Tractive Flows Adjacent to Site for Submarine Sewage Pipeline

by John L. Luternauer, Geological Survey of Canada, Vancouver, BC, Can,
Robert D. Macdonald, Geological Survey of Canada, Vancouver, BC, Can,

Document Type: Proceeding Paper

Part of: Coastal Zone '87


Twin 3200 m long submarine sewage pipelines for the city of Vancouver are being placed across the outer tidal flats and upper slope of the Fraser River delta to a water depth of 107 m. Geological and bathymetric surveys of the slope reveal a possible hazard to the pipeline: an elongate trench or chute and hummocky deposits downslope. The deposits are as much as 350 m wide and extend to a water depth of at least 120 m. We conclude these features are maintained by intermittent tractive flows discharged from the outfall channel. We recommend diminishing the potential for flow concentration along the outfall channel, when the channel no longer is needed, in order to reduce the possibility of further sediment accumulation in the hummocky zone which may lead to slope failure.

Subject Headings: Tides | Underwater pipelines | Slopes | River flow | Sewage | Channels (waterway) | Water pipelines | Canada | Vancouver | British Columbia

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