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<br />IMPACT ANALYSIS RESULTS <br /> <br />No Action Analysis <br />Since the foundation of impact determination is the future condition without implementing the <br />flow recommendations, a model run for this level of depletion was completed. In all the <br />following results, the comparison data listed as "No Action" come from this analysis. Detailed <br />model output for the 1929-1993 modeling period appear in the Modeled Output - No Action <br />Alternative at the end of this document. <br /> <br />. <br /> <br />Preferred Plan - 250/5000 Alternative <br />Water resources under the Preferred Plan are impacted two ways; first from changing the <br />historical release patterns from Navajo Dam and secondly from allowing new depletions in the <br />basin by meeting the criteria of the flow recommendations thereby reduce annual river flow <br />volumes. On the San Juan River from Navajo Dam to the confluence of the Animas River, the <br />main concern is minimum releases impacting the ability of existing diversion structures to divert <br />their water rights. The impacts to the Animas River result more directly to the ALP than from <br />changing release patterns of Navajo Dam. Impacts to the San Juan River from the Animas River <br />confluence to Lake Powell, are the result of implementing the flow recommendation operating <br />criteria, and the affects of diversions and return flows of ALP and the completions ofNIIP. <br />Modeling has shown that the flow recommendations for endangered fish could be met and that <br />existing water users and NIIP and the ALP Project would have an adequate water supply. <br /> <br />. <br /> <br />San Juan River at Archuleta Impacts <br />Potentially adverse impacts could occur to existing diversion structures in the San Juan River <br />from Navajo Dam to Farmington, New Mexico, as a result of reservoir operations that would <br />reduce minimum releases from Navajo Dam to 250 cfs. A seven day Summer Low Flow Test <br />(Test) was conducted July 9 to July 16,2001, to evaluate the effects of low summer flows on <br />various resources. The Test indicated that the water supply would not be a problem for most <br />diverters, though inadequate facilities may have contributed to some shortages. Three diversions <br />were adversely impacted during the test. (See diversion structures section in chapter 111 for more <br />detail.) Table 2 summarizes San Juan River flows measured during the Test. The minimum <br />flow was 63 cfs measured below the Hammond Diversion. Under actual conditions, flows could <br />be higher or lower than flows measured during this Test. <br /> <br />Table 3 presents the mean, minimum and maximum monthly average flow at the San Juan River <br />at Archuleta for the No Action, Preferred Plan and 500/5000 Alternative. The average annual <br />impact is a reduction in flow of about 172,000 af for the Preferred Plan. Flows are generally <br />higher than the No Action alternative during March through June and lower the rest of the time. <br />Figures 3-5 are daily plots of typical dry, average and wet years that compare the No Action and <br />Preferred Plan. The stair step nature of the hydro graphs reflect the nature of reservoir releases <br />remaining constant over certain time periods. Figure 6 is a frequency distribution of Navajo <br />Dam releases comparing the three alternatives. It shows that under the Preferred Plan, monthly <br />releases will be less than the No Action Alternative about 76% of the time. Detailed model <br />output for the Preferred Plan appears in Modeled Output - 250/5000 Alternative at the end of <br />this document. <br /> <br />00361 <br />