Abstract:
This study was under taken to evaluate suitability of Dirma watershed for surface irrigation
potential. The methodology included evaluation of slope, major soil physical properties and
surface water resources availability of the watershed. Suitability of the area with respect to
slope, soil and surface water resources availability were evaluated using Arc GIS 10.1. In the
weighted overlay analysis, high weight was given to slope, since it is the determinant factor
for surface irrigation development. Potentially suitable sites for surface irrigation
development were evaluated for selected vegetable crops, Potato and Tomato. The reference
evapotranspiration and net effective rainfall for each of the climatic station (Gorgora and
Gonder) and net and gross irrigation requirement for each of the crop for each of the climatic
station was estimated using CROPWAT software. The minimum water requirement of
Tomato was found to be equal to 0.07 m
3
/s/ha in April during the development stage at
Gonder meteorological station and 0.07 m
3
/s/ha in January at initial stage at Gorgora station.
The maximum water equal to 0.15 m
3
/s/ha for tomato crop was required in March at Gonder
and 0.15 m
3
/s/ha in May at Gorgora station. In case of Potato crop, minimum water equal to
0.19 m
3
/s/ha was required in January at Gorgora and 0.157 m
3
/s/ha at Gonder at initial stage.
However, the maximum water equal to 0.38 m
3
/s/ha was required in March at Gorgora and
0.257 m
3
/s/ha at Gonder in mid stage. The total value of the gross water requirement for both
the crops for both the climatic stations varied from 0.17 m
3
/s to 0.93m
3
/s. The water available
from Dirma River during Jan, April and May was more than the gross irrigation water
requirement. However, the water available during Feb and March was less than the
requirement. Result of the suitability model revealed that about 68.3% (300.93 km
2
) of the
total watershed area (440.6 km
2
) was in the range of highly to marginally suitable for surface
irrigation development with respect the suitability of slope, soil and water resource
availability factors.
