Agenda - Council - 09/14/1993 - Laserfiche WebLink

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I I I i I I I I MEMORANDUM DATE: August 19, 1993 Ramsey City Council City Administrator Ryan Seh.rtw~m- FROM: C'iry Engintcr Steve 3ankowsJd SUBIECT: Lot 6, Block 2, Gorharns Sandy Acres At the August 10, 1993 City Council meeting, concern was raised regarding the impact on the drainage that filling of the subject tot for residential home rrmy have on the ama drainage, The lot is largely a depression which is approxi,mamly I2 feet below the grade of the adjacent streets. Lacking detailed topographic information for the are2.., 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 bo noted that the drainage system is somewhat poorly developed in the area in that some dr/vt enn'anees are not provided with culverts and, consequently, some drainage within thc 10 acre area may never r~ch thc 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 m~.-ing the above storm event a conservative limit. It should also ~ noted that a natural wetland exists less than 300 feet from the subject lot which could be urilize, d 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 .c. apaciB'. SZJ/kaj