Mobile Mapping of the Resuspension Potential of Toxic Sediment
Project Number: R/EM-012, Completion Report
Start Date: 9/1/1990
Completion Date: 8/31/1992
|Principal Investigator(s)||1.||Charles Libicki, Civil Engineering The Ohio State University*|
|Co-Principal Investigator(s)||2.||Keith W. Bedford, Civil Engineering The Ohio State University*|
|This shows the current affiliation and may not match affiliation at time of participation. *|
|Source: Ohio Sea Grant College Program|
|Source Fund||State Match||Pass Through|
|Total||$ 65,491.00||$ 37,224.00||$ 0.00|
To develop and deploy ultrasonic sensors, to be mounted on a Remotely Operated Vehicle (ROV) which, once appropriately calibrated, will have the capability of determining near-surface sediment properties that are of particular importance to resuspension, without actually coming into contact with or materially disturbing the sediment. These properties include sediment type (e.g., clay vs. sand), porosity and small-scale bed features. The unit will be closely terrain-following and collect data from a continuous swath of a width of the same order as the height of travel.
Throughout the Great Lakes, a number of areas of concern have been identified. These sites have been subject to intense and expensive sampling and investigation, that yet, because of its disruptive nature, often does not indicate the true risk (in terms of exchange rates and exposure) that the toxic sediments pose to the environment. It is critical, from an engineering standpoint, to characterize the physical properties of the sediment, and the susceptibility of these sites to resuspension and migration, or conversely, their relative stability and inertness. At this point, many of the technologies we have developed for measuring sediment entrainment at fixed locations are ready to move onto a mobile unit, to create maps of the resuspension potential of portions of the Great Lakes, in a form that may be directly accessible to engineering models.
We propose to use two acoustic search units. The first, a 3 MHz device, operating in a pure tone-burst mode, will estimate the near-bottom sediment load. The second, a broadband (100 kHz-2 MHz) time-domain unit, will characterize the sediment type and porosity with a 0.5 cm resolution, to a depth of 5-20 cm depending on sediment type. Year 1 of the project will consist of instrument design, testing, refinement and proof-of-concept of the broadband instrument, the principal new technology being pursued. Spanning both years of the project is the further refinement of acoustic transmission and scattering models, in particular the application of scattering theory to broadband time-delay arrays.
Benefits & Accomplishments
The mapping of the resuspendability of toxics-laden sediments will have immediate applicability, both in terms of identification of those sites which are the most unstable, and therefore pose the greatest exposure threat, and also as a practical aid in selecting amongst competing remediation procedures. The most immediate pragmatic result will be more precise data in IJC Areas of Concern. Additional programs include EPA's programs of Whole Basin Exposure for risk assessment. This technology is completely adaptable to other environments, such as near-shore, estuary, oceanic, etc.
Publications & Media
|Libicki, C,. and K.W. Bedford. 1991, Sudden, extreme Lake Erie storm surges and the interaction of wind stress, resonance, and geometry|
Made available by Ohio Sea Grant as OHSU-RS-133.