Mapping exchange and residence time in a model of Willapa Bay, Washington, a branching, macrotidal estuary

N. S. Banas, B. M. Hickey

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

The numerical model GETM is used to examine transport pathways and residence time in Willapa Bay, Washington, a macrotidal estuary with a complex channel geometry. When the model is run with realistic forcing, it reproduces both tidal velocities and the decrease of the salt intrusion length with increasing river flow with errors of 5-20%. Furthermore, a more stringent test, when the model is run with tidal forcing only, it reproduces the along-channel profile of the effective horizontal diffusivity K, a direct measure of the strength of subtidal dispersion, which is known from previous empirical estimates. A Lagrangian, particle-tracking method is used to map subtidal transport pathways at the resolution of the model grid. This analysis reveals an interweaving of coherent lateral exchange flows with discontinuous, small-scale dispersion as well as tidal residual currents that in some locations, sharpen rather than smooth gradients between water masses. Comparison between these Lagrangian results and an Eulerian salt flux decomposition suggests that along-channel complexity (channel junctions and channel curvature) is at least as important as cross-sectional depth variation in shaping the subtidal circulation. Finally, a nonconservative tracer method is used to produce high-resolution, three-dimensional maps of residence time. This analysis shows that consistent with previous observational work in Willapa, at all except the highest winter-storm-level river flows, river- and ocean-density-driven exchanges are discernable but secondary to tidal stirring. In all seasons, despite the fact that half the volume of the bay enters and leaves with every tide, average retention times in the upper third of the estuary are 3-5 weeks. 

LanguageEnglish
Article numberC11011
Pages1-20
Number of pages20
JournalJournal of Geophysical Research: Oceans
Volume110
Issue numberC11
DOIs
Publication statusPublished - 17 Nov 2005

Fingerprint

estuaries
Estuaries
branching
residence time
Rivers
estuary
rivers
Salts
river flow
Tides
salts
Numerical models
salt
strength (mechanics)
diffusivity
Fluxes
Decomposition
tides
tracer techniques
stirring

Keywords

  • Willapa Bay
  • tidal dynamics
  • estuarine dynamics

Cite this

@article{6c533b799354402381f06dc326dd4656,
title = "Mapping exchange and residence time in a model of Willapa Bay, Washington, a branching, macrotidal estuary",
abstract = "The numerical model GETM is used to examine transport pathways and residence time in Willapa Bay, Washington, a macrotidal estuary with a complex channel geometry. When the model is run with realistic forcing, it reproduces both tidal velocities and the decrease of the salt intrusion length with increasing river flow with errors of 5-20{\%}. Furthermore, a more stringent test, when the model is run with tidal forcing only, it reproduces the along-channel profile of the effective horizontal diffusivity K, a direct measure of the strength of subtidal dispersion, which is known from previous empirical estimates. A Lagrangian, particle-tracking method is used to map subtidal transport pathways at the resolution of the model grid. This analysis reveals an interweaving of coherent lateral exchange flows with discontinuous, small-scale dispersion as well as tidal residual currents that in some locations, sharpen rather than smooth gradients between water masses. Comparison between these Lagrangian results and an Eulerian salt flux decomposition suggests that along-channel complexity (channel junctions and channel curvature) is at least as important as cross-sectional depth variation in shaping the subtidal circulation. Finally, a nonconservative tracer method is used to produce high-resolution, three-dimensional maps of residence time. This analysis shows that consistent with previous observational work in Willapa, at all except the highest winter-storm-level river flows, river- and ocean-density-driven exchanges are discernable but secondary to tidal stirring. In all seasons, despite the fact that half the volume of the bay enters and leaves with every tide, average retention times in the upper third of the estuary are 3-5 weeks. ",
keywords = "Willapa Bay, tidal dynamics, estuarine dynamics",
author = "Banas, {N. S.} and Hickey, {B. M.}",
year = "2005",
month = "11",
day = "17",
doi = "10.1029/2005JC002950",
language = "English",
volume = "110",
pages = "1--20",
journal = "Journal of Geophysical Research: Oceans",
issn = "0148-0227",
number = "C11",

}

Mapping exchange and residence time in a model of Willapa Bay, Washington, a branching, macrotidal estuary. / Banas, N. S.; Hickey, B. M.

In: Journal of Geophysical Research: Oceans, Vol. 110, No. C11, C11011, 17.11.2005, p. 1-20.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Mapping exchange and residence time in a model of Willapa Bay, Washington, a branching, macrotidal estuary

AU - Banas, N. S.

AU - Hickey, B. M.

PY - 2005/11/17

Y1 - 2005/11/17

N2 - The numerical model GETM is used to examine transport pathways and residence time in Willapa Bay, Washington, a macrotidal estuary with a complex channel geometry. When the model is run with realistic forcing, it reproduces both tidal velocities and the decrease of the salt intrusion length with increasing river flow with errors of 5-20%. Furthermore, a more stringent test, when the model is run with tidal forcing only, it reproduces the along-channel profile of the effective horizontal diffusivity K, a direct measure of the strength of subtidal dispersion, which is known from previous empirical estimates. A Lagrangian, particle-tracking method is used to map subtidal transport pathways at the resolution of the model grid. This analysis reveals an interweaving of coherent lateral exchange flows with discontinuous, small-scale dispersion as well as tidal residual currents that in some locations, sharpen rather than smooth gradients between water masses. Comparison between these Lagrangian results and an Eulerian salt flux decomposition suggests that along-channel complexity (channel junctions and channel curvature) is at least as important as cross-sectional depth variation in shaping the subtidal circulation. Finally, a nonconservative tracer method is used to produce high-resolution, three-dimensional maps of residence time. This analysis shows that consistent with previous observational work in Willapa, at all except the highest winter-storm-level river flows, river- and ocean-density-driven exchanges are discernable but secondary to tidal stirring. In all seasons, despite the fact that half the volume of the bay enters and leaves with every tide, average retention times in the upper third of the estuary are 3-5 weeks. 

AB - The numerical model GETM is used to examine transport pathways and residence time in Willapa Bay, Washington, a macrotidal estuary with a complex channel geometry. When the model is run with realistic forcing, it reproduces both tidal velocities and the decrease of the salt intrusion length with increasing river flow with errors of 5-20%. Furthermore, a more stringent test, when the model is run with tidal forcing only, it reproduces the along-channel profile of the effective horizontal diffusivity K, a direct measure of the strength of subtidal dispersion, which is known from previous empirical estimates. A Lagrangian, particle-tracking method is used to map subtidal transport pathways at the resolution of the model grid. This analysis reveals an interweaving of coherent lateral exchange flows with discontinuous, small-scale dispersion as well as tidal residual currents that in some locations, sharpen rather than smooth gradients between water masses. Comparison between these Lagrangian results and an Eulerian salt flux decomposition suggests that along-channel complexity (channel junctions and channel curvature) is at least as important as cross-sectional depth variation in shaping the subtidal circulation. Finally, a nonconservative tracer method is used to produce high-resolution, three-dimensional maps of residence time. This analysis shows that consistent with previous observational work in Willapa, at all except the highest winter-storm-level river flows, river- and ocean-density-driven exchanges are discernable but secondary to tidal stirring. In all seasons, despite the fact that half the volume of the bay enters and leaves with every tide, average retention times in the upper third of the estuary are 3-5 weeks. 

KW - Willapa Bay

KW - tidal dynamics

KW - estuarine dynamics

UR - http://www.scopus.com/inward/record.url?scp=30344460952&partnerID=8YFLogxK

U2 - 10.1029/2005JC002950

DO - 10.1029/2005JC002950

M3 - Article

VL - 110

SP - 1

EP - 20

JO - Journal of Geophysical Research: Oceans

T2 - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

SN - 0148-0227

IS - C11

M1 - C11011

ER -