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<br />~ <br />Due to a lack of reservoir storage, about 82,000 acres of land does not <br />have a full growing season water supply. Canals of the conveyance <br />system are in earth section and subject to seepage losses. For the most <br />part, on-farm systems are in earth section and need to be up-dated. <br />With an up-date of the on-farm systems, management will show a marked <br />improvement. <br /> <br />Improvement Needs <br /> <br />Improved water management is needed throughout the existing conveyance, <br />distribution, application, and return systems. Improvement in the <br />irrigation efficiency and reduction in salt loading will require a total <br />system emphasis on diverting the amount of water needed for crop con- <br />sumptive requirements, soil leaching, cultural practices and unavoidable <br />seepage and spillage losses or deep percolation. Because the source of <br />a large portion of the salt pickup is from the underlying Mancos shale <br />formation and alluvial aquifers, the overall emphasis will be placed on <br />reducing canal and lateral seepage losses, deep percolation, and in <br />maintaining positive control over return flows to el iminate erosion from <br />fields and drains. <br /> <br />Watershed Treatment Needs <br /> <br />Prel iminary evaluations indicate that the contribution of salt loading <br />in the erosion process is from local ized watershed areas with high <br />erosion rates from soils with high salt content. <br /> <br />The opportunity for greatest reduction in stream sediment load I ies in <br />treatment of high sediment yield areas. For the Lower Gunnison Unit, <br />this is a 539-square mile area mapped as having a sediment yield greater <br />than 0.5 acre-foot per square mile per year. Structural treatment <br />measures such as debris basins, streambank protection, grade control, <br />etc., will provide sediment reduction. Over time, the most effective <br />treatment measures may be improved vegetation and less disturbance of <br />the soil surface. Such measures include proper grazing use, range <br />seeding, livestock exclusion, tree planting, woodland improvement, etc. <br />A combination of structural and vegetation improvement measures may be <br />necessary in some areas. <br /> <br />The specific potential for reducing the annual sediment yield of 1,086.5 <br />acre-feet, including a portion of the 408,000 tons of soil loss annually <br />from streambank erosion, and the 592,000 tons of total dissolved sol ids <br />. from watershed areas of the Lower Gunnison Unit is not known. <br /> <br />003082 <br /> <br />7 <br />