How to setup the settling velocity of the sediment particles when using the sedimentdrift module?

[lihu8918]

Hi, guys. I'm using the sedimentdrift module to simulate the drifting process of sand particles in a river mouth, how to setup the settling velocity of the sediment particles when using the sedimentdrift module? and how to setup the seafloor if I have a depth data (e.g., ETOPO or GEBCO) at hand?

[knutfrode]

Hi,
The settling velocity (element property terminal_velocity) can be provided at time of seeding, as in this example:
https://opendrift.github.io/gallery/example_sediments.html
Here 1 mm/s is used for all particles, but you can also provide an array with different speed for each particle.

Some other modules implement the method update_terminal_velocity which updates this terminal velocity with time - but no such temporal variation is implemented for the SedimentDrift module.
See e.g. for the larvalfish module:
https://github.com/OpenDrift/opendrift/blob/master/opendrift/models/larvalfish.py#L104

For seafloor, you need to add a reader which contains/provides the standard_name sea_floor_depth_below_sea_level
If your ETOPO/GEBCO-files are CF-compliant netCDF-files, you should be able to use the genric netCDF-reader, or simply add with
o.add_readers_from_list([<bathymetry-file.nc>])

[lihu8918]

@knutfrode thank you very much. I have another question, you mentioned it's possible to apply a particle-varying or time-varying terminal_velocity, are there any example scripts to illustrate how to use the update_terminal_velocity method? thanks.

[knutfrode]

This is automatically used whenever vertical_mixing is activated, if defined in your module:

Here are the implementations for respectively OpenOil and PelagicEgg:
https://opendrift.github.io/_modules/opendrift/models/openoil/openoil.html#OpenOil.update_terminal_velocity
https://opendrift.github.io/_modules/opendrift/models/pelagicegg.html#PelagicEggDrift.update_terminal_velocity