A lot of uncertainties exist about the impact of deep-sea mining on the Benthic environment. One of these uncertainties concerns the sediment plumes created by the mining operation. The return slurry released above the sea floor creates a large plume of sediments. With numerical models the behavior of such plumes is modelled in order to minimize these uncertainties. Particle size distributions in these plume models are currently based on individual particle sizes. In situ, at the bottom of the ocean in an salt water environment, flocculation can occur. Flocculation can have effects on the particle size distribution, settling rates and floc structure. The objective of this research is to investigate the significance of flocculation on the settling behavior and if it should be taken into account in these plume models. Shear rate and particle concentration, as function of time, are the most governing processes that have effect on the flocculation behavior. The influence of these parameters on the flocculation process are investigated. Different methods are used in the search for a suitable technique to measure the in situ particle size distribution. Next to the particle size distribution the floc shapes, structure and settling rates are measured under the influence of the factors mentioned above. In the shear range of 6 s-1 and particle concentration of 0.7 to 40 g/l flocculation does occur and has a large impact on the settling behavior of the sediment. Flocculation at other shear rates and particle concentrations remain unknown. Figure \ref{fig:vol_dem_salt_floccu1} shows the time until 100 $\%$ of the mass is settled when the suspension is released at a height of 10 m. This graph shows the difference in settling time between a suspension in demi and salt water. A settling time difference of 85 days (25 days for salt water and 110 days for demi water) shows the importance of including flocculation behavior in plume models. ... 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.
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