Two-dimensional (2D) hydraulic modeling has come of age. Recent advances in computing power, user interface improvements, and training resources have made this 25-year-old technology readily available for application to hydraulic modeling analyses.

Promotion through the Every Day Counts (EDC) initiative on collaborative hydraulics: advancing to the next generation of engineering (CHANGE) has encouraged transportation agencies to adopt 2D modeling to improve project outcomes. The number of States at the demonstration, assessment, or institutionalized stage of CHANGE deployment has nearly tripled from 17 at the beginning of 2017 to 46 today.

Agencies are finding that 2D models provide a more accurate representation of complex hydraulic conditions typically encountered in the real world because they avoid many of the assumptions required by traditional one-dimensional (1D) models. These 2D models also aid in communicating hydraulic concepts to stakeholders through intuitive graphics and videos.

“We have a much better understanding of site conditions hydraulically, so it enables us to come up with better solutions that result in more reliable, more resilient, and safer structures,” said Scott Hogan, Federal Highway Administration senior hydraulic engineer and CHANGE team co-leader.

FHWA developed “Two-Dimensional Hydraulic Modeling for Highways in the River Environment” to explain the advantages of 2D hydraulic modeling for transportation applications and provide an overview of model development and execution. The reference document covers information relevant to all 2D hydraulic models and includes a user’s manual for the SMS/SRH-2D graphical user interface, which FHWA recommends for bridge hydraulics and scour analyses.

The CHANGE team is collaborating with the National Highway Institute on training courses, including a course on 2D Hydraulic Modeling of Rivers at Highway Encroachments that now offers a virtual option. “There has been a very high demand for this training, and we will continue to schedule courses until the demand runs out,” said Hogan. “The virtual version will reach many who did not have access to the instructor-led courses.”

In addition, more than 1,500 members participate in the 2D Hydraulic Modeling User’s Forum, which delivers bimonthly webinars on best practices, technical support for users, and tips for efficient modeling.

States Succeed With 2D Modeling

The Arizona Department of Transportation (ADOT) is among the agencies that set a goal to institutionalize the use of 2D hydraulic modeling tools to design safer, more cost-effective, and more resilient structures on waterways. To meet the goal, ADOT developed standardized 2D modeling project assessment scoping language, bridge hydraulic guidance, and stormwater design guidance.

ADOT has nine pilot projects involving 2D hydraulic modeling identified, underway, or completed. ADOT reports that over 2 years, it leveraged $100,000 in State Transportation Innovation Council Incentive funds to gain $400,000 in design engineering benefits on projects. This was achieved by including funds in project design budgets to use 2D hydraulic modeling instead of traditional 1D methods.

The Mississippi Department of Transportation (MDOT) is also seeing the value of incorporating 2D modeling into hydraulic analyses. MDOT used the technology to analyze a complicated bridge rehabilitation project on Lynch Creek in Jackson. The modeling needed to accommodate merging floodplains, multiple hydraulic structures, and skewed flow.

MDOT found that 2D modeling captured the Lynch Creek site conditions with a level of detail that 1D modeling could not convey. The 2D models also offered MDOT superior options for presenting results to project stakeholders. Using 1D modeling would have provided results only where cross sections were placed, while 2D modeling provided results over the entire project area and could be rendered in an easy-to-interpret visual format with images of detailed water flow paths, elevation, and velocity.

The Washington State Department of Transportation (WSDOT) has used 2D modeling on several projects, including bridge replacements, bridge scour countermeasure design, fish barrier removal projects, and bridge scour emergencies. After the removal of two dams on the Elwha River in northwest Washington, the State declared an emergency on the existing U.S. 101 Elwha River Bridge because of changes in river conditions and susceptibility of the foundations to scour. WSDOT used 2D modeling to assess the vulnerability of the bridge and reported that 2D modeling was instrumental in communicating risk in the department and ensuring driver safety.

For the proposed bridge replacement, WSDOT has used 2D modeling throughout the project delivery process. This includes assessing the performance of a scour countermeasure constructed during the emergency declaration, designing the new structure, evaluating potential environmental effects such as aquatic habitat impacts, and identifying potential stream diversion parameters to be used during construction.

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