Laserfiche WebLink
5.7 MINIMUM REQUIREMENT #7: FLOW CONTROL <br />Section 2.2.7 of the Volume I of the Everett Manual says that "stormwater discharges shall match developed City of <br />Everett Stormwater Management Manual discharge durations to predeveloped durations for the range of predeveloped <br />discharge rates from 50 percent of the 2-year recurrence interval peak flow up to the full 50-year peak flow. The <br />predeveloped condition to be matched shall be a forested land cover." Since the site is discharging into a combined sewer <br />system, there is an exemption that the predeveloped condition should be matched to the existing site conditions instead <br />of forested land cover. The existing site conditions consist of solely impervious surfaces. <br />Existing Condition (cfs) <br />Post developed (cfs) <br />2-Year <br />0.195 <br />0.165 <br />5-Year <br />0.238 <br />0.203 <br />10-Year <br />0.267 <br />0.228 <br />25-Year <br />0.309 <br />0.271 <br />50-Year <br />0.340 <br />0.299 <br />Given the peak flow for a 50-year storm of 0.299 conveyance should be adequate to convey this discharge. Using the <br />Manning's equation for an 8-inch diameter pipe with a minimum slope of 2% at 80% capacity we calculate a Flow of 1.8 cfs <br />which is sufficient to convey the necessary storm event. <br />Koz North Broadway <br />ngs Conveyance Calculation <br />Set units: I m l mm I tt I in <br />Pipe diameter, do B in <br />Manning roughness, n ? 012 <br />Pressure slope (possibly ? equal to pipe slope), So 2 % rise/run <br />Percent of (or ratio to) full depth (10D% or 1 if flowing full) go off, <br />Results <br />Flow. Q <br />1.8096 <br />cfs <br />Velocity, v <br />6.0445 <br />6.8141 <br />43-IM <br />17.7144 <br />fusee <br />Velocity head, hv <br />in <br />in <br />Flow area <br />Wetted perimeter <br />Hydraulic radius <br />2.4335 <br />in <br />Top width, T <br />6.4000 <br />1.42 <br />in <br />Froude number, F <br />Shear stress (tractive force). tau <br />31.8813 <br />N/m^2 <br />M The post -developed peak discharge durations match those for the existing site conditions for the range of rates from 50 <br />percent of the 2-year recurrence interval peak flow up to the 50-year peak flow. <br />5.8 MINIMUM REQUIREMENT #8: WETLAND'S PROTECTION <br />There are no wetlands onsite and the site is discharging into a new catch basin to be installed in 10th street. <br />® The requirement is not applicable to the site conditions. <br />8 ■ <br />3/07/2018 <br />Rev. 10115119 <br />