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Understanding Dredging

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Multipurpose Environmental Monitoring in an Estuarine System

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Presented during:

WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.

Authors:

M. Huygens, F. Caron, M. Achour, A. Gustaytis


Abstract

"Due to the very productive, phytoplankton-based food web in Arctic waters, major disturbances in photosynthetic communities would have a cascading effect through higher trophic levels. Present strong seasonal fluctuations, rendered in a wide salinity and temperature range, in addition to water quality, bed sediment composition and depth in the studied bay, seem to control the present community. Dredging, ploughing and disposal activities might disturb this highly sensitive ecosystem of the estuary. To manage potential environmental effects in a pro-active and adaptive way, DEME deployed a dedicated operational environmental monitoring during recent dredging works. A series of field measurements - next to the strict environmental compliance observations - focused on turbidity management, salt-wedge dynamics (halocline- thermocline), and water and sediment quality. Moreover, in-house dedicated designed environmental buoys recorded water quality parameters - providing online and real-time information during marine works. Additional seabed positioned ADCP measured specific estuarine hydrodynamics over the local water column, while discrete mobile handheld measurements with water quality probes completed the environmental picture of the complex bay system during the marine works. To complement, weather and wave conditions were included to obtain a holistic analysis. Both 2020 and 2021 environmental monitoring program results showed that natural estuarine processes seem to influence water quality parameters the most - mainly driven by decreasing water temperatures and slowly increasing salinity, combined with bad weather events. Singular storm events co-occurred with increased wind/wave action and maximum turbidity values. Recorded turbidity values during works stayed well within the natural range of the estuarine bay system throughout the project. Dredging, ploughing and disposal activities only affected suspended sediment concentrations locally and briefly. Consequently, DEME's pro-active environmental monitoring approach prevented long-term consequences for the ecosystem."

Keywords: operational environmental monitoring, Arctic ecosystem, turbidity readings, estuarine dynamics (halo- and thermocline)

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