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<br />0019\)1. <br /> <br />. <br /> <br />. <br /> <br />Sedgwick, and Washington Counties, and part of Larimer County. Of this area, <br />the alluvial aquifers cover about 2,600 mi2 (4,300 km2). The alluvial <br />aquifers consist of unconsolidated interbedded sand, gravel, clay, and silt. <br />Depths to water range from less than 2 ft (0.6 m) to more than 121 ft (36 m). <br />The saturated thickness ranges from 0 to about 300 ft (0 to 90 m). Water from <br />these aquifers is used as a supplemental supply for irrigation in the South <br />Platte River valley and some of the tributary valleys. The alluvial aquifers <br />are the primary water supply for irrigation in several of the tributary <br />valleys. The alluvial aquifers range from less than 1 mi (1.6 km) to as much <br />as 10 mi (16 km) wide and are found in valley fill deposited in broad troughs <br />cut into the underlying sedimentary bedrock formations or in terrace gravel <br />deposited on the bedrock of Late Cretaceous to Tertiary age. <br /> <br />. <br /> <br />Water levels fluctuate in response to recharge from precipitation, <br />recharge from applied irrigation water, and discharge resulting from ground- <br />water pumpage, seepage to surface water, and evapotranspiration. In areas <br />where pumpage is the predominant source of irrigation water, with little or no <br />surface-water application, water levels generally have declined; the magnitude <br />of the decline depends on the volume of water withdrawn. Such is the case in <br />Kiowa Creek and Bijou Creek valleys where changes ranged from a decline of <br />12.8 ft (3.9 m) to a rise of 4.6 ft (1.4 m) from March 1976 to March 1977. In <br />areas where surface water and ground water are used conjunctively, such as <br />most of the main-stem South Platte River valley, and major tributaries, such <br />as the Cache la Poudre River valley, water levels fluctuate during the <br />irrigation season but generally return to about the same level from season to <br />. season. In these areas, water-level changes from March 1976 to March 1977 <br />ranged from a decline of about 1.5 ft (0.46 m) to a rise of about 1.0 ft <br />(0.30 m). In the few isolated areas of predominantly surface-water <br />application, ground-water levels tend to respond to the amount of surface- <br />water application. <br /> <br />Ground-water levels measured in March 1977 are the result of irrigation <br />withdrawals and applications during the 1976 irrigation season and residual <br />effects of withdrawal and applications from previous years. Low 1976-77 <br />winter precipitation will affect surface-water supplies available for the 1977 <br />irrigation season. March 1978 water levels will reflect this deficiency <br />because most recharge is from infiltration of irrigation water. <br /> <br />WELL LOCATION <br /> <br />In this report, the locations of wells are based on the U.S. Bureau of <br />Land Management system of land subdivision (fig. 2). <br /> <br />. <br /> <br />The local well number locates a well within a 10-acre (4.0-ha) tract <br />using the U.S. Bureau of Land Management system of land subdivision. The <br />components of the local well number proceed from the largest to the smallest <br />land subdivisions. This is in contrast to the legal description, which <br />proceeds from the smallest to the largest land subdivision. <br /> <br />3 <br />