No abstract

No abstract

The dispersion of harmful nonindigenous biological organisms that may be present in discharged ship ballast water is an issue of international interest. The present paper examines this issue as it applies to Vancouver Harbour and Juan de Fuca Strait, British Columbia, and the adjacent U.S. waters. The objective is to determine whether potential mechanisms exist to transport viable organisms that might be present in discharged ballast water to favourable reproductive habitats within British Columbian coastal waters. The study applied three-dimensional harmonic finite element models to generate representative tidal, atmospheric, and density-driven flow fields. Particle-tracking techniques were used to simulate representative trajectories of passive and active ballast water organisms discharged at existing deballasting sites. It was determined that the safest deballasting sites are off the west coast. Under normal conditions, organisms move southward (summer) or northward (winter) in the Shelf Break Current and only under strong eastward or northward winds are they transported to the Washington or Vancouver Island shorelines. Key words: ship ballast water, discharge, microorganism, trajectory, Vancouver Harbour, West Coast.

The Fraser River delta, south of Vancouver, is the largest delta in western Canada. It is an important agricultural and waterfowl area and a vital link in the Fraser River salmon fishery. It is also an area of rapid urban and industrial growth and lies within the most seismically active region in Canada. The delta has formed since deglaciation 11 000-13 000 (14C date) years ago. Sand and mud slope deposits constitute the bulk of the deltic sedimentary package. The delta's distributary channels are estuaries characterized by intrusion of saline water from the Strait of Georgia. Sediment transport is controlled by river and sediment discharges, tidal conditions, and the position of the salinity intrusion. Mud is accumulating on the Sturgeon Bank slope and in the adjacent Strait of Georgia at rates of <1-2 cm�a-1. Sand deposition is concentrated off the mouth of Main Channel. The main geological hazards are failures of the delta slope, burial and scour on the slope, and earthquake-related liquefaction and ground motion amplification. The main areas of concern are the urbanized delta plain, port facilities, a lighthouse, and submarine cables and pipelines on the delta slope. Human activity has contributed pollutants to the delta and degraded important coastal habitats. Causeways and other large engineered structures, as well as river dredging, have altered sediment and water dispersal patterns and contributed to erosion of parts of the western tidal flats. River training has concentrated sand deposition in small areas, possibly promoting delta slope failures.