engleski

Sinking, losing and underground karst streamflows

Sinking, losing and underground streamflows are typical and relatively frequent karst phenomena. A sinking surface streamflow can be defined as a surface river or stream flowing onto or over karst and which then disappears completely underground through a swallow hole and which may or may not rise again and flow as a resurgent surface river or stream. A losing streamflow can be defined as an open stream or river that loses water as it flows downstream. A losing streamflow is a surface stream that contributes water to the karst groundwater system in localized areas. It has cracks in its bed which allow water to flow into the groundwater. A direct way for surface water to become groundwater is by the capture of surface streams in subsurface voids through swallets. These features swallow the surface stream and represent a rapid and direct manner of for groundwater recharge. Losing stream segments are important groundwater recharge zones for underlying karst aquifers. A losing streamflow is one with a bed, which allows water to flow directly into the groundwater system. The level of water in a losing stream is above the water table ; in comparison to the level of water in a gaining stream is below the water table. In a losing stream water infiltrates underground because the water table is below the bottom of the stream channel. Losing streamflows are often used in relation to karst aquifers ; the aquifers gain the water that the losing stream deposits. Underground or subterranean streamflows are subsurface karst passages with the main characteristics of open rivers or streams. In underground streamflows water flows through caves, caverns, karst conduits and large galleries in karst underground. The karst underground system provides access to fragments of the abandoned conduit system which has comparable, but not identical, hydraulic geometries to those of surface rivers or streams. Due to very special and complex underground and surface karst forms there are a variety of different cases of sinking, losing and underground streamflows in karst. An attempt at their classification is given in the paper. Paper treats mainly hydrological aspects of sinking, losing and underground streamflows. Several cases of the special hydrological behaviour of sinking, losing and underground streamflows mainly in the Dinaric karst, are also explained.

karst hydrology; sinking; losing; underground streamflow

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