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December 23, 1980 <br />May 18, 1981(Revised) <br />File No. 80-208 <br />• <br />Reid, Middleton & Associates, inc. <br />Engineers • Surveyors • Plonners <br />STORM WATER RETENTION CALCULATIONS <br />FOR <br />RAM ENTERPRISES ON <br />LOT 15, BLOCK 1 BEVERLY HILLS DIV._#4 <br />EVERETT, SNOHOMISH COUNTY, WASHINGTON <br />Existing Site Conditions <br />Area = 0.344 acres <br />Slope = 6.6/200 = 3.3% in the northwest direction <br />Site Conditions: Completely covered with grass, a few trees found along the <br />north boundary. <br />Existing runiff coefficient - c = 0.15 <br />Time of concentration = Tc = L + 10 <br />V <br />Where L = longest distance travelled = 250 feet and V = 1.35 ft/sec <br />T = 250 + 10 = 13.2 minutes <br />c T-3 TU <br />Intensity = 1.6 in/hr (10-year rainfall frequency Everett Curve) Area A <br />Usi)g Q = CiA <br />Q existing = 0.15 x 1.6 x 0.344 = .0826 <br />0 allow)ble = .0826 c.f.s. <br />Using Yrjanainen - Warren method to determine the required volume necessary to <br />detain 100% of the 10-Year frequency storm, the calc. ations are as follows: <br />5 .i Q.)^ <br />'.rh Av,�nun North. Straw goo. Ftimnnrl•., Wcr••hingion 98C)go (90h) 77 <br />