Régimes hydrologiques, Transport solide et changements climatiques dans le bassin du Chéliff

Abstract

In Northern Algeria, the Cheliff watershed has been severely affected by a decline in annual runoff since the 1970s due to a decrease in rainfall. However, the sensitivity of watersheds to this decline is variable and involves complex processes. This basin contains several dams that supply the population with water for drinking as well as for irrigation purposes to ensure a good agricultural yield necessary for food security of more than 5 million inhabitants. Rational and optimal management becomes an absolute necessity in new climatic conditions. It will be done based on efficient modelling tools. The development of high-performance models is more than necessary for a better assessment of potential and risks in the short, medium and long term, to adopt an efficient strategy in the water sector which have to be in line with ground reality. To do this, the soil and water assessment tool (SWAT) is a very reliable way to simulate the hydrological behaviour of the region. In this study, the SWAT model was applied to five dam-feeding basins in the Cheliff basin and its outlet on a monthly scale. The results obtained are very satisfactory with R2 values ranging from 0.69 to 0.79, Nash–Sutcliffe efficiency coefficient between 0.68 and 0.78 and bias percentage between 21% and -1.5%. The Oued Cheliff hydrogram modelled by the SWAT at the Sidi Belattar station (basin outlet) showed that surface flow represents 58.3% and 37.3% lateral flow and 4.4% that feeds deep aquifers. The spatio-temporal variability of runoff caused by climate change has a major impact on hydrological processes and the quantities of water mobilized at watershed scale. Flow predictions upstream of the five dams were carried out using the RCA4 regional climate model, following three global circulation models. Future flow projections showed negative trends for both periods (2021-2040) and (2041-2060), and according to both RCP4.5 and RCP 8.5 scenarios, with one small exception marked by the Ec-Earth driving model, with a slight increase in flows for the most pessimistic scenario.RCP 8.5. The SWAT model was also used to simulate specific erosion at the Oued EL Abtal hydrometric station, with a result +5% higher than the average value observed at the same station. The models developed will be used as decision-making tools by water-resource managers.