Dredging is a process in which a large quantity of rock is pulled up from the ground and pushed out of a riverbed to a location where it is filled with gravel and sand.
A company that operates the dredge machinery, called a pipe dredger, then excavates the rock to fill a hole or break a pipe.
The amount of rock needed is usually in the thousands of tonnes, which is a significant amount of sand to fill the hole.
The dredge works are typically used for mining or mining operations that are very close to the water.
Some are used to create temporary storage facilities for coal and natural gas that are needed to fill mines or to create natural gas wells that will take energy away from other sources of energy.
A number of countries are investing heavily in natural gas infrastructure, particularly in China and South Korea.