Water Works: Making Stormwater Control Measures More Resilient
Resiliency can be defined as the ability to bounce back under stress, and it’s an important topic as it relates to stormwater infrastructure. More-resilient stormwater control measures (SCMs) must be designed to meet tomorrow’s design needs.
Across the globe, communities are facing increasing stressors brought on by stronger, more frequently occurring storms associated with climate change. These intense events exacerbate existing drainage issues created by increasing urbanization within our communities. Impacted communities face the immense challenge of addressing these stressors while balancing economic growth, maintaining a healthy environment and enhancing the social wellbeing of residents.
The Challenges
The American Society of Civil Engineers “2021 Infrastructure Report Card” notes that damages from urban flooding cause $9 billion in losses annually. In addition, the U.S. Environmental Protection Agency says urban stormwater is the only major source of water pollution that’s growing all over the country. These facts should concern us all. What are some contributing factors?
Continued Urban Sprawl
Sprawl isn’t a new phenomenon. Development’s “golden age” occurred in the 1960s and 1970s prior to enactment of the Clean Water Act (CWA). Modern stormwater rules and regulations were virtually non-existent. Growth created additional impervious areas in communities ill-equipped to address additional development and pollution sources.
We still experience sprawl today with the passage of poor land-use decisions as well as other factors such as less-expensive land prices and lower taxes that incentivize development further out into the suburbs. Affected communities continue to feel the strain established more than 50 years ago.
Aging Infrastructure
Much of our existing, conventional stormwater infrastructure (i.e., conveyance pipes and storage systems) has exceeded or is nearing the end of its useful lifespan. In addition, even if they don’t need replacement or repair, these systems are likely undersized given today’s rainfall trends. Upgrading large networks of aging, undersized systems underneath densely populated areas is costly and creates engineering challenges.
Outdated Regulations
Despite greatly improved regulations since the inception of the CWA in 1972, the underlying precipitation data used in the design of stormwater infrastructure is outdated. A recent study from researchers at the University of Wisconsin-Madison and Carnegie Mellon University indicates that rainfall events that exceed common engineering design criteria, including 100-year events, have increased in frequency in most parts of the United States since 1950.
Another study from researchers at the University of Tennessee-Knoxville and the Ohio State University suggests climate change also poses significant risk to green stormwater infrastructure (GSI) practices, indicating that GSI won’t be able to continue effectively managing urban stormwater runoff under current design standards (bit.ly/3FdZgRR).
Limited Stormwater Management Compliance Toolbox
Alongside outdated regulations are a compliance toolbox that doesn’t always prioritize the right solution for the specific site constraints. The current suite of available SCMs is insufficient to address future demands from more intense, more frequently occurring storms and accompanying increases in pollutants. Design adaptations accounting for the increased runoff volumes and additional pollutant loads are needed. Existing infrastructure will have to be upgraded and/or retrofitted. GSI is most frequently promoted as a best practice for addressing climate change, but the aforementioned studies indicate some uncertainty with that approach. Local policies that encourage innovation and alternatives within the compliance toolbox can address these needs.
Potential Solutions
We have a clear problem. Where problems exist, we need to devise reasonable solutions. While not comprehensive, the following suggestions can begin to mitigate the forthcoming challenges by assisting in the development of more-resilient SCMs.
Incentivize Denser Development
Future precipitation projections will require larger SCMs due to runoff volume increases. Depending on the SCM selected, this may require more land area. Denser developments that optimize the available land area and/or redevelop existing impervious sites can help accelerate upgrades to existing infrastructure, lead to the installation of SCMs where none previously existed, and protect unimpaired waterbodies in outlying areas. Certain aboveground GSI SCMs may not be suited for these highly impervious sites due to their space needs. Alternatively, certain underground SCMs that can combine treatment and storage should be considered since the area above them can be utilized for other beneficial uses such as green space or parking.
Maintain Existing Stormwater Assets
Generally, society does not think twice about completing preventative maintenance on our homes or cars, yet we frequently do the opposite with stormwater infrastructure. It’s no wonder our infrastructure continues to fail. Prioritizing recurring and preventative maintenance of existing SCMs will help critical infrastructure meet performance expectations and minimize the need for total replacement under projected future rainfall conditions.
Modernize Stormwater Regulations
SCMs are designed to current standards, which often rely on 50-year-old or greater precipitation data. Stormwater programs should base SCM design standards on the most-current precipitation data available. National Oceanic and Atmospheric Administration (NOAA) Atlas-14, released in 2013, incorporates more-recent precipitation events than alternatives and is the official U.S. government source of precipitation frequency estimates. Some communities, such as Virginia Beach, Va., have gone further by revising their local design rainfall depths to NOAA Atlas-14 plus 20 percent as part of its Sea Level Wise Adaptation Strategy. NOAA Atlas-15, which will contain even more recent precipitation data, is anticipated to be available in 2027.
Innovative and Hybrid Infrastructure
Traditional thinking, policies and tools often are not resulting in the development of resilient infrastructure. Stormwater policies that incentivize innovation are needed as are ones that support the use of hybrid infrastructure: combined gray and green systems. Policies that allow for acceptance of innovative SCMs would encourage the development of systems that can treat increased runoff without sacrificing pollutant removal performance.
Hybrid infrastructure, particularly those aimed at increased volume capture, should be constructed since these practices are more readily adaptable to expected future precipitation conditions. An example of a hybrid system would be an engineered high-flow biofiltration system paired with an underground infiltration system or detention system to maximize co-benefits of GSI while providing additional water quality and quantity protection underground in space-constrained urban areas.
We can no longer ignore the fact that our communities are experiencing more intense and frequently occurring storm events. It’s critical to our wellbeing that we consider future stormwater needs now and begin implementing SCMs designed and constructed with resiliency in mind. Our communities and local water quality truly depend on it. 
About Jacob Dorman
Jacob Dorman is a regional regulatory manager at Contech Engineered Solutions; email: [email protected].
