2017-05-26_REVISION - M1995017 (7)

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104 GEOLOGY AND GROUND WATER, SOUTH PLATTE RIVER VALLEY CONCLUSIONS Ground water in sufficient quantities for irrigation and other supplies is contained in the alluvial deposits that underlie the val- leys of the South Platte River and its tributaries. An estimated 12,700,000 acre-feet of water is stored in the alluvium within the project area. Wells that would yield 500 to 1,000 gpm could be de- veloped in the alluvium in most places and wells that would yield as much as 2,000 gpm probably could be developed in the thick saturated sections of the alluvium in the valley of the South Platte River. The alluvium is recharged chiefly by infiltration from irrigation systems and by precipitation on local and adjacent areas. Water is discharged from the alluvium chiefly by seepage into the South Platte River, by evaporation and transpiration, and by pumping. Recharge to the ground-water reservoir from infiltrating irri- gation water has raised the water table and caused seeps in some low-lying areas bordering the South Platte River. These seeps could be drained by lowering the water table a few feet, either by decreasing the recharge or increasing the discharge of ground wa- ter in the area. The amount of recharge could be decreased by lining the canals or by decreasing the amount of water that is applied to the land; the discharge of ground water could be in- creased by installing drains andby pumping additional water from the gound-water reservoir. If the pumped water were used for irrigation, the amount of surface water that is needed for this purpose would by reduced. Consequently, a balanced surface- and ground-water irrigation system could be established. In parts of the area where the ground-water reservoir is replenished by re- charge from the South Platte River and from adjacent areas during the nonirrigation season, large quantities of water could be pumped from the ground-water reservoir into canals and reservoirs during the irrigation season. Discharge of ground water by pumping in areas that depend en- tirely on ground water for irrigation has lowered the water levels in the valleys of Bijou and Kiowa Creeks and in parts of the Fort Morgan area and Beaver Creek valley. This condition is most serious in the vicinity of Gary, Colo. , where the alluvium is rel- atively thin. Surficial deposits in the valley yield water of acceptable quality for most purposes. The alluvial deposits yield hard water of mod- erate to high concentrations of dissolved solids, much of which is calcium sulfate. This water is of satisfactory quality,as a rule, for irrigation and domestic uses. Groundwater from the alluvium overlain by dune sand and from the Ogallala formation is softer and is preferred, when available in sufficient quantities, to water