Estimating effective longitudinal dispersion in the Chesapeake Bay

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An analysis of Environmental Protection Agency's Chesapeake Bay Program hydrographic dataset shows that the bay responds coherently to variability in freshwater flux. Mean salinity and salinity stratification both respond to variability in freshwater flux on time scales of roughly 90 days. Stratification is also influenced by local wind forcing but on much shorter (4-5 day) time scales. The volume of available data allows the effective longitudinal dispersion coefficient to be estimated as a function of either time or space. Values for this dispersion coefficient vary between 200 and 1000m 2s-1, with mean values around 650m2s -1. The spatially dependent structure has a maximum roughly 75km from the head of the estuary, and decreases gradually towards the mouth. The temporally varying effective dispersion varies spatially as the inverse of the estuarine cross-section, and temporally as the cube root of the freshwater flux, and is at least qualitatively consistent with models of estuarine circulation and results of previous field studies. Estimates of the numerical values of the dispersion are useful for better understanding distributions of other tracers within the bay, as well as providing another metric against which numerical models should be measured.

Original languageEnglish (US)
Pages (from-to)359-368
Number of pages10
JournalEstuarine, Coastal and Shelf Science
Issue number3
StatePublished - Jul 2004

Bibliographical note

Funding Information:
During the writing of this manuscript, the author was sponsored by The Center for Coastal Physical Oceanography, Old Dominion University. Data were provided in the public domain for this work by the Environmental Protection Agency, Chesapeake Bay Program, the United States Geological Survey, and the National Data Buoy Center. Arnoldo Valle-Levinson provided the gridded bathymetry. The author would also like to thank Parker MacCready, Jamie Pringle and Neil Banas for their input, as well as two anonymous reviewers, whose comments have resulted in a substantially improved manuscript over the original.

Copyright 2008 Elsevier B.V., All rights reserved.


  • Chesapeake Bay
  • dispersion
  • estuary
  • mixing
  • salinity
  • stratification


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