Large-scale mass-wasting events on the Fraser River delta front near Sand Heads, British Columbia

Abstract

Although the Fraser River delta front supports coastal structures including ports, a lighthouse, jetties, submarine power cables, and sewage pipelines, the stability of the delta front is little understood. Five large-scale mass-wasting events at the mouth of the Main Channel near Sand Heads have been detected by comparing successive bathymetric surveys conducted by Public Works Canada between 1970 and 1986. These events can involve the downslope movement of more than 1 × 106 m3 of silty sand and the landward retrogression of the delta-front crest of up to 350 m or more. Morphologic and sedimentologic evidence suggests that these events are slope failures which result from the liquefaction of silty sand. Rapid deposition at the river mouth is likely a prerequisite for failure, although interstitial gas, tidal currents, waves, and earthquakes also may contribute to failure. These results have important implications for the foundation stability of the Sand Heads Lighthouse and future coastal structures in the area. Key words : bathymetry, mass wasting, liquefaction, hazard, Fraser River delta.