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-------- 122 GROUND WATER, SOUTH PLATTE RIVER BASIN - - about 23 feet per mile south of Hudson, but it decreases to about. 18 feet per mile and is nearly uniform northward from Hudson. In the vicinity of sec. 11, T. 4 N., R. 64 1Y., however, there is a flattening of the slope, probably due to an increase in the permeability of the sedimentary rock. Depths to water and the shape or the water table show that Box Elder Creek was not gaining water from the ground- water reservoir in November 1957. The creek is dry during much of the year but is a source of recharge to the ground-water reservoir when - it flows and especially so when it is at flood stage. Other sources of recharge are surface water that is spread for irrigation lI.nd precipita- tion that falls within the basin. Immediately after a flood, when water from Box Elder Creek is recharging the ground-water reservoir a ridge probably is formed on the' water table beneath the bed of th~ creek. The contours around Horse Creek, however, indicate that the creek is gaining ground water, probably by seepage from Horse Creek . Reservoir. Recharge from the Ireland Reservoir No.5 apparently is causing the mound in the water table downstream .from the reservoir. The contours in the area where the valleys of the Beebe Draw and Box . Elder Creek valley merge show that some of the ground water in Box Elder Creek valley is .moving into the. valley-fill deposits in Beebe Draw. The slight. inward movement of ground water along the edges of the va II e;v probably- is_ caused by the slope of the bedrock surface. Depths to water in the valley range from less than 5 feet to about .40 feet and average 22 feet. Hydrographs of the U.S. Geological . Survey's observation wells (figs. 11, 12, and 13) show that the maxi- mum.annual fluctuation in weB Bl-65-12ccd2 waS about 13 feet, part or which was due to the pumping or a .nearby irrigation well. The records of the long-term observation wells, except well B2-64-30cbc, show a pronounced downward trend in the water levels since 1950 (fig. 10). In the vicinity of this well, ground-water underflow from Ireland Reservoir No.5 probably recharges the ground-water reservoir. Although the water levels had risen by the spring of 1958, they still were far below the average of record in most of the wells. The only . surface water available for irrigation in the district is that diverted from the few reservoirs and from Box Elder Creek when it is at flood stage. Therefore, irrigation is largely dependent on water pumped from wells. All the large withdrawals or ground water from the valley-fill deposits, except from the Hudson municipal wells, are used for irrigation. Code's well-location map (1043) shows only 70 irri- gation wells in ] 940; by the end of 1957 there were 210. The number of wells per section ranges from 0 in several to 12 in sees. 12 and 13, 'I." 1 ~., R. 65 lV., and the> average is three. Locally, however, the ir- rIgatIOn wells are too closely spaced, and as a result mutual inf,erfereoee - - - __CL~ _ - _..v _ decreases yields and increases drawdowns. Most of the wells are drilled to bedrock, are lined with metal casing, and are equipped with electrically driven turbine pumps. A few of the wells are dug and lined with concrete casing. Only two wells are equipped with centrif- ugal pumps and .only one pump is driven by an internal-combustion engme. Hudson (population 430) is supplied with water from two drilled metal-cased wells that obtain water from the valley-fill deposits. The wells; which are outside the city limits, are equipped with electrically driven turbine pumps that force water into a 44,OOO-gallon elevated steel tank. An average {)perating pressure of about 35 psi is main- tained in the city distribution system. About 125,000 gpd, or about 140 acre-ft per year, is pumped from the wells for municipal use~ Pumping from the irrigation wells in this district has been very heavy during recent years. Yields from the wells that were measured by the U.S. Geological Survey:ranged from 85 .to 1,090 gpm and averaged 550 gpm.Drawdowns-ranged from 7 to 32 feet and specific capacities ranged from 5 to 135. The coefficients of permeability and transmissibility. are relatively low (table 5). compared to those in the rest of the report .area. . The water levels in many of the wells south of Hudson declined to the pump intakes during the 1957 pumping sea- son, and some wells were not. used. . The largest yields generally are obtained from. wells near the.axial part of the valley ; the slope':wash deposits along the edges of the valley fin are poor 'producers. The comparatively small.average yields of wells in' the district probably are due to the' declining water table and to .the lower permeability of the valley-fill deposits, which contain a large percentage of clay and silt; Heavy pumping eventually could' lower the regional water table below the intakes of SOl'1.e pumps. . It - is: estimated that about 20',000 acre-feet of ground water is . pumped from the valley-fill deposits during a normal year. The estimated quantity of recoverable ground water in storage in Novem- ber 1957 was about 320,000 acre-ft. Declining water levels indicate that ground \yater is being taken from storage; that is, recharge is not balancing discharge. The decline of the water table in this district is the most marked in the report area. In the soutJlern part of this district, the water generally has a spe- cific conductance of less than 1,400 micromhos per cm and is of the calcium bicarbonate type. In the' northern part, the water generally has a specific conductancc of morc than 1,800 micromhos per cm and is of the calcium sulfate type.