Rating Curve issues

[Simon Roberts]

Hi everyone,

I’m having some issues with my rating curves after running a model, it’s a shame I can’t post a screenshot if the issues but I’ll try and describe as best as I can.

I have a small reach I’m modelling ~450m with a single bridge along the reach.

I’ve managed to import cross sections from a survey and I’ve been able to couple this to 2D areas with varying Manning’s n roughness which is exactly what I was after.

I have good volume balance <1% and the cross section plots and profile plots all appear smooth.

However, when I check the rating curves, there are quite violent oscillations present on pretty much all the cross sections upstream of the bridge. Does anybody know why this could be? I appreciate it is difficuly without chekcing the model. I’m happy to share the files with you if that would help?

Any help would be greatly appreciated.

Thank you.

[Luis Partida]

You need to have a look at the HTab parameters of the structure, the internal and bounding manning’s values as well. By adding any information in the Htab parameters that states (recommended), this helps dial in a smooth convergence at the structure

[Simon Roberts]

Hi Luis, thanks for the response.

I’m now re-building the model, and have looked at the HTab parameters of the bridge and the cross sections, also looking at the conveyance curves to make sure they are smooth.

I have imported my cross sections and have now run a 1D only model of just the channel, and I’m still getting oscillations in my rating curves. Is this a sign of instability? I’ve tried changing the location of the bank markers, and the number of points and increments in the HTab parameters but nothing seems to work?

Thanks!

[Simon Roberts]

I’ve just had a look at the ‘Bald Eagle Creek’ example that comes with the software and the rating curves on this are oscillating too, maybe I’m reading too much into it?

[Luis Partida]

Hi Simon, I wouldnt say Oscillating rating curves is an instability as long as the output hydrographs AND stage does not have oscillations. If the hydrograph and stage oscillate, attention should be brought to the computational time step (either decrease or increase)

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