The quantity of water available from an aquifer depends on the ability of the aquifer to store and to transmit water. The ability of an aquifer to store water is measured by its storage coefficient and the ability to transmit water by its transmissivity. These hydraulic properties are in turn dependent upon the dimensional and geological parameters of the aquifer.
Three aquifer tests were made to determine the storage coefficient, the transmissivity, and the hydraulic conductivity of the valley-fill deposits in Walnut Creek valley. The test data were analyzed by methods referred to as the Thiem method, the Theis nonequilibrium method, and the Jacob modified nonequilibrium method (Ferris and others, 1962; Stramel, Lane, and Hodson, 1958). Each test was analyzed by all or some of the preceding methods in an attempt to arrive at aquifer coefficients judged to be most nearly correct. The theory and mathematical derivations of the methods are presented in the references noted.
Results of analysis of the tests are presented in table 9. Under the heading of hydrologic properties both the terms previously used by the U.S. Geological Survey, coefficient of transmissibility and field coefficient of permeability, and the terms currently used, transmissivity and hydraulic conductivity (Lohman and others, 1972), are listed.
Table 9--Aquifer-test results.
(gal per day
(ft2 per day)
(gal per day
(ft per day)
|August 3-5||2,733||100,000||13,400||1,650||221.1||2.6 X 10-4|
3.6 x 10-2
|August 15-22||10,095||70,000||9,380||1,750||234.5||3.1 X 10-2|
4.4 X 10-3
|July 16-17||1,840||100,000||13,400||2,850||381.9||1.2 X 10-2|
1.4 x 10-1
The storage coefficients determined by the three aquifer tests range from 1.4 x 10-1 (unconfined aquifer) to 2.6 x 10-4 (confined aquifer). The disparities in storage coefficients could result from partial penetration of the aquifer by the pumping well or the observation wells, localized confining layers in the aquifer, insufficient length of aquifer tests, or some combination of these or other factors. The aquifer is considered to be generally unconfined in Walnut Creek valley and to be similar to aquifers in other stream valleys where storage coefficients of 0.15 and 0.20 have been used. Thus, a storage coefficient of 0.15 was assigned to the valley-fill deposits.
Kansas Geological Survey, Geology
Placed on web Aug. 22, 2008; originally published July 1973.
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