Hey RAS Users. HEC just put out this very informative document that helps and guides the modeler with the decision between building a steady versus unsteady model, as well as when to go with a 1D, 2D, or 3D model. Modeler Application Guidance for Steady vs Unsteady, and 1D vs 2D vs 3D Hydraulic Modeling. […]
Situation: Advances in HEC-RAS now allow for improved simulation of overbanks using 2D Flow Areas. Coupled 1D/2D models where 1D cross-sections represent the bank-to-bank cross-section data and 2D flow areas represent overbank areas has greatly improved the accuracy and robustness of HEC-RAS models. This is particularly the case in flat, urban areas with significant overbank […]
This question (or some variation of it) comes up quite a bit on The RAS Solution: “I have an unsteady flow model. When I run it, it goes completely unstable. What is causing this?” Many times a screen shot of the computation window with the dreaded “red bar” is attached. While the person asking the […]
The new 2D features and mapping tools are the most anticipated new features in HEC-RAS 5.0. However, HEC also added a couple major new sediment features, as well as many minor features and a few substantial bug fixes (e.g. SI Units). The two major features are the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM) […]
Check out this great RAS2D presentation that Kevin Denn gave at the NHEC Conference last week.
As a follow up to the just-posted Critical Depth Primer, I want to share a trick for getting HEC-RAS to compute and display critical depth at every cross section for unsteady flow. As I mentioned in the previous post, if you are running a steady flow model, there is an option to have RAS compute […]
Another simple, yet very convenient tool not found discussed in the manuals is the ability to zoom in on one of the axes of a graphical plot. This is especially useful when trying to determine if you’ve captured the true peak discharge in a steeply rising hydrograph. Take the following example: an unsteady flow dam […]
Lateral structures can be used in HEC-RAS to transfer flow from a river/reach to a storage area, or to another river/reach. With the coming release of HEC-RAS with 2D capabilities (estimated beta release January/February 2014), you’ll be able to hook a river/reach to a 2-D area using a lateral structure. Although its primary function in […]
One of the most frustrating aspects of unsteady HEC-RAS modeling can be the model stabilization process. You know, you’ve gone to great lengths collecting the best survey/topo data and solid hydrology. Then you’ve painstakingly spent hours…possibly days entered all of that data only to find that once you press the “Compute” button, the model crashes. […]
Hi everyone. For those of you who are HEC-RAS dam breach enthusiasts, I will be teaching a 3-day course on dam breach modeling with HEC-RAS in Boston in a few weeks. The course will be held next to the historic MIT campus overlooking the Charles River and downtown Boston, May 1-3. In this course you’ll […]
What are the implications of having a cross section that is too short and doesn’t extend all the way out to the highest computed water surface elevation? Does it affect the results? Take this cross section for example. It is missing much of the left overbank (presumably). Image courtesy of Adam Bohnoff First of all, […]
One of the limitations of HEC-RAS is that it is a one-dimensional model. Simply put, RAS assumes all flow moves along a singular dimension. For a given cross section, all of the flow is assumed to move either downstream, or all of it moves upstream, along the singular dimension (which can be defined as a […]