Lagrangian Modelling Techniques Simulating Wave and Sediment Dynamics ...
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where n is the number of particles while dx, dy and dz are the dimensions of the
averaging area.
Grain size classes are selected by the user and defined by median fall velocity
(and the erosion thresholds for bedload and suspended load). An "accumulation" file then specifies the relative abundance of mass in each grain size class in
each model cell at the commencement of the model run. The model updates the
mass in each class as the simulation proceeds so that changes to the grain size
distribution with time are modelled.
Specifically, the model considers the bed to consist of an erodible layer of a
known depth. The fraction of mass for each size class in each model cell is then
specified in the "accumulation" file as a fraction of this total depth with units of
metres. Assuming that the sediment is uniformly mixed, the depths have the
same distribution as the masses in the grain size classes. By treating each size individually' winnowing, which may cause the fines to be lost leaving an armoured
or lagged surface, is modelled.