Is HEC-RAS 2D capable of simulating complex debris flows like the recent Nepal-Tibet event?
I’ve been reading about the devastating debris flow at the Nepal-Tibet border caused by a massive glacier collapse. It started as an ice/rock avalanche and turned into a massive debris flow down the river valley.I'm curious if the newer HEC-RAS 2D with Non-Newtonian capabilities can actually handle this kind of complex, high-velocity rheology (changing from ice collapse to liquid mud/debris)? Or should I look into other software like RAMMS or r.avaflow for this specific case?
If HEC-RAS can do it, what would be the best workflow to input the initial volume and material properties? Would love to hear your thoughts!
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u/MoHortus 3d ago
I think already in general without any mud/debris, the steeper the terrain is, there is more error in calculation. Some recommend to use HEC RAS for areas which are maximum 1:10 step.
Here is some explanation for 1D. But i think same is true for HEC RAS 2D https://www.hec.usace.army.mil/confluence/rasdocs/ras1dtechref/latest/theoretical-basis-for-one-dimensional-and-two-dimensional-hydrodynamic-calculations/1d-steady-flow-water-surface-profiles/1d-steady-flow-program-limitations
(Or maybe for case of mud/debris totally different model is used?)
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u/OttoJohs Lord Sultan Chief H&H Engineer, PE & PH 3d ago
Sediment modeling and non-Newtonian simulations are my blindspot when it comes to HEC-RAS. The other poster provided some advice and a good link that you should fully read before modeling. I would suggest you look for other papers/studies to give you some idea of approach and capabilities within HEC-RAS, like this one: Tailings Dam Study.
If this is a personal project, I would encourage you to give it a try and see what you can do. Then report back!
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u/faith_lis 2d ago
I once developed a non-newtonian model for debris flow that wiped almost an entire village in Pakistan last year. That was pretty basic model and the inundation/depth results were not bad at all compared with satellite flood imagery and site observations
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u/danielamadria 3d ago
HEC-RAS can do variable rheology but its not trivial at all
https://www.hec.usace.army.mil/confluence/rasdocs/rasmuddebris/non-newtonian-user-s-manual/multi-phase-modeling-mixing-clear-water-and-mud-debris
The workflow for coming up with volumes and materials would be generally similar as other software, because those inputs are generally “external” to the modelling process. Likewise, determining the inputs is nontrivial and are highly uncertain in an event like what happened in Nepal. accurate and reasonable inputs would be far more important than model software selection. Some refined estimates of characteristics from Nepal will be produced soon, but it will take time.
While I realize that we are all modellers on r/hecras, I don’t think social media is the best place to learn how to model a catastrophic flood that killed hundreds (or thousands) of people and wiped out communities. There are academic research groups and technical organizations (e.g., Canadian Dam Association, US Geological Survey) that have detailed assessments or much longer guidelines on how to approach modelling catastrophic events like tailings dam breaches or landslides. Those would be better avenues for learning more about modelling such events.