Hydrodynamic modelling of tidal-fluvial flows in a large river estuary. (15th November 2018)

• Record Type: Journal Article
• Authors: Sandbach, S.D.; Nicholas, A.P.; Ashworth, P.J.; Best, J.L.; Keevil, C.E.; Parsons, D.R.; Prokocki, E.W.; Simpson, C.J.
• Is Part Of: Estuarine, coastal and shelf science. Volume 212(2018)
• Page Start: 176
• Page End: 188
• Publication Date: 2018-11-15
• Subjects: Sediment transport -- Tidal constituent -- Residual flow -- Tidal-fluvial interactions -- Columbia river estuary -- Model parameterisation; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2018.06.023
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: The transition between riverine and estuarine environments is characterised by a change from unidirectional to bidirectional flows, in a region referred to herein as the Tidally-Influenced Fluvial Zone (TIFZ). In order to improve our understanding of the hydrodynamics and morphodynamics of this zone, we present a combined field and numerical modelling study of the Columbia River Estuary (CRE), USA, tidally-influenced fluvial zone. The CRE is large measuring 40 km in length and between 5 and 10 km wide. A shallow water model (Delft3D) was applied in both 2D and 3D configurations and model sensitivity to the key process parameterizations was investigated. Our results indicate that a 2D model constrained within the estuary can sufficiently reproduce depth-averaged flow within the TIFZ of a stratified estuary. Model results highlight the interactions between tidal-, fluvial- and topographic-forcing that result in depth dependent tidal rectification, and thus zones of residual sediment transport that: i) may be flood-directed along shallow channel margins and in the lee of bars, and simultaneously ii) is ebb-directed within deeper channel thalwegs. This condition is enhanced at lower discharges, but increased fluvial discharge reduces the number and size of regions with net flood-directed sediment transport and flow. These sediment transport patterns provide a mechanism to extend the bar/island topography downstream, and generate flood-directed, ebb-directed, and symmetrical bedforms, all within the same channel. Analysis of the model data reveals flood-directed sediment transport is due to both tidal variability and mean flow. These results highlight the need to include the mean flow component (M0 ) when considering the long-term morphodynamic evolution in a TIFZ. Graphical abstract: Image 1