HYDROLOGICAL ASPECTS OF THE PROTECTION OF DRINKING WATER RESOURCES

Protecting of drinking water resources is one of the principal technical and scientific tasks of our days. The aquifers of the Great Hungarian Plain are one of the largest freshwater bases in Europe. The Pleistocene and Upper Pannonian layers of the Great Hungarian Plain are reservoirs of huge amount of fresh water and 80 per cent of wells are drilled on these aquifers. In the first half of the last century most of the wells were effluent ones. The extended abstraction of large quantities of water resulted in remarkable declines of the potentiometric surface (hydraulic head) in aquifers and produced drawdowns of regional scale. Since the 1990 s, the water extraction has been decreased in Hungary by 40-45 per cent. Subsequently, the hydraulic heads began to rise in the vicinity of water works, but at larger distances (8-10 km) they kept on sinking. This phenomenon is a clear manifestation of hydraulic continuity of large stratified sediment basins.In the first half of the 20th century the focus of attention was the aquifer, a geologic unit that can yield economic quantities of water. Active groundwater development has led to the recognition over the past quarter of a century that aquifers are vulnerable to overdraft leading to declining productivity and that aquifer exploitation may cause adverse consequences such as land subsidence and deterioration of wetlands. Experience shows that aquifers are components of larger hydrogeological units and that the notion of “protection of aquifers” has broader implications in space and in time. Because of the open nature of the hydrologic system, protection of aquifers must involve planning on a basin-wide scale. This requires that water management must be aided by long-term monitoring of the hydrogeologic system for water quantity as well as quality.The concept of multi-aquifer systems has been developed in which aquifers can receive water through subjacent and superjacent aquitards. The problem was mathematically analyzed first by Dutch hydrologists and engineers, and later by Jacob and Hantush. The first important Russian contribution on this subject came from Mjatiev, who analyzed the interaction of pervious strata separated by semiconfining beds. Hubbert (1940) published “The Theory of Ground-Water Motion”, a paper that still remains definitive. He examined the physical meaning of the fluid potential, derived a tangent law for the refraction of flow lines, and established the foundations for the study of regional groundwater systems. In the 1960’s attention has again turned to the regional scale, with the groun