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Classification of Estuaries by Hydrodynamics

momentum balance:. continuity:. salt balance:. equation of state:. Classification of Estuaries by Hydrodynamics. Hansen and Rattray, 1966, Limnol. Oceanogr., 11 , 319-326. Looking at Partially Mixed estuaries and ignoring lateral variability:. Non-dimensionalizing:

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Classification of Estuaries by Hydrodynamics

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  1. momentum balance: continuity: salt balance: equation of state: Classification of Estuaries by Hydrodynamics Hansen and Rattray, 1966, Limnol. Oceanogr., 11, 319-326. Looking at Partially Mixed estuaries and ignoring lateral variability: Non-dimensionalizing: current velocity as river flow salinity as a function of x and z

  2. ; B2 is the width of the estuary 1) The tidal mixing parameter M : 2) The gravitational circulation based on the Estuarine Rayleigh number: Results are cast in terms of two dimensionless parameters for the case of zero wind stress: We can use surrogates of the above two parameters to characterize the estuary:

  3. A) The circulation parameter, which is the ratio of the net surface current us to the mean freshwater velocity through the section Uf The larger this ratio, the stronger the gravitational circulation. This ratio is typically  1 B) The stratification parameter, which is the ratio of the top-to-bottom salinity difference  Sto the mean salinity over the section S0 At mixed conditions,  S = 0

  4. gravitational convection ceases; upstream salt flux entirely by diffusion diffusion is unimportant; upstream salt flux almost entirely by gravitational convection both advective and diffusive fluxes are important in the horizontal balance The diffusive fraction of the total upstream salt flux  in an estuary can be determined as a function of these two parameters (circulation and stratification)

  5. 2 1 S / S0 10-1 gravitational convection ceases; upstream salt flux entirely by diffusion  = 0.01 diffusion is unimportant; upstream salt flux almost entirely by gravitational convection  = 0.5  = 0.99  = 0.9  = 1  = 0.1 both advective and diffusive fluxes are important in the horizontal balance 10-2 1 1.5 10 100 1000 us / Uf Note that the advective component of salt flux is not necessarily proportional to salinity stratification.

  6. 10 1 4 No Mixing Mh 10 0 M l Ch Cl Sh 3b 1b 2b J17 J11 10 -1 JF S / S0 Sl NM 1a 2a 3a 10 -2  = 0.01  = 0.5  = 1  = 0.99  = 0.9  = 0.1 10 -3 1 1.5 10 10 2 10 3 10 4 10 5 us / Uf Types of Estuaries 1) No vertical structure in u seaward flow at all depths diffusive flux of salt dominates 1a) well mixed 1b) stratified 2) Flow reverses with depth advective and diffusive fluxes of salt contribute 2a) well mixed 2b) stratified 3) Strong gravitational circulation - advective flux of salt is dominant 4) Salt wedge

  7. Flushing Rate F The greater F, the lower  , indicating less diffusive and more advective effects Fint R Estimate  from flushing rate estimates Officer and Kester, 1991, ECSS, 32, 99-103

  8. Geyer’s new classification short rapid flushing Mississippi Fraser Merrimack highly stratified Columbia Snohomish Hudson high UR/(βgsoh)1/2 partially-mixed Hudson low James Chesapeake long slow flushing Delaware well-mixed UT/(βgsoh)1/2

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