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<br />e <br /> <br />001625 <br /> <br />e <br /> <br />pulse count and duration, and number of flow reversals). Again, flow augmentation ~ <br />appeared to be Il:sponsible. Parameters describing high flow characteristics were found to <br />be more highly altered during the SJRlP period than they were during the post-Navajo <br />period. April and June median flows were moderately altered, as were all Group #2 <br />maximum. flow parameters, with most values being positive, indicating these higher flows <br />were falling witl:in the RV A ranges more frequently than expected. Overall, the mean HA <br />value for the SJRIP period was 0.50, indicating moderate alteration. <br /> <br />Comparison of San Juan with Colorado and Green Rivers <br /> <br />Similar investigations using the IRA approach have been conducted in the Upper Colorado <br />River Basin (UCRB). In a case study of the Colorado and Green Rive~chter et a1 (1998) <br />identified six of the 33 IRA parameters as those most greatly affected by reselVoir <br />development an.d operation, including the one-day II18Xima, 30-day minima., dates of annual <br />maxima and minima, high pulse duration, and number of hydrograph reversals. A spatial <br />comparison of these data with those for the San Juan River near Bluff allow us to <br />evaluate the degree of hydrologic alteration observed with that for oth DC stems <br />where recovery efforts are also underway for Colorado pikeminnow and razor ack sucker. <br /> <br />f <br /> <br /> <br />Hydro ogic alte:ration on the San Juan tends to be at the low end of the range when <br />com ared with :;tations from the Colorado and Green (Table 2) ased on the average of <br />the six paramet(:J"s, e an uan or e post-Navajo peno was the least impaired of the ten <br />stations (mean HA of 0.26), while the SJRIP period had the third lowest mean HA value <br />(0.38). Regarding individual parameters, perhaps the most interesting results are for the <br />one-day maxima, where the post-Navajo period was the least impaired (HA = -0.07), while <br />the SJRlP period had the only positive value (HA = +0.59) indicating the high flow was_ <br />within the R V A range more fre uentl than expected. Overall, these resUlts indicate <br />ydro o' eration has been less severe within the San Juan River and suggest stream <br />flow modification may have layed a lesser role in the decline of the endangered species <br />than elsewhere in th DC. (> <br /> <br /> <br /> <br /> <br />DISCUSSION <br /> <br />Fish CommuJlity and Physical Habitat Trends <br /> <br />Sampling of the San Juan River fish community and physical habitat since initiation of the <br />SJRIP has been both extensive and intensive. It is perhaps safe to say that few rivers in the <br />world, ti it~,~ize, have experienced the sampling levels achieved on the San Juan. The <br />volume""df dat::. accumulated since the early 1990's is truly staggering and a tribute to those <br />dedicated to n~storing the endangered fishes in the system. <br /> <br />7 <br /> <br />EOS-~ 810/010"d 99v-1 <br /> <br />-WOJ~ Wd61:10 EO-80-l~O <br />