According to the American Society of Civil Engineers’ (ASCE) 2021 Report Card for America’s Infrastructure, 42% of the more than 617,000 bridges across the U.S. are at least 50 years old and 7.5% are considered structurally deficient. An additional complicating factor is that many of these older bridges are crossing rivers and streams located in urban areas that were developed prior to modern-day floodplain management standards, putting these communities at greater risk of flooding. This fact, combined with increasingly severe storms that cause more frequent flooding and rising sea levels, can make designing a feasible bridge replacement daunting to any department of transportation (DOT). Citizens and permitting agencies are becoming more aware of the impacts and costs of these bridge replacements and are seeking more detailed information for any proposed replacements.

To meet these increasing demands, many state and local DOTs are turning to a state-of-the-art 2D modeling software developed by the Bureau of Reclamation and supported by the Federal Highway Administration (FHWA) called Sedimentation and River Hydraulics-Two-Dimension (SRH-2D). The software is integrated into the SMS software package developed by Aquaveo, and this integration allows for the development of complex and highly detailed 2D meshes which can be applied to a range of projects, including river hydraulic modeling, coastal modeling, and bridge structure projects.

While the SRH-2D program has only been in existence since 2004, its uptake by numerous state DOTs has been swift due to its ability to provide a high-level of hydraulic detail that can help identify potential design cost-savings as well as give the public and regulating agencies greater detail regarding the positive and negative impacts of the project." Emma Bones

Modeling to Save Taxpayers’ Money

One of the first SRH-2D models I did was for a municipal client in coastal Georgia. The client had a bridge that experienced repeated flooding, and we designed an hydraulically feasible bridge to mitigate the ongoing flooding. We identified SRH-2D as the ideal model for this situation for several reasons:

1. The bridge was tidally influenced
2. The floodplain was extremely wide and likely experienced 2D flow in multiple directions
3. The client requested a high-level of detail regarding the hydraulic impacts of the bridge especially with respect to velocities surrounding the bridge opening, given the close proximity of homes to the bridge

Using an SRH-2D model, my team was able to evaluate if expanding the bridge opening would help alleviate flooding. Ultimately, our team determined through the modeling that a new bridge opening would provide negligible benefits to flood threats and did not justify the investment. Our modeling process ended up costing a fraction of what would have been over a $1.5-million new bridge project.

These video models showcase additional project applications of the SRH-2D software:

Another 2D modeling success story comes from the Colorado Department of Transportation (CDOT) which has shared its implementation of the 2D Quick Checks Initiative. As part of project scoping, it requires the development of a high-level SRH-2D to assess the efficiency and resilience of each project. Within the first year of program implementation, CDOT recorded a $22.4 million-dollar cost savings as well as an increase in safety and design enhancements.

Improving Scour Assessments with SRH-2D

Scour is a critical consideration as part of the hydraulic design process for a bridge. Bridge scour, or the removal of sediment around bridge abutments or piers, is the leading cause of bridge failure. According to ASCE, Nearly 21,000 bridges were found to be susceptible to overtopping or having their foundations undermined during extreme storm events. SRH-2D can be leveraged to design more effective solutions for scour given its ability to model 2D flows within the bridge structure and around piers. To allow SRH-2D to communicate with the FHWA’s Hydraulic Toolbox, the SMS software program has created a scour module that allows users to draw arcs at critical points in the model that represent the inputs for the scour equations developed by the FHWA. This allows users to extract precise and detailed data that provides more accurate scour estimates than could be produced by a traditional 1D model. This data can further contribute to cost savings as well as improved design and safety enhancements for the bridge.

Projects with complex bridge hydraulics pose a unique set of challenges when it comes to design and scour analysis. With advancing software tools, like SRH-2D, we can better analyze impacts to project designs, which ultimately will contribute to more cost-effective and safer infrastructure nationwide.