DREDGE MOUND SEDIMENT DISPERSAL STUDY, BRUNSWICK, GEORGIA, USA

摘要

A sediment tracer study was conducted between December 2002 and August 2003 as part of a larger study investigating the dispersal and fate of maintenance dredge material placed in mounds in the fall of 2002 and the fall of 2000, offshore of Brunswick, Georgia, US. The recent mound is located further offshore and exposed to wave activity; the older, historic mound was located on the ebb shoal to Brunswick Harbor and is much more sheltered to wave activity. The comprehensive field data will be used to validate US Army Corps of Engineers dredged sediment fate and dispersion numerical models. Four different coloured fluorescence sediment tracers were used; 2 colours were very fine sand to silt and 2 colours were fine to medium sand. A sand tracer and a silt tracer were used to label both the historic and recent dredged mound in January/February 2003 followed by the collection of sediment grab and core samples collected over a 30 weeks period after tracer release. Sediment trap and suspended sediment samples were collected during the study. The majority of the silt to very fine sand sized sediment was eroded and advected from both sites over a wide area within a few weeks of release, which is of great significance for nearshore dredge placement operations. At both the inshore and offshore site the coarser sediment tracer (fine to medium sand) remained close to the release locations and was buried up to 0.4m at the sheltered inshore site and up to 1m at the offshore site. However at the more wave-exposed site, dispersion of sand and sand tracer was far greater than the inshore (wave sheltered) site. Comparison of the detailed mulitbeam bathymetric surveys and calculated volume change was consistent with the sediment tracer migration that was measured.