Hancock County, Kentucky

 

 

 

GEOLOGIC HAZARDS

 

The most prominent geologic hazard for Hancock County is flooding. Areas underlain by alluvium are often subject to flooding. Urban development often exacerbates flooding, and therefore potential flooding should always be considered in urban development plans. Areas of steep-walled drainage, such as that formed in terrain underlain by the Tradewater and Caseyville geologic formations, are conducive to flash flooding, especially in developed areas. Flood information is available from the Kentucky Division of Water, Flood Plain Management Branch, www.water.ky.gov/floods/.

 

None of the faults that occur in Hancock County are considered to be active; however, the proximity of active seismic zones such as the New Madrid, Wabash, or East Tennessee does call for precautions to be taken for earthquake damage mitigation. The presence of thick alluvium, which normally has a high groundwater table, should also be treated with special concern because of the possibility of augmented shaking and liquefaction during a strong earthquake. In addition, alluvium often contains high amounts of clay minerals, which can give soil a high shrink/swell capacity.

 

Steep slopes are present, especially along streams in areas underlain by the Tradewater and Caseyville geologic formations, throughout the county. Steep slopes can develop soil creep and landslides if not properly treated during development. Proper engineering techniques should be followed when developing on hillsides, and care should be taken not to affect property above and below a development site on a hillside.

 

Several underground coal mines are in Hancock County. The locations of known mine workings and shafts are shown on the map. Precautions need to be taken when developing over old mined areas because of the possibility of mine subsidence. Mine subsidence insurance is available in Kentucky.

 

Surface coal mine areas are prone to settling after reclamation, which may affect structural foundations and roads. Surface mine areas also lack soil structure, which inhibits the growth of vegetation during summer months.  Abandoned deep and surface mine boundaries shown on the map are approximate and do not represent all the mining that has occurred in the county.

 

Soil piping is the phenomenon whereby subsurface tunnels or pipelike cavities are formed by water moving through the soil. Piping may occur in various soil types, but particularly in alluvium and loess. The only way to treat soil piping is to fill the holes with rock or soil to keep the holes from enlarging and to divert drainage from the area.

 

 

FLOODING

 

 

Repairing the floodwall in Hawesville. The wall was breached by floodwaters of the Ohio River in 1997. Flat, low-lying areas associated with alluvium are subject to flooding. Photograph courtesy of Diane Perkins, Hancock County Extension Agent for Agriculture and Natural Resources.

 

 

The stream erosion pictured here is a result of the 1997 flood that swept the area. Many corridors sustained damage and were costly to restore. Funding was provided by the Emergency Watershed Protection Fund through the Federal  Emergency Management Agency to assist in the restoration process. Photograph courtesy of Rick Burbridge, Hancock County District Conservationist.

 

 

 

THE OHIO RIVER

 

 

The 1600-foot Cannelton Locks and Dam spans the Ohio River. Completed in the 1960's, the structure creates a 114-mile-long lake that stretches from Hancock County to Louisville. The lake is used for various recreational activities such as boating and picnicking. Photograph courtesy of Rick Burbridge, Hancock County District Conservationist.

 

 

The Bob Cummings Lincoln Trail Bridge is the only bridge crossing the Ohio River in Hancock County, making it a vital part of the county's economy. Photograph courtesy of Rick Burbridge, Hancock County District Conservationist.

 

 

 

EARTHQUAKE HAZARDS

 

None of the faults which occur within Daviess County are considered to be active; the proximity of active seismic zones, such as the New Madrid, Wabash, or East Tennessee, however, calls for precautions to be taken for earthquake damage mitigation. The presence of thick alluvium, which normally has a high water table, should also be treated with special concern, because of the possibility of augmented shaking and liquefaction during a strong earthquake. In addition, alluvium often contains high amounts of clay minerals, which can give a soil a high shrink/swell capacity.

 

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

 

 

 

EROSION CONTROL

 

 

During construction, erosion-control fences such as these may be needed to prevent silt from entering local streams. Photo by

Bart Davidson, Kentucky Geological Survey.

 

 

Riprap drainage control and erosion protection. Photo by Stephen Greb, Kentucky Geological Survey.

 

 

GROUNDWATER

 

The alluvium along the Ohio River is the best source of groundwater in the county. Nearly all drilled wells less than 150 feet deep in the alluvium are adequate for domestic use. Most wells yield more than 50 gallons per minute; some wells yield as much as 750 gallons per minute. In the northern three-quarters of Hancock County, most wells less than 300 feet deep that penetrate sandstone are adequate for a domestic supply. In the southern quarter of the county, only a few wells yield enough water for a domestic supply.

 

Generally, groundwater is hard to very hard, and iron and salt may be present in objectionable amounts. Often in deep wells, groundwater becomes too mineralized to use. For more information on groundwater resources in the county, see Carey and Stickney (2001).

 

 

THE LAND

 

 

The topography of Hancock County ranges from flat, broad lowlands to very steep-sloped uplands. The elevation ranges from about 380 feet above mean sea level at the river to about 830 feet in the uplands. Photograph courtesy of Rick Burbridge, Hancock County District Conservationist.

 

 

 

Agriculture is a major land use in Hancock County. According to the Kentucky Agricultural Statistics Service, 19,197 acres (16 percent) of the 120,940 acres available were planted in corn, soybeans, and tobacco in 2002-2003. Photograph courtesy of Diane Perkins, Hancock County Extension Agent for Agriculture and Natural Resources.