Well, actually I am looking for a dam-break study which show the simulation of the dam during breaches. Unfortunately, I only see simulation with high flow in many online website and youtube. That's not a dam-break simulation.
First, there shall be a description on how to simulate the dam-break using HEC-RAS. What are limitations of software and simplified assumption. Let's talk about a real case of dam-break. Dam-break could happen due to failure of its embankment structure either due to overspilling or piping. For low-dam structure, overspilling is possible as it was not designed in high safe level. For high dams, piping failure is more common occurred.
After, we have decided what kind of failure that we will simulate, the next step is to build dam breach size and time. How big the dam breach and when it progress until it totally breaches. An example of dam breach parameters and time progress to breach can be seen below:
https://www.hec.usace.army.mil/software/hec-ras/Ok, remember in any dam, it always any spillway structure for emergency. It means when flood occurs the high flow will go to spillway structure. So, you need to model spillway structure as a weir and breach parameters along the embankment.
The example above is sine wave progression of breach. Normally the breach progresses constantly until it reaches maximum and start to breach total. That's why in many cases, it was simulated in sine wave progression. Of course, you are free to choose linear progression.
Once you have done with the breach parameters setup, it is important to set the geometry of the dam and 2D flow area. It can be set as 2D connection between storage and 2D area. In the example below, I set 2D connection within 2D flow area. It means the simulation will be in totally 2D. If you use connection from storage to 2D flow area, it will simulate the storage first which I don't really interest on it. So, remember to take the inflow directly from the outlet of the dam.
You may have error messages when you started to run. In my case, the error is : "has a weir elevation lower than the cells they are connected to". The error is obvious that your weir levels some are lower than the 2D elevation levels. What you need to do is change the weir elevation higher. Make sure all are higher. As my original weir levels were determined from terrain levels, there will be slightly different due to interpolation and cell size matter. The easiest way is just copy the weir levels and add with roundup formula in excel.
If no error messages again, you can see that the model is running again. Wait until it finishes run and check the results. Make sure that everything is make sense and as what you wish for.
The last but not least is to check the results. This is the tricky part. You have at least understand the concept of hydraulic. Imagine how much flow it is and where it flows and whether the process from low to high to breaching time all are make sense.
If you are just focusing on maximum values, it could be enough. But I like the process where the starting point, the progress and final flood maps shall be acceptable. In some cases, you may need to refine your 2D meshing area and cell size.
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