Agenda Packets - 1987/01/05 - Laserfiche WebLink

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ITEM 8 MEMO TO: Clerk -Administrator and City Council FROM: Director of Public Works/Community Development DATE: December 31, 1986 SUBJECT: RED OAK PARK SUBDIVISION Attached please find the following: 1. Letter from Suburban Engineering dated December 22, 1986. 2. Storm water calculation dated December 22, 1986. 3. Proposed Development Agceement No. 86-78, Exhibit 2A. Existing run-off from the Red Oak Park site flows over land into property with the address of 8180 Eastwood Road. The existing run-off from the Red Oak site ponds in the back yard of this property and seeps into the ground. The calculations dated December 22, 1986, by Suburban Engineering, Inc. are based on the premise that the amount of water leaving the site after development cannot exceed the amount of water leaving the site prior to development. The calculations indicate that the amount of water leaving the site prior to development is 0.33 acre-feet. The calculations also indicate that the amount of water leaving the site after the pond is constructed is 0.28 acre-feet (0.65 acre-feet minus 0.37 acre- feet). (. In addition, the developer is proposing to install a one-way check valve inside the proposed control structure to prevent storm water from backing up into their Red Oak pond from the existing storm sewer. The developer has also verbally agreed to install a 4 foot diameter, 4 foot deep eccentric manhole, with steps as the control structure so that people can work on the check valve when necessary. Check valves have a tendency to clog or stick in the open or closed position from time to time. Page 2 of the December 22, 1986, letter from Suburban Engineering indicates that the water level in the back yard of 8180 Eastwood Road can reach the elevation of 910.17 without flooding the basement of said house. The developer, at my request, is proving an emergency overflow route for storm water from the existing low area to further protect the residents at 8180 Eastwood Road. This is necessary because in the unlikely occurrence of a 1 in 500 year storm, there should be a place for water to flow. The developer is proposing to do this by adjusting the existing manhole located near the north property line of the Red Oak Park subdivision to a rim elevation of 909.5 and provide a drainage swale from the existing low area to this catch basin. To construct the swale on the property at 8180 Eastwood Road, approval from the property owner is necessary.