Characterization of Aquifers and Hydrochemistry in Volcanic Terrain of Central Ethiopia
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Date
2010-06
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Addis Ababa Universty
Abstract
This thesis work aimed to characterizing the different aquifer systems and their hydrochemistry of volcanic aquifer in central Ethiopia which encompasses Upper Awash, Jema, Mugher and Guder River basins surrounding the city of Addis Ababa.The area can be divided in to three geomorphologic features (zones): central gentle slopes and plateau, western, northwestern and northeastern deep gorges of Blue Nile, Guder, Muger and Jema rivers and low elevation area, and elevated picks of mountains and ridges. The main rainy season of the study area is from June to September. The recent Quaternary deposits, Quaternary basalt, Tertiary basalts, ignimbrites, rhyolites, trachytes and Mesozoic sediments are the stratigraphy of the area from youngest to oldest. The hydrogeological classification is done using qualitative and quantitative approaches. On the basis of hydrogeological characteristics of lithologic units and different data collected from different organization, the classification leads to different aquifers and aquiclud. High productive porous aquifers of sandstone (T=100-500 m2/d, Q=5-25l/s). High productive fissured and/or karst aquifers of limestone (T= 50-100 m2/d Q=2-5 l/s). High productive fissured aquifers of Tertiary and Quaternary basalt (T=100-500 m2/d, Q=5-25 l/s). Moderate productive fissured aquifers of Aiba basalt Lower ignimbrite and aphanitic to Medium grained vesicular trachyte and trachy basalt (T=50-100 m2/d, Q=2-5 l/s), Moderate productive porous aquifers of sandstone and Quaternary deposits, (T=50-100 m2/d, Q=2-5 l/s) Low productive aquifers of Entoto rhyolite and trchyte ( T=1-10 m2/d and Q=0.05 l/s) and aquiclud or minor aquifers with limited ground water resources. Moreover, different types of maps and their analysis result indicate widely variable aquifer characteristics. Hydro chemical data shows that evolution of major ions, such as Na, K, Ca, Mg, SO4, NO3 and HCO3 and analyze some physical parameters PH, TDS and Conductivity, water types. The result shows that the dominant water type is bicarbonate especially Ca-Mg-HCO3, Ca-Na-HCO3 and Ca-HCO3. The water quality analysis mad based on Florid, Chloride, Nitrate and Total Dissolved Solids (TDS) results approved the potential of groundwater contamination in the area. Generally the ground water of the area is suitable for domestic use. However, there are also exceptions which are susceptible for pollution and needs proper follow up of its quality
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Hydrochemistry in Volcanic