1114.3.1.1 Storage volume.
PC § 1114.3.1.1
The storage volume of an on-site stormwater disposal system shall be measured 3 feet (610 mm) above the level of the water table. The location of the water table shall be verified at the time of the field investigation conducted in accordance with Section 1114.2. Unless otherwise approved by the New York City Department of Environmental Protection, the storage volume of the on-site stormwater disposal system shall accommodate the total stormwater volume calculated in this section. The stormwater volume shall be calculated as follows: 1. Compute the runoff rate using Equations 11-1 and 11-2.
2.Calculate the outflow rate due to infiltration, in cubic feet per second, using Equation 11-3.
3.Calculate the outflow rate, in cubic feet per second per acre, of imperviousness using Equation 11-4.
4.Calculate the duration of the design storm in minutes using Equation 11-5.
5.Calculate the maximum required retention volume using Equation 11-6. Qinf = (FAmin × isoil) / 43,200 (Equation 11-3) where: Qinf = outflow rate due to infiltration in cubic feet per second FAmin = minimum footprint or surface area of the stormwater disposal system isoil = soil infiltration rate in inches per hour Qo = CWT × i x AT (Equation 11-4) where: Qo = the average outflow rate in cubic feet per second during the rainfall event CWT = the weighted runoff coefficient for the tributary area i = the average rainfall intensity in inches per hour for the event AT = the area tributary to the detention facility in acres tV = 0.27 × (CWT × AT/QDRR)0.5 - 15 (Equation 11-5) where: tV = the duration of the storm in minutes, with a 10 year return frequency, requiring the maximum detention volume with a variable outflow CWT = the weighted runoff coefficient for the area tributary to the detention facility AT = the area tributary to the detention facility in square feet QDRR = the detention facility maximum release rate in cubic feet per second VV = (0.19 × CWT × At / (tV + 15) - 40 × QDRR) × tV (Equation 11-6) where: VV = the maximum required detention volume in cubic feet with a variable outflow CWT = the weighted runoff coefficient for the area tributary to the detention facility At = the area tributary to the detention facility in square feet tV = the duration of the storm in minutes, with a 10 year return frequency, requiring the maximum detention volume with a variable outflow QDRR = the detention facility maximum release rate in cubic feet per second
