In the framework of the european project F-ECTS, a three-dimensional Lagrangian 
model for suspended particulate matter (SPM) transport is applied to Venice 
Lagoon. Purpose of the project is ther simultaneous determination of macroalgae 
growth and SPM transport and their feedbacks. Main difficulty was the adaptation 
of velocities from an existing hydrodynamical model with finite element 
structure to a finite difference scheme in order to apply the existing SPM 
transport model. This paper describes the modifications and lists the additional 
information which is necessary for the transport of particles with the 
transformed currents. Bathymetry values have to be recalculated into the volume 
conserving equivalent and besides depths, the area which is covered per grid 
cell, has to be known. Given the transport over the boundary of a rectangular 
box wall, the length of the wall is needed to determine the velocity at the 
relevant grid point. To prevent particle presence in the entire box area, where 
only a fraction is covered the FEM structure, particle movements have to be 
restricted to a smaller box size. Therefore, 'wet' box areas are transformed 
into rectangulars of equivalent area which box lengths are prescribed for 
particle positions. First results are shown and interpreted with this approach.