Flow and Stratification in a Bedrock Confined Estuary

Abstract

<p>This research describes the impact of the bedrock island structure on the circulation and stratification of a macrotidal, partially mixed estuary in northwestern Canada (the Skeena River Estuary). Due to ongoing development in this formerly remote region, pressures have increased within the Skeena River Estuary over the past decade. However, there is still limited understanding of the estuary's morphodynamics due to its deviation from a 'typical' estuarine morphology. Located along an emergent, fjordal coastline, the Skeena Estuary River drains into a basin confined by bedrock and interrupted by multiple, irregular bedrock islands. Observations suggest that a subaqueous delta, associated facies, and the surface plume are split between several bedrock passages with limited information on the governing hydrodynamic processes. To overcome this, Acoustic Doppler current profiler cross-sectional transects and conductivity, temperature, depth, and turbidity profiles were taken in the nearshore (under 40 m) at locations across the estuary over two different (by ~1000 m<sup>3</sup>s<sup>-1</sup>) river stages. Over multiple dates with various river inflows, the tidal ratio to river inflow produces varied stratification patterns at a given site. During one point in time and river stage, bedrock passages are disproportionally exposed to marine and fluvial inflows, creating spatially diverse stratification patterns across the estuary. Stratification and passage morphology interactions determine the characteristics of tidal slack transitions, with horizontal and vertical separation occurring during well-mixed conditions and stratified conditions, respectively.</p>