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RE: Bed slope effect

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Mahmoud Abdelbaky, modified 20 Days ago.

Bed slope effect

Keen Forecaster Posts: 2 Join Date: 11/11/20 Recent Posts
Hellow I have A question related to the Bed Slope Effect, How to consider this effect while simulating 3D state simulation. I found 3 Methods (Equations) that deal with this bed slope effect. I mean is there any additional parameters should be added to the model to activate the bed slope effect. and what is the difference between longitudinal and transverse slope effect? 
Victor Chavarrias, modified 20 Days ago.

RE: Bed slope effect

Advanced Augur Posts: 39 Join Date: 4/24/20 Recent Posts
[wrong date. changed when moving to new thread]

Hi, 
It does not really matter if your simulation is 2D or 3D. The same bed-slope-effect closure relations apply. The difference is that only in a 2D simulation the direction of the (depth-averaged) velocity is corrected by the secondary flow intensity to find the direction of the bed load. In a 3D simulation, this direction is the one of the flow layer closest to the bed. 
The are 4 different closure relations implemented. Indeed, each of them need different parameters that need to be specified in the mor-file. If unspecififed, default values are used. To see which parameters you need to specify, you can check the manual here:
https://oss.deltares.nl/documents/183920/185723/Delft3D-FLOW_User_Manual.pdf
Note that this is the Delft3D-4 manual, but in case you use FM, morphology is exactly the same. For instance, if you use Kock and Flokstra (Islope=3), you need to specify: Ashld, Bshld, Cshld, Dshld.
The streamwise coefficient AlfaBs will increase the bed slope effect component in streamwise direction. The transverse one will increase in the transverse direction. This second only applies to Bagnold formulation. In my view, you should keep these two values equal to 1.