Author(s): Myriam Benkirane; Abdelali Gourfi; Agustín Millares; Nour-Eddine Laftouhi; Said Khabba

Linked Author(s): Myriam Benkirane

Keywords: Soil loss; Flash floods, Sedimentation, Remote sensing, RUSLE, Snow cover, Semi-arid conditions.

Abstract: Mediterranean countries are increasingly confronted with decreasing rainfall, increasing drought, and high demographic growth, which has severely contributed to the scarcity of water resources which management is becoming increasingly difficult. High-mountainous environments, where the hydro-meteorological drivers and geomorphological processes condition soil erosion and transport, are especially sensitive facing these changes. Indeed, the construction of large dams, often considered as the most effective solution to increase water availability and access, could be importantly affected by changes on erosion and sedimentation patterns. The Moroccan High Atlas watersheds and reservoirs give us an opportunity to assess how siltation processes are affected by changes on both forcings and land-uses in order to propose effective adaptation strategies for the future. The objective of this study is to quantify the erosion rates of the N'fis basin during extreme events and to determine the processes influencing sedimentation downstream at the Lalla Takerkoust reservoir. The sedimentation patterns in this reservoir point out the pulse dynamics of strong erosion at the hillslopes during extreme events representing a major risk, inducing a loss of storage volume, a decrease in the life of the dam, damages to the hydromechanical equipment and a deterioration of the water quality. The data used can be classified into two categories, a) quantitative mapped data, including soil characteristics, watershed morphology and vegetation cover, and b) measured data including rainfall, water discharge, siltation monitoring at the reservoir, and mineralogical analysis of the deposited sediment. Three approaches were implemented: (1) use of the Revised Universal Soil Loss Equation (RUSLE) as well as the Geographic Information System (GIS) and remote sensing (RS) to calculate soil erosion rates in the watershed. (2) Examining the spatial and temporal variation of land use, extreme events, and snow dynamics using remote sensing to assess their impacts on soil erosion. (3) Application of advanced statistical analysis to understand the factors controlling the distribution of specific sediment yield (SSY) in relation to the data used. The results highlight the dominant role of precipitation intensity in downstream erosional and sedimentary processes versus others. Also the importance of snow cover in the lamination of erosion processes and in the location of sediment sources. The latter is of great importance since future estimates without snowfall fraction warn of a significant increase in sedimentation processes. The adopted methodology will help to better understand this phenomenon and can be applied in regions with a similar climate.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022SS368

Year: 2022