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e",�-�p n �.��y ��,�.�.t«.._., <br />��i I���G�L�4y 0[ �O.�BC��CQ, -/GY. ENGINEERS • SURVEYORS • PLANNEkS <br />3:d 1.fom SVicel • FdmonJ:. Ylaz�ing�an 9b0.0 • i_pbi 775.?.114 <br />October 2, 197a <br />File No. 5589A <br />ORt1 DRAIN R[TENTION CALCULATIONS <br />FOR <br />SEATA4IA FOODS C0. <br />I. Area = 63•��135) + 188.48(135) + 2(100) = 23� = 0.687 ac. <br />613.69 - 605.59 <br />2. Slope = 3�— = 2,65% from SW corner to NE corner <br />3• Site condition: Short grass pasture w/sparse trees <br />4. Exis[in9 coefficient of runoff = CeX = 0.20 <br />Using the Yrjanainen-Warren meChod to detennine Che re[en[icn volume necessary <br />Co detain 100% of a 10 year frequency sCorm: <br />Longest dis[ance from headwaters to point of dishcar9e = 306 ft. <br />Overland flow velocity = 1.15 f.p.s. - 2.G5� @ site conditions noted above-Chart 1 <br />Tiine to concentration = L/V(60) + 10 =(306)/(1.15)60 + 10 = 14.43 min. <br />Intensity = i�� = 1.53 in/hr from Everett curve for 10 year s[orm - Chart 18 <br />Qallok�able = Qexis[ing = CexilOA =(0.20)(1.53)(0.687) = 0.21 c.f.s. <br />Prorate fuCure coefficient of runoff: <br />Roof 6 concrete = 37� 86)+3�33)+75 _ 0.077 ac. (� 0.90 0.069 ac. <br />�3 , 5.�— <br />Asphal[ = 0.687-(0.077+0.108) <br />Planter area = ���•09)400+272 <br />3,� <br />= 0.502 ac. ( 0.85 0.426 ac. <br />= 0.108 ac. @ 0.20 0.022 ac. <br />0.� 0.517 ac. <br />Cfut = � 517 a�' = 0.753 <br />0.� <br />Qall. �•21 = 0.41 c.f.s./AC <br />QO - cfut A- 0.753 0. <br />T = -25 + 2�5 = -25 + 055, = 49.2 min. <br />vs = �36o7)i y ou�T _ (360.�)�.z) _ 40(0.41)(49.2) = 1584.8 fe.3/nefue. <br />T+25 <br />Vtotal = Vs(A)Cfut = (1584.8)(0.753)(0.687) = 819.8 Pt.3 <br />SiZE THE RETENTION SYSTEM <br />Using ponding and subsurface storage volume: <br />�= 3��a+ Y A B+AB) Ag = 10.8(0.3)= 1.62 ftz <br />- 3(4.5+ 4.5)(1.62 +1.62)-3(8.82) <br />AA = 18(z.5) = 4.5 fc.z <br />h1UNICIPAL ENGINEERING • Wr�TER SUPPLY •\VASTE TfiEAT�dENT • SURVEYS G CAD�STItAL EIJLIt�EERRJG <br />AIRPORT PL�PINING G DESIGN • A1AkI�lAS • rour u IHDUSTRIAL DF.vELOVtdENT • FEA5161LITY STU01[S <br />��. <br />