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

underlayer/ initial bed composition problem

Brendan Yuill, modified 4 Years ago.

underlayer/ initial bed composition problem

Youngling Posts: 1 Join Date: 4/11/13 Recent Posts
My model has 3 sand fractions of the same size: one fraction enters the domain at the upstream boundary (sediment feed), one fraction composes the domain bed in all grid cells except the top-most layer in 1 mid-domain cell (bed sediment), and one composes the top most layer in only that one mid-domain grid cell (simulating tracer sediment). Only one size fraction is supposed to enter the upstream boundary as defined by a time series in the .bcc file.

The initial bed composition is defined by 2 layers:

Layer 1 is 1 m thick at the cell with tracer sediment and 0.0 m thick everywhere else. It is fully composed of tracer sediment.

Layer 2 is 9.0 thick at the cell with tracer sediment and 10 m thick everywhere else. It is fully composed of the size fraction not simulating tracer sediment.

The transport layer thickness is set at 0.1 m, I am tracking 50 underlayers, each at 0.2 m thick.


A small (< 0.01 kg/m2) amount of bed sediment is leaking out of the upstream boundary even though the .bcc file prescribes only the sediment feed fraction.

The map file indicates that at time zero, the 'sediment fraction top layer' is composed of an equal mixture of all three sediment fractions. The 'available mass of sediment' or 'sediment volume fraction' at time zero and z=1, equals that prescribed, i.e., the tracer sediment is only in 1 grid cell, not an equal mixture. However, at time 1, the 'available mass of sediment/sed vol. fraction' at time =1 indicates that a small amount of tracer sediment has likely entered the domain from the upstream boundary or something equally nutty.

What is the difference between the 'sediment fraction in the top layer' and 'sediment volume fraction' at z= 1...? Why might a small amount of sediment be entering my upstream boundaries despite by .bcc stating that for the modeled time period the input is zero? the equilibrium sand transport at the boundaries is turned off, of course.

Thanks for any and all help...I am stumped.