1d-2d model instability problems

[belis Kal]

Hi, i try to build a 1d-2d model as shown in the picture      https://drive.google.com/file/d/1sMocR43ZXQK8aiO9VrcPIoR9dVa6bkff/view?usp=sharing.
The structure of the model is : 1d geometry → 2d flow area with 2 dams → 1d geometry. The model runs quite well but the total volume accounting error is 95%. I have noticed that water does not pass to the final 1d geometry at all, but i can’t figure out the reason. I have also noticed that if i delete the upstream 2d flow area the error drops to 4% and water flows normally. Also big discharges affect the error percentage. I can’t understand why this kind of model I try to build is so sensitive to small changes and depends so much on the structure or the flow hydro-graph. I would really appreciate any recommendations on the parameters that may affect the stability of the model, and any hints to directly connect 2d flow area to 1d geometry. I start thinking whether i should change my structure and build the conventional way : 1d geometry + lateral structures everywhere in the river.

thanks in advance

[Luis Partida]

The connection from 1D to the 2D flow area…are you separating them with a 1D storage area? Same with the transition from 2D flow area to 1D geometry downstream?

That alone improves stability greatly

[belis Kal]

No, I just use 2dflow areas. Do I have to use storage areas in the connection?

[Luis Partida]

Yes it is HIGHLY recommended, connect the 1d reach to the storage area and connect the 1d storage area to the 2D flow area via a SA/2D conn. Add an initial depth in the unsteady flow data editor for the 1D storage area that will create a realistic starting WSEL

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