Groundwater Recharge Estimation of Upper Awash Basin Using WETSPASS Model

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Addis Ababa University


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.



Abstraction Rate, Groundwater Recharge, Sustainable Yield, Upper Awash Basin Wetspass Model