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

Confusion over bed roughness formulations in 3D

Simon Waldman, modified 5 Years ago.

Confusion over bed roughness formulations in 3D

Youngling Posts: 4 Join Date: 7/16/14 Recent Posts
Hi all,

I'm using Delft3D-FLOW in 3D. The manual states that bed shear stress is a function of the velocity in the bottom layer and the square of the "3D chezy value (C_3D)" (eqn 9.57). It then goes on to explain how the C_3D is derived, making it clear that it is in effect a log-law-based hydraulic roughness formulation.

I'm trying to understand how this relates to the options available in the GUI. Presumably if one selects "z0" in the GUI, then equation 9.60 is used to calculate C_3D for each cell and time step. However, if one selects "Chezy" for the roughness formulation, then is C_3D fixed to the value that the user specifies, using just equation 9.57 for each cell and timestep?

Thank you for any clarity.