Assessment of Vulnerability of Alluvial Aquifers of Transition Zone to Contamination: The Case of Danakil Basin, Northeastern Ethiopia
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Date
2022-06
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Addis Ababa University
Abstract
Groundwater is indispensable to humankind, but with the increasing load over this precious
resource, it has become necessary to study it in detail with geological as well as hydrogeological
aspects
to understand the nature of the groundwater resource of a Danakil basin to
manage it well and use it sustainably, vulnerability assessment of the resource is conducted to
highlight the areas which are more susceptible to contamination. In the present study, an attempt
has been made to account for the groundwater vulnerability using an overlay index method,
DRASTIC, which is used to prepare a vulnerability map using GIS, of the study area, Danakil
basin. The DRASTIC Vulnerability index (DVI) is calculated as the sum of the product of ratings
and weights assigned to each of the parameters on a scale of 1 to 10 and 1 to 5 respectively.
And a 2D finite element groundwater flow and solute transport model were developed to
simulate the spatial and temporal variations of the salinity intrusion in the alluvial aquifer of the
Danakil basin taking into account the transition zone between freshwater and saltwater. The
available historical records of water table levels were used to calibrate the developed model.
Emphasis was devoted to the response of the transition zone to different pumping scenarios in
the study area. The vulnerability index ranges from 50-149 and is classified into three classes it
reduced approximately 20%, 50% and 30% of the area lies in low, medium, and high
vulnerability zones. Results from the solute transport model also indicated that the saltwater
intrusion problem has evolved during over-abstraction (pumping). Unlike previous
investigations, this study presents the most qualitative assessment of the available groundwater
in the alluvial aquifer under different pumping scenarios. In conclusion, Danakil basin alluvial
aquifer is vulnerable to geogenic sources of salt intrusion due to over abstraction. Results can be
an important input for policymakers in the development of sustainable groundwater protection
and abstraction strategies for the region.
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Keywords
Alluvial Aquifers, Contamination, Danakil Basin, Vulnerability