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

Trouble in initiating storm surge simulation using Delft3D FM (

Yongsu Na, modified 1 Year ago.

Trouble in initiating storm surge simulation using Delft3D FM (

Youngling Posts: 1 Join Date: 10/25/19 Recent Posts
Hello everyone,

I've been trying to simulate storm surge case using Delft3D FM ( However, the program couldn't start the simulation showing a message "Initialization of tst05 has failed." ("tst05" is the name of the case).

I made a single irregular grid by utilizing Delft Dashboard and RGFGRID. A few quadrangular regular grids with different resolution were generated with DDB first, and they were transformed to irregular grids, and then merged together with triangular irregular grids in between. I tried to maintain the orthogonality of the grid below 0.5, even though it increased as I interpolate the grid with *.xyz bed level file (don't know why).As for bed level data, I combined GEBCO 2019, SRTM 4.1 (both obtained via DDB and a high resolution local data (obtained from an external source).Also, I generated a spider web file via DDB using JTWC best track file.

When I ran the model, FM gave me (!) messages, namely "Roughness&Viscosity&Diffusivity contains unspecified points, the calculation kernel will replace these with default values". I thought it was due to a kind of grid and bed level problem since at first the model gave the same message for Bathymetry "Bathymetry contains unspecified points, ~". However, Roughness&Viscosity&Diffusivity message were kept shown even after I modified the grid and solved bathymetry problem.

Because there is no relevant information in the manuals and websites, not to mention that the model does not allow me to look into it closely, I don't know how to solve this.Please take a look at the files I attached. Any help or discussion will be appreciated.

Thank you and Best,
Yongsu Na 

--- - original grid file (w/o bed level). - some grid cells were eliminated (parts of Yeosu, South Korea). - bed level was interpolated.
P.S. I could not add any post at Delft3D FM Form ( There weren't any buttons. Does anybody know?
Dmitry Kushnir, modified 1 Year ago.

RE: Trouble in initiating storm surge simulation using Delft3D FM (

Jedi Knight Posts: 108 Join Date: 11/9/12 Recent Posts
There are some small flow links on the D-Flow FM model mesh, which have to be removed. I've tried to run your test model and it gave me this error (see diagnosis file attached):

** ERROR  :     4 small flow links discarded. Run 'merge circumcenters' to remove small flow links or increase threshold

This was previously discussed in this thread. Solution: merging small circumcenters of the mesh, using RGFGRID: Operations --> Grid --> Merge Circumcenters. 
Kind regards,


Brandon Huntley, modified 8 Months ago.

RE: Trouble in initiating storm surge simulation using Delft3D FM (

Youngling Posts: 1 Join Date: 7/25/20 Recent Posts
The problem is that sometimes the communication between flow and wave does not work immediately after the restart TheFreshMarketSurvey (the problem does not occur in the middle of the tidal cycle), but this happens at a random moment in the simulation (not always during the first restart for example). I cannot figure out what the problem is, and hope that you can help me. When the simulation crashes a com-file is present
William Burch, modified 3 Months ago.

RE: Trouble in initiating storm surge simulation using Delft3D FM (

Youngling Posts: 1 Join Date: 12/15/20 Recent Posts
The coupled Delft3D Flexible Mesh (D3D FM) - SWAN model with an unstructured grid has been developed recently to simulate storm surge and waves; and another open source model, Telemac-Tomawac, has been widely used for storm surge and wave propagation simulation in coastal areas for more than 20 years. However, the choice of a hydrodynamic model for a specific area in terms of cost, efficiency and accuracy is often a dilemma at the beginning of a modeling project. The objective of this research is to examine the effects of two software packages in terms of accuracy and performance with a case study in the Shanghai area of China. Model performance has been assessed based on model configuration, model calibration, grid generation and computational efficiency. Comparing measured water levels with model results, both approaches were able to accurately predict hydrodynamic conditions in a complex estuarine environment. Both models showed that it can efficiently simulate hydrodynamics in the coastal area under various scenarios for further climate adaptation research. Additionally, both models were used to simulate inundation propagation due to hypothetical failures of flood defenses in the coastal area. A comparison of inundation extent and maximum inundation depth showed that they were equally well-suited for overtopping and inundation simulation.