01-14-10 Planning Comm. Agenda - Laserfiche WebLink

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Planning Commission January 7, 2010 Page Three Sheet 6 1. The storm sewer inlets near Station 9+00 should be moved west to the edge of the development or the street grades modified so that the pavement west of the inlets drains to the east. 2. A grading easement will be necessary for the grading to the west of rain garden 1 and outside of the development property. 3. Drainage swales need to be created between the lots within the drainage and utility easements to prevent water from adjacent lots discharging onto another lot outside of the easements orright-of-way. 4. The hold down details should be modified to account for the 30-foot setback. 5. Walls over four feet in height will need plans signed by a licensed engineer. Fence will need to be installed along the walls over four feet. All walls should be constructed outside of the public drainage and utility easements. 6. A gradual berm should be installed to the east of the catch basins at Station 1+70 to ensure that water runoff is collected by the storm sewer inlets and does not continue to the east off-site. Drainage Calculations 1. The drainage calculations and area maps should be expanded to include the four future proposed lots adjacent to the development that will be comprised of the combination of Outlot B with the adjacent properties. The emergency overflow for rain garden 1 should be moved to the street instead of directed towards one of the future lots. 2. Based on the proposed contours it appears that a portion of the front/side lot of Lot 5, Block 2 will discharge to the southwest. The drainage area maps should be reviewed and adjusted. 3. It appears that the proposed flow rate to the south is greater in the post- developed conditions than in the pre-conditions. The total flow rate for the post- developed conditions to the south will be reviewed against the existing rate. In other words, the combined flow from the direct discharge to the Manage B wetland to the south and the flow rate from the pond to the wetland will be compared to the existing rate. 4. For the purpose of reviewing pre versus post-development runoff rates no infiltration should be assumed for the rain gardens to ensure rate control if the infiltration practice fails. 5. The curve number for the pond area contained within the normal water level should be 100. 6. The time span covered by the HydroCAD calculations should start at 0.0 hours. 7. Notes and drainage pipes if necessary should be added to the plans and notes added to the proposed drainage area map indicating that all roof discharge will be directed to the street for Lots 1, 2, 3, and 4, Block 1 and Lot 4, Block 2. 8. The slopes noted within the time of concentrations for the proposed Subcatchments appear to be steeper on the plans then noted in the calculations. This should be reviewed and adjusted. Ltr-010710-PC 10062 Flanders Court NE, Blaine, MN 55449 -Phone: (763) 780-0450 -Fax: (763) 780-0452