Stream flow variability and sediment yield in North-West upper Tana basin, Kenya

Abstract

The North-West Upper Tana River (NWUT) Basin is one of Kenya’s most important basins as it provides water for urban-rural water supplies, hydro-electric power (HEP) generation and irrigation. This study therefore investigated the influence of rainfall variability on the river discharge and sediment yield in the basin. The study relied on data archived by Water Resources Authority (WRA) and Kenya Meteorological Department (KMD) for the period 2010-2012. The methods applied in the study included the use of time series, double mass curve and the use of other statistical methods. The study established that there is a significant relationship between river discharge and rainfall in the basin. The variations in stream flow can largely be explained by variations in rainfall in the basin. There is however evidence of shift in rainfall patterns so that rainfall during the short rainy season seems to be more dominant than that experienced during the long rainy season. There is also a significant relationship between sediment yield and stream flow. The basin generally experiences high rates of sediment production due to inappropriate land use practices and lack of application of soil and water conservation measures on cultivated lands. Mathioya, Saba Saba, Thika and Maragua sub-basins exhibited high rates of sediment production rates due to high rates of soil erosion in these sub-basins. The high sediment yield in the basin has potential of reducing the benefits associated with Masinga Dam in terms of water supply, irrigation, flood control and HEP generation. The study recommends implementation of enhanced programmed for land and water conservation in the basin, including implementation of payment for Ecosystem Services (PES).