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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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D-Flow Flexible Mesh
DELWAQ

Cohesive sediments & muddy systems

 


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How to decide the Reflection parameter alpha value? (flow)

EE
Esther Espinoza, modified 1 Year ago.

How to decide the Reflection parameter alpha value? (flow)

Padawan Posts: 25 Join Date: 4/6/17 Recent Posts
Hi, I'm modelling water level for an estuary area (1 month) and I would like to know if you can explain me a little bit about the reflection parameter alpha that it's needed in the bounday section of the flow module. I've read the manual, but I'm not sure how to decide it's value or how big is the influence of that parameter on the results of the water level simulation.

Thank you
water level d-flow alpha coefficient alpha boundaries
Erin King, modified 1 Year ago.

RE: How to decide the Reflection parameter alpha value? (flow)

Youngling Posts: 12 Join Date: 10/5/16 Recent Posts
High values of the parameter can result in a phase offset in the simulated results. The parameter makes the boundary "less reflective" however large values of this can result in a phase offset at the boundary. I think for a large domain and a large alpha coefficient I had up to a 30 minute offset in my water levels. I think this is due to it applying a time derivative of the Riemann invariant to the boundary condition, therefore it may hold back the boundary condition for a period to achieve this, though I may be mistaken in that interpretation.

At the bottom of page 207 in the manual there is an equation to determine a suggested value for alpha. Although another way could be to do a sensitivity analysis, testing different values and finding one that works.

Another suggestion you could try is to use a locally high viscosity in the direct vicinity of the open boundary (a value of 100 m2/s over the first 5 cells). A space-varying viscosity field can be generated using Quickin in a way similar to the way you generate a bathymetry field. The format of the viscosity needed for the *.edy file is identical to the format of the *.dep file. The *.edy file also needs to contain a block of data containing the horizontal diffusivity values as well.
DK
Dmitry Kushnir, modified 1 Year ago.

RE: How to decide the Reflection parameter alpha value? (flow)

Padawan Posts: 84 Join Date: 11/9/12 Recent Posts