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

Sediment Simulation - TriDiag File

PS
Patrick Specht, modified 6 Years ago.

Sediment Simulation - TriDiag File

Youngling Posts: 4 Join Date: 3/11/13 Recent Posts
Hallo everyone,

within my actual sediment simulation I get follwoing lines in the tri-diag-files:

Sediment erosion shortage at NM 6757 Fraction: 1 Mass available : -0.2684E-04 Mass to be eroded: -0.2684E-04

What does that exactly mean and how can I avoid that problem?

Many thanks and kind regards.
Patrick
Qinghua Ye, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Jedi Council Member Posts: 612 Join Date: 3/2/11 Recent Posts
Dear Patrick,

The message means in that cell, there is no sediment left for erosion at this timestep (bare bed, at least seem from the model ). There is possibility that this cell would get sedimentation as well. So it is not a problem, just a message for you to be aware of.

Regards,

Qinghua
PS
Patrick Specht, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Youngling Posts: 4 Join Date: 3/11/13 Recent Posts
Dear Qinghua,

thank you for your answer.

I get this warnings right after starting the morphological changes and I have an initial sediment layer thickness of 25 m (uniform). That's why I wondered, why there should be no sediment left for erosion.

Kind regards.
Patrick
Qinghua Ye, modified 6 Years ago.

RE: Sediment Simulation - TriDiag File

Jedi Council Member Posts: 612 Join Date: 3/2/11 Recent Posts
Hi Patrick,

I would not expect so as well. Did you observe big shear stress at the points as well? A bit strange and we need more info to analyze it.

Regards,

Qinghua
AE
Ahmed Elkut, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Youngling Posts: 9 Join Date: 5/20/14 Recent Posts

Hi everyone

I keep getting the same warning with initial sediment thickness of 5 meters, and I do not get it, I don't understand where is the erosion shortage occur for example if the error states: Sediment erosion shortage at NM 18538 Fraction: 1 Mass available : -0.138E-02 Mass to be eroded: -0.138E-02 

1. Where is that cell (NM 18538), does it mean (n,m)=(185,38) or (18,538)?, which is not either of them for me, or it is something else?

2. How can the mass available is exactly equal to the mass to be eroded?

3. How can I keep getting this error at the early stage of my simulation with maximum cum/erosion/sedimentation not exceeding 0.3m?

4. Does this error impact my simulation results, even though they qualitatively make sense?

I will appreciate any help

Thanks

Richard Measures, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Jedi Knight Posts: 178 Join Date: 3/23/11 Recent Posts

Hi Ahmed,

A few thoughts in (partial) answer to your questions:

1. The reference to NM 18538 I think refers to an internal model coordinate system where all cells are given a unique "nm" number. In the source code there is a function called "n_and_m_to_nm.f90" which uses the calculation "nm = n + nmaxddb * (m - 1 + ddb ) + ddb". ddb relates to domain decomposition so assuming you're not using multiple domains this simplifies to: NM = N + Nmax * (M-1). Using this equation you should be able to convert NM back to N & M based on Nmax.

2. I have no idea!

3. Do you have multiple sediment fractions? For multiple sediment fraction beds this warning relates to the amount of sediment available in the active (surface) layer, thus if there is insufficient sediment of a given fraction in the active layer you will get a warning even though there may be sediment available in the subsurface. Fixes can include reducing the timestep or increasing the thickness of the active layer.

4. If the warning is only for 1 or two cells I would tend to ignore it. If it covers large areas of your domains for long periods of time then you probably need to fix it.

Hope that helps.

Richard

AE
Ahmed Elkut, modified 1 Year ago.

RE: Sediment Simulation - TriDiag File

Youngling Posts: 9 Join Date: 5/20/14 Recent Posts

Hi Richard

Thanks a lot for your quick and resourceful reply.

I was able, using the equation of NM, to estimate the location of the error. The problem seems to be located at the boundaries, and it covers few cells. 

I have only one sandy sediment fraction. I will try to reduce the timestep and check on the boundaries to fix this warning.

Thanks again for your help.

 

Ahmed