River dynamics and nanopaticles formation: A comprehensive study on the nanoparticle geochemistry of suspended sediments in the Magdalena River, Caribbean Industrial Area

Ospino, S.; Restrepo, J.C.; Otero, L.; Pierini, J., and Alvarez-Silva, O., 2018. Saltwater intrusion into a river with high fluvial discharge: A microtidal estuary of the Magdalena River, Colombia. The Magdalena River (Bocas de Ceniza) forms a microtidal estuary subjected to numerous interventions aimed to guarantee navigability towards the port of Barranquilla, Colombia. Significant sedimentation processes are still frequent in this area, however. Understanding the dynamics of both saltwater intrusion and mixing conditions is a fundamental requisite to understanding the sedimentation dynamics in these types of estuaries. The effects of river discharge, tide, and winds on stratification patterns, and mixing and saltwater intrusion dynamics in the estuary of the Magdalena River were evaluated, focusing on the effects of river discharge variability. The three-dimensional hydrodynamic model MOHID was implemented, and calibration and validation of the model were carried out using in situ velocity, te...

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Saltwater Intrusion into a River with High Fluvial Discharge: A Microtidal Estuary of the Magdalena River, Colombia

The concentrated benthic suspension (CBS) of mud, as a major contributor of sediment transport in the turbidity maximum of the estuary, is of great challenge to be correctly monitored through field measurements, and its formation mechanism is not well understood. A tripod system equipped with multiple instruments was deployed to measure the near-bed hydrodynamics and sediments in the North Passage of the Changjiang Estuary, with the aim at determining the formation mechanisms of CBS. The measurements detected a significant dominance of high sediment concentration in the near-bed 1-m layer: ~20 g/L at the southern site and ~47 g/L at the northern site. Strong CBS occurred under weak tidal mixing condition and was directly relevant to the sediment-induced suppression of turbulent kinetic energy and the enhanced water stratification due to saltwater intrusion and sediment suspension. During the weak-mixing neap period, the typical thickness of CBS was about 0.2–0.3 m, with a life time of ~2.83 hr (suspended-sediment concentration > 15.0 g/L). Enhanced water stratification reduced vertical mixing and confined the sediment entrainment from the near-bed layer to the upper column. This enhancement was due to the suppression of turbulent kinetic energy as a result of the sediment accumulation in the near-bottom column during the slack waterand also due to the appearance of a two-layer salinity structure in the vertical as a result of saltwater intrusion near the bottom. These physical processes worked as a positive feedback loop during the formation of CBS and can be simulated with a process-oriented, one-dimensional vertical CBS model. Plain Language Summary In the turbidity maximum, concentrated benthic suspension (CBS) frequently dominates the near-bed sediment transport, which, however, is difficult to be correctly observed, especially in the stratified condition. And the formation mechanism of CBS is complex due to the interaction of sediment and hydrodynamics. In a stratified tide channel of the Changjiang Estuary, China, a comprehensive tripod system, integrated with many cutting-edge instruments, is developed and deployed tomeasure the CBS and to determine the formation process. This system detected the existence of CBS in the lower near-bed 1-m layer, ~20 g/L at the southern site and ~47 g/L at the northern site, with the mean thickness of 20–30 cm. The corresponding salinity, tidal velocities, wave, and turbulent kinetic energy were also recorded. During the formation of CBS, tidal mixing is weak. And the salinity/sediment-induced stratification greatly limits the vertical mixing and suppresses the turbulent kinetic energy production. The saltwater intrusion creates a two-layer structure of salinity, leading to stratification and decreasing the mixing. These physical effects work like a positive feedback loop. A one-dimensional vertical model had been developed to successfully simulate the formation process of CBS, indicating the stable CBS during weak-tidal-mixing neap cycle.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JC013876

Formation of Concentrated Benthic Suspension in a Time‐Dependent Salt Wedge Estuary

Fluvial and oceanographic influences on suspended sediment dispersal in the Magdalena River Estuary

The hydrodynamics of the TagusROFI (Regions of Freshwater Influence) is affected by the coastal upwelling, the estuarine tidal flow, the thermohaline circulation that is modulated by the Tagus freshwater discharge, and by its complex bathymetry. The use of numerical models is the best way to explain the processes that characterize this region. These models are also crucial to answer important scientific and management questions. Nevertheless, the robustness of the products derived from models depend on their accuracy and therefore models must be validated to determine the uncertainty associated. Time and space variability of the driving forces and of bathymetry enhance flow complexity increasing validation difficulties, requiring continuous high-resolution data to describe flow and thermohaline horizontal and vertical variabilities. In the present work, to increase the precision and accuracy of the coastal processes simulations, the sub-systems coastal area and the Tagus estuary were integrated into a single domain, which considers higher resolution grids in both horizontal and vertical directions. The three-dimensiosal (3D)-MOHID Water model was validated for the TagusROFI by comparing statistically modelling results with in situ and satellite L4 data. Validation with a conductivity, temperature, and depth probe (CTD), an acoustic doppler current profiler (ADCP) and satellite data was performed for the first time. Validation against tidal gauges showed that the model is able to simulate tidal propagation inside the estuary with accuracy. A very good agreement between CTD data and surface sea water temperature (SST) and salinity simulations was observed. The validation of current direction and velocity from ADCP data also indicated a high model accuracy for these variables. Comparisons between model and satellite for SST also showed that the model produces realistic SSTs and upwelling events. Overall results showed that MOHID setup and parametrisations are well implemented for the TagusROFI domain. These results are even more important when a 3D model is used in simulations due to its complexity once it considers both horizontal and vertical discretization allowing a better representation of the heat and salinity fluxes in the water column. Moreover, the results achieved indicates that 3D-MOHID is robust enough to run in operational mode, including its forecast ability, fundamental to be used as a management tool.

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Validation of the 3D-MOHID Hydrodynamic Model for the Tagus Coastal Area

Estuarine and sediment dynamics in a microtidal tropical estuary of high fluvial discharge: Magdalena River (Colombia, South America)

. This study evaluated the influence of
low-frequency oscillations, that are linked to large-scale
oceanographic–atmospheric processes, on streamflow variability in small
tropical coastal mountain rivers of the Sierra Nevada de Santa Marta,
Colombia. We used data from six rivers that had > 32 years of
complete, continuous monthly streamflow records. This investigation employed
spectral analyses to (1) explore temporal characteristics of streamflow
variability, (2) estimate the net contribution to the energy spectrum of
low-frequency oscillations to streamflow anomalies, and (3) analyze the
linkages between streamflow anomalies and large-scale, low-frequency
oceanographic–atmospheric processes. Wavelet analyses indicate that the
8–12-year component exhibited a quasi-stationary state, with a peak of
maximum power between 1985 and 2005. These oscillations were nearly in phase
in all rivers. Maximum power peaks occurred for the Palomino and Rancheria
rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a
change in river variability patterns between 1995 and 2015, characterized by
a shift towards the low-frequency oscillations' domain (8–12 years). The net
contribution of these oscillations to the energy spectrum was as high as
51 %, a value much larger than previously thought for rivers in
northwestern South America. The simultaneous occurrence of hydrologic
oscillations, as well as the increase in the amplitude of the 8–12-year
band, defined periods of extremely anomalous wet seasons during 1989–1990,
1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations
in modulating streamflow variability in these rivers. Cross-wavelet transform
and wavelet coherence revealed high common powers and significant coherences
in low-frequency bands ( >96  months) between streamflow anomalies and
Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and
the Tropical North Atlantic Index (TNA). These results show the role of
large-scale, low-frequency oceanographic–climate processes in modulating the
long-term hydrological variability of these rivers.

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Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

Silvio Ospino

Papers

Estuarine and sediment dynamics in a microtidal tropical estuary of high fluvial discharge: Magdalena River (Colombia, South America)

Saltwater Intrusion into a River with High Fluvial Discharge: A Microtidal Estuary of the Magdalena River, Colombia

Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

Variability of suspended sediment properties in the saline front of the highly stratified Magdalena River estuary, Colombia