4.6.4 Runoff Model Representation

In the runoff modeling, similar permeable pavement designs throughout a development can be summed and represented as one large facility. For instance, walkways can be summed into one facility. Driveways with similar designs (and enforced through deed restrictions) can be modeled as a single facility. In these instances, a weighted average of the design infiltration rates for each location may be used. The averages are weighted by the size of their drainage area. The design infiltration rate for each site is the measured infiltration rate multiplied by the appropriate correction factors. A site variability correction factor should be considered for native soils below permeable pavement.

As an alternative, walks, patios, and driveways with little storage capacity in the underlying aggregate base underdrain can be entered as lawn/landscape areas in the model. Suggested modeling approaches for various permeable pavement configurations are represented in Table 4.6.3.