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4 portations have been used in the upper basin above the Narrows area. The lower basin has benefited from the use of return flows. Most of the return flows haye been used by means of ground water with- drawals, leaving surface flows in the river about the same as pre- Colorado-Big Thompson conditions. The 166,370 acres of land that would obtain supplemental irrigation water are in Morgan, Logan, Washington, and Sedgwick Counties, along the main stem of the lower South Platte River in northeastern Colorado. All of the land is now or has in the past been irrigated. The South Platte River is the only significant source of surface water for irrigation in the proposed Narrows unit. Ground water aIso constitutes a major source of water in the basin. Thirty-three irrigation systems now serve lands within tbe Narrows area. Four offstream reservoirs serve about 10 to 12 of the ditch systems. None of the reservoirs have sufficient capacity to assure adequate supplies for the systems served. The remaining ditch systems rely on direct stream- flows for their major source of supply. Water shortages occur every year, primarily because storage facilities are lacking on some of the ditch systems. The principal feature of the proposed development is the Narrows Dam and Reservoir to be constructed on the South Platte River neax Fort Morgan, Colo. Also proposed is the acquisition and development of the existing Jackson Lake Reservoir, including some rehabilitation of the dam, for recreation and fish and wildlife enhancement. Federal construction of irrigation distribution facilities would not be involved, since the water developed by the unit would be conveyed by existing systems. Hydroelectric power development was found to be economi- cally infeasible. Lack of any foreseeable requirement for additional municipal and industrial water precludes the need for such facilities at this time. The water supply for the Narrows unit would be derived from regulation of surplus streaniflow and from direct flow water rights associated with irrigated lands to. be acquired for the !?roposed Narrows Dam and Reservoir. Irrigation storage capacity m Jackson Lake .Reservoir _would be transferred to the proposed Narrows Reservoir. Project water stored in the proposed Narrows Reservoir would be released either into the South Platte River through a river outlet works for delivery to existing downstream diversion works or through a canal outlet works directly into the Fort Morgan Canal. Supplemental water requirements for 23 of the ditches which serve 98.4 percent of the irrigable land in the Lower South Platte Water Conservancy District would be 178,000 acre-feet at the river headgate based on the 1947-61 period of study. Reservoir operation studies indicate that average annual supplemental yields of 119,400 acre-feet would be obtained under the proposed plan of development. In addi- tion, the divertible return How from project deliveries would average 21,300 acre-feet. These sources would yield a total of 140,700 acre-feet of supplemental water at the river headgates. The difference of 37,300 acre-feet annually represents diversion shortages, which occur in 3 of the 15 years of study. The Bureau of Sport Fisheries and Wildlife has formulated a plan for conservation and development of the fish and wildlife resources. It would include minimum flow of 50 cubic feet per second in arid public access to 5.5 miles of the South Platte River immediately below the " 5 . proposed .N \>rrows Reservoir, rehabilitation and stabilized operation of the exlStmg Jackson Lake Reservoir, development of a wildlife manage:r.nent area, and a zoning plan for the proposed Narrows ReserVOIr. The National Park Service has recommended a recreation plan that would incl,;,de four public use areas. Two of the areas would be located adjacent to the proposed reservoir shoreline and would function at all poolleveIs, a third area would be located below the ~ropose1 dam and reservoir, and the fourth would be at Jackson Lake eservolr. The Bureau of Outdoor Recreation finds that the recreation development recommended is consistent with the objectives of the Colorado outdoor recreation plan. The Cor!?s of Engineers evaluated the flood control re'l.uirements for t~e umt. It recommended the provision of reservOIr storage capaCIty o.f 550,000 acre-feet for downstream Hood protection. Of that capaCIty, 75,00q acre-feet would be used jointly for flood control and water conservatIOn purposes. The dam would have a river outlet capacity of. 8,600 cubic feet per second and a spillway capacity of 27,600 CUbIC feet 'per second. Operation of the reservoir for flood control would .be m accordance with regulations prescribed by the Secretary of the Army. In its .preliminary report, the Public Health Service indicated that a ~h degree of waste treatment and a minimum streamflow of 25 CUbIC feet per second are needed below the proposed Narrows Reservoir to obtai'! the desired water quality. Normal reservoir seepage, tri~utary inflows, and return flows would provide more ~han ~he desired Hows. The Federal Water Pollution Control Admin- IStratIOn (FWPCA) recommends that the operating procedures for the unit provide for maintenance of that streamflow but finds that the w.ter would be. usable for other purposes rather than water quality con~rol as dIScussed later in this report in connection with the alternatIve._plan. As re~ommended. by t~e Public Health Service, every effort will be made m cooperatIOn WIth the effected interests to assure that development and activities on the unit will minimize any potential public health hazards. TheBureau of ~ines advised that petroleum and natural gas are the only significant milleral resources present in the dam and reservoir area. A small fleld has shown a steady decline in production since 1~56: In Octoher ~965 only 34 of 108 wells that had been drilled W!thin the !eservOIr area at the flood control pool elevation were still produc~. Cons~dering a construction perIOd of 9 years, the Bureau of Mmes antICIpates that all oil and gas wells in the site will have been abandoned. As presented.in the attached regional director's report, the estimated total constructIOn cost of the Narrows Unit would be $61820000 based on October 1965 price leveIs. Interest during co~tru~tio,{ would ~d $4,?18,600 making the total investment cost $66,738,600. OperatIOn, mamtenance, and replacement costs would total $216 500 !"",ually. The annual co~ts of the unit for econoinic analysis, which mcludes the annual eqmvalent of the net project investment and annual operation, maintenance, and replacement costs, have been computed to be $2,275,200. The evaluated annual benefits to he derived by the several functions are as follows: