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The Summer of Porous Asphalt

Pavement that absorbs water became vogue in 2012

When the storm of the century deluged west central Oregon last winter causing millions of dollars of flood damage to homes, businesses and infrastructure, one area that was conspicuously untouched was a high-profile environmental community with a unique stormwater control system.

Pringle Creek in Salem, Oregon was conceived as a low-environmental-impact community, from its building designs, landscaping and energy systems, to its stormwater control scheme, which relies on roads and parking lots made of porous asphalt pavement to filter and store stormwater and allow it to percolate back into the ground rather than add to the loads on drainage systems that flow into creeks and rivers.

The system worked well from the beginning, but no one knew for sure how it would perform in severe conditions. So it was a true "watershed" moment in time when January's epic storm flooded roads and rivers all over the Salem area, while Pringle Creek experienced nothing more than a puddle or two

The community's green stormwater system had not only protected the environment, it had saved residents from potentially thousands or millions of dollars of storm damage.

Porous Asphalt's Big Year

Pringle Creek's performance opened the curtain on a remarkable year in porous asphalt pavement's long march to acceptance among the engineers and planners who design U.S. roads and parking lots. That march climaxed in the summer construction season, when dozens of porous pavement projects, large and small, public and private, were installed all over the country.

One of the highest-profile projects being built is in New York's picturesque Adirondack Mountains. The use of porous asphalt pavement for Beach Road on the south end of Lake George has been called "one of the most important lake saving projects in the history of Lake George" by the Lake George Association.

Adding to the project's significance was the fact that Beach Road is the heaviest-travelled roadway in New York to incorporate porous asphalt pavement. The road is used by 5,800 vehicles daily.

Porous asphalt solves an environment problem for Lake George, where stormwater is the number one source of contaminants entering the lake, and Beach Road serves an area of intense development that heightened concerns for the lake's water quality.

An urban flooding solution

Downstate, in the New York City borough of Queens, porous asphalt pavement was being tapped as part of a multi-year project to solve chronic flooding problems in the Springfield Gardens area. It is a low-lying area with poor drainage which is exacerbated by impervious surfaces like roads and sidewalks which create more stormwater run-off from rains and snow melts.

Porous asphalt is part of a long term plan that includes lake draining and the creation of wetlands to relieve flooding. This application underscores porous asphalt's value in flood relief.

"Porous asphalt pavement is an important flood relief tool in places like Queens where space is at a premium," explains Mike Kvach, Executive Director for the Asphalt Pavement Alliance. "You can reduce or eliminate stormwater infrastructure such as detention basins and storm sewer outlets. On top of the cost savings, porous pavements actually improve the water quality of the outflow."

Widespread acceptance

The acceptance of porous asphalt extended all over the United States in the construction season of 2012.

The pavement was demonstrated at the National Sustainable Design Competition last spring on the National Mall in Washington, DC and was cited by Popular Mechanics magazine as one of the top "11 clever greentech concepts" in the exhibit. The demonstration was also a crowd favorite, drawing attention from hundreds of exhibit-goers from all over the U.S. and the world.

Around the country, dozens of parking lots were constructed from porous asphalt, many owned by private companies using porous asphalt’s water management characteristics to satisfy zoning requirements without sacrificing parking space. Porous asphalt parking lots are also popular with environmentally sensitive institutions, including Lock Haven University in Pennsylvania, which completed a two-year porous asphalt parking lot project this summer.

One of the most notable street projects took place in Buffalo, New York, where the city unveiled the first of seven planned residential streets to be converted to porous asphalt pavement to relieve flooding in North Buffalo.

Many benefits

Enhanced water quality and flood control are the two most popular benefits of porous asphalt pavement, but there are many others.

Because water rapidly flows through the pavement surface, porous asphalt improves skid resistance. Another benefit in the urban landscape is that porous asphalt is one of the coolest pavement choices available to engineers concerned about the urban heat island effect. Porous asphalt also requires less road salt than conventional pavements to remove snow and ice. (Sand should never be used on these pavements, since it can eventually clog the pores at the pavement surface.)

How it's made

Porous asphalt pavement consists of one or more layers of “open-graded” asphalt mix placed atop a stone reservoir of large, single-size crushed stone. The engineering term “open-graded” indicates that the stone is sized to create voids throughout the structure that allow water to quickly filter through.

Porous pavement has been around for many years – an early example built in the 1970s at Walden Pond, Massachusetts, is still functioning – but its strength and durability have been enhanced in recent years by the evolution of high-performance materials and improved engineering practices.

Contact Mike Kvach