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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How Ulva are defined in WAQ

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How Ulva are defined in WAQ
Answer (Unmark)
2/9/15 4:04 PM
Hello,

I am hoping to get a better understanding of how Ulva are defined in WAQ.

I am most confused about the concept of Ulva defined as a non-transportable substance. Consider the following: SDMixAlg, when defined as a -ve number <1, specifies the extent over the water column Ulva occupies. For me this would be on average 1.2 m (SdMixAlg = -0.75). However, my bottom segment, in the 5th of five layers, is on average only 0.3 m deep. I have noticed that Ulva biomass only increases in my bottom segment and will always decrease in any other segment within layers 1-4. This is when I define a uniform initial condition.

I am confused how if SdMixAlg = -0.75, meaning that Ulva exists to a water height of 1.2 m, I see in layers 2, 3, and 4 (which are still within the 1.2 m height of Ulva extent), decreasing Ulva concentrations but increasing concentrations in the bottom segment (layer 5). It appears the biomass that I want to be distributed over 75% of the water depth is contained to the bottom segment only, and thus affects that segment's water quality unrealistically.

Any help in understanding how these macro algae are defined would be of great help.

Thank you,

Martin
RE: How Ulva are defined in WAQ
Answer (Unmark)
2/17/15 10:28 AMas a reply to Rudy Schueder.
Hey Martin,
I haven't used the Ulva module very much, but here is what I recall from discussions with colleagues and my previous experiences with the module.

The Ulva module considers an algae (macrophyte) that can be both suspended in the water column and attached to the sediment. Delwaq makes the distinction between the two types, suspended and rooted. Only the rooted type is considered by Delwaq as a passive, non-transportable, substance. The process UlvaFix handles the resuspension/sedimentation (based on bottom shear stress), and ergo the mass exchanges between the two types. Parameter FixAlg defines whether it is suspended or attached (see the manual on process technical description, section 6-26). The properties of the two types are identical, except for the parameter SDMixAlg, which indicates the position in the water column. Value is 1.0 by default for the suspended type, meaning that the algae is mixed over the water column. For the rooted type, a negative value is given by the user (e.g. -0.75) indicating that the algae is mixed over the lower 75% of the water column. Numerically, it means that the calculation of growth and respiration for that algae takes into account nutrient and light climate in this lower 75% of the water column.

Therefore, although the rooted type is numerically handled by Delwaq as a passive substance, it can "feel" the nutrient and light conditions in any given percentage of the water column. This "emulates" a macrophyte spread over several layers of water column and is the meaning of the parameter SDMixAlg. In addition, your (suspended) Ulva concentration may decrease in all the water segments because you have more sedimentation than resuspension.

Finally, note that the module is named "Ulva", but is suitable to model any type of macrophyte, e.g. seagrass (providing proper calibration of course).

Hope that helps,
Cheers,
-Mathieu.
RE: How Ulva are defined in WAQ
Answer (Unmark)
2/23/15 3:14 PMas a reply to Mathieu Chatelain.
Hi Mathieu,

This clears up the concept for me. Thank you very much for the explanation.

Martin
RE: How Ulva are defined in WAQ
ulva sdmix
Answer (Unmark)
2/24/15 11:23 AMas a reply to Rudy Schueder.
Hi Martin,
My own experience with using Ulva fixed to model benthic algae are these:
It works fine in a 2D model grid
In a 3D model grid, the production is sometimes (much) lower than in a 2D grid. This is due to the solver in the primary production module, that solves the biomass of algae per layer. To the best of my knowledge, this is an issue that is being worked on at Deltares, and will be solved in a future version of Delwaq. I can only advice you to critically inspect the results of your Ulva fixed species.
The SDmix should in a 3D model be -1, if you want algae that grow in the bottom segment layer. I don't think it is meaningful to use other values.
One other issue is that the output parameter UlvaF (which should be the sum of the ULVAF types) is currently in gC/m3, while the individual types are in g C / m2. This is fixed in version
https://publicwiki.deltares.nl/display/DELWAQ/Revision+5.02.00.35583.4067
Hope this is of any use.
Cheers, Willem
RE: How Ulva are defined in WAQ
Answer (Unmark)
3/2/15 3:33 PMas a reply to Willem Stolte.
Willem,

Thank you, your comments are most appreciated and useful!

Martin
RE: How Ulva are defined in WAQ
Answer (Unmark)
5/25/17 12:36 PMas a reply to Rudy Schueder.
Hi, how do I define the location (x,y) of the algae in the domain?

Thanks,

Amelia