Impacts of in-stream Sediment Extraction on the Morphology of Ephemeral River Channels, a Case Study of River Kalundu in Kitui County, Kenya

Abstract

This research aimed to investigate the impacts of in-stream sediment extraction on the morphology of ephemeral river channels, focusing on the case study of River Kalundu in Kitui County, Kenya. The study objectives were to determine the contribution of various hydraulic factors (slope, width, depth,) to sediment production in River Kalundu, estimate the magnitude of in-stream sediment extraction and evaluate the impacts of sediment extraction on the hydraulic geometry of the channel section. Random sampling technique came up with active extraction site. Systematic sampling technique was employed to collect data at specific points within the river channel at a regular interval of 10meters (length). Field measurements provided data on channel depth, width, slope angles, riverbank position, vegetation cover and erosion status. Similarly systematic sampling technique was used to collect socio-economic data by categorizing the respondents that were actively involved in the activity as sand miners, loaders and household heads. The spatial extent of sediment extraction along River Kalundu was mapped using ArcMapGIS version 9.1. Descriptive statistics, graphs, and percentages were used to analyze the quantitative data. Binary logistic regression analysis was employed to identify factors influencing sediment production in the river channel, while multiple logistic regression analysis was used to examine the impacts of sediment extraction on the channel's morphology. From binary regression analysis, the study was able to establish that river channel width (P = 6.263e-06), depth (P = 7.363e-05), slope angles (P = 3.2843e-05), and bank position (P = 2.001e-15) significantly influenced sediment production in the channel. Moreover, from multiple logistic regression analysis the study established that sediment extraction had significantly modified the river channel morphology, leading to increased depth (P = 7.33339e-02), width (P = 9.853705e-03), and slope angles (P = 9.138643e-03) at the active mining sites compared to the control sites. The study also examined the socio-economic impacts of in-stream sediment extraction in the River Kalundu sub-catchment area. A descriptive survey design was employed, and questionnaires were administered to 150 respondents. The findings indicated that sediment extraction was a prevalent activity in Kalundu River, with an average of 10 Lorries per day involved in extracting and selling sediment locally and outside the area. It was observed that sediment extraction led to community conflicts, depletion of water in the sand aquifer, increased drug and substance abuse, insecurity, drying of river water, and pollution. The chi-square test confirmed significant social impacts of in-stream sediment extraction χ2 (3, N=119), = 39.98, P = 0.000). However, sediment extraction had positive economic impacts, including improved living standards, infrastructural developments, and increased employment for miners and loaders χ2 (3, N=119), = 214.94, P = 0.000.). The study recommended the pivotal role of the County Government of Kitui to collaborate with regulatory authorities such as NEMA to develop guidelines in regulating sediment extraction operations to mitigate environmental risks. This entails active monitoring and enforcement of established guidelines to promote sustainable extraction practices, safeguarding the river ecosystem. The recommendation includes issuing limited licenses to sediment miners, coupled with rigorous criteria to assess the environmental impact and long-term sustainability of proposed extraction operations. It further suggests the implementation of public education programs to raise awareness about the ecological importance of the river and promote responsible practices, resource preservation, and long-term benefits for the environment and the community