Agenda Packets - 1987/01/05 - Laserfiche WebLink

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[®en►a��r►es_ _ SUBURBAN ENEINEERING, ►NE. QuII, Municipal & Environmental Engineering 0 Land surveying 0 Und Planning 0 Soli Testing December 22, 1986 Mr. Steven Thatcher City of Mounds View Public Works 2401 Highway 10 Mounds View, MN 55112 Re: Red Oak Park Dear Mr. Thatcher: OrC1S56 fllyOF ED UUryps VIEW Several questions were raised at our meeting on December 19, as to whether the stormwater detention system for the Red Oak site would operate properly during a severe storm. The questions stem from the fact .that the existing storm sewer system downstream la undersized, causing water to back-up into the storm sewer network to undetermined elevations. The concern is that during a severe storm, water would back-up into the depressed area designated for the detention of stormwater from the Red Oak site. This would use up some of its storage capacity, forcing some runoff from the site to spill over into an existing low area to the north of the Red Oak site. We feel that the probability of this situation occuring is highly unlikely. However, as a simple and workable solution to this possible problem we propose the following: 1. Provide a one-way check valve inside the proposed control structure manhole to prevent stormwater from backing up into the Red Oak detention area. 2. Demonstrate that there will he no negative impact on the low area to the north of the site in the event of the 100 yr. - 24 hour rainfall. (See the attached calculation summary). 3. Provide a positive over flow route for stormwater from the existing low area to further protect residents from the danger of flooding.1, This will be accomplished by: A. Adjusting existing manhole to R.E. - 909.5 and providing a beehive type catch basin. (See plan sheet) B. Providing a drainage swale from the low area to this catch basin. 6R75 Highway 65 N.E. P.O. Box 32308 .Mlnneapolls, A1N 55432 (612) 571.6066 12203 Nicollet Ave. So. Burnsville, MN 55337 (612) 890.6510