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

waterbalance does not add up

Karoline Wischnewski, modified 3 Years ago.

waterbalance does not add up

Youngling Posts: 5 Join Date: 12/1/16 Recent Posts
Hello everyone,

I am trying to simulate the flow regime within a reservoir with Delft3D-FLOW. The model has no open boundaries. I am pumping water in and out of the system via defining Discharges under the Tab Operations. Hence I am controlling 100% what goes in and out. I wanted to make sure that the storage in the system grows by the same volume as the difference of input and output. Unfortunately it does not and of course I am wondering why.

Now the question for me is what I did wrong in either setting up the model or looking at those volumes. THe way I went about that was to export (using Quickplot) the surface area of my grid cells and the water depth at two different times during my simulation - multiply water depth and surface area for each time and substracting them from oneanother resulting in a number that was 20% larger than what actually was added to the system (at an earlier time step the difference was smaller suggestiong the error cummulates).

How can it happen that the system produced all that extra water? Is there a better way to extract the total volume in the system at various timepoints?

It gets even more confusing, when I compare my results with the real life situation I am trying to follow, where the real life waterlevel rises faster than the modelled waterlevel, leading to the assumption, that not enough water goes into the system.

I would highly appreciate any advice on how to go about narrowing down the mistake.

Adri Mourits, modified 3 Years ago.

RE: waterbalance does not add up

Yoda Posts: 1221 Join Date: 1/3/11 Recent Posts
Hi Karoline,

Two tips:
1. If the computation is not converging, strange results will be produced. Please check that the diagnosis file being produced ("tri-diag.<runid>") does not contain related errors/warnings. Also try with a smaller time step (e.g. deltat/10.0). Do you still get the same error?

2. Dry points may contain water. If they become wet during the calculation, the "dry" contents will be added to the summation. Can you try your calculation while being sure that dry points are not becoming wet? For example by setting the bedlevel constant (and low enough) in the full domain?

If this doesn't help: please zip the input files and add it to a post here on the forum.