Ground water potential evaluation and use trends in upper Awash basin: with special emphasis to Koka- Becho area
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Date
2016-05
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Addis Ababa Universty
Abstract
The study area lies in the central part of Ethiopia within the upper Awash River basin with
particular reference to the Koka and Becho areas. Koka is located in East Shewa Zone of Oromia
regional state the center is located at North latitude of 8 026'27.56'' and longitude of 39 01'54.45''
East about 90 km south of the capital Addis Ababa. The Becho area is located between elevations
of 2062and 2109 m.a.s.l and the center is at 8.84° latitude and 38.36° longitude, with a total area
of about 509 km2.
The main objective of this research is to evaluate the groundwater potential and to study the
changes in groundwater use trends with time. In addition to convectional hydrogeology study
attempt was made to evaluate the recharge and discharge conditions. For the study of change in
use trends of ground water different data on ground water like the number of shallow dug wells,
amount of land irrigated with those wells, and others are collected for the past five years and
analyzed for future management options of ground water.
On annual basis, the Koka area has 900.3 mm; 721 mm, and 27.31 mm of mean total rainfall,
Actual Evapotranspiration (AET), and groundwater recharge respectively, and for the Becho area
the results show that the mean annual rainfall of the area is 1026mm with actual
evapotranspiration (AET) of 637mm, and recharge 227.34mm. The percentage of groundwater
recharge to rainfall is about 22.2% in Becho while it is only about 3.03% of rainfall that
recharges ground water.
Quaternary alluvial and lacustrine deposits are major hydrogeologic units in the study area in
addition to this units, the Becho part is covered with massive ignimbrite which acts as regional
aquiclude which separates the upper and lower volcanic basaltic aquifers.The major water
bearing horizon of this aquifer is the fractured features resulted in secondary permeability.
The amount of land irrigated using shallow ground water in Koka area was only 330Ha in the
year 2004 and in the year 2008, the area irrigated is about 1262Ha. The corresponding number of
shallow ground water wells used to irrigate this amount of land is increased from 250 to 2305
within the past five years. In Becho area the amount of land irrigated using shallow ground water
is increased from only 97 Ha to 496 Ha in the last five years with the increase in number of
shallow wells from 202 to 935. Different reasons are identified for change in ground water use trend in the study area among
them: technology access, on-demand groundwater services, water shortage in Awash, Modjo and
Teji Rivers and market demand for agricultural products are identified.
The shallow ground water table data around the Koka area shows that the ground water table
becomes deeper and deeper as we go away from the lake and in turn the size of the lake is
decreasing as a result of the shallow ground water pumping is increasing from year to year.
This study clearly identified problems in irrigation based agriculture. More innovative
groundwater use in a sustainable manner demands proper water management practice. This has to
be supported with better systematic control and research based groundwater use.
Key words: Ethiopia, Groundwater potential, Ground water use trends, Koka and Becho areas,
Upper Awash River basin.
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Keywords
Ethiopia, Groundwater potential, Ground water use trends, Koka and Becho areas, Upper Awash River basin