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WCS Properties LLC May 17,2023 <br /> Drainage Memo Page 3 of 4 <br /> Appendix:Rational Method and Manning's Equation Calculations <br /> Rational Method-Developed Conditions <br /> for: WCS Properties LLC Frontage Pipes <br /> Q=CaV9iA <br /> Tc= 6.00 (assumed,since all pipe flow) <br /> Area(ac) C <br /> Dense Forest 0.10 Can't 0.82 <br /> Light Forest 0.15 <br /> Pasture 0.20 <br /> Lawns 0.009 0.25 <br /> Gravel 0.80 <br /> Pavement&Roofs 0.060 0.90 <br /> Open Water 1.00 <br /> Otherl 0.00 <br /> Total Area(A)= 0.07 acres <br /> i= (Pr)(ir) Pr=total precipitation at the project site for 24-hr duration storm <br /> it unit peak rainfall intensity factor <br /> it-- (ar)(Tc)^(-br) ar,br—coefficients from Table 3.2.1.13 of KCSWDM <br /> 002= 0.56 i2= 0.838341 Qz= - <br /> (ir)io= 0.78 iio= 1.356473 Qlo= _ <br /> 0025= 0.83 i25= 2.241027 Q2 5= 0.13 <br /> (ir)ioo= 0.84 i.00= 2.954427 Qtuu= 0.17 <br /> C Rational Method By BJL Date 5/17/2023 <br /> o Chkd JpU Date 5/17/2023 <br /> ENGINEERING Developed Conditions <br /> 250 4th Ave. South scale N.T.S. sheet No. <br /> Suite 200 Job No. <br /> Edmonds,WA 98020 IWCS Properties LLC 18088.20 <br /> Figure A-I:Rational Method Calculation <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 />