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

• Published in: Journal of geophysical research. Oceans Vol. 119; no. 10; pp. 7190 - 7204
• Main Authors: Díez-Minguito, M., Baquerizo, A., de Swart, H. E., Losada, M. A.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-10-2014
• Subjects: Advection; Biogeochemistry; box model; Covariance; Estuaries; estuarine turbidity maxima; Fluid flow; Geomorphology; Geophysics; Guadalquivir estuary; Mathematical models; Neap tides; Particulate matter; River flow; Sediment transport; SPM balance; Spring tides; suspended particulate matter; Transport; transport mechanisms; Turbidity; Upstream; ANE, Spain, Andalucia, Guadalquivir Estuary
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2014JC010210

A study is presented on the transport of suspended particulate matter (SPM) in the Guadalquivir estuary during low river flow conditions. Observations show that tidally induced SPM exceeds that associated with catchment-derived inputs. The main mechanisms that contribute to longitudinal transport are identified and quantified by analyzing the tidally averaged and depth-integrated SPM flux decomposition over time and space. The net transport is generally directed upstream, although differences in the direction between spring and neap tides are identified. The transport is largely controlled by the mean advection, the tidal pumping associated with the covariance between SPM concentration and current, and the tidal Stokes transport. The convergence of the transport associated to these mechanisms alone explains the presence of primary and secondary estuarine turbidity maxima. The tidal reflection at the upstream dam appears to play a significant role in their generation, as evidenced by the convergence zones of the M4 and M2 induced tidal pumping transports. The spatial structure of the transport motivates the development of a box model that describes the concentration of SPM and its exchange between different stretches along the estuary at subtidal time scales. The model is fed by the net SPM transport obtained from observations. Analysis of the morphodynamical state of the estuary using the box model indicates that erosion is dominant in the stretches close to the estuary mouth and that this sediment is transported upstream and deposited in the middle part of the estuary. This process is more influential during spring tides than during neap tides. Key Points * Transport due to M4 and M2 current-SPM interaction controls the setting of ETM * Mean advection, current-SPM covariance, and Stokes transport are the main drivers * The semianalytical box model permits an evaluation of the morphodynamic balance