Chicago installed tree tubs and permeable pavement at Navy Pier; it helps capture stormwater while reducing annual pollution by 3 lb of phosphorus, 47 lb of nitrogen and 2 tons of sedimentSynopsisChicago's Navy Pier showcases an impressive green infrastructure designed for efficient stormwater management. Featuring seventy-seven tree tubs and permeable pavement, the system effectively captures and filters rainwater runoff, preventing pollutants from contaminating local waterways year after year. Not only do the trees enhance the shore with shade, but they also significantly improve air quality while managing water. This innovative initiative stands as a prime example of urban water management solutions.The project is estimated to prevent about 2 tons of sediment, 47 pounds of nitrogen and 3 pounds of phosphorus from entering waterways every year.Picture credit: navypier.orgChicago’s Navy Pier is one of the city’s major tourist destinations, known for its Ferris wheel, restaurants and views of Lake Michigan. The 3,300-foot-long pier and its facilities cover approximately 50 acres and feature a 45-meter-tall Ferris wheel, the Chicago Children’s Museum, Chicago Shakespeare Theater, shops, restaurants and an exhibition hall. But beneath and around the busy tourist attraction lies an unusual system designed to deal with a much less glamorous problem: stormwater.To address the issue, the city has incorporated green infrastructure throughout Navy Pier, including 77 tree tubs and about 43,000 square feet of permeable pavement. The system is designed to capture, filter and manage runoff where it falls rather than allowing rainwater to immediately run across hard surfaces and into conventional drainage systems.According to a case study by the National Oceanic and Atmospheric Administration (NOAA), the project is estimated to prevent about 2 tons of sediment, 47 pounds of nitrogen and 3 pounds of phosphorus from entering waterways every year.How does the system work?Traditional urban surfaces such as concrete and asphalt are largely impermeable. When heavy rain falls, water can rapidly flow across these surfaces, picking up pollutants before reaching storm drains and waterways. At Navy Pier, stormwater from the South Dock once flowed directly into the Chicago River, potentially carrying pollutants with it and contributing to drainage and flooding challenges.To address this, the pier incorporated trees into specially engineered containers designed to help capture and manage stormwater. The tree tubs were equipped with steel baskets placed within each opening to support the weight of a steel vault, concrete tub, soil and the root base of a tree.Once the trees were planted, each tub was covered with a steel lid that was made flush with the surrounding pier surface. Permeable pavement was then installed around the trees. The result is a system that allows the trees and surrounding infrastructure to perform some of the functions of a natural landscape — despite being located on a heavily developed pier.The permeable pavement allows rainwater to move through the surface instead of simply flowing across it. Stormwater falling on the South Dock can enter the tree tubs, where it helps nourish the trees before being filtered and slowly drained toward Lake Michigan. Water that is not absorbed by the tree tubs is then captured by the surrounding permeable pavement, and passed through bio-infiltration basins and directed into storage cisterns. The stored water is then reused as the primary source of irrigation for other landscaped and planted areas.The trees are doing more than providing shadeThe trees at Navy Pier aren't simply to decorate the landscaping. Urban trees can intercept rainfall in their canopies, reducing the amount of water reaching the ground at once. Their root systems can also help with water uptake and infiltration. Combined with engineered infrastructure beneath and around the trees, the landscaping becomes part of the site's stormwater-management system.The trees also provide other environmental benefits. According to the project documentation, they help reduce the urban heat-island effect and improve air quality and the microclimate around Navy Pier. Many of the trees were locally sourced and are native to the Chicago ecoregion. Species were selected with assistance from the Morton Arboretum, creating a new green habitat while also adding recreational and aesthetic value to the pier.A small intervention with a measurable effectThe Navy Pier project illustrates an increasingly important idea in urban planning: cities don't necessarily need to transform entire neighborhoods into forests to make their infrastructure greener.Sometimes, the change comes in much smaller pieces — a tree planter here, permeable pavement there, a rain garden along a street or a green roof on a building.Individually, these interventions may appear modest. But when combined with conventional infrastructure, they can help reduce stormwater runoff, improve water quality, conserve water and make heavily built-up areas more resilient to intense rainfall.And that's perhaps the most interesting part of Chicago's Navy Pier experiment: the trees and pavement aren't just landscaping and walkways. They're also part of the pier's water-management system.Read More News on