Spatio‐temporal distribution, along‐channel transport, and post‐riverflood recovery of salinity in the Guadalquivir estuary (SW Spain)

Abstract

[1] This paper presents an experimental analysis of the salinity distribution, the salt balance, and the variation of the saline intrusion in comparison to the freshwater discharge in the Guadalquivir estuary, which is a mesotidal system regulated and normally subjected to extremely low river flows. In such low-flow conditions, it is positive, well-mixed, and tidally dominated. The estuary is also characterized by a nonstationary, effective longitudinal dispersion coefficient, whose probability density becomes increasingly narrower and whose mean value is higher further upstream. The tidal-averaged salt flux is controlled by the following mechanisms (in order of importance): the nontidal transport, the Stokes transport, and the tidal pumping induced by the covariance between the current and salinity. These three factors account for more than 98% of the flux variation. In high river-flow conditions, the subtidal response and recovery of the estuary to changes in the river flow is analyzed. The increase in the tidal-averaged salinity during the first 2 weeks of the post-riverflood recovery in the middle and upper sections of the estuary is found to be linear in time. During that time, the celerity of the salt intrusion front was 4 cm/s. The 2 psu isohaline salt intrusion X 2 exhibits a complex dependence on the river flow Q d , including the effects of human interventions in the estuary. Three regimes are identified for the intrusion: X 2 = 57.02. 1

Structure of the turbidity field in the Guadalquivir estuary: Analysis of observations and a box model approach

“…The values employed are for and for the rest of the boxes, similarly to those obtained for salinity in Díez‐Minguito et al . []. A sensitivity analysis is performed on these parameters.…”

“…Under normal or low river flow conditions, i.e., with freshwater flows below , this is a tidally energetic estuary, which results in well‐mixed conditions, except for a partial stratification in the mouth area. A vertically sheared circulation is observed, but its effects on the salt transport are clearly lesser than the tidal effects [ Díez‐Minguito et al ., ]. The analysis of the stratification‐circulation parameters under normal conditions establishes a Type‐2a estuary according to the scheme of Hansen and Rattray [].…”

Mechanisms of Tidal Oscillatory Salt Transport in a Partially Stratified Estuary

“…Taylor (1954) showed that the interaction between the vertical gradient of velocity and vertical mixing could lead to the horizontal dispersion of salt or other contaminants. This shear dispersion theory was applied in many estuarine studies to explain the mechanism of tidal oscillatory salt transport (Bowden 1965;Fischer 1976;Uncles et al 1985;McCarthy 1993;Díez-Minguito et al 2013). Tidal shear dispersion is important when the time scale of vertical or transverse mixing is comparable to the tidal time scale (Fischer et al 1979;Geyer et al 2008).…”

Response of the Snowy River Estuary to two environmental flows

“…Most field studies have measured the response of only a limited number of biological, chemical, hydrodynamic or geomorphic parameters. The pioneering study of Nichols (1977) and the later studies of Eyre (Eyre & Twigg 1997;Hossain et al 2001) and Diez-Minguito et al (2013) are notable for their scope and careful treatment of the data. Such detailed case studies can provide a basis for management and, more generally, guidance on the processes that must be retained in a model and those of lesser importance that may be approximated or omitted.…”