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<br />Year Aoril Mav June Julv AUI! SeD Oct Nov
<br />1969 2,839 7,417 6,672 3,711 392 236 1,217 1,685
<br />1970 1,159 12,366 12,277 3,805 633 1,175 1,155 2,080
<br />1971 3,664 6,835 13,115 5,226 807 908 804 1,797
<br />1972 1,485 4,459 9,062 1,422 197 513 999 2,023
<br />1973 646 8,455 12,989 .7,194 1,303 415 761 1,846
<br />1974 1,747 9,798 8,939 2,525 497 130 511 1,579
<br />1975 1,175 4,747 10,927 7,147 1,141 380 615 1,690
<br />1976 1,261 4,674 5,512 1,322 301 269 552 1,381
<br />1977 315 421 762 0 0 0 0 769
<br />1978 1,493 5,257 12,346 3,712 77 0 68 1,297
<br />1979 1,560 8,346 13,588 6,404 812 76 470 1,577
<br />1980 1,833 8,907 13,361 3,271 255 76 184 1,246
<br />1981 430 1,272 3,318 200 0 0 199 1,043
<br />1982 893 5,228 9,908 4,640 1,317 1,058 1,191 1,969
<br />1983 908 7,898 24,671 14,877 4,714 865 915 2,048
<br />1984 2,662 18,874 21,098 13,331 4,487 2,278 1,937 2,769
<br />1985 4,923 14,925 15,356 5,037 1,380 447 1,393 2,443
<br />1986 5,705 12,046 15,168 6,327 1,422 1,199 1,623 2,617
<br />1987 2,763 7,073 5,908 949 392 53 46 1,652
<br />
<br />Summarizing Table 1 for the 55 years presented, there are four times in July where the average
<br />monthly flow was below 100 cfs, 20 times in August, 36 times in September, and 18 times in
<br />October.
<br />
<br />Since the GVIC Diversion Dam becomes a barrier to fish migration at a Colorado River flow
<br />below about 12,000 cfs, the dam would be a barrier to fish passage for nearly the entire period
<br />presented above. Even without means to supplement flows going over the diversion dam, the
<br />data indicates the fish passage structure would offer a marked improvement in fish access to
<br />upstream habitat.
<br />
<br />The above flows are the Il)ean monthly flows. It is not unrealistic to anticipate that there will be
<br />periods when the flows will be lower and higher than the mean values within each month in Table
<br />1. In the interest offish recovery, it is preferable to have continual fish passage, however,
<br />intermittent passage may be sufficient. Based upon the above data it appears there may be years
<br />where passage will not be possible for several months at a time. Since the subject fish species are
<br />long-lived and have historically survived wildly fluctuating rivers, most fishery biologists do not
<br />believe fish passage is absolutely essential all year every year, Because of the long-lived nature of
<br />the subject endangered fish, reproduction is not essential every year, therefore passage is not
<br />essential every year.
<br />
<br />B-3
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