KARST GEOLOGY
The term "karst" refers to a landscape characterized by
sinkholes, springs, sinking streams (streams that disappear underground), and
underground drainage through solution-enlarged conduits or caves. Karst landscapes form when slightly acidic water from rain
and snow-melt seeps through soil cover into fractured and soluble bedrock
(usually limestone, dolomite, or gypsum). Sinkholes are depressions on the land
surface where water drains underground. Usually circular and often
funnel-shaped, they range in size from a few feet to hundreds of feet in
diameter. Springs occur when water emerges from underground to become surface
water. Caves are solution-enlarged fractures or conduits
large enough for a person to enter.
ENVIRONMENTAL
PROTECTION
Never use sinkholes as
dumps. All waste, but especially pesticides, paints, household chemicals,
automobile batteries, and used motor oil, should be taken to an appropriate
recycling center or landfill.
Make sure runoff from
parking lots, streets, and other urban areas is routed through a detention
basin and sediment trap to filter it before it flows into a sinkhole.
Make sure your home septic
system is working properly and that it's not discharging sewage into a crevice
or sinkhole.
Keep cattle and other
livestock out of sinkholes and sinking streams. There are other methods of
providing water to livestock.
See to it that sinkholes
near or in crop fields are bordered with trees, shrubs, or grass buffer strips.
This will filter runoff flowing into sinkholes and also keep tilled areas away
from sinkholes.
Construct waste-holding
lagoons in karst areas carefully, to prevent the
bottom of the lagoon from collapsing, which would result in a catastrophic
emptying of waste into the groundwater.
If required, develop a
groundwater protection plan (410KAR5:037) or an agricultural water-quality plan
(KRS224.71) for your land use.
(From Currens,
2001)
CONSTRUCTION IN KARST
AREAS
Cover-collapse sinkholes
(outlined in red) are typical in areas of karst
geology. Many sinkholes such as these have not been mapped. The construction
implications of these features must be addressed for any type of development. Photo by Bart Davidson,
RESIDENTIAL
CONSTRUCTION
Limestone
terrain can be subject to subsidence hazards, which usually can be overcome by
prior planning and site evaluation. "A" shows construction
above an open cavern, which later collapses. This is one of the most
difficult situations to detect, and the possibility of this situation beneath a
structure warrants insurance protection for homes built on karst
terrain. In "B," a heavy structure presumed to lie above solid
bedrock actually is partially supported on soft, residual clay soils that
subside gradually, resulting in damage to the structure. This occurs where
inadequate site evaluation can be traced to lack of geophysical studies and
inadequate core sampling. "C" and "D" show the close
relationship between hydrology and subsidence hazards in limestone terrain. In
"C," the house is situated on porous fill (light shading) at a site
where surface and groundwater drainage move supporting soil (darker shading)
into voids in limestone (blocks) below. The natural process is then accelerated
by infiltration through fill around the home. "D" shows a karst site where normal rainfall is absorbed by subsurface
conduits, but water from infrequent heavy storms cannot be carried away quickly
enough to prevent flooding of low-lying areas. Adapted from
AIPG (1993).
RADON
Radon
gas, although not widely distributed in
EPA
recommends action be taken if indoor levels exceed 4 picocuries per liter, which is 10 times the average outdoor
level. Some EPA representatives believe the action level should be lowered to 2
picocuries per liter; other scientists dissent and
claim the risks estimated in this chart are already much too high for low
levels of radon. The action level in European countries is set at 10 picocuries per liter. Note that this chart is only one
estimate; it is not based upon any scientific result from a study of a large
population meeting the listed criteria. (From the U.S.
Environmental Protection Agency, 1986.)
EROSION CONTROL
During
construction, erosion-control fences such as these may be needed to prevent
silt from entering local streams. Photo by
Bart
Davidson,
Riprap
drainage control and erosion protection. Photo by Stephen Greb,
GROUNDWATER
In the central and
southeastern half of the county, about three-quarters of the drilled wells
yield enough water for domestic use. In low-lying areas, a few wells yield
adequate amounts of water for a domestic supply, except in the northwestern
corner of the county close to the
River. In the northwestern corner, most wells are adequate
for a domestic supply, especially from wells that penetrate small solution
openings within the limestone bedrock.
Springs are present
throughout the county, with flow rates ranging from several gallons per minute
to 670 gallons per minute. Some springs are sufficient to supply domestic
needs, but most go dry during extended dry periods in late summer and fall.
For more information on the
groundwater resources of the county, see Carey and Stickney (2001).
POND CONSTRUCTION
Successful pond construction
must prevent water from seeping through structured soils into limestone
solution channels below. A compacted clay liner, or artificial liner, may
prevent pond failure. Getting the basin filled with water as soon as possible
after construction prevents drying and cracking, and possible leakage, of the
clayey soil liner. Ponds constructed in dry weather are more apt to leak than
ponds constructed in wet weather. The
Dams should be constructed
of compacted clayey soils at slopes flatter than 3 units horizontal to 1 unit
vertical. Ponds with dam heights exceeding 25 feet, or pond volumes exceeding
50 acre-feet, require permits. Contact the
WASTEWATER TREATMENT
Sewage lagoons are often
constructed near industrial facilities to aid in pretreatment. Dams and
embankments of lagoons like this one should be monitored for leakage, which may
migrate and affect local streams and groundwater. Photo by
Bart Davidson,
WASTE DISPOSAL
A large poultry processing
plant near
NATURAL RESOURCES
The lumber industry is a
common land-use feature of
MINERAL RESOURCES
Limestone is a major product
of
ENERGY RESOURCES
Oil and gas development in
TOURISM
76 Falls
is a scenic area adjoining
RECREATION
The land-use planning guides
on this map series take into account intensive and extensive recreation.