Measurements of velocity and salinity near the mouth and head of the Espinheiro channel (Ria de Aveiro lagoon, Portugal) are used to study the local variation of physical water properties and to assess the balance, under steady conditions, between the seaward salt transport induced by river discharge and the landward dispersion induced by various mixing mechanisms. This assessment is made using data sampled during complete tidal cycles. Under the assumption that the estuarine tidal channel is laterally homogeneous and during moderate tidal periods (except for one survey), currents and salinity data were decomposed into various spatial and temporal means and their deviations. Near the channel's mouth, the main contributions to the salt transport are the terms due to freshwater discharge and the tidal correlation. Near the channel's head, this last term is less important than the density driven circulation, which is enhanced by the increase in freshwater discharge. The remaining terms, which are dependent on the deviations from the mean depth have a smaller role in the results of salt transport. The computed salt transport per unit width of a section perpendicular to the mean flow is in close agreement to the sum of the advective and dispersive terms (within or very close to 12%). An imbalance of the salt budget across the sections is observed for all the surveys. Considerations are made on how this approach can inform the management of hazardous contamination and how to use these results to best time the release of environmental flows during dry months.
References
[1]
Miranda LB, Castro Filho BM (1996) On the salt transport in the Cananéia sea during a spring tide experiment. Revista Brasileira de Oceanografia 44(2): 123–133 doi: 10.1590/S1679-87591996000200003.
[2]
Fischer HB (1976) Mixing and dispersion in estuaries. Annual Review of Fluid Mechanics 8: 107–133 doi: 10.1146/annurev.fl.08.010176.000543.
[3]
Hunkins K (1981) Salt Dispersion in the Hudson Estuary. Journal of Physical Oceanography 11(5): 729–738 doi: 10.1175/1520-0485(1981)011.
[4]
Dias JM, Lopes JF, Dekeyser I (1999) Hydrological characterisation of Ria de Aveiro, Portugal, in early summer. Oceanologica Acta 22(5): 473–485 doi: 10.1016/S0399-1784(00)87681-1.
[5]
Dias JM, Lopes JF, Dekeyser I (2000) Tidal propagation in Ria de Aveiro lagoon, Portugal. Physical Chemistry of the Earth (B) 25: 369–374 doi: 10.1016/S1464-1909(00)00028-9.
[6]
Araújo I, Dias JM, Pugh D (2008) Model simulations of tidal changes in a coastal lagoon, the Ria de Aveiro (Portugal). Continental Shelf Research 28: 1010–1025 doi: 10.1016/j.csr.2008.02.001.
[7]
Picado A, Dias JM, Fortunato A (2010) Tidal changes in estuarine systems induced by local geomorphologic modifications. Continental Shelf Research 30(17): 1854–1864 doi: 10.1016/j.csr.2010.08.012.
[8]
Vaz N, Dias JM, Leit？o PC (2009) Three-dimensional modelling of a tidal channel: the Espinheiro Channel (Portugal). Continental Shelf Research 29: 29–41 doi: 10.1016/j.csr.2007.12.005.
[9]
Dias JM (2001). Contribution to the Study of the Ria de Aveiro Hydrodynamics. Ph.D. Thesis, University of Aveiro, Aveiro, Portugal.
[10]
Moreira MH, Queiroga H, Machado MM, Cunha MR (1993) Environ mental gradients in a southern estuarine system: Ria de Aveiro, Portugal, Implication for soft bottom macrofauna colonization. Netherland Journal of Aquatic Ecology 27(2–4): 465–482 doi: 10.1007/BF02334807.
[11]
Vicente CM (1985) Caracteriza？？o hidráulica e aluvionar da Ria de Aveiro, Utiliz？？o de modelos hidráulicos no estudo de problemas da Ria. Jornadas da Ria de Aveiro, III, Edi？？o da Camara Municipal de Aveiro, Portugal. 41–58.
[12]
Borrego C, Pinho P, Costa F, Cardoso da Silva M (1990) The case study of Ria de Aveiro. Draft report, GRIA, Aveiro. 61 p.
[13]
Vaz N, Dias JM (2008) Hydrographic characterization of an estuarine tidal channel. Journal of Marine Systems 70: 168–181 doi: 10.1016/j.jmarsys.2007.05.002.
[14]
UNESCO (1985) The international system of units (SI) in oceanography, UNESCO Technical Papers in Marine Science 45, IAPSO Publication Scientifique N°32, Paris France.
[15]
Kjerfve B (1975) Velocity averaging in estuaries characterized by a large tidal range to depth ratio. Estuarine and Coastal Marine Science 3: 311–323 doi: 10.1016/0302-3524(75)90031-6.
[16]
Dyer KR (1974) The Salt Balance in Stratified Estuaries. Estuarine and Coastal Marine Science 2: 273–281 doi: 10.1016/0302-3524(74)90017-6.
[17]
Miranda LB, Bérgamo AL, Mendes de Castro B (2005) Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil. Ocean Dynamics 55: 430–440 doi: 10.1007/s10236-005-0028-z.
[18]
Dyer KR (1997) Estuaries. A Physical Introduction, 2nd Edition. john Wiley and Sons. 195 p.
[19]
Bowden KF (1963) The mixing processes in a tidal estuary. International Journal of Air Pollution 7: 343–356.
[20]
Kjerfve B (1986) Circulation and salt flux in a well mixed estuary. In: Physics of Shallow Estuaries and Bays. J. van de Kreeke. Springer Verlag, Berlin. 22–29.
[21]
Dyer KR (1982) Mixing caused by lateral internal seiching within a partially mixed estuary. Estuarine, Coastal and Shelf Science 15(4): 443–457 doi: 10.1016/0272-7714(82)90053-1.
[22]
Dyer KR, New AL (1986) Intermittency in estuarine mixing. Academic Press, New York.
[23]
Bérgamo AL (2000) Caracteristícas da Hidrografia, Circula？？o e Transporte de Sal: Barra de Cananéia, Sul do Mar de Cananéia e Baía do Trapandé. MSc. Thesis, Instituto Oceanográfico, Universidade de S. Paulo, S. Paulo.
[24]
Mantovanelli A (1999) Caracteriza？？o da dinamica hídrica e do material particulado em suspens？o na Baia de Paranaguá e em sua bacia de drenagem. MSc. Thesis, Universidade Federal do Paraná, departamento de Geologia. 152 p.
[25]
Miranda LB, Bérgamo AL, Ramos e Silva CA (2004) Dynamics of a Tropical Estuary: Curimataú River, NE Brazil. Journal of Coastal Research SI39 (Proceedings of the 8th International Coastal Symposium): 697–701.
[26]
Fischer HB, List JE, Koh RCY, Imberger J, Brooks NH (1979) Mixing in Inland and Coastal Waters. Academic Press, New York.
[27]
Simpson JH, Gong WK, Ong JE (1997) The Determination of the Net Fluxes From a Mangrove Estuary System Estuaries. 20(1): 103–109.
[28]
Jay DA, Geyer WR, Uncles RJ, Vallino J, Largier J, et al. (1997) A review of recent developments in estuarine scalar fluxes estimation. Estuaries 20: 262–280.
