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<br />001656 <br /> <br />Technical Memorandum No. NA V -8130- TM-98-I <br />OUTLET WORKS DISCHARGE CAPACITIES - NAVAJO DAM <br /> <br />1. Purpose and Scope of Work <br /> <br />The San Juan River Basin Recovery Implementation Program (SJRRIP) is a IS-year effort <br />designed to recover two endangered fish, the Colorado squawfish and the razorback sucker, while <br />allowing for water development to proceed in the San Juan Basin. As part of this program, the <br />Bureau of Reclamation (Reclamation) is participating in a hydrological modeling effort to define <br />the existing water supply in the basin and evaluate alternatives to meet the water development <br />needs) while protecting the endangered fish. Reservoir operation modeling has been completed <br />for various flow scenarios to determine optimum operating rules and to assess water development <br />potential. In testing these operating rules) changing the Navajo Dam peak release from 5,000 fi3/s <br />to 6,000 ft!/s markedly increased the frequency and duration of the larger magnitude flows <br />believed important for the recovery of the endangered fish for all levels of development analyzed. <br />If peak releases can be increased to 6,000 fi3/s for a duration offrom one to three weeks in May <br />and June of each year, then an increase in allowable depletions for water development of at least <br />60,000 acre-feet may be possible compared to that allowable for a 5,000 ft!/s release [1]. <br /> <br />I~ <br />III <br /> <br />A fonnal request has been made by the Biology Committee of the SJRRIP to detennine whether <br />the channel capacity between Navajo Dam and the Animas River can be increased to 6,000 fi3/s, <br />and to evaluate the hydraulic capacity of the dam to release 6,000 ft!ls. The Technical Service <br />Center (TSC) was requested by the Western Colorado Area Office, Southern Division, to provide <br />an assessment of the outlet works discharge capacity at Navajo Dam. This technical memorandum <br />documents the results of this assessment, and is based on available design and operation records, <br />and on additional hydraulic analyses perfonned for this study. Recommendations' are provided <br />pertaining t-o the proposed future operational tests. <br /> <br />n. Hydraulic Design Considerations <br /> <br />A. Main Outlet Works <br /> <br />The intake to the main outlet works is a tower-type concrete structure extending 280 feet above a <br />bedrock foundation, The intake sill at elevation 5882.50 provides a circular bellmouth entrance to <br />a 10-foot-diameter drop inlet shaft, and also serves as a seat for a spherical emergency bulkhead. <br />Six streamlined columns braced laterally by horizontal struts support II.8-foot-wide steel <br />trashracks for a height of 117.5 feet. A 90-degree elbow at the bottom of the inlet shaft provides <br />a contraction from a diameter of 10 feet to about 8.7 feet, followed by a horizontal enlargement <br />to a tunnel diameter of 18.75 feet. The concrete-lined tunnel extends 474.5 feet to a gate <br />chamber and shaft which houses a 6- by 13-foot fixed-wheel emergency gate. Steel transitions are <br />provided over a distance of 50 feet between the upstream tunnel and a downstream 110-inch- <br />diameter steel pipe. The steel pipe is located within a concrete-lined downstream access tunnel, <br />and extends over 1,040 feet to the downstream tunnel portal and access house. Three 20-inch- <br /> <br />I <br />