For the transportation of the produced energy at offshore windfarms to the onshore grid, export cables have to be installed in the sea bed. Usually, at first trenches are dredged, in which approximately one month later the cables are installed. During this period the trench should remain sufficiently open to install the cables, fulfilling the depth requirements. This thesis focusses on the influence of sand wave fields on the sedimentation rate. It is investigated how trench sedimentation can best be assessed: with a simple model in combination with an extensive probabilistic assessment, or with a more complex model in which a less detailed probabilistic assessment is possible. The research is based on a case study at the Borssele Wind Farm Zone, for which the sedimentation rate is determined during the month April. The sedimentation is primarily caused by a reduction in (the perpendicular-directed) flow velocity. Shifting of shoals or banks does not occur during the short timescale. The same holds for the sand waves, which do not migrate significantly during this time. Under influence of bedload transport however, the largest sedimentation rates are found for trenches around the sand wave crest. Closer to the troughs, less sedimentation can be expected. During the probabilistic assessment of the trench sedimentation in flat bathymetries, it was found that the uncertainty obtained by Latin Hypercube Sampling (LHS) with an 2DV-model is reduced compared to the Monte Carlo-analysis (MC-analysis) in SedPit: the median is for both cases 0.06m, the 5-95 percentiles are 0.03m-0.09m and 0.04m-0.13m respectively. Including (idealized) sand wave perturbations in the 2DV-model, increases the range of the P05-P95 values for in trench sedimentation to 0.01 and 0.13m. Based on the results, it is concluded that SedPit can be used as first assessment tool for the trench sedimentation, since it covers the range obtained with the more complex 2DV-model. The main advantage is the limited computation time of around 1.5 hours, compared to around 48 hours with the sand wave model. On the other hand, the 2DV-model is able to produce more accurate results. The siltation rate in trenches located at sand wave crests is underestimated by SedPit compared to the results obtained from the 2DV-model. The opposite holds for trenches located at sand wave troughs, in which more sedimentation is predicted by SedPit. Adjusting the calibration parameter of sand transport in SedPit within the ranges provided in Van Rijn (2013) (0.5 for a sand wave trough and 1.0 for a sand wave crest), can at most decrease the difference between the models. For trenches located near a sand wave crest or trough, it is therefore advised to use at least the 2DV-model to assess trench sedimentation. Furthermore, the 2DV-model can only be used in the case of perpendicular flow with respect to the trench-axis. Inclusion of the sand wave processes, which act in the 2DV-direction, for non-perpendicular flows therefore requires 3D modelling.

Growth of world population, sea level rise, land subsidence and climate change gives new challenges for the present and the future. A new innovative approach of engineers is needed to reach socio-economic development with care for the environment. In the Netherlands, an EcoShape consortium is initiated where multiple experts came together from the Dutch private and public sector. In this consortium governmental organisations, knowledge institutes and business companies are involved to search for adaptable and sustainable engineering solutions to exploit and promote the ‘Building with Nature’ program. The main goal is to move from building in nature towards building with nature, using the natural forces present in the system. Chile has shown interested in the Dutch Building with Nature program and the question raised whether a similar concept could be introduced in the country. Therefore, the organisational structure of the Chilean water sector related to coastal engineering is investigated in this research, as well as several case studies are used to illustrate the potential of Building with Nature in Chilean projects. These projects are the coastal erosion in Pichilemu, a port expansion in San Antonio and coastal erosion in Los Vilos. The Chilean coast shows in different aspects a very dynamic behavior. For the design of a coastal structure it is important to understand this dynamic behavior and the possible consequences. In addition, the study concluded that Chile is a very privatized country which is important to consider when applying Building with Nature into coastal projects. The privatization has the consequence that a substantial amount of stakeholders need to be involved in the projects also funding can be a challenge. In general, the conclusion can be drawn that there is lack of information on the coastal characteristics in Chile. More data needs to be conducted to implement trustworthy Building with Nature designs. Additionally, one could state that there is a communication gap between the governmental parties as the Dirección de Obras Portuarias and Ministerio de Obras Públicas and the local parties involved in coastal projects. This is important to solve, as these parties needs to be involved in all coastal projects. Another outcome of the case studies is the absence of an environmental vision for most of the initiated coastal projects investigated and the absence of a long term vision of coastal management. Meeting with various engineering consultancy firms showed the presence of a strong incentive to enlarge the consciousness on the environmental and societal aspects in Chile, and the ambition for a more co-creative and multidisciplinary design approach. Arcadis Chile has shown interest to establish a platform to introduce the Building with Nature approach in Chile. Together with the Universidad de Valparaíso, Arcadis Chile can be the initiator for the implementation of the philosophy and the increase of awareness among other important actors in the water sector.