Turbidity Caused by Spillage from a Dredging/ Mining Transverse Axis Cutter

Seabed mining introduces the potential for new mineral resources, but raises serious concerns about the environmental protection of our oceans. With potential developments located in more than 1500m of water, environmental consequences may be concealed, remote and problematic to monitor. All underwater dredging and seabed mining operations have consequent spillage from the cutter and suction configurations. The environmental impacts of this spillage can be severe, causing change and often degradation in habitat at a local and potentially regional scale. While spillage causes an increase in turbidity levels it can also release metals and other contaminants into the water column. Contaminants include ore, and gangue minerals as well as legacy deposits lying at the bottom of harbours that are mobilized during dredging. This paper reports on a spillage test, using turbidity as an indicator of contamination, in a specially designed tank with a transverse axis dredging/mining cutter, suction cowl and pump system. The paper reports the levels of increased turbidity relative to the cutter system and indicates the influence of the cowling design in reducing spillage levels. It discusses appropriate monitoring locations for optimal turbidity measurements. Experiments on spillage from new designs of seabed mining tools will enable modeling of mining best practice to minimize impact.