Seasonal Variability and Estuary–Shelf Interactions in Circulation Dynamics of a River-dominated Estuary

Abstract

The long-term response of circulation processes to external forcing has been quantified for the Columbia River estuary using in situ data from an existing coastal observatory. Circulation patterns were determined from four Acoustic Doppler Profilers (ADP) and several conductivity-temperature sensors placed in the two main channels. Because of the very strong river discharge, baroclinic processes play a crucial role in the circulation dynamics, and the interaction of the tidal and subtidal baroclinic pressure gradients plays a major role in structuring the velocity field. The input of river flow and the resulting low-frequency flow dynamics in the two channels are quite distinct. Current and salinity data were analyzed on two time scales-subtidal (or residual) and tidal (both diurnal and semidiurnal components). The residual currents in both channels usually showed a classical two-layer baroclinic circulation system with inflow at the bottom and outflow near the surface. However, this two-layer system is transient and breaks down under strong discharge and tidal conditions because of enhanced vertical mixing. Influence of shelf winds on estuarine processes was also observed via the interactions with upwelling and downwelling processes and coastal plume transport. The transient nature of residual inflow affects the long-term transport characteristics of the estuary. Effects of vertical mixing could also be seen at the tidal time scale. Tidal velocities were separated into their diurnal and semidiurnal components using continuous wavelet transforms to account for the nonstationary nature of velocity amplitudes. The vertical structure of velocity amplitudes were considerably altered by baroclinic gradients. This was particularly true for the diurnal components, where tidal asymmetry led to stronger tidal velocities near the bottom.

Quantifying the Effect of Salinity Stratification on Phytoplankton Density Patterns in Estuaries

“…For DF-S, the magnitude of u is large throughout the domain. Both magnitudes and vertical profiles of the modelled u agree well with those of the observed subtidal current (Chawla et al 2008). Fig.…”

“…These choices will be further discussed in "Insights from Additional Sensitivity Studies in the Electronic Supplement" section. Parameter U T was estimated as the amplitude of depth-averaged tidal current at x = 11 km using field data of Chawla et al (2008). The location x = 11 km (that is Station red26 in Chawla et al 2008) was chosen to estimate U T because its depth is approximately 16 m. Using the field data of Roegner et al (2011), the tidally-averaged bottom-to-surface salinity difference s was also estimated at x = 11 km.…”

“…The abbreviations denote: DF default cases, W weak stratification, S strong stratification. Additional sensitivity studies to the values of the parameters with subscript 'DF' are presented and discussed in the Electronic Supplement Sources are (a) Cheng et al (2013), (b) Chen and de Swart (2016), (c) derived from data of Roegner et al (2011), (d) Jay and Musiak (1996), (e) derived from data of Chawla et al (2008) The salinity where…”

Hydrodynamic controls of morpho-sedimentary evolution in a rock-bounded wave dominated estuary. Tina Menor (N Spain)

“…The drift currents from the incoming waves transport sediments in a south westerly direction, creating the incipient barrier after breaking down the two-layered flow during the spring and neap tides (Chawla et al, 2008), as well as during the same tidal cycle with less saline ebb current surface and marine current flows. In this case, the barrier is poorly developed and is anchored on the eastern side due to the dominant incoming waves from the NW.…”

Infrastructure for collaborative science and societal applications in the Columbia River estuary

“…By contrast, the chemical estuary, defined by the presence of salinity upstream of the mouth, is limited to~45 km (Chawla et al, 2008), with actual extent dependent primarily on river flow and tidal conditions.…”