Backward erosion piping is a form of internal erosion where small pipes are formed below a dike. These pipes are formed in a direction opposite to the flow that transports sand particles. Piping is a very important failure mechanism in the protection of dikes, which can be unpredictable due to the different soil characteristics. Piping is well managed in the Netherlands, but there is a lot to be discovered regarding theerosion processes inside the pipe. For example, how fast the pipe develops and what this is dependent on. The objective of this thesis is to monitor and study the development of the pipe, to extend the knowledge about the different processes that influence the progression rate of the pipe. The main research question is: How do the different parameters and processes influence the progression and the sediment transport rate in laboratory experiments of backward erosion piping? To monitor the development of the pipe, different small-scale laboratory experiments were performed to obtain new data regarding piping and to study the influences of different parameters. The piping experiments were performed in three series: (1) configuration of the setup, (2) effect of grain size and (3) hydraulic loading. These experiments were performed in the previously developed setup of Vera van Beek (Van Beek, 2015). This setup was modified to measure the pore pressures and to guide the pipe through the middle of the setup. While conducting the experiments, different measurements were performed. This included measuring of the pipe length and geometry, collecting the sand boil and a dye injection to follow the flow. The literature study performed for this thesis has shown that in the past many experiments were performed regarding piping, but these studies did not focus on the different processes and the sediment transport rate of the pipe. By focussing on the progression phase of the pipe (continuous transport), the experimental data is compared to existing models (primary and secondary erosion). Sellmeijer’s model (Förster et al., 2012) is the current rule that is applied in the Netherlands for dike safety, but this model does not include time-dependency. This research showed that the development of the pipe is not a stationary process but depends on various conditions, such as
soil characteristics. The hypothesis formed at the beginning of this thesis listed several soil parameters which influence the progression rate of the pipe. Concerning the sediment transport rate of the pipe, Cheng’s model for bedload transport (Cheng, 2004) is evaluated and compared with the measured results. The analysis showed that the adapted formula of Cheng (Equation 2.24) overestimates the sediment transport rate in the pipe. From the analysis of the experimental results, it can be concluded that two parameters play an important role in the progression and sediment transport rate of the pipe: the particle diameter and hydraulic permeability. These parameters showed an influence on the progression rate which can be used to study piping on a larger scale. The most interesting result is the fact that experiments with a larger particle diameter have an overall larger progression rate.

Rapid urbanisation and globalisation are bringing increasingly complex issues to the forefront. Improper planning of human activities and over exploitation of the surrounding natural resources has successfully damaged the biodiversity and the natural processes. Today humanity is at a stage where these ecosystem services are essential for our existence but the resources have been exploited beyond their capacity. In addition, climate change adds additional long-term threats due to erratic weather patterns and extreme natural events. Coastal Lagoons are one such geographical feature where such complexities are very visible. Given the high fertility of the surrounding land and the biodiversity hosted by the lagoons, they are rich resource banks for settlements to thrive on. This has led to issues like water pollution, loss of biodiversity and urban encroachment. Despite protection from the international communities like the Ramsar Convention, most wetlands are degrading everyday. The need of the hour is to find innovative middle ground solutions, where the services can be availed without degrading the environment. Further, to plan these services in a way that they are instrumental in reviving and enriching the lost ecosystem. This project attempts to present on such design and strategy for the Muni-Pomadze Lagoon (MPL) in Ghana. Considering the complexity of the issues, the project chose a interdisciplinary and collaborative approach to produce a holistic solution for the site. Further, it uses the principles of Nature-Based Design and 4-P framework (People, Planet, Prosperity and Project) to guide and reflect on the design. (van Dorst & Duijvestein 2004) This report attempts to contribute to the research on interdisciplinary design processes. Further, it aims to be a starting point and guideline for the Forestry Commission and Municipal body of Winneba, for better conservation of the Muni Lagoon.