THURSDAY, SEPTEMBER 14, 2023
A team of researchers is reportedly working to advance efforts to enhance infrastructure information-sharing by building an inventory of stormwater control measures (SCMs) currently operating in 23 U.S. cities.
The report states that researchers from six universities, as well as the Water Research Foundation (Alexandria, Virginia) and the U.S. Geological Survey, are reportedly attempting to identify patterns among the types of SCMs cities pursue and the various physical, climatic, socioeconomic and regulatory factors driving those choices.
Research Background
According to the report, cities often struggle to use each other as models for stormwater infrastructure planning due to its inherently site-specific nature. Two identical copies of the same SCM could reportedly differ in their performance based on their surrounding geography, the amount of rainfall they receive and how their owners measure success.
Even the terms of different SCMs can reportedly vary among different jurisdictions, complicating efforts to understand whether an SCM that works in one city will work in another.
Infrastructure inventories help cities compare stormwater strategies @WEFstormwater #water https://t.co/rIKnlthyqj
— BC Water News (@BCWaterNews) September 8, 2023
“Cities have been shifting their approaches to stormwater management, with more cities using green stormwater management recently,” said Aditi Bhaskar, study co-author and University of Colorado Boulder environmental engineer.
“To understand how all this relatively new green stormwater infrastructure is working, we need to know where it is. 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.”
In 2021, the research team reportedly called on cities to improve the way they documented and shared information about their SCM networks through focusing on functions rather than the SCMs' names.
Following guidelines suggested in the Water Environment Federation Manual of Practice 23: Design of Urban Stormwater Controls, the researchers introduced a new set of terminology for different SCM categories based on their mechanics—green roofs reportedly became filters, while permeable pavers became infiltrators.
The researchers then reportedly condensed dozens of potential SCM types into just seven categories, including basins, swales and strips, filters, infiltrators, gross pollutant traps, disconnection and a miscellaneous "catch-all" category for other types. The researchers stated that they used this new terminology to create a more standardized database of the SCMs that exist in different cities.
In their more recent study, the team reportedly sought a better understanding of why these types of SCMs were pursued.
Current Research
Working closely alongside stormwater professionals in these cities with sufficient information about their SCM networks, the researchers reportedly compared the frequency and density of different SCM classes against a series of other city characteristics.
These characteristics reportedly included the city’s average slope and proximity to the water table, as well as its typical climate, its population density, whether it contained combined or separate collection systems and if it was subject to a consent decree or other atypical regulatory requirements.
According to the report, through drawing clearer connections among the types of common constraints that might make one type of SCM more cost-effective than another, the study reportedly seeks to help cities of all sizes reveal what makes a particular piece of infrastructure site specific.
Other studies, in addition to ongoing information-sharing partnerships between cities, have reportedly attempted to make these links clearer, though the researchers stated that this study had been the first to do so on a national scale.
The researchers hope that clearer linkages will help smaller cities with less-established SCM networks identify larger cities as relevant models for infrastructure-planning decisions. They also reportedly have the potential to assist larger cities as they expand their SCM networks and as pressures related to climate change and urban development shift the expectations that have aided their past decisions.
“Cities with more resources can lead on advancing knowledge and practice by monitoring and evaluating SCM networks,” Bhaskar said. “These cities can also benefit from learning about the approaches used by other cities, for example, to share information on effectiveness of approaches.”
Using statistical methods, researchers teased out multiple patterns that detail which city characteristics hold the most sway over the types of SCMs they pursue.
Such physical considerations as the amount of impervious space in each city, its average slope, its distance to the water table and its use of groundwater were reportedly the strongest determinants of the type of SCMs cities built.
The report states that as an example, cities that were not limited by a shallow water table generally chose infiltrators over basins, strips and swales, or filters, but infiltrators were less common in lower-elevation cities.
The infiltrators class included SCMs like infiltration basins and vaults, trenches, dry wells and permeable pavers. In contrast, such climatic variables as average precipitation and temperatures, aridity and water-vapor pressures reportedly had little or no correlation with any particular type of SCM.
Five out of the 23 cities were reportedly under U.S. Environmental Protection Agency consent decrees. Filters, a class that included sand filters, bioretention schemes, green roofs and others, were stated to be more common in these cities.
The researchers state that filters were also implemented more often in cities with a greater percentage of regulated waterways classified as impaired, as well as those that struggle with chronic combined sewer overflows.
This finding could potentially show that U.S. cities regard filters as the most reliable or cost-effective route to reach regulatory targets related to water quality. Basins—such as wetlands, cisterns and forebays—reportedly tended to be less common in cities with stricter regulatory obligations.
Results also noted noticeable differences in the scale and diversity of urban SCM networks. For example, Los Angeles was found to maintain the lowest density of SCMs, with as few SCMs as 0.46/km2 (0.74/mi2) of impervious area, indicating a preference toward larger, regional interventions.
Washington, D.C. reportedly operates as many SCMs as 314/km2 (505/mi2) of impervious area, demonstrating a more piecemeal approach. Additionally, some cities reportedly relied on only a few types of SCMs.
Finally, with a high number of infiltration basins and no other SCM classes documented in the study, the City of Pocatello, Idaho, was reportedly the most extreme example. By contrast, Baltimore boasted the highest SCM diversity, containing an eclectic range of basins, filters, and infiltrators.
The study was reportedly published in the journal Environmental Research: Infrastructure and Sustainability.
Tagged categories: Environmental Controls; Flood Barrier; Green Infrastructure; Health & Safety; Infrastructure; Infrastructure; Locks and dams; non-potable water; Port Infrastructure; potable water; Program/Project Management; Research; Research and development; Stormwater; water damage; Water/Wastewater; Water-resistive barrier
