McCracken County, Kentucky

GEOLOGIC HAZARDS

There are seven shallow, concealed faults located throughout McCracken County. Currently there is no evidence that these faults are active. However, because of the proximity of McCracken County to the New Madrid Seismic Zone, strong earthquake activity is possible. Soil creep, slumps, and landslides along steep slopes may occur from erosion or ground motion associated with a strong earthquake. Areas associated

with alluvial material are subject to liquefaction during a strong earthquake. These areas are also subject to flooding. Soils derived from alluvial deposits have a moderate to high shrink swell capacity, which may affect structural foundations and roads. For more technical information about the engineering geology of the area, see Finch (1968a, b). Flood information is available from the Kentucky Division of Water, Flood Plain Management Branch, www.water.ky.gov/floods/

This picture of the 1937 flood in Paducah was taken before the Ohio River crested on February 2, 1937. Flood waters covered more than 90 percent of the city and flood damage exceeded $22,000,000. Photo courtesy of the William Clark Market House Museum.

The bank clock (left center) is located in the same spot as it was in 1937 (see Paducah 1937 flood picture above). Photo by Glynn Beck, Kentucky Geological Survey.

This 12.5 mile long flood wall was constructed by the U.S. Army Corps of Engineers after the 1937 flood to prevent future flood damage in Paducah. Photo by Glynn Beck, Kentucky Geological Survey.

SURFACE WATER DRAINAGE

Because of the large percentage of flat to gently sloping areas associated with the Ohio River, development, such as subdivisions, can cause flooding if proper drainage designs are not implemented as part of the planning and development process. Watersheds can also be impaired from improper sewage treatment and urban and industrial runoff.

Metropolis Lake is a natural lake located in the Wabash-Ohio Bottomlands ecoregion along the Ohio River (Woods and others, 2002). Metropolis Lake is currently contaminated with PCB’s and mercury, which demonstrates why industrial planning is necessary. Photo by Glynn Beck, Kentucky Geological Survey.

EARTHQUAKE HAZARDS

Peak ground acceleration at the top of rock that will probably occur in the next 500 years in Kentucky

Although we do not know when and where the next major earthquake will occur, we do know that an earthquake will cause damage. Damage severity depends on many factors, such as earthquake magnitude, the distance from the epicenter, and local geology. Information on earthquake effects is obtained by monitoring earthquakes and performing research. Such information is vital for earthquake hazard mitigation and risk reduction.

The most important information for seismic-hazard mitigation and risk reduction is ground-motion hazard. One way of predicting ground-motion hazard is by determining the peak ground acceleration (PGA) that may occur in a particular timeframe. The map above shows the PGA at the top of bedrock that will likely occur within the next 500 years in Kentucky (Street and others, 1996). It shows, as expected, that PGA would be greatest in far western Kentucky near the New Madrid Seismic Zone. Ground-motion hazard maps for the central United States and other areas are available from the U.S. Geological Survey. These maps are used to set general policies on mitigating damage. For example, maps produced by the USGS in 1996 were used to determine seismic design in building codes. For additional information pertaining to earthquake hazards visit the Kentucky Geological Survey website at www.uky.edu/KGS/geologichazards/geologichazards.html

GROUNDWATER

Groundwater resources in McCracken County are abundant and have fair to good water quality. All areas of the county have the ability to produce water from drilled wells at reasonable depths in quantities sufficient for domestic use. Multiple zones of production are common throughout the county. Depths to uppermost production range between 30 and 200 feet. Generally, depth to groundwater is less than 100 feet, except in the uplands of southwestern McCracken County where sufficient groundwater is obtained at depths greater than 100 feet. Water quality generally is good except in areas where downward percolation of surface water, fluids from domestic sewage-disposal systems, and other sources of domestic or industrial pollution have contaminated the aquifer. Groundwater sometimes contains naturally occurring iron in objectionable amounts from the deeper zones. In some formations with slightly acidic groundwater, a chemical reaction between the acidic groundwater, steel well casings, and pump equipment will produce high iron content in the water which is not naturally occurring. For more information about groundwater resources in the county, see Carey and Stickney (2001).

Groundwater is a valuable resource to residents, industry, and farmers in McCracken County. Kight Pecan Orchard shown above—the largest pecan orchard in the state (80 acres)--and the 6.5-acre tomato farm shown below, utilize groundwater for drip irrigation. Proper resource management and planning will be essential to preserving good groundwater quality in McCracken County. Photos by Glynn Beck, Kentucky Geological Survey.

RESOURCES

Ohio Valley Gravel and Sand Company quarry in McCracken County. This quarry is the most productive gravel and sand quarry in the eight county Jackson Purchase Region. Photo by Glynn Beck, Kentucky Geological Survey.