modeling with HEC-RAS. As mentioned, the project area had bridges overlapping other bridges. If we’d used HEC-RAS for Lynch Creek, we would have had to combine structures in the model, overlapping the bridges to complete the picture, but it wouldn’t have given us the infor- mation we needed. There would be parts of the model where we would have had to make assumptions about water flows. When it comes to determining the structural integrity of a bridge, guessing won’t cut it. For example, a 1D model would be able to show the velocity of a water flow but not the vector. That is, it can show the force of the water but not the exact location it will affect. With a 2D model, we’re able to see both the water flow velocity and a vector, which is vital in determining whether a bridge is scour critical.
ing a model to the public and clients. The 2D model below shows the velocity contours and vectors for a bridge during a 100-year event. It clearly depicts the topography and structures, as well as the water flow and intensity. This provides and easy-to-understand visual that hydrau- lic engineers can use to explain their findings to clients and the public. The 2D model of a project provides a much better tool for engineers to explain their work to the public and clients than the HEC-RAS images, which simply feature lines.
While 2D modeling has numerous advantages over 1D, development and adoption of this technology has been slow. Given that HEC-RAS is free and easily available to the public, it has been ingrained in the industry as the standard for modeling. Nevertheless, the future of hy- draulic modeling is two dimensional for two reasons—it’s easier and can handle much more complex issues. Our team adopted a 2D-modeling program because it was essential to completing a project and, in the process, we discovered that the tech- nology has the potential to revolutionize hydraulic engineering. The program generates highly interactive models that allow engineers to learn more about a project area while making it easier for those outside of the industry to understand the findings. Beyond scouring, 2D modeling has applications in flood-plain model - ing for rivers and streams, as well as roadway hydraulics. The technol- ogy is finally available to make these programs a reality. It’s only a matter of time before they become the new industry standard. The 2D model of a project provides a much better tool for engineers to explain their work to the public and clients than the HEC-RAS images, which simply feature lines.
Simplified, customizable modeling 2D models aren’t only easier to understand, they are easier to create. In HEC-RAS, you need to make several assumptions with ineffective areas, such as bridges and culverts, where flow is not conveyed. These are educated guesses, of course, but guesses all the same. HEC-RAS also requires the input of a significant number of variables, all of which can have different interpretations depending on the engineer. For ex - ample, to add one building into a model, hydraulic engineers need to take several detailed measurements and enter multiple coordinates for different parts of the structure. Once entered, the program still only shows a sliver of the actual building in the final rendering. Thus, the program requires a great deal of work to generate a model and the final product isn’t necessarily 100 percent accurate. Each bridge pier in HEC-RAS requires an engineer to manually input its dimensions. With 2D modeling, you simply draw what you see. The program allows you to draw the footprint of the pier, which is often supplied by the survey files. This streamlines the modeling workflow while also providing a more accurate and detailed model. Improved client and public engagement If you use HEC-RAS models on a regular basis, you understand the 1D renderings. One of the biggest challenges with any project is explain - A 2D model inserted over an aerial image of the Lynch Creek bridges. This shows the exact angle and intensity of the flows attacking each pier and pillar, which provides a more accurate result.
WHIT HAWKINS is a hydraulics engineer with Stantec.
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June 2021
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