In Situ Localization and Quantification of Sediment Deposits after Dredging and Disposal Interventions in Sydney Harbour, Canada, Using a Dynamic Penetrometer

Abstract

In late 2011 more than 4.2 million cubic meters of seafloor sediments dredged from the central channel of Sydney Harbour (Nova Scotia, Canada) were relocated to a coastal site near Edwardsville, on the west side of the South Arm of the Harbour. Dynamic penetrometer measurements were carried out in October 2012 for rapid geotechnical characterization, localization and quantification of dredged material deposits, using the lightweight dynamic penetrometer Nimrod. Complementary sediment samples and digital images were taken at selected positions using a small grab sampler and underwater camera. Sydney Harbour is characterized by a large variety of sediment types. Muddy sediments ranging from low to moderate consolidation states were found, as well as compacted fine sands. The dynamic penetrometer results allowed the localization and quantification of deposited dredge disposal material in a cost-and time-efficient manner. The spatial distribution of sediments is in good agreement with a sediment dynamics model by CBCL Limited. However, the deposited sediment layers were thicker than anticipated, being on the order of 10-20 cm, and reaching several tens of centimeters when mixed with finer, muddy deposits.