Referencing of particle position to moving free surface

[MatthiasKramer]

As shared through some email exchanges in 2023, there seems to be a problem with the referencing of the particle's position to the moving free surface in TrackMPD, which can lead to some irregularities, such that (1) particles do not settle at the bottom, (2) particles are transported with incorrect advection velocities, and some other implications, which have not been explored in detail.

[IJalonRojas]

Hi Matthias, sorry for my late response, but I was on maternity leave last year. As shared via email, this problem has been solved in version 3. After numerous tests, we found that the referencing system of the particle position to the moving free surface in previous versions did not affect most applications with TrackMPD, as in most cases changes in the free surface are small or slow. Even in applications with significant changes in the free surface, the effect of the reference system on advection trajectories is much smaller than the stochastic motion induced by turbulent dispersion, so general horizontal transport trends are not affected by this. However, we detected a problem when resuspended particles are in shallow environments subject to rapid changes in the free surface (e.g., wave-dominated environments). For that reason, we have corrected the problem in version 3, and we encourage users to switch to this version, particularly in applications in macrotidal or wave-dominated environments. Thanks again for your valuable feedback!!!