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<br />(only 24 cfs below the recommended level of.1,6~.d cfs) in January 1975
<br />(Biological Assessment, Appendix B, Attachment 6, page 1 of 8, top table).
<br />The Project's largest calculated make-up fl s also do not represent the most
<br />significant impacts. This approach does- n take into account the degree to
<br />which baseline flows are already belo rec mmended levels. For the year 2045
<br />level of development, a arges make-up ows occu May 1978 and May 1991
<br />and are equivalent to the Project's flow reductions in these months
<br />(Biological Assessment, Appendix B, Attachment E.6). The Project's flaw ~~
<br />reduction in May 1978 reduces the baseline flow by 64.1 cfs (1.3 percent) from
<br />4,937 cfs to 4,873 cfs. The Project's flow reduction in May 1991 reduces the ~?~
<br />baseline flow by 55.5 cfs (1.2 percent) from 4,538 cfs to 4,482 cfs. '~,,~ ;~~ ~~
<br />~~~ ~
<br />The most significant flow reduction impacts li ly occur when t se in ,0,~ '
<br />flows are already well below recommended leve s, when t Oect c s ~.~(~
<br />relatively large flow reductions, and whe the a Water' aversions
<br />are being replaced by replacement reservoi eleases. The 1 Best impacts , ~/yo~
<br />representing these conditions can be id ified by calcul ing make-up flows ••
<br />as a percentage of baseline flows (Biological Assessme ,Appendix B, ~1~~`"`~
<br />Attachment E.6, column 14). Using this ap the year 2045 level of ~,,.~'"P~
<br />development, the largest impact occurs i S 19 The baseline flow ~.,~`
<br />in this month was computed to be zero while~'e ro0ec s make-up flow is ,~`~
<br />10.3 cfs. Although flows below .zero cfs are obviously impossible, the ~+~~,
<br />post-Project flow in the 15-mile reach was calculated to be -10 cfs in this ~s ~
<br />month. The hydrological model computed a negative flow because of the ,,. ~~;'
<br />inaccuracy of historic flow del in uts and of assumptions ~'
<br />upon w is t e mo el was based. For the year 2045 level of development, the
<br />four largest impacts identified using this approach are:
<br />~i~fi Month Baseline Flow Post-Pro.iect Flow % Reduction
<br />/~U,~~y~,v SEP 79 0 -10 100 ~ ~ ~ ~
<br />$ ~`" AUG 76 175 148 15.1
<br />APR 77 104 89 14.7
<br />`~ SEP 85 251 215 14.3
<br />~~
<br />Of the three months August 1976, April 1917, and September 1985, although the
<br />`~ ~i~ ~°~highest percentage reduction occurs in August 1976, the largest impact likely
<br />occurs in April 1977 because the baseline flow in this month is substantially
<br />`~.~; less than in the other two months yet the percentage reduction of flow in this S
<br />,~ a ` month is similar to that of the other two months. Also, the large impact in ~aa.; f ~
<br />C'_~ April 1977 is particularly evident when one considers that the recommended -(v~
<br />%c ,a flow for this month (1,860 cfs) is higher than for the other two months yo*''~•~
<br />(1,240 cfs and 1,630 cfs). However, for the entire period of record, the ~~~'•~''~•
<br />` `` maximum make-up flows calculated as a percentage of baseline flows generally
<br />;,<<~ r~ '~. occur in the summer months of August, September, and October.
<br />One could argue that the most significant impacts occur when the post-Project
<br />`' flow is the lowest regardless of the percentage flow reduction caused by the
<br />Project. For the year 2045 level of development, this approach simply reveals
<br />that, as expected, the lowest monthly post-Project flow for each year in the
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