Work method of Dustpan dredgers
Dustpan dredgers are a specialised type suction dredger with a suction head shaped like a dustpan. They are designed for use on rivers where high bed loads and/or suspended solid concentrations of sand and small gravel are present. The suction head of the dustpan is approximately as wide as the dredger’s hull, as much as 15 metres wide. The suction head is lowered to the waterbed facing the material to be removed. The material is agitated, loosened and then fluidised by the use of high velocity water jets along the top of the digging face of the dustpan. This slurry is then drawn into the suction head and the dredge pipe, up the suction pipeline, through the pump and through a relatively short floating discharge line.
Dustpan dredgers are capable of moving very large volumes of material from localised areas and being discharged outside of the navigation channel, preferably at a place on the river where high energy currents keep the material suspended and carry it downstream and away from the constricting sandbar. Alternatively the material can be loaded into barges or pumped ashore.
Types of material
Dustpan dredgers are effective for removing solid concentrations of soft sand and fine-grained gravel, which can easily be fluidised.
The width of the dustpan dredger makes it efficient for wide river situations but not suitable for narrower channels.
One of the largest dustpan dredgers on the Mississippi River is a 300-foot-long dredger capable of removing over 3800 cubic metres of silt from the river bottom each hour.
Dustpan dredgers are especially designed for use in large river navigation systems, especially waterways where sand and gravel lead to the formation of sandbars which obstruct navigation channels. They may dredge year-round, following a schedule driven by shoaling but working within environmental windows.