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Preliminary Stormwater Site Plan Everett, WA <br /> I <br /> Detention Volume Calculations: <br /> ' Per the Everett Stormwater Management Manual figure 1-3.1 Volume Correction Factor for <br /> g g <br /> ' Streambank Erosion Control BMPs, and the assumed 80 percent impervious coverage, a <br /> volume correction factor of 1.43 shall be applied to detention facility. <br /> ' Correction Factor = 1 .43 <br /> Design Volume = 146,858 cf <br /> ' Required detention volume = 146,858 x 1 .43 =210,007 cf <br /> Provided detention volume = 237,057 cf (volume calculated from design contours) <br /> Water Quality <br /> A wetpond has been utilized to provide water quality. The wetpond has a permanent pool <br /> volume equal to the runoff generated by the 6-month, 24-hour storm using the developed <br /> conditions. The wetpond shall be constructed to the standards set forth in section 3-3.5.1 <br /> in the Everett Stormwater Management Manual. Since there are two discharge locations, <br /> two wetland treatment cells were designed so that one is located before each discharge. <br /> Since the Edgewater Creek discharge is a considerably greater flow, it has a significantly <br /> ' larger wetland treatment cell. <br /> Required Treatment volume = 1.8189 Acre-feet (see page 11) = 79,231 cf <br /> ' Treatment volume provided = 79,300 cf <br /> Volume provided in open water cell = 67,250 CF (84.8%) <br /> Volume provided in wetland treatment cell 1 = 1,950 CF <br /> ' Volume provided in wetland treatment cell 2 = 10,100 CF (15.2% total) <br /> Required Length to Width Ratio <br /> As shown on Exhibit A the pond meets the requirement of a minimum 3:1 length to width <br /> ratio from the pond inlet to each of the pond control structures. <br /> ' Control structure #1 : 206' : 65' (3.2 : 1) <br /> Control structure #2: 180' : 58' (3.1 :1) <br /> 1 <br /> PACLAND Job # 50175001 Page 14 <br />