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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.

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Cohesive sediments & muddy systems

 


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Total discharge boundary condition failure

Jacob A Morgan, modified 11 Months ago.

Total discharge boundary condition failure

Youngling Posts: 3 Join Date: 4/27/18 Recent Posts

I am trying to set up a morphodynamic river model with multiple upstream boundaries/tributaries specified as total discharge boundaries. The total discharge at each of the boundaries is an unsteady hydrograph. However, at the upstream main-stem boundary (and a couple tributaries) the discharge drops off to zero after the discharge increases for some time. I can delay the failure of the boundary discharge by reducing the time step but it always eventually fails. The channel gradient at the boundary is fairly steep (~1%). I can specify a water level time-series boundary condition and it seems to work fine. But this type of boundary is not desired as the bed level will not necessarily be constant at the boundary.

Is there a better way to introduce flow at a steep boundary? Is there some Courant number requirement for a total discharge boundary?

 

Thanks,

Jacob

boundary conditions total discharge river discharge boundary conditions problem river modelling river boundary conditions
Richard Measures, modified 10 Months ago.

RE: Total discharge boundary condition failure

Jedi Knight Posts: 178 Join Date: 3/23/11 Recent Posts

Hi Jacob,

I have had similar problem at total discharge boundaries before in steep rivers - no quick fix but a few things to try/check could be:

  • What is your threshold depth for drying/wetting? Sometimes increasing this can help stabilize things.
  • Check the elevation assigned at the cell edges along the boundary (you can get this from the TRIM file in quickplot I think) - sometimes (depending on grid MN orientation relative to the boundary and how bed levels are specified) I have ended up with a situation where elevations along the cell-edges at the boundary were very wrong due to interpolating null values.
  • What is happening to the morphology at the boundary when it goes unstable - could the underlying cause be morphological? Do you get the same problem if you turn morphology off?

Good luck finding a solution!

Cheers,

Richard

boundary condition total discharge upstream boundary
Jacob A Morgan, modified 9 Months ago.

RE: Total discharge boundary condition failure

Youngling Posts: 3 Join Date: 4/27/18 Recent Posts

Thanks for your suggestions, Richard!

The threshold depth for wetting/drying seemed to work for a while but just increased the discharge threshold where failure occurs. The elevations at the cell edges also seem to be interpolated correctly. Although the end goal is a full morphodynamic model, this test includes only hydrodynamics.

We *tentatively* solved the issue by adding a "flume" of several cell lengths to the upstream portion of the boundary with a milder slope. However, we have since concluded that for stability (and computational time limitations) it is best to move our upstream boundary a short distance downstream to exclude this steepest part of the domain.