aggregation period ranging from 15 min to 3 hours. For PDS, the two-parameter exponential distribution is the most adequate distribution linked to the number of exceedances λ=1.65, the series of maximum daily precipitation corresponding to this number have been selected to deduce the intensity-duration-frequency curves (IDF) characterizing the studied watershed. The climatic exponent of the selected stations (0.69, 0.59, 0.62) was revealed by the graphical method, following Montana model. The correlation is significant (97-99%). As for AMS, the fitting results reveal the best adaptation of the Log Normal (Galton) law to the data series as well as the doubly exponential (Gumbel) law presenting the climatic exponent values; 0.67, 0.54, 0.62 for Oued Zeboudj, Ouzera and Somaa respectively, following the same model with a correlation coefficient of 0.99, 0.97 and 0.98. The comparison between the two methods revealed a very small difference in climatic exponent "b" of the order of 0.02 to 0.05 respectively for the stations of Oued Zeboudj and Ouzera. Somaa kept the same exponent. As for the climatic index “a”, a considerable variation was highlighted. Both stations; Oued Zeboudj and Ouzera, have almost the same root mean square error (RMSE) values between 20% and 40%. Somaa station represents higher values (up to 66%). Then, the study of the C–Q relationship at the annual, seasonal, monthly and flood scales was modeled by a power function Y=aX . The sensitivity of the rocks to erosion, the intensity of precipitation and the disturbances of the flow regime mean that the flow of suspended solids (SS) transported by Oued Mazafran reaches very high values varying from one sub-basin at the other, 500 t/km b at Oued Chiffa and 365 t/km 2 at Oued Djer Bouroumi, 682 t/km22 at Oued Mazafran, i.e. a total of 1547t/km 2 over the entire basin.