intro story D-Flow FM


D-Flow Flexible Mesh

D-Flow Flexible Mesh (D-Flow FM) is the new software engine for hydrodynamical simulations on unstructured grids in 1D-2D-3D. Together with the familiar curvilinear meshes from Delft3D 4, the unstructured grid can consist of triangles, pentagons (etc.) and 1D channel networks, all in one single mesh. It combines proven technology from the hydrodynamic engines of Delft3D 4 and SOBEK 2 and adds flexible administration, resulting in:

  • Easier 1D-2D-3D model coupling, intuitive setup of boundary conditions and meteorological forcings (amongst others).
  • More flexible 2D gridding in delta regions, river junctions, harbours, intertidal flats and more.
  • High performance by smart use of multicore architectures, and grid computing clusters.
An overview of the current developments can be found here.
The D-Flow FM - team would be delighted if you would participate in discussions on the generation of meshes, the specification of boundary conditions, the running of computations, and all kinds of other relevant topics. Feel free to share your smart questions and/or brilliant solutions! 


We have launched a new website (still under construction so expect continuous improvements) and a new forum dedicated to Delft3D Flexible Mesh.

Please follow this link to the new forum: 

Post your questions, issues, suggestions, difficulties related to our Delft3D Flexible Mesh Suite on the new forum.





Sub groups
D-Flow Flexible Mesh
Cohesive sediments & muddy systems


Message Boards

about sediment transport

chen ling, modified 8 Years ago.

about sediment transport

Youngling Posts: 14 Join Date: 1/2/12 Recent Posts
I recently simulate sediment transport, but there are three problems I could not resolve by myself.
The first is that I want to set the sediment as bedload in the <.sed> file, but the SedTyp could only be setted as “sand” and “mud”, how to set sediment as bed load?
The second one, how to decide the Neumann boundary condition with time-series, could you give an example?
Third, there are several difference sizes of sediment in the bed composition, but I do not find where to set the initial bed composition, could you give me some advice?

Thanks very much and best regards.

Chen ling
Estelle Serrero, modified 4 Years ago.

RE: about sediment transport

Hi Chen,

I am having the same problem with the "bedload" command in the *.sed file (see file attached). I can only import the file in the GUI when I enter the words "sand" or "mud", even though I chose the non-cohesive option. Did you find a solution to this problem?

I also have different sediment sizes and I'm not sure how to set the bed composition. Apparently you can use keywords "SedMinDia" and "SedMaxDia" in the *.sed file, to enter minimum and maximum sediment diameters. The bed composition is then interpolated using a Loguniform distribution (see p.551-553 of the Delft3D-FLOW_User_Manual). If you choose to enter the median diameter only (keyword SedDia), Delft uses a piecewise log-uniform distribution: SedD10 = 0.75 SedD50 & SedD90 = 1.5 SedD50. Apparently, you can also enter any Dxx, as well as a geometric standard deviation of sediment diameter (keywoard SedSg).

You can also create a *.d50 file if you have a spatially varying grain size, but I don't think that's your case.

Best Regards,
Qinghua Ye, modified 4 Years ago.

RE: about sediment transport

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Chen, Estelle,

Thanks Estelle!

For Bedload, you cannot specify through GUI. The only way is to modify the *.sed file. Make sure the sed/mor file are used in the mdf as well.

For bed composition, you may refer to the Underlayer module in SED. Pls refer to Delft3D-FLOW manual pp 561 and then on, for example, there you can use IniComp=#inicompositionfilename# in sed to set a initial bed composition. And in Section B9.9, there is a detailed description of the format of initial bed composition file.

I hope this is a little bit useful?


Qinghua Ye, modified 4 Years ago.

RE: about sediment transport

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Dear Chen,

Regarding to Neumann Boundary condition, do you mean the hydrodynamic or sedimen transport boundary?

The rest 2 questions were replied in the previous post.


Manuela König, modified 3 Years ago.

RE: about sediment transport

Youngling Posts: 14 Join Date: 3/31/17 Recent Posts
Hej Qinghua,

can you explain the differences of the BC to me, I am a bit confused about the structure.

I have 3 Boundaries for the hydrodynamics (water level and discharge) but in the GUI you also have to define/add the transport conditions within each of the boundaries.
I also read that the Sediment BC should be implemented with the Neumann BC...

Moreover I want to implement 2 fractions (cohesive and non-cohesive) but the input- data (sed.-concentration) I want to use is only available for the sum of the fractions.... Shall I use it for both fractions.
Do you have an idea for a good option/solution of the initials....

Thanks and cheers, hope to get some help soon.
Qinghua Ye, modified 3 Years ago.

RE: about sediment transport

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Manuela,

You can specify each sediment fraction in the boundary, and also both sediment fraction as Neumann BC type.

For initials, you may generate an ini file, or use restart files. Refer to Delft3D-FLOW manual.