Influence of tea plantations, forest and mixed farming on stream flow and sediment loads, case of Sondu Miriu river basin, Kenya

Abstract

The changing patterns of land cover and land use in the tropical river basin over time are critical. The hydrological phenomena at basin and sub basin scale are affected positively or negatively by dynamics of the land cover and land use patterns. Hence identifying causes and driving factors aid in taking appropriate measures to avert the impacts. 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. Field-based investigations were conducted through sampling of flow velocities, turbidity and TSSC obtained from existing River Gauging Stations established within the three sub basins. The sub basin dominated by mixed farming land cover exhibits high turbidity approximately 620 NTU and high levels of total suspended sediment concentration (TSSC) of the order of 630 mg/l in wet seasons. The turbidity levels and TSSC were low in sub basins dominated by forest and tea plantations with approximately mean value of 17 - 29 NTU and 0.019 g/l. The sediment loads in sub basin dominated by mixed farming in the pre planting season in January to February were about 900 tonnes/day higher than that in crop growing season. In sub basins dominated by forest cover and tea plantations, sediment loads were low ranging between 2 - 7 tonnes/day. The relationship between stream flows and area under tea plantations, forests and mixed farming ranged between R2 of 0.025 and 0.16. Tea plantations and forests influence the stream flows and sediment yields in long term duration while in mixed farming variations were observed seasonally. The strong relationships between rainfall and stream flows at the sub basins ranging between R2 of 0.84 and 0.97 revealed the significance of rainfall in hydrologic response of the Sondu Miriu River Basin.