The process of urbanization has significant adverse effects on the volume and quality of stormwater runoff that enters our lakes and streams (Davis, 2005; Wang et al., 2001; Williamson, 1993). When natural land covers, such as grasslands and forests, are replaced with impermeable surfaces like streets and parking lots, the ability of the soil and vegetation to retain water is lost. This results in increased runoff, leading to hazardous floods, erosion of stream channels, reduced groundwater recharge, and degradation of aquatic habitats. Moreover, impervious surfaces transport various pollutants found in urban areas, including nutrients, sediment, bacteria, pesticides, and chloride. In severe cases, the pollutant levels in urban runoff make it unsafe for swimming or fishing in local waters.
To mitigate the impact of urban runoff, efforts have been made at the federal, state, and local levels. The Clean Water Act (CWA), through the National Pollutant Discharge Elimination System (NPDES) program, regulates water quality in the United States, imposing pollution limits on entities discharging into water bodies, including cities. Wisconsin, for example, issues NPDES permits through the Wisconsin Department of Natural Resources (WDNR), requiring cities to create management plans that employ best management practices (BMPs) to meet the prescribed limits. Permeable pavement is one such BMP believed to enhance water quality and reduce the consequences of urban runoff.
Permeable pavement is a porous surface typically made of open pore pavers, concrete, or asphalt, with an underlying stone reservoir. This type of pavement captures precipitation, rain, and surface runoff, storing it in the reservoir, where it slowly infiltrates the soil below or discharges through a drain tile. Permeable pavement is commonly used in parking lots, low-traffic roads, sidewalks, and driveways.
General Hydrologic benefits:
Cold-Weather Benefits:
Here are some of the concerns and questions about permeable pavement:
Durability – Will permeable pavement last as long as traditional pavement?
Upkeep and Maintenance – Permeable pavement can clog with sediment and pollutants, reducing its permeability and beneficial productivity.
Water Quality – How much pollutant reduction can be expected? Of particular interest, low reductions have been observed for nutrients (phosphorus and nitrogen). This concern has two implications:
Temperature – What temperature reductions can be expected with permeable pavement?
Residence Time – How long does the runoff need to stay in the storage layer to adequately treat the runoff?
Model Accuracy – How well can existing urban runoff models predict the water quality benefits of permeable pavement?
To address these concerns and determine the benefits of permeable pavement, a study has been designed with the following objectives:
A small portion of green space, adjacent to the overflow parking lot serving the Madison Streets Division’s East Office, in Madison, Wis., has been designated as the study location (fig. 3 and 4). The white study area shown in figure 4 is split equally into three smaller study plots, each receiving similar volumes of runoff from the adjacent parking lot. These plots will test three types of pavement: permeable pavers, permeable concrete, and permeable asphalt (fig. 5). Each plot is equipped with instrumentation to measure reductions in runoff volume (water quantity) and pollutants (water quality).
Runoff from the parking lot flows toward an existing curb cut, which is equipped with a calibrated flume. Runoff enters the flume and drains into a concrete structure that divides the runoff into three equal portions, each draining to one of the three test plots (fig. 5). The runoff either infiltrates into the permeable subsurface or exits the plot as overflow runoff. Each test plot is lined with an impermeable membrane, which captures and routes infiltrated runoff through a buried drain tile (fig. 6). Runoff that does not infiltrate into the permeable surface is captured by an overflow surface grate. The test plots are constructed to prevent cross-contamination from adjacent test plots and surrounding soils.
Both the drain tile and surface grate are routed into a monitoring facility, where the volume of infiltrated and overflow runoff is captured separately (fig. 7). The monitoring facility accurately measures all inputs and outputs of water using calibrated flumes.
Water-quality samples will be collected from seven locations:
Water Quality samples will be tested at the Wisconsin State Lab of Hygiene, a certified USGS analytical laboratory. Samples will be tested for concentrations of the following pollutants:
Nutrients
Solids
Other
Ancillary data will also be collected, including, but not limited to: precipitation, sand/salt application during winter months, runoff temperature at depth, and a record of maintenance.
This permeable pavement test site will be operated and maintained through 2018.
Davis, A.P., 2005, Green engineering principles promote low-impact development: Environmental Science and Technology, A-pages, v. 39, no. 16, p. 338A–344A.
Houle, K., Roseen, R., Ballestero, T., Briggs, J., and Houle, J., 2009, Examinations of Pervious Concrete and Porous Asphalt Pavements Performance for Stormwater Management in Northern Climates: World Environmental and Water Resources Congress 2009: p. 1–18.
Roseen, R., Ballestero, T., Houle, J., Briggs, J., and Houle, K., 2012, Water Quality and Hydrologic Performance of a Porous Asphalt Pavement as a Storm-Water Treatment Strategy in a Cold Climate: Journal of Environmental Engineering, vol. 138, no. 1, p. 81–89.
Wang, L., Lyons, J., Kanehl, P., and Bannerman, R., 2001, Impacts of urbanization on stream habitat and fish across multiple spatial scales: Environmental Management, v. 28, no. 2, p. 255–266.
Williamson, R. B., 1993, Urban runoff data book: a manual for the preliminary evaluation of urban stormwater impacts on water quality. Water Quality Centre, Ecosystems Division, National Institute of Water and Atmospheric Research
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