In this study, we evaluate the soil erosion and solid transport in the oued Mekerra watershed in north-west Algeria. The study area is subject to a semi-arid climate characterized by irregular rainfall and showers, which are often accompanied by significant floods. These floods of large volumes transport large amounts of solid input to the Sarno dam, which is in the outlet of oued Mekerra. Therefore, the water storage capacity of this dam is gradually decreasing, and it might reach the volume of dead water. For this study, we utilized the hydrometric database provided by the National Agency of Water Resources (ANRH). The operating period was 24 years, from 1988 to 2012. This period was extended by classic regression to 65 years, which allowed extracting a series of annual maximum instantaneous flow rates (Q IXA ) and subsequently quantified the sediment yield during floods. The specific degradation mean created by the 11 floods was quite high, in the order of 20 t km 2 year −1 . The highest value of solid contribution was observed during the floods of October 2000 (250,000 t), and the value of liquid contribution was 7,151,608 m 3 . The extracted results from the analysis of the graphs of concentration as a function of the liquid flow (C = f′(Q l )) showed four types of hysteresis curves: clockwise loop, counterclockwise loop, shape of eight, and straight line curve. Class II (clockwise loop) was the dominant class in the four events, namely the floods that occurred on 09/22/1992, 09/21/1998, 09/27/1999, and the 08/24/2002. From these results, the water resource sector managers could formulate various methods for protection from floods and against the risk of sedimentation in storage structures.

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La modélisation QdF (Débit-durée-Fréquence) est un moyen de représenter le régime de crue d'un bassin versant et constitue un outil bien adapté à la prédétermination des crues rares et extrêmes. Cet article a pour objectif d'étudier les conditions d'application de la modélisation QdF et, par conséquent, la détermination des courbes correspondantes sur le bassin versant de l'oued Mekerra, dans le Nord- Ouest algérien. Les courbes QdF sont d'abord déterminées localement, directement à partir d'une analyse statistique des débits moyens (VCXd) sur différentes durées, à partir des données disponibles à la station de Sidi-Bel-Abbès. Ces courbes sont ensuite comparées à celles obtenues en appliquant différents modèles régionaux (Vandenesse, Florac ou Soyans), dans lesquels sont pris en compte deux indices de la crue caractéristique du bassin versant, une durée descriptive de la dynamique des crues (D) et le débit instantané de période de retour dix ans (QIXA10). Les modèles régionaux les plus proches du modèle local sont le modèle Soyans pour les périodes de retour inférieures à 100 ans, et le modèle de Florac pour les périodes de retour supérieures à 100 ans. Ces résultats pourront être exploités pour construire des courbes QdF sur des bassins algériens non jaugés. Il est cependant nécessaire de répéter cette étude sur d'autres bassins afin de confirmer ces premiers résultats.

Extreme streamflow drought is the direct problem of serious on damaging and on social impacts, so the frequency analysis of hydrological drought is an important work can be done to studying the drought phenomenon in catchments. So the hydrometric data for a river conducts to the establishment of the flow duration curve (FDC) as an important index of streamflow drought regime, from this characteristic, a threshold level can be defined for both perennial or intermittent streams. Well, two partial duration series can be derived for each year; the deficit volume and drought duration series. In the catchment of Wadi Mekerra in the North-West of Algeria, the minimum value estimated from the Pareto’s annual maximum instantaneous flood population (0.60 m3∙s−1) is considered as the threshold level index where, the largest deficit volume and the largest drought duration occurring in a given year are taken into consideration. Hence, the frequency analysis of the streamflow drought regime of the catchment is analysed with Weibull distribution for both deficit volume and drought duration combined with the probability of occurrence which is determined under some criterion in order to forecasting the streamflow drought in the catchment.