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<br />r roo.' .... <br />~u~\) <br /> <br />. <br /> <br />PART VIII--HYDROLOGY <br /> <br />WATER RESOURCES <br /> <br />Analyses of water supply for the unit were made in accordance <br />with_applicable water rights. Studies were made of historic water <br />use and associated shortages in order to derive estimates of future <br />uses and shortages with the Narrows Unit in operation. These studies <br />included the effects of the development on the magnitude of downstream <br />flows. The l5-year period 1947-l96l was selected as the period of <br />study because it is representative of long-term conditions in the area. <br /> <br />Surface Water Supplies <br /> <br />- <br /> <br />The only significant surface water source for irrigation in the <br />unit is the South Platte River. During the period of study, 1947 through <br />1961, the average annual flow of the South Platte River at Kersey, Colo., <br />(a few miles upstream from the Narrows Reservoir site' was 537,000 acre- <br />feet. At the Narrows Dam site, the average annual flow was about <br />365,200 acre-feet, and at Julesburg, COlo.,(near the Colorado-Nebraska <br />state line) the annual flow was 315,000 acre-feet. Of the 365,200 total <br />flow at Narrows, an average of 187,700 acre-feet ~er year was considered <br />storable. This quantity, determined by a point-flow analysis, is made <br />. up of high runoff when the river flows exceed the downstream direct <br />diversion needs or capabilities and of nonirrigation season flows when <br />there is no need for diversions. Hence, a storage reservoir is necessalY <br />to develop this water for project use. The need for storage is also <br />manifested by the wide fluctuations in annual storable flows--the ex- <br />tremes ranging from 5,100 acre-feet in 1953 to 485,000 acre-feet <br />in 1958. <br /> <br />In addition to the supplies made available through regulation of <br />storable flows, a second source of project water would be realized <br />from direct flow water rights for irrigated lands to be acquired for <br />rights-of-way for the Narrows Reservoir. The historic yield of these <br />rights has averaged 32,900 acre-feet annually. However, for future <br />project operations the Weldon Valley rights conversion will provide <br />the unit with 31,000 acre-feet annually from direct diversions plus <br />an additional 1,900 acre-feet annually which could be stored in the <br />Narrows Reservoir during months when there was no other request for <br />it on the river. <br /> <br />*- <br /> <br />The hydrology study presumes that historic surface water flows <br />would be representative of future conditions. This assumption slants <br />the analysis toward a conservative estimate of future water supply <br />because municipal importations into the South Platte River Basin should <br />tend to increase rather than deplete basin surface water supplies. <br /> <br />61 <br />