Green Alleys: Small Spaces with Environmental Impact

April showers bring May flowers; sometimes, in the municipalities Kapur serves, they also bring renewed interest in transforming alleys into eco-friendly corridors.

As communities seek creative ways to build resilience into aging infrastructure, green alleys are proving to be a possible piece of the sustainability puzzle. Kapur has been at the forefront of helping reshape the way cities think about sustainability, with one of its most notable efforts incorporating green infrastructure into alley reconstructions as part of a program in Shorewood.

What exactly makes a green alley ‘green’? We asked one of our municipal department project managers, Brad Jors, PE, who helped design the undertaking, to break it down.

‍

How do green alleys compare to traditional alleyways?

Green alleys provide stormwater treatment, while traditional alleys do not. Traditional alleys direct surface runoff to catch basins and direct entry into the storm sewer system. Green alleys allow surface runoff to infiltrate through the pavement structure, filtering it as drains into the underlying stone storage layers, releasing it more slowly into the storm sewer system, or infiltrating into the natural soil.

‍

How do green alleys help manage stormwater?

The stone base material under the pavement/pavers is an open-graded drainage stone. It acts as a filter for stormwater as it drains through it, filtering out pollutants like oil, heavy metals, and sediment. The stone has a lot of open space inside—about 40%—which lets it hold rainwater. Water can then slowly soak into the ground or be carried away by a drainage system, eliminating or reducing the flow rate of stormwater into the downstream storm sewer system.

‍

How do green alleys benefit the environment?

Green alleys treat stormwater before it enters the storm sewer system and waterways. Some systems enable water to seep into the ground, which also helps replenish the underground water levels.

‍

Who determines when green alleys are utilized?

Green alleys are an option when replacing any traditional paved alley, but typically, the municipality will be the one to initiate exploring their implementation.‍

‍

Do we attempt to make every alley green?

No. For several reasons, most alleys are still constructed with traditional pavement.  

The initial cost of a green alley is higher than a traditional alley. The additional costs and maintenance requirements may not be justified if stormwater benefits are not a driving factor.

Not to mention, regular cleaning is critical for the functionality of a green alley. If it is not properly cleaned, it will get plugged and not function as intended. Many municipalities do not have the equipment (i.e., vacuum trucks) needed properly maintain the systems.

Conflicts with existing infrastructure, particularly underground utilities, may also occur. If shallow utilities (gas, electric, fiber) are present, the stone storage layer may not be deep enough.

Additionally, permeable pavement systems are typically not best suited for heavy traffic or large vehicle loads. This is why alleys, parking lanes, and pedestrian areas are good areas to target.  

‍

What materials are used to create green alleys, and how are they chosen?

Green alleys are typically made with materials like permeable pavers or pervious asphalt. Permeable paver systems use concrete pavers with joints filled with chip stone, allowing stormwater to pass through the gaps and soak into the ground. Pervious asphalt, on the other hand, is made with a special mix that’s more porous than traditional asphalt, letting water filter directly through the surface.

The choice between these materials often depends on the client’s specific needs—factors like budget, appearance, expected traffic(pedestrian or vehicle), and familiarity with certain products. Many manufacturers offer a variety of paver styles, colors, and patterns. Some even provide pre-assembled paver sections, making installation easier. It’s also important to choose a product that’s readily available from a local supplier to avoid delays.

‍

 What are the challenges of implementing green alleys?

The largest challenge is the high initial costs and the additional requirements for ongoing maintenance.  

Installation can be more challenging than traditional pavement, and fewer contractors may have the necessary experience. If done incorrectly, it can lead to premature failure or poor drainage.

For permeable pavers, users may not like the feel of driving or walking on the system.  

Green alleys are just one part of the broader conversation around sustainable urban design. With the right planning and engineering, these upgrades can deliver long-term benefits for both people and the planet. Here at Kapur, we remain committed to exploring how engineering can help our communities adapt, grow, and thrive.