User Forum of Software BASEMENT

Matthias

Advanced_User

Registered: 2014-12-16

Posts: 29

Bedload simulation with fixed bed

Hi everyone

I am trying to run a bedload simulation with a fixed bed.

My default layer thickness is -20 m. I tried various approaches to get a "fixed bed" where the bed does not erode below the initial geometry but there may happen deposition along the way.

My approaches were:
- 1. reduce layer thickness to -0.001 m
- 2. delete the "Layer" Block in the Soil_def (it says a fixed bed is then assumed)
- 3. delete the Soil_Defs in the geometry at each cross section

The results of 1 and 2 are identical to my default setting with a layer thickness of 20 m (erosion and deposition happening) and with approach 3 I get no erosion nor deposition in my model.

What would be the right approach to run a simulation with the above mentioned condition?

Thank you for your help

Best regards
Matthias

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Bedload simulation with fixed bed

Hi Matthias,

as you can read here: http://www.basement.ethz.ch/docs/doc_BA … .3.4.2.3.1

"The LAYER blocks have to be defined ordered by their relative height to the surface, from the uppermost layer to the lowest layer. The bottom of the lowest soil layer automatically defines the fixed bed."

About your proposed solutions:

1. and 2. are respectively very close and the same as fixed bed. Using 1mm layer thickness means that the material that can actually be transported is few so after few time-steps you will have a fixed bed, but no sediment transport. On the other hand, as you said, deleting the Layer Block gives a fixed bed. It is strange to me that these two options give the same result as the 20m layer you have as default.

With your third option you just delete sediment transport, so you won't have erosion or deposition.

If your goal is to simulate sediment transport on a fixed bed my suggestion would be to use one of your first two options, but setting also a sediment discharge at the upstream boundary condition or at a defined cross section. If you don't set any sediment source and your bed is fixed you won't have any erosion or deposition.

I hope this helps.

Best regards,

Matteo

Michi

User

Registered: 2015-04-20

Posts: 3

Re: Bedload simulation with fixed bed

Hi there!

I've got the same problem as Matthias.
I tried his approach nr.2 but I got strange results when looking at the sed.txt-file at it's last timestep.
I am getting very low Active Layer thicknesses. For example a layerthickness of 1.79674e-009 m at cross sections with no deposition. (If layers would be set, it should be 0,2 m.) On another cross section I am even getting small erosions!? Why?

Why can there result a layerthickness?
Automatically when there exists a layer, grainsize is varying although it shouldn't, becuase I fixed my bed in the way of approach 2 from the upper beginning of the modell. I've set a sediment discharge at the upstream boundary but the grain sizes are varying within the fixed sections!?

Do you have any idea how to fix bed correctly. I have to restart my model with the SedRestart.dat file an I do not want to continue with this wrong grain sizes.

Thank You and Best Regards
Michi

Michi

User

Registered: 2015-04-20

Posts: 3

Re: Bedload simulation with fixed bed

Hi again!

Another question: Where can I see volume fraqction (grain size) of the deposition which results on a fixed bed? The deposition,which I can find in the out-file, is not expressed in the resulting small layerthicknesses of the blocked cross sections!?
Thank You and BYE
Michi

Michi

User

Registered: 2015-04-20

Posts: 3

Re: Bedload simulation with fixed bed

Hallo again!

I have changed to the new version 2.5.
Now I can't restart calculations with fixed bed. It turns up an error or warning like " No sublayers are found".
But I don't want to have sublayers. I don't want to have any layers! I want to fix bed because I want to stop interaction between incomming grain an soil! This is the way it works in nature, so we assume. Is there anything wrong with my methode?

Thanks everyone
Michi

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 281

Re: Bedload simulation with fixed bed

Hi Michi!

Could you please attach as image (or copy paste) the log files of the two simulations you run? I mean the one that you use to generate the restart file and the one in which you actually use the restart file.

This would be helpful to understand if there are some errors in your BASEMENT files.

Thank you very much!

Bests

Matteo