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

Implementing bottom growth / algae cover

Danker Kolijn, modified 5 Years ago.

Implementing bottom growth / algae cover

Dear DELWAQ community,

I am currently modelling a coastal domain with very dense macroalgae growth covering large portions of the sandy surface. These algae have a considerable impact on nutrients in the nearshore. I believe the daily temperature and light exposure in the shallower portions of the model should be influenced by these algae.

At the moment I have a z-layer model being fed by currents/waves from a FLOW model. I have defined my bed layers as S1 (0.05m) and S2 (1.0m) where i've used a spatial QUICKIN map to define gC/m2 in layer S1 (~45gCm/2) and in my water column (2gC/m3). However, after running the model and viewing vertical profiles, I feel that the algae is having little effect. I wonder whether this is because the S1 layers has not been activated by the wave-driven shear stresses? Perhaps there is no exchanges happening between the water column and layer S1?

Is there another way to define algae on the bottom surface instead of in layer S1 which would have more of an exposed impact? Has anyone ever had trouble with this type of scenario?
Any recommendations is much appreciated.

Danker Kolijn
Rudy Schueder, modified 5 Years ago.

RE: Implementing bottom growth / algae cover

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

I too am working on a project that involves modeling benthic macroalgae, although in a shallow lake and not a coast. In my experience there are two options. In BLOOM, you can use fixed ULVA species to model macroalgae that extend from the sediment into the water column. In DYNAMO, you can use Diatoms in layers S1 and S2 as fixed algae species. I expect based on your referencing of S1 and S2 that you are using benthic diatoms in DYNAMO currently? I have found that using both formulations will have significant effects on the overlying water quality. My current biomass density of S1 diatoms is ~15 gC/m2, a density I also prescribed using QUICKIN.

Have you looked at primary production of your algae? Are they in fact growing and/or respiring? I know that if you do not specify a value for the parameter "PPMaxDiaS1" in your input file, then benthic diatoms will not grow, because by default the maximum growth rate is set to = -1 and is not included in the substance file.

Danker Kolijn, modified 5 Years ago.

RE: Implementing bottom growth / algae cover

Hi Rudy,

Thanks for the response. I am indeed using DYNAMO and haven't activated the primary production feature, thanks for that tip. Do I understand correctly it's not a switch you can flip in the PLCT but has to be manually entered in block #6 of the .inp file? How much impact did your algae have on DO?

Also, i've noticed something a bit peculiar while implementing my QUICKIN generated diatoms in layer S1. In addition to algae i'm also interested in TSS (total suspended solids) which have to be activated by my wave induced shear stresses. I've defined a certain quantity of sediment on the bed and have noticed that when using the S1 map file it is barely activated, whereas when I specify the same S1 value for the whole bottom instead of using a map file, there is significantly more sediment activated and suspended into the water column. Do you have any experience with this?