Abstract
Keya Hydropower Plant (HPP) is a run-off-river plant which can be an effective green solution contributing to the current energy demand in Rwanda but a huge amount of sediment contained in water of Sebeya River on which this plant is built results in loss of the plant capacity. The aim of this study was to conduct the performance evaluation of Keya HPP sediment basin located in Rubavu district, western province of Rwanda. Specifically, laboratory tests of sediment, efficiency of the basin, assessment of sedimentation problems on HPP operations, proposition of technical options for increasing the removal efficiency of sediment basin and other options for reducing sediment at the source of generation were performed using different methods including interviews and questioning Keya hydropower technicians, field sediment sampling followed by hydrometer and Particle Size Distribution (PSD) analysis. Analysis was made in University of Rwanda (UR) Soil Mechanics laboratory. MICROSOFT EXCEL and Graphisoft Archicad 18 softwares with Massachusetts Institute of Technology (MIT) soil classification were used as data analysis tools. Results showed that the overall efficiency removal of the diversion headwork was 85%. However, after comparing sediment concentration at the inlet and outlet of the sediment basin, it was found that the basin removed only 22% of sediment from diverted water toward the turbine. This means that 78% of sediment escapes the basin to cause erosion on the turbine components resulting in reduction of the plant capacity from 2.2 MW to 900 KW. To ensure sustainable solution to sediment issues in Keya HPP, an upstream sediment trap reservoir is proposed. It is recommended also that Rwanda Energy Group (REG) should work together with Rwanda Natural Resource Authority (RNRA) at national level to ensure sustainable development of erosion control in the Sebeya catchment area.
Highlights
For most of power plants in rivers with sediment problem, there must be sediment basin systems
Keya Hydropower Plant (HPP) is a runoff river project established in July 2011, in Nyundo Sector, Rubavu District of Western Province of Rwanda with a capacity of 2.2 MW and draws its water from Sebeya River and the hydropower plant is facing with different issues of sedimentation
Using interview and field visits, we found that rainfall-driven erosion process enhanced by deforestation and cultivation practices presently adopted on sloping lands appears to be the primary cause of soil erosion in the catchment areas of Keya HPP
Summary
For most of power plants in rivers with sediment problem, there must be sediment basin systems. A sediment basin is built for trapping suspended sediment particles before they reach the turbine components. Run-off-river projects are HPP constructed to utilize the available water throughout the year without having any storage. These projects usually consist of a small diversion weir or dam across a river to divert the river flow into the water conveyance system for power production (Figure 1). These projects do not have dam reservoirs to retain sediment but should be able to bypass the incoming bed load to the river downstream. Settling basins are constructed close to the intake to trap certain fractions of the suspended sediment [2]
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