6101 ASSOCIATED BLVD BASE FILE 2017-06-05

t Short duration rain gauge records from across the United States High Flow Control +and.Canada were analyzed to determine the percent of the total The high flow control, or weir, is sized to pass the peak system annual rainfall that fell at a range of intensities. US stations' capacity minus the peak orifice flow when the water surface depths were totaled every 15 minutes or hourly and recorded in elevation is at the top of the weir.This flow control is also a 0.01-inch increments. Depths were recorded hourly with 1-mm Cippoletti type weir. resolution at Canadian stations. One trend was consistent at all sites;the vast majority of precipitation fell at low intensities The weir flow control is sized by solving for the crest length and and high intensity storms contributed relatively little to the total head in the following equation: annual depth. These intensities,along with the total drainage area and runoffQweir= Cd 'L' (h)3/2 coefficient for each specific site, are translated into flow rates using the Rational Rainfall Method. Since most sites are relatively Where: small and highly impervious,the Rational Rainfall Method is appropriate. Based on the runoff flow rates calculated for each Qweir=flow through weir,cfs(L/s) intensity,operating rates within a proposed Vortechs system are Cd = Cippoletti weir coefficient= 3.37(based on lab testing) determined. Performance efficiency curve determined from full h = available head,ft(m)(height of weir) scale laboratory tests on defined sediment PSDB is applied to L= design weir crest length,ft(m) calculate solids removal efficiency.The relative removal efficiency at each operating rate is added to produce a net annual pollutant Bypass Calculations removal efficiency estimate. In most all cases, pollutant removal goals can be met without Once a system size is established,the internal elements of the treating peak flow rates and it is most feasible to use a smaller system are designed based on information provided by the site Vortechs system configured with an external bypass. In such engineer. Flow control sizes and shapes,sump depth,oil spill cases,a bypass design is recommended by CONTECH Stormwater storage capacity,sediment storage volume and inlet and outlet Solutions for each off-line system.To calculate the bypass orientation are determined for each system. In addition, bypass capacity,first subtract the system's treatment capacity from the weir calculations are made for off-line systems. peak conveyance capacity of the collection system(minimum of Flow Control Calculations 10-year recurrence interval).The result is the flow rate that must be bypassed to avoid surcharging the Vortechs system.Then use Low Flow Control the following arrangement of the Francis formula to calculate the The low flow control, or orifice, is typically sized to submerge depth of flow over the bypass weir. the inlet pipe when the Vortechs system is operating at 20% of its treatment capacity.The orifice is typically a Cippoletti H = (Qbypass/(Cd - Q)213 shaped aperture defined by its flat crest and sides which incline outwardly at a slope of 1 horizontal to 4 vertical. Where: H = depth of flow over bypass weir crest,ft(m) Qorfice= Cd • A ' 2gh Qbypass = required bypass flow,cfs(L/s) Where: Cd = discharge coefficient= 3.3 for rectangular weir L= length of bypass weir crest,ft Qorifice= flow through orifice, cfs(L/s) Cd = orifice coefficient of discharge= 0.56(based on lab tests) The bypass weir crest elevation is then calculated to be the A= orifice flow area,ft2(m2)(calculated by orifice geometry) elevation at the top of the Cippoletti weir minus the depth of h = design head,ft(m) (equal to the inlet pipe diameter) flow. g =acceleration due to gravity(32.2-ft/s2 (9.81-M/52) Hydraulic Capacity In the event that the peak design flow from the site is exceeded, ,The minimum orifice crest length is 3-in(76-mm)and the it is important that the Vortechs system is not a constriction to minimum orifice height is 4-in (102-mm). If flow must be runoff leaving the site.Therefore, each system is designed with restricted beyond what can be provided by this size aperture, a Fluidic-Amps" HydroBrake flow control will be used.The enough hydraulic capacity to pass the 100-year flow rate. It is HydroBrake allows the minimum flow constriction to remain at important to note that at operating rates above 100-gpm/ft2(68-Lps/m2)of the swirl chamber area (peak treatment capacity), 3-in (76-mm)or greater while further reducing flow due to its captured pollutants may be lost. unique throttling action. When the system is operating at peak hydraulic capacity,water will be flowing through the gap over the top of the flow control wall as well as the orifice and the weir. 3