At a time when climate change has made weather events more severe and unpredictable, hydraulic flows can have a serious impact on com - munities and infrastructure. Understanding and predicting the effects can prove difficult. In working to develop designs that help commu - nities adapt and become more resilient against such risks, engineers seek to answer these questions using hydraulic modeling technology to analyze the impact of water flows. Yet the technology available today remains deficient when it comes to modeling complex terrains and infrastructure, which can cause uncer - tainty when trying to implement lasting solutions. In response to this challenge, we adopted a two-dimensional (2D) modeling software that would give our team and clients more accurate and actionable informa- For decades, creating hydraulic models has meant using a program called HEC-RAS, which creates 1-dimensional (1D) renderings. De - veloped by the Army Corps of Engineers in the late ’90s, the program became the unofficial industry standard for hydraulic modeling, as it is free and easily available. At the time it was released, HEC-RAS was the first system that could create a visual model of water flows, allowing engineers to create basic stream and hydraulic models. tion to solve these complex issues. Bringing in a new dimension Completing the picture: The future of hydraulic modeling is two dimensional 2D modeling brings more clarity to the impact of hydraulic flows on critical infrastructure. By Whit Hawkins
The release of HEC-RAS gave hydraulic engineers the first visual rep - resentation of hydraulic flow, albeit in thin, 1D slices. It gives a more user-friendly method of modeling basic streams and flows that is easier to understand than a HEC-2 numerical read out. When working with complex terrain, however, creating models with HEC-RAS can be a challenge and, in some cases, almost impossible. This was the case on a project for the Mississippi Department of Transportation (MDOT). Our project team was tasked with determin - ing whether three sets of US Interstate 20 bridges that cross Lynch Creek in Jackson were scour critical—that is, figuring out whether they would withstand a 100-year flood event. Bridges that are scour critical are at risk of losing structural integrity during heavy flooding and could collapse. For a project with a single bridge, HEC-RAS would work well. In this case, however, we had to model bridges that ran underneath other bridges. Because a 1D model only displays a small slice of the area, it would be incredibly difficult, if not impossible, to complete a model using HEC-RAS, as it wouldn’t accurately detail the affect water flows have on the structures. So, we decided to do something completely different for the Lynch Creek project—we went 2D. We needed a method of modeling that could generate an aerial view of the project area so we could better understand the impact of a major flood event on the three bridges. This required a tool that would let us create a 2D model. Advances in computer technology and processing power allowed us to implement a 2D modeling program into our tool kit, something that simply was not possible 20 years ago. 2D modeling allows us to cre - ate more complex topographies that provide more information and are easier to understand. Compared to the HEC-RAS model above, here is what a 2D model looks like:
A HEC-RAS model, left, compared to HEC-2 numerical printout.
Visualizing velocities In project areas like Lynch Creek, there are serious challenges in Here we can see a complete view of the terrain, the bridges, surrounding structures, and the creek. Though in its infancy, 2D modeling technology represents the future of hydraulic modeling with significant benefits over HEC-RAS.
While providing a basic visual, the HEC-RAS technology offered a significant improvement compared to earlier tools. Prior to its release, hydraulic engineers had to rely on a system called HEC-2, which gen - erated a numerical printout and 1D model with minimal details.
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June 2021
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