The Nyando River is one of the major Rivers in the Lake Victoria Basin. It drains parts of Nandi,
Kericho and Nyando districts. It has a catchment area of about 3600 km−2 of Western Kenya and an
average discharge of approximately 15 m3 s−1, and has within
5 it some of the most severe problems of environmental degradation and deepening poverty
found anywhere in Kenya. The Nyando River drains into the Winam Gulf of Lake Victoria and is a
major contributor of sediment.
The primary role of GIS in hydrological modeling is to integrate the ever increasing volumes of
diverse spatial and non spatial data. This can be the model input or output.
10 Recent advance in GIS (hardware and software) technology offer unprecedented ca-
pabilities for storing and manipulating large quantities of detailed, spatially-distributed
watershed data (ASCE, 1999). SWAT, which is an interface of Arc View GIS, uses Arc View to prepare
input data and display the model output as spatial maps, charts or time series data. This makes it
easy to study and display the information for assimilation by
15 SWAT.