Traditional infrastructure design often makes extreme flooding events worse

The issue lies in traditional planning’s failure to acknowledge flood connectivity: how surface runoff from driveways, lawns and streets — and the flows in river channels and pipes — are all interlinked. The result’s interactions, often unanticipated, between different stormwater systems that could make flooding worse.

“After we design, we typically concentrate on localized solutions,” said Valeriy Ivanov, U-M professor of civil and environmental engineering and co-first writer of the study published in Nature Cities. “We’ve an area of concern, sometimes it is a single plot of land, or a set of parcels that must be connected by stormwater infrastructure, and we design specifically for those areas.

“But those areas are impacted by flooding that happens around them, and which means designed stormwater infrastructure can have unintended consequences.”

The study is predicated on record-breaking rainfall that hit Metro Detroit on Aug. 11, 2014, leading to flooding across the region. The disaster closed highways, stranded drivers, and caused power outages and property damage to over 100,000 homes, with a value of $1.8 billion. Researchers analyzed data from that event, particularly from town of Warren, and placed their findings within the context of current U.S. stormwater design standards and flood warning practices to develop policy recommendations.

Those include:

• Stormwater system designs should take a holistic, systemwide approach to flood mitigation, slightly than the standard approach focused on local solutions.
• Design guidelines for stormwater systems ought to be revised to think about connectivity in urban landscapes, including flows in subsurface infrastructure equivalent to pipes and sewers, open channel flows equivalent to rivers and streams, and overland flows over natural and built surfaces.
• Advanced computer models that represent the total spectrum of stormwater elements and the behavior of water in them ought to be mandated.
• Design scenarios should represent the varied spectrum of things that control water flow in urban areas, equivalent to complex rainfall patterns, antecedent soil water conditions, and the operation of existing stormwater drainage systems.
• Flood hazard mapping approaches should expand their focus beyond river-adjacent floodplains to incorporate risks in urban areas that could be removed from everlasting bodies of water.

“Current flood mapping practices are indicative of outdated considering that needs to vary,” said Vinh Tran, U-M assistant research scientist in civil and environmental engineering and co-first writer. “Whether it is the Federal Emergency Management Agency or another person producing it, they only provide estimates for floodplains which are near rivers. But here’s the issue: In cities, flooding can occur removed from any river or stream.

“Take Warren, Michigan, for instance. The official flood maps didn’t show flood risks in parts of town that were miles from any major waterway. And it is not just Warren — that is typical everywhere in the country.”

In keeping with FEMA, flooding is “essentially the most common and expensive disaster within the U.S.” That risk is increasing on account of climate change.

Financially, it’s an issue. FEMA notes that between 1980 and 2000, FEMA’s National Flood Insurance Program paid out $9.4 billion in insurance claims. Over the next 20-year period, this system paid out $62.2 billion — a rise of over 660%.

“Without updated designs, the economic impact of flooding will only grow, placing a heavier burden on governments and taxpayers,” said Jeff Bednar, environmental resources manager for Macomb County and a research contributor on the project. “By investing in resilient infrastructure now, we not only protect our surroundings but in addition strengthen the muse for economic growth.”