Analysis of Fluorescent Sediment Tracer for Evaluating Nearshore Placement of Dredged Material
Type:
Presented during:
WODCON XVIII - 2007 Orlando, Florida, USA
Authors:
Smith-SJ, et al
Abstract: Nearshore placement of sand dredged from coastal navigation channels is a continuing and growing interest for coastal zone managers, scientists, and residents. The long-standing practice of placing sandy dredged material offshore as the least-cost, project-specific alternative in the U.S. is being replaced with a more holistic, regional sediment management approach that frequently calls for placement of dredged material in the nearshore environment. Several studies have been conducted to monitor dredged material mounds in depths of 10-20 m, but few if any have monitored mounds in depths less than 6 m.
Nearshore placement of sandy dredged material has been approved by state regulatory agencies for sediments dredged from the Brunswick Federal Entrance Channel on the Atlantic coast of Georgia. The placement of dredged material in 2-8 m water depth presented an ideal opportunity to evaluate the performance of the selected nearshore placement sites and practices. As part of this monitoring and modeling study, fluorescent tracers representing siltand sand-sized particles were deployed at two nearshore placement sites and monitored over a period of 7 months. Sampling and analysis of the tracer data presented difficulties associated with the spatial and temporal variability of sediment transport processes and scales of interest. However, valuable insights into the sediment transport processes operating at the nearshore mounds were possible through the sediment tracer application. Combined with other observations, the sediment tracer study provided key information regarding: winnowing and fate of fine-grained silt from the mound, transport directions and deposition of sandy sediment from the mound, morphological feedbacks between the mound and hydrodynamics, and factors limiting tracer studies for evaluation of long-term sediment transport processes. The sediment tracer study, combined with other monitoring components and numerical modeling are leading to improved design of nearshore placement methods in the coastal environment.
Keywords: Dredging, beneficial uses, Brunswick, sediment transport, numerical analysis.