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<br />~'i <br /> <br />00 1614- <br />/ <br /> <br />e <br /> <br />Summary Report - Channel Capacity Below Navajo Dam and the Potential for Increasing It To <br />6,000 Cubic Feet Per Second <br /> <br />August 1998 <br /> <br />By: Rege Leach, Bureau of Reclamation (BOR) and Dick Kreiner, Corps of Engineers (COE) <br /> <br />Purpose: This analysis was done to implement a peak flow request from the San Juan River <br />Basin Recovery Implementation Program Biology Committee of 6000 cubic feet per second (cfs) <br />during the spring of 1998. This is a test flow to help determine the long term flow <br />recommendations as part of the Recovery Implementation Program. <br /> <br />e <br /> <br />Scope: Based on the results of the 7 year research the Biology Co~mittee plans to include in the <br />flow recommendation a 6000 cfs peak release. Pe* releases frcini.bia~have been <br />~cfs, the interim channel caRacity used by the COE for the reach of the S~ <br />River from the dam to its confluence with the Animas River. There are also hydraulic release <br />Cip;city limitations of the dams outlet works and Farmingtions hydro-electric power plant. <br />These limitations will be addressed in a separate report. The COE was willing to evaluate the <br />river channel at nows higher than 5,000 cfs for a test period to determine if nows can be safely <br />be passed. A test plan was developed in which the river channel was observed at 5000 cfs. If no <br />critical flood damage concerns are identified, nows would be increased in 500 cfs increments and <br />observations made. Increases and observations would continue until reaching 6,000 cfs or until <br />flood damage occurred. If at anytime during this test, unnecessary flood damage or the public <br />endangerment was suspected to occur, the increase in release would be suspended and flows <br />returned to 5,000 cfs. <br /> <br />e <br /> <br />Summary: With approximately 5,000 cfs oftlow in the San Juan River at the Archuleta gaging <br />station, the river channel was surveyed from Farmington above the Animas River to the dam. <br />Flows throughout this section of river were stabilized with no measurable intervening flows. The <br />slirvey was the first step in the test to determine if releases coulcfbe-in~re;sed with~ut- ~ - <br />unnecessarily endangering public safety. Channel banks, recreation facilities, domestic water <br />and waste water systems, residences, temporary structures, bridges, and diversion structures we <br />observed. An assessment was made at each site defining the impact of additional flow on the <br />area and the nature and significance of the impact. <br />~ [e.gllts showed an}': increase in flow above 5,000 cfs may unnecessarily endanger existing <br />s~ctures along the river: The potentially impacted areas were three_hous~an4-anjrrigati6n <br />d~.:. These areas were determined to be of high significance and at risk of <br />damage with higher flows. The test, at flows above 5,000 cfs, could not be safely run until these <br />areas were protected. This protection could not be completed in time for higher test flows in the <br />spring of 1998. <br />O~acts identified were channel bank ~tQu1S-hin~_an~r9sion, seR.tk.s~em_problems,-and <br />gel!~ral public 9anger resulting from high water flows.. These are considered significant for long <br />term annual operation'butnOtfor asnort ternl't~st ~fvery controlled higher flows. They must be <br />addressed with the anticipation of longer term annual replication of flows above 5,000 cfs. The <br />