Abstract:
Proper land suitability evaluation of land resources in irrigation command area is a prerequisite
for better utilization of land resources which helps to optimize and sustain the productivity of
these land resources. However, in the Geba Watershed, there is no study available on the
assessment of irrigation potential. Hence, this study is aimed to assess the surface irrigation
potential of the Geba River Watershed in the Ilubabor Zone of Oromiya Regional State through
Geographical Information System (GIS) techniques. Watershed delineation, identification of
potentially irrigable land, estimation of irrigation water requirement, and surface water
resources of the river were the steps followed to assess this irrigation potential. To identify
potentially irrigable land, irrigation suitability factors such as soil, slope, land cover/use,
distance from water supply (sources), and distance from the road were taken into account.
Irrigation suitability factors are classified based on the Food and Agricultural Organization
Guideline for land evaluation. The suitability of each factor was first analyzed individually and
finally weighted using Analytical Hierarchy Process (AHP) method from the pair-wise
comparison matrix to obtain potentially irrigable land. The irrigation suitability analysis of
these factors indicate that 50.21% of slope,50.47% of LULC,65.07% of the distance from the
water source, and 52.46% of the distance from the road of the study area are in the range of
highly suitable to marginally suitable for surface irrigation and 77.39% of the soil in the study
area is in the range of highly suitable to moderately suitable. By weighing analysis of all factors
about 88.07 % of the study area was found in a range highly suitable to marginally suitable
whereas about 11.93 % was restricted for surface irrigation developments. To grow on these
identified irrigable areas, three crops such as potato, tomato, and cabbage are selected and their
gross irrigation demand was computed from climate input data using CROPWAT 8.0 software.
The low flow (90% time of exceedance flow of Geba River) was estimated by the flow duration
curve. By comparing the required water and available monthly low flow of the Geba River, the
river had insufficient capacity for irrigation application of the command area. Therefore,
construction of storage structures or using ground water can be an option to meet irrigation
potential
