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

Wave-induced longshore currents - LSTF

JG
João Gil, modified 7 Years ago.

Wave-induced longshore currents - LSTF

Padawan Posts: 29 Join Date: 10/24/12 Recent Posts
Good afternoon,

I'm sorry for reposting this thread, whereas I am not sure if "General" is the right section as nobody answered the other topic untill now.

I’m currently working on a project which main goal is the simulation of wave-induced longshore currents using the Delft-3D software and its comparison with laboratorial data from LSTF (Visckburg, USA, US Army Engineer Research and Development Center’s Coastal and Hydraulics Laboratory). The experiment intends to represent an infinitely long beach with invariant depth in alongshore direction. For that, the experimental layout uses a recirculation system which is responsible for the uniformity of the longshore currents pattern – see attachment.

Firstly, I would like to know which type of lateral boundaries – LB1 and LB2 in the attachment – you would suggest me to use. I have firstly thought about a kind of “periodic” lateral boundaries. Starting with zero values for the current, they should iteratively be redefined with the calculated values of the longshore current at CS1 in the previous iteration – see attachment. I am hoping this should be a way to represent the uniformity of the flow in longshore direction. The iterations will continue till a stationary condition is achieved. Is there any chance of simulating the problem on this way? If no, which one would you recommend? Would the use of a larger grid for the wave module, in comparison to the grid for the flow module, be a better solution ?

Finally, I would appreciate if you could tell me what type of data I need to input in Neumann boundaries using “time-series” forcing. I have already been looking on the flow manual. Unfortunately I have reached no conclusion.

Thanks in advance,
João Gil
Dano Roelvink, modified 7 Years ago.

RE: Wave-induced longshore currents - LSTF

Youngling Posts: 2 Join Date: 3/23/11 Recent Posts
Hi Joao,

The preferred way in Delft3D would be to use Neumann boundaries on both sides. Just make the grid rectangular, aligned with shoreline, and have Neumann bc's at inflow and outflow. The value to specify is the longshore water level gradient, which should be zero for wind- or wave-driven, longshore uniform situations. So just set the values to zero. Put a water level boundary (also) zero on the offshore boundary. Only in case of longshore tide-driven currents do you need to figure out the actual varying water level gradients, see the manual.

You do have to make the wave grid bigger, especially on the updrift side, to ensure you have a fully uniform wave field on your flow grid.
A final trick: in order to have uniform bathy, water level and current data on your wave grid (including outside the flow grid) use the option 'use and extend' for all the variables you pass from flow to wave (somewhere in the wave GUI).

Good luck,

Dano
JG
João Gil, modified 7 Years ago.

RE: Wave-induced longshore currents - LSTF

Padawan Posts: 29 Join Date: 10/24/12 Recent Posts
Dear Dano,

Thanks for your fast reply. I'm already anylising the obtained results.
I appreciate your consideration.

Best regards,
João Gil
JG
João Gil, modified 7 Years ago.

RE: Wave-induced longshore currents - LSTF

Padawan Posts: 29 Join Date: 10/24/12 Recent Posts
Good evening,

I must say I still have a question regarding boundary conditions.
As for the land-sea boundary of my model, I would like to define a “wall boundary” where all the waves would be absorbed and, consequently, no reflection towards the domanin would take place.

Is there any way I can do it? If yes, do I have to define this boundary in both WAVE and FLOW module?

Thanks in advance
João Gil