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'Memo n Bonestroo -=- Rosene ~ Anderlik & '\J' Assodates Engineers & Architects Project Name: Plan Review for Deer Pass Client: City of Centerville To: Tom Peterson File No: 616-99-104 From: Jeff McDowell Date: April 14, 1999 Re: Stormwater plan review for Deer Pass Development Remarks: As you requested, I reviewed the Deer Pass development plans for compliance with the City " of Centerville's stormwater standards. Two drainage features do not meet the City's freeboard requirement. The City should request the developer comply with the freeboard requirements prior to approving the development. The plan set reviewed was prepared by Metro Land Surveying and Engineering and was dated 3-29-99. Stormwater Analysis Our stormwater analysis consisted of running the 1 DO-year storm event using Hydrocad and comparing the pre-development runoff (16.86 cfs) with the post-development runoff (6.77 cfs). The plan meets the City's requirement of post-development runoff being less than pre-development runoff. We also determined the 1 DO-year High Water Levels in each of the seven proposed backyard pond/depressions. The following pond/depressions do not meet the City's minimum freeboard requirement of 2.0 feet: 1. The proposed stormwater pond in lots 3, 4, and 5 has only 1.9 feet of freeboard. Our model estimates the 1 DO-year HWL will be 909.1. Lots 3, 4, and 5 have walk out elevations at 911.0. Please raise lots 3, 4, and 5 to a minimum elevation of 911.1 2. The proposed depression in lots 6,7, and 8 has only 0.7 feet of freeboard. Our model estimates the 1 DO-year HWL will be 908.8. Lots 6 and 7 have walk out elevations of 909.5. Please raise lots 6 and 7 to a minimum elevation of 910.8. Weir Detail To improve the amount of flow occurring through the course aggregate, we recommend providing a minimum depth of 12" of course aggregate between the lowest treated plank and the geotextile fabric and compacted backfill. Bonestroo, Rosene, AnderJik and Associates