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Pamela Sheldon <br /> June 6, 1997 • <br /> Page 2 <br /> We-suggest the public works department make a preliminary investigation to determine if a curb cut <br /> will remain as the primary means to drain Eastwood Road in the future. Another option may be to <br /> install catch basins and storm.sewers which discharge to the ditch. A review of the submitted survey <br /> data indicates that it may be difficult to construct catch basins due to the low elevation of Eastwood <br /> Road and high elevation of the Highway 10 ditch. <br /> If the curb cut remains, the existing swale needs to be relocated to drain around the pond if the city <br /> wishes to maintain a direct discharge to the highway ditch. Another option is to work with the <br /> devel;fer and have the pond expanded to provide water quality improvements for both their site and <br /> the roadway. If Eastwood Road does drain into the pond,the developer's engineer must include this <br /> additional drainage area in their hydrologic calculations. <br /> Site Grading Plan <br /> Upon review of the plan, we do not have the ditch, parking lot, and pipe slopes. A quick check of the <br /> site indicates that the parking lot has a flat slope which does not provide good drainage. If a surface <br /> elevation of 910.8 is at the northern most end of the site and the pond discharge is at 908.0, the slope <br /> in the parking lot is 0.49 percent (3.8 feet/570 feet). This is a relatively flat slope and may cause <br /> drainage problems such as standing water and ice patches in the parking lot. A final grading plan <br /> should show how this site drains. <br /> Pond Grading Plan <br /> The developer provided a rough outline of the pond but did not provide final contours. Due to it's <br /> location near pedestrian traffic, a safe pond should be designed by the developer and reviewed by the <br /> City. The City needs to verify that the pond meets retention pond standards for safety and function. <br /> At a minimum the pond should include 10 to 1 side slopes in the first foot of retention volume (or <br /> be fenced), have a water depth of at least four feet, and discharge at an elevation that will be high <br /> enough to drain to the highway ditch. <br /> Hydrologic Calculations <br /> A summary of the hydrologic calculations were provided but this information contained no detailed <br /> darn We would like to review all of the hydrologic calculations, including input data, that was used <br /> to determine the highwater elevation(s) and sediment pond size. <br /> RJK/rjk/IID <br /> s:\WATIM+ ON ROCxy\wArOTYPINGWAMSZWPD <br /> S <br />