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I <br /> � however the Rational Rainfall Method can accommodate other removal efficiency or particle size <br /> target,. It can also be used ro estimate annual hytlrocarbon load redi�cGons. <br /> On�.a a System size is established, the internal elements of the Syslem will be designed based on <br /> infermation provided by the site engineec Flow contro' sizes and shapes, sump depth, spill storage <br /> capacity,sediment srorage volume and inlet and outlet orientation are detartnined for each System. In <br /> addilion, bypass weir calculations are made for oH-tine Sys!ems. <br /> I Flow Control Calculations <br /> The Orlfice <br /> IThe low=r flow control or"orifice"is typically sizcd to submerge lhe inlet pipe when the Vortechs <br /> System is opereting at 20%of its'trealment capaciry. The orifice is rypically a Cippoletti shaped <br /> aparture def ned by ils flal crest and sides which incline outwardly at a slope of 1 honzontal to J <br /> Ivertical. <br /> • Flow lhrough onfice = Q��� = C�.p.�Z�h�os <br /> I Where Cd= Orifice contraction coeHicient=0.56�based on coNTecH scom,waier sow��ona iaoorarori <br /> leslinq) <br /> A = Orifice flow area,ffZ (ulwlareC Ey CONTECH Stomiwater SoWtions techniwl staf� <br /> h = Design head, ft�equal w the inlet pipe diametr.r) <br /> � The min�mum orifice crest length is 3-inches and the minimum onfice height is 4-inches. If Oow must te <br /> restricted beyond whal can be provided by this size aperture, a Fluidic-AmpT"' hydro-brake flow control <br /> will be used. The hydro-braka allows the m!nimum flow constriction to remain at 3-inr.hes or greater <br /> Iwhile further reducing Flow due to its unique lhrottling action. <br /> The Welr <br /> � The hic,h flow rontrol or'�veir' is sized to pass the peak System capacity minus the peak orifice Ilow <br /> when t�•e water surface elevation �a at the top of the weir. This flow control is also a Cippoletti type <br /> weir. <br /> IThe weir flow conlrol is sized by solving for ihe crest length and head in the following equation: <br /> � Flow through weir = Qw�„ = C�•L•(h)�` <br /> � Where Cd= Cippoletti Wei�coefTlCienl=3.37�based on CONTECH Slortnwatar SaWtions laboratory lesting) <br /> h = Available head,fl(height ol wair) <br /> L = Design weir crest lengih, fl (wlculaeea by coNrECH Stoimwa�er solulions locnniwl stat� <br /> , Bypass Calculations <br /> In some cases, pollutant removal goals can be met w�thoul tr�atir�g peak ilow retes and it is most <br /> feasible to use a smaller Vortechs System configured with an external b�pass. In such cases,a bypass <br /> � design is recommended by CONTECH Stormwater Soluhons for each off-line System.To calcula;e the <br /> bypass capaciry,first subtract the System's treatment capac�ry from the peak conveyance capacity o� <br /> the collection system (minimum o(10 year recurrence interval). The result is the Aow rate tha!must be <br /> ! bypassed to avoid surcharging the Vortechs System. Then use the following arrangement of the <br /> Francis formula to calculate the depth o(flow over the bypass weir. <br /> . , <br /> ♦ Flow over bypass weir = N = (Qy�P,,,-lc�•Ll)- <br /> Where <br /> Cd = Discharge CoeNcient= 3.3 for rectangular weir <br /> H = Depth of flow over bypass weir crest, ft <br /> � L = Length of bypass weir crest,ft <br /> i <br /> The bypas� weir crest elevatien is then calculaled lo be the elevation at the lop of lhe ippo eth weir <br /> m�nus the depth of flow. <br /> I <br /> I <br /> I �2006 CONTECH Slormwaler Sulutions 115 <br />