Groundwater exploration

Most of the liquid freshwater resources are stored underground as groundwater (99 %). The regional distribution on Earth, however, varies and depends essentially on climatic conditions as well as the subsurface geology. In contrast to many raw materials, a large part of the groundwater is renewed in the hydrologic cycle by percolating precipitation or infiltration of surface water.

Only a detailed knowledge on groundwater resources allows a sustainable use with adapted management. Groundwater exploration therefore goes far beyond the classic sinking of new boreholes and aims at understanding the groundwater system as a whole. Important parameters to be determined are the spatial extent, the hydraulic storage properties of the host rock, the interactions with under- and overlying aquifers or surface waters, and the spatial and temporal variations of groundwater properties. Groundwater recharge, natural discharge, and extraction rates must also be known for sustainable management. An important aspect for the use of groundwater is also its age, since many deep aquifers contain very old or fossil groundwater that is not or only partially renewable.

Groundwater sampling in northern Namibia Source: BGR

Today, groundwater exploration uses a multidisciplinary methodological approach based on the analysis of large-scale geology and tectonic conditions. For the spatial exploration of groundwater, geophysical and remote sensing methods play a central role. Among geophysical methods, electrical (geoelectrics) and electromagnetic methods (transient electromagnetics and airborne electromagnetics) are most commonly used to explore groundwater conditions because aquifers, aquitards and bedrock often differ in the measured quantity of resistivity or electrical conductivity.

Applying the SNMR method on Langeoog Source: BGR

In areas where groundwater resources are tied to geologic faults, magnetic methods can be promising if the fault systems can be detected with contrasts of rock magnetic susceptibility. These geophysical methods can be applied by measurements on the ground and by measurements from the air (mostly by a helicopter). The depths of exploration range from a few meters to depths of several kilometres, although for aquifer exploration only depths up to about 1,000 m are important. The nuclear magnetic resonance method uses excited proton spin to explore the water content. This is the only method that directly measures water content in sediment from the surface. However, the exploration depth of this method is limited to about 100 m.

Other data for groundwater exploration are obtained from observations and measurements at boreholes and wells. Drilling of boreholes is usually combined with borehole geophysics, petrographic analysis on borehole probes, mineralogical investigations and hydraulic tests. The latter, together with measurements of groundwater levels, are used to investigate the yield of wells and hydraulic properties of groundwater. Hydrochemical tests are not only used to determine groundwater quality, but together with results from isotope investigations can also provide information on the genesis of the groundwater. Age dating is performed using the tritium-helium and radiocarbon methods and, in addition, using the naturally occurring radioactive trace element chlorine-36 and the noble gas isotopes argon-39 and krypton-81.

Groundwater flow measurement Source: BGR

Databases, combined with GIS methods, are used for data management and presentation. The evaluation is mainly digital and spatial analysis is increasingly performed in 3D. It covers all areas from conceptual hydrogeological models to numerical models of groundwater flow and solute transport.

BGR participates in research projects and technical cooperation with developing countries or works together with the geological services of the German states in connection with federal tasks. It advises foreign and domestic institutions on the use of groundwater exploration methods, trains foreign partners and further develops application-oriented methods.

Current projects:

• D-AERO - German-wide airborne geophysical mapping
• Exploration of deep groundwater systems in the Cuvelai-Etosha Basin (Western Kalahari Basin in Angola and Namibia)

Find a compilation of all groundwater related projects in the English or German project list.