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WCS Properties LLC May 17,2023 <br /> Drainage Memo Page 2 of 4 <br /> Rational method calculations are included in the Appendix. Manning's equation was used to determine a conveyance capacity <br /> of 2.52 cfs for a 12" NDS Pipe sloped @ 0.5%. Per the rational method calculations,this pipe is sufficient to convey not only the <br /> 25-year peak flow from both catchment areas combined, but also is large enough that the 100 Year peak flow is less than 10% <br /> of the pipe's overall capacity. Refer to the appendix for Manning's equation calculations. <br /> Conclusion&Recommendations <br /> Per the calculations above,we believe that substituting 12" pipe for 18" pipe would be appropriate for the two frontage storm <br /> pipes proposed by the project. <br /> Please reach out to us with any questions. <br /> Sincerely, <br /> CG Engineering <br /> Greg illen, PE,SE <br /> Principal <br /> DISCLAIMER <br /> This recommendation is the professional opinion of CG Engineering PLLC based on the information provided.This memo was prepared subject to the standard of care applicable to <br /> professional services at the time the services were provided. <br /> 250 4th Avenue South,Suite 200 <br /> Edmonds,WA 98020 <br /> ENGINEERING ph.425.778.8500 I f.425.778.5536 <br /> www.cgengineering.com <br />