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Hi all,

I am simulating effluent releases from a number of sources on a beach over a few tidal cycles.

Due to the small volume being released and the relatively flat topography of the beach, on the ebb tide when the beach is 'dry', the released effluent is spread out over a large area in a thin film (in the region 0.001m or less), which results in a very (unrealistic) high concentration of bacteria.

Is there a way to force the model to discount tracer below a certain depth?

Hopefully these images help explain my problem.

Water levels on ebb tide showing area of depth > 0.05m:



Including overlay of tracer:



In reality a small portion of the release travels down to the waterline in a stream (I appreciate that without making further adjustments to the mesh or other it isn't possible to model this) or just infiltrates into the beach sand disappears. The later is what I want to simulate so when the cell is below a threshold depth (i.e. 0.05m) to ignore the input from the source point.

Thanks
Jonathan

Hi Jonathan,

EDIT: Ups, didn't notice this was the T3D sub-forum. I'm not sure if this exists for T3D too... I'm leaving this just as a failed attempt to help.

You could try to define the (small) water depth theshold necesary for "motion", in telemac's keyword lenguage a.k.a : "TRESHOLD FOR RECEDING PROCEDURE", which could prevent that small ponds generate those thin films and hence decrease the total area affected by the effluence (which is maybe an input for the "bacteria concentration" model?).

This is an emergency procedure in dykes modelling when re-meshing is not an option, JMH mentions it works for tracers too. Small values like few centimeters generally are enough, please check this discussion for further info.

regards,

José Díaz.

Hi Jose,

Thanks for the tip but unfortunately that keyword isn't in TELEMAC 3D.

I would have thought that the keywords set below are for this purpose but they are activated as such in my case but I still get the problem mentioned.

TREATMENT ON TIDAL FLATS FOR K-EPSILON = 0
TREATMENT ON TIDAL FLATS FOR VELOCITIES = 0
TREATMENT ON TIDAL FLATS FOR TRACERS = 0

Does anyone else have any ideas?

Thanks
Jonathan

Hello,

There is nothing automatic and these keywords are not active at the moment (they would cast some doubt on mass conservation). I would say that you enter bacteria AND water, so this gives a concentration, and this concentration normally cannot increase, so what you find in the model is the data you enter. I would suggest to stop releasing bacteria when you are under a given threshold of water. I would suggest that what you are asking for (clipping high values) should be done only as a post-treatment not interfering with what does the model, e.g. drawing the concentrations within a given range only. It could be done also at the level of preres_telemac3d, substituting a corrected variable only to print it in the results file.

With best regards,

Jean-Michel Hervouet