Abstract:
In Ethiopia the use of groundwater for agriculture is very low. Many irrigation schemes obtain
water from river diversions in which only farmers with land near the rivers gets profit from
irrigation, while others are waiting for the rainy season rather than using groundwater for
irrigation. There is high degree of rainfall variability and unreliability. As the irrigation water
requirement increases by an expanding number of farmers, the stream flow has decreased
significantly this can cause conflict among the upstream and downstream water users. This
study was conducted in Awash Basin of Ethiopia to assess suitable land for surface irrigation
using shallow groundwater potential. AGIS based Multi-Criteria Evaluation techniques was
applied to assess suitable land for irrigation, to increase agricultural productivity, creating food
self-sufficiency, overcome the conflict between river water users and to involve farmers those
waiting for rain season. Key factors that significantly affect irrigation suitability evaluated in
this study include groundwater depth, geology, groundwater yield, slope, soil capability index,
population density, rainfall deficit, drainage density, land use/land cove, and road. Pair-wise
cooperation matrix and expert’s option were used to assign weights for each factor and then
overlaid all factors to identify suitable land for irrigation. CROPWAT 8.0 model was used to
calculate reference evapotranspiration utilizing groundwater resources as complementary
irrigation to increase income of farmers and as supplemental irrigation to reduce the failure of
crop during shortage of rainfall. The available groundwater potential was estimated from
British Geological survey data. The study indicated that the suitable land of the basin with
shallow groundwater were about 11908.99km
2
or 10.45% of the total area. 1548.17km
2
or
13.18% of the suitable land can be irrigated with the available shallow groundwater. The
validation result showed that 72.9% of the actual well data were correctly failed on the suitable
area. The estimated total groundwater storage ranges between1Mm
3
/km
2
to 50Mm
3
/km
2
and the
borehole yield over the growing period of dominant crop were ranges from 1166 to
233280m
3
/km
2
. The total Net Irrigation Requirements over the growing period of dominant crop
were ranges from 144.00mm to 10329.30mm. The evaluation between available groundwater
potential and total Net irrigation water requirement showed that shallow groundwater alone
may not be sufficient to supply all suitable land of the basin.
Keywords: Awash basin, shallow Groundwater irrigation, ArcGIS, AHP, CWR