Abstract:
Water resource available was not well managed due to rainfall variability and
unavailability, insufficient knowledge about available water resource and coordination in
water resource management, population growth, expansion of irrigation. and
environmental requirements, particularly during low flow periods. These clearly show
that there was a need to analyze the water balance of the river basin and formulate water
allocation strategies and principles for the present and future. To achieve this general
objective Soil and Water Assessment Tool (SWAT) model was used to determine the
surface water potential. The types of data that used to achieve this objective were Digital
Elevation Model (DEM), land use and land cover (LuLc), Soil data, Meteorological data,
Hydrological data, population data irrigation data, annual water use rate, and crop
types. After sensitivity analyses, calibration and validation of the model by SWAT-CUP
the Water evaluation and Planning (WEAP) model was used to analysis current and
future water demand and under scenario development. The result revealed that an
estimated mean annual precipitation was 144.11mm. Total surface water potential from
the watershed was 350.76 million-cubic meter (Mm
3
) annually during the current
account year (2021). The model was calibrated and validated by using 18-year (1996-
2013) stream flow data. The performance was found good during calibration (R2 = 0.83),
Nash-Sutcliffe efficiency (NSE)=0.69, and PBIAS=-19%, while validation (R2= 0.86,
NSE=0.76, and PBIAS=-18%). In the base year 109.47Mm
3
of water was required by
both consumptive use and non-consumptive use (environmental flow requirement). In the
base year (2021) there was no unmet water demand annually. The estimated total annual
consumption water demand may be expected to be for reference scenario, high
population growth scenario, increase irrigation area scenario, and increase water
demand scenario were 82.44Mm
3
, 161.4Mm
3
, 173.2Mm
3
, and 210.6Mm
3
respectively.
High flow during rainy season and low or no flow during dry season hence, congestive
use of water is recommended
