Abstract:
The first and foremost step in assessing land and water resource is to be certain about the
extent of their potential, in water resource development. The present study is aimed at estimate
potential surface runoff and identifying suitable areas for supplementary irrigation by existing
Rainwater Harvesting Structures (RWHS) in the Laga Sure watershed that cover 85 square
kilometers in Ganale Dawa River Basin. Runoff potential was estimated using the Soil
Conservation Service Curve number method. Land evaluation was made from soil, slope,
landuse/landcover and vicinity to water source point of view based on FAO land evaluation
guideline for irrigation agriculture. The CROPWAT software was used to calculate the crop
water requirement for selected dominant crops in the area, viz., maize. The result shows that,
the runoff potential of Dhawa and Danbi-Korba sub watershed and the whole Laga Sure
watershed is 1.034Mm
3
, 2.375Mm
3
and 11.887Mm
3
, respectively. Though the watershed has
large runoff potentials, Dhawa and Danbi-Korba RWHS harvest 1.3% of it. The land
evaluation result indicates that 71.85% and 69.3% of the study area are potentially suitable
for sprinkler and surface irrigation system, respectively. The demand analysis reflects that
42.02% of harvested water is consumed by committed water use and atmospheric demand. The
remaining 57.98% usable volume of water can be used for irrigation purpose. As a result, the
selected RWHS have a potential to irrigate 29.11ha and 45.87ha by applying surface and
sprinkler irrigation methods, respectively, on identified suitable land.
Therefore, it can be concluded that the vastly available surface runoff is lost through direct
runoff from watershed due to limited capacity of rainwater harvesting structures and the
existing RWHS have irrigation potential, which has not been efficiently utilized in previous
time. It is recommended that construction of new appropriate rainwater harvesting structures
and rehabilitation of the existing one in the sub watershed could increase the irrigation
potential of the Laga Sure watershed.
