The Rainfall and Stream Flow Analysis of Yala River (1F) Catchment

Abstract

Kenya consists of 5 basins: Lake Victoria, Rift valley, Athi River, Tana River and Ewaso Ngiro. The Yala River catchment is one the various catchments that constitute Kenya’s Drainage Network. It basically forms part of the Lake Victoria North catchment and it falls under the Middle catchment category, which is vastly covered by undulating hills that are dissected by the rivers Nzoia, Yala, Sio and their tributaries. The catchment of the Yala River has an estimated area of 3351 km2 and the Yala River is one of the main Kenyan rivers draining into Lake Victoria. The Yala River is approximated to be about 219 km long and it originates from the Nandi Escarpment water tower traversing Kakamega, Bondo, and Siaya counties as it flows. The basin has an annual average discharge of 28m3/s with its location being at latitude 0⁰30′N - 0⁰10′S and longitude 34⁰00′E - 35⁰40′E.

The main purpose of the project is the study of the hydrology of the Yala River catchment with respect to rainfall and stream flow analyses. The data available for both the rainfall and stream flow in the basin were processed using the appropriate methods after which they were presented in the form of tables, graphs and diagrams. The rainfall data aided in the drawing of line graphs which depicted the seasonal variation of rainfall in the basin. For instance, in Baraton station the highest rainfall was 202.6mm occurring in May and a low of 55.2 mm in January. For RGS 1FG01, the median flow was found to be 26 m3/s with the 95% flow being 6.6 m3/s. The mean annual rainfall for the entire catchment was found to be 136.27mm and 128.35 mm using the Arithmetic mean and Thiessens Polygon methods respectively.

The project was therefore carried out successfully using the available data.

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