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,. ■ <br /> ., , <br /> DRAINAGE CALCULATIONS <br /> GAFFNEY/JOHNSON <br />� 10505 19T" AVENUE S.E. <br /> Page 2 <br /> DEVEIAPED CONDITIONS <br /> With buffers/landscaped areas, the pervious area is 0.22 acres; <br /> CN = 86 and T� = 23.81 Minutes because lawn conditions will <br /> continue to prevail. <br /> Use a 10' x 34' concrete wall in combination with the upper 1/3 <br /> of a 6-foot diameter (60-feet long) pipe. <br /> In computer program, use Stage-Storaqe Structure <br /> 5 ��' <br /> Volume @ SC�3", .� Vault + Pipe = 0 <br /> 0� X Volume @ 564 ' � ,y- 340 + 305 = 645 <br /> I Cjdj,�0 'J" Volume @ 3.65 = 680 + 992 = 1, 172 <br /> �j'�'' v� Volume @ 566� ' � 1020 + 492 1,512 <br /> > In Discharge, use Stage-Discharge and use 16 qpm at all <br /> elevation levels. <br /> i WATER QUALITY <br /> � Use wetpond <br /> 6-Month Developed at Precipitation = 0.99 Inches <br /> Volume = 1, 940 c.f. , <br /> Use combination wet vault and pipe storage and dead storaqe in <br /> CB# <br /> Vault = 2' deep @ 10' x 34' = 680. 0 c.f. <br /> Pipe = Bottom 2/3 = 0.72 x 60 x 28.3 = 1,220.0 c.f. <br /> (ratio of 2/3 d/o vs. Area) <br /> + 2 L.F. - 36" Diameter = 14.0 c.f. <br /> + 5 V.F. = 54" Diameter Manhole @ = 79.5 c.f. <br /> 1, 993.5 c.f. <br /> GRASSLINED SWAT.R <br /> 5 Minutes = Required Residence Time <br /> Lenqth/Average Velocity = Residence Time � <br /> n = 0.24; S = 1. 0$; 1' Bottom Width; <br /> Straight Wall (one side) , 3: 1 (other side) , 100' Minimum Length <br /> At 16 gpm, V = 0.15 fps @ 100 foot <br /> Residence Time = 100/0.18 = 555 Seconds = 9.25 Minutes <br />