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P McAteer

14/03/2017 10:26:34

Good morning - I have an overflow reservoir linked to a 1D channel via a spill. When running the 1D - 2D model, I receive this warning:

'Sending lateral inflow to unit S6 with no d/s unit - sending to upstream unit S5 instead'.

Both S5 and S6 are in the main channel. The warning occurs when rising river levels meet the invert of the spill. Immediately downstream of S6 is a junction with two outlets, the 1D channel (s7) and the spill linked to the reservoir. As there appears to be nothing wrong with the 1D model, should I assume that the problem lies with the link between the spill and the downstream reservoir? Altering initial water levels in the reservoir appears to make no difference.




14/03/2017 12:13:05


Unless I've misunderstood your description of your setup, I think the issue here is as follows:

Lateral spills connected to an open channel section are trying to add/remove water from the reach between the connected open channel unit (here S6) and the next downstream open channel unit. In your case, you don't have a next open channel unit downstream, you have a junction. From that message, it would seem that FMP is managing to accomodate your schematisation by letting the spill add/remove water from the open channel reach between your connectted section (S6) and the next section upstream instead (S5).

And if the above is a correct reading of your schematisation and that message then I'd like to add an expression of my surprise, as this sort of setup has historically always resulted in a simulation failure; this apparent ability to decide to take flows from the reach upstream instead is new. Perhaps one of the devs would be kind enough to comment?

P McAteer

14/03/2017 13:37:52


I think you have understood the setup correctly. The setup is is intended to model a lateral spill between S6 and S7, and is connected to a junction only because I couldn't work out how to connect it to the channel any other way. You seem to be suggesting that this is not the correct method? Whether FMP then assumes that I intended the spill to be between S5 and S6, I don't know, although that seems to be what the message is saying. My query originally arose because there shouldn't be any flow into the channel - only from the channel into the reservoir via the spill.



14/03/2017 14:21:23

Ok. Well, to address your original query first then, the message may be saying "Sending lateral inflow to unit..." but all it means is 'there is flow exchanged' here; the flow that is "sent" could readily be a negative flow. You said this message first occurs when levels in the river exceed the spill level, so that all sounds about right to me.

As regards the connectiviy of the spill, if you're looking for flow over-bank between S7 and S6, then you should just need to add your spill node lable (the one that's not connected to your reservoir) into the "First Spill Label" box in S7 (and remove it from the junction). However, if that's not working for you, then it may well be sufficient to have it connect to the junction as levels there may be close enough and representatove of the levels in the channel just upsteam; this will depend upon how much gradient you have you on your river.

HJope that helps!

P McAteer

15/03/2017 09:31:45

Thank you for your responses, they are very helpful. However, the warning recurs almost 200,000 times, so that is concerning. I will try again to connect the spill directly to the section to see if that helps - previously when I have tried this, the model runs as expected except that there is no flow over the spill.

Thanks again.

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