Agenda - Council - 08/24/1993 - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I MEMORANDUM DATE: August 19, 1993 Ramsey City Council City Adminiswator Ryan Schroed~ FROM: City Engineer Steve Jankowski SUBJECT: Lot 6, Block 2, Gorhams Sandy Acres At the August 10, 1993 City Council meeting, concern was raised regarding the impact on the area drainage that ffiling of the subject lot for residential home may have on the area drainage. The lot is largely a depression which is approximately 12 feet below the grade of the adjacent streets. Lacking detailed topographic information for the area, I have made a windshield survey of the area and have concluded that an area of approximately 10 acres may ultimately drain into this depression. It should be noted that the drainage system is somewhat poorly developed in the area in that some drive entrances are not provided with culverts and, consequently, some drainage within the 10 acre area may never reach the subject depressed lot. Assuming that half of the lot was retained in its present state for drainage purposes and run off coefficients consistent with subdivision-type development on sandy soil, I calculate that the remaining depression would accept an 8 to 9 inch precipitation event assuming no percolation out of the base or sides of the depression. From a practical standpoint, considerable percolation could be anticipated, particularly under a high head condition making the above storm event a conservative limit. It should also be noted that a natural wetland exists less than 300 feet from the subject lot which could be utilized as a repository for area drainage. I have reviewed these calculations with the Public Works Superintendent who had originally raised concern about the filling of this lot. It is our opinion that retaining one half of the existing area for drainage would provide a reasonable mount of storm water capacity. SJJ/kaj