Iowa State University climate researchers have led the development of a new method that could help transportation departments to better plan for excessive flooding, the type of which has closed and damaged some of Iowa’s and the Midwest’s busiest highways and bridges in recent years.
ISU’s Chris Anderson and Gene Takle, in collaboration with scientists from the Iowa Flood Center at the University of Iowa, studied two Iowa river basins using the innovative methodology to produce scenarios of future flood conditions.
Transportation agencies could use projections of this type to prepare and plan for maintenance, repair, and replacement of highway structures in the coming years, the researchers say. Sponsored by the Iowa Department of Transportation(DOT), the research is the first to combine climate and streamflow projections with highway engineering metrics, Anderson, the assistant director of ISU’s Climate Science Program, says.
“To make the study relevant to transportation departments, we made it a priority to use existing engineering practices along with the projections,” Anderson says.
Excessive rainfall that can lead to flooding has increased in frequency and severity, according to climate scientists. They point to climate change as the cause due to increased humidity transported from above the Atlantic Ocean. Excessive flooding can block roads, causing driver inconvenience and disrupted commerce. Raging flood waters can also damage pavement, road embankments, and bridges, all of which can be costly to repair to replace.
“In the past we assumed the climate was stationary over the long haul with ups and downs,” Takle, an atmospheric sciences professor and the Climate Science Program director, says. “Traditionally, we looked at past records to establish climate trends. However, historical methods no longer work. With climate change, we have to use credible climate projection data to estimate change in peak flow of flooded rivers.”
Anderson and Takle’s research looked at the Cedar River basin in eastern Iowa and the Skunk River basin in central Iowa to evaluate the strengths and weaknesses of their technology to project future flood scenarios. Anderson used 19 different climate projections, more than 22,000 precipitation data points across Iowa, and hydrological data from the Iowa Flood Center to generate streamflow simulations from 1960 through 2100. Using high-end computing, he analyzed 22.1 billion data points, generating a continuous 140-year streamflow simulation.
The projected streamflow levels were integrated with the Iowa DOT bridge and roadway asset infrastructure database to assess how changes in future flood levels will affect roads, bridges, and other structures within the two basins.
The results told the researchers the probability exists for increased severity of floods in Iowa in the years to come.
“Our project is the first to compute with well-tested simulation systems and standard engineering software the likelihood of change in overtopping of bridges by extremely high streamflow as climate changes over the lifetimes of bridges,” Anderson says.
The methodology used in the project proved to be suitable for analysis of “big floods” in river basins of 100 square miles and larger. Similar studies in other large basins would give transportation planners “the ability to evaluate, bridge by bridge, the structures in the basin using cost-benefit analyses to make planning decisions,” Anderson said.
The Iowa DOT plans to integrate the information into its real-time warning system to protect travelers from highway locations that are vulnerable to overtopping due to flooding. The results of the study may also influence design guidelines of the state’s highway bridges and culverts.
“The research is a very good example of using climate science for improving decision-making,” Takle says.
ISU’s Institute for Transportation administers 15 centers and programs that are leaders in transportation research, outreach, education, and workforce development.
Christopher Anderson, Climate Science Program, (515) 294-9948
GeneTakle, Atmospheric Sciences and Agronomy, (515) 294-9871