Water Injection Dredging is a hydrodynamic dredging
technique that should be taken into consideration as a
cost-effective, environmentally sound solution to some
specific dredging operations. Dredging works can be complex
and costly, accounting for a substantial proportion of the
budget of a maritime project. To effectively plan and execute a
dredging operation, to be able to select the most appropriate
dredging plant, requires extensive knowledge of the material
to be dredged as well as the environmental circumstances of
the site to be dredged. Since the mobilisation and capital costs
of dredging plant are quite significant, choosing the wrong
vessels and methods can have severe economic consequences.
Appropriate ground and environmental surveys are
fundamental to the success of dredging operations, from both
a technical and an economic perspective. Water Injection
Dredging has very specific limitations but in the appropriate
situation it also has very specific benefits.
Water Injection Dredging is a relatively new hydrodynamic
dredging technique, developed by engineer R.N. Van Weezenbeek a little more than 25 years ago, which has been gradually gaining popularity for maintenance dredging.
Since port authorities are continually confronted with the siltation of the harbours and access channels, regular maintenance dredging is a necessity to ensure safe navigation depths in these waterways. However, especially for smaller ports, the financial demands of dredging can become burdensome.
Generally speaking the larger the port project, the more
cost-efficient dredging becomes using traditional dredging
techniques – trailing suction hopper dredgers and cutters for
instance. But for the regular maintenance of smaller harbours,
the technology of Water Injection Dredging can be an
effective, economical and environmentally sound solution.
Water Injection Dredging is a technique in which a specially
developed Water Injection Dredger injects large volumes of
water at a low pressure into the sediment, using pumps with
a series of nozzles on a horizontal jetbar. This fluidises the
sediment by effectively overcoming the cohesion in fine grained
(cohesive) soils or internal friction of coarse-grained
(granular) soils. This fluidised sediment then remains close
to the river or channel bed, flowing down to deeper areas.
Fluidised soil is also sometimes referred to as fluid mud,
fluid bed or density cloud, but since the sediment remains
just above the bed, the term “fluidised soil layer” is generally
agreed to be a more apt description.
Staying close to the bed creates a density current that
then, either by the force of gravity or through a natural or
artificially created slope, flows downwards to deeper water.
This all occurs with a minimum of disturbance to the
equilibrium of the ecosystem. In this way, instead of
mechanical transportation, nature takes care of the sediment
transport, making Water Injection Dredging under certain
conditions a very cost-efficient dredging technique.