Juan Camilo Restrepo

Sediment Transport and Geomorphological Change in a High-Discharge Tropical Delta (Magdalena River, Colombia): Insights from a Period of Intense Change and Human Intervention (1990–2010)

ABSTRACT Restrepo, J.C.; Schrottke, K.; Traini, C.; Ortiz, J.C.; Orejarena, A.; Otero, L.; Higgins, A., and Marriaga, L., 2016. Sediment transport and geomorphological change in a high-discharge tropical delta (Magdalena River, Colombia): Insights from a period of intense change and human intervention (1990–2010). There is strong indication that environmental changes and human interventions have affected freshwater discharge and sediment flux in the Magdalena River (northwestern South America) within the period from 1990 to 2010. Thus, stream flow, suspended sediment load (SSL), and riverbed dynamics were analysed in this study for estimating changes in the suspended sediment transport regime as well as of erosional/depositional patterns in different zones of the delta. It can be shown that stream flow increased at a higher rate than suspended sediment transport, promoting changes in the sediment transport regime. Erosion appeared at the mouth/frontal bar and the outlet zones and modified the sedimentary balance within the prodelta in the early 2000s. There is indication that cycles of erosion and accretion were controlled by the magnitude of fluvial discharge and riverbed scouring in the river outlet, whereas effluent diffusion and sediment dispersion were dominant in the delta front. High freshwater discharge, as buoyancy inputs, promoted the transfer of sediments from the river channel to the outer prodelta through the upper layers of the water column. Total sediment accumulation in the delta corresponded to <5% of the annual mean SSL of the Magdalena River. Overall, delta morphology remained relatively stable, experiencing a slow progradational state with highest sedimentation rates (≤1430 mm y−1) in the deepest zones.

Factors Influencing the Distribution and Characteristics of Surface Sediment in the Bay of Cartagena, Colombia

ABSTRACT Restrepo, J.C.; Escobar, J.; Otero, L.; Franco, D.; Pierini, J., and Correa, I., 2017. Factors influencing the distribution and characteristics of surface sediment in the Bay of Cartagena, Colombia. This study evaluated patterns of coastal sediment movement and deposition under different seasonal conditions (warm and cold phases of the El Niño–Southern Oscillation [ENSO] and normal conditions) in Cartagena Bay, Colombia. A calibrated numerical model (MOHID modeling system) was applied to assess the spatial distribution of sediments transported by the Canal del Dique to the bay and studied the spatial distribution and major textural characteristics of 234 surface sediment samples. Currents in the Bay of Cartagena are controlled primarily by the strength and direction of the wind. Model results show major sediment deposition in the southern sector of the bay during the dry season. More homogenous spatial distribution of sediments throughout the Bay of Cartagena occurs with an increase in river inputs from the Canal del Dique. These patterns were enhanced or weakened, respectively, by cold and warm phases of the ENSO. Predominant sediments were medium size (ϕ = 5.35 ± 1.2), poorly sorted (σ = 1.63 ± 0.8), with notable asymmetry (Sk = −0.052 ± 0.2) and kurtosis (k = 0.84 ± 0.4). Sediments with lower sand content (<5%) are located along a latitudinal axis from the Canal del Dique delta to the western end of the island of Tierrabomba. CaCO3 content of the sediments is <10%. Water and sediment flow, controlled by the Canal del Dique, has favored the transport and deposition of poorly sorted, symmetric, and mesokurtic mud in most of the Bay of Cartagena. As a result, autogenous calcareous sediments have been covered by fine terrigenous sediments that were delivered via the Canal del Dique. Thus, the channel plays a more prominent role in sediment transport and deposition in the Bay of Cartagena than thought previously.

Discriminating between different streamflow regimes by using the Fisher-Shannon method: An application to the Colombia rivers

The Fisher-Shannon (FS) information plane, defined by the Fisher information measure (FIM) and the Shannon entropy power (NX), was robustly used to investigate the complex dynamics of eight monthly streamflow time series in Colombia. In the FS plane the streamflow series seem to aggregate into two different clusters corresponding to two different climatological regimes in Colombia. Our findings suggest the use of the statistical quantity defined by the FS information plane as a tool to discriminate among different hydrological regimes.

Changes in seasonal streamflow extremes experienced in rivers of Northwestern South America (Colombia)

A measure of the variability in seasonal extreme streamflow was estimated for the Colombian Caribbean coast, using monthly time series of freshwater discharge from ten watersheds. The aim was to detect modifications in the streamflow monthly distribution, seasonal trends, variance and extreme monthly values. A 20-year length time moving window, with 1-year successive shiftments, was applied to the monthly series to analyze the seasonal variability of streamflow. The seasonal-windowed data were statistically fitted through the Gamma distribution function. Scale and shape parameters were computed using the Maximum Likelihood Estimation (MLE) and the bootstrap method for 1000 resample. A trend analysis was performed for each windowed-serie, allowing to detect the window of maximum absolute values for trends. Significant temporal shifts in seasonal streamflow distribution and quantiles (QT), were obtained for different frequencies. Wet and dry extremes periods increased significantly in the last decades. Such increase did not occur simultaneously through the region. Some locations exhibited continuous increases only at minimum QT.

Medición de la concentración de sedimentos en suspensión mediante dispositivos ópticos y acústicos: aplicación en sistemas tropicales (Delta del río Mira, Colombia)

In recent years, the use of optical (Optical Backscatter Sensor, OBS) and acoustic (Acoustic Current Doppler Profiler, ADCP) instruments has allowed monitoring the temporal and spatial variation of the suspended sediment concentration (SSC) in coastal and estuarine environments with greater resolution. However, the development of the application of those techniques in tropical environments is incipient. For this study, an OBS-3A calibration procedure was implemented, taking dry and desegregated sediment from the study zone as a calibrating pattern. Moreover, we present the corrections required for the ADCP signal to be useful in the estimation of SSC due to geometrical spreading, the attenuation of sound by water, and the particles in suspension. The ADCP and OBS-3A were used to measure SSC in the Mira River delta system (Morro Island and principal river mouth), located on the Pacific coast of Colombia, a coastal tropical environment where some oceanographic and estuarine factors determine the signal response of the instruments.

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

ABSTRACT 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, temperature, and salinity data, obtaining Skill values greater than 0.90. To cover a wide range of variability in the main forcing factors (fluvial discharge, tide, and wind), the conditions recorded in 2010 were simulated when both phases of the El Niño–Southern Oscillation phenomenon occurred. During that year, the river discharge ranged between 2465 and 16,463 m3 s−1. Results revealed a stratified, saltwater wedge estuary, the dynamics of which were mainly dominated by river discharge. Tide and winds altered saltwater intrusion dynamics, mainly during low-discharge periods.

Swash Oscillations in a Microtidal Dissipative Beach

ABSTRACT Conde-Frias, M.; Otero, L.; Restrepo, J.C.; Ortiz, J.C.; Ruiz, J., and Osorio, A.F., 2017. Swash oscillations in a microtidal dissipative beach. This paper evaluates the relationship between gravity and infragravity energy with swash oscillations as well as the models ability to reproduce the transformation of the wave as it approaches the shore on a dissipative beach. For this purpose, numerical experiments were conducted in a dissipative beach from Cartagena, Colombia. Mean free surface measurements were carried out for 2 days in February 2014 by installing a cross-shore array of pressure sensors, as well as a Fourier analysis from these measurements to identify frequency components that characterize the waves and the energy associated with them. To implement the numerical modelling, the SWASH model (The Simulation WAves till Shore is a numerical model that resolves nonlinear shallow-water equations) was set up by using the bathymetric profile of Bocagrande Beach obtained during the field campaign. The results of this numerical modelling enabled the study of the infragravity energy growth mechanism and the evolution of gravity energy as the wave approaches the shore, as well as the relationship between gravity and infragravity energy with swash oscillations. Overall, the results show that the model is able to reproduce the significant wave height and significant wave height associated with infragravity energy; moreover, the model is able to accurately describe processes of energy dissipation and energy transfer. Furthermore, through a spectral analysis applied to the swash oscillations time series it was possible to find that saturation occurs at low-frequency significant swash height and high-frequency significant swash height as the significant wave height increases, since its increase is not linear with respect to the signficant wave height incident.