Yield of near-surface groundwater resources

Groundwater is the source of more than 80% of the water supply of Switzerland. For this reason, an urgent task of both the population and the administration is to seek a sustainable exploitation and optimal protection of groundwater resources. Groundwater flow patterns are very complex and can almost never be directly observed, unlike the case of surface water systems. Groundwater flow depends on the geological structure of the subsurface, of which often little is known.
After infiltrating into the subsurface, groundwater circulates through interstices of the aquifer and reappears at discharge points (springs or pumping wells). An aquifer is a geological formation in which a large amount of groundwater circulates through openings. These can be pores between the rock grains, open fractures or even large cavities, such as in karstic rocks. The zone where the openings are filled with water is known as the saturated zone of the aquifer. Because of the great complexity of natural groundwater systems, only simple hydrogeological situations are illustrated in this map to make the circulation patterns in the main aquifers of Switzerland more readily understandable.

In Switzerland, it is possible to distinguish roughly between six major types of aquifers

Recent fluvial deposits
Many valleys in Switzerland have been shaped by Quaternary glaciers. As the glaciers retreated, fine lacustrine sediments were first deposited. Then, the rivers built up alluvial floodplains made up of coarse sand and gravel.

Fluvio-glacial deposits
are similar to recent fluvial deposits, but they fill former periglacial valleys. Fluvio-glacial deposits are rarer than more recent fluvial deposits, and are often completely covered by moraines.

Molasse rocks
Molasse rocks, which make up the Central Plateau, are very heterogeneous sedimentary rocks composed of clays, marls, sandstones and conglomerates. Only the sandstone and conglomerate layers can contain enough water to supply springs.

Calcareous karstic rocks
Limestones and dolostones form aquifers of highly heterogeneous permeability. Groundwater flows through small fractures and pores, and in conduits and cavities, which are sometimes of considerable.

Karstic evaporites
Evaporites are sulphate-bearing rocks. In Switzerland, such rocks occur mainly in Triassic formations.

Crystalline silicate rocks
Tectonics are a decisive factor for the circulation of groundwater in crystalline massifs. Silicate rocks (e. g. granite, gneiss and serpentinite) are neither porous nor soluble. Discontinuities of tectonic origin – such as faults, slip faults and joints – are responsible for the heterogeneous, low permeability of these massifs.