Assessing Effects for Disposal Sites off San Francisco

by Peter Hamilton, (M.ASCE), Science Applications Int Corp, Raleigh, United States,
Allan Y. Ota, Science Applications Int Corp, Raleigh, United States,

Document Type: Proceeding Paper

Part of: Estuarine and Coastal Modeling


A simple particle tracking model has been used to estimate the size of deposition footprints and transient turbidity effects in the water column resulting from disposal of dredged material at proposed sites on the continental slope off San Francisco. Three sites are seaward of two marine sanctuary areas in water depths of 1000 to 3000 m. The model uses extensive current meter from 6 moorings deployed for a year-long period to provide the local advective field. The total volume of material to be disposed is estimated to be 4.5?106 m3/year. Two different material compositions, mostly-sand and clay-silts, are assumed to be composed of seven size classes (fine silt to coarse sand). The model tracks each size class, separately, by using surrogate particles for dispersing clouds. Results show that footprints cover areas of the sea floor of order 500 km2 with maximum accumulations of less than 100 mm/year for mostly-sand and 700 mm/year over smaller areas (approximately 280 km2) for clay-silts which incorporate cohesive clumps. The model uses the tracks and ages of individual size class clouds to estimate visitation frequencies and average concentrations of turbidity events in the water column. Under conservative assumptions, only fine silt class material has the potential to reach the boundaries of the sanctuaries with visitation frequencies of less than 1% and cloud concentrations of less than 2 mg/L.

Subject Headings: Soil analysis | Particle size distribution | Turbidity | Dredged materials | Silt | Clays | Waste sites | California | United States

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