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Dutch Bros. Coffee Stormwater Site Plan Everett, Washington <br /> utilizing Manning's equation, shown below, was employed with a Manning's Roughness <br /> Coefficient (n) of 0.012. Conveyance calculations are provided in Appendix B. <br /> Manning's equation - Q=1•49n xAxRZi3xS'12 <br /> With: Q = Flow (CFS) <br /> n = Manning's Roughness Coefficient (0.012) <br /> A = Flow Area (SF) <br /> R = Hydraulic Radius = Area /Wetted Perimeter (LF) <br /> S = Slope of the pipe (ft/ft) <br /> The site discharges to the City combined sewer via an 8" dia. PVC pipe, which has a flow capacity <br /> up to 0.997 cfs. From Table 7, the developed site has a restricted flow rate of 0.122 cfs for the <br /> 100-year storm event; therefore, the conveyance system can more than adequately handle both <br /> the 25-year and 100-year events. <br /> Spill Control <br /> Because this site discharges to the City combined sewer system, oil and spill control is not <br /> necessary. However, within the flow control structure, there is sufficient depth below the invert <br /> elevation of the pipe inlet to detain oil and other floatable pollutants before they discharge via <br /> the flow control restrictor and enter the City system. <br /> 100-Year Flood/Overflow Condition <br /> Review of the current FEMA FIRM maps indicates that the project site lies within the Zone X, <br /> which is determined to be outside of the 100-year flood plain. The stormwater system for this <br /> project has been designed to address the storm events in accordance with design criteria <br /> described previously. While each pond has provided an additional 0.5' of freeboard, in the <br /> event of a major storm event that exceeds the 100-year, water would likely flow out of the pond <br /> via the curb scuppers and travel to the lower points of the site. In this case, water would flow up <br /> the curb ramp adjacent to the building and sheet flow around the building, towards Broadway. <br /> Interlocking pavers have been proposed for the area east of the building, which can help reduce <br /> the amount of surface runoff as water would seep through the joints before flowing onto the <br /> public sidewalk and into the City system in Broadway. <br /> Section 9 - Operations and Maintenance Manual <br /> The owner or operator of the project shall be responsible for maintaining the stormwater <br /> facilities in accordance with local requirements. Proper maintenance is important for adequate <br /> functioning of the stormwater facilities. The following maintenance program is recommended <br /> for this project: <br /> nnr-i nnin n 1s <br />