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<br />The abatement of saline return flows is accomplished by reducing irrigation system <br />conveyance losses and on-farm losses. While the salinity control program is aimed at <br />reducing tbe seepage that causes return flows, it also reduces the "non-productive" or <br />"incidental" consumptive use that occurs during irrigation. The incidental consumptive use <br />of water involves pennanent, but unintentional, loss of water from the basin by evaporation <br />from exposed water surfaces and. evapotranspiration by noncrop vegetation. These <br />incidental losses are reduced by combining ditcbes, replacing open ditcbes witb pipe, <br />eliminating standing water, drying up water logged soils, and reducing wetland acreage. <br />Based on climate data for tbe Grand Valley it is estimated that every mile of 2-foot wide <br />lateral placed in pipe reduces evaporation losses by 1 AF per year. Every acre of wetland <br />lost wiIl yield approximately 2 AF per year of reduced incidental consumptive use. Data in <br />the 1986 Grand Valley Stage II verification memorandum indicate tbat at full build-out <br />Stage II would line or pipe 325 miles of canals or laterals and reduce wetland acreage by <br />300 acres. This scale of project would reduce historical incidental depletions and thereby <br />produce 950 AF per year or less of "salvaged water" from the Grand VaIley. Witb a <br />construction cost of $37 million (excluding all overhead and design costs) this salvaged water <br />would bave an annual cost of approximately $3,700 per AF. <br /> <br />The original Stage II program proposed by the Bureau was expected to reduce total <br />seepage losses by 42,900 AF per year, 6,500 AF of which were from the GVIC system. <br />Nearly all this seepage historically returned to the Colorado River system within the Grand <br />VaIley. As more is learned about salinity in the Grand Valley, as construction costs <br />increase, and as the voluntary participants opt in and out of tbe program, it is unlikely that <br />all increments wiIl remain cost effective and some will be deleted from the final <br />implementation plan. Recent estimates indicate tbat tbe combined salinity program of <br />USBR and SCS in the Grand Valley will reduce irrigation seepage by approximately 70,000 <br />AF per year. As of December 1990, the USBR/SCS program in the Grand Valley had <br />reduced irrigation seepage by approximately 27,000 AF per year. It is important to <br />understand tbat tbese seepage reduction estimates are made for the purpose of determining <br />salt loading, not quantifying water availability. As the hydrosalinity model data are revised, <br />these seepage estimates may also change. <br /> <br />The majority of the irrigation water potentially made available through improved <br />efficiencies was not previously lost through consumption, but returned to the Colorado River <br />below the confluence with the Gunnison. While these return flows are not lost to the river <br />system, they historically have not been of benefit to users in Colorado because of the <br />proximity of the Utah state line, the adequate supply of water that exists in the Colorado <br />River below the Gunnison River, and lack of demand below Grand Junction. Those return <br />flows support instream uses in the Colorado River between Grand Junction and Utah. <br />Current demands for Colorado River water, and shortfalls in supply are in the headwaters <br />areas, and the water that eventuaIly becomes return flow has already been caIled past those <br />demands. This water called past upstream headgates does provide significant instream <br />values between the headwaters of the Colorado and the Cameo diversions. <br /> <br />5 <br />