Fish bypass (looped system) running unstable (RAS 4.1)

[AWPOLLARD]

Hi,

I am fairly new to HEC-RAS so I maybe making a simple mistake but any advice or help somebody could give me that would be great.

I am trying to model a fish bypass that departs from the main channel joining again 63m downstream. The channel is very small capacity (2m wide, 0.5m high) relative to the main channel

There is no control structure to the fish pass so I have included just two junctions, one at the exit from the main channel and one at the re-entry. Do I have to do anything special for the junctions?

The model will run steady and unsteady without the bypass and steady with it but immediately goes unstable when running unsteady with the bypass.

Again, any advice would be great,

Many thanks

[Anonymous]

If an unsteady run is going unstable immediately, increasing the number of warm up time steps will sometimes help (from unsteady run editor> options> calculations set warm up steps to a large number like 1000).
If you have the option, you might see if it works better with the new 5.0 release.

[Anonymous]

Thanks Jarvis, i did increase the warm up time step the max it will allow which is 200. I cannot help thinking the fault maybe with the junctions although the work fine as they are in a steady run. Do you think a lateral weir maybe worth a try or is the problem likely to be elsewhere?

Many thanks

[Author]

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