Laserfiche WebLink
<br />001662 <br /> <br />available for operation throughout the life of the project, unless it is operated and maintained in <br />such a way as to ensure its continued availability [9]. <br /> <br />C. NIIP Canal Outlet Works <br /> <br />The Main Canal headworks for the Navajo Indian Irrigation Project (NIIP) is located on the left <br />abutment of Navajo Dam, and is used for water deliveries to the Main Canal, Gravity Main Canal, <br />and pipe lateral distribution systems [3]. Diversion flows enter a trashracked intake structure (sill <br />elevation 5975.0) and an 18-foot-diameter concrete-lined tunnel. The flows are controlled by two <br />9- by 12-foot fixed-wheel gates and two 9- by 12-foot top-seal radial gates provided within a gate <br />structure and shaft, and pass through a transition section to Tunnel No.1. The minimum <br />reservoir operating level for the canal headworks is elevation 5990.0. The design discharge <br />capacity for the canal outlet works is 1,800 ft3/s, based on downstream canal capacity, which <br />results in a flow velocity of 7.1 ftls in the upstream tunnel section, and 8.3 ftls through the gates. <br /> <br />Diversion flows pass through Tunnel Nos. 1 and 2, and Cutter Reservoir, before entering the <br />Main Canal at Cutter Dam. The canal headworks at the dam includes a single 24- by 14-foot <br />radial gate with a discharge capacity of 1,800 ft3/s. Cutter Dam also contains a small river outlet <br />works, consisting of a 27-inch-diameter upstream conduit, a 36-inch-diameter downstream <br />conduit, and two 2- by 2-foot slide gates with a discharge capacity of about 110 ft3/s. An <br />uncontrolled spillway overflow crest and concrete-lined chute are located on the left abutment, <br />with a spillway crest at elevation 5963.9 and a discharge capacity of 2,460 ft3/s at maximum water <br />surface elevation 5974.1 [3]. River outlet works and spillway releases return to the San Juan <br />River through Largo Canyon, about 15 miles downstream from Navajo Dam, and therefore may <br />serve as a wasteway for canal releases. A second wasteway for the Main Canal is available for <br />emergency releases to Gallegos Wash, which intercepts the San Juan River about 40 miles <br />downstream from Navajo Dam. Releases to the Gallegos Wash in the past have caused some <br />erosion and have threatened some 30-inch-diameter oil pipelines. Some channel improvements <br />may be necessary in order to use either canal wasteway for supplemental releases to the San Juan <br />River to meet downstream discharge requirements. <br /> <br />D. Power Plant <br /> <br />A 16 MW hydroelectric power plant was designed by R.W. Beck and Associates in 1986, and was <br />constructed for the City of Farmington the following year to the left of the main outlet works, A <br />IIO-inch-diameter steel penstock extends about 124 feet from the wye branch on the main outlet <br />works to a concrete-encased steel bifurcation, branching to two 72-inch-diameter steel pipes and <br />two butterfly guard valves, Steel reducers provide'a sharp transition to the 60-inch-diameter <br />entrances to the two spiral cases and 16,000 horsepower vertical Francis turbine units. Power <br />plant releases enter a concrete-lined tailrace which is parallel to the main outlet works stilling <br />basin, and discharge into a common outlet channel to the San Juan River. <br /> <br />Performance curves for the power plant units are provided on figure 1. Discharges for each unit <br /> <br />7 <br />