The IRC is a non-governmental organization operating in 26 countries in the world. IRC started operation in Ethiopia in year 2000, currently working in five regions in providing relief services to refugees, victims of drought, and war affected populations.
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Geophysicist
Posting Date: May 18, 2017
Closing Date- May 24, 2017
Vacancy Code- 01/458
INTERNATIONAL RESCUE COMMITTEE / ETHIOPIA PROGRAMME
TERMS OF REFERENCE
Background
The IRC is a non-governmental organization operating in 26 countries in the world. IRC started operation in Ethiopia in year 2000, and is currently working in five regions in providing relief services to refugees, victims of drought, and war affected populations.
Under Emergency WASH Resilience project IRC Ethiopia is implementing water supply activities to the target beneficiaries in the Afherom Woreda (Tigray Region). The major activities are bore holes and shallow well drillings and scheme construction works. For these purpose it is planned to undertake groundwater resource assessments in the project intervention kebeles. The aim of this study is to assess the groundwater potential and select the appropriate sites for water well drillings. This will be carried out by evaluating the geo-electrical and hydrogeological characteristics of the aquifer in the area.
Objective
To deploy one senior geophysicist to the proposed two drilling area and undertake the electrical resistivity data collection and analysis. The electrical resistivity method is more powerful for it provides a quantitative measure of the conducting properties of subsurface materials which in turn largely depend on the moisture content. The method is one of the most sensitive geophysical methods to determine the presence of water saturated horizons in the subsurface, the depth to these zones and also groundwater flow pattern. The Vertical Electrical Sounding (VES) is done by introducing a low current into the ground through the stainless steel electrodes and the resistance of the earth material is measured during the passage of the current simultaneously. The geophysical survey significantly supplements the subsurface geological and hydrogeological assessments and provide additional subsurface information.
Specifically the VES survey was aimed to:-
1. Detect and outline subsurface structures and thickness of the deposits
2. Determine the depth to the top of the saturated zone
Scope and focus
1. According to the standard VES data collection process and field procedures undertake Vertical Electrical Sounding (VES) readings in the two shallow well drilling areas (2 VES for each sites).
2. During the survey properly set and configure the Terrameter and its accessories and progressively increase the current electrode separation.
3. Take the resulting potential difference or potential drop readings properly and plot the curves.
4. The sounding curves collected in the field needs has to be interpreted by two layer master curves and auxiliary point charts (curve matching), the layer parameters obtained by curve matching has to been used as a starting model (initial guess).
5. A combination of resistivity data interpretation software (RESIX IP, RESIST and/or Win Resist) has used to obtain the initial models and the layer parameters (layer resistivity’s and depths) from the sounding data.
6. The inversion algorithm then generate theoretical Schlumberger apparent resistivity curves, and then adjust the starting model in a number of iterations until a satisfactory best fit between the observed(field curves) and computer generated theoretical sounding curves are obtained .
7. Interpret the various geo- electrical layers in terms of hydrogeological layers and correlate it with the geological features of the study areas.
8. The individual is supposed to avail the necessary surveying equipments such as:
· Portable Terrameter SAS 4000, powered by 12V battery that has very high resolution accompanied with four principal components: -
· An electronic unit that feeds electric current to the electrode and measures the resistivity of the entire circuit and other necessary materials
9. identify the potential drilling sites for each localities Out of the VES readings taken
10. Present the final outputs and interpretation document of the survey soft and hard copies
The IRC’s responsibility
Outputs and deliverables
1. Identify & present the potential drilling sites (one for each localities)
2. Present the study final report document in soft and hard copies.
Time line: Activity to be completed up to end of May 2017.
Experience:
· MSc or BSc Degree in Geophysics or directly related fields
· At least 8 years of direct experience with accredited entities in groundwater resources assessment.
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