Guest Column | November 3, 2023

Diverse Cities, Diverse Solutions: A Deep Dive Into Urban Stormwater Management

By Christian Bonawandt


Data from 23 U.S. cities reveal the drivers and differences in the development of stormwater control measures, with findings that can inform best practices for municipalities nationwide.

With growing urbanization, aging infrastructure, and climate change, effective stormwater management has become as difficult as it is essential. A new research paper explores the complex factors that influence the selection and deployment of stormwater control measures (SCMs) in major U.S. cities. Traditionally, stormwater management primarily focused on flood mitigation through water conveyance systems. However, newer SCMs, which encompass a range of approaches like cleaning, harvesting, infiltrating, detaining, and retaining storm runoff, have gained prominence.

The findings emphasize the importance of considering SCM networks at both the site and city scales, underlining the need for cities to learn from each other’s experiences, especially smaller cities looking to develop their stormwater plans. The researchers sought to understand the key drivers and constraints shaping SCM designs in different cities and aimed to answer two crucial questions: How do SCM density and assemblages differ among U.S. cities, and which physical, climatic, regulatory, and socioeconomic variables explain these differences?

Many Factors Affect The Final Solution

The study examines SCM inventory data from 23 U.S. cities and analyzes numerous variables. These variables encompass physical factors like topography and depth to the water table, climatic data, socioeconomic variables such as population density and median housing age, and regulatory aspects like combined sewer systems and consent decrees. Key findings include:

  1. Influential Factors. Various factors were identified as influential in shaping SCM designs within cities. The study found that physical factors like topography, depth to the water table, and imperviousness had notable impacts on SCM selection. For example, cities with shallow water tables preferred infiltrators as their primary SCM type. Socioeconomic variables, particularly median household income, played significant roles in determining the selection of filter, basin, and swale and strip SCMs. Climatic variables, while important, were found to be more influential when treated as categorical indicators.
  1. Variability in SCM Density. The research reveals a significant disparity in SCM density among the cities studied. For instance, Los Angeles had a relatively low SCM density of 0.74 SCMs per square mile of impervious area, while Washington, D.C., boasted a much higher density of 505 SCMs per square mile of impervious area. The study also highlighted that MS4 Phase I cities with combined sewer systems tended to have the highest SCM densities. This finding underscores the importance of context-specific stormwater management strategies and the diverse needs of different urban environments.
  1. Roles of Regulatory Variables. Federal regulatory variables, including the presence of combined sewer systems and consent decrees, were crucial in shaping SCM designs. Cities under consent decrees were more likely to adopt filter-based SCMs, whereas those with combined sewer systems tended to utilize a more diverse range of SCMs.
  1. Threshold Relationships. The authors uncovered several threshold relationships between SCM types and certain variables, particularly climatic factors. For instance, infiltrators were favored in arid climates with deeper water tables, indicating that these SCMs are more suitable for regions with specific climatic conditions. These thresholds underscore the importance of tailoring stormwater management approaches to the unique environmental characteristics of each city.

One Size Cannot Fit All

The research shows that stormwater management is a multifaceted endeavor influenced by a combination of complex factors. The key takeaway is the importance of understanding and considering these diverse factors when designing stormwater management plans for urban areas. In particular:

  1. Context Matters. The study emphasizes that there is no one-size-fits-all approach to stormwater management. Different cities have varying needs and challenges based on their physical characteristics, regulatory environments, socioeconomic factors, and climatic conditions. Therefore, stormwater management solutions must be context-specific to effectively address local issues.
  1. Data Collection and Research Needs. To advance stormwater management practices, comprehensive data collection is crucial. The study suggests expanding databases of implemented SCMs and conducting qualitative research to explore the functions and implications of SCM assemblages. This would help cities gain a deeper understanding of how different SCMs interact and contribute to broader city- and watershed-scale goals, such as coping with climate change and improving environmental equity.
  1. Regulatory Impact. The research highlights the significant influence of federal regulations, consent decrees, and the presence of combined sewer systems on SCM selection. This underscores the need for collaboration among local governments, regulatory bodies, and stormwater professionals to develop effective and compliant stormwater management strategies.

The complexity of stormwater management necessitates a holistic and adaptive approach. Understanding the interplay of different factors is crucial for designing effective stormwater management plans that meet the evolving needs of urban areas in the face of urbanization and climate change. Ultimately, learning from the experiences of other cities and tailoring solutions to local contexts will be key to achieving sustainable stormwater management goals.

About The Author

Christian Bonawandt is an industrial content writer for Water Online. He has been writing about B2B technology and industrial processes for 23 years.