New study sheds light on varying stormwater measures across U.S. cities

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stormwater control measure
The researchers say that many cities are shifting towards green SCMs, and in order to understand how effective these measures have been, the location needs to be considered in the analysis. Photo Credit: sunflowerey, stock.adobe.com

A new study attempts to identify meaningful patterns among different stormwater control measures in 23 cities with varying climates across the U.S. 

The study, produced by researchers from six universities, as well as the Water Research Foundation and the U.S. Geological Survey, is an attempt to understand more about what makes a particular piece of stormwater infrastructure “site specific.” By examining various physical, climatic, socioeconomic, and regulatory factors driving the choices behind each city’s stormwater strategy, researchers could compare the different stormwater control measures (SCMs) in terms of slope and proximity to the water table, its typical climate, population density, whether it contained combined or separate collection systems, and the strictness of regulatory obligations.

“Cities with more resources can lead on advancing knowledge and practice by monitoring and evaluating SCM networks,” said Aditi Bhaskar, study co-author and environmental engineer at the University of Colorado Boulder. “These cities can also benefit from learning about the approaches used by other cities, for example, to share information on effectiveness of approaches.”

Bhaskar says that many cities are shifting towards green SCMs, and in order to understand how effective these measures have been, the location needs to be considered in the analysis. 

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“Our work contributes to sharing of information about what type of stormwater management is used where, in a way that other cities can understand the terminology used,” Bhaskar added. 

In 2021, the same group of researchers attempted to simplify and condense stormwater terminology to create a more standardized database. They asked cities to focus on the functions or mechanics of particular SCMs, rather than their names. Green roofs became a category of filters, for example, while permeable pavers became infiltrators. In this way, they condensed dozens of potential SCM types into just seven categories: basins, swales and strips, filters, infiltrators, gross pollutant traps, disconnection, and a miscellaneous catch-all category for other types. 

In the researcher’s latest study, when it comes to understanding why a city chooses a particular stormwater control measure, the study found that the strongest determinants were physical considerations such as the amount of impervious space, its average slope, its distance to the water table, and its use of groundwater.

For example, those of the 23 cities that were not limited by a shallow water table, generally chose infiltrators over basins, strips and swales, or filters, but infiltrators were far less common in low-lying cities. The infiltrators class included such SCMs as infiltration basins and vaults, trenches, dry wells, and permeable pavers. By contrast, such climatic variables as average precipitation and temperatures, aridity, and water-vapour pressures seemed to have little or no correlation with any particular type of SCM, the study found. 

Among the five cities in the study that are subject to orders from the U.S. Environmental Protection Agency, filters such as sand, bioretention schemes, green roofs, and others, were substantially more common, the study found.  

Los Angeles was found to maintain the lowest density of SCMs, with as few as 0.46 per square kilometre of impervious area, while Washington, D.C. operates as many as 314 SCMs per square kilometre.

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