06-18-1997 - Laserfiche WebLink

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yr err • ..rte -.v V •ar• va. -•••••• ry.. -V r ...a.,4410141D,m .yyr Tjvvv Pamela Sheldon June 6, 1997 Page 2 We suggest the public works department make a preliminary investigation to determine if a curb cut will remain as the primary means to drain Eastwood Road in the future. Another option may be to install catch basins and storm sewers which discharge to the ditch. A review of the submitted survey data indicates that it may be difficult to construct catch basins due to the low elevation of Eastwood Road and high elevation of the Highway 10 ditch. If the curb cut remains,the existing swale needs to be relocated to drain around the pond if the city wishes to maintain a direct discharge to the highway ditch. Another option is to work with the developer and have the pond expanded to provide water quality improvements for both their site and the roadway. If Eastwood Road does drain into the pond,the developer's engineer must include this additional drainage area in their hydrologic calculations. Site Grading Plan Upon review of the plan,we do not have the ditch,parking lot,and pipe slopes. A quick check of the site indicates that the parking lot has a flat slope which does not provide good drainage.If a surface elevation of 910.8 is at the northern most end of the site and the pond discharge is at 908.0,the slope in the parking lot is 0.49 percent(3.8 feet/570 feet). This is a relatively flat slope and may cause drainage problems such as standing water and ice patches in the parking lot. A final grading plan should show how this site drains. Pond Grading Plan The developer provided a rough outline of the pond but did not provide final contours. Due to it's location near pedestrian traffic,a safe pond should be designed by the developer and reviewed by the City. The City needs to verify that the pond meets retention pond standards for safety and function. At a minimum the pond should include 10 to 1 side slopes in the first foot of retention volume(or be fenced), have a water depth of at least four feet,and discharge at an elevation that will be high enough to drain to the highway ditch. Hydrologic Calculations A summary of the hydrologic calculations were provided but this information contained no detailed data. We would lice to review all of the hydrologic calculations,including input data,that was used to determine the highwater elevation(s)and sediment pond size. RJK/rjk/JTD WATTMANOIRBCANIOCCII vNTOTITI KMAN3ZA O S