User Forum of Software BASEMENT

flussbau-iC

User

Registered: 2016-04-05

Posts: 2

Outflow backwater

Hi,

I am currently modelling a riversite and made a boundary-condition for the outflow:

BOUNDARY {
                name           = Outflow
                type           = hqrelation
                string_name    = Outflow
                slope          = 0.5
                weighting_type = conveyance
}

Output:
SPECIAL_OUTPUT {
                type                = boundary_history
                output_time_step    = 100
                boundary_values     = (Q)
                flush_all_num_steps = 0

My problem is now, that there occurs backwater at the boundary, and not even at the time of the peak discharge. What makes me wonder is that it doesn't look strange in a graph showing the outflow-results of the boundary for Q; there, everything looks perfectly normal.

[Unfortunately I cannot post an image here, could use a little help for this thank you!]

Do you have any suggestions what the problem may be?

Thanks a lot,
Elisabeth

flussbau-iC

User

Registered: 2016-04-05

Posts: 2

Re: Outflow backwater

I think I found a solution:
I increased the slope to 5 %o, no more backwater occurs! But now the curve is really zick-zacking with an amplitude of 50 m³/s!? (peak for the Inflow is 40 m³/s)

Lukas Vonwiller

Developer

Registered: 2014-09-04

Posts: 130

Re: Outflow backwater

Hi flussbau-iC

The hqrelation with a slope gives you uniform flow at the boundary.
Therefore, backwater effects can occur in your domain depending on your slope you defined.

The problem with the zig-zag outflow discharge is still unclear to me.
Please explain this in more detail.
Plots or images can be shared with links, such as dropbox.

Hope this helps!
Best, Lukas