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Surface waters and groundwater in karst

Karst is defined as a terrain, generally underlain by limestone or dolomite, in which the topography is chiefly formed by the dissolving of rock, and which is characterised by sinkholes, sinking streams, closed depressions, subterranean drainage and caves (Field 2002). A wide range of closed surface depressions, a well-developed underground drainage system, and a strong interaction between circulation of surface water and groundwater typify karst. Due to very high infiltration rates, especially in bare karst, overland and surface flow is rare in comparison with non-karst terrains. Carbonate rocks are more soluble than many other rocks. They are subject to a number of geomorphological processes. The processes involved in the weathering and erosion of carbonate rocks are many and diverse. The varied and often spectacular surface landforms are merely a guide to the presence of unpredictable conduits, fissures and cavities beneath the ground. But at the same time these subsurface features can occur even where surface karstic landforms are completely absent. Diversity is considered as the main feature of karstic systems. They are known to change very fast over time and in space, so that an investigation of each system on its own is needed. Karstification is primarily a geological characteristic important for water circulation and storage. It can be defined through density, frequency and number of all types of karst voids. Generally it is greatest at the surface and decreases with the depth of a karst massif. Karstification is a continuous process governed by natural and man-made interventions. In karst terrains, groundwater and surface water constitute a single dynamic system. The groundwater and surface water are hydraulically connected through numerous karst forms which facilitate and govern the exchange of water between the surface and subsurface (Katz et al. 1997). A complex underground conduit system, as well as interplay of pervious and impervious layers of karst massif are an inherent characteristic of many (practically all) karst systems. Groundwater and surface water exchange with booth adjacent and distant aquifers through underground routes or inflows from surface streams, natural lakes and in recent time artificial reservoirs. Due to this reason one of the almost inevitable characteristics of open streams, creeks and rivers in karst regions is that they either have partial water loss along their course or completely sink into the underground (Bonacci 1987). de Marsily (1986) states that the study of the water cycle or hydrology in its wider sense is usually divided into three separate disciplines: meteorology, surface hydrology and hydrogeology or groundwater hydrology. What is difference, and what is identical in karst hydrology and hydrogeology? Usual definitions of hydrogeology and hydrology are UNESCO and WMO (1992): (1) hydrogeology is branch of geology, which deals with groundwater and especially its occurrence, while (2) hydrology is science that deals with the processes governing the land areas of the Earth, and treats various phases of the hydrological cycle. From these definitions is hardly possible to strictly distinguish between the two scientific disciplines. In engineering practice the division is grounded in argument that hydrology deals with surface water and hydrogeology with groundwater. However, strictly enforcing such division could have harmful consequences on the development of both sciences, especially in case of investigations of the karst water circulation. Synthesis of hydrogeological and hydrological approach could expedite progress in karst surface water-groundwater system understanding. Hydrogeology generally deals with groundwater occurrence and circulation in aquifers. Aquifers are in turn geological units involved in transmission of quantities of water under ordinary hydraulic gradient. At the same time interest of hydrology is manly focused on water balance, which is basically accounting of the inflow to, outflow from, and storage within a hydraulic unit such as a drainage basin or aquifer. Very often it is impossible and harmful to separate two above mentioned approaches, but in practice it predominantly occurs.

Karst, Aqufer, Spring, Ponor

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