ESTIMATING SWISS GROUNDWATER RESOURCES BASED ON A MULTIPLE APPROACH TAKING INTO ACCOUNT MAJOR HYDROGEOLOGICAL UNITS

Switzerland is rich in groundwater due to favorable climatic, hydrological and hydrogeological conditions. More than 80% of Swiss drinking water requirements are met by groundwater, and groundwater therefore represents a social and economic asset of national importance.

Knowledge about the extent of the resource is essential for sustainable groundwater management. This is of particular interest given the pressure on groundwater resources due to increasing water demand, intense underground engineering activities and climate change. In this context, two fundamental questions arise: How much groundwater is available underground? And how much groundwater is renewable and can thus be used in the long-term? The first issue is described by the groundwater volume, while the second is expressed by the safe yield.

To date, neither parameter has been determined at the national level or in a quantitative manner. Specific approaches were therefore developed which account for the major hydrogeological units and the geographical diversity of the country. These are based on a GIS-available Groundwater Resources Map of Switzerland on a 1:500,000 scale.

Highly productive porous aquifers along large river valleys represent the main drinking water resources in Switzerland. The groundwater volume stored in such aquifers was assessed by considering aquifer geometry and porosity. Estimates of groundwater volume in fissured aquifers were made from tunnel inflow measurements at selected sites in crystalline alpine rocks. Finally, a geological-tectonic approach enabled estimates of the groundwater volume in the saturated zone of karstified aquifers.

As fissured and karstified aquifers are discharged naturally by springs, discharge data from representative spring inventories were used to evaluate the safe yield for both aquifer types. Porous aquifers, however, are fed to a large extent by the infiltration of river water. In this case, a modelling approach for an extraction scenario along a river with typical aquifer characteristics provided maximum extraction rates. For porous aquifers not connected to surface streams, estimates of safe yield were derived solely from recharge by precipitation.