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Sedgwick County Geohydrology

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Ground Water, continued

The Water Table and Movement of Ground Water

The water table is not a flat surface but has irregularities that are related to and strongly affected by the topography, geology, and hydrology of the area. The shape of the water table in parts of Sedgwick County is shown on Plate 1 by means of contours. All points along a contour line have the same altitude, and the lines show the shape and slope of the water table in the same manner as the land surface is shown on a topographic map. The configuration of the water table where shown is very similar to the surface topography but is more subdued. In those parts of the County where the water-table contours are not shown on Plate 1 it lies beneath the surface of the consolidated bedrock. Contours are omitted where control is inadequate. The water table may be discontinuous or absent in some areas. The ground water in the bedrock is under artesian pressure in some areas and the relationship of the piezometric surface to the water table is not known.

The water table in the Arkansas Valley has a rather uniform slope to the southeast that averages about 7 feet per mile. Locally the slope of the water table may be as low as 5 feet or as high as 10 feet per mile. Ground-water movement is in the direction of water-table slope, or at right angles to the water-table contours. In the valley, ground-water movement is, in general, toward the Little Arkansas River and the Arkansas River below the junction of the two. At any particular point in the valley and at different depths below the land surface, the direction of ground-water movement may be slightly different from that indicated by the water-table gradient, owing to local conditions. In stratified and lenticular deposits of different permeability such as are present in the Arkansas Valley, the water pressure at a given depth below the surface may be slightly different than at other depths and the pressure gradients in a different direction than indicated by the water table. However, the resultant direction of water movement will be as indicated by the gradient on the water table.

The smooth surface of the water table in the Arkansas Valley is marked by a number of anomalies most of which are related to discharge of ground water. Along the Arkansas River northwest of Wichita the water-table contours show no flexure as they cross the river, indicating that at normal river stage the water table is in equilibrium with the river and the ground-water reservoir neither receives nor discharges water in this reach of the stream. Along the Little Arkansas River, the Arkansas River from Wichita south, and the larger tributary creeks west of the river, the water-table contours turn sharply upstream, indicating discharge of ground water to these streams. The southern end of the Wichita municipal well field is in the northern part of T 25 S, R 2 W, and the northwest corner of T 25 S, R 1 W, and withdrawals of ground water in this area have affected the shape of the water table. In the area of largest withdrawal near the northeast corner of T 25 S, R 2 W, the water table is flattened or depressed and the gradient reduced, shifting the direction of ground-water movement toward the well field. West of this pumping center the gradient is appreciably steepened in the direction of the well field. A noticeable distortion of the water-table contours in T 25 S, R 3 W, is probably caused by withdrawal of ground water by irrigation wells, causing water to move from the river in a small area; but it may be due, in part, to inadequate control on the water-table altitude. Other areas where withdrawals from wells have changed to some extent the direction of ground-water movement are located in Wichita and southwest of it, but these are not well defined by the water-table contours.

The water table in the alluvium and terrace deposits of the Ninnescah Valley shows the direction of ground-water movement to be downstream but with a strong component of movement toward the river. The Ninnescah River is influent throughout its course in Sedgwick County.

The water-table gradient becomes markedly steeper west of the Arkansas Valley as the land surface rises to the upland level. Within this zone, about 2 miles wide, the water table passes from the sand and gravel of the valley into loess mantling, the valley slope. The water-table gradient in this zone is as much as 50 feet per mile locally and indicates the low permeability of the loess. Sand and gravel underlie the loess in a part of the upland area southwest of Goddard, and the water-table gradient is much less than in the loess-covered slopes. The configuration of the water table in this area shows the ground water to be moving from the uplands toward the Arkansas and Ninnescah valleys.

The rate of movement of ground water is very low compared to the movement of surface water. Typical rates of movement in the County are not known, but in unconsolidated materials such as are common there, the rate may range from a fraction of an inch per day in silt and clay to several feet per day in well-sorted sand and gravel.

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Kansas Geological Survey, Geology
Placed on web Nov. 1998; originally published Dec. 1965.
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