Recent research from the University of Michigan reveals that much of the nation’s stormwater infrastructure, which was originally built many decades or even a century ago to manage flooding, can actually worsen the flooding during severe weather events that are becoming more frequent worldwide.
The issue stems from traditional planning not accounting for the interconnectedness of flooding: how runoff from driveways, lawns, and streets—along with the water flow in rivers and pipes—are all linked. This can create unexpected interactions between various stormwater systems, which can complicate flooding situations.
“Typically, our focus during design is on localized solutions,” explained Valeriy Ivanov, a professor of civil and environmental engineering at U-M and co-first author of the study published in Nature Cities. “We concentrate on specific areas of concern, which can be a single lot of land or a group of parcels that need stormwater management, designing specifically for those spots.”
“However, these areas are influenced by flooding in the surrounding regions, meaning the stormwater infrastructure created might have unintended effects.”
The research is based on unprecedented rainfall that struck Metro Detroit on August 11, 2014, which led to widespread flooding in the area. Highways were closed, drivers were stranded, and significant power outages and damage occurred, affecting over 100,000 homes and costing $1.8 billion in total. The research team analyzed data from this event, focusing on the city of Warren, and compared their findings to current U.S. stormwater design standards and flood warning practices to formulate policy recommendations.
These recommendations include:
- Stormwater system designs should adopt a comprehensive, systemwide perspective for flood management, rather than sticking to the old model of local solutions.
- Design guidelines for stormwater systems should be updated to account for connectivity in urban environments, including flows from both below-ground infrastructure like pipes and sewers, as well as above-ground flows in rivers and streams, and overland flows across both natural and constructed surfaces.
- Advanced computer models that can accurately represent all aspects of stormwater elements and their water behavior should be required.
- Design scenarios need to reflect a wide array of factors influencing water flow in urban settings, including varied rainfall patterns, existing soil moisture conditions, and the functioning of current stormwater drainage systems.
- Flood risk mapping should broaden its scope beyond areas near rivers to incorporate potential hazards in urban regions that might be far from any permanent bodies of water.
“Current flood mapping practices highlight a dated mindset that requires changing,” stated Vinh Tran, a U-M assistant research scientist in civil and environmental engineering and co-first author. “Whether it’s the Federal Emergency Management Agency or other entities creating these maps, they typically provide flood risk estimates only for areas adjacent to rivers. The reality is that flooding can occur in urban settings far from any river or stream.”
“For instance, in Warren, Michigan, the official flood maps did not indicate flood risks in parts of the city located miles from major waterways. This is a trend that is seen across the entire country.”
According to FEMA, flooding is recognized as “the most common and costly disaster in the U.S.,” with risks rising due to climate change.
Financially, this issue poses significant challenges. Between 1980 and 2000, FEMA’s National Flood Insurance Program paid $9.4 billion in claims. In the following two decades, this figure surged to $62.2 billion—an increase of over 660%.
“If designs aren’t updated, the economic toll of flooding will only increase, creating a heavier burden for governments and taxpayers,” warned Jeff Bednar, environmental resources manager for Macomb County and a research contributor to the project. “By investing in resilient infrastructure now, we not only safeguard our environment but also lay a stronger foundation for future economic growth.”
