Regular maintainance dredging is a large expense to the Port of Rotterdam, therefore the installation of sediment traps is considered. By increasing the bathymetry locally, an increase of local accumulation is expected and a decrease deeper in the harbour basin. This thesis describes the functioning of sediment traps in a stratified tidally energetic estuary, where sediment is supplied by the river and sea. A numerical 2DV representation is set up for the Botlek Harbour with the hydrostatic Delft3D software. A calculated salinity time-series by Operationeel Stromingsmodel Rotterdam (OSR) is combined with a measured water level time series for the same time period to describe the hydrodynamic boundary conditions. Simulations are done with a variable and constant Suspended Particulate Matter (SPM) time series boundary conditions, that were generated based on the measurements of De Nijs (2012). Flow expansion caused by the sediment trap reduces the flow velocity, but increases the turbulent kinetic energy locally. A reduction of bed shear stress is observed in the trap, except near the edges where an increase is observed. Density currents caused by salinity differences govern the vertical flow velocity distributions, while tidal filling causes the net exchange. The depth of the trap plays a significant role in the internal flow characteristics. The sediment trap changes the properties of the internal flow, which may change the hydraulic state of the flow, i.e. from supercritical to subcritical, resulting in large instabilities and even an internal hydraulic jump. Shallow sediment traps result in less frequent internal hydraulic jump and weaker jumps compared to deeper sediment traps. To investigate the dominant mechanism for the trapping of sediment in the sediment trap, a distinction is made between an erosion and a fluid mud scenario. The erosion scenario shows the largest agreement with the survey data, i.e. maintenance dredging data and Echosounder multibeam surveys, but contribute only marginally to the trapping of sediment. The fluid mud scenario yields the largest contribution to the trapping of sediment. The decreased amounts of accumulated sediment in the basin for substantial to lots of fluid mud behaviour may vary between 10% and 14%, depending on how this fluid mud behaviour is modelled. Various shapes have been tested on erosion and fluid mud scenarios. Both for erosion and fluid mud a more extreme choice of parameters might yield also more extreme results, this is however not considered realistic. The creation of an overdepth has shown to result in a marginal improvement in the capturing of sediment in an environment where erosion is important. A regular sediment trap decreases accumulation in the harbour basins by 2%. A trap twice as shallow increases this amount to 4%, but deepening the trap further may even enhance accumulation in the basins. A shorter or longer trap did not improve the situation. Installation of a sill did however result in a decrease of 6% compared to the situation without trap. It is concluded that this effect can be largely contributed to the internal flow properties and the presence of internal hydraulic jumps. The presence of an overdepth results in a significant improvement in the capturing of fluid mud flow. For the trapping of fluid mud flow, an overdepth results in 6% less sediment in the harbour basins no matter the depth or shape of the trap. The length of the trap did influence the accumulation in the basins. A trap twice as short shows an increase of 4 % of accumulation in the basins compared to a regular trap. A trap twice as long or installation of a sill results in similar accumulation in the harbour basins as a regular trap. For fluid mud flows, any type of overdepth decreases accumulation of sediment considerably. The amount of overdepth or the shape does not influence this. The length of the trap should be sufficient. A trap that is too short results in an increase of accumulation in the basins. For environments where erosion is important, only shallow sediment traps have proven to reduce accumulation in the basins. Traps that are too deep actually increase accumulation in the basins. A sill has proven to be the best measure for both mechanisms. If overdepth is desirable for navigation a shallow sediment trap is advised. This leads to a reduction of accumulation in the harbour basins for both erosion and fluid mud scenarios. ... Read more

Colombia’s economy has been growing steady in the past decades, partly because of the increase in tourism. However, this tourism also has a downside. Hotels and restaurants are constructed one after another, preferably along the coast. This, combined with factors such as climate change and land subsidence and the fact that people tend to prefer living close to the coast, leads to a vulnerable and erosive coast, especially in the departments of La Guajira and Magdalena. Therefore, Project Colciencias was initiated by three local universities and two companies, a large scale study to improve and implement coastal projects in this area. Focus is on areas that experience critical erosion; erosion that puts local economy, environment and national heritage at risk (Oceanus, 2013). Ten objectives are formulated by the five different parties, e.g. characterization of the coast, development of pilot projects and socialisation of coastal projects.
The goal of this multidisciplinary research conducted by TU Delft students in cooperation with Oceanus International is to improve the Colciencias project by combining Dutch and Colombian expertise, technology, efficiency and theory. After analysing the political, cultural, social, hydraulic and environmental situation, and after consulting various stakeholders three research objectives were stated and elaborated.
The first goal is to create a framework to ensure a consistent and efficient implementation of the intended pilot projects. Not only does it cover the hydraulic aspects of a project, it also takes into account the socio-economic, environmental and legal factors. To support the part of the framework that comprehends the hydraulic analysis and the development of alternatives for coastal protection, a detailed document on numerical models is written. This is objective number two. Next to information on numerical models in general, the three main types of coastal models are discussed; coastline, regional - and local morphodynamic models. Eight specific models are then further highlighted, resulting in a decision tree that helps in choosing the best model for your specific engineering application. To test the framework, a case study was executed in one of the critical erosion zones, the village of Ciénaga. The framework was followed concisely to evaluate its effectiveness and efficiency. Among other things, a field trip was organised to carry out experiments and execute a survey to explore the socio-economic values of the region. Next to that, interviews were carried out with officials and local parties to obtain information on past projects and the local legal framework. From the case study it was concluded that the framework functions, but that it should be noted that the case study is only a test of the framework, and that much further research needs to be conducted for the actual design and implementation of the coastal plan for Ciénaga.
Lastly, our goal was to start a dialogue about the impact of integrated coastal zone management and coastal erosion problems. In practice this resulted in many interviews, a survey, attendance of local community meetings, presentations at the Universidad del Norte for stakeholders of the project and an informal gathering of students at the Universidad de Cartagena. Furthermore, the framework shall be distributed to possible stakeholders as well as an informative presentation along with an introductory movie.
... Read more