Environmental Engineering Reference
In-Depth Information
Geomorphic Features of Karst
Karst
refers in general to the characteristic, readily recognizable terrain features that
develop in the purer limestone. The important characteristics of karst topography are its
predominantly vertical and underground drainage, lack of surface drainage systems, and
the development of circular depressions and sinks. At times, streams flow a short distance
and suddenly disappear into the ground.
Youthful karst
is characterized by numerous sinkholes and depressions as well as
deranged and intermittent drainage (see
Table 6.2)
as shown in
Figure 6.25,
a USGS quad
sheet of an area near Versailles, Kentucky.
Mature karst
is characteristic of humid tropical climates. The landform consists of
numerous rounded, steep-sided hills (“haystacks” or “pepinos”) as illustrated in
Figure
6.26,
a portion of the USGS quad sheet for Manati, Puerto Rico.
Buried karst
is illustrated by the ERTS image of Florida (see
Figure 6.27),
showing numer-
ous lakes that have filled subsidence depressions. In the Orlando region, the limestone is
often buried under 60 to 100 ft of alluvium.
Groundwater Pumping Effects
Significance
Groundwater withdrawal greatly accelerates cavity growth in soluble rocks, and lower-
ing of the water table increases overburden pressures. The latter activity, which substan-
tially increases the load on a naturally formed arch, is probably the major cause of ground
subsidence and collapse in limestone regions (Prokopovich, 1976). Even if groundwater
withdrawal is controlled with the objective of maintaining a water balance and preserv-
ing the natural water table, the water table drops during severe and extensive droughts
and collapse activity increases significantly, as occurred in central Florida during the
spring of 1981.
Examples
Pierson, Florida:
The sink illustrated in
Figure 10.19,
20 m in diameter and 13 m deep,
formed suddenly in December 1973 after 3 days of continuous pumping from nearby irri-
gation wells. The limestone is about 30 m in depth.
Johannesburg, South Africa:
A large pumping program was begun in 1960 to dewater an
area, underlain by up to 1000 m of Transvaal dolomite and dolomitic limestone, for gold
mining operations near Johannesburg. In December 1962, a large sinkhole developed sud-
denly under the crushing plant adjacent to one of the mining shafts, swallowed the entire
plant, and took 29 lives. In 1964, the lives of five persons were lost when their home sud-
denly fell into a rapidly developing sinkhole. Between 1962 and 1966, eight sinkholes larger
than 50 m in diameter and 30 m in depth had formed in the mine area (Jennings, 1966).
Paris, France:
Groundwater withdrawal has increased the solution rate and cavern
growth in old gypsum quarries beneath the city and some suburban towns (Arnould,
1970). Ground collapse has occurred, causing homes to be lost and industrial buildings to
be damaged. In one case, it was estimated that pumping water from gypsum at the rate of
about 85 ft
3
/min removed 136 lb of solids per hour.
Hershey, Pennsylvania:
Increased dewatering for a quarry operation caused groundwater
levels to drop over an area of 5000 acres and soon resulted in the appearance of over 100
sinkholes (Foose, 1953). The original groundwater levels were essentially restored after the
quarry company sealed their quarry area by grouting.
Round Rock, Texas:
The Edwards limestone outcrops in the area and is known to be cav-
ernous in some locations. During a study for new development, interpretation of stereo-
