Determining the Impact of a Dam on the Natural Hydro-Sedimentary Dynamics Using Remote Sensing and GIS: Case of the Hassan Ad-Dakhil Dam (South-East Morocco)

The construction of dams has significantly altered natural hydro-sedimentary dynamics, raising concerns about their environmental impacts. In response, this study proposes an integrated geomatics approach to determine the impact of a dam on the natural hydro-sedimentary dynamics through the estimation of the annual sediment rate trapped in a dam using two complementary formulas, which are simultaneously applied for the first time. The initial equation assesses hydrological erosion occurring upstream of the dam, providing an estimation of the annual erosion-susceptible soil rate within the dam's watershed. This assessment leverages the integration of Geographic Information Systems (GIS) and Remote Sensing technologies with the Revised Universal Soil Loss Equation (RUSLE). The subsequent equation proposed by Williams (1977), computes the sediment delivery ratio, facilitating the estimation of sediment transportation rate towards the dam's reservoir through overland flows. The validation of the estimated annual sediment rate trapped in the dam is done by comparing it to the measured rate. The pilot case of this study is the Hassan Ad-Dakhil dam in South-East Morocco. Remote sensing data, a digital elevation model, precipitation, and pedological data were used for hydrological modeling of the dam's watershed associated to the Ziz River. The results include maps showing factors influencing hydrological erosion, the rate of lands sensitive to erosion, sediment delivery ratio, and the annual rate of lands trapped in the reservoir. This approach could enable biologists to simulate disturbances in downstream aquatic ecosystems caused by dams and hydrologists to estimate the dam's lifespan without dredging during dry months.