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).
