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<br />GU020i <br /> <br />. <br /> <br />Carlson Ditch. The Carlson Ditch is the last ditch diverting in <br /> <br /> <br />Colorado, its diversion point being 8 miles upstream from the Julesburg <br /> <br /> <br />gaging station. The Carlson Ditch irrigates about 2,000 acres on the <br /> <br /> <br />south side of the river. The average diversion during the IS-year study <br /> <br /> <br />period was 1,600 acre-feet per year. The lowest diversion was 0 acre-feet <br /> <br />in 1960 and the highest was 3,000 acre-feet in 1954, The estimated delivery <br /> <br /> <br />efficiency of the Carlson Ditch is 75 percent. <br /> <br /> <br />Study reach efficiency <br /> <br /> <br />For the study reach, the outflow items of the stream-aquifer budget <br /> <br /> <br />in Table 2 which have the greatest potential for modification in order to <br /> <br /> <br />increase beneficial consumptive use and reach efficiency are (1) the stream <br /> <br /> <br />outflow at Julesburg and (2) phreatophyte consumptive use. <br /> <br /> <br />Except for the May and June snowmelt-runoff period, most of the water <br /> <br /> <br />passing the Julesburg station is composed of irrigation return flow. About <br /> <br /> <br />127,500 acre-feet of the 314,500 acre-feet average annual outflow at Jules- <br /> <br /> <br />burg during the IS-year period occurred during the 5-1/2 months when the <br /> <br /> <br />Colorado-Nebraska Compact was not in effect, The last opportunity for <br /> <br />diversion to storage during the non-compact season in Colorado is by the <br /> <br /> <br />Julesburg Reservoir. The point of diversion for the Julesburg Reservoir <br /> <br /> <br />(headgate of the Harmony No. 1 Canal) is 37 miles upstream from the Jules- <br /> <br /> <br />burg gage. Therefore, any return flow to the stream within this 37-mile <br /> <br /> <br />sub reach during the non-irrigation season is physically unavailable even <br /> <br /> <br />if legally available, Return flows reaching the river above the Julesburg <br /> <br /> <br />Reservoir inlet is also often lost because the Julesburg Reservoir has no <br /> <br /> <br />difficulty in filling during most years, <br /> <br />. <br /> <br />Studies by the U. S. Bureau of Reclamation indicate that operation of <br /> <br /> <br />the proposed Narrows Reservoir would reduce the average annual flow at <br /> <br /> <br />Julesburg by about 75,000 acre-feet, The effect of the reservoir would be <br /> <br /> <br />to reduce the flow during the spring runoff period and provde more water <br /> <br /> <br />to the study reach during the late summer and early fall months, It is <br /> <br /> <br />likely that the return flow accruing in the reach during the winter months <br /> <br /> <br />will be increased somewhat by operation of the Narrows Reservoir. <br /> <br />. <br /> <br />-44- <br />