Porous pavement system is a multi-layer system that promotes stormwater infiltration while securing structural stability. The pavement model is shown in the figure below. A typical application of porous pavement includes parking lots and roadway pavements. In porous pavement, inflow infiltrates through the pavement surface into the storage layer and then drains through lateral underdrain pipes or percolates into native soils. Infiltration rate is a function of the hydraulic characteristics of pavement system that vary widely (Drake et al., 2013). In VO single and continuous event simulations, Permeability (m/s) from pavement surface () to the storage layer is determined by users. The pavement layer is assumed not to limit infiltration, but detention capacity is determined by infiltration settings. If inflow rate (m³/s) is larger than the infiltration rate (m³/s), the ponding storage capacity is calculated based on the depth- area curve and calculated by Equation 10.25.



where Vol is cumulative ponding volume up to specified depth (m³); d is depth; A is Area at specified depth (m²); t is the last time step.

Then, the amount of water stored in the ponding storage layer is calculated using a continuity equation:


where is volume of water in a ponding layer (m³) during the time step t; is the inflow to the pavement (m³/s). is the permeability from a pavement layer to a storage layer and provided by users (m/s). is the area of porous pavement (m²). Surface runoff would be calculated if volume of ponding water () exceeds the ponding storage capacity (Vol(t)).

Continuity equations were used to account water content of the storage and native soil layers:


Where and are volume of water in a storage layer (m³) and soil moisture, respectively. , which is constant (m/s) in a single even t and using Green-Ampt Mein-Larson (GAML) equation to calculate infiltration in a continuous model. is the underdrain flow rate (m³/s) and PC is the percolation rate in the soil base to native soils (m/s).