Urban Runoff Mitigation by a Permeable Pavement System over Impermeable Soils

The respective runoff from a 200-m(2) permeable pavement test site and an adjacent 850-m(2) conventional asphalt road catchment in Auckland, New Zealand, was monitored concurrently between 2006 and 2008. Despite installation over relatively impermeable subgrade soils, and on an atypically high slope (6.0-7.4%) and active roadway, the overall hydrologic performance of the permeable pavement was exceptional. Measured discharge from the permeable pavement underdrain demonstrated peak flow (81 storms) comparable to or below modeled predevelopment conditions for most storms, regardless of antecedent conditions, including a 10-year, 24-h annual recurrence interval event. For large events (5% exceedance), underdrain discharge volume was comparable to predevelopment conditions, but it was substantially less than asphalt runoff for all events up to approximately 70% exceedance. The distributions of peak flow and volume were statistically different between the asphalt catchment runoff and the permeable pavement underdrain discharge (0.05 level of significance). Runoff coefficients ranged from 0.29-0.67 for underdrain discharge (10th-90th percentile events), and from 0.41-0.74 when permeable pavement comprises about one-half of an otherwise impervious catchment. Underdrain lag time and hydrograph duration were reminiscent of a vegetated area. Spearman correlation indicated influences of rainfall depth, intensity, and duration on runoff parameters from both catchments, while antecedent moisture condition was correlated to underdrain discharge lag time. Surface infiltration measurement at four permeable pavement sites revealed that surrounding land uses likely have more influence on pavement clogging than does traffic load. Permeable pavements should be given strong consideration as an low impact development source control, and can also mitigate conventional large design storm flows, but care must be taken during installation to ensure proper function.