Have you ever looked at your profile plot from an unsteady flow model and found “walls of water” on top of your bridge? Or just unexplained unrealistically large amounts of energy loss over a bridge? Take this for example: Notice the three large “steps” in energy grade line (and water surface elevation). It’s hard to […]
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. […]
A very convenient way to troubleshoot instability problems with very complex models is the use of a hotstart run with a stepdown scheme. Creating a stepdown scheme hotstart plan is covered in detail here. In a previous post, I explained some problems with running the stepdown scheme when you have bridges. Here I want to […]
An advantage of running a step-down scheme hotstart run is the ability to spatially evaluate stability issues with difficult reaches. One of the elemental features of the step-down scheme is the artificially raising of the downstream boundary during the hotstart simulation to “drown-out” the reach and effectively create a very stable environment. During the hotstart […]
I’ve mentioned this a lot in this blog, but I’m finding more and more that a good, solid definition of your HTab parameters up front will go a long way in helping construct a nice stable unsteady flow model in HEC-RAS. First, let me recap how they work. In unsteady flow, HEC-RAS will convert the […]