Increase in Bridge Scour Causing Increase in Foundation Costs

Recent increases in extreme weather conditions have created impacts, such as flooding, which are causing an increased need in resiliency for foundation systems. Bridge scour has been identified as the leading cause of bridge failures worldwide. Studies show significant structural and economic consequences of climate-driven flowing. In many cases, the effects of this increased resiliency come in the form of substructures becoming more expensive due to deeper design scour depths, changes away from locally common foundation types, and/or more complex construction concerns. The first case study is a roadway on the border of Nebraska and Iowa that flooded during intense storms in Spring 2019 which led to an extended road closure requiring a 2-h traffic detour. Ultimately, the flooding and concerns for future extreme events led this roadway to be replaced with a 1,097-ft-long bridge founded on driven piles in fall 2021. The second and third case studies are bridges that the design depth of scour was increased by approximately 2 ft when design criteria changed from a 100-year flood to a 200-year flood to reflect the higher frequency of extreme storm events. In both cases, due to load demands and the soil/rock stratigraphy within the creek channel, driven piles would not provide adequate lateral resistance, requiring a change to foundation type to drilled shafts, a foundation type not commonly used by the Iowa DOT.