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Hello,

I'm using two kinds of liquid boundaries in my Telemac2D Model. One is the sea boundary with imposed water levels and the other one is the river boundary with prescribed constant discharge 99 m3/s.

However, the river boundary seems not working very well because in the result I have a variable called SCALAR FLOWRATE in which the values at river boundary were zero.

I'm wondering what is the right way to impose discharge at river boundary?

For my case I used keywords
PRESCRIBED FLOWRATES = 99.0;0.0
VELOCITY PROFILES = 4;0
to impose impose discharge at river boundary.

Thanks in advance!

Hello,

The first thing to check is whether your river boundary is boundary 1 or 2. You can see it in the boundary conditions file, the first boundary is the one that appears first in its entirety in the list of points.

Then check what is said in the listing, that should give the fluxes accross every boundary (if it is correct here this would be a problem with the SCALAR FLOWRATE variable).

With best regards,

Jean-Michel Hervouet

Hi,

As far as I understand the river boundary is liquid boundary 1 because I prescribed different values of the tracer at these boundaries and they had the right values. So I think the this is not the problem.

PRESCRIBED FLOWRATES
MOTREA( 34)= 99.00000

PRESCRIBED FLOWRATES
MOTREA( 35)= 0.000000

I looked at the printout of the telemac2d and I found the flux at boundary 1 was changed over time. To be more specificly, it was decreasing from 98.1 m3/s at the beginning to 66.8 m3/s at the end. It's not constant...

Hello,

I am not sure that the discharge will be exactly 99. because the velocities are based on a depth at the old time step, but 66.8 would imply huge changes of the depth in one time step, this is very strange and tells that something is wrong. I assume that depth is free at this boundary, that's what it should be.

JMH

Hi,

Yes, you're right. The depth was supposed to be free at this boundary.

I'm sorry that I didn't say it clearly. 66.8 m3/s was the the value of discharge at the end of simulation which means 10 days after the beginning.

How can I use a constant discharge at this boundary?

I think I should use the fixed water depth at this boundary so the discharge will be constant, should I?

No no, a free water depth is correct if your boundary is fluvial (I mean Froude number less than 1). So the variation of the discharge at this boundary is not normal and this is a problem somewhere, to my opinion it can be explained only by strong variations or oscillations of depth at this level. Check if you have dry zones on this entrance (and if you declared TIDAL FLATS : YES if you have dry zones, this could be a hint), try a simpler velocity profile (1 for example), but well that cannot explain the problem, there is certainly something else.

JMH

Thanks for your advice!
I have dry zones on this entrance. Now I'm trying the velocity profile 1. I will post my results when it finishes.

Well, dry zones should not prevent you from getting a correct discharge (but TIDAL FLATS : YES is necessary), however dry zones means that you may have a supercritical flow at some points of your entrance, which is not well posed if depth is free (though many people do that and have no problem). Velocity profile 5 instead of 4 may give a beter result and will clearly not enter water on dry zones. Unlike what I said and because you have dry zones, velocity profile 1 will put velocities on dry zones, which is not very good.

JMH

Thanks. But in the dictionary file I didn't find the fifth option of the velocity profile. There are only four options which are

1:constant normal profile
2:u and v given in the conlim file
3:normal velocity given in ubor in the conlim file
4:sqrt(depth) profile