An In Situ Assessment of Seabed Stability in Baynes Sound, British Columbia, Canada

Abstract

Sutherland, T.F. and Amos, C.L., 2020. An in situ assessment of seabed stability in Baynes Sound, British Columbia, Canada. Journal of Coastal Research, 36(3), 472–486. Coconut Creek (Florida), ISSN 0749-0208.The Sea Carousel, an annular flume, was deployed to examine (in situ) fundamental parameters of seabed stability in Baynes Sound, British Columbia, Canada. Sediment grain size, water and organic contents, and chlorophyll and phaeopigment concentrations were collected to establish a hierarchy of factors associated with seabed stability. Sediment stability increased toward the Sound entrance in concert with decreases in water, organic, and silt–clay contents and a transition from cohesive to noncohesive properties. Bed-stress estimates, based on the quadratic stress law and turbulent kinetic energy (TKE) methods, showed a decrease in the drag coefficient from the inner (0.04) to the outer (0.0015) Sound. Surface erosion thresholds ranged between 0.04 to 0.28 Pa, whereas the friction coefficients (e.g., the failure envelop) were on average 12°, representing normally consolidated sediments. Type I (floc) erosion occurred at low shear stresses, whereas type II (mass) erosion happened at higher values. Erosion rates (E, for type I erosion) fitted a power function of excess shear stress (Em = τ0 – τcrit,z)m with zero offset, where 0.81 < m < 2.32. The lowest and highest values for a given excess-shear stress occurred in the inner Sound and outer Sound, respectively. Settling of (resuspended) sediment after an exponential decay law [d(SSC)/dt] = SSC0 (exp–kt), where k fell within that of published values (3 < k < 539). Higher values of k (fastest settling) were observed in the inner Sound relative to the outer Sound. The sedimentation diameter (ds) fell in a coarse–silt to fine-sand range and was larger in the outer Sound, reflecting a coarsening of bed sediments.