1114.3.1 Runoff rate.
PC § 1114.3.1
The runoff rate shall be calculated using the rational method, Equation 11-1. The calculation shall incorporate the total site area with a rainfall intensity value of I = 5.95 inches per hour. The weighted runoff coefficient shall be calculated using Equation 11-2 and shall incorporate the different combinations of surfaces using the C values listed below. Q = Cw × I × A (Equation 11-1) where: Q = developed flow, cubic feet per second Cw = weighted runoff coefficient I = the rainfall intensity value, 5.95 in/hr A = the total site area, acres (ac) Cw = (1/A) Σ (Ak × Ck) (Equation 11-2) where: Cw = weighted runoff coefficient A = The total site area, acres (ac) Ak = The area of each surface coverage type, acres (ac) Ck = The runoff coefficient associated with each surface coverage type The following C-values shall be used for calculating a site's weighted runoff coefficient: 0.95 = roof/concrete 0.85 = asphalt 0.7 = porous asphalt/concrete or permeable pavers 0.7 = green roof with four or more inches of growing media 0.65 = gravel parking lot 0.3 = undeveloped areas 0.2 = grass areas 0.2 = rain gardens, vegetated swales and other surface green infrastructure practices (Am. L.L. 2023/077, 6/11/2023, eff. 6/11/2023) Editor's note: For related unconsolidated provisions, see Appendix A at L.L. 2023/077.
