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<br />developed and imported from foothills <br />reservoirs to the north. <br /> <br />Erie Dam site is located in Weld County on <br />Coal Creek 1 mile south of Erie. An earthfill <br />structure creating a plains reservoir for <br />reregulation of water supplies was studied <br />for this site. <br /> <br />Reservoir Enlargement <br /> <br />As stated earlier, consideration was given to <br />the enlargement of the existing Carter Lake <br />and Horsetooth Reservoirs by raising the <br />height of the dams and retention dikes. <br />Preliminary studies show that the maximum <br />practical height to which these dams could <br />be raised is approximately 20 feet. <br /> <br />HYDROLOGIC STUDIES <br /> <br />General <br /> <br />Hydrologic studies consisted of collecting <br />basic data on surface water, ground water, <br />and water quality published in Geological <br />Survey publications. Additional information <br />was obtained from irrigation districts' <br />operation records. Most of the Front Range <br />data are several years old and any new study <br />should include more recent data on those <br />areas affected by the increased use of <br />ground water and where there is <br />considerable conversion of irrigation water <br />use to M&I use. <br /> <br />Tabulations of decreed water rights for each <br />of the major streams were obtained from the <br />Colorado State Engineer. Monthly <br />precipitation and temperature data were <br />collected and tabulated for the study period <br />at all major recorder stations in the study <br />area. <br /> <br />Studies of consumptive water use were <br />made for different areas and different <br />drainages. A computer program was written <br />to determine monthly potential <br />evapotranspiration. Projected population <br />and M&I water requirements for the 1980 <br /> <br />and 2000 periods were computed based on <br />the present use, as shown in table IV-2. <br /> <br />Previous investigations of irrigation water <br />requirements for the Cache la Poudre study <br />area disclosed the following average canal <br />and lateral system losses: <br /> <br /> Losses in <br /> thousands Percent of river <br />Month of acre- ft headgate diversion <br />April 1.7 46 <br />May 20.1 36 <br />June 34.5 29 <br />July 29.6 26 <br />August 22.3 24 <br />September 13.1 25 <br />October 3.8 36 <br />November 1.4 38 <br />Season 126.5 28 <br /> <br />Although such losses are incurred by the <br />canal and lateral systems, the water lost is <br />not necessarily consumed but becomes <br />available from the ground-water aquifer or <br />as seepage return to the stream and creek <br />channels. Many of the canal companies <br />depend on return flows for a portion of their <br />water supply. <br /> <br />Water supplies are inadequate to meet the <br />requirements of presently irrigated lands <br />and the M&I needs for projected population <br />in the years ahead. Therefore, the studies <br />were based on the premise that M&I water <br />requirements would be met by acquiring <br />some of the irrigation water rights. A <br />schematic water diagram showing native <br />tributary and main stream runoff and a <br />water budget summary for the Front Range <br />Unit is included as exhibit IV-6. <br /> <br />Flood and sediment studies were made for <br />the potential reservoirs. Ground-water <br />studies were limited to a review of <br />ground-water data in a study prepared by <br />the Geological Survey. Previous water <br />utilization studies for the area had indicated <br /> <br />IV-9 <br /> <br />