1605 SE EVERETT MALL WAY BOBS BURGER AND BREW 2025-07-25

Bob's Burger and Brew City of Everett, WA Stormwater Site Plan December 21,2009 I ' Table 3: Existing and Proposed Release Rates Basin Storm Event 2-year, 24-hour 10-year, 24-hour 100-year,24-hour Existing Runoff Rate 0.2506 0.5091 0.7013 Upstream Runon 0.0835 0.1437 0.1853 Proposed Release Rate ',z 0.2-CON 0.2088 0.6528 0.8866 Based on the design flows from Table 3, the flow control structure was designed ' with the following orifices. Table 4: Flow Control Structure Orifices ' Orifice Diameter(in) Elevation (ft above detention pipe lE) 2.20" 0 ' 4.25" 2.5 1" 3.5 According to the Stormshed3g file, the designed detention pipe should be 95' long and have a 48" inside diameter. As noted in the City of Everett Stormwater Management Manual there is a correction factor that must be applied to a redeveloped site based on the percent impervious. The percent impervious for the proposed site is approximately 82.5%. By using this percentage, a factor of 0.435 ' should be added to the proposed detention pipe. This will result in a detention pipe 136' long with a 48" inside diameter. The volume correction factor chart has �! been included as Figure 6 in Appendix A. ' The existing detention system will also need to be modified to allow the building and proposed improvements to be constructed onsite. The existing onsite catch 1 basin will need to be shifted southwest along the existing 54" detention pipe approximately 32' to ensure all structures do not incur lateral loads from the proposed building footing and to allow room for the proposed detention pipe ' layout. The pass through runon from the Top Food's truckwell will be rerouted through separate pipes and conveyed around the proposed detention facility. The ' portion of the existing detention pipe to be removed will be replaced by the same diameter, 54", pipe that will be installed at an angle to provide sufficient clearance from parallel pipes. The new detention pipe will be 32' long to replace the pipe that is to be demolished. This layout has been shown on the grading and drainage plan attached in Appendix A. PACLAND's proposed design will release stormwater runoff into the existing system. This will ensure the natural drainage course will be preserved. PACLAND Project#30182002 Page 6