Ethiopia was hit by an El Nino induced drought during 2015/2016 that left millions across the country without access to adequate water supply. More than 220 districts throughout the country faced water supply emergencies. These areas are characterized by frequent shortage/shifting of rainy season and resulting water supply problems. During normal rainy years, the communities in these areas rely on rainwater harvesting, traditional ponds, hand dug wells excavated along wadis and a few shallow groundwater wells.
The United Nations Children’s Fund (UNICEF) has a programme of rural water supply and is also the Emergency WASH cluster lead in Ethiopia. Hence it supports the government and other partners in the rehabilitation, maintenance and construction of new water supply systems in response to the drought.
This report presents the first part of a joint hydrogeological study of UNICEF and the European Commission Joint Research Centre (JRC) in nine selected woredas in the lowland areas of Afar, Somali, SNNPR, and Oromia regions in Ethiopia. The study aims to improve groundwater sector knowledge and the access to safe water in these woredas. Specifically, the main goal of the project is to locate drilling sites with a substantial increase in drilling success rate.
In order to improve the success rate, it is vital to undertake reliable groundwater investigations. However, conventional methods to generate detailed hydrogeological maps require a huge amount of time, manpower, logistical and financial resources. Besides hydrogeological field studies, remote sensing (RS) based analysis can be carried out to identify the most feasible sites for drilling. The advantage of using RS data is their large spatial coverage and homogeneous data acquisition. Although there is no satellite-based sensor to measure the occurrence and amount of groundwater directly, different RS-based parameters (e.g., elevation, precipitation, evapotranspiration, vegetation) can be utilized in the assessment of groundwater potential as several studies have demonstrated that spatial variability in groundwater levels is controlled by surface and subsurface topography, vegetation, soil- and bedrock properties. The use of RS data does not eliminate or exclude the in situ data collection, which is needed to verify the accuracy of RS data and to aid their interpretation, but RS data helps to minimize field data collection.
A combined approach was therefore applied in this study aiming to use all available information to increase the rate of successful drilling. The approach consists of three phases: 1) Remote sensing and overlay analysis, 2) Hydrogeological and geophysical field surveys, and 3) Drilling of productive test wells. The present report covers the first phase that comprised two main steps: a) data acquisition, processing & RS analysis, and b) overlay analysis. The RS analysis aims to generate thematic maps from RS-based products that are potentially relevant for the assessment of groundwater occurrence. Different RS datasets have been used to generate maps of the study woredas related to topography, geological structures (lineaments), climate (precipitation and evapotranspiration), vegetation, and hydrology. Information derived from these RS-based maps and other sources (e.g. geological maps) are then combined in a weighted overlay analysis to derive maps indicating the probability of groundwater occurrence (groundwater potential).
Parameters assumed to be related to the main factors for the occurrence of groundwater (namely permeability of the geological unit, lineament density, slope, and recharge) were directly integrated in the overlay analysis that resulted in the generation of a groundwater potential map. Senior professionals from the Ethiopian groundwater sector were consulted for the weighting process. Other parameters (like NDVI, TWI, river network) and existing water point information were then utilised to check the plausibility of the map and to determine target areas for further analysis. Since the interest was also in deep groundwater exploration, the groundwater potential maps were adapted for deep groundwater using conceptual models and deep well data wherever the information was available. Afterwards, ground-truthing work, including the identification and prioritization of permanent settlements and villages with critical water supply problems and the collection of additional local hydrogeological information was undertaken in the target areas and the surroundings to check the results of the overlay analysis. The results of the ground-truthing revealed that the selected target areas for further analysis were appropriate.
In the next steps, detailed hydrogeological and geophysical investigations will be conducted for the siting of drilling spots over the selected target areas. Similarly, based on the evaluation of the drilling results, the methodology will be up-scaled for further application to other areas.
A precursor methodology was previously applied in selected woredas of Afar and Tigray. The results from this and actual drilling results obtained, as well as the present field verifications indicate that the method can certainly add value to the conventional hydrogeological investigation methods to improve drilling success rates. The applied approach allowed us with relatively low cost to identify areas with a high groundwater potential and therefore reduced the expenses for field work. Drilling results of about seven boreholes drilled within Afar and Tigray have been productive. Therefore, we recommend this approach should be encouraged and expanded to a larger scale over the country, continuing the successful partnership between UNICEF and JRC.
KETEMA Abebe;
LEMECHA Gezahegn;
SCHUCKNECHT Anne;
KAYITAKIRE Francois;
2016-11-04
Publications Office of the European Union
JRC103616
978-92-79-63205-1,
1831-9424,
EUR 28179,
OP LB-NA-28179-EN-N,
https://publications.jrc.ec.europa.eu/repository/handle/JRC103616,
10.2788/050278,
