Runoff Estimation and Water Management for Holetta River, Awash Subbasin, Ethiopia
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Date
2013-06
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Addis Ababa University
Abstract
The hydrology of Holetta River and its seasonal variability is not fully studied. In addition to
this, due to scarcity of the available surface water and increase in water demand for
irrigation, the major users of the river are facing a challenge to allocate the available water.
Therefore, the aim of this research was to investigate the water availability of Holetta River
and to study the water management in the catchment using Geographical Information Systems
(GIS) tool, statistical methods, and hydrological model. The rainfall runoff process of the
catchment was modeled by Soil and Water Assessment Tool (SWAT). According to SWAT
classification, the watershed was divided in to 6 subbasins and 33 hydrological response units
(HRUs). The only gauged subbasin in the catchment was subbasin one that is found in the
upper part of the area. Therefore, sensitivity analysis, calibration, and validation of the model
was performed at subbasin one and then the calibrated model was used to estimate runoff at
the ungauged part of the catchment. The performance of SWAT model was evaluated by using
statistical (coefficient of determination [R2], Nash-Sutcliffe Efficiency Coefficient [NSE] and
Index of Volumetric Fit [IVF]) and graphical methods. The result showed that R2, NSE, and
IVF were 0.85, 0.84 and 102.8 respectively for monthly calibration and 0.73, 0.67 and 108.9
respectively for monthly validation. These indicated that SWAT model performed well for
simulation of the hydrology of the watershed. After modeling the rainfall runoff relation and
studying the availability of water at the Holetta River, the water demand of the area was
assessed. The survey form was used to identify information, which includes the number of
Holetta River consumers, major crops grown by irrigation and the total area coverage.
CropWat model was used to calculate the irrigation water requirement for major crops.
Based on the result of CropWat model and survey analysis, the irrigation water demand for
the three major users of Holetta River was calculated. The total water demand of all three
major users was 0.313, 0.583, 1.004, 0.873 and 0.341 MCM from January to May
respectively. The available river flow from January to May was taken from the result of SWAT
simulation at subbasins 2,3,4 and 5. The average flow was 0.749, 0.419, 0.829, 0.623 and
0.471 MCM from January to May respectively. From the five months, the demand and the
supply showed a gap during February, March and April. This indicated that there is shortage
of supply during these months with 0.59 MCM. Therefore, in order to solve this problem alternative source of water supply should be studied and integrated water management
system should be implemented.
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Keywords
runoff estimation, Holetta River, Awash basin, Ethiopia, hydrological modeling