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<br />o <br />o <br />'-' <br />~j~ <br />l>- <br />e <br /> <br />15. Comment: <br /> <br />Response: <br /> <br />The San Juan Basin Hydrology Model was used in the evaluation offlow <br />recommendations for the 1929 to 1993 hydrologic period, Gains and <br />losses between Farmington and Bluffwere analyzed as part of the natural <br />flow development and were therefore incorporated into the flow <br />recommendation analysis, <br /> <br />Recreationflow thresholds are addressed in Comment No, 35, <br /> <br />The draft EA states that the test will not significantly impact San Juan <br />River flows below the confluence of the Animas River. With no <br />supportive data this conclusion is impossible to make, In addition, the <br />draft EA states that inflow from the Animas River should keep flows <br />above 500 cfs below Farmington, To understand the potential effect of <br />such flows, the historic flows at this location should be specified so a <br />comparison can be made. <br />River flows downstream from the Animas will be reduced by <br />approximately 250 cfs during the test, <br /> <br />Historic Animas River forecasted runoff was compared to historic San <br />Juan River flows to estimate the July 2001 flows at Bluff, UT. This was <br />accomplished in the following way: A comparison of the May 2001 <br />forecasted April-July runoff for the Animas River at Durango was made to <br />the 1971-1999 historic Durango forecasts, Years with forecasted runoff <br />within +/- 15% of 2001 forecasts were selected as representative of this <br />year, The historic daily flows for these ten years were used in the <br />following equation to estimate possible flows in the San Juan River near <br />Bluff during the proposed test period. July 9th-18th: <br /> <br />Blufh./Y2oo/= A vailable-water at Farmington - loss between Farmington <br />and Bluff or Blu./f;.'Y2oo}=Animas@Farmington+San Juan above Animas- <br />[San Juan@Farmington - San Juan near Bluff] <br /> <br />Based on calculations made from streamflow measurements collected in <br />August 2000. is was estimated that a 250 cfs Navajo Dam release will <br />result in a 150 cfs flow in the San Juan River above the confluence with <br />the Animas River, <br /> <br />Results of this analysis showed that only 1 in 10 years failed to meet the <br />500 cfs minimum flow requirement at Bluff and therefore there is about a <br />90% chance that sufficient flows over 500 cfs will be available to allow <br />the test to go forward, The test will be ended if flows go below 500 cfs, <br /> <br />14 <br />