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To: From: Date: Re: MEMORANDUM Ramsey Planning & Zoning Commission City Engineer March 3, 1987 Policy on drainage and temporary and permanent dead end streets and cul-de-sacs As requested at your February 3, 1987 Planning & Zoning Commission meeting, I have written this memorandum to explain the City's current policy on drainage and dead end streets or cul-de-sacs. I. Drainage City Code Article 170.037 C.G. states that a developer must provide a method of disposing of surface water drainage and method of conveying surface water drainage within and beyond the limits of the plat to publicly owned or controlled drainage facilities or storm sewers. In plats adjacent to publicly owned drainage facilities, pipe or drainage swales are used to convey storm water to the drainage facility. In areas with no publicly owned drainage facilities, the developer usually provides a ponding area. Sizing of the ponding area is based on the following two situations: situation No 1: This situation is based on no outlets to the ponding area other than normal percolation and groundwater flow. The required pond is based on providing storage for a 40 inch snowmelt with no percolation. The runoff is estimated to be 4 inches. Following is an example of providing ponding for 30 acres with 4 inches of runoff: 4 in. Volume of Runoff = x 30 AC = 10 Ac. Ft. 12 in/ft ASSUME DEPTH OF WATER STORAGE is equal to 4 feet. Therefore, the pond size required is equal to 10 Ac. Ft. divided by 4 feet or 2.5 acres. The Environmental Protection Ordinance states that the elevation of the lowest floor including basements shall be consistent with Stat,wide Standards and Criteria for Management of Flood Plain Areas of Minnesota or at a level at least three feet above the highest known water level for lakes, ponds and flowages. Therefore, I have recommended placing the lowest floor of any structure three feet above the highest, projected pond level.