Abstract:
Assessing available land and water resources for irrigation is important for planning their
use. This study is initiated with the objective of assessing the water and land resources
potential of river catchments in Segen sub-basin for irrigation development
by using Geographic Information System(GIS).
The Segen sub-basin was selected as a case study for this thesis work which is located at the
Southern part of the Rift Valley River Basin covering an area of about 20,517 km
2
.
The evaluation of land in terms of the suitability classes for surface irrigation is based on the
method as described in FAO guideline for land evaluation. The essence of land evaluation for
irrigation is to compare or match the physical resource of soil, water, topography and others
with the irrigation requirement. A land unit is obtained by the overlaying of selected theme
layers, which has unique information of land qualities for which the suitability is based on.
The selected theme layers for this study include soil types, with their corresponding physical
and chemical characteristics that affect irrigation agriculture, land cover, and slope layer,
which is derived from the Digital Elevation Model of the study area. As its being the most
limiting factor for the realization of, especially for surface irrigation method, the slope layer
was used as the base map for the overlaying analysis.
The suitable land identified categorized according to the different climatic zones along the
Weito and Segen River in the sub-basin. They are mostly concentrated in the South central
and North Eastern part of the sub-basin. The 95, 90, 85, and 80 percentage time exceedance
flow of the available surface water in the respective climatic zones was estimated and the
area that can be irrigated with this flow was computed using the sel ected climatic station data
and estimated ETo. When these factors were weighted using weighted overlay in Arc GIS,
the potential irrigable land for surface irrigation was reduced to 43,191ha.
