2017.04.17 CC Packet - Laserfiche WebLink

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Adelaide Landing Residential Development EAW, Hugo January 31, 2017 For the following reasons, it is anticipated that site development will have minimal effects on receiving water quality: Preservation and creation of approximately 56.0 acres of open space (26 percent of the site), and Temporary sediment basins will be designed, and BMPs implemented, in accordance with the General NPDES/SDS Permit for Construction Activities to protect water quality and control erosion. Based on preliminary stormwater modeling, we anticipate the development will increase the stormwater rates and volumes. However, this will be addressed with the onsite stormwater management system. As demonstrated in the tables below, the project meets the intent of the stormwater management requirements of the City of Hugo, the Rice Creek Watershed District and the State of Minnesota. Through the proposed stormwater management system, rate control of site runoff will be maintained to near or less than existing during the 2-, 10- and 100-year 24- hour critical rain events. The preliminary stormwater modeling indicates the following for rate control: Max Discharge Based Proposed 100-year on 0.1 cfs/ac (cfs) Peak Discharge (cfs) North Drainage 13.71 8.91 East Drainage 6.29 6.01 Southeast Drainage 1.42 1.33 Existing North Existing East Existing Southeast Rain Event Drainage (cfs) Drainage (cfs) Drainage (cfs) 2-Year 0.94 4.76 9.08 10-Year 5.39 18.88 24.34 100-Year 37.69 69.26 68.62 Proposed North Proposed East Proposed Southeast Rain Event Drainage (cfs) Drainage (cfs) Drainage (cfs) 2-Year 1.14* 1.06 0.54 10-Year 4.83 1.86 100-Year 8.91 6.01 0.85 1.33 *Note that the 2-year discharge rate to the north exceeds the existing by 0.2 cfs. This is utilizing 4 " orifices to limit the proposed discharge rate. Orifices less than 4" are not recommended due to plugging potential. Therefore, this minor deviation from the desired 2-year rate is unavoidable. 19