The amount of ground water discharged into the streams was obtained by separating the base flow from the total discharge of Elk River at the gaging station near Elk City in Montgomery County, only a few miles downstream from the boundary of Elk County. Elk River drains about 64 percent of the area of Elk County. Flows for November, December, and January were used in calculating the base flow, as evapotranspiration is low during these months, and periods were Selected when there was no direct surface runoff from precipitation; therefore, the flow of the stream represented essentially ground-water discharge. A curve representing base flow or ground-water discharge was drawn from hydrographs prepared from records for several years. Assuming that the base flow is nearly constant throughout the year, the annual ground-water discharge for the basin was computed to be about 27,000 acre-feet, which is equivalent to about 5.5 percent of the annual precipitation (2 inches). Extending this figure to cover the whole county, the total ground-water runoff would be about 42,000 acre-feet.
Discharge of subsurface water has been divided by Meinzer (1923) into ground-water discharge (discharge from the zone of saturation) and vadose-water discharge (discharge of soil water or other water not derived from the zone of saturation). In Elk County, water is discharged from the zone of saturation by seeps and springs, evapotranspiration, and withdrawal from wells. Ground water is also discharged from Elk County by percolation through consolidated and unconsolidated rocks into adjacent areas, although this quantity is probably offset by the amount gained by percolation into the county from outside areas.
Discharge from Evaporation and Transpiration
The quantity of ground water discharged from an aquifer by evaporation and transpiration depends on the climate, type of vegetation, depth to the water table, and type of rocks and soil above the water table. In most of Elk County the water level is too deep for much discharge of ground water by evaporation and transpiration; these processes are most active in the valleys, where the water table is shallow.
The total discharge of water from the area by evapotranspiration, of which the discharge of ground water makes up only a small part, can be estimated by subtracting the total runoff from the total precipitation on the area when ground-water storage remains about constant and pumpage is small. In Elk County the precipitation was about normal in 1946. The total runoff was about 116,000 acre-feet, or about 15 percent of the precipitation; hence, about 85 percent was discharged by evapotranspiration. The manner in which precipitation falls will cause considerable variation in the quantity of water discharged by evapotranspiration. The precipitation in Elk County in 1946 and 1947 was 35.37 and 36.63 inches, respectively, but the distribution in the two years was different. Total evapotranspiration during 1946 and 1947 was about 85 and 60 percent, respectively.
Discharge from Seeps and Springs
Most of the ground-water discharge in Elk County takes place through seeps and springs along the outcrops of the aquifers. The base flow of all perennial streams in the county is maintained by seeps and springs. The total discharge by these means was computed to be about 42,000 acre-feet per year.
Discharge from Wells
All municipal and large industrial water supplies in Elk County are obtained from surface-water sources. Ground water is withdrawn from wells for domestic and stock use. Domestic and stock wells are generally drilled or dug, but a few wells in the alluvium of Elk and Fall Rivers are driven. The yearly pumpage from wells in the county is about 110 million gallons, or about 338 acre-feet. The yield of domestic wells in Elk County ranges from as much as 50 gallons a minute for some wells in the Wreford limestone in the northwest corner of the county and in the alluvium of Elk and Fall Rivers to only a few gallons an hour from some wells in sandy shales and massive limestones.
Kansas Geological Survey, Geology
Web version July 2002. Original publication date July 1958.
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