2019 CSDMS meeting-078


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Patterns and Rates of Sedimentation in a Bedrock Confined Estuary: The Skeena River Estuary and Marine Approaches

Amanda Wild, University of Victoria Victoria , Canada. awild@uvic.ca
Eva Kwoll, University of Victoria Victoria , Canada. ekwoll@uvic.ca
Gwyn Lintern, Pacific Geoscience Center Sidney , Canada. gwyn.lintern@canada.ca
Kim Conway, Pacific Geoscience Center Sidney , Canada. kim.conway@canada.ca
Vaughn Barrie, Pacific Geoscience Center Sidney , Canada. vaughn.barrie@canada.ca
Robert Kung, Pacific Geoscience Center Sidney , Canada. robert.kung@canada.ca

This study investigates riverine sediment dispersal within a bedrock confined estuary in British Columbia, Canada using the HydroTrend and Sedflux models. The models are evaluated using multibeam and acoustic backscatter surveys, piston cores, and grab samples across the Skeena Estuary and its contiguous marine areas. The data has been compiled to produce an overview of seabed geomorphology, texture, and sedimentation rates in the estuary and marine approaches. The model HydroTrend was used to estimate incoming sediment load from the Skeena River. Model estimates of suspended sediment load are higher than past estimates due to a large contribution of suspended sediment from a portion of the Skeena watershed previously excluded due to a lack of available hydrographic data. Over thirty kilometres from the river mouth, cores recovered mud sequences in the deeper proximal bedrock confined channels that indicated sedimentation rates of up to 2.83 cm yr-1. These deeper estuarine passages are seaward of the sandy deposits that make up the delta platform. In comparison, sedimentation rates in the further offshore marine approaches to the Skeena Estuary are as low as 0.004 cm/yr. Sedimentation rates within the estuary agree with the SedFlux model outputs using the HydroTrend sediment load results. More specifically, a sedimentation rate of 2.9 cm/yr was predicted using the SedFlux model at the same distance from the river mouth as the mud sequence radiocarbon dated cores. A relatively high sedimentation rate and seaward fining trend in grain size are interpreted as indicators of high riverine input to the seabed regionally. This initial evaluation of model performance encourages further examination of sedimentation conditions in the Skeena Estuary, including those of importance to eelgrass beds and major port development areas.