Groundwater Recharge Estimation of Upper Awash Basin Using WETSPASS Model
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Date
2019-06-06
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Addis Ababa University
Abstract
The Present research study is conducted in the upper awash basin which is located in central
Ethiopia at the western margin of the main Ethiopian rift. Nowadays the consumption of
water for the industrial, domestic and agricultural usage in the upper awash basin dominantly
depends on Groundwater. Government organizations and several private companies are
engaged in construction of deep wells in the study area due to increasing population.
However there is no well-organized system to monitor and manage groundwater resource of
the study area. Abstraction of groundwater in the study area is increasing without giving
proper attention to important hydrogeological factors. One such factor is recharge. To use the
groundwater without adversely affecting the groundwater table and the potentiometric level,
the abstraction rate need to be proportional to the groundwater recharge. The main objective
of this research is to estimate the ground water recharge and recommend the sustainable yield
of the upper awash basin. To accomplish this thesis Wetspass model method is applied.
Wetspass model is water and Energy transfer between soil, plants and atmosphere under
quasi-steady state which is a physical based model for estimation of long term average spatial
patterns of groundwater recharge, surface runoff, interception, soil evaporation and
evapotranspiration from long term average meteorological data.
Mean monthly and annually recharge, actual Evapotranspiration and surface runoff was
estimated using wetspass model by preparing grid maps with 200m cell size of land use,
Ground water depth, soil, slope, topography and major meteorological parameters such as
temperature, wind speed, rainfall and potential evapotranspiration. From the wetspass model
output the mean annual recharge of upper awash basin is about 110mm which accounts about
11% of the total mean annual precipitation which means 1,292,280,000.00 m³/year of water
stored in the Upper Awash Basin. In addition to wetspass model baseflow separation method
was applied to estimate the recharge of Upper Awash Basin which is about 95mm/year.
Mean annual actual evapotranspiration and Mean annual surface runoff of the study area is
about 603mm and 310mm respectively which accounts 60% and 30% of the mean annual
precipitation of the study area.
The sustainable yield of a certain area ranges from 10% to 70% of the groundwater recharge.
For the upper awash basin the sustainable yield is assumed to be 40% of the mean annual
recharge which is about 44mm/year.
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Keywords
Abstraction Rate, Groundwater Recharge, Sustainable Yield, Upper Awash Basin Wetspass Model