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<br />e <br /> <br />001627 <br /> <br />e <br /> <br />,) <br /> <br />--- . <br /> <br />(ed.), 1999){ COllcuITently, it is likely channel depth has increased, width-to-depth ratio has <br />declined, ~. ~j~ater velocities have been elevated, secondary channels have been <br />cut-off, bed matl:rial has co sened, rip . tion has encroached, and overall, <br />. unplific:ation has occurr - '1e this rocess has perhaps provided bene 15 m <br />e s 0 co ar quan quality, i resulted in an ove~ channel <br />~ The, recently observed reduction m ackwater habitats of up to SO%jgolden <br />~n, 20(3) is likely a manifestation of this continuing channel evolutio1i1f\ related <br />change in the waer temperature regime has also been observed. A modeling effort by <br />Bliesner and Lamarra (2000) found that summer water temperatures have likely been <br />depressed between the Animas River confluence and Shiprock, NM due to cool water <br />releases from Navajo Dam Suc epresslOn may e ay the time t water temperatures <br />~h egree!: (the temperature at which Colorado pikeminnow spawn (Vanicek and <br />," arner, 1969; Hamm.arl, 1981; Tyus, 1990)) in the Shiprock area by up to several weeks <br />; aJild potentially {:ould affect recruitment by reducing the growth of young pikeminnow going <br />into the winter Beason. These observed changes in physical habitat, when combined with the <br />relative stability of the fish community, give little indication of a positive response to the <br />flow recommen.dations. <br /> <br /> <br /> <br /> <br /> <br />ffi <br /> <br />Hydrologic AUeration and the SJRIP Flow Recommendations <br /> <br /> <br />The IHA/RV A :results for the San Juan River near Bluff station are surpris~at the very <br />least. Overall, 1he stream flow regime for the SJRIP period was found to be more highly <br />altered than dwring the post-Navajo Dam pegod.Jwhen each was compared to pre-Navajo <br />conditions. PeJrhaps even more importantly, the variability of most hydrologic parameters <br />was found to hE: substantiall less durin the SJRIP than the post- 0 Findings <br />sue as ese nm con ary to the Cefteepts tm6 assumptions of e SJRIP in developing and <br />implementing 1~1'e' flow recommendations based on mimicry of the natural hydrograph. <br />Perhaps such r';:sults help to explain the lack of res pons b the fish community over the <br />ast 11 years and the predominantly negative re ical ha' . <br />~,~~ <br />The IHA/RV A approach offers a somewhat new aM.-...::u..:."1...e perspective on how hydrologic ~ <br />mimicry can b: evaluated. A more traditional review of the median monthly hydrographs ~_ <br />presented in Figure 1 would lead e~te mthc~y'Conclu~ strong ~ <br />similarities betNeen the pre-Navajo and SJRIP periods, and substantial differences between ~ <br />the pre- and post-Navajo periods. However, when the intra- and inter-annual variability for I <br />each hydrologic parameter is considered, and the measure of alteration is based on the ~ <br />frequency of ol;currence within a range defined by that parameter's inherent, 1'I3.ttu:al <br />variability, th~: conclusions reached ~differ substantially. By incorporating measures of <br />central tendency within the hydrologic record with measures of dispersion, or variability, <br />the lHA/R V A approach provides insight into how we might better achieve mimicry of the <br />natural hydrograph. <br /> <br /> <br />4 <br /> <br /> <br />\-t-'~ tS ~.A.c, <br />9 <br /> <br /> <br />EOS-~ BlO/ZlO'a 99v-1 <br /> <br />-WOJ~ WdOZ:IO EO-80-l~O <br />