Abstract

River floods can persist for days to weeks in river basins with gently sloping landscapes like those found in parts of Iowa. The basins drain slowly, creating an extended period over which new rainfall can amplify a flood pulse in the river system and flood bridges and adjacent roadways. To evaluate future flood conditions, Iowa DOT developed a methodology to integrate climate projections of rainfall within a river system model to predict river flood response to climate change. Iowa DOT tested this methodology in two river basins to evaluate its ability to produce scenarios of future flood conditions. They analyzed the potential impact of the predicted future floods on six bridges to evaluate vulnerability to climate change and extreme weather and inform the development of adaptation options.

Scope

The Iowa DOT collaborated with Iowa State University and the University of Iowa Flood Center to create daily rainfall simulations and future peak discharge flows from 1960 to 2100. The basins chosen for detailed analysis represent one small basin (South Skunk River) with drainage time of about one day, and one larger basin (Cedar River) with drainage time of about one week. Both basins have experienced record flood events in recent years that have overtopped primary highways and the Interstate.

Objectives

• Collect information, monitor, predict, and evaluate the performance of existing highway structures and roadway embankments with respect to flood inundation during severe rainfall events. 
• Determine relevant precipitation metrics in climate projections for transportation infrastructure calculations.
• Quantify the sensitivity of simulated streamflow to projected precipitation change.
• Conduct an assessment of bridge vulnerability to simulated streamflow change using an integrated asset database and bridge-monitoring software application called BridgeWatch.
• Provide adaptation strategies for climate change impacts and review design policy to incorporate climate change.