Articles / May 27, 2025

Thoughts From Engineers: Stormwater Brings Change to the Modern American City

Every age has its infrastructure challenges.
The Industrial Revolution, for example, drove scores of people to the largest cities in search of work. Urban areas grew as they never had before, and widespread illness and death resulted from improper sewage disposal and poor sanitation. Cities such as London managed the resulting public health crisis poorly at first, but later more effectively. Through trial and error, analysis, innovation, and tenacity, simplistic solutions gave way to methodologies that became more sophisticated and effective with time. Systems evolved in fits and starts until modern sewers came to be what they are today.

Today’s flooding and nuisance stormwater brought about by a warmer climate may be an imperfect analogy to the 19th-century sewage crisis, but cities were tested then in a way not unlike how our cities are being tested today. Uncertainties and unknowns abound. If we were to map our progress on a trajectory leading to long-term stormwater solutions, we’d still be in the early stages, swamped by more questions than answers—but we would be recording real gains as well.

Some of our most urbanized and heavily populated cities, New York City (NYC) and Copenhagen, Denmark, for example, are deep in experimentation. Different tools and strategies—from ultrasonic sensors and IoT technologies collecting critical data in real-time to blue-green infrastructure and remotely operated gray infrastructure—are being tested to see which strategies give our communities resilience and confidence going forward.

The Challenges of Modeling Urban Stormwater

Modeling stormwater flow and flood prediction is difficult anywhere, but it’s particularly challenging in highly urbanized areas. A few major reasons stand out. The first one relates to the complex hydrology of water movement through urban landscapes. Unlike flow through a confined channel, water in an urban environment can travel in many different directions as it seeks lower elevations. This is movement somewhat like a ball spinning and bouncing off the different points and angles of a pinball machine before eventually disappearing down the trap. Consider the many planes and interfaces—the curb and gutters, roadways, walled obstructions and other vertical and horizontal surfaces—and then think about the different types of substrates with variable characteristics—dirt, pavement, gravel, grass and more—that affect infiltration and flow dynamics.

The other challenge relates to the absence of basic information necessary to build computer models. Consider the value a detailed GIS map or similar dataset brings to an engineering question—without it, we’re flying blind. Current precipitation data for the many micro-environments of a city (and there can be plenty of variability within urban boundaries) as well as data relating to structural and topographic characteristics are key.

Here’s another source of uncertainty: cities are dynamic. Construction, expansion and redevelopment of city blocks is routine along with the continuous conversion of land uses. An abandoned car dealership on a gravel lot is repaved to accommodate new office buildings, for example, creating very different surface conditions. Baseline data relating to the spatial and built environment, but especially data characterizing rainfall in terms of intensity, duration, amount and other parameters, are critical for stormwater and flood flow predictions.

Copenhagen and NYC: Data Collection and Adaptive Design

Some cities are hard at work filling the aforementioned data gap. Copenhagen and several limited areas within NYC leverage smart analytics to guide many aspects of stormwater management, ranging from real-time operation of gray infrastructure components to shaping development of coupled 1D and 2D hydrologic models for surface flow simulations.

Copenhagen already has retrofitted nearly 1,500 miles of sewers as well as more than 200 pumping stations with SCADA systems. Blue-green infrastructure in Copenhagen, of which there are more than 300 active projects, collect data through distributed sensor networks, which allow for remote operation of sluice gates for slow water release and other functionality. In some cases, soil moisture sensors are tucked into the underlying soil along with water-level gauges. The bottom line is that real-time data streams that describe on-the-ground conditions are a game-changer, allowing stormwater infrastructure to evolve with time as conditions dictate.

New York City recently launched pilot projects known as “cloudburst hubs” in several neighborhoods with chronic flooding. Again, much like Copenhagen, the hubs capitalize on a blended strategy that uses smart analytics, known as FloodNET, consisting of some 80-plus ultrasonic sensors, to deliver flood alerts as well as establish a baseline of information with which to design other elements of the stormwater system. Cloudburst hubs include gray infrastructure in the form of underground storage tanks as well as blue-green infrastructure such as parks that function in multiple ways.

Data collection is the backbone of this effort and drives much of the activity within each hub. IoT-enabled overflow control devices located in storm drains trigger pumps when water reaches critical limits; subsurface storage tanks are equipped with real-time valves for optimal water release, among other capabilities. All collected data—some citizen-sourced—are ultimately integrated into the NYC Stormwater Flood Map, a public platform that acts as a key source of critical baseline information.

Cities as Laboratories: Finding Stormwater Tools for the Long Haul

It may be self-evident, but in our efforts to experiment with real-time data-feed applications, develop frameworks that blend infrastructure for effective mitigation, and refine design protocols and core tools, we’re making key progress toward long-term mastery and competence. These efforts are necessary to build a globally shared knowledge base of the structural and non-structural methodologies that advance flood risk management, recognizing that different configurations will need to be adapted to the specific characteristics of each locale. In time, as more urban communities experience success, efficiencies in costs and other aspects of management and prevention will emerge as well. Each age has its defining crises—the trials that challenge us in unexpected ways. Urban flooding is the challenge
of our age.