Hydrogeology and Major Ion Hydro-Geo-Chemistry of Borkena River Catchment Awash Basin Amhara Regional State South Wollo Ethiopia
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Date
2021-06-29
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Addis Ababa University
Abstract
The study was conducted at Borkena River Catchment 1192km2, in Amhara regional state, south wolo zone, encompasses Dessie, Kombolcha, Harbu and Kemisse towns to characterize the hydrogeology of the catchment by giving particular emphasis to major ion hydrogeochemistry. Data has been analyzed using GIS and remote sensing, Aquachem and Strater softwares. The results indicate that, the highland receives more precipitation than the lowland, the highest rainfall which is 1573.6 mm recorded at 2428m elevation in western part in Albuko station and the lowest rainfall which is 1013.3 recorded in Cheffa station at 1400m elevation. Areal depth of precipitation of the area was estimated by using Arthemetic, Thiesson and Isoheytal methods. All the three methods provide nearly closer value. The analysis result of three methods is used as the annual average rain fall of the study area. Potential evapotranspiration (PET) of the area was estimated using Thornthwaite method. The estimated value of PET is 1462.6mm. Wetspass modeling and baseflow separation was used to estimate recharge. The average annual long term groundwater recharge is estimated using wetspass as 145.95mm of which 110.63mm occurs during wet and 35.329 mm occurs during dry seasons. About75.7% of the annual groundwater recharge of the watershed occurs during the wet season (summer), and the remaining 24.3 % in dry season (winter). The annual average precipitation (1190.1 mm) is distributed as 49% Evaporation, 43.3 %runoff, and 12.26 % recharge. The alluvial deposits in the central part are the major aquifers of the area. The general ground water flow direction is from the northwestern part to southeaster part. The geology, recharge estimation, hydrogeological system and hydrogeochemistry of the study area assessed using respective approaches. Based on test wells and previously drilled wells studied by ADSWE aquifer parameters and qualitative hydrogeological interpretation, the study area is characterized in to high, medium to high, medium, low and very low aquifer productivity. To characterize the aquifer system of the area pumping test data, well completion reports, well logs and geology of the area were analyzed. The pumping test analysis results indicate that the hydraulic conductivity of the area ranges from 0.2 – 20.2m/d and the mean and the transmissivity of the area ris greater than 500. Aquachem software has been employed to identify the different water types. Piper plots and Durov plot were used to classify the water chemistry and evolution of water type respectively. The dominant water type of the area is Ca-Mg-Hco3 .Waters of the area generally has Ca-Hco3 and Ca-Mg-Hco3 in the recharge area with Low TDS to Na-Ca-HCO3 discharge area with high TDS evolutionary trend this is due to the process of hydrolysis silicate minerals
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Hydrogeology, Major Ion Hydro-Geo-Chemistry, Borkena River Catchment, Awash Basin Amhara Regional State South Wollo, Ethiopia