CASE STUDY
Case Study - Pinpointing groundwater wells in Somaliland
Sustainable water surveys in Somaliland
Our sTEM+ instrument has recently been used to pinpoint groundwater wells in Somaliland. The client is Dairy without Borders, a Danish NGO focused on establishing and supporting milk and dairy sector projects in developing countries. The project is funded by the Ramboll Foundation and undertaken by Peter Thomsen, NIRAS, Max Halkjær, Geophysical Imaging Partners, and a local geophysicist, Ahmad Khalif. TEMcompany donated the sTEM+ instrument for project use. The results are astonishing, clearly showing the aquifer layers.
Project Background
The pastoralist community Af-Galmadow, located 40 km east of Erigavo, has limited access to water for parts of the year. Currently, water is transported by foot hours away twice a week. A well field can ensure a sustainable and continuous water supply and, in the future, act as the cornerstone for a local dairy.
Geophysical investigations, especially resistivity soundings, have provided valuable knowledge about hydrogeological conditions. For the hydrogeological mapping program near Erigavo, the Time-domain Electromagnetic (TEM) method has been introduced. Since TEM soundings are easy and fast to perform, dense spatial pseudo-3D mapping is possible.
The state-of-the-art sTEM+ system from TEMcompany collected soundings during three field days. The sTEM+ system provides high-quality soundings to a depth of approximately 200 m. The TEM soundings were spaced densely along a number of profiles to obtain a good resolution of the potential water-barring structures. In the following phase, the geophysical results are used to identify the optimum site for a new production well.
Results
During the three-day fieldwork, 47 high-quality soundings were collected. The data were inverted with a 1D-resistivity model using Seequent’s SPIA software. The resulting models were imported to the software package Workbench and presented on GIS and along model sections.
Based on the hydrogeological knowledge, the area is dominated by a thin package of sediment above limestone. The aquifers consist of a fractured zone in the upper parts of the limestone. From existing resistivity sounding, it is estimated that the fractured limestone making up the aquifers ranges in resistivity from 10 to 30 Ωm.
Benefits of the survey
Based on the sTEM+ survey results, the site with the most potential for a well field is designated. Based on the expected regional hydrogeological conditions, the aquifer is interpreted to be 20 to 50 meters thick. Compared to traditional geophysical resistivity surveys, e.g., VES, this sTEM+ survey has improved the resolution significantly, thereby minimizing the risk of drilling a dry well.
