problem with channels in 2D

[ckatsoulas]

I am having an issue in 2D when introducing a channel with a vertical drop. I have a flowpath that I’m trying to intercept with a channel around a structure to reduce the flood level rise that is caused by the structure. The issue is that, when I include the channel, it seems to have capacity as it is not full, however, it still shows an increase in flood level upstream that would not seem realistic. I expected a drop in the flood level since the flow over the edge is at critical depth causing draw down into the channel.
I have provided an image showing the flood rise (red colours) and fall (blue) upstream of the small structure. The red line is the location of the cross section and the cross section shows the change in the flood level with the channel and without the channel.
LEGEND:
D.Blue -flood level with channel
Red -flood level without channel
orange -ground level without channel
cyan -ground level with channel

The second image shows that without the channel there is only afflux behind the structure. Note there is a major channel behind the small structure and further south there is also a small vertical drop across the boundary.

[ckatsoulas]

Sorry I should have added, has anyone had this problem before and can someone shed some light as to how I could fix this issue without the use of a 1D channel.

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