A NONSTATIONARY BOX MODEL TO DETERMINE RESIDUAL FLUXES IN A PARTIALLYMIXED ESTUARY, BASED ON BOTH THERMOHALINE PROPERTIES - APPLICATION TOTHE RIA DE AROUSA (NW SPAIN)
G. Roson et al., A NONSTATIONARY BOX MODEL TO DETERMINE RESIDUAL FLUXES IN A PARTIALLYMIXED ESTUARY, BASED ON BOTH THERMOHALINE PROPERTIES - APPLICATION TOTHE RIA DE AROUSA (NW SPAIN), Estuarine, coastal and shelf science, 44(3), 1997, pp. 249-262
An improved two-layered box model for calculating the residual fluxes
in a Spanish ria is developed in the present paper. This kinematic bi-
dimensional model has two characteristics that make it different to pr
evious models. Firstly, for calculating the horizontal and vertical ve
locities and also vertical diffusion coefficients, the present model t
akes into account the distribution not only of salinity but also of te
mperature. Evaluation of both river discharge and heat exchange betwee
n water surface and atmosphere is required. Two sets of fluxes are com
puted; one for the distribution of salinity, and another for that of t
emperature. They are then weight-averaged according to the vertical gr
adient of both properties. Secondly, and due to the high density of sa
mpling (twice a week), it is possible to introduce the non-stationary
term in the convection-diffusion equation; thus, time variations of bo
th conservative tracers are taken into account. Coherent solutions of
equations are obtained in strong upwelling-downwelling and/or very low
river volume situations where the estuary behaves virtually as a well
-mixed estuary, and salt balance/non-stationary box models described p
reviously were inapplicable. The strong coupling between estuarine cir
culation and upwelling is shown, and an equation is proposed in order
to quantify this relationship. On the hypothesis of linear variation o
f thermohaline properties with time, fluxes at the intermediate time b
etween two samplings were also calculated. Comparison of salinity betw
een two stations at the mouth of the ria allows the computation of the
correction due to Coriolis outward flux deflection, which was then ap
plied to the whole ria. (C) 1997 Academic Press Limited.