Snare Performance for Sunken and Submerged Oil Detection and Monitoring

Abstract

ABSTRACT - 687127 Most oil spill response strategies, tactics, and equipment are designed to address floating oil. Previous research and historic events have shown that spilled oil can suspend (i.e., submerged oil) or sink (i.e., sunken oil) as a function of the oil's density relative to that of the receiving waters. Processes such as wave action or current velocity, sediment entrainment, and oil weathering (e.g., evaporation) may change the buoyancy of floating oils causing them to submerge or sink. Non-floating oil is more difficult and expensive to detect and poses significant challenges for containment and cleanup. Many existing detection techniques for non-floating oils rely on oleophilic sorbents, such as snare, which are weighted depending upon the oil's location in the water column and then towed behind a vessel in designated transects. Currently, there is no quantitative method to relate the amount of oil collected by snare to the amount of oil encountered during towing. In addition, the dynamics and interactions of towed snare and oil remain largely unknown. To address these knowledge gaps, various components of snare performance have been evaluated since 2016 by the Coastal Response Research Center (CRRC) at the University of New Hampshire (UNH). The research has evaluated: (1) the impacts of temperature, salinity, oil type, and tow velocity on adsorption and desorption of oil to snare, (2) snare dynamics and position in the water column as a function of tow velocity, (3) the impacts of material type and potential alternatives to snare (e.g., mosquito and fishing nets, plastic debris) for lesser developed countries (LDCs), and (4) the interaction of snare with sunken and submerged oil. The results determined: (1) adsorption of oil to snare was best for less viscous oils (No. 6 Fuel Oil) and lower water temperatures (5°C) and desorption was greatest at low temperatures (6°C) and low current velocities (< 1 knot), while salinity had no significant effect. (2) Tow depth for snare arrays decreased with increased velocity unless a vane was used. (3) Optimal spacing of snare on a chain is a function of tow and current velocity, and drag forces on the tow chain. (4) Snare alternatives with greatest potential for sunken oil detection in LDCs were nylon mosquito netting and plastic bags. The findings from this research improves understanding of the behavior of snare and how it interacts with sunken and submerged oil and can improve towing techniques used by oil spill responders, leading to more effective detection.