Influence of Permeable Interlocking Concrete Paver Performance on Infiltration and Temperature in and Urban Watershed

Abstract

Urbanization is a form of land use change that typically results in an expansion of impervious surfaces and increased soil compaction. These urban-induced changes in watershed hydrology can result in stream channel erosion, degraded water quality and stream aquatic habitat, increased ambient air temperatures, and increased peak flows, all of which pose challenges to stormwater management. Recent efforts to improve stormwater treatment have included the implementation of green stormwater infrastructure (GSI), which include a range of measures that use plant or soil systems, permeable surfaces or other features to store, infiltrate, or evapotranspire stormwater and reduce flows to storm sewer systems and surface waters. Permeable Interlocking Concrete Pavers (PICP) are one type of GSI implemented in urban settings to reduce runoff through infiltration of stormwater at its source. Over the past decade, East Carolina University has been implementing GSI on their Greenville, NC East Campus, and has installed approximately 0.3 hectares (3,000 square meters) of PICPs, to reduce flooding and ponding and urban stormwater impacts to local streams. Surface infiltration rates were measured at 18 PICP, 10 forested, 21 campus lawn, and 12 fractured asphalt locations to evaluate the effectiveness of PICPs on campus. Infiltration rates between the groups were significantly different (p < 0.05). The median infiltration rate of PICP sites was 587.41 cm/h and it was estimated that peak discharge to local streams may be reduced by approximately 11.47 cubic feet per second (cfs) with current PICP installations. Regular asphalt (RA) sites were tested for infiltration where fractures in the pavement intersected, with a median infiltration rate of 3.8 cm/h; however, there were not enough data to draw conclusions on the secondary permeability of fractured asphalt in this study. Forested and campus lawn soils had median infiltration rates of 5.46 cm/h and 0.95 cm/h, respectively. A total of 93 soil cone index values (kPa) were taken at campus lawn (n = 63) and forested (n = 30) sites to determine the effect of existing surface conditions on infiltration rates. There was a significant difference between infiltration rates (p = 0.007) and maximum compaction values (p = 0.000) for forested and campus lawn sites. Surface temperatures were taken at each PICP site and RA parking lots for comparison. Recorded surface temperatures for both asphalt and PICP were lowest between 9 pm and 6 am, with the median temperature of asphalt being 1.64 °C warmer. Data collected and analyzed from this study showed that fractured asphalt and campus lawns had significantly lower infiltration rates compared to forested soils and PICP installations. Moreover, relative to PICPs, asphalt displayed elevated surface temperatures for longer periods of time that contribute to local environmental warming. The results in this study indicate that PICPs are effective in sandy soils for the management of stormwater runoff in urban settings as an alternative or addition to traditional gray infrastructure (pipes, ditches, concrete curbs, and culverts), and PICPs have the potential to minimize effects of the UHI by maintaining lower nighttime temperatures and shorter periods of peak temperatures.