Determining the Influence of Tea Plantations, Forest and Mixed Farming on Stream Flow and Sediment Flux, Case of Sondu Miriu River Basin, Kenya

Understanding the changing patterns of land cover and land use in the tropical river basin over time is critical. Primary land conversions especially in the 21st century have occurred due to increasing demands for the scarce natural resources within the water catchment areas. These alterations affect hydrological phenomena at basin and sub basin scale. However, there is limited data and information on the extent to which hydrological processes response to dynamics of alterations of the primary land covers in various river basins. The initial land cover in Sondu Miriu River Basin has been undergoing transformations and it is important to investigate effects of land cover and land use on quantity and quality of the basin’s water resources. This study determined the influences of sub basins dominated by tea plantations, forests and agricultural land uses in terms of streamflow and sediment flux variability in Sondu Miriu River Basin in Kenya, East Africa. Seasonal variability of stream flows and sediment fluxes were determined by hydrological modelling and field-based investigations. In the three upstream sub basins of the river basin, sampling of flow velocities, turbidity and Total Suspended Sediment Concentration (TSSC) were conducted. The results showed that the sub basin dominated by mixed farming land cover exhibit high turbidity approximately 620 NTU and high TSSC levels of about 630 mg/l in wet seasons. While in sub basins dominated by forest and tea plantations, the turbidity levels and TSSC were low with approximately mean value of 17-29 NTU and 0.019g/l. The sediment loads in sub basin dominated by mixed farming in the pre planting season in January to February was high about 900 tonnes/day than crop growing season. While in sub basin dominated by forest and tea plantations cover, sediment loads were low being of the order 2-7 tonnes/day. The mean annual sediment yields at the downstream of Sondu Miriu River Basin was approximately 140 tonnes/ha/annum. The positive and negative relationships between stream flows, sediments and area of land cover showed that hydrological components respond differently to land use changes in the sub basins.