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)
Sinkholes are common in the Bardstown
area along the margins of relatively flat uplands formed in thin shales but underlain by limestone. Photo
by Stephen Greb,
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).
Population
growth leads to residential construction, new roads, and water and sewer
infrastructure. Depth and type of bedrock influence the cost of constructing
water and sewer lines, road beds, basements and recreation facilities.
Increasingly, mixed land uses are juxtaposed, as in the case of this
residential neighborhood next to a golf course, with industrial construction
nearby. Photos by Stephen Greb,
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,
FLOODPLAINS AND
WETLANDS
Broad floodplains are common
along Rolling Fork and between the knobs in the western part of the county.
These valleys are underlain by alluvium, which is unconsolidated sand and
gravel, and those planning any construction here must carefully consider
possible future flooding. Photo by Stephen Greb,
The
J.C. Williams Wildlife Management Area is located in the floodplains of Beech
Fork and Rolling Fork. Such areas are restricted from development. Wetlands in
this and other areas are important because they moderate flooding, improve
water quality, and provide habitat for wildlife. Photo by
Stephen Greb,
SLOPE STABILITY
Part of
Steep slopes in the Knobs
Region and in the eastern part of the county are susceptible to sliding and
slumping because they are composed of thick shales.
Builders should avoid cutting into the toe (base) of hills or past slides in
these areas, cutting vegetation from stable slopes, or directing water toward
the heads of slopes. Bent trees on slopes, hummocky (bumpy) topography, and
water seeps at the base of slopes are indicators of past or potential movement.
Photo by John Kiefer,
WATER RESOURCES
Water treatment facility and
impoundment (foreground) reservoir west of Bardstown. Large and growing
populations require water for many uses. Photo by Stephen Greb,
POND CONSTRUCTION
Shale is generally
impermeable, and areas where it forms the bedrock may be favorable for ponds.
In areas underlain by limestone, 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 U.S. Department of Agriculture--Natural Resources Conservation
Service can provide guidance on leak prevention measures.Ponds
with dam heights exceeding 25 feet, or pond volumes exceeding 50 acre-feet,
require permits. Contact the Kentucky Division of Water,
GROUNDWATER
In the larger valley bottoms
of the Rolling Fork and Beech Fork of the
Since the late 1700’s,
GETHSEMANI
Our Lady of Gethsemani Abbey in the southern part of the county. The
abbey is located along Monks Creek. The monastery has its own water-treatment
plant. Photo by Stephen Greb,
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
MINERAL RESOURCES
The Laurel Dolomite has been
quarried in several parts of the county for road metal (base), asphalt filler,
aggregate, and concrete. Dolomite was used as a building stone for many stepping
stones, foundations, walls, and historic homes in the county. Siltstone from
the Borden Formation (“creekrock”) has been used for
stepping stones, foundations, and facing stones on buildings and homes
(Peterson, 1966, 1968). Photo by Stephen Greb,
MY OLD KENTUCKY HOME
My
Stephen Greb,
AGRICULTURE
Agriculture is the dominant
land use across much of the county. In the eastern part of the county, gently
rolling topography is characteristic of limestone bedrock, but the topography
is more dissected where the bedrock consists of interbedded
shale and limestone, or shale. Photo by Stephen Greb,