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NATURAL HERITAGE

Living on Karst

A Reference Guide for Landowners in Limestone Regions

Produced by the Cave Conservancy of the Virginias, June 1997



Sinkhole Management

Sinkholes are natural drainage points for our groundwater system, so they should never be filled. If a sinkhole is plugged, water will not drain properly, may run off onto adjacent property, and possibly may cause flooding, subsidence, erosion, and pollution. The downstream springs, caves, wells, and streams which receive water from the sinkhole should be identified.

If collapsed sinkholes present a hazard to health and safety, and structures, they often can be stabilized in a way that maintains natural drainage abilities.

Always contact a geologist or engineer experienced in sinkhole repair before attempting to backfill or "seal" a sinkhole.

Do not locate a septic system, feed lot, animal waste lagoon, or storm water basin, near known or suspected sinkholes or caves. If sinkholes appear near such sources of bacterial contamination, use appropriate methods to prevent runoff from these areas from entering the sinkholes. Minimize unnatural or increased drainage into sinkholes.

Do not apply any fertilizer, pesticides, or other chemicals within at least 100 feet of a sinkhole. Notify your contractor of the location of all sinkholes.

If you purchase property where trash has already been dumped in sinkholes, consider cleaning them out and restoring vegetation to improve water quality. Check with your local Natural Resources Conservation Service (NRCS) office, Soil and Water Conservation District, utility district, state conservation agency, or US Fish and Wildlife Service office. These groups sometimes have funding to assist with the cost of trash removal in certain watersheds. Volunteer labor and equipment also can be a big help. Contact local cave clubs and the county litter control officer for support. County public service authorities will sometimes waive the landfill tipping fee for waste materials collected in sinkhole dump clean-ups.

Contact the above agencies for help with these recommendations.

How does this affect my drinking water?

Contaminants entering the groundwater system through sinkholes present a significant health concern, because many wells tap water-filled cavities that are directly connected to the surface. In karstlands, groundwater usually resurfaces at spring and therefore carries the contamination into streams and rivers that also may be used as water supplies.

a typical progession in a limestone area

Sinkholes are natural depressions in the landscape caused by solution and subsidence of earth materials.

Sinkhole Management Protects Property Values

Sinkholes are common throughout about one-quarter of the U.S. Generally sinkholes can be recognized as circular or oval depressions in cultivated fields that may or may not pond standing water after rain events. Sinkholes can also have open bottoms, swallowing entire creeks, springs, or streams, which disappear underground. Both circumstances have one thing in common: caves and/or broken, weathered limestone bedrock near the soil surface. Over thousands of years, flowing groundwater gradually dissolved channels through the limestone. This process created underground caverns of various sizes which can not always support the weight of overlying soil and rock. A sinkhole is created when the surface materials collapse or are dissolved into the underground cavern or cave stream.

  • Surface water or irrigation runoff can wash soil sediment, fertilizers, animal waste, bacteria, and agricultural chemicals into the groundwater below. In sinkholes with open or rocky bottoms, this bypasses the natural filtration and biochemical breakdown processes that occur as water percolates through the soil.

Management Methods

  • If you have sinkholes or caves on your property, help prevent excessive runoff from entering groundwater by planting a vegetative barrier and/or fencing around the sinkhole.

  • Avoid structures that divert water naturally flowing into sinkholes. Soil-lined diversion ditches often collapse when storm water erodes through to caves and underground cavities.

  • The size and shape of the vegetated zone needed will depend on the slope of the land and the distance from the disturbed area. A 100-foot-wide grass filter strip is ideal; a 50-foot strip is still helpful; and grass strips even as narrow as 13 feet can trap enough sediment to be effective. Filter strips will remove sediment only from shallow, sheet-type flows; they are less effective in deeper, rapidly flowing water, such as in gullies or ravines.

  • Leave a wide natural buffer of trees and under story vegetation around sinkholes and caves when clearing land, harvesting timber,or disturbing ground in the drainage area.

  • Never dump trash, dead animals, or debris into sinkholes. This is illegal in most areas because it can directly and rapidly funnel leachate to springs and wells.

  • Immediately after disturbing any soil, lightly fertilize, seed, and mulch the area to control erosion. A geotextile may be needed on very steep slopes. Water the area frequently until grass seed germinates. To protect embankments and channels until grass is established, build secure silt fences out of mesh plastic, anchored to the soil, and staked to hay bales.