Modelling of Sediment Transport and Deposition in Generating River-Mouth Closure: Oum-Errabia River, Morocco

River mouths are dynamic systems that can respond rapidly to both fluxes in fluvial water and sediment discharge and marine energy conditions, notably waves. On semi-arid wave-exposed coasts, the morphosedimentary behaviour of river mouths is particularly sensitive to variations in water discharge, which can be significantly influenced by climate variations, in addition to anthropogenic actions such as the construction of dams for water resource needs. In this climatic setting, an increasingly common consequence of decreasing river water discharge is the more or less prolonged closure of river mouths. Most studies have addressed river-mouth closure using analytical, parametric, numerical, or statistical models. The present study uses output from four numerical models to elucidate the hydrodynamic and sedimentary behaviour of the mouth of the Oum-Errabia River (catchment size: 35,000 km2), which debouches on the Atlantic coast of Morocco. The historical evolution of the river mouth and the impact of human interventions, such as the construction of dams, are discussed. The study also briefly discusses the impact of the recent closure of the river outlet, in response to particularly low water discharge, on the marine ecosystem and water quality. The modelling results covering a one-year simulation in this situation of closure indicate a deposition of 427,400 m3 of sediment in front of the mouth of the Oum-Errabia. Ensuring permanent river-mouth opening and tidal flushing and renewal of this river's estuarine waters will necessitate costly regular dredging.

Automated summary

River mouths are dynamic systems that can respond rapidly to changes in water and sediment discharge as well as marine energy conditions. This study uses numerical models to analyze the hydrodynamic and sedimentary behavior of the Oum-Errabia River mouth in Morocco. The study discusses the historical evolution of the river mouth, the impact of human interventions such as dam construction, and the recent closure of the river outlet. The results show a significant deposition of sediment in front of the river mouth during the closure, highlighting the need for regular dredging to maintain a permanent opening.