This study investigates the capacity of an open inverted filter to stabilize the interface between the sand fill and core fill in a rubble mound breakwater. The strength of this filter relies on the arching mechanism of the base material, which is directly influenced by factors such as stability ratio and effective stresses. These forces arise from porous flow, and its quantification involves both parallel and perpendicular hydraulic gradients.
A full-scale physical model, with a 760 mm open inverted filter, is employed to determine the critical hydraulic gradients required to initiate erosion. The model consists of three compartments, with the central compartment containing the open inverted filter. The two side compartments are filled with water, with one of them featuring a plunger mechanism to induce flow. Pressure sensors and water level gauges are used to measure the hydraulic gradients. In addition to the physical model, a numerical model is developed to gain insights into the flow dynamics within the system.
The tests reveal that an increase in effective stress results in higher critical parallel and perpendicular gradients. Furthermore, the addition of fines at 5% or 10% seems to enhance the critical parallel and perpendicular gradients. A negative correlation was found between SR and 𝑖⊥,𝑐𝑟𝑖𝑡, the results were fitted to a hyperbolic function. The findings further indicate that, even after erosion occurs, a stable interface can be reestablished. Therefore, designing solely for the single largest wave is not imperative.
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In many places in Uganda, people do not have a connection to the drinking water supply system and there is a lack of treated water supply, meaning that people only have access to water a certain part of the day. As a result many people rely on springs, handpumps, rivers or lakes, of which the quality cannot be monitored or controlled.

During this multi-disciplinary project, we worked together with the National Water & Sewerage Corporation (NWSC) and the Ministry of Water and Environment (MWE) to research the possibilities of extending the water supply system of two project areas, Bugiri District and Hoima City. The current water supply in both areas use groundwater as a source and the possibilities for the extension also consider using surface water besides groundwater.

The different alternatives for the extension of the water supply in Hoima City and Bugiri District are evaluated using a multi-criteria analysis (MCA), consisting of a financial analysis, a performance analysis and a risk analysis. By evaluating the different options using an MCA, the decision-making process can become less complicated.

The MCA-tool that is set up in this research can be used by engineers to study different areas in Uganda and make it easier to compare different options for the extension of a drinking water supply system in an early design stage. The tool is for the two project areas as examples, after which it is also tested during a case study with engineers from both NWSC and MWE. Useful feedback came out of this session which will be used to finalize the tool and elaborate on it.

To design the different alternatives for the project areas and to get insight into the drinking water supply of Uganda, Hoima and Bugiri are visited at the beginning of the project.

For both project areas, it is recommended to improve the operational performance of the already existing groundwater supply system as a short-term (5 years) solution. The long-term (25 years) solutions consider groundwater options as well as surface water options, using for example Lake Victoria, Lake Albert and River Nile as water sources.


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