Évolution des caractéristiques pluviométriques entre 1979 et 2009 dans le micro-bassin versant de l’oued Rhiou (bassin de Cheliff) Algérie / Recent trends in Oued Rhiou micro watershed rainfall (1979-2009)

Abstract

The Gargar Dam is a large-scale hydraulic structure commissioned in 1989 with an initial capacity of 450 million cubic meters. It is intended for irrigation and drinking water supply. On the basis of its first bathymetric survey carried out in 2004 by the National Agency of Dams and Transfers, the dam was reduced by a volume of 92 million cubic meters in fifteen years of operation due to an accelerated siltation. This study thus aims to analyze the rainfall variations recorded at the meteorological station of the Gargar dam (Oued Rhiou) between 1979 and 2009, located 5 km from the town of Oued Rhiou, wilaya of Relizane. It appears that precipitation and their characteristics are decreasing during the period that we analyzed. Linear decreasing trends were observed on the average rainfall from wet days (SDII) as well as on the total number of days with rainfall> = 10 mm (P10), total precipitation annual (PTOT), total number of wet days (rain ≥ 1 mm) (JP), total number of days with rainfall> = 20 mm (P20), maximum daily rainfall (Px1J), rainfall frequency intense (P95p), extreme (P99p). Moreover, the linear trends (expressed in % per decade) calculated for the eight rainfall indices from 1979 to 2009 significantly decrease significant downward (P(t) < 0.05). The application of statistical tests on the metrological series of the Gargar Dam metrological station (randomness verification tests, Normality method, Lee and Heghinian Bayesian method) allowed to determine the breakup period so the posterior probability density of the position of climate variability. This allowed us to verify that the decrease in annual precipitation does not lead to a decrease in runoff. Indeed, we observed that runoff and erosion significantly increased between 1985 and 2014 in the watershed of Oued Rhiou. Further studies are thus needed to understand this erosive dynamic.