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. CHAPrER IV GRAVITY PIPELINE PLAN Stream depletions With development of the gravity pipeline plan, the flows of the Colo- rado River would be depleted by an average of 9,100 acre-feet annually. Approximate:q 3,800 acre-feet of this depletion would be attributable to municipal and domestic use and the remaining 5,300 acre-feet to irrigation and outdoor residential uses. Development of the plan would increase the salinity concentration of the Colorado River at Hoover Dam by an estimated average of 0.9 mg/l. Ap- proximately 0.1 mg/l would be attributed to salt loading from return flows and 0.8 mg/l to the concentrating effects resulting from stream depletions. Project Features Landis Pipeline . The Landis Pipeline would head at the outlet works of Ruedi Dam on the Fryingpan River and would extent northwestward 17.7 miles. In its initial 3.5 miles the pipeline would be located along the south side of the Fryingpan River. It would cross the river in a buried siphon and then continue 14.2 miles along the north side of the river. A turnout would be made to the first treatment plant near Basalt. The pipeline would have a capacity of 160 cubic feet per second to the treatment plant and a capacity of 145 cubic feet per second beyond the plant. It would be a buried high-pressure pipe with a diameter ranging from 76 to 60 inches. Three rate-of-flow control stations would be constructed along the pipeline. Each station would consist of a valve structure and adja- cent downstream tank to "stairstep" the static head and control the flow of water. Air valves and blowoff structures would be provided as re- quired. Considerable effort was utilized to select a route for the Landis Pipeline that would have the least environmental impact and still meet design standards and be economical:q justified. Two main alternatives to the selected route were considered. The first involved the construc- tion of the Landis Pipeline on grade along the south side of the Frying- pan River Canyon. A pipeline along the south side of the canyon would be less cost:q than along the north but the environmental impacts would be more serious because of the steeper and more rugged slopes on the south. The second alternative would be a high-pressure pipe along an existing Forest Service highway from a point just below Ruedi Dam to Basalt. This route was not selected because of the problems that would arise with the temporary closing of the highway during construction and also the high construction costs. . 34