Since 2017, when it was initially selected as a Federal Highway Administration (FHWA) Every Day Counts Round 4 (EDC-4) innovation, PennDOT has continued to champion and advance Collaborative Hydraulics: Advancing to the Next Generation of Engineering (CHANGE) through a variety of bridge projects around the state.
Extreme weather events place added pressure on designers to incorporate better resiliency into infrastructure. Historically, engineers have relied on one-dimensional modeling to understand the complex relationship between waterways and built infrastructure. One dimensional (1D) modeling requires designers to make assumptions about stream flow characteristics to evaluate potential flooding impacts. Experience around the nation has shown this can lead to costly and destructive design errors.
Two-dimensional (2D) modeling helps bridge the gap, and provides infrastructure engineers with valuable, verifiable data to support design decisions.
Using 2D modeling, designers can produce varied and specific projected stream flows around bridge structures and evaluate the potential impacts on surrounding areas. Thousands of elements are shown representing floodplain geometry, and computations are performed at each element.
The 2D models provide more detailed and accurate results than 1D models and contain graphic visualization features, which can better communicate modeling results and impacts to project stakeholders. 2D models eliminate many of the limiting assumptions required by 1D models.
Like traditional 1D modeling, 2D model results are only as good as the model inputs. Detailed survey of the channel, especially in the case of very narrow/small/less defined channels, is essential to capture the terrain data required for a 2-dimensional analysis. PennDOT hosted a training conducted by representatives from FHWA and the software developer, Aquaveo, in August 2019.
Project managers and engineers must effectively define and communicate project survey needs to the survey unit early in the project design.
Updates on projects utilizing 2D modeling:
District 1 – In Warren County, the bridge carrying State Route 4007 over a tributary of Little Brokenstraw Creek in Bear Lake Borough required 2D modeling to analyze and enhance the current hydraulic conditions of the proposed bridge. The project was selected due to a preexisting cross-pipe approximately 30 feet from the original structure and a nearby home located just near the culvert outlet. After modeling, it was determined that a larger cross-pipe was necessary to mitigate flow velocities. The bridge's construction was completed in September 2022.
"It gives you a lot of great data that 1D modeling isn't able to convey," said Senior Civil Engineer Supervisor for District 1 Matthew Antrilli. "It took a little time to get acclimated, but it was a great tool to use. I can see this becoming normal practice down the road."
District 2 – On State Route 1011 over the Genesee River in Bingham Township, Potter County, a permit and model were submitted to DEP in May 2022 and authorized the following August. Construction was completed in July 2023.
The project was selected for the 2D modeling pilot due to its proximity to nearby buildings, ponds and additional tributaries. Project managers report that the 2D method provided a more refined model, which allowed them to look at specific areas around the bridge in greater detail.
"All hydraulic modeling involves some level of interpretation and assumptions," said Senior Civil Engineer for District 2 Anthony Puccio. "While the 2D modeling can minimize the interpretation, it can expand on assumptions."
District 3 – Due to its complexity, a consultant was hired to draft a model of State Route 14 over Towanda, Tannery and Springbrook creeks in Canton, Bradford County. The four options modeled in SRH-2D provided the Borough with detailed analysis and enhanced graphics they could use to proceed with the option that was the most engineering and economically prudent. Currently, the project is in design and is expected to be let in February of 2025.
District 11 – PennDOT completed review of the model for State Route 65 over Bennett Run in North Sewickley Township, Beaver County, and the project was let in December 2022. Based on the potential overtopping behavior and project schedule, the culvert replacement project was chosen for the 2D modeling pilot.
"2-dimensional modeling produces much more detailed and comprehensive results compared to traditional 1-dimensional methods," said District 1 Project Manager Dominic Altieri. "The results also allow project managers and engineers to determine acute impacts flow may have within the floodplain."