Monitoring the Physical Effects of Sediments and Contaminants During Dredging Operations to Assess Environmental Impact

Dredging, by its very nature, causes an environmental impact. The relative scale of the impact is a function of many factors including the dredging operation, the hydrography of the area and the sensitivity of the site. During the last two decades, environmental impact was often measured by the immediate and long-term impact on flora and fauna at a species level, but regulators and environmentalists alike now feel that the optimum way of protecting single species is to sustain the health and balance of a habitat. Determination of environmental impact by measuring biological effects can be costly, long term and inconclusive leading to considerable debate between port management, regulators and environmentalists. If dredged sediment never actually reaches a sensitive site or is only deposited at levels well below natural ambient then long-term biological monitoring is at best likely to lead to further monitoring over a longer period and increased costs. It is proposed that significant cost-savings can be made and delays for port developments reduced if, initially, physical effects are monitored and understood and the data used to relate to biological impact or focus in on the specific needs for any biological monitoring that is required. The use of sediment tracers coupled with a standard suite of marine survey techniques provides tangible data on sediment transport rates and deposition in order to assess environmental impact.