Stormwater pollution has quietly become the most pervasive environmental issue that cities face today. As U.S. cities discharge trillions of gallons of untreated stormwater, wastewater, and raw sewage into clean waterways every year, a collective paradigm shift is desperately needed in urban water management. Larger storms are dropping more rain in less time, revealing what years of rapid urbanization and deteriorating infrastructure have done to our natural water systems.
The EPA estimates a substantial funding gap for stormwater management over the next 20 years, and surely lack of funding can always be a convenient scapegoat. But as cities continue to lean heavily on old solutions to solve new water challenges, we’re reminded of something: if a problem worsens with the more money you throw at it, then you’ve got a broken paradigm. And like it or not, this characterizes the current state of stormwater infrastructure in the U.S.
The combination of increasing rainfall and vast impervious surface area in cities has introduced overwhelming volumes of stormwater that legacy infrastructure simply can’t contend with. Even super-sized tanks and larger system designs are scrutinized as outdated in the face of today’s extreme weather. As is the case with almost every facet of life, the status quo is no longer viable.
Fortunately in the midst of all of these headwinds, there is a silver lining. The unlikely combination of forward-thinking legislation, advanced technology development, and new realities are already ushering in the future of stormwater management. In combination, these three inflection points are poised to drastically change urban stormwater infrastructure moving forward.
New Realities usher in New Beliefs
For decades, regulators and decision-makers operated from the reactive belief that stormwater was a waste product to be captured and treated. Depending on the region, land was developed to withstand 10, 25, and even 100 year storms, and grey infrastructure was built and sized for the expectations of an era that is long gone. This one-size-fits-all configuration for managing the collection, treatment, and discharge of water has really never resulted in the best use of discharged water, as conditions constantly change. Never has this been more obvious than today.
As urban water systems deal with larger quantities of stormwater, regulators have been forced to adjust their lens. For every 1 degree (Fahrenheit) increase in temperature, the atmosphere holds about 4 percent more water vapor. Inevitably this is leading to much heavier and more intense rain events in certain areas. Stormwater management design used to primarily deal with water quality - ie., limiting the flow of chemicals, nutrients, and sediment into clean waterways. But in just a few recent years, the challenge of controlling water pollution has morphed into the growing challenge of protecting property and livelihoods.
All of this has brought forth a subtle and important change in how stormwater management is viewed. Over the past decade, green infrastructure was mostly given lip service as an integrated stormwater management approach. But today, the transition to green is seen as a necessity to confront the dual threat of urban flooding and increased water pollution. As many cities face budget cuts that make large grey infrastructure projects impractical in the near future, a more natural approach to stormwater management is proving to have both economic and environmental benefits for cities of all sizes.
Regulation with an eye toward the future
Regulators deserve some credit for acknowledging the situation that cities are in when it comes to stormwater management. By ushering in the bi-partisan provisions of the 2019 Water Infrastructure Improvement Act, legislators have given cities big incentives to integrate green infrastructure into the larger water infrastructure objectives of their capital plans.
It’s my belief that green infrastructure will be prioritized at levels we’ve yet to see in U.S. cities and the integrated planning framework serves to reinforce that. Cities that routinely defer large wastewater treatment projects or grey infrastructure projects can now use integrated planning to meet Clean Water guidelines in lieu of those large and often unaffordable capital projects. This framework can be especially beneficial to municipalities with existing consent decrees.
Innovative green infrastructure approaches that prove to achieve the same desired outcome of a traditional grey approach can be used to satisfy existing consent decrees and to meet Clean Water Act obligations. As municipal budgets shrink, this framework opens the door for large-scale green infrastructure in our cities. But this will only be possible IF and WHEN innovation in green infrastructure finally comes of age.
Green Infrastructure: Great in Theory.
As a theory, green infrastructure is a no-brainer. The multiple roles that it can play in natural stormwater drainage, pollution control, aquifer recharge, and reducing urban heat island effect have the potential to supply cities with major environmental, societal, and economic benefits. But as it exists today, the current green infrastructure toolkit has clear limitations.
To date, green infrastructure has carried the stigma of expensive maintenance and lack of scalability. Rain gardens, vegetated swales, and stormwater ponds require specialized and often tedious maintenance. In many cases these solutions also consume usable space without adding tangible value to a property (ask any developer how they feel about setting land aside for stormwater detention).
Permeable pavement was developed with the duality of filling the stormwater management role while maintaining the usefulness of normal pavement, but existing technologies have been the same for decades - still prone to clogging and too weak for wide scale implementation. Simply put, existing green infrastructure technologies do not scale at a level that makes them easily integrated into larger water infrastructure objectives. But just as market and regulatory inflection points have bubbled to the surface recently, so too has an inflection point in material technology and engineering design. This technology inflection point may redefine the role of hard surfaces in green infrastructure and finally pave the way to its wide-scale implementation.
Reimagining 1,000,000 miles of hard surfaces
Despite the known short-comings of existing permeable pavements, the ability to utilize a hard surface material to manage stormwater onsite, while still providing the functionality of normal pavement has a major role to play in the future of urban water management. New permeable material technologies are being advanced with unique characteristics in strength, permeability, and material porosity that measures less than 5 microns in size - capable of filtering dirt, debris, and particulate matter onto the surface of the material for easy and cost-effective maintenance.
These materials are being developed for wide-scale integration into urban stormwater management systems as part of engineered designs that turn the edge of streets and sidewalks into permeable drainage zones, greatly reducing the footprint of existing stormwater facilities. Instead of full permeable street sections, or land set asides for stormwater ponds, we can reimagine the curb, gutter, and sidewalk as a natural stormwater drainage facility. Designed with the proper runoff coefficients, hydrologic, and structural factors in mind, the street becomes part of an infiltration corridor where groundwater recharge happens within existing cityscapes.
Deployed at scale we imagine the impact to be significant over the coming years.
Like so many things in our society, the status quo has run its course. Mitigating urban flooding and reducing the volume of stormwater to treatment facilities is both critical and achievable for a sustainable water future. As technology and institutional decision-making comes of age, the innovation deficit in water management will continue to disappear. So we better act with urgency.