Ground Water, continued
The Water Table and Movement of Ground WaterThe upper surface of the zone of saturation in ordinary permeable soil or rock has been termed the ground-water table, or simply the water table. Where the upper surface is intersected by impermeable material, the water table is interrupted, and artesian conditions are said to exist. The water table is not a plane surface but has irregularities comparable with and related to those of the land surface, although the water table is less rugged. The water table does not remain in a stationary position, but fluctuates up and down. The irregularities are caused chiefly by local differences in geology and topography, and the fluctuations are due to gain or loss of water.
The shape of the water table in Reno County is shown on Plate 1 by contour lines drawn on the water table. All points along a contour line have the same altitude, and the lines show the shape and slope of the surface of the water table as the land surface is shown on a topographic map. The water moves down slope in a direction at right angles to the contours. In general, the shape of the water table in Reno County conforms to the surface of the land. The water table is high in the dune-sand area, in areas north and east of Hutchinson, and in local areas in the western part of the county. The water table is near the surface in these areas because the surface material is relatively permeable and admits large quantities of water.
The North Fork of the Ninnescah River, Cow Creek, and Little Arkansas River are effluent streams throughout most of their courses in Reno County; that is, they are perennial streams, the channels of which have been cut below the water table and the streams are thereby gaining water from the zone of saturation. This movement of water from the underground reservoir to the channels of these streams has caused troughs to be formed in the water table that follow the courses of these streams, as indicated by the upstream flexure of the contours. The water-table contours cross the Arkansas River approximately at right angles, which indicates an apparent balance between the level of water in the stream and the adjacent water table, the stream neither gaining nor losing water. At times of low water, however, the Arkansas River will gain water from the ground-water reservoir and at times of high water the river will lose water to the ground-water reservoir.
Recharge is the addition of water to the ground-water reservoir. Precipitation is the original source of all ground-water recharge, although in a particular area the ground-water reservoir may be recharged in several ways. The principal source of recharge in Reno County is precipitation. At times of high water the streams, especially the Arkansas River and parts of Cow Creek, contribute water to the ground-water reservoir. The amount of water contributed by the streams is only a small part of the total amount of recharge. Water moves into Reno County from the west and also from the north. Williams (1946) estimated that about 500 acre-feet of water a year moves across each mile of border area into the sandhills north of Hutchinson. He estimated also that about half the precipitation in the sandhills region becomes ground-water recharge.
The sand, soil, and topography in the sandhill area north of Hutchinson and in western Reno County are favorable for ground-water recharge. Many undrained basins hold the precipitation, and the sandy soil and subsoil allow it to percolate downward to the water table.
The sandy soil and flat topography of the terrace deposits and the alluvium in the Arkansas River valley are favorable to recharge. East of Reno County in Sedgwick and Harvey counties, wells drilled in deposits similar to those in the Arkansas River valley in Reno County were equipped with automatic water-stage recorders and have been observed since 1938. A study of these records indicates that about 20 percent of the annual precipitation reaches the water table (Williams and Lohman, 1949). The deposits described by Williams and Lohman are continuous with those in the Arkansas River valley in Reno County, so that probably about 20 percent of the annual precipitation in the valley in Reno County also reaches the water table; 20 percent of the precipitation would amount to about 300 acre-feet or about 100 million gallons on each square mile. Figure 14 shows the hydrographs of three wells in the Arkansas River valley, the monthly precipitation, and the cumulative departure from normal precipitation. The period of measurements is short, but the fluctuations of the water levels correlate fairly well with the precipitation.
In the upland areas in central and southern Reno County the slopes are steeper and the soil is not as sandy as in the valley plain. Hence a larger fraction of the water runs off the upland surface and there is much less recharge than in the valley.
In the areas underlain by Permian shales, the soils are compact and have a very low permeability. In these areas the recharge is much less than in either the upland areas or the Arkansas River valley.
Ground-water discharge is the water discharged from the zone of saturation or the capillary fringe and may take place by flow directly into streams, from springs and seeps, or by evaporation and transpiration. Discharge of water by these methods is called natural discharge. Discharge of water by pumping from wells or infiltration galleries is artificial discharge.
Before wells were drilled in Reno County, the water table was in approximate equilibrium; that is, the annual discharge by evaporation, transpiration, and discharge into streams was approximately equal to the annual recharge from precipitation and seepage from streams. At the present time water is discharged into the Ninnescah River, Little Arkansas River, and Peace Creek. The Arkansas River is in approximate equilibrium with the water table and does not add water to or receive water from the ground-water body in most of its course through Reno County (P1. 1).
Transpiration is the process by which water is taken into the roots of plants and is evaporated into the atmosphere. The depth from which plants will obtain their water from the water table varies with the plant species and type of soil. Ordinary grasses and field crops will not send their roots more than a few feet in the search for water, but alfalfa and certain desert plants may send their roots to a depth of as much as several tens of feet to reach the water table (Meinzer, 1923).
Discharge of ground water by transpiration and evaporation is relatively great in Reno County, owing to the shallow depth to the water table in much of the county. The greatest discharge by transpiration and evaporation probably is in the Arkansas River valley, where the water table is shallow. The quantity of ground water discharged in Reno County by evaporation and transpiration is probably much greater than the amount discharged by all other means.
The discharge of water from wells in Reno County is now one of the principal means of discharge of ground water. The average pumpage of water for industrial, municipal, and farm use is about 15,000 acre-feet annually, which is probably between 5 and 10 percent of the total recharge in the county.
Kansas Geological Survey, Reno County Geohydrology|
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Web version Feb. 2001. Original publication date Aug. 1956.