Morphological modelling of the Atrato river delta in Colombia

Morphological modelling of the Atrato river delta in Colombia

Post, S.

De Vriend, H.J. (mentor)
Mosselman, E. (mentor)
Sloff, C.J. (mentor)
Geleynse, N. (mentor)
Luijendijk, A.P. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2011-08-12

The Colombian government aims to establish a connection that bridges the Atlantic Ocean and the Pacific Ocean. The new connection will largely take place on the current Atrato River, which has not yet been upgraded for a more extensive use of navigation in the near future. A bottleneck in the river is the delta area. Without structural dredging activities the river is completely inaccessible. This study investigates the morphodynamics of a river mouth of the Atrato delta, in order to improve its accessibility to provide navigation in the future and to minimize the dredging activities. In short, the main objectives of this study are (1) to gain insights into the morphodynamics of the delta, (2) to develop a hydrodynamic model on an unstructured grid, (3) to develop a morphodynamic model on a structured grid and consequently (4) apply these models to investigate measures that aim to improve the accessibility of a river mouth. In this study an approach is used to model the hydrodynamics first at a large scale and subsequently modelling the morphodynamics at a more detailed level. A hydrodynamic model is set up with an unstructured grid, which appears to be a powerful tool to model a topographical complex area such as the Atrato delta. The hydrodynamic model gives insights into the hydrodynamics of the delta and is capable to create specific time-dependent boundary conditions for the more detailed morphodynamic model. This approach solves the problem of enormous backwater adaptation lengths, which are initiated by the tidal movement and a large amount of bifurcations. Subsequently, a model with a structured grid has been set up to simulate the morphology around a river mouth. The morphodynamic model is able to identify the major processes that cause sediment deposition. The key process appears to be the sudden spreading and deceleration of the riverine water when the river flows into the Golfo de Urabá. As the result of the relative strength of the outflowing fresh water compared to the tidal power, the flow velocities are almost constantly located seawards. This explains the low sediment deposition rates in the river part of the delta. The enhanced flocculationin saline water results in a compact zone of sedimentation. This report discusses four possible measures that aim to improve the navigability in the delta and to minimize dredging activities. Modelsare set up to simulate their effects on the delta hydrodynamically as well as morphodynamically. The modelled measures are (1) a sand trap, (2) an artificial outlet channel, (3) sediment diversion channels and (4) the artificial extension of a river mouth. The model forecasts that none of the investigated measures will avoid dredging activities completely. A navigable artificial river mouth situated more upstream in the river even leads to closuresof the current river mouths. Of the examined measures, the implementations of a sand trap and sediment diversion channels raise the most potential to reduce the sediment supply to the current river mouths, without deteriorating the navigability in other parts of the river. The artificial extension of a river mouth with breakwaters does not decrease the sediment supply towards the river mouths. However, the sediment deposition process takes place in deeper water, which minimizes the dredging maintenance for at least several years. The findings of this study should be regarded as the first step in the extension of knowledge on the morphodynamics of the Atrato delta. At this stage the models will help to understand the morphodynamics at the delta in more detail and hopefully encourage the collection of more valuable data. For that purpose a measuring and monitoring program is presented in this report.

delta
navigability
morphodynamics
river mouth
unstructured grid

http://resolver.tudelft.nl/uuid:a7ff9f3d-414d-4f1e-99c0-0257332bb157

2011-09-05

Student theses

master thesis

(c) 2011 Post, S.