Surface and Groundwater Resource Evaluation of Upper Guma Sub-Catchment (Bonga)
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Date
2005-06
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Addis Ababa Universty
Abstract
The development of a balanced plan for water resources utilization requires full knowledge of
quantity, quality and distribution of water resources and also the changing pattern of land use in
the entire water shade of and its influence on the river flows in the study area (Guma Sub
Catchment) which is located and is bounded within7010' N- 70 25' N latitude and 360 05’ E - 360
30' E longitude.
The total aerial coverage of the study area is about 876 km2study area. Prior to this research work,
the contribution of information about the water resources and water budget components were not
known.The combined effects of climate and geology on the catchment topography yield an
erosion pattern which is characterized by a net work of channels or streams. Topography of the
area ranges from flat to mountains and gorges. The average monthly rainfall ranges from about
253.51 mm in the highlands in the northeastern part of the study area and 48.86 mm in the
northwestern part of the area.
Hydrologic and hydrogeologic investigation and water balance calculation were used to study
the surface-ground water interaction in Upper Guma Sub-Catchment with emphasis given to
hydrochemistry.Classification of water types in the area according to the tri-linear piper diagram
plots show that, most of the hand dug wells are Ca-Na-HCO3 and Ca-Mg-Cl water type where
as springs show, Ca-Na-HCO3 and Ca-Mg-HCO3 water type. The borehole result has a water
type of Ca-Mg-HCO3 and Na-Ca-HCO3 which signifies the dominancy of volcanic terrain.
Based on major cations and anions, the general water quality for public supplies, irrigation and
industry are identfied in the study area.
Values of net groundwater recharge estimate is determined from water balance calculation and
found to be 110.7 MCM annually accounting not greater than ten percent of the annual
precipitation indicating that groundwater resources should be wisely exploited giving due
attention to the integration of the surface water resources of the area. The result of this study can
be used as data source for future sustainable development and management the catchment area.
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Keywords
Guma Sub-Catchment