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Goldfmch Brothers <br /> Drainage Study <br /> 1 August 27,2008 <br /> 4. SITE HYDRAULIC ANALYSIS <br /> EXISTING SITE: <br /> Total Area of the Proposed Site= 88,890 SF (2.0406 Acres) <br /> Wetland Area = 12,982 SF <br /> Buffer Area = 23,735 SF <br /> Wetland+Buffer Area= 36,717 SF (0.8429 Acres) <br /> Development Area = 52,173 (1.1977 Acres) <br /> Ll = 325' Overland Sheet Flow @ 1.25% <br /> L2 = 231' Channel Flow @ 1.75% <br /> P6-month=0.99 <br /> P2 = 1.55 <br /> P 10= 2.25 <br /> P100= 3.25 <br /> As per the Soil Survey of the Snohomish County Area,the entire site is <br /> Alderwood-urban land, complex, and 2 to 8 percent,which corresponds to <br /> a Type C soil. For calculation purposes, a Type C soil was used. Site is <br /> treated as undeveloped forest for the purpose of detention design. <br /> Site is subject to Everett development standards. Therefore, for the <br /> purposes of drainage design,the entire site is considered second growth <br /> forest and brush for drainage calculations. <br /> CN= 81 <br /> Tc=91.5Min. <br /> DEVELOPED SITE: <br /> Developed Impervious: <br /> Developed Area= 1.1977 <br /> Future Commercial Rooftop = 11,380 Sq. Ft. (0.2612 Acres) <br /> Proposed ASPH Pavement = 36,218 Sq. Ft (0.8315 Acre) <br /> Total New Impervious = 47,598 Sq. Ft. (1.0927Acres) <br /> CN=98 <br /> Tc=7.0 Min. (Assumed minimum) <br /> Developed Pervious: <br /> Landscaped Areas=0.938—0.832=0.106 Acres <br /> CN= 86 <br /> Site Percent Impervious= 0.938 /2.0406 = 5% <br /> CN=98 <br /> Detention Correction factor= 32.0% <br /> I, <br /> I <br /> 1 6 <br />