Agenda - 11-19-1985 - Laserfiche WebLink

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t • i , . 4 period from 1931 to 1970 by the Eno River Gage at Hillsborough. The modeling assumed that 40 years is a 1:. suitable statistical sample to plot operating alternatives - and see the resulting impact on the river and Lake Orange, the back-up reserve water supply. . q , $ V. FiNDINGS ,. . . . Records from the Eno River Gage at Hillsborough indicate SI that for the 40 years of record, there was some flow in the ..' river every day. Only 6 years of that 40 year record show !, periods of 7 days where the flows were less than one cfs. However, the Eno hydrology is quite fragile. The record indicates that there are extensive periods where the flow is less than 10 cfs. In fact, 19 out of the 40 years had periods of 60 days or more where the flow was less than 10 .-; cfs. This led to posing nine . hypothetical with- , , - drawal/conservation/instream flow alternatives set forth in " the table. . The first alternative (Number 1) is the present condition. Withdrawal is at a high rate, although not as high as agreements would allow (CNW, could purchase up to 2 million gallons a day) . Of the 3.50 mgd, .6 mgd is the '-: recorded amount withdrawn by OA during July and August of ,'. . 1983, and 1.3 or more was withdrawn by nilleborough for Town , customers six of the twelve months of 1983 (January, ,-. February, July, August, November, December) , and an additional 1.6 was withdrawn by Hillsborough in September for .sale to OWASA (1.3 in October) . Conservation measures are not in place and no allowance is made for maintaining a prescribed instream flow level. The likelihood of problem is set forth in columns 4 thru 9. Eighty four percent of the time Lake Orange would be in normal state (i.e. greater than or equal to 60% storage) . There would be 11 crisis periods- ', one lasting 116 days; another 79, another 68 and 8 lasting 60 days or less. Storage would be drawn to almost dry or dead pool for many of those periods—measured at 4.51 cfs (cubic feet per second)--days, or .25 mg of net storage left or 0.1 usable day of storage remaining (2.4 hours) . Alte. . i e --, assumes a rate of withdrawal where water-use restrictions are in place during a drought yet no conservation or instream flow requirements apply. Under this senario Lake Orange would be in normal state 91.2 percent of the time. There would likely be 2 periods of crisis where Lake Orange would be at 20% or less of supply lasting 72 and 5 days in duration. Least storage as days left in such case would be 4.99 cfs-days or .55 mg net storage left and .3 remaining 1 I days (7.2 hours) for which storage could be relied upon. , `. aternetive 3 assumes that withdrawals would be limited to the level of Lake Orange's full safe yield. Also it is assumed that conservation measures would be adopted by all jurisdictions utiliiing the water and that the jurisdictions would agree to the State's recommendation to release and pass •J. through 1.1 mgd (1.7 cfs) for instream flow below Lake Ben Johnson. This would result in Lake Orange being in normal ..e. state 71.0% of the time. There would be 19 crisis periods ;.,