Ground Water, continued
DischargeGround-water discharge is the removal, by any method, of water from the zone of saturation. Ground water in Sumner County is discharged by transpiration and evaporation, by seepage into streams, by wells, and by subsurface movement into adjacent areas.
Discharge by Transpiration and EvaporationTranspiration is the process by which water is taken into the root system of plants directly from the zone of saturation, or from the capillary fringe just above it, and discharged into the atmosphere. The depth from which plants will lift the ground water differs with plant species and type of soil. Ordinary grasses and field crops will not send their roots more than a few feet in search of water, but alfalfa, some trees, and certain desert plants draw water from much greater depths. The water table along most of the major valleys in Sumner County is within easy reach of such deep-rooting plants, and much water is discharged from the zone of saturation in this way. Groundwater can be discharged by evaporation only where the water table is within a few feet of the land surface, and in Sumner County this condition is limited chiefly to areas along streams.
That considerable ground water is discharged in Sumner County by transpiration and evaporation is illustrated by the significant rise in the water table in valley areas in the fall when vegetation becomes dormant and evaporation decreases. The rise in the water table may be several feet, although there may be no recharge from precipitation. In Sumner County the quantity of ground water discharged by evaporation and transpiration is probably greater than the amount discharged by any other means.
Discharge by Springs and SeepsGround water is discharged by springs and seeps at points where the water table intersects the land surface. In Sumner County springs and seeps occur in the banks of streams that are cut below the water table and at the margins of Pleistocene sand and gravel deposits that are underlain by impermeable shale. Springs are especially noticeable at the south margin of the Nebraskan deposits in the area west of Conway Springs. The amount of ground water discharged by springs and seeps in Sumner County probably ranks next in importance to the amount discharged by transpiration and evaporation.
Discharge by WellsMost of the water used in Sumner County is derived from wells. Although wells are the most obvious means of ground-water discharge and are increasing in number, the quantity of water withdrawn by pumping is not large compared with the amount discharged by other means. The amount of ground water pumped in Sumner County could not be determined accurately, but figures based on reported pumpage for irrigation, municipal, and industrial use and estimated pumpage for rural domestic and stock use indicate that a total of about 3.5 billion gallons, or 10,800 acre-feet, of water was withdrawn in 1955. This would be equal to about 0.17 inch of water spread over the county. Much of this water, had it not been discharged by pumping, would no doubt have been discharged by natural seepage or by transpiration.
Discharge by PercolationThe amount of ground water moving out of Sumner County by percolation is probably a little less than the amount moving into the county by this means. Within the major valleys of the county the amounts of water entering and leaving the county by percolation are probably about equal. The amount of water that could percolate into or out of the county through the relatively impermeable Permian shale is insignificant and can be disregarded. In the area of Nebraskan deposits west of Conway Springs, however, and in the area between Ninnescah and Arkansas Rivers on the Sumner-Sedgwick County line, ground water in appreciable quantities moves into Sumner County. Most of this water is discharged within Sumner County by springs and seeps, by transpiration, and by wells.
RecoveryWhen a well is at rest, under static conditions, the level of the water in the well is the same as the level of the water in the surrounding material, and there is little or no movement of the water. When water is withdrawn from the well, the water level in the well is lowered, and water flows into the well from the surrounding material. The amount of lowering of the water level in the well may be so small that it is not noticeable, but some lowering must occur before water can move into the well. When pumping is continued for some time, the water table is lowered around the well to form a depression in the water table that somewhat resembles an inverted cone. This depressed area is known as the cone of depression or cone of influence. As the pumping rate of the well is increased, the drawdown becomes greater. When a well is first pumped, the water level falls very rapidly, but as pumping is continued, the drawdown increases at a diminishing rate. When the pump is stopped, the water level rises rapidly at first, then more slowly, and may continue to rise for a long time.
The yield of a well is the rate at which it will deliver water continuously after the water stored in the well has been removed. The yield depends upon the quantity of water available, the thickness and permeability of the water-bearing bed, and the construction and condition of the well. The yield of a well is usually expressed in gallons per minute (gpm). Reported yields of wells in Sumner County range from 1 gpm for some domestic wells to about 2,500 gpm for some irrigation wells.
The specific capacity of a well is the rate of yield per unit of drawdown and is expressed in gallons per minute per foot. In testing the specific capacity of a well, pumping is continued until the water level remains approximately stationary. Specific capacities as great as 175 gpm per foot were reported for some wells in Sumner County.
Kansas Geological Survey, Sumner County Geohydrology|
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Web version January 2003. Original publication date August 1961.