A new analysis from the nonprofit Headwaters Economics finds that millions of culverts and stream crossings across the U.S. are undersized for today’s heavier, more frequent storms. Culverts are the pipes or channels that funnel water under roadways. When they’re too small, they can clog, overflow or wash out, leaving people cut off.
“If a culvert fails, people can become isolated from emergency services, their jobs and schools and more,” said Bridget Mitchell, a researcher with Headwaters Economics.
Nationwide, there are more than 3.5 million outdated culverts that are likely too small for modern flood risk, according to the analysis. In the Mountain West, Arizona has the most outdated culverts at 224,800, followed by Montana (193,557), New Mexico (192,781), Nevada (181,868), Wyoming (160,136), and Idaho (142,085). Colorado is the only state in the region that has updated its guidelines.
Without statewide standards, decisions about culvert design often fall to local road agencies, some of which may still follow rules written decades ago. That can create weak points in places where storms are getting more intense, Mitchell said.
One approach gaining momentum is known as stream-simulation design. Instead of forcing water through a narrow pipe, these crossings mimic the natural shape and flow of the stream, allowing water, sediment and even fish to move through more easily during big storms.
Mitchell said updating design standards — and securing funding to replace aging crossings — will be key as Mountain West communities prepare for future flooding.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
