Abstract
Hydrometeorological information is important in planning and management of natural resources. The northern Ethiopia in general and Illala sub-basin in particular is lacking reliable information with regard to groundwater recharge, evapotranspiration and surface runoff. The main objective of the study is to estimate the distributed groundwater recharge, surface runoff and evapotranspiration amount of Illala sub basin using WetSpass modeling method. Long term mean hydrometeorological data and physical characteristics of the catchment such as land use/land cover, soil type, topography, groundwater level and slope are used as an input to the model. The mean annual groundwater recharge, evapotranspiration and runoff were found to be 66, 440 and 40mm respectively. Accordingly, recharge accounts for 12% of the precipitation while the rest 81% and 7% becomes evapotranspiration and surface runoff respectively. The study area is characterized by low groundwater recharge due to the presence of high evapotranspiration rate associated with high temperature, dry wind, low rainfall and relative humidity though it is a little bit large compared to some parts of the northern Ethiopia. Keywords : Groundwater, WetSpass, Recharge, Illala, Catchment, Tigray, Ethiopia
Highlights
Groundwater recharge is the process by which water percolates down the soil and reaches the water table either by natural or artificial methods to replenish the aquifer with water from the land surface
The same is true in many parts of Ethiopia like Tigray region where being semiarid it remains dry for major part of the year
The uneven distributions of the climatic parameters associated with variations of land-use/landcover, soil type, topography and slope are responsible for variations of the water balance element within the catchment
Summary
Groundwater recharge is the process by which water percolates down the soil and reaches the water table either by natural or artificial methods to replenish the aquifer with water from the land surface. In arid and semi-arid areas, its assessment is a key challenge in determining sustainable yield of aquifers (Yongxin and Beekman, 2003; Crosbie et al, 2010). The same is true in many parts of Ethiopia like Tigray region where being semiarid it remains dry for major part of the year. Recharge is estimated by chloride ion mass balance method, empirical method, water-balance method, water budget model method or by multiplying the magnitude of water-level fluctuations in wells with the specific yield of the aquifer material. Commonly groundwater recharge is determined to a large extent as an imbalance at the land surface between precipitation and evaporative demand (Gebreryfael, 2008).
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