Integrated Water Resources Potential Investigation of the Weybo River Catchment Welayita-Hadiya Zones, Southern Ethiopia

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Addis Ababa Universty


The Weybo river catchment is located in the southern part of Ethiopia. It is confined by the major Omo-Gibe Basin and situated at the south-west margin of the Main Ethiopian Rift. The area is dominantly covered by acid volcanics, both pyroclastic flows and falls, of Miocene to Pliocene age. Integrated approaches are adopted to effect the assessments of water resources potential of the catchment. The different components, controls and/or parameters in each of the methods are estimated, computed or qualitatively described applying different empirical and physical techniques. The different techniques greatly help compare resultant values of some parameters, controls or components. It is this comparison that help generate ideas on the power of workability of that specific technique in the study area. This new work reveals an overall balance among the components of the water budget. Soil moisture deficits are recorded in months of November through mid March and the remaining 7 months remain in surplus. However, it has been investigated that the ground water recharge is declining in an appreciable rate for a small decrease in precipitation and a moderate increase in surface runoff. The remaining hydrometeorological parameters show a lower to moderate increase for the last 15-20 years. Ground water potential of the Weybo River catchment is seen to be under the control of fracturing intensity and degree of weathering. Higher hydraulic conductivity zones are mapped at or near fractured regions and their values are decreasing away from the structures. It has also been seen that aquifers that are formed from the deeply weathered ignimbrites, rhyolites and trachytes yield low and possess a lower hydraulic conductivity generally in the order of 0.1-0.5. The apparent resistivity values do not show a clear contrast between the highly weathered aquifer formations and the fractured ones. Lower and nearly similar values (1-10Ω-m) are obtained in both regions. Both graphical and statistical presentations of the physical and chemical parameters of the water samples provide a good deal of information on the characteristics of ground water flow systems, recharging and discharging zones, and aquifer interconnectivity in east and north-east parts of the study area and its neighboring watershed. Piper, Collins, Schoeller, HCA and 2-dimentional surfer plots have been used to facilitate analyses and interpretations of the data. Chloride-mass-balance technique results an over-estimated rate of recharge in the study area, which is calculated to be 123.5mm/annum. The most likely justifications are cited, and suggestions are also forwarded in a view to bring the method in to effect



Weybo River Catchment