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WATER LEVELS IN THE ALLUVIAL AQUIFERS OF THE <br />LOWER SOUTH PLATTE RIVER BASIN, COLORADO <br />1994 <br />By Chuck Roberts <br />The purpose of this report is to provide water level data for 67 wells within the Lower South Platte <br />Alluvium for the period of Spring of 1988 through the Spring of 1994. The data presented in this <br />report is a result of cooperation between well owners, the Central Colorado Water Conservancy <br />District, and the Colorado Division of Water Resources. Funding for this project is supplied in <br />part from well permit fees collected and managed by the Colorado Division of Water Resources <br />as a result of the passage of Senate BIII 200 during the 1987 legislative session. <br />The following table of this report includes up to 13 water level measurements for the indicated <br />period in addition to a water level measurement taken at the time of construction of the well, if <br />available. Measurements are usually taken twice yearly, typically in the spring before irrigation <br />pumping commences and in the fall after irrigation pumping has ceased. The measurement <br />values in this report are expressed in feet below ground surface to water surface and were <br />obtained utilizing an electric sounder device or steel tape. All measurements were done by <br />Division 1 Water Commissioners (DWR) or the Central Colorado Water Conservancy District <br />(CCWCD) as indicated for each well. All of the wells are completed in unconsolidated gravel, <br />sand, silt and clay deposits predominantly of alluvial origin. Figure 1 is a map showing the <br />approximate location of the wells measured for this report. The South Platte River is shown in <br />blue. <br />The observation wells can be subdivided into two types: those which lie within or very near the <br />South Platte River floodplain, and those located in tributary valleys. The number of observation <br />wells in tributary valleys exceeds the number along the South Platte floodplain by 10. <br />An evaluation of the data of beginning water levels as compared to Spring 1994 levels reveals <br />that approximately 71 % of the wells have experienced a water level decline as compared to 70% <br />reported as declining in the 1993 report. Conversely, 29% of the wells experienced a rise in the <br />Spring 1994 as compared to the Spring 1988 water level. Declines of Spring 1988 to Spring 1994 <br />range from - 7.62' to - 0.03'. Declines on the order of 0.10' are insignificant in that such changes <br />can be caused by wind, earth movement, and the effect of evapotranspiration and phreatic <br />consumption or maybe errors in data recording. Water level rises ranged from 0.06' to 9.50' with <br />a median value of 1.41' for tributary valleys and less than 0.1' for the South Platte River <br />floodplain. <br />These data also reveal that the degree of these water level declines and rises of wells within the <br />tributary valleys exceed the water level declines and rises of wells within the South Platte River <br />floodplain by a factor of approximately 4.2. <br />Water level declines over the past five years have averaged 0.21 ft/yr in the floodplains and 1.12 <br />ft/yr in the tributary valleys. Water level rises over the past five years averaged .39 ft/yr (only 1 <br />to 4 records showing a rise) in the floodplain, and 0.528 ft/yr in the tributary valleys. <br />Page 1 of 2 <br />