3201 56TH ST SW 2023-05-23 - Laserfiche WebLink

Option I . Dispersion Design Worksheet *This BMP can only be used for roof runoff per the SWMMWW* • Roof area requiring mitigation(ft2): 665 • Minimum 50 ft flow path provided: x Yes No Dispersion systems with 25-50 ft flow path must be modeled using a continuous runoff model to confirm project meets the flow control requirements, attach modeling results to this worksheet. Dispersion is not allowed where less than 25 ft flow path can be achieved and another BMP shall be used to meet the flow control requirement. • Number of splashblock downspout dispersions: 2 and/or Downspout dispersion • trenches (Minimum of two-50 ft long downspout dispersions and one per 350 sf of roof area,is required to meet the flow control requirement using this worksheet) Downspout Dispersion areas do not overlap. One of the following must be met for the dispersion area(s), check one: The vegetated flow path consists of well-established lawn or pasture, landscaping with well-established groundcover, native vegetation with natural groundcover, or an area that meets BMP T5.13: Post-Construction Soil Quality and Depth.The groundcover is dense enough to help disperse and infiltrate flows and to prevent erosion. BMP T5.13 Post-Construction Soil Quality and Depth is being provided for dispersion areas (area to be shown on project plans) The following design criteria shall be met (check each to confirm the requirement has been met): I. Maintain a setback of at least 5 feet between any edge of the trench and any structure or property line. x 2. Setback requirements in Section 4-4.1 (3) of the DCSS have been met. x Including: • 50 feet setback from slopes greater than 15 percent and greater than 10 feet in height. 3. Maintain a vegetated flow path of at least 50 feet between the discharge point and any property line, structure, slope steeper than 15%, stream,wetland, lake, or other impervious surface. Sensitive area buffers may count toward flow path lengths. x 4. A maximum of 350 square feet of roof area may drain to each splashblock or dispersion trench. x 5. Place a splashblock or a pad of crushed rock(2 feet wide by 3 feet long by 6 inches deep) at each downspout discharge point. x City of Everett Public Works Small Project Stormwater Site Plan Report for Projects in `f the Combined Sewer Area-April 2021 13