Preliminary hydrogeological aspects in the Kilimanjaro region, North East Tanzania

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University of Dar es Salaam
Kilimanjaro region is situated in the north-earthen part of Tanzania. Its bedrock is composed of intermediate to basic volcanic of Neogene age to the north and Precambian metamorphic rocks of Usagaran system in the south. The overburden consists of transported and materials whose thickness increase towards the south, reaching whose thickness increases towards the south reaching maximum of more than 200m in Kahe-miwaleni basin which is the main discharge area of the region. The study attempts to evaluate and review hydrogeological aspects of Kilimanjaro region based on desk studies and supplemented by limited field mapping, sampling and testing of waters, soils and rocks, sixty three representative water samples, thirty four disturbed soil samples and thirty three bulk rock samples taken in the field between September 1988 and November, 1988 together with previous hydrological, hydrogeological and hydro chemical data were assessed. The combinations of statistical and hydro chemical analysis, geological and hydrological features have been used to evaluate the ground water potential for future development. The movement and storage of underground water in metamorphic rocks, volcanic rocks and alluvial formations is controlled by the amount and connectivity of fracture channels and granular porosity respectively. The southward movement of ground water towards the Kahe Miwaheni basin has been deduced from the directions of lava flows, tilting of rock massifs, presence of contact spring as well as the increase in the amount of chloride and total dissolved solids. For economical exploration and development of boreholes with sufficient amount of yields, drilling up to < 10-25m, 50-60m and 65-85m.b.g.i in alluvial, volcanic and metamorphic aquifers respectively is recommended. However in the eastern part of the Kilimanjaro Mountain ground water aquifers are deeper than the rest of the study area that is down to 100-150m.b.g.i. Based on trilinear diagram, three types of waters have been identified as sodium bicarbonate, magnesium bicarbonate and non-dominant types. Hydro chemical facies for anions have been identified as bicarbonate facies in alluvial deposits and bicarbonate chloride sulphate facies in basic and intermediate volcanic rocks as well as alluvials. Hydro chemical facies for cations are sodium calcium and calcium sodium. Both surface and groundwater’s are suitable for domestic, industrial and irrigation purposes. A synoptic hydrogeological map prepared in the present studies shows four distinct findings that are relevant in community planning of water resources. Firstly, within middles slopes of the mountains, the construction of dams and gravity annals is appropriate, secondly within the lower slopes of mountains and plains (discharge zone), a combination of spring tapping and borehole construction is economical, thirdly, the Kahe Miwaleni basin which is about 700 square kilometers requires detailed evaluation, development and management of its ground water resources for domestic, hydroelectric and irrigation purposes, fourthly water supply to the eastern part of Kilimanjaro mountain settlements can be augmented from water supplies in the central parts of the mountain or lake Chala and its spring in Kenya.
Available in print form, EAF collection, Dr. Wilbert Chagula Library, class mark ( THS EAF GB1149.M9 )
Hydrogeology, Kilimanjaro, Tanzania
Mwende, E ( 1991 ) Preliminary hydrogeological aspects in the Kilimanjaro region, North East Tanzania, Preliminary hydrogeological aspects in the Kilimanjaro region, North East Tanzania,Masters dissertation, University of Dar es Salaam, Dar es Salaam.