Thoughts From Engineers: A River Runs Through It: When Green Infrastructure Is More Than a Bit Player
Urban water management is on course to complete an evolutionary circle. When cities began to modernize more than 100 years ago, the goal was to dispose of wastewater as quickly as possible. Engineers studied the physics of natural systems with an eye toward building the structures needed to subdue them. Sewer mains, large tunnels and massive pumps have faithfully rerouted and diverted unwanted water through our pipes and treatment facilities for most of the 20th century and into the 21st.
Focusing exclusively on grey infrastructure worked … for a time. But cities across the country are being hit by storm systems that seem to defy all forecasts and planning. Urban areas and populations continue to grow. Due to aging infrastructure, lack of capacity, or a blend of the above, our cities are coming to terms with a new reality: old formulas for managing water are no longer up to the task.
Simple and Effective
As we filled wetlands and paved over streams, we ignored the obvious: trees and plants have a role to play in the urban mix. Look to the design of a living organism when you think about how efficiently water is used. Simple and to the point, green infrastructure works because it combines the genius of a living system to cycle water with a plan engineered to work in an urban space.
Implemented on small or large scales, green infrastructure can include such elements as green roofs, rain gardens, bioswales and permeable pavements. On larger scales, natural river corridors have been restored with their associated wetlands and floodplains, and large tracts of vacant or underused land have been reconfigured to host the communities of plants that cycle water naturally.
Water Filtration Curbside
The roads and endless swathes of pavement that define our urban spaces channel stormwater but little else. More cities are understanding that a sustainable and resilient city creates natural infiltration zones, allowing plants to take up nutrients and excess water to percolate slowly into the soil to regenerate groundwater or be stored and reused for irrigation or other purposes.
Houston, famous in 2017 for historic rainfall from Hurricane Harvey and aerial views of vast stretches of highways underwater, is shifting tactics to address an urgent need to manage water. With a 3,000-acre project known as Bayou Greenways (bit.ly/37s8E1t), the flood-prone city is restoring miles of river corridors that run through the city with a distinct purpose of reestablishing wetlands and capitalizing on these natural systems for water management and flood control.
Houston and other cities in the United States and overseas are reclaiming large industrial spaces—whether retired railroad yards, shopping malls or other commercial corridors—and restoring them to former wetlands, floodplains and other native communities, recognizing that for green infrastructure to work its magic, considerations of scale are key.
A River Runs Through It
Communities are unearthing buried river systems, and innovative project plans feature stormwater strategies prominently in the landscape. A neighborhood in the 2,700-acre Lick Watershed in Cincinnati (bit.ly/2QE4JIc) is bringing to the surface (or “daylighting”) a river that was paved over some 100 years ago as one part of a larger citywide project known as “Project Groundwork.” Floodwater detention basins, native plantings, bioswales and other strategies are used to holistically manage stormwater and revive a neglected community in the process.
On a retired Ford assembly site in St. Paul, Minn., plans include bringing a buried creek back to the surface, where it will be the focus of a large public park in St. Paul’s Highland Neighborhood (bit.ly/39B5IS4). The original stream corridor will be restored, and the stormwater flushed through from adjoining properties will ultimately connect with the Mississippi River in a much cleaner state. This sustainable and pioneering project is being used to address a large-scale runoff issue where purely structural strategies fell flat. No longer an after-thought or secondary consideration, cities are keen to exploit water features that serve multiple roles in the landscape.
‘Stacked’ Green Infrastructure Is Cheap and Sustainable
Grey infrastructure will always be a part of stormwater management, but green infrastructure now is more than a bit player. Projects with “green” components yield multiple benefits, including increasing property values, creating pockets of beauty in the city, and cleaning and trapping urban runoff. These projects often are called “shared, stacked green infrastructure,” because multiple benefits can be reaped from one well-designed project.
Consider Venice Island Park and Performance Center in downtown Philadelphia. Beneath a modern amphitheater and public green space on the banks of the Schuylkill River sits a massive sewage overflow tank, built to stow rainwater and manage chronic flooding in the neighborhood. As part of Philly’s Green City, Clean Waters initiative (bit.ly/2tlCaHw), this multipurpose park represents just one of the city’s recent efforts to survive rogue storm events and experiment with less-mainstream infrastructure tools.
Where Are We on the Trajectory to Sustainable Cities?
Green infrastructure in a community means water is managed, collected and used onsite. Filtration occurs locally on the banks of creeks and streams that wander through the city’s neighborhoods. Not only is water taken up by the green spaces that spruce up the neighborhood and increase property values, but the water is reused for irrigation, flushing park toilets and other uses. Most importantly, water is allowed to move through the landscape and do what it has always done: sustain life on multiple levels.
The shift to valuing living systems for the role they play in water filtration and improving a community’s quality of life is picking up momentum across the country. On a smaller scale, in a typical backyard, rain gardens and native landscapes are gaining acceptance as desirable lawn design. Western states are removing dams in the interests of restoring natural river corridors for fish habitat, erosion control and beauty. We are learning to value the role of coastal wetlands for erosion control and shore stabilization, a principle that was lately codified in the 2018 Water Infrastructure Act.
At last, green infrastructure is taking center stage in urban spaces across the country. As historic storm systems sweep across the country and wreak havoc on aging and over-extended wastewater and stormwater systems, it couldn’t have come at a better time.
About Chris Maeder
Chris Maeder, P.E., M.S., CFM, is engineering director at CivilGEO Inc.; email: [email protected]