Fraser River delta: geology, geohazards and human impact

Abstract

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.