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Ground-water Resources, continued
Discharge of Ground Water
In Miami County ground water is discharged by evaporation and transpiration, by seepage into streams, by subsurface movement to adjacent areas, and by springs and wells. The rate of natural discharge depends on climatic factors and the stage of the water table. Local differences in geology and topography cause more water to be discharged in some parts of the county than in others. Wells account for only a minor amount of the ground-water discharge.
Discharge by Evaporation and Transpiration
More ground water is discharged by evaporation and transpiration than by all other means combined. Direct evaporation of ground water occurs where the water table is near the land stir-face. Ground water is also transpired by plants. In the stream valleys the roots of many plants penetrate the zone of saturation or the capillary fringe. The water table in the upland areas is relatively deep and discontinuous, and few of the plants take water from the ground-water reservoir.
Discharge by Seeps and Springs
Ground water is discharged through springs and seeps along valley walls. Some of this discharge is evaporated directly into the atmosphere and some is transpired by plants during the growing season. The remaining water flows into streams and leaves the county as surface runoff. After the growing season, the amount of stream flow resulting from ground-water discharge increases, as the ground water that was previously intercepted by vegetation is then discharged into the streams.
Discharge by Subsurface Movement
Subsurface movement of ground water into adjacent areas is relatively unimportant. The small amount of water that does leave the county in the subsurface probably does so through consolidated aquifers across the western and northern borders of the county, owing to the effect of the regional dip of the sediments.
Discharge by Wells
Three types of wells are used to obtain water supplies. The type of well depends upon the use for which the well is intended, the geologic materials to be penetrated, the depth to water, and the depth to which the well is to be constructed or drilled. The following paragraphs describe briefly the three types of wells used in. the county.
Dug Wells—These are large-diameter wells ranging from 2.5 to 10 feet in diameter and are excavated with either hand tools or power equipment. These wells are usually cased with rock, but tile and concrete casing are also used. Most wells of this type penetrate the aquifer for only a short distance below the water table. Few dug wells are used in areas underlain by Pleistocene deposits. However, in the upland areas underlain by stratified deposits of Pennsylvanian age, there are many dug wells. This type of well is often desirable in both upland and valley areas as it provides additional storage space within the well, which compensates to some extent for the slow rate at which water drains into the well from deposits of low permeability. Another factor that makes dug wells desirable in areas underlain by Pleistocene deposits is the ease with which such a well can be constructed.
Driven Wells—Driven wells are small-diameter wells consisting of 1 1/4- to 2-inch pipe having a screen attached to the bottom of the casing. The use of this type of well is limited to areas that are underlain by unconsolidated materials and in which the water table is relatively shallow. The pipe is driven into the aquifer so that the screen is below the water table. Owing to the silty and clayey texture of the Pleistocene deposits in Miami County, few driven wells yield more than 1 gpm (gallon per minute).
Drilled Wells—Drilled wells in Miami County range in diameter from about 4 to 36 inches and are constructed with either percussion or rotary drilling machines. Decision as to the diameter of a well usually is based on the quantity of water needed. Wells drilled in unconsolidated deposits must be cased for their full depth and screened in the saturated zones. Wells drilled into the Pennsylvanian bedrock may be uncased except for a length of casing through the weathered surface rock. The surface casing prevents rock in the weathered zone from falling into the well and also seals out water from the surface and the weathered zone. Most domestic and stock wells in the county range in diameter from 4 to 8 inches. Their yields range from 1 to 3 gpm.
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Kansas Geological Survey, Miami County Geohydrology
Comments to webadmin@kgs.ku.edu
Web version June 2002. Original publication date June 1966.
URL=http://www.kgs.ku.edu/General/Geology/Miami/08_gw3.html