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Hi,
I am checking sediment mass conservation in sisyphe (run coupled with telemac 2d).I am running a single sediment class with bedload transport only (SUSPENSION = NO) and no exposed areas of the seabed.

I’m outputting the quantity

TOTVOL = SUM (ZF%R(I) - ZR%R(I)) * VOLU2D%R(I)

where, as far as I understand, VOLU2D%R(I) represents the ‘area around each node’ (this is used by sisyphe to calculate the variable totvol in init_avai for example).

Thus TOTVOL should give the total sediment volume (m-3) in the system (as there is no suspension, all sediment should be in the bed at all times)?

As I am running a closed system with no transport across any boundaries I would expect TOTVOL to remain constant with time. However TOTVOL shows significant variation over time. I am running with tides and can see a tidal variation in this quantity together with a very slow decrease in total sediment when run over a 15 day period.

Is this expected? As far as I understand the FE solution does not ensure exact mass conservation but I would expect it to be close ? The result seems to get worse if I set FINITE VOLUMES = YES.

Can anyone advise on whether I am calculating everything correctly?

Thanks
John