Characterization and frequency analysis of flooding solid flow in semi-arid zone: case of Mekerra catchment in the north-west of Algeria

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 (QIXA) 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 km2 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 m3. The extracted results from the analysis of the graphs of concentration as a function of the liquid flow (C = f′(Ql)) 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.