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article imageClimate-related bridge collapses — We're underestimating the risk

By Karen Graham     May 1, 2017 in Environment
Repairing or replacing the nation's crumbling bridges is just one part of President Trump's $1.0 trillion budget proposal to update U.S. infrastructure. However, our current means of assessing their vulnerability may need to be updated.
U.S. Transportation Secretary Elaine Chao said in March that President Trump plans to unveil his trillion dollar infrastructure plan later this year, but how he plans to fund the massive project is still up in the air. But it is desperately needed.
America's infrastructure is old and in need of massive repairs and updates, from roads and highways to dams and airports, including everything in between. And one of the major issues we will need to deal with is our crumbling bridges. California is a case in point.
Nic tweeted:  My photos from the start of demolition of the Pfeiffer Canyon Bridge in #BigSur which ...
Nic tweeted: "My photos from the start of demolition of the Pfeiffer Canyon Bridge in #BigSur which started today."
Nic Coury
In March, a bridge along the state's iconic Big Sur coast collapsed, isolating communities and costing local businesses millions of dollars. And while California's extreme rain events were likely to damage infrastructure, the risk assessment standards in use today made it difficult to identify which structures might be most vulnerable.
However, it is questionable if the White House has considered the predictions that take into account the building of bridges based on climate and land-use change we are dealing with in the world today. And this is one obstacle to spending infrastructure funds wisely. Current means of assessing bridges may underestimate their vulnerability, according to a new study published in the Journal of Infrastructure Systems.
The I-5 Skagit River Bridge collapse in Washington state caused three people to be injured.
The I-5 Skagit River Bridge collapse in Washington state caused three people to be injured.
John Lloyd from Washington
Climate and land-use change — A harbinger of things to come
"This winter in California has highlighted the vulnerabilities of our nation's infrastructure," said Noah Diffenbaugh, a professor of Earth system science at Stanford and the Kimmelman Family Senior Fellow at the Stanford Woods Institute for the Environment.
"Updating our infrastructure will require both making up for deferred maintenance, and preparing for the increasing risk of extreme events that comes along with global warming," he added. The study points out that as climate change and land use changes open the way for more frequent and extreme flooding, we will see the collapse of more of our 500,000 or more water-spanning bridges.
Making accurate damage estimates is complicated because of a number of factors, but regional and national studies have set direct climate change costs due to bridge collapses at around $250 million. But that figure is conservative because the figure doesn't take into account the loss to businesses or inability to commute to work.
Collapsed I−40 Bridge  near Webbers Falls  Sequoyah County  Oklahoma — in 2002.
Collapsed I−40 Bridge, near Webbers Falls, Sequoyah County, Oklahoma — in 2002.
Xpda
The study also found that bridge risk assessments generally are based on the probability that a bridge may collapse when a 100-year flood (a stream flow with a 1.0 percent probability of being exceeded in any given year) occurs. This assumption underestimates the risk because not all stream flow conditions are taken into account.
A sensible model for determining vulnerability
The researchers basically considered the full range of flooding scenarios, as opposed to the once in 100-years flood risk. This approach gave them a better sensitivity in identifying changes in flood frequency. The study looked at 35 documented bridge collapses in the U.S.
Of the 35 bridge collapses, floods caused 13, erosion of sediments around bridge foundations — called scour — caused 16, a hurricane caused one and other influences (such as waterborne or hydraulic debris) caused five. The authors also note that 23 of the bridges collapsed from lower flow floods, meaning they were less than 100-year floods, but they were also built before modern bridge design standards were put into place.
Collapsed Cypress Street Viaduct in Oakland  from the 1989 Loma Prieta earthquake. (As seen from  gr...
Collapsed Cypress Street Viaduct in Oakland, from the 1989 Loma Prieta earthquake. (As seen from ground-level) Note detachment of upper vertical elements from lower and the lack of reinforcement at the point of detachment.
H.G. Wilshire, U.S. Geological Survey
Here is the reason why this study is so very important, folks. Most U.S. bridges, along with most of our infrastructure, pre-date modern design standards. And this study highlights the risks of extreme climate events on our infrastructure, as well as the importance of using updated risk assessment models in analyzing the vulnerability of our bridges.
"To balance funding between the backlog and climate adaptation, bridge managers will need robust data on collapse risk," said lead author Madeleine M. Flint, an assistant professor of civil and environmental engineering at Virginia Polytechnic Institute and State University. "Our study is a step in that direction."
More about Bridge collapse, Infrastructure, climaterelated, 100year floods, Models
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