DEVELOPMENT OF A HIGH-RESOULTION NON-NUCLEAR DENSITY PROFILER FOR DREDGING RESIDUALS AND FLUID MUD

摘要

The presence of fluid mud and dredging residuals impacts dredging projects for navigation and environmental cleanup purposes. Fluid mud is a high concentration aqueous suspension of fine grained sediment in which settling is substantially hindered by the proximity of sediment grains and flocs, but which has not formed an interconnected matrix of bonds strong enough to eliminate the potential for mobility, leading to a persistent suspension (McAnally et al. 2007). As per Bridges et al. (2008) dredging residuals refer to contaminated sediment found at the post-dredging surface of the sediment profile, either within or adjacent to the dredging footprint and typically occur as a thin veneer (1 to 10 cm thick) of fine-grained material, with relatively low density. The ability of sampling equipment to capture this low density thin veneer of residual sediment can affect monitoring results that determine if clean-up levels have been achieved. The lack of a sensor to efficiently quantify dredging residuals has hindered complete site characterizations of American environmental dredging site sediment conditions, and ambiguous depth measurements resulting from the presence of fluid mud have resulted in hindered optimization of navigation dredging projects. Several density profilers exist for use in fluid mud navigation projects, but all these probes have vertical measurement resolutions of approximately three centimeters or greater, and several require significant calibration using on-site fluid mud and water to improve measurement accuracy. The United States Army Corps of Engineers (USACE) and United States Environmental Protection Agency (USEPA) are, under an interagency agreement, currently developing a high-resolution, non-nuclear (acoustic) density profiler with a design vertical measurement resolution of approximately one centimeter that does not require on-site calibration using site-specific fluid mud and water. This paper describes the research and development activities of this project.