Dredged Sediment Movement Tracing in San Francisco Bay Utilizing Neutron Activation.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MISS
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In 1973 a study was initiated on the environmental impacts of dredging and aquatic disposal operations in San Francisco Bay. One part of this study was a program to determine the movement and recirculation of dredged materials after their aquatic disposal. The movement and circulation of sediments in San Francisco Bay result from the complex interactions of tidal flows, wind-wave resuspension and recirculation and variations of freshet conditions with associated sediment loads, stratification, and shifting of nodal point. A program was instituted to physically trace the movement of dredged materials with the objective of quantifying the horizontal and vertical recirculation of the dredged sediment. Tracing was accomplished by tagging Bay sediments with iridium, neutron-activating sediment samples collected from an extensive test area, and using gamma-ray spectrometry to determine the quantity of iridium and hence the amount of dredged material present. This technique was successfully proven. Although somewhat expensive, iridium was found to be the most cost-effective chemical element for tagging and tracing sediments for the conditions existing in San Francisco Bay. With the neutron activation process, however, other chemical elements can definitely be used and may be more cost-effective for tracing dredged sediments elsewhere.
- Physical and Dynamic Oceanography
- Civil Engineering