##
Sediments

### Cohesive Sediment Dynamics -
Introduction

The
Mohid model is able to simulate cohesive sediment
transport, by combining the advection-diffusion module for simulating
the transport in the water column
and the free vertical
movement
module
to
compute the
settling
velocity,
therefore
the vertical displacement of the suspended particles.
Processes
like
flocculation or hindered settling are considered
to compute the
settling velocity. The
bottom module
computes
the
erosion and deposition
fluxes using
typical critical shear stress formulation.

Mohid's cohesive
sediment transport model influences other simulated particulate
properties fate, becoming an important tool to compute contaminants
transport and fate, due to
the important percentage of these
elements adsorbed on to cohesive sediments
surface. Regarding the contaminant
transport model, a sediment module was
recently developed, in order to simulate its specific processes, meaning
that the once deposited, cohesive sediment (and other properties
adsorbed on to it) do not exit the modelled system and can continue to
evolute, namely through consolidation and diagenetic processes.

The
cohesive sediment transport model
is currently being
applied in an annular flume, using
experimental data for validation.

###
Cohesive Sediment Dynamics -
Implementation

The
implementation of the cohesive sediment transport model consists in
tuning two different types of parameters. The first is the definition of
the method to compute the settling velocity. The model considers two
ways of computing the settling velocity: a constant velocity or using a
formulation in which the velocity depends on the suspended cohesive
sediment concentration, in order to account with the hindered settling.
Other parameters that must be tuned by the user are the critical shear
stress of erosion and deposition. These parameters are responsible in
controlling the fluxes of cohesive sediments between the water column
and the bottom.