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Re: Boundary condition not respected in steady flow analysis
If the stream water surface is the same as the lake and this water surface is below critical deth, then the flow is supercritical at that location.
For steady flow, the program can not do the subcritical [downstream to upstream] backwater starting from supercritical flow. So it starts at critical depth and goes upstream. However, if the flow really should be supercritical, and the user has the mixed flow regime flag checked, the program should, in theory, get the supercritical answer when it does the [upstream to downstream] supercritical pass. If it doesn't, then it probably means that the flow wasn't really supercritical. But in either case, it does not take any more work for the user.
Unsteady flow will allow you to enter (and use) a supercritical downstream water surface. However, if the flow really shouldn't be supercritical at that point, then you can get wild and bad answers.
Even if the downstream boundary really is supercritical, unsteady flow struggles to get good results with a downstream, supercritical boundary. In general, it would be better to find some location that was subcritical (or at least, at critical depth).
Actually, I have found that unsteady flow does a poor job in general with supercritical flow anywhere. However, checking the mixed flow flag does seem to help.
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