A methodological modelling approach to assess the potential environmental impacts of dredging activities
CEDA Dredging Days 2015 - Innovative Dredging Solutions for Ports, Rotterdam
Feola A, Lisi I, Salmeri A, Venti F and Romano E - ISPRA - Institute for Environmental Protection and Research, Italy; Pedroncini A - DHI, Italy
Abstract: Dredging activities might cause adverse impacts on aquatic ecosystem, water quality and human health. Dredging plume is advected far from the dredging site by currents and its behavior is complex to be described both in time and space. The increase of Suspended Solid Concentration (SSC) and the subsequent redeposition (DEP) of transported sediments are considered a prominent environmental issue. Well-established international guidelines are available to support environmental studies related to dredging activities. These often include numerical modeling applications to reproduce spatial and temporal evolution of dredging plume. Plume dynamics are studied with regard to environmentally sensitive targets (i.e. Sites of Community Importance, bathing water quality, fish farming) and to achieve the environmental objectives while maintaining desired production rates. This paper presents an application of the Dr-EAM method to numerically estimate and compare the evolution of plumes generated by dredging operated with different mechanisms of sediment release in the water column. In order to evaluate the SSC spatial and temporal evolution as a function of the flow field variability, a series of consecutive dredging scenarios, occurring during an entire reference year of climatic conditions, was considered. The implementation of this method allows to objectively synthesize numerical results in term of SSC and DEP variability. Events of exceedance of environmental meaningful thresholds of SSC are described in term of magnitude, duration and frequency. An integrated index, SSCnum, is proposed for impact assessment. Maps presenting meaningful and spatially distributed statistical measures of the SSC and DEP time series are produced. The proposed approach is applied to Augusta Harbour (Eastern coast of Sicily Island - Italy) case study. Results, obtained for two hypothetical dredges and two different dredging areas, are comparatively analyzed to show the ability of the proposed tool to support technical choices during planning and operational phases.
Key words: dredging plume mapping; 3D transport modelling; environmental impact assessment; magnitude, duration and frequency of turbidity event