User Forum of Software BASEMENT

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

simple channel with weir DS boundary

Hi

I am modelling a simple rectangular channel in 1D (sections every 1km) and a fixed slope, with a weir as downstream condition. I need to have the weir about 20m high, creating a lake upstream. I started with a very low weir, and I am trying to gradually make it higher, however I keep getting into unstable conditions hydraulically. I tried both standard and critical for the calculation type, but either seem to fail. I started with a low flow of 85m3/s, now I am working with a 300 m3/s, which seems a bit better.
So far I managed a stable condition with a weir of nearly 5m. But each time I need to start going slower or it becomes unstable.
I am not sure how I can do this better? Or should I make it even slower? It seems to be taking a lot of time.

I tried other options such as zhydrograph, but I had even worst stability problems.

If there would be better options, or how to improve it, let me know.
I need to create a sort of lake while the sediments must be able to pass.

Thanks!

Alyssa

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 286

Re: simple channel with weir DS boundary

Hi Alyssa,

I am not quite sure what you are trying to is feasible, but I would try to put the weir somewhere far from the downstream boundary condition, to lower the instability. That is, try to build a channel downstream of the weir to dampen the boundary instabilty.

Best
Matteo

Alyssa

User

From: Aix-en-Provence, France

Registered: 2019-10-28

Posts: 41

Re: simple channel with weir DS boundary

Hi Matteo

Thanks for the advice. It is what I did in the end, with an inner boundary dam far away. with the downstream boundary condition it doesn't work.

best wishes
Alyssa