Hydrogeological Investigation of the Upper and Middle Borkena River Catchment, Northern Ethiopia, Wollo
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Date
2001-07
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Addis Ababa Universty
Abstract
The geology, hydrology, hydro geology and hydrochemistry of the Borkena catchment which is
located on the western edge of the Afar rift was studied based on conventional geologic and
hyd rogeological mapping, river discharge measurements, water sample analysis and assessment
and interpretation of hydrometeorological data. The main objective of this work is to
understand the different lithologic unit and to characterize and group them into
hydrostratigraphic unit and map them, to analyze the water balance and to study the water
quality.
Four hydrostratigraphic units were recognized and mapped. These are: colluvial and river
channel deposits, alluvial deposits, scoraceous and basaltic lava flow and fractured massive
basalt, welded tuff and rhyolite. Generally the volcanic rocks lie with in the recharge zone
while the Quaternaiy sediments lie in the discharge zone. Accordingly the hydrostratigraphic
unit located on the Quaternary sediments are characterized by many springs and hand dug well
where as low or rare in the volcanic regions.
From storage, utilization and abstraction point of view, the colluvial and river channel deposits
are the most promising units than other units as a result most of the springs, hand dug wells
and boreholes are located in this hydrostratigraphic units.
Generally seven rock units and three set of faults are identified and mapped at the scale of
I :50,000. Among the rock units, scoraceous and basaltic lava flow and alluvial deposits cover
more than 70 percent of the catchment. From hydrochemical analysis, measurement of TDS, EC and other variables, the water bodies
are characterized by low total dissolved solids (TDS) and low electrical conductivity (EC)
values as a result they are classified as fresh water and their utilization for vanous purposes
scarcely bring danger.
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Hydrogeological