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

Sediment Transport Differences

Alfonso M JR, modified 4 Years ago.

Sediment Transport Differences

Youngling Posts: 8 Join Date: 1/22/14 Recent Posts
Hello everyone,

I’m using Delft3D-FLOW to compute a mass balance of a only sediment fraction (named mud20, cohesive sediment) in a lagoon connected to the Ocean through several tidal inlets. In order to quantify the sediment mass that exits the domain, I defined cross-sections over the open boundaries of the model.

I plotted the results obtained for one of the cross sections and I’m not able to understand the differences between the different outputs obtained (SEE ATTACHED FIGURE). In the attached figure is shown (1) the cumulative total transport of mud20, (2) the cumulative advective transport of mud20, (3) the cumulative dispersive transport of mud20, and (4) the sum of cumulative advective and dispersive transport of mud20. The cumulative total transport was multiplied by the mud20 density to have kilograms of mud20.

I wonder if someone knows the difference between Cumulative Total Transport (black line) and Cumulative Advective+Dispersive Transport (red line), since I supposed the must be the same quantity.

Thank you very much in advance!

alfonso m
Qinghua Ye, modified 3 Years ago.

RE: Sediment Transport Differences

Jedi Council Member Posts: 612 Join Date: 3/2/11 Recent Posts
Hi Alfonso,

If it is still a problem for you, I tried to find a reply from our colleague, Bert Jagers in a previous mail/post(?). See if this answers your question.

The cum. advective transport is based on the local flow rate times the central average of the concentrations before and after the cross-section.
The cum. dispersive transport is based on the average of the diffusion coefficients before and after the cross-section and the concentration difference across the cross-section.
The flow engine of D-Flow2D3D uses an ADI scheme with two half time steps; both aforementioned output quantities are accumulated based on only the results of each second half time step assuming that the first half time step has identical behaviour.
To be accurate we should use the results of both half time steps and the same higher order and/or upwind schemes, so the approximate quantities “cum. advective/dispersive transport” on the his-file are not accurate enough for a detailed analysis.

Furthermore, these quantities consider only the suspended load, which is OK for MUD fractions, but not for SAND fractions which are also transported as bedload.
Finally, the suspended transport by the Delft3D advection diffusion solver is integrated over the full depth while the “near bed” suspended transport (below the reference height) is also included in the general definition of bed load, so there is actually some double counting of transport. To correct for this, we integrate the suspended transport below the reference height and subtract this from the suspended transport. The “cum. advective/dispersive transport” quantities have not been corrected for this, resulting in a yet another difference.

The cumulative total transport is computed by QuickPlot as the sum of cumulative bed load transport and cumulative suspended transport.
The latter two quantities are still based on the results of the second half time step only, but they are based on the correct numerical discretization and include the near bed corrective flux.


Noel Leo, modified 5 Months ago.

RE: Sediment Transport Differences

Youngling Posts: 13 Join Date: 12/24/19 Recent Posts
The good thing is we discuss it with each other and people are interested in discussions and they have knowledge too. I hope novo resume review soon starts something new for all of us and helps us in those topics which we don't know.
Young Hope, modified 7 Days ago.

RE: Sediment Transport Differences

Youngling Posts: 1 Join Date: 5/20/20 Recent Posts
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