open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

we are modelling reservoir flushing with TELEMAC internally coupled with SISYPHE. This week we found out that SISYPHE is generating some bed load input at the inflow - but we did not use the conlit file and specified no sediment input.

We integrated the incoming sediment and found out that is may correspond to the sediment transport capacity derived by the MPM formula (about 79,5kg/s over the section with a discharge of 300 -400m3/s).

We solved this in one case by using the conlit file and setting the sediment inflow for all fractions to 0.

But my question is: Where is this sediment input coming from?

In another case we used rigid beds at the river bank. But after 1800 iterations with a timestep of 1s we got erosion at 3 nodes in the area of the rigid bed (-8m !). How can this happen?

Many thanks for any hint,
Gabi

Hello again,
1) what are you looking at is probably the sediment transport capability computed by some of the implemented sediment transport formula.
2) are you sure that your rigid bed zonification has been implemented correctly? please take a look to some of telemac2d's examples...

best,

Pablo

Also hello again,

1) no, we have sediment inflow in the first nodes (at the boundary). We also checked the integrated volume of the evolution in the inflow section. The depositions are much higher than the erosion. If there would be no sediment inflow, the total volume of deposition must be smaller or zero.

2) I am pretty sure, I also checked the Rigid bed zone in Blue Kenue (export of the variable RB in SISYPHE). The ZR value was correct for these nodes.

We used a previous computation file with the implemented rigid bed, could this be the problem? We usually prepair these "start" files before sending the computation to the cluster and never noticed problems.

Thank you very much,
Gabi

Hi Gabi,

I assume you have set the boundary condition for the sediment to zero using
EQUILIBRIUM INFLOW CONCENTRATION = NO

If not, SISYPHE is likely to calculate the transport at the boundary to saturated values using the grain sizes used in the model (ignoring the fact that the bed is non erodible there.

Dear Mafknaapen,

thank you for your answer, but we are dealing only with bedload. The EQUILIBRIUM INFLOW CONCENTRATION is just for suspension.

Best regards,
Gabi

Thanks for clarifying this Gabi. I realise I was stating the obvious (and missed the fact that you are using a total load /bedload formula.

I suspect this is a bug, but am in contact with Pablo to see if I misssed anything in the code.

However, if you want, you can try copying
bedload_solid discharge.f to the prinfi-file and
to comment out the following lines:

DO I = 1 , NPTFR

IF(LIQBOR%I(I).EQ.KENT) QSC%R(MESH%NBOR%I(I)) = QBOR%R(I)

ENDDO

Michiel

Dear Michiel,

thank you for this solution. I will try it.

Best regards,
Gabi