ABSTRACT

The Sand Heads Seavalley is a submarine channel system seaward of the mouth of Fraser River, Canada. Soundings and sonographs reveal that the Seavalley is composed of tributary channels that coalesce downslope into a single sinuous channel that splits into distributary channels at the base of the slope. The channels are inferred to result from turbidity currents generated by periodic liquefaction of sandy sediment at the mouth of the river.

Bathymetric surveys of a river mouth slope failure in 1985 are used to estimate sediment transport rates for a turbidity current generated by the failure. These rates are compared to predictions using a turbidity current model based on relationships between settling velocities of surface sediments and shear velocities required to transport the sediment as suspended and wash loads. Model predictions that assume suspended load transport are much lower than estimates from the landslide, but predictions based on wash load transport show reasonable agreement. The better agreement with the wash load model may be because grain sizes in the deposits are controlled by the sizes of sediment supplied to the distributary mouth bar by the river, rather than by the competency of the turbidity curre t itself.