The effect of islands in the Río Magdalena on discharge and sediment transport into the Canal del Dique, Colombia

Abstract

Controlling the distribution of water and sediment at river bifurcations is one of the main challenges in river engineering and management. This distribution affects the stability of river bifurcations as well as the distribution of flooding risk, navigability and environmental conditions. The governing factors are the hydrodynamics of the two branches downstream as well as the spatial distribution of sediment transport in the area of the bifurcation. Fluvial islands at the bifurcation may affect both. This thesis focusses on the effect of size, position and shape of fluvial islands in the Río Magdalena on discharge and sediment distribution into the Canal del Dique, Colombia. Where the high amount of fine sediments in the Río Magdalena has negative environmental impact on the coastal area downstream of the Canal del Dique, therefore a solution needs to be found to reduce the high amount of sediment entering the Canal del Dique. A model study has been carried out with the use of Sobek-RE and Delft3D-FLOW in order to gain insight in the hydrodynamics and morphodynamics on a respectively one-dimensional and two-dimensional (depth-averaged) scale. It was found that size and position of the islands have an appreciable effect on the discharge and sediment in the Canal del Dique by influencing the water level at the entrance. Whereas, the shape of the islands have small influence, where protrusions and sharp edges both seem to evolve into smooth bank lines along smooth streamlines. Furthermore it was found that bathymetrical differences have an appreciable effect. However, a maximum reduction of discharge into the Canal del Dique of 8% can be obtained when the island is located just in front of the offtake. Furthermore, the amount of coarse sediment can be reduced with a factor 2.5.