Settling of ocean-dumped dredged material, Townsville, Australia

• Published in: Estuarine, coastal and shelf science Vol. 35; no. 5; pp. 473 - 489
• Main Authors: Wolanski, Eric, Gibbs, Ronald, Ridd, Peter, Mehta, Ashish
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 1992; Elsevier
• Subjects: Australia coast; dredging; Earth sciences; Earth, ocean, space; Exact sciences and technology; Marine; Marine and continental quaternary; mud suspension; sea dumping; sedimentation; settling; Surficial geology; Australia; Australasia; Queensland; Australia, Queensland, Townsville; ISEW, Australia, Queensland, Townsville; sea dumping; Australia coast; settling; dredging; sedimentation; mud suspension; experimental studies; models; plumes; harbors; clastic sediments; sedimentary rocks; suspended materials; modern; channels; erosion; acoustical methods; marine sedimentation; mud
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/S0272-7714(05)80026-5

Mud is dredged from the Port of Townsville, Australia, and its navigation channel and is dumped offshore in typically 12 m depth. There are two stages to the settling: initial, rapid descent as a negatively buoyant jet, forming a high concentration suspension near the bottom, followed by subsequent slower settling of mud flocs. In calm weather, mud flocs settled out of this layer in about 15 min and the suspension did not move out of the dump site. In rough weather, the settling of mud flocs was inhibited by wave-induced turbulence, and the suspension was mobile and was transported away from the dump site. In quiescent waters, this suspension compacted to about 8% of its original volume in approximately 4 days. Even after compaction the mud was resuspended, presumably by pumping by long waves since no strong currents were observed, forming a mobile, 1 m thick, high concentration suspension at the bottom.