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TitleSedimentary processes at the mouth of the Fraser Delta: new insights from submarine observatory measurements
AuthorHill, P RORCID logo; Lintern, D GORCID logo
SourceSedimentology 2021 p. 1-22, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200612
PublisherBlackwell Publishing Ltd
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
AreaFraser River
Lat/Long WENS-128.7694 -119.8981 51.0828 48.1514
Subjectssedimentology; marine geology; geophysics; Nature and Environment; Science and Technology; rivers; deltas; tides; geophysical surveys; acoustic surveys, marine; sedimentary environment; marine environments; sediment transport; sediment dispersal; facies; Fraser Delta; observatories
Illustrationslocation maps; profiles; time series; tables; geophysical profiles; rose diagrams; schematic representations
ProgramMarine Geoscience for Marine Spatial Planning
Released2021 03 23
AbstractThis paper examines particle settling dynamics in a tidally-influenced delta, including observations of convective settling, strongly modulated by seasonal discharge and tidal cycles. Long time series of Acoustic Doppler Current Profiler backscatter, a proxy for suspended sediment concentration in the water column, current and sediment accumulation measurements from the slope of the Fraser River delta show variability of sedimentary processes over timescales from semi-diurnal to annual. Acoustic Doppler Current Profiler backscatter shows a lagged response to river discharge and strong diurnal/semi-diurnal variability. Most of the tidal cycle is characterized by a buoyant effluent plume. During the ebbing phase of diurnal major tides, discrete settling events are observed extending through the entire water column. The pulse-like nature of these events is the result of downward plunging fingers characteristic of convective settling, similar to those observed in laboratory flume experiments, and appear to be initiated at the interface between the surface buoyant plume and the underlying ambient water. Currents show strong variability in a three-layer water column. The surface plume shows offshore and southward directed transport of sediments. The remaining water column is influenced by tidal flows, but near surface and intermediate water-depth currents are out of phase by several hours, indicating a stratification of the basin water and decoupled propagation of surface and internal tides. This phase lag is unlikely to cause discernible facies changes, but may have implications for basin-fill patterns in restricted basins with strong tidal range. The results of this work will help to better understand river mouth sedimentation processes and dispersal patterns in other modern deltas and in the geological record.
Summary(Plain Language Summary, not published)
This paper reports on how sediment carried by the Fraser River is dispersed into the Salish Sea. It uses long-term current profile data from the Ocean Networks Canada Delta Dynamics Laboratory, a seabed installation located at the mouth of the Main Channel of the Fraser River, and describes the various effects of strong river discharge in the spring and daily tides on the way that sediment is dispersed. Sediment supply to the sea is strongest during periods of strong river discharge and ebbing spring tides. At these times a process termed convective settling operates which accelerates the settling of particles through the water column. This process has been documented in laboratory flume tanks, but not definitively in natural systems until this paper.

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