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

WAQ Coupling

NJ
Nick Jewitt, modified 5 Years ago.

WAQ Coupling

Youngling Posts: 3 Join Date: 1/4/15 Recent Posts
Hello,

I have tried the same flow model with two separate time steps. When I try to couple the hydrodynamics with WAQ, the com file does not include the defined start and stop times defined in the flow procedure but instead converts to the same day but at hour 24. Example:

Flow Start: 17 04 2014 00 00
Flow Stop: 24 04 2014 00 00

When opening the com file in WAQ coupling

Couple Start: 16 04 2014 24 00 00
Couple Stop: 23 04 2014 24 00 00

When I change them to be the "correct" value indicated in the flow start and stop, I then get the error that the stop time of conversion must be at or before the stop time of the coupled hydrodynamic database. If I leave it, I get the error that there are imprper values in the date/time fields.

This only happens when I use the magnitude lower timestep in flow of 0.001 compared to the normal 0.01 where I don't get the above error but have more velocity change errors.

Any suggestions?

Thanks in advance,
Nick
AM
Arjen Markus, modified 5 Years ago.

RE: WAQ Coupling

Jedi Knight Posts: 223 Join Date: 1/26/11 Recent Posts
This is most probably due to rounding errors in the computation of the number of seconds from timestep in minutes that is used within Delft3D-FLOW (this is a floating-point number and that may cause such issues, though this is a new one in the 20+ years I have been dealing with the coupling FLOW-WAQ).

A possible workaround: let the FLOW calculation continue slightly further than 24 september 0:00. A single minute may be enough. Then the time you specify and which is consequently converted time is at least within the available range. Let us know if this solves the problem. Also if it does not, because then we will have to dig deeper.
MJ
Michel Jeuken, modified 5 Years ago.

RE: WAQ Coupling (Answer)

Jedi Knight Posts: 154 Join Date: 1/21/13 Recent Posts
Hi Nick,

That is strange behaviour. My first suggestion would be to skip the com-file for WAQ, and to write the WAQ input directly. This can be switched on on the Output section of the FLOW GUI. Switch on Export WAQ input, and go to "Edit WAQ inpit >>" to specify the periods/interval

Michel
AM
Arjen Markus, modified 5 Years ago.

RE: WAQ Coupling (Answer)

Jedi Knight Posts: 223 Join Date: 1/26/11 Recent Posts
Argh, I should have checked the source code:

Rather than comparing the actual _date and time_, the GUI compares the _internal string representation_ of the date and time. This gives the correct result, EXCEPT for the equivalence of day+24 hours and day+1 and 0 hours.

So, the error message has nothing to do with FLOW using a floating-point number for the timestep (well, that is in the 24 versus 0 hours issue). If you let the FLOW calculation continue just a wee bit, the GUI should be forced to do the right thing.
NJ
Nick Jewitt, modified 5 Years ago.

RE: WAQ Coupling

Youngling Posts: 3 Join Date: 1/4/15 Recent Posts
Thanks!

I will try both possible solutions.

Nick