Factors influencing boat and propeller induced
increases in suspended sediments
- The shallower the water, the greater the suction
created by the vessel moving through the water
at the bed resulting in increased re-suspension
of sediment. The depth of influence will vary
on a site by site basis.
- Where a vessel passes through a narrow channel,
occupying a large proportion of its cross sectional
area, the wave generated and the under-keel
clearance, can result in a greater mobilisation
of sediment from the bottom and margins of navigation
- The extent and duration of vessel activity is
related to the resuspension of sediment within
an area. Areas that are heavily used offer little
time for the sediment to resettle and as a result
receive more disturbance than an area that is
not used frequently. It has been observed that
one hour after vessel activity has stopped the
sediment will begin to resettle, although this
will depend upon the size distribution of the
material stirred up and the hydrodynamic regime.
- Sediment characteristics have an important influence
on turbidity. Finer materials such as silt will
be more easily re-suspended than larger particles.
- The hydrodynamic conditions at the site determine
where suspended sediments will be re-distributed.