GAIA documentation: sand suspension

There is no documentation for what is done in GAIA, in case of non-cohesive sediment suspension, when it is coupling with TELEMAC-3D. It seems that the non-cohesive deposition rate depend on the concentration in the first layer near the bed, and does not require the Rouse profile assumption made in 2D. Does it use the mean value below Zref for instance or only the first layer (what about vertical discretisation) ? Thanks in advance.