9424 18TH AVE W 2018-01-02 MF Import

berms within the buffer. Under normal conditions, all runoff that enters the rain gardens is fully infltrated. The depth of the underdrain in rain gardens RG-3 and RG-4, unlike the other four, is too low to discharge into RG-7. Therefore, these flows disperse above the compost fiiter berms within the buffer. Northem Tier. Runoff Dispersion and Infiltration A Rey element of low-impact development is to avoid concentration of runoff. One method of achieving this is to disperse concentrated runoff as soon as possible. This gives the greatest opportunity for absorption and attenuation to take place. Dispersion of roof runoff is allowed provided that the following conditions are met: 1) A vegetated flow path of at least 60-feet is maintained between the discharge point and any downstream property line, structure, steep slope, stream or wetland. in the case of the northern lots, the length of the backyard fiow path averages roughly 20-feet, with an additional 45-feet provided beyond the bubble-up basin before the edge of Kasch Bog is reached. Similarly along the south the yards and wetland buffer provide nearly 100-feet of flow path before the bog's edge. 2) A maximum of 700 square feet of roof area may drain to each downspout. The proposed footprint of each buildin� is roughly 800 square feet, which will drain to two downspouts in the back yard. Therefore, approximateiy 400 sq.ft. of roof is provided to each downspout. 3) A splash-block or crushed-rock pad shall be placed at each downspout. This requirement is shown on the civil construction plan details. The meeting of the three requirements listed above allows the use of full dispersion credit for the roof runoff component of this project.Z Southem Tier: RunoffDispersicn and Infiltiation Lots 9-16 are treated in a manner similar to the Northern Tier. However, no French drain coliection system is provided. The Southern Tier ber�efits from the southwesterly slope of the buffer. This lets tYie yards and roof downspouts disperse and infiltrate naturally at the buffer's edge. Each of the lots has its own bubble-up basins for dispersion of footing drains at the edge of the buffer. See �OE 2005 SMMVWV Volume III, page 3-15. HEARrHSTONE LANE 9 DRAINAGE REPORT APRIL 2006