Four ways asphalt green alleys help with stormwater runoff

By Holly Read-Myers

Stormwater runoff is the number one cause of stream degradation in urban areas. It is also the leading cause of water pollution, because of this, scientists, engineers and city planners have been creating initiatives to decrease stormwater runoff.

The concept of permeable asphalt is not a recent idea, this concept was originally introduced in the late 1960s. It was hypothesized that porous asphalt would help promote filtration which in turn would reduce stormwater and associated flooding. The increased filtration would also assist in replenishing the water table. Beginning in the 1970s the U.S. Environmental Protection Agency (EPA) determined there was sufficient benefit to the idea of porous asphalt and to provide best management practice for stormwater runoff issue and groundwater recharge. 

In more recent times, as municipalities become more urbanized and space comes at more of a premium, cities are forced to look at underutilized land – alleys. Green alley programs were developed to transform alleys into areas that are designed and constructed using best management practices of environmentally sustainable design. Green alleys that are properly installed have been shown to reduce annual runoff by up to 80 percent.

The construction of a green alley is beneficial for many reasons, the following are four ways that replacing existing alleys with porous asphalt can improve water management.

1. Groundwater

Permeable asphalt allows water to infiltrate into the ground, this recharges the groundwater table as well as reduces runoff and improves water quality. One of the major benefits of green alleys is how it reduces the impact of stormwater on the environment. Replacing existing alleys with porous asphalt allows the stormwater to seep back into the ground rather than it adding to the load on the drainage system which eventually flows into the community’s river systems.

2. Runoff

Green alleys utilize methods to manage stormwater runoff, which in turn reduces the amount of runoff and improves the quality of the water before it enters storm sewers or streams. Less runoff reduces the need for construction and maintenance of stormwater facilities, which provides cost savings to communities in the long term.

3. Flooding

Stormwater runoff can cause dangerous flooding and the erosion of fragile ecosystems. Residents of the community can benefit from green alleys in those areas where they have been utilized have proven to benefit from a reduction in flooding damage from storms. 

4. Economics

Reduction in water runoff reduces demands on storm sewers and water management infrastructure.  The utilization of porous asphalt can reduce the need or construction and maintenance of stormwater facilities. Cost savings that communities can reap the benefits in the long term.

Take the city of Chicago for an example, Chicago has more miles of alleyways than any other city in the world. Chicago implemented a green alley program and has measured discernible improvements in the reduction of stormwater runoff. Green alley programs utilizing porous asphalt have become a proven method for communities to help protect the environment as well as improve the quality of life for their residents.

Read-Myers is the Director of Supply Chain at SWT Group in Ontario, Canada.