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Construction Corner: Flood waters continue to rise in a warming world

0 54 Technology

by Korky Koroluk

Climate change is often seen as posing the greatest threat to the world's coastal areas. But inland cities face perils of their own, including more intense storms and more frequent flooding.
Construction Corner: Flood waters continue to rise in a warming world

Revised flood forecasts from the U.S. Army Corps of Engineers has got inland American cities scrambling. It seems that many of their bridges are going to be too low to cope with increased river flows as the climate warms.

A little more than a decade ago the city of Des Moines, Iowa, spruced up an old train trestle, turning it into a pedestrian and cycling pathway across the Des Moines River. But little more than a decade later, crews were back to the site with a crane to hoist the span 1.4 metres at a cost of $3 million. That was after the corps concluded that the river's flood risk was nearly double earlier estimates.

The findings suggested that the bridge could actually act as a dam during bad storms, sending waves of backed-up floodwater into a business district that had only lately been refurbished.

It was, says city engineer Pam Cooksey, "like a bomb was dropped in our lap."

Even as the U.S. began withdrawing from the global climate agreement reached in Paris, many American river communities are responding to climate change by raising or replacing bridges that suddenly seemed too low to stay safely above water.

It's not just Des Moines. Iowa City has started a $40-million project to raise not only a bridge over the Iowa River but part of an adjacent street as well. In Milwaukee, bridges have been raised as part of $400 million in flood-management projects across the metro area that includes 28 communities. In Reno, Nev., about $18 million was spent to replace a bridge over a fairly insignificant river and there are plans to replace three more.

Jim Schwab is the manager of the Hazards Planning Centre at the American Planning Association, which is working with nearly a dozen cities in flood-mitigation options. Because the cities are inland, he says "a lot of these are not the kind of places that people are used to thinking of being in the forefront of climate change."

Schwab says he's sure hundreds — maybe even thousands — of bridge-raising projects have already been completed or are planned.

Apparently no one in the U.S. is tracking all this work, but the Federal Emergency Management Agency (FEMA) says it now routinely provides money for that purpose, although no figures are available.

FEMA says that generally speaking, floods "are expected to be more frequent and more severe over the next century, due in part to the projected effects of climate change."

David Easterling, director of the national climate assessment unit at the National Oceanic and Atmospheric Administration, says that increasing humidity from the warmer air as a result of climate change has resulted in more intense downpours.

"It causes day after day of rainfall, and that leads to flooding," he says.

In Cedar Rapids, Iowa, the normally placid Cedar River topped the previous record flood by 3.4 metres as a result of the series of rainstorms in 2008. More than 1,100 blocks in the city wound up under water.

Shortly after that the Corps of Engineers raised the city's projections for a 100-year flood by eight per cent.

"What used to be the norm is no longer the norm," says Rob Davis, the city's flood-control program manager. "The norm is much higher."

Every day, it seems, we're getting new clues about how the phenomenon of climate change is going to play out. But it seems certain that the construction industry is going to be kept busy raising bridges, building dikes, flood proofing water treatment plants and all the other things that need to be done to protect ourselves in a warming world.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@journalofcommerce.com.

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