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Dear TELEMAC users,
I currently modelling a river bend using TELEMAC2D coupled with SISYPHE, however i am not sure about how to use the slope effect option with is correcting the value of the critical Shield stress

SLOPE EFFECT=YES (obviously activated)
FORMULA FOR DEVIATION =2
PARAMETER FOR DEVIATION = 0.85 - 3
FORMULA FOR SLOPE EFFECT = 1

This option is not well explained in the SISYPHE manual, could anyone kindly explain them in more detail or bring me a link where it was previously explained in other forum discussion?.

In addition, another question come up: What is the slope which is taken into account in the correction formula? is it performed in each cell?. In my study case the bathymetry is not quite detailed and some regions even could have one slope.

I can send the files of my model if it is needed.

Hello,
the only formula correcting the Shields stress in Sisyphe is from Soulsby which can be chosen by FORMULA FOR SLOPE EFFECT = 2 and calibrated with the FRICTION ANGLE OF THE SEDIMENT. If you want to use this you have to choose a threshold transport formula (e.g. Meyer-Peter Mueller) otherwise the correction of the critical SHields value will not have any effect.
As the slope effect is the opposite effect of the secondary current effect it is useful to have that in mind while calibration.

All formulas are written in the manual including the references where more detailed information can be found. May be you have an old manual. The newest can be found here: wiki.opentelemac.org/doku.php?id=documentation_v8p1r0

The slope is calculated in each cell. The slope effect will usually smooth your bathymetry. This effect will be less obvious in coarse grids then in fine grids as coarse grids already tends to smooth the results.

Regards, Rebekka

Hello Rebekka

I think that you did not understand or possibly assume that I am using an old version or manual. I was not so precise in my question, sorry. The version i am using is v8p0r2.

Regarding to the topic, i have not been satisfied with either the manual or the articles because there is no detailed information about how-to-use, otherwise I would not ask for more detail. My fear is that i am using maybe without consideration of a suitable studied case, bathymetrical resolution, etc.

Thank you for your response, I will wait for the response of another member of the forum, maybe the sediment transport experts can help us more.

I think you will need to explain more about the problem you have with the slope effect settings, if Rebecca's answer doesn't help.

FORMULA FOR SLOPE EFFECT = 2 will mean you use Souslby's correction of the critical shear stress. However, this setting will only have an effect for those formulae that use a critical shear stress (such as MPM). FRICTION ANGLE OF THE SEDIMENT then provides the calibration parameter (default 40)

FORMULA FOR SLOPE EFFECT = 1 increases the transport rate downslope and reduces it upslope by the factor (1-B*dz/dx), rather than changing the critical shear stress. The not very helpful keyword BETA than allows to change the parameter (default 1.3)

The options
FORMULA FOR DEVIATION =2
PARAMETER FOR DEVIATION = default 0.85
change the direction of the transport downslope if the flows are along the slope.

Be careful with what you write, by the way, there are very few users on this forum more expert in sediment than Rebecca!

Thank you for your response Michiel,

However, I think it was not enough with the apologies I asked above for not being so precise. I would appreciate not feeling alluded to because I wanted to wait for an expert, and not take it as a personal comment. Apparently I understood that an expert (I have seen several categories in the forum) can help us more with their experience and knowledge than a "Fresh Boarder" (I am too), i think any person can comment and can put any detail (like my picture, a bear) therefore, i can not be aware with who i am talking (junior or senior). I have published very little in the forum and I don't know each member in detail, I don't know their identity either. I apologize if any of you felt alluded to with my comment.

Regarding again to my topic, i am convinced that your comments (setting and procedimental) are quite explained in the manual. To be more precise i am uploading a picture to show what is


I kindly ask you for help also with my last lines of my first comment: What is the slope which is taken into account in the correction formula? is it performed in each cell?. In my study case the bathymetry is not quite detailed and some regions even could have one slope.

I can send the files of my model if it is needed (by e-mail)

If i am wrong in the reasoning i kindly ask you feeback, thanks in advance!.

Yes, the bed slope is calculated per element. The slope and its direction within each element is based on the differences in the bed levels of the nodes in that cell. The slope and direction are then used to calculate dzdx and dzdy.

Hello,

Maybe you can find some answers in this paper:

henry.baw.de/handle/20.500.11970/104277

Regards!