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�. % <br /> � Trepanier Ensinee� <br /> Pro%ssional Civil Engineering � T� <br /> O� <br /> � I <br /> DRAINAGE CALCULATIONS <br /> GAFFNEYIJOHN$ON i <br /> 10505 19� AVENUE S.E. �� <br /> Job 97-060 � <br /> A�NAL <br /> February 13, 1998 <br /> EXPIRES 8/2/�8 � <br /> GENERAL CHARACTERISTICS <br /> The site has a slope of about 2.5$, sloping down from east to <br /> west. The site previously had two buildings and associated <br /> driveways and impervious areas. <br /> PLANNED CONDITIONS � <br /> The site drainage is being designed for the ultimate development � <br /> of the site into commercial buildiags. Th.e drainage features <br /> include a biofiltration swale, storni pump for the 2-year storm <br /> event, a wetpond, underground pipe storage and ara overflow for <br /> the greater than 2-year storm event. <br /> CAI.CULATIONS <br /> The stormwater pump will be designed to carry � of the existing <br /> 2-year storm event and the water quality features will be <br /> designed using the 6-month storm event. <br /> The calculations will be completed using WaterWorks - SBUH Storm <br /> Methodology. <br /> EXISTING CONDITIONS <br /> Area = 0.85 Acres <br /> Precipitation = 1. 6 Inches <br /> Pervious Area = 0.70 Acres @ CN 86 <br /> Impervious Area = 0.15 Acres @ CN 98 <br /> T�; = Sheetflow @ 220' ; ns = 0.15; S = 2.5$ <br /> = 23.81 Minutes ' <br /> QZyp = 0. 09 cfs; Therefore use 0.045 cfs or 20 �gpm as allowable I <br /> Pump Selected = Little Giant - 1/6 h.p. I <br /> Submersible utility pump delivering 16 gpm @ 10' of. head <br /> Use 16 gpni for all conditions on live storage calculations ' <br /> � <br /> 1420 Hewitt • Ever�tt,Washinptan 98201 • Everett (208)259-5558 • FAX(206)259-5558 <br />