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|Title: ||HYDROGEOLOGICAL AND HYDROGEOCHEMICAL CHARACTERIATION OF BELES RIVER BASIN, NORTHWESTERN ETHIOPIA|
|Authors: ||Girma, Addisu|
|Advisors: ||Tenalem Ayenew (Prof.)|
|Copyright: ||Jun-2010 |
|Date Added: ||30-Apr-2012 |
|Abstract: ||Beles River Basin is part of northwestern lowlands and its adjacent highlands. It is found in
the southwestern direction of Lake Tana, It has the total areal coverage of 14,200 sq. Km and
elevation varies from 500 to 2,700masl. The Basin has all climatic zones, except alpine. The
objective of the thesis work was characterizing the hydrgeology and hydrogeochemistry of the
basin using integrated methodology and approaches. Secondary data has been collected from
the respective institutes and organizations and primary data of water samples for water
chemistry was analyzed in the laboratory.
The rainfall pattern of the Basin is unimodal. It has an aerial depth of precipitation of
1352.9mm/yr that was computed using isohyetal cotour map method. The precipitation
condition has high orographic effect. The hydrograph of the two main rivers reflects the
unimodality of the rainfall. The variation of these rivers discharge is very high from dry to
rainy season that shows the infiltration of the Basin is low.
The Basin has geology of Precambrian basement complex, undifferentiated formations,
tertiary and quaternary volcanic and quaternary sediments. It has lithological units of gneiss
and associated high-grade metamorphic rocks, low-grade supra-crustal metamorphic rocks,
syn- and post-tectonic intrusive of acidic to intermediate composition, Cenozoic volcanic
rocks, and quaternary sediments. The most important tectonic settings are dominantly aligned
N-S and NE-SW direction.
Hydrogeological map of the Basin was produced based on previous reports and maps and
field observations of geology, topography and water point inventory, weathering and
fracturing condition of the formations. Accordingly the hydrogeological characterization of
the area revealed; porous aquifers (alluvium, colluviums), fissured and karst aquifers
(marble), fissured aquifers (sandstone and volcanic rock), fissured aquifers of low potential
(some non-carbonate metamorphic and intrusive rocks) and aquitards (some non-carbonate
metamorphic and intrusive rocks). Accordingly the aquifer of the basin was classified in to
very low, low, intermediate, intermediate to high and high productive formations.
The regional recharge zones are the highlands of the Basin Such as; Wombera, Balay, Dangur
and Kar mountains and highlands areas of Dangila and Achefer. The discharge areas are
intimately linked with groundwater flow lines and the regional groundwater flow direction is
to the southwest following the topographic gradient.
Hydrochemical data shows that evolution of major ions, water types, and direction of
groundwater flow. It shows a general trends increasing total ion concentration along flow
Graphical 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, recharge and
discharge zones, and evolution of major ions in the basin. The general natural water type of
the basin is Ca dominated cation and HCO3 dominated anion (Figure6.9) and has low (fresh|
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