Urban Stormwater Systems Go Green

Concentrating development makes sense. Locating populations and jobs in existing urban and suburban centers encourages community and a sense of place, while protecting fragile headwaters, aquifers, streams and wetlands. Higher-density areas are more energy-efficient as well, because homes often share walls and residents drive less.

But this form of development isn't without its disadvantages from an environmental point of view. In many older cities and suburbs, impervious surfaces such as rooftops, parking lots, streets and sidewalks dominate the landscape, preventing rainwater from being absorbed into the ground. Instead, the water quickly flows over the concrete and asphalt, picking up pollutants before finding its way into nearby streams and rivers. The lack of porous surfaces means that even routine storms and rainfalls can overwhelm sewers and treatment plants, which in turn means untreated wastewater is discharged into sensitive lakes, rivers and seas.

Given this tension, the challenge is to find ways to improve drainage and stormwater management in urban areas, without sacrificing or discouraging the concentration of development that generates many environmental and economic benefits.

In urban areas, the standard ways of dealing with stormwater are both expensive and limited in scope. Retrofitting stormwater systems so that they are separate from sewer systems is particularly costly in cities. And while separating storm and sewer systems helps reduce the risk that wastewater will be discharged into waterways, it doesn't address the problem of pollutants found in urban runoff. Another option, expanding treatment plants, is extremely expensive. The growing number of high-intensity storms exacerbates these problems. What this means is that traditional engineering solutions of pipes, storage tanks and other physical structures are no longer sufficient for coping with Mother Nature.

What does hold promise are so-called green infrastructure techniques that have evolved in recent years. In general, green infrastructure seeks to mimic natural processes while placing less emphasis on heavy equipment and systems. Many of these techniques are detailed in a recent Regional Plan Association report, "9 Ways to Make Green Infrastructure Work." It provides a tool box for municipal planners and officials who are increasingly asked to work with water-management professionals to address water issues.

While gentle in approach, such techniques can prove resilient even under intense pressure, such as during Hurricane Sandy. For example, sand dunes proved a formidable barrier against the large storm surge, leaving areas with healthy dune structures far better off in the aftermath of the storm.

Encouraging green infrastructure will require persistence. Existing regulations and building codes often discourage private developers and public agencies from incorporating green infrastructure into new construction. Revising codes requires political will.

To overcome these issues, cities and suburban centers must encourage and market green solutions. Assessing a stormwater utility fee on property owners while providing opportunity for reduction of the fee through mitigation efforts can incentivize implementation. The creation of mitigation banks and other alternatives can provide a market for green infrastructure when implementation is not feasible on a particular site.

Towns and cities are also looking to their own property to put in place cost-effective water management strategies. A particular focus is streets and sidewalks. These networks generate and move large volumes of stormwater. Over the last several months RPA has been working with landscape architects dlandstudio to establish two pilot "Sponge Park" sites to demonstrate green infrastructure techniques. When fully built, they will capture stormwater flowing from downspouts on the elevated Long Island and Van Wyck expressway interchange. The two innovative basins will remove hydrocarbons as well as other highway pollutants and slow water before releasing it back to Flushing Creek, where it currently is discharged untreated. Through initiatives like these, RPA will continue its role in planning, implementing and advocating for green infrastructure to become standard practice in our cities and suburbs.

Read "9 Ways to make Green Infrastructure Work."