Ground Water, continued
DischargeNatural discharge at the surface--Before any wells were drilled the groundwater reservoir of Thomas County was in a state of approximate equilibrium - that is, the average annual recharge was balanced by an approximately equal average annual discharge. The greater part of the discharge occurred by groundwater movement out of the county beneath the surface to the north, east, and south. A small amount of discharge probably occurred from seeps along the valley of South Sappa Creek where it is at the level of the water table and a small amount of water was discharged by direct evaporation and by transpiration from trees, grasses, and shrubs in the shallow water areas along the major valleys.
Discharge from wells--At the present time wells constitute one of the principal means of discharge of ground water within the county. Although the quantity of water pumped annually from wells in Thomas County is not known, the city supplies of Brewster, Colby, and Rexford and several railroad supplies are obtained from wells, and several irrigation wells have been in operation. Most of the rural residents of the county obtain their domestic and livestock supplies from wells, but the total volume of water pumped for such use is comparatively small.
Fluctuations caused by pumping--The water table in the vicinity of a well that is being pumped declines and an inverted cone with its apex at the well (fig. 9) is developed. This cone represents a loss of storage by the unwatering of a portion of the previously saturated material surrounding the well. When pumping stops, the movement of water from surrounding areas into the depressed area continues until the depression is filled. This results in a slight decline of the adjacent regional water table. In an area such as the city well field at Colby where several wells are pumped intermittently, the fluctuations of water level in any one well are complicated and represent the sum of the effects of pumping or recovery from many nearby wells.
Figure 9--Diagrammatic section of two closely spaced pumping wells showing mutual interference between wells and the resulting cones of depression.
Kansas Geological Survey, Thomas County Geohydrology|
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Web version Nov. 2001. Original publication date Dec. 1945.