Ground Water, continued
Recharge of Ground WaterThe amount of water in storage in the underground reservoir does not remain the same for any long period, as indicated by the fluctuations of water levels in wells. There is visible evidence that water is continually being discharged from the underground reservoir through streams, marshes, and wells; and the addition of water to the groundwater reservoir is clearly indicated by the fact that the water levels in the observation wells rise in response to precipitation.
The addition of water to the underground reservoir is termed recharge and may occur in several different ways. All ground water within a practical drilling depth beneath Barton and Stafford Counties is derived from the water that falls as rain or snow either within this area or on areas to the west. The underground reservoir in Barton and Stafford Counties is recharged by local precipitation, by seepage from streams and intermittent ponds, and by subsurface percolation from the west.
Recharge from Local PrecipitationA part of the precipitation that falls on the surface of this area recharges the underground reservoir. The normal annual precipitation in Barton and Stafford Counties is about 24 inches, but only a small percentage of this amount passes through the soil and reaches the zone of saturation. Of the total precipitation, part is lost by evaporation and transpiration, part leaves the county as surface runoff, and the remainder finds its way to the underground reservoir and eventually is discharged.
The amount of water lost through evaporation into the air varies from one season to another, the rate of evaporation being highest in summer when temperatures are highest. In an average year most of the precipitation in the counties comes during the summer, when the rate of evaporation is greatest. It is reasonable to assume, therefore, that a large proportion of the annual precipitation in Barton and Stafford Counties returns to the atmosphere through evaporation.
A part of the precipitation that falls is used by plants through the process of transpiration. The amount consumed in this way is obviously greatest during the growing season, which closely coincides with the period of maximum rainfall.
The amount of water leaving the county by runoff in streams is determined principally by the duration and intensity of the rainfall, the slope of the land surface, and the type of soil and vegetation. The runoff from a gentle rain as a rule is much smaller than the runoff from a heavy downpour; hence the amount of groundwater recharge from a gentle rain of long duration generally is greater than the recharge from a heavy downpour of short duration, providing all other factors are equal. The slope of the land is an important factor in determining the amount of runoff, and in general the steeper the slope the greater the runoff. Runoff is also greater in places where the surface is underlain by fine-grained, relatively impermeable material than in places where the surface material is sandy and loosely compacted. The latter type of material allows a part of the water to percolate into the ground, thus decreasing the amount of surface runoff. Vegetation tends to decrease the velocity of the runoff, thereby offering a better opportunity for the water to seep into the ground.
The most favorable areas for recharge in Barton and Stafford Counties are those areas underlain by dune sand. They include most of the area south of Arkansas River and the small area of sand hills southwest of Claflin (Pl. 1). Because of the high porosity of the dune sand and the presence of many undrained basins that serve as catchment areas for the rainfall, much water percolates downward to the zone of saturation. The sandy surficial material and the gentle slopes in this area reduce surface runoff to a minimum, so that very little water is lost by runoff in the sand hills except in narrow belts along the few streams. Throughout most of the areas of sand hills the material between the land surface and the water table is sufficiently permeable to allow water to percolate downward with little interruption. In a few places, lenses of relatively impermeable material probably hinder downward movement of water. Such lenses, however, are believed to be of limited horizontal extent so that the water detours around them and eventually reaches the water table.
The hydrographs of wells 20-11-20cc and 21-13-27dd in Figure 14 indicate that during periods of abundant rainfall a large amount of water is added to the Meade formation by precipitation in the sand-dune area south of Arkansas River. This is shown by the close relation between the precipitation graph and the hydrographs.
The rainfall as recorded at Great Bend was below normal in 1943, but during 1944 and the early part of 1945 it was considerably above normal. As a result, the net rise of water level in well 20-11-20cc was about 3.6 feet from October 1942 to August 1945, and the net rise of water level in well 21-13-27dd was about 8 feet from August 1942 to August 1945.
The valley areas in Barton and Stafford Counties are also excellent areas for groundwater recharge from precipitation. The factors that favor recharge in valley areas are the shallow depth to ground water, the sandy, porous soil, and the relatively fiat surface which keeps runoff to a minimum. The water levels in shallow wells tapping alluvium in valley areas respond quickly to precipitation. This is shown by the hydrographs of well 18-15-28cc1 in Walnut Valley and well 20-11-3dd in Arkansas Valley. The high peaks on the hydrographs of wells 18-15-28cc1 and 20-11-3dd are probably the result of recharge from high water in Walnut Creek and Arkansas River, since the wells are near the streams. The general trend of the hydrographs, however, is directly controlled by the local precipitation.
A large amount of water also reaches the water table from precipitation on Cheyenne Bottoms. Water will also be diverted into Cheyenne Bottoms from Walnut Creek and Arkansas River. Since there is no runoff in this area, the amount of rainfall that eventually joins the underground reservoir is the total precipitation less the loss from evaporation and transpiration. The superficial material underlying Cheyenne Bottoms consists of silt and clay and is relatively impervious. During dry seasons the floor of Cheyenne Bottoms in many places is honeycombed with cracks that are several inches in width. A part of the water that falls as precipitation probably moves downward through the impervious cover to the shallow water table through these sod cracks and through rodent burrows. The close relation between rainfall and the increment to underground water storage beneath Cheyenne Bottoms is indicated by comparing the hydrograph of well 17-12-33dd with the curve showing cumulative departure from precipitation in Figure 14. Well 17-12-33dd is a shallow well located in the northern part of the Bottoms.
The amount of water that reaches the water table from precipitation on areas underlain by the Sanborn formation is very small in most places compared with the sand dune and valley areas, for the areas underlain by the Sanborn have thick silt beds between the surface and the water table. The silt, which has a low permeability, retards the downward movement of water. It will be noted that the hydrograph of well 18-11-28dc, located in the Cow Creek drainage area where the surface is underlain by thick silt, shows little or no correlation with the precipitation. This indicates that recharge from local precipitation in this area is very small or does not occur at all.
The underground reservoir beneath the area underlain by the Pleistocene deposits in the vicinity of Galatia in northwestern Barton County probably receives water directly from local precipitation. Recharge from precipitation may be particularly high in those places where Pleistocene sand and gravel is exposed at the surface. Very little of the water from local precipitation reaches the underground reservoir in most of northern Barton County, for most of this area is underlain by impervious Cretaceous clay and shale. Some water may enter the Dakota formation in those areas of its outcrop where sandstone is at the surface, but the amount is probably small because of the steep slopes, which favor rapid runoff.
Recharge from Streams and PondsTwo factors determine whether a stream is capable of supplying water to the underground reservoir: (1) the water surface of the stream must be above the water table, and (2) the material between the stream channel and the water table must be sufficiently permeable to permit water to percolate downward and outward from the stream. Streams that satisfy these conditions are called influent or losing streams. Although no evidence of recharge from streams is apparent on the water-table contour map, it seems probable that some of the streams are supplying water to the underground reservoir. Arkansas River in Barton County is normally an effluent or gaining stream - that is, the stream surface is lower than the water table; hence, ground water moves toward the river. During flood stages of the river, however, the direction of movement of the ground water with respect to the river would be reversed and there would then be recharge from the river. The channels of Rattlesnake Creek and the North Fork of Ninnescah Creek in Stafford County and of Cow and Little Cheyenne Creeks in east-central Barton County are above the water table in the upper part of their courses and below the water table in the lower part. Where their channels lie above the water table and when they are flowing, these streams probably furnish some water to the underground reservoir. Where their channels lie below the water table, they are receiving water from the groundwater reservoir. The channels of Peace Creek in east-central Stafford County and Dry Walnut Creek in southwestern Barton County are above the water table throughout this area and may lose water to the groundwater reservoir. The same is true of many smaller streams in Barton and Stafford Counties at times when they are flowing.
During rainy seasons water draining from the adjacent uplands accumulates in Cheyenne Bottoms and forms a large, shallow temporary lake. The water remains there for several weeks or months. Since there is no surface outlet, the water is lost through evaporation, transpiration, and seepage downward to the water table. The amount of water that is added to the groundwater reservoir by this means is thought to be relatively small because of the low permeability of the materials underlying the surface of Cheyenne Bottoms. Cracks and crevices that develop in the Bottoms during dry periods may provide a pathway for the downward movement of water for a time after Cheyenne Bottoms is flooded, but they may become sealed after water has stood over them for several days.
Recharge from Outside the AreaThe water-table contours on Plate 1 show that the ground water in this area is moving from west to east, indicating that water percolates into the groundwater reservoir of this area from Rush, Pawnee, and Edwards Counties.
Kansas Geological Survey, Barton and Stafford County Geohydrology|
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Web version Dec. 2001. Original publication date Dec. 1950.