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6. Future Water Supply The future water supply developable by a potential Cache la I?oudre Project will consist of native flows at the mouth of the canyon and upper basin transbasin imports. The total future surface water supply available for conservation purposes in the lower basin will consist of these developable flows, transbasin imports delivered through the COlorado-Big Thompson Project facilities, useable return flows, some Big Thompson River flows, rainfall and snowmelt in the lower basin, and groundwater inflow into the lower basin. An average of 271,000 acre-feet per year of developable native flows is estimated to be available in the future from the upper basin catchment. An estimate of these native flows at the mouth of the canyon was made on a monthly basis using historic data for the hydrologic study period as described earlier in this Chapter. An average of 37,000 acre-feet per year of developable flow is esti- mated to be available in the future from upper basin transbasin imports. It was assumed these flows would be available on the same monthly basis as were historic flows during the hydrologic study period. Transbasin imports into the upper basin could be increased in the future with rehabilitation of the two ditches not now in operation, increased maintenance of the other ditches or the development of additional storage, It is estimated that such an in- crease could add from 5,000 to 10,000 acre-feet per year to the water supply in the Cache la Poudre Basin. This possibility is primarily one of economics of maintaining the ditches or building the storage, and was not considered as part of the future water supply during this study. Water deliveries through the Colorado-Big Thompson facilities are assumed to continue along with the future supply from the Windy Gap Project presently under construction. The Windy Gap Project is scheduled for com- pletion in this decade. Discussions with officials from the U.S. Bureau of Reclamation indicate that an annual average of 115,000 acre-feet of water will be delivered into the lower basin from these two projects in the future. It was assumed that this water would be available on demand on a monthly basis according to historical agricultural and municipal and industrial uses. Return flows from the Fort Collins treatment plant will continue to be available for subsequent uses. The amount available is estimated to aver- age 65 percent of the total supplied to the city. The Rawhide Power Plant uses will be fully supplied by this water with the remainder available for agricultural uses according to the historic monthly use pattern. Return flows from the City of Greeley pass out of the basin and, therefore, are not con- sidered as part of the future available supply. The cities of Windsor and Greeley have water rights for use of water from the Big Thompson River. In 1981 the City of Greeley used approximately 9,000 acre-feet of water from the Big Thompson River. It is anticipated that as the City of Greeley grows an increasing amount of water will be available to them from this source on a monthly basis. II 1-4 I I I I I I I I I I I I I I I I I I I