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Dear all,

I'm trying to simulate sediment transport in a river considering both suspended load and bed load.But the diameter distribution for suspended load and bed load is usually different,how can I define it in the file? Thank you.

Hello Ding,

it is not possible to have a different behavior between the sediment classes if you have non cohesive sediments: the bedload or the suspended load once activated, they are applied to all sand classes.
So if you declare 2 non cohesive sediment classes (i.e. 2 different diameters etc.) and you want to use suspended load and bedload, they will be applied to both classes and it is not possible to associate a different transport mechanism to each class.

On the contrary if you want to model bedload with a non cohesive sediment and suspended load with a cohesive sediments, this is possible.
You can find in the reference manual (which corresponds to the GAIA's dictionary) the corresponding keywords.
Here some hints:
CLASSES TYPE OF SEDIMENT: NCO,CO
CLASSES SEDIMENT DENSITY = XX,XX
CLASSES SEDIMENT DIAMETERS = XX,XX
for NCO part:
BED LOAD FOR ALL SANDS : YES
BED-LOAD TRANSPORT FORMULA FOR ALL SANDS : XX
... (other keywords related to the transport formula used and eventually bed parameters)
for CO part:
CLASSES SETTLING VELOCITIES = XX,XX (if user wishes to set a settling vel)
LAYERS MUD CONCENTRATION = XX
LAYERS CRITICAL EROSION SHEAR STRESS OF THE MUD = XX
LAYERS PARTHENIADES CONSTANT = XX
Then you have to set all the keywords for initial and boundary conditions, related to both sediments/mechanisms...

Hope it helps.
Best regards,
Sara

Hello Sara,

Thank you very much for your very helpful and clear answer.
So if the suspended and bedl load are both non-cohesive, Telemac would think they have the same diameter distribution and I can only define it by the keywords "CLASSES SEDIMENT DIAMETERS" and "CLASSES INITIAL FRACTION".

Thank you and best regards,

Ding

Hi Ding,

In my case, both bedload and suspended load are non-cohesive. I want to set 0.0005 meter for bedload and 0.00025 meter for suspended load. Can you tell me if it is doable? In this case, what will be the keywords to define these two sizes and define one is bedload and another is for suspended load? If it is not possible in Telemac, then I will want to know if my bedload is 0.0005 meter and suspended load is 0.0625 mm , I mean one is cohesive and another is non-cohesive, then what will be the keywords in sisyphe steering file?

Hi Sara,

My question for you is- you mentioned the following keywords if we want to set a cohesive sediment as the suspended load. Now, can you tell me if I don't define these keywords in stterring file, will it still work with default settings? Because I am not sure what they mentioned through layers of mud concentration, if it is a percentage (no guidance about the value in manual) or fraction.
CLASSES SETTLING VELOCITIES = XX,XX (if user wishes to set a settling vel)
LAYERS MUD CONCENTRATION = XX
LAYERS CRITICAL EROSION SHEAR STRESS OF THE MUD = XX
LAYERS PARTHENIADES CONSTANT = XX

Hi Ding,

You should provide the grain size of the bed material, not of the material being transported.

Michiel

Hi Knaapen,

Thank you for your reply.
So the Telemac treats that suspended load has the same diameter distribution as that of
bed load?

Best regards,

Ding

If you define a single grain size, the transport predictors calculate the transport rates based on a distribution with that define median grain size. So the concentrations will be assuming only the finer fractions are suspended, but the material moved will have the defined d50. If you want to differentiate the behaviour of different grain sizes, you can define multiple non-cohesive grain sizes (with the same distribution as the bed material). The model will then start moving the fine material as suspended load at a much higher rate than the coarser material.

I see, thank you very much for your clear answer.