Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 8 DREDGER
d) Beach nourishment: mining sand offshore and placing on a beach to replace sand eroded by storms
or wave action. This is done to enhance the recreational and protective function of the beaches,
which can be eroded by human activity or by storms. This is typically performed by a cutter-suction
dredge or trailing suction hopper dredge.
e) Removing trash and debris: often done in combination with maintenance dredging, this process
removes non-natural matter from the bottoms of rivers and canals and harbors.
8.3 TYPES OF DREDGER
a) Self propelled
b) Non propelled
a) Self propelled dredger
i) Water Injection Dredger
- A water injection dredger injects water in a small jet under low pressure (low pressure
because the sediment should not explode into the surrounding waters, rather it is carefully
moved to another location) into the seabed to bring the sediment in suspension, which then
becomes a turbidity current, which flows away down slope, is moved by a second burst of
water from the WID or is carried away in natural currents.
- As a side note: Water injection results in a lot of sediments in the water which makes
measurement with most hydrographic equipment (for instance: singlebeam echosounder)
difficult and should make use of filtering to produce better results.
ii) Trailing suction hopper dredger
- A trailing suction hopper dredger (TSHD) trails its suction pipe when working, and loads the
dredge spoil into one or more hoppers in the vessel. When the hoppers are full the TSHD
sails to a disposal area and either dumps the material through doors or pumps the material
out of the hoppers.
Fig. 8.2 Typical Hopper Dredge Systems
8-2 March 2009