A suction hopper dredger is usually used for maintenance dredging. Tianjin Port is by necessity largely man-made through dredging and reclamation. The canals required extensive maintenance, with frequent closures for dredging. The seabed contains enormous reserves of minerals which can be exploited by dredging. There was much dredging and filling along the river. A marina was started in 1979 by dredging the upper harbour and laying pontoons. Here the sand from the dredging ships was sprayed on to the land. To retrieve the sand, the method of hydraulic dredging is used. Locations with shipping lanes, dredging, or commercial harbors are known as continuous broadband sound. In all she was supplied with of Italian hemp for sounding, trawling and dredging. Fishing was traditionally done by hand, spearing, diving or dredging. The Jones Act includes dredging and salvage operations. The vessel chosen for the dredging is the Queen of the Netherlands. The dredging and traps were for biological investigation of the bottom. These are extremely useful in facilitating night navigation, pilotage and dredging.