intro story DELWAQ


DELWAQ is the engine of the D-Water Quality and D-Ecology programmes of the Delft3D suite. It is based on a rich library from which relevant substances and processes can be selected to quickly put water and sediment quality models together.

The processes library covers many aspects of water quality and ecology, from basic tracers, dissolved oxygen, nutrients, organic matter, inorganic suspended matter, heavy metals, bacteria and organic micro-pollutants, to complex algae and macrophyte dynamics. High performance solvers enable the simulation of long periods, often required to capture the full cycles of the processes being modelled.

The finite volume approach underlying DELWAQ allows it to be coupled to both the structured grid hydrodynamics of the current Delft3D-FLOW engine and the upcoming D-Flow Flexible Mesh engine (1D-2D-3D) of the Delft3D Flexible Mesh Suite (or even other models such as TELEMAC).

'DELWAQ in open source' is our invitation to all leading experts to collaborate in further development and research in the field of water quality, ecology and morphology using Delft3D. Feel free to post your DELWAQ related questions or comments in this dedicated forum space. If you are new to DELWAQ, the tutorial (in the user manual) is a good place to start. A list of DELWAQ related publications is available here.




Sub groups
D-Flow Flexible Mesh

Cohesive sediments & muddy systems


Message Boards

simulation time step

Patrick Specht, modified 6 Years ago.

simulation time step

Hallo all,

I have to do a long-term simulation with a sediment model and I use parallel computing. Right now I am varying the simulation time steps to get the simulation finished in a certain time.

Using the "Check Time Step" function within quickplot, I get a maximum allowed timestep for horizontal advection of 2.3 seconds. Then I used a time step of 1.2 seconds and got following lines in several of the tri-diag files:

*** MESSAGE Courant number for U-velocity in U-point equals 1.00 for (m,n,k) = (1,31,7), at nst = 249. Advised time step: 0.200E-01 minutes.
*** WARNING Negative concentrations for l, k, nst: 1 6 250
*** WARNING Negative concentrations for l, k, nst: 1 6 250

Can you explain what that means for my results and how these warnings can be avoided?

Thanks in advance and kind regards.
Adri Mourits, modified 6 Years ago.

RE: simulation time step (Answer)

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

If the messages are local in time and space and are not in the region of main interest (time and space), you can ignore it. Otherwise you will have to adapt your model. Some tips:
  • The time step predictor in Quickplot can not take into account all modelling aspects. May be there is one aspect that spoils it all, for example when the initial conditions do not meet the boundary conditions smooth enough. The reported warnings should help you to find the cause.
  • May be the problem does not appear when not running in parallel. Then you can choose: parallel with a smaller time step or sequantial with a bigger timestep


Sunny Becker, modified 3 Months ago.

RE: simulation time step

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