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. 
 

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

 

 

Message Boards

RE: Concentration in FLOW: Pollutants and tracers

MR
Miguel Reyes, modified 4 Years ago.

Concentration in FLOW: Pollutants and tracers

Youngling Posts: 5 Join Date: 8/26/14 Recent Posts
Hi everyone:
I have a problem when assessing the results of Pollutants and tracers.

At a certain moment "t1", I define a discharge (normal, block interpolation) in one (M,N) location (Flow rate " Q1" and Tracer concentration "c1"). In the next time "t2" ("t1"+history interval), the value of the discharge is null. When I open the trih file in this observation point, the initial concentration "c1-trih" does not correspond to the defined value in the discharge "c1". I mean, I played with the concentration, flow rate and grid cell volume of the discharge; but I found no relation between "c1" and "c1-trih". What I could see is that a linear increase in the discharge (2*Q1) implies a linear increase in this concentration (2*c1-trih).

I did the same calculus, but instead of defining a discharge, I worked with a .ini file and the tracer concentration "c1" in a grid point close to (M,N). At the initial instant "t0" I can observe ,in the trim file, that the defined "c1" is the same as "c1-trim" in the spill point.

My questions are,

1) When defining a discharge of a tracer in a specific grid cell, in the results of the concentration of this tracer: which is the relation between the defined concentration of the discharge ("c1") and the concentration in the grid cell ("c1-trih")? Which is the "reference time" I should work with (time-step vs time history?) ?

2) Is correct to suppose that, when using .ini file, the concentration is referred to the total volume of water in the grid cell?

Thanks in advance,
Miguel Á.
Adri Mourits, modified 4 Years ago.

RE: Concentration in FLOW: Pollutants and tracers (Answer)

Yoda Posts: 1224 Join Date: 1/3/11 Recent Posts
Hi Miguel,

1) In pseudo code:
"c1-trih" = ("Q1" * "c1" + "volume_cell" * "c0-trih") / ("Q1" + "volume_cell")

with "volume_cell" = volume of the cell at the old time step, "c0-trih" = the concentration in the cell at the old time step

The reference time (=reference date, 00:00:00 hours) in the discharge file must be the same as in the mdf file. The GUI should help you with this.

2) Yes. When using an ini file you prescribe "c0-trih".

Regards,

Adri
MR
Miguel Reyes, modified 4 Years ago.

RE: Concentration in FLOW: Pollutants and tracers

Youngling Posts: 5 Join Date: 8/26/14 Recent Posts
Thanks a lot, Adri, it solved my problems!
MO
Michael O'Shea, modified 2 Years ago.

RE: Concentration in FLOW: Pollutants and tracers

Youngling Posts: 7 Join Date: 3/24/15 Recent Posts
Hi Adri,

I have a similar issue,

I have specified a discharge in one cell only with low velocity 0.01 m3/s and concentration of 1800 kg/m3 over a time period within a Delft Flow simulation. The purpose is to simulate plough dredge sediment release.

When I view the results in Quickplot for a plan view of the discharge I am unsure of the units being displayed for the spread of the discharge.

What units are the default? it appears to be Kg/m3 but its not clear?
Bert Jagers, modified 2 Years ago.

RE: Concentration in FLOW: Pollutants and tracers

Jedi Knight Posts: 201 Join Date: 12/22/10 Recent Posts
Hi Michael,

What quantity are you looking at: the concentration of the plough dredged sediment on the trim-file?
Do you model the sediment in Delft3D as a sediment fraction or as a pollutant/tracer?
In the former case (sediment fraction) QUICKPLOT should indicate the unit kg/m^3 .... which version of QUICKPLOT are you using?
In the latter case (pollutant/tracer) QUICKPLOT doesn't know what unit quantity is specified in because Delft3D never asks you for the unit - you can use any volumetric concentration (m3/m3, kg/m3, mg/m3).

Best regards,

Bert
MO
Michael O'Shea, modified 2 Years ago.

RE: Concentration in FLOW: Pollutants and tracers

Youngling Posts: 7 Join Date: 3/24/15 Recent Posts
Thanks Bert,

See attached screen shots. I have a sediment (Sediment 2) and a pollutant (dredge material) specified as discharges.
They both have units of kg/m3 as default inputs. I want to simulate the effect of plough dredging by discharging sediment in one grid cell over an 8 hour period.
I believe the sediment fraction is the correct approach. My figures show 2600 kg/m3 of sediment2 released at a rate of 0.02 m3/s. Am I correct in saying this equates to a total discharge of 576m3/ day (8hours)?
KL
Karoline Lillie, modified 11 Days ago.

RE: Concentration in FLOW: Pollutants and tracers

Youngling Posts: 1 Join Date: 12/8/19 Recent Posts
Hello everyone,
I have a very similar question and would like to verify if I understand the "unit" of the tracer correctly. I am working with the Flexible Mesh, but I assume this is still handled the same way:
I have a flow model with no temperature, no sediment, just tracer. I defined a source with a constant discharge (0.5 m3/s) and a constant "concentration" for the tracer of 100 (the GUI shows kg/m3 as unit).
When I extract the model results for my tracer with matlab/quickplot the unit is empty "". And following the response from Bert Jagers that is because there is no unit attached to the tracer.
The question is: If i go in with 100 for my tracer, could I regard the results as Percent of the input concentration and substitute with any volumetric concentration? Lets say a particular cell gives me the result of 0.5 for the tracer, is that then 0.5% of my original 100 tracer? And hence if I assume i go in with 100 mg/l that means I will have 0.5mg/l in that particular cell? I do believe, that is how it works but I would like to be sure.
I hope this makes sense...
RJ
Reed Jonas, modified 8 Days ago.

RE: Concentration in FLOW: Pollutants and tracers

Youngling Posts: 1 Join Date: 8/1/20 Recent Posts
Nice, thanks for sharing this information tellthebell.