10/13/2021 P&Z Packet - Laserfiche WebLink

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The following drainage &utility easements are r-equir-e shown on the Preliminary Plat and are required on the Final Plat: oo CSAH 54/20t'Avenue=20 ft oo Side Lot Lines = 10 ft oo Amelia Lake=Delineated Wetland+ 10 ft or oo Amelia Lake=Floodplain 100 yr. Elevation+ 10 ft (whichever is greater) oo Wetlands =Delineated boundary+ 10 ft oo Stormwater Facilities =HWL+ 10 ft Storm Water Management and Erosion and Sediment Control Per City Code Section 1011.011, a stormwater management plan is required for all proposed land development activity if the site is within the 100-year floodplain or within 1,000 feet of a public water. Lake Amelia Woods is within the floodplain and shoreland district. Per the Storm Water Management Plan prepared by Civil Methods, Inc. dated June 18, 2020, the project is expected to disturb approximately 5 acres and add 2.22 acres of new impervious area to the site. Runoff from the site enters Lake Amelia at 4 general locations. Drainage patterns will be maintained from existing to proposed conditions. No other properties will be impacted by runoff from the project. Drainage from the proposed impervious area will be conveyed to stormwater treatment basins and ultimately to Lake Amelia as it does under existing conditions. oo Water Quality Treatment Volume The City requires treatment of runoff based on 1.1" over the new impervious surface. Eight Six 6 biofiltration basins with native vegetation are proposed for water quality treatment. Infiltration is not feasible due to presence of clay and the site is within the Drinking Water Supply Management Area(DWSMA). oo Runoff Rate Control The City requires no increase in peak flow rates for the 2, 10 and 100 yr. frequency events. With the proposed basins, runoff rates are held or reduced for the overall project. oo Water Quality Control Water quality control is being provided through a series of biofiltration basins (raingardens). A minimum 75 foot wide vegetated wetland buffer along Wetland A(lake) equivalent to the shore impact zone area shall be required is provided as a stormwater management best management practice (BMP)to minimize runoff pollutants from entering the lake. This is supported by City Code Section I IO2.07(1)(c)3c. 6