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34 Grand River Ditch normally diverts from the middle or.end of May to early in September. The basin tributary to the Ditch comprises Some 21 square miles, lying at elevations ranging from 10,175 to the summit of Mt. Richtofen at 12,940 feet. Timberline varies from 10,200 to 11,000 feet. The yield of the basin tributary to Grand River Ditch is appreciably greater than the Ditch's historic diversions to the Poudre basin. The yield potential of Grand River Ditch is not utilized for several reasons: I. In periods of surplus or "free" water on the Cache la Poudre River, water normally may not be imported to the Poudre from the Colorado. Such periods of surplus water occur in the high flow years for a period of days or weeks. Grand River Oitch water is then spilled before it can cross the Divide. 2. There are times of no surplus when other rights are satisfying direct flow demands and Long Draw Reservoir is full. The Grand River Ditch then spills. 3. There are periods when the yield exceeds the capacity of the Ditch. 4. There are periods of substantial yield when the snow has not yet been cleared out of the Oitch. . i; ,. 5. Grand River Ditch :loses. large amounts of water by see~age, ~arti- cularly in certain rocky reaches of the Ditch that have fissures and fractures, and generally high permeability ra~es. > A part of the presently unused yield potential can be utilized by two means. First, the enlargement of Long Oraw Reservoir; and second, lining of portions of Grand River Ditch. Analyses of the records of daily diversions over a 10-year period indi- cate that annual diversions could be increased by an average of 2,500 acre feet with an additional 6,000 acre feet of reservoir capacity. In several years, notably the drought years of 1954-1956, additional storage would not in itself result in increased diversions. In high runoff years, diversions could increase to the full extent of additional reservoir capacity. Grand River Ditch seepage losses are estimated to be 30%. The loss rate is not uniform over the length of the Ditch, but is particularly high in certain reaches. Lining of 1.72 mi les is proposed to reduce losses in these reaches. The over-all loss wil I be reduced from an estimated 30% to 24% by this construction. The gain in diversions by the loss reduction averages 1500 acre feet per year over the study period. The summary of the proposed loss reduction in the Grand River Ditch for the 10-year study period is given in Table IV-E, along with the estimated increased yield as a result of enlarging Long Draw Reservoir. The estimated increased yield is conserva- tiveo