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T 206.52Seattle,Washington <br /> 1 i = , , www.p2cla2.951nd.com0 <br /> TURNING VISIONS INTO REALITY <br /> F. Conveyance Analysis <br /> As required by Volume I, Chapter 3.2.6.G. of the Manual an analysis of the proposed <br /> conveyance system pipes has been performed. Per Volume I, Chapter 5 of the Manual the <br /> Rational Method was used to determine design flows. See Appendix B — Conveyance <br /> rCalculations for more information and the results of the calculations. <br /> On-site stormwater conveyance has been calculated through gravity flow analysis of the <br /> piping network. Based on a 25-year storm event, peak runoff was routed through the <br /> system and determined to be adequate. Uniform Flow Analysis utilizing Manning's <br /> equation was employed with a Manning's "n" value of 0.012. <br /> ii Q_ 1.49xAxR7xS12 <br /> Manning's Equation: n <br /> With: Q = Flow (cfs) <br /> n = Manning's Roughness Coefficient (0.012) <br /> IA = Flow Area (sf) <br /> R = Hydraulic Radius = Area/Wetted Perimeter (If) <br /> S = Slope of the pipe (ft/ft) <br /> Calculation of an example onsite stormwater pipe: <br /> Q = Flow (cfs) — to be determined <br /> n = 0.012 <br /> _ A = 0.7707/(12"/12) = 0.7707 SF (Appendix 16.A.Civil Engineering Reference Manual) <br /> R = 0.2864/ (12"/12) = 0.2864 LF (Appendix 16.A.Civil Engineering Reference Manual) <br /> S = 0.005 <br /> Q= 1.49/0.012 * 0.7707 * 0.2864(2'3) * 0.005(1/2> = 2.94 CFS <br /> Additional information regarding the conveyance calculations summary can be found in <br /> Appendix B. <br /> '1 Large Storm Event/Overflow Condition <br /> The proposed stormwater conveyance system for this project has been designed to address <br /> I storm events in accordance with the design criteria described above. During events larger <br /> than the design criteria or as a result of clogged/blocked pipes there may be overflows <br /> within the system. The low rim elevation in the system is the catch basin at the southwest <br /> corner of the parking lot. In the event the 21" outlet pipe from the flow control structure is <br /> blocked, stormwater would overtop this catch basin and flow onto the neighboring <br /> properties to the south and west. <br /> —Everett Mall Plaza Parcel III Retail Expansion Stormwater Site Plan Page 24 <br /> I <br />