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r <br /> 0 <br /> .F <br /> i �I N Lehtinea <br /> StructuraU Civil Engi�eers <br /> 3216 Wetmore�ve. <br /> Everett, WA 98201 <br /> (206)252-2373 <br /> Feb. 5, 1998 !'"� „ ; <br /> � ,, <br /> Basis: Use SBUH/SCS Me��thod for sizing and design of storm w ter detention system <br /> with allowable peak di�CEaru�e flow rate being equal to 50% of th _"6Zne. Developed" <br /> 24 Hour peak rate, while rnaintaining 4he peak rates of both the "10 Yr. And 100 Yr. <br /> Developed" 24 Hour stor�:a events, by use of on-site storage and controlled release. � <br /> Determine the total precipation from the isographs for a <br /> � / ' ; ( �-Hr.-Storc�"= 15 Hundreds = 1.5 Inches. <br /> � "lOYr.-24 Hr.-Storm" =28 Hundreds = 2.5 Inches. <br /> "100 Yr:24 Hr. Storm" = 39 Hundreds = 3.5 Inches. <br /> Cal�ulate ti`�e "Time of Cor.centration" for both the "Unc�cveioped" and the <br /> "Developed ' site for each of the three storm events using Manning's Equation. <br /> Tc = 0.42 (n:L)°�8 <br /> PzsZ'(So)°'� <br /> Where T� = Time of Concentration in Minutes. <br /> ns = The "sheet flow" Manning"Rouglmess Coefficient" <br /> L = Length of flow of the site <br /> P. =Precipation of a "x" Year Storm <br /> So = Slope of the site in ft./ft. <br />