Ground Water, continued
Ground-water DischargeGroundwater is discharged in Ford County by transpiration and evaporation, seepage into effluent streams, springs, underflow that leaves the county, and by wells. The rate at which it is discharged varies with many factors, but especially with the stage of the water table and with the season of the year. Local differences in conditions cause more groundwater to be discharged in some parts of the county than in others. More groundwater is pumped from irrigation wells in the Arkansas valley than in the upland parts of the county. More water is withdrawn from the zone of saturation by plants by evaporation in areas adjacent to Arkansas River and other perennial streams than in areas where the water table lies at great depth. Natural discharge of groundwater also takes place in the form of water moving slowly out of the county toward the east, as indicated by the water-table contours on the map, plate 1. The water moving out of the county as underflow along the Arkansas valley represents one phase of this type of ground-water discharge. The amount of water that moves out of the county is approximately the amount that enters from the west plus whatever additions to or subtractions from the groundwater reservoir have been made within the county.
It is probable that before any water was pumped from wells in Ford County, the annual discharge of groundwater by natural processes was approximately equal to the annual recharge. Artificial discharge by pumping represents an additional amount of water taken from the underground reservoir without any increase in the amount of replenishment. The development of the groundwater resources of Ford County necessarily will cause some lowering of the water table until the natural discharge through springs and seeps into perennial streams and underground movement of water out of the county is decreased by an amount equal to the withdrawal by pumping. Such adjustments, however, will proceed slowly over a period of many years with only a gradual regional lowering of the water table, as the amount of water in storage is very large. Although quantitative estimates are available for the amount of water discharged from wells in Ford County, the amount of natural discharge is not definitely known.
Transpiration and EvaporationThe roots of plank may draw water directly from the zone of saturation and discharge the water into the atmosphere by the process of transpiration. The rate at which water is withdrawn from the zone of saturation varies with the type of plants, the depth to the water table, the climate and the season of year, the character of the soil, and possibly other factors. The limit of lift by ordinary grasses and field crops is not more than a few feet, but some types of desert plants have been known to send their roots 60 feet or more below the surface to reach the water table (Meinzer, 1923. p. 82). In parts of the county along the valley margins and on the uplands; where the water table is considerably below the reach of the roots of most plants, water is withdrawn from the belt of soil moisture, thereby depleting the supply of soil moisture, but in the Arkansas valley and some of the other stream valleys many of the plants draw water directly from the zone of saturation. Evaporation of water directly from the zone of saturation is confined almost exclusively to the dry bed of Arkansas River and to the land immediately adjoining the stream, where the water table is very shallow. Most of this water is drawn from the zone of saturation and is evaporated at the top of the capillary fringe. In areas where the water table lies at considerable depth no water from the zone of saturation is lost by direct evaporation; in such places only the soil moisture is evaporated. The amount of water discharged by plant transpiration in the Arkansas valley and other parts of Ford County is not definitely known. Wenzel (Lugn and Wenzel, 1938, p. 151) estimated that in the Platte River valley between Chapman and Gothenburg, Nebraska:
"If an average of 12 inches of supplemental water is used annually by the plants whose roots extend to the zone of saturation, the resulting quantity of water discharged by transpiration ... would amount to about 390,000 acre-feet a year, or about 12 times the quantity of water pumped annually from wells."It is believed that the total quantity of water withdrawn by plant transpiration in the Arkansas valley in Ford County is rather large, but probably is less than in the central Platte valley in Nebraska. The areas bordering Arkansas River in which the water table lies within 10 feet of the surface are much smaller in extent than in the Platte valley.
Seepage into StreamsA stream that stands lower than the water table may receive water from the zone of saturation, and is known as an effluent stream. The principal streams that receive groundwater discharge in Ford County are Arkansas River, during periods of low flow, and Sawlog and Crooked creeks.
As pointed out under the discussion of shape and slope of the water table, groundwater moves in toward the Arkansas valley from both sides as shown by the water-table contours on plate 1. Thus, except at flood stage, the Arkansas River is a gaining stream throughout its course in Ford County; that is, it is effluent with respect to the water table. Where tributary streams have out their channels below the general water table, their flows are also augmented by groundwater during most of the year. Seepage of groundwater occurs along the banks of these streams and in some instances groundwater is discharged through springs along the valley sides. Although water has been observed in the channel of Crooked Creek in that part of its course in Ford County, the stream bed is known to be dry for long periods at points downstream, near Fowler, Meade County. At the county line the creek is entrenched about 15 feet below the general land surface and its channel may or may not be below the water table. Groundwater may be discharged into Crooked Creek during part of the year, but it is probable that stretches of the creek in Ford County would go dry during a part of the year if it were not for several small dams that have been constructed to impound water for stock and for irrigation.
Discharge by SpringsIn Ford County some water is discharged through springs. Most of the springs observed are in the northern part of the county along Sawlog creek and its tributaries, and no springs were observed south of the Arkansas valley. The water table under the south uplands lies at considerable depth, and in general the channels of tributary streams lie above the water table; hence, few, if any, opportunities for springs exist. The total quantity of water discharged by springs in Ford County is not definitely known, but it is thought to be small as compared to discharge by other means. The known springs are described below under Recovery.
Discharge from WellsDischarge of groundwater from wells in Ford County constitutes the principal discharge from the groundwater reservoir. In 1938, approximately 10,435 acre-feet of water was pumped from irrigation wells in the Arkansas valley and from industrial and public supply wells in the county Most of the rural residents of the county derive their domestic and livestock supplies from wells but the total volume of water pumped from these wells is comparatively small.
Kansas Geological Survey, Ford Geohydrology|
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Web version April 2002. Original publication date Dec. 1942.