03-08-1982 Council Minutes - Laserfiche WebLink

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REGULAR MEETING OF THE ORONO COUNCIL, MARCH 8 , 1982 PAGE -6- . The low point of the old Gray' s Bay Dam is 928 . 6 . GRAY ' S BAY DAM CON' T. That low point was a very small notch at the end of the Dam. The average height of the Dam was actually 929 . 0 . When the new structure was built as a fixed crest structure, the top of the Dam is now 930 . 0 feet. When the water of the lake reaches 930 feet it will merely go to the top of the Dam and flow unrestricted down to Minnehaha Creek . There is a spill-way at the side of the Dam and when the gates are open and the stop logs are removed, it actually has the ability to drain the lake down to 926 . 0 . The level that the gate is open depends on this management study. The original plan was principally during the summer months , April , May, June & July there will be no water discharge when the lake falls below 929 . 3, which is 1/10 below the ordinary high water level of the lake. Then in August they would drop it 1/10 and again in September 1/10 , October & November another 1/10 and then in December, January and , February, March they would drop it another 1/10 . The idea was that starting in August and continuing all through the year to March they were going to lower the level of the lake down to 928 . 6 so that in April when the spring thaw came there would be a low lake level and the lake then could build uP to 929. 4 rapidly to prevent downstream flooding. when the lake would build up to 929 . 3 in the spring no discharge would occur as it builds up above 929 . 3 to 929 . 6 it would discharge 50 cubic feet per second. It would discharge at that rate until it got up to 930 . 0. The figure of 250 cu. ft. per second was what was determined to be flood capacity of the creek. If it got over 250 cu. ft. per second it would flood. In the original plan this was worded as control flow at 250 cubic feet per second. After the Dam was operated for one year, the Watershed found that it had a problem with the winter time plan of letting the lake down . The problem was that they were letting water out of the lake when the lake was frozen, and the water would trickle out underneath the ice and it would run down the creek and freeze. Then more water would run out and freeze on top of that so they had a constant build up of ice. When the lake thawed in the spring there was a lot of frozen ice and the creek would flood. Last year they proposed a modification of the plan. The modification was that they would leave it at the same elevation , it would discharge below 929. 3 during April , May, June, and July, but in August they proposed droppinq it down to 928 . 6 . The City did not object to this but the City did object to it being dropped down in July.