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The Bahía Blanca estuary is a complex system of channels and tidal flats where the most important deep water harbour system of Argentina is located. The main goal of the present work was to obtain a hydrodynamic conceptual model for the Bahía Blanca coastal area. For this reason, a combined analysis of observed data and numerical modelling has been performed for the whole area. The gained knowledge on the system hydrodynamics could aid in the decision support for navigation security, waste water discharges management, sediment dredging and rejection operations among other applications. Due to the Bahía Blanca coastal vast area, hydrodynamic observations are scarce and located near the populated areas. In order to describe the hydrodynamics of such a complex and large system, the analysed tidal and current data from different periods have been completed through numerical modelling. Data analysis served to determine the main processes governing the Bahía Blanca hydrodynamics, to characterise the area using general descriptors, to provide inputs for the numerical model and to aid in evaluating its performance. In addition, a 2-dimensional application was set up using the MOHID water modelling system for the Bahía Blanca estuary. This application aimed to gain a better understanding of the system dynamics, to explain and test the consistency of the observed data and to reproduce the processes taking place. Model results were in good agreement with the analysed data and served to confirm an inconsistency found on the sea level observations. The combination of both methodologies served to further describe the hydrodynamic processes governing this coastal area and also to obtain a conceptual model for the water and property circulation in the Bahía Blanca estuary. [ABSTRACT FROM AUTHOR]

Abstract: The management of coastal systems where overlapping economic interests compete for the same resources make the use of integrated approaches indispensable. The Integrated Coastal Zone Management (ICZM) focuses mainly on three major goals: (1) overcoming the conflicts associated with the sectorial management, (2) preserving the productivity and biological diversity of coastal systems, and (3) promoting and equitable and sustainable allocation of coastal resources. The DPSIR (Drivers-Pressures-State-Impact-Responses) framework is a common tool that allows the description of environmental problems by defining the relationships between anthropogenic activities and the environment. In this context, the use of numerical models as integrative tools in ICZM has grown significantly over the years. This work focused on three estuarine systems in South America: Santos estuary (Brazil, 24° S) and Bahía Blanca estuary (Argentina, 39° S) in the Atlantic coast and Aysén fjord (Chile, 45°S) in the Pacific coast. These estuaries differ significantly in their physical, chemical and biological conditions, as well as on their socio-economic settings and human-related problems. Numerical models have been used to study the relation between the pressures derived from human activities and their impact on the state of each system. The results presents a contribute to increase the scientific knowledge needed to support the implementation of local legislations and policies, to assess different scenarios of coastal activities and sources use, to support management decisions and, ultimately, to promote sustainable of coastal resources. [Copyright &y& Elsevier]

Abstract: By means of surveys carried out with a Phase Measuring Bathymetric System and current profiles obtained through an ADCP of the internal area of the Bahía Blanca estuary, a field of large dunes was analysed. There are two different and well-defined zones characterized by particular dune morphology and differing hydrodynamics. The reduction in the channel cross-section by a geological control leads to the increase in tidal current velocity, which together with the available sediment leads to the formation of Very Large Dunes (H >4m and L >100m) with the typical morphology of a limited amount of sediment overlying a rigid substrate. The migration rate of these dunes, between 65 and 130myear−1, decreases as the bedform height increases. Differing sediment transport rates across the channel result in a non-uniform migration rate, which is responsible for the formation of dunes with linear crests oblique to the tidal current direction. This fact indicates that determination of the sediment transport direction by using only large bedform orientation may be subject to a significant error. [Copyright &y& Elsevier]

The fractal dimension (D) was estimated for nine tidal channels depicted in thematic mapper (TM) Landsat-5 imagery to derive information about the degree of geomorphological control on a tidal channel network characteristic of the Bahı´a Blanca Estuary (Argentina). Two methods, box counting and contiguity, were used to estimate fractal dimensions for each tidal channel. All channels produced D values close to 1, meaning that they are self-affine fractal features. However, these fractal dimensions do not represent the meandering pattern complexity characteristic of the tidal channels analysed. Although both methods allowed for estimation of D, the contiguity method showed that three of the channels actually are not fractal but have sinusoidal characteristics, a condition that was not detected by the former method. [Copyright &y& Elsevier]

Variations in the physico-chemical characteristics of estuaries, such as surface water salinity and temperature, lead to the establishment of gradients that are closely related with the distribution of nutrients and suspended sediment. This affects light penetration, which in turn influences Chlorophyll-a (Chl-a) concentration and primary productivity. We used MODIS imagery to identify spatio-temporal patterns of sea surface salinity, temperature, and Chl-a concentrations from 2003 to 2017, to explore relationships between these variables and oceanographic factors, such as streamflows, winds and currents in the mouth of Colombia's Magdalena River, which discharges to the Caribbean Sea. Sea surface salinity (SSS) in the study zone varied in time and space from estuarine to marine. Mean SSS was 10.8 ± 3.4 at Bocas de Ceniza, and 28.4 ± 0.4 in the Caribbean Sea, with the horizontal salinity gradient providing evidence for the existence of a salinity plume. Mean monthly sea surface temperatures (SST) averaged across all years were 27.6 ± 1.5 °C at Bocas de Ceniza, and 27.6 ± 1.3 °C in the Caribbean Sea. A significant, increasing trend in temperature was observed throughout the years of the study period. Average Chl-a values were 3.3 ± 1.4 mg m−3 at Bocas de Ceniza, and 1.5 ± 1.2 mg m−3 in the Caribbean Sea and the calculated average Trophic State Index (TSI) for Bocas de Ceniza indicated that the estuary trophic state varied between oligo-mesotrophic (30 < TSI≤40) and mesotrophic (40 < TSI≤50). The highest concentrations of Chl-a were found in intermediate salinities in the estuarine zone. Outside the saline plume, there is a considerable decrease in Chl-a concentrations (<0.5 mg m−3). Winds played the most important role in influencing spatio-temporal distribution of chemical and physical variables in the study zone. Our results emphasize the importance of physical processes on biological dynamics in the Magdalena River mouth. • MODIS images are a powerful tool for understanding the dynamics of river plumes. • Magdalena River mouth is turbid with spatio-temporal SSS, SST and Chla patterns. • Chl-a showed a clear transition zone between coastal and open (Caribbean Sea) waters. • The trophic status of the estuary ranged from mesotrophic to oligotrophic. • The SSS, SST and Chl-a variability at the Magdalena River mouth is related to winds. [ABSTRACT FROM AUTHOR]

The Magdalena River is the main contributor of fresh water and sediment to the Caribbean Sea. Hydrological inputs from the Magdalena River are 10,287 and 4068 m3 s−1 at high and low flows, respectively. Sediment delivery from the Magdalena River is among the largest in the world, with 142 × 106 t yr−1 of transported suspended matter. We used MODIS images to develop a regional model and assess the spatial and temporal variability of suspended sediment concentration at the mouth of the Magdalena River, map the extent of the turbidity plume using its morphometric properties, and identify the main fluvial and oceanographic factors associated with plume variability. We analyzed monthly average suspended sediment concentration data for the period 2003–2017. MODIS images were calibrated with in situ measurements of suspended sediment concentrations in surface waters of the study area. A finite mixing model was used to identify turbidity thresholds and define areas within the plume. Calculated suspended sediment concentrations indicate high turbidity in the Magdalena River mouth (178.6 ± 78.7 mg L−1), values that are of the same order of magnitude as those measured in the Yangtze, Huang He and Amazon River mouths. Calculated plume areas (diffuse, solid and mixing) and their shapes suggest that the Magdalena River plume has a limited area, related to conditions such as wind speed and direction, streamflow, and sediment transport. Calculated areas and shapes demonstrate the ability to generate a near-field area, which indicates the presence of a clear convergence front. The data also emphasize the importance of sediment transport from the Magdalena River to the Caribbean Sea. Such fluvial transport is important in the biogeochemistry of estuarine systems, especially in turbid estuaries, where there is marked variability in the distribution of sediment in surface waters. • MODIS images are a powerful tool to build SSSC models. • Magdalena River mouth is a turbid system with seasonal and spatial SSSC patterns. • A finite mixing model was used to define thresholds to delimit turbidity plumes. • Magdalena River Plume areas indicate the presence of a clear convergence front. • SSSC variability is related to streamflows, wind and sediment transport. [ABSTRACT FROM AUTHOR]