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    GROUNDWATER POTENTIAL ASSESSMENT OF AGULAE CHINFERS RIVER CATCHEMNT, NORTHEN ETHIOPIA
    (Mekelle University, 0011-10-25) Hadush weldemichaeal
    The general objective of the research is to study the hydrogeological system of the Agula-Chinferes catchment by giving particular emphasis to groundwater potential assessment, and recharge-discharge conditions. The Agulae_Chinfers river catchment is found in the Tigray National Regional state, Northern Ethiopia, which is about 783km from Addis Ababa on the way between Mekelle and Wukro in the western part of Giba Basin. It has a total area of 697 km2 with altitude ranging from 1769 m to 2853 m above mean sea level. The area is covered by alluvial deposit, dolerite rocks, limestone-shale-marl intercalation, limestone, adigrat sandstone, enticho sandstone and meta -volcanic. These rocks mainly meta- volcanic and adigrat sandstone in composition are emplaced along an NW-SE tectonic lineament. Different approaches are used to estimate the groundwater recharge, characterize the aquifer and assess the hydro geochemistry of the catchment. Soil moisture balance, and surface water balance approaches are used to estimate recharge. Annual precipitatrion by estimated arithmetic mean is 632mm/year, by Theissen polygon 626.3mm/year,by Ishyetal method 630.84mm/year,potential evapotranspiration by Penman method 815.97mm/year, potential evapotranspiration by Thornwaite method 817.41mm/year, average by two methods 816.7mm/year and the actual evapotranspiration by Turc method 339.14mm/year, Thornthwaite and Mather standard soil water balance model 458.5mm/year The results of estimated annual direct groundwater recharge in the catchment shows that the recharge estimated by soil moisture balance 54.7mm/year .the recharge estimated by water balance 45.34mm/year,average from two methods 50.02mm/year ( 8% of the precipitation in the watershed) .So, the recharge estimated by soil moisture balance is higher than the values estimated by water balance method. The groundwater potential and surface water (drainage pattern) and the discharge recharge is controlled by the topography, the geology, and structure. In the limestone, limestone-shale-marle intercaltion and sandstone rocks, which are the major aquifers in the area the hydraulic parameter varies with the fracture distribution. The structures that control the recharge discharge condition and areas of groundwater potential are associated with the regional tectonic structures of the faults. The source and alignment of springs is also associated with the joints, fractured and hill said. Geology, land use and land cover, soil types, dreaning density, linamant density, rainfall and slope are used to show groundwater potentioal zones and groundwater flow system, recharge discharge conditions. The analysis result of the above parameters overlaps with the hydrogeology which indicates that the south -eastern, eastern and northwestern part of the area is the potential zone for ground water exploitation. Piper plots are used to classify the water chemistry. There is variation in water type from low TDS Ca-HCO3 and Ca-Mg-HCO3 through intermediate type Ca-Na-HCO3 to high TDS Na-HCO3 type. There is no strong variation in PH of the waters as such and the low TDS, low alkalinity, waters have similar near neutral PH with the high TDS, high alkalinity water, reflecting the existence of chemical reaction that affect the hydrogen ion.PH of the study area(6.56-7.95),groundwater of the study area based on total dissolved solids (by WHO standard) fresh water (238-1000mg/l) and brackish water (1000-1469.6mg/l) so, the groundwater of the area has Total Dissolved Solids ranging from less than 615.41 mg/l in the high lands (recharge area) and sandstone geological formation to about 1469.6mg/l in low lands especially in areas of limestone intercalation with shale-marl geological formation. The total Hardens of the study area range from 85.2 to 947 (mg/l). so, by the classification of water (Jasrotia & Kumar, 2014) from medium hard to very hard (in areas of limestone intercalation with shale-marl geological formation .