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<br />- <br /> <br />I, <br /> <br />e <br /> <br />e <br /> <br />- <br /> <br />....~ <br /> <br />00161 ,- <br />/ <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 />recommt:ndations as part of the Recovery Implementation Program. <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. ~~~I~ases_~aj.Q,D_am have been <br />limited .-!.Q5.0.00-c.[s.Jhe i.!!t~tiI!l. channel caQacity used by the CO E for the reach of ~@ Ju'!!l <br />River from the dam to its confluence with the Animas River. There are also hydraulic release <br />capacity 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 />endange:rment was suspected to occur, the increase in release would be suspended and flows <br />returned to 5,000 cfs. <br /> <br />SummaJY: With approximately 5,000 cfs of flow 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 />survey ,M.iSille first step in thetest to determfile1frcleases'could b~'increased without' .- <br />unnecessarily endangering public safety. Channel banks, recreation facilities, domestic water <br />and wa~;te water systems, residences, temporary structures, bridges, and diversion structures we <br />observe:d. 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;mlts showed an): increase in flow abo~~OOO cfs may unnecessas.ib: eE.dang~r existing <br />structw-es along the river. The potentially impacted areas were threeJ!~I!~~Lan~LanjrrIgation <br />c(i;ersicm structure. The~ areas were determined to be of high significance and at risk of <br />~- - <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~..llnpacts identified were channel bank sl.Q.ughing.and_er9sion, sep-t!9_~ystem.problems,-and <br />g_~ner~]l.public .dang.t?!,J:'~sulting from high water flo~.. These are considered significant for long <br />term atmual operation but noTfor a-sllOrt term test of very controlled higher flows. They must be <br />addres:;ed with the anticipation of longer term annual replication of flows above 5,000 cfs. The <br />