intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 




Sub groups
D-Flow Flexible Mesh
Cohesive sediments & muddy systems



Message Boards

How Ulva are defined in WAQ

Martin Schueder, modified 6 Years ago.

How Ulva are defined in WAQ

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts

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,

Anonymous Anonymous, modified 6 Years ago.

RE: How Ulva are defined in WAQ (Answer)

Jedi Master Posts: 333 Join Date: 7/30/20 Recent Posts
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,
Martin Schueder, modified 6 Years ago.

RE: How Ulva are defined in WAQ

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts
Hi Mathieu,

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

Willem Stolte, modified 6 Years ago.

RE: How Ulva are defined in WAQ

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
Hope this is of any use.
Cheers, Willem
Martin Schueder, modified 5 Years ago.

RE: How Ulva are defined in WAQ

Padawan Posts: 52 Join Date: 10/8/13 Recent Posts

Thank you, your comments are most appreciated and useful!

Amelia Araujo, modified 3 Years ago.

RE: How Ulva are defined in WAQ

Youngling Posts: 13 Join Date: 7/7/15 Recent Posts
Hi, how do I define the location (x,y) of the algae in the domain?