Karst Groundwater

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Published on: Mar. 2, 2000

Last revision: Nov. 4, 2010

rainfall by using fire hydrants and hoses to introduce a 30-minute pulse of water and a harmless dye into a sinkhole. We then measured the response in the cave stream. We tested six sinkholes this way, and each accepted water faster than we could deliver it with a fire hose.

The recharge water from each sinkhole increased water levels at the sampling station on the cave stream in 45 minutes or less, even though the underground travel distances were as much as a quarter mile. Intense thunderstorms in the area would add water to all sinkholes at once, and would substantially increase the travel rates over what we observed in our study.

The experiment shows how rapidly caves and springs respond to surface runoff that enters the groundwater system through discrete recharge zones. Because intense rainstorms can cause rapid and lethal flash floods on cave streams, and water may totally fill passages, people should give careful consideration to the weather before entering caves.

Although sinkholes are easy to identify, other discrete recharge zones show little or no surface evidence of the direct connections between the surface and the groundwater system. If septic fields intercept such discrete recharge zones they contaminate the groundwater. In a karst area, the fact that "everything goes away" does not necessarily mean that a septic field system is adequately treating the sewage.

Losing streams are also discrete recharge zones. A losing stream is a surface stream that contributes water to the karst groundwater system in localized areas. In the Ozarks, almost every stream that lacks year-round flow has losing stream segments.

Losing stream valleys are important groundwater recharge zones in the Ozarks. Although valley areas represent about 10 percent of the land area, they are responsible for about 40 percent of the groundwater recharge to karst groundwater systems. Protection of water quality in these valleys is critical for protection of groundwater quality in wells and springs.

The typical losing stream in the Ozarks is a dry gravel stream bed, except for a few days or weeks after major rainfall. Many of the losing stream segments were once sinkholes that were filled with coarse stream gravel washed in during storm flows. Losing stream segments can move a few gallons to a few hundreds of gallons per minute of water from the surface stream into the groundwater system.

One losing stream segment we studied made slurping sounds as it transported over a million gallons per

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