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Geological Survey of Canada, Pacific Geoscience Centre, P.O. Box 6000, Sidney, British Columbia V8L 4B2 Canada
Throughout the Holocene, the river dominated Fraser Delta on the Pacific coast of Canada has prograded by continuous channel switching and avulsion into a deep (>300 m) basin. However, at the beginning of the 20th century the delta was modified to provide a navigable channel and port facilities for the city of Vancouver. Now most of the sand brought down by the river (35% of the sediment load) is removed from the system by dredging. The remaining fine-grained sediment is transported in a plume past the intertidal estuary within the distributary channels then deflected northwards by the dominant flood tidal flow into the basin. Two causeways to the south of the main channel and one to the north that cross the intertidal zone to the delta foreslope act as barriers to the dominant northward sediment transport causing estuarine and localized seabed erosion. An eroded distributary channel failure complex has been exposed on the delta foreslope, off the southern causeways, by flood tidal flows that scour the seabed and form northward migrating subaqueous dunes, further increasing the delta slope. This, combined with slow sea-level rise and seismicity, intensifies the risk of further erosion and instability of the delta, particularly along the subaqueous delta front and the intertidal estuaries.
