Ground-water DischargeWhen water derived from precipitation or other sources reaches the zone of saturation, it moves down gradient in the direction of the slope of the water table. The water remains a part of the ground-water body until removed or discharged by natural or artificial means. Water may be discharged from an aquifer by evaporation. plant transpiration, seepage into streams. as discharge from springs, or by pumping from wells. Discharge from the ground-water reservoir takes place by one or more of these methods most of the time. Over a period of years, or a climatic cycle, the quantity of ground-water discharge is about equal to the quantity of recharge, although this balance may be upset locally in areas of heavy pumping.
Discharge by Evaporation and Transpiration
Plants normally derive their water supply from water stored within the soil zone but under favorable conditions may take up water directly from the zone of saturation or from the capillary fringe above it and discharge it into the atmosphere by the process of transpiration. The depth from which plants lift water varies with the plant species and the type of soil in which the plant grows. Most grasses and field crops common to this area lift water only a few feet; however, alfalfa and certain types of water-loving trees and shrubs of arid regions have been known to extend roots to depths of as much as 60 feet to reach a water supply. Where the water table or the capillary fringe is near the land surface, significant quantities of ground water are discharged by direct evaporation from the ground-water reservoir.
Within the County a significant quantity of ground water is discharged by evaporation and transpiration and this quantity probably exceeds that by all other forms of discharge. Throughout most of the Arkansas Valley, the depth to water is less than 20 feet, and in the area of Recent alluvium and Wisconsinan terrace deposits (Pl. 1) the water table is commonly less than 10 feet below the land surface. A large quantity of ground water is evaporated and transpired along the Arkansas, Little Arkansas, and Ninnescah rivers, and along Cowskin and Big Slough creeks by the dense growth of vegetation along these streams that intercepts water that would normally be discharged into these streams. Lesser, but still significant quantities of ground water are discharged by this means along the smaller tributary streams and the floodway west of Wichita. Within the Wichita well field in Harvey and Sedgwick counties a large part of the apparent recharge is believed to be water that would have been discharged by evaporation and transpiration had the water table not been lowered to a degree that reduces their effectiveness as a means of discharge.
Discharge into Streams
Stream flow at low stages of the Little Arkansas, the Arkansas, and the Ninnescah rivers and their larger tributaries in the County is maintained by ground-water discharge. Discharge into the streams occurs mainly through seeps in and along the stream channels. Upstream from near the mouth of the Little Arkansas River, where the Arkansas River is in approximate equilibrium with the water table, very little or no seepage enters the river. During prolonged droughts flow ceases because the water table drops below the river bed and any flow that might come from upstream percolates down to the water table. Seepage maintains the water level in several small lakes occupying sinks in the north-central part of the County by replacing water lost by evaporation from the water surface.
The quantity of seepage into streams is not known, but it is believed to be quite large. Most of the ground water moves toward the Little Arkansas and Arkansas rivers below the junction of the two, and any water not discharged by evaporation, transpiration, or by wells, eventually reaches these streams. Seepage measurements on the Little Arkansas River above Valley Center were made in September 1961, by the Surface Water Branch, U. S. Geological Survey. Some transpiration losses were probably taking place adjacent to the river, but these losses were probably slight as most vegetation either had ceased growing or was approaching dormancy. Unpublished data from two measuring stations in Sedgwick County, located in SE SW sec. 4, T 25 S, R I W., and NW SW sec. 36, T 25 S, R I W, showed an increase in flow of about 20 cubic feet per second or 12.93 million gallons per day. The distance between the two stations normal to the direction of ground-water flow is about 5.5 miles, and the discharge to the river was about 2.35 million gallons per day per mile. The discharge by seepage varies greatly depending upon river stage, ground-water stage, time of the ear, and probably time of day, so that the seepage figure given above cannot be applied without some qualification. However, it does give a suggestion of the magnitude of seepage into the streams.
Discharge by Springs
The distinction between seeps and springs is not sharp, but ground water issuing from well-defined openings in rocks is properly classed as a spring. Several large springs are present in the drainage basin of Four Mile Creek east of Wichita and these issue from the Wellington Formation. Two of these springs, located in SW SW SW sec. 13, T 27 S, R 2 E, and SW NE NE sec. 36, T 27 S, R 2 E, were visited during the course of field work for this report. The springs issue from a gypsiferous zone in the Wellington Formation that has been exposed by erosion near the creek channels. This zone contains water under artesian pressure. The discharge of the spring in section 36 could not be measured, but that in section 13 was measured at 235 gpm. Local residents report that the discharge of the springs fluctuates in response to precipitation, but the range of fluctuation is not known.
Other springs are known to issue during wet periods near creek channels along the east wall of the Arkansas Valley and in T 28 S, R 2 W, and T 28 S, R 3 W. In both areas the springs issue at the contact between the unconsolidated deposits and the underlying, impermeable shale. The discharge from springs in these areas is not large and ceases during dry periods.
Discharge by Wells
Most of the water used in the County is obtained from wells. Water is pumped for municipal, industrial, irrigation, stock, and domestic use. The largest withdrawals take place in the Arkansas Valley where the Wichita well field and most of the industries are located. Most of the farms are supplied with water from wells, although some water for livestock is derived from ponds. The quantity of water pumped for each of these uses, insofar as it is known, is presented in the section of the report on utilization of water.
Kansas Geological Survey, Geohydrology of Sedgwick County|
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Web version April 1998. Original publication date Dec. 1965.