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Dear All,
since I'm quite new to two-dimensional flow modelling I have a more general question and hope you can help me.
I want to simulate the flow along a natural river stream which is constricted by abutments at one location and with piers in between the two abutments. I defined the scope of the model and have three boundary conditions:

1. An Inflow boundary condition with a maximum inflow of 2,275 m³/s,

2. An Inflow boundary condition with a maximum inflow of 760 m³/s,

3. An Outflow boundary condition with a water level of 440.0 m asl.

The domain is shown on the following screenshot:



At the inflow boundaries water levels of 452.0 m asl and 455.0 m asl are expected, respectively (derived from a quick and dirty one-dimensional simulation). This means the water level is 12 m and 15 m higher than at the outflow boundary condition.

What I want to simulate as initial condition is the situation that the main river channel (and maybe part of the floodplains) is filled with water (or at least wetted).

My question now is: How can I define such initial conditions which I can use to simulate as long as necessary to reach a steady state with the above listed boundary conditions?

I tried different approaches and none of them worked satisfactory. Those were, inter alia:

• Initial Elevation of 440.0 m asl: The major share of the domain is dry and there is no water at the inflow boundaries, which leads to a cancellation of the simulation due to problems at the inflow boundaries.
• Initial Elevation of 460.0 m asl: The simulation is aborted as well. I do not really know why. ( see my other topic: "Initial Elevation not maintained - Simulation aborted")
• Sloped Initial Elevation from 440.0 m asl (at the outflow boundary) to 455.0 m asl (at the inflow boundaries): Prepared by the use of Blue Kenue this initial condition also leaded to a cancellation of the simulation.
• Constant Depth of 3.0 m: Simulation cancelled. etc. etc

I hope someone can help me.

Best Regards
Heidi

Dear Heidi,

I would start with an inital water level of 460m asl and give a liquid boundary file with slowly rising Q for the inlets (starting from 0)and slowly decreasing H at the outlet (from 460 to 440m).

Best regards,
Gabi

Dear Gabi,
thank you for your reply. Actually, that is one of the approaches I tried as well (I just didn't list it). This aproach resulted in negative depths at the downstream end of the domain - propagating in upstream direction.

Regards
Heidi

Dear Heidi,

If there is that much water in the domain (about 20m!!); how can there be negative depth at the outlet after 20 time steps??


Regards,
Gabi

That's a good question. I don't know how this can happen. I guess it is a numerical problem or maybe a mesh problem. I'm not sure what is wrong.

Please find attached all my input files.

Regards
Heidi

Hello

Maybe you can try 450 or 452 m initial Elevation because this is in the range of your real Elevations upstream and downstream..

Have you tried with variable Time step?

Can you send your cas-file?

kind regards
Stefan

Dear steffinew,
yes I have tried an initial elevation of 452.0 as well and aslo I tried the variable time step. But still the simulation does not work satisfactory.

Please find attached my *.cas file.

Regards
Heidi

Dear Heidi

I don't see the definition of the boundary conditions like this:

/

---

/ EQUATIONS, BOUNDARY CONDITIONS
/

---

OPTION FOR LIQUID BOUNDARIES =1;1

PRESCRIBED ELEVATIONS =0;25

PRESCRIBED FLOWRATES =2280;0

VELOCITY PROFILES =4;1


I am a fresh user of Telemac and maybe cant help but I also use the keyword
CONTINUITY CORRECTION =true

kind regards
Stefan

Sorry, I think the boundary conditions are defined in your liquid boundaries file, did not see this...

Dear Heidi,

as JMH suggested, I would start from a cas-file of a test case. I also attached one of my cas-files for a flood case with mesh sizes of approx. 1-5m (including flow over Weirs, therefore the low time step). You can increase the time step depending on your mesh-size. The TYPE OF ADVECTION keyword has been changed in v7p1 or v7p0, I have it still in my file due to compability.

You find the description of the keywords and the Default settings in the Manual or in telemac2d.dico in your sources Folder (C:\...\v7p1r0\sources\telemac2d or something like that).

Best regards,
Gabi