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

QH Boundary Condition

Nick Jewitt, modified 5 Years ago.

QH Boundary Condition

Youngling Posts: 3 Join Date: 1/4/15 Recent Posts

I've been having issues with my effluent QH boundary condition.

I have set my bathymetry and QH relation of the boundary condition so that the water level (WL) should be ~0 during the operation of the stabilization pond that I am modelling. Unfortunately the WL is finding equilibrium at 0.3m. Though my range of discharges goes up to 1.4 m for stability, the observation point I have located at my effluent has the corresponding 0m WL discharge rate. It also has a velocity vector pointing the incorrect way.

I also tried switching the QH relationship in case that it was depth based. Therefore I made the flow at WL 0m at 0 m3/s and shifted everything up. This resulted in equilibrium reached at 0.7m (same as before but +0.4m which was the original depth). Once again the discharge was equal to what would now have been 0.4m. Differently from the original and more logical case was that now the velocity vector was always pointed out of the system.

Any thoughts or suggestions?
Qinghua Ye, modified 5 Years ago.

RE: QH Boundary Condition (Answer)

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

Usually the QH boundary is not used for the downstream boundary, since it might be overwhelmed by the information from upstream.

For the numbers, probably we need more descriptions to understand your system.