Juan D. Restrepo

A Spatial Simulation Experiment to Replicate Fluvial Sediment Fluxes within the Magdalena River Basin, Colombia

Spatial variation of natural conditions (geomorphology, geography, and geology) and human perturbations (deforestation and reservoir retention) in river basins determine the variability of within-basin riverine sediment fluxes. Originally developed to determine a 30-yr normal of sediment load at a river mouth or for a “whole basin,” the scaling model BQART is validated to predict the sediment discharge from “within-basin” tributaries. Subbasins of the monsoonal-influenced Magdalena River are used here as case studies. By taking into account spatially variable geological, climatological, and human influences of the Magdalena tributaries, and by incorporating observational data to adjust for floodplain trapping due to a tectonic depression, the BQART model overestimates the cumulative sediment flux of 21 tributaries by 25% compared with observations ( ). For a given subbasin, BQART estimates are well within a factor of 3. The relatively short durations of the observations of each of the tributaries (6–25 yr), in combination with rapidly changing subbasin environments (like deforestation and mining intensification), likely affect the goodnesses of fit of the comparisons.

Sediment Transfers from the Andes of Colombia during the Anthropocene

This chapter reviews data, models, and analyses on Anthropocene-impacted sediment fluxes in the Andes of Colombia and provides examples on how direct human alteration has increased sediment flux during the last decades. Firstly, it describes the context of the northern Andes in terms of sediment production within the whole Andes Cordillera. Secondly, it presents a summary of major land cover changes witnessed in the region from 8000 years ago to the beginning of large-scale land transformation that occurred in Colombia during the last three decades and analyzes major human-induced drivers of change. Also, trends in sediment load during the 1980–2010 period are documented. Finally, it compares modern and prehuman conditions of sediment flux by using some applied models in global and Colombian rivers.

An environmental magnetism approach to assess impacts of land-derived sediment disturbances on coral reef ecosystems (Cartagena, Colombia)

We used environmental magnetism methods to study recently deposited marine sediments from the estuarine ecosystems on the Caribbean coast of Colombia. Cartagena region has undergone an increasing sediment load during the last decades via sediment plumes from Magdalena River and its distributary man-made channel. Concentration dependent magnetic parameters show an increasing abundance of ferrimagnetic minerals on the uppermost sediments on sites located close to the continent (remanent magnetization SIRM = 5.4-9.5 × 10-3Am2 kg-1) as well as faraway sites (SIRM = 0.5-1.7 × 10-3Am2 kg-1 near Rosario Islands coral reef complex). The magnetic grain size and mineralogy along the cores are variable, showing the dominance of the magnetite-like minerals (remanent coercivity Hcr = 34.3-45.3 mT), with a minor contribution of high-coercivity minerals (Hcr = 472-588 mT). In addition, there is a moderate enrichment of elements Cu, Mo, and Zn (enrichment factor EF = 1.5-3.8) that indicates the additional land-derived contribution on sediments. The environmental magnetism approach, which shows significant signals of magnetic minerals and trace elements, is a reliable tool to prove the presence of continental sediment supply in coral reef ecosystems.

Satellite-Based Estimation of Water Discharge and Runoff in the Magdalena River, Northern Andes of Colombia

The Magdalena River and its most important tributary, the Cauca, drain the northern Andes of Colombia. During the wet season, flood events affect the whole region and cause huge damage in low-income communities. Mitigation of such natural disasters in Colombia lacks science-supported tools for evaluating river response to extreme climate events. Here we introduce near-real-time estimations of river discharge toward technical capacity building for evaluation of flood magnitudes and variability along the Magdalena and Cauca. We use the River Watch version 3 system of the Dartmouth Flood Observatory (DFO) at five selected measurement sites on the two rivers. For each site, two different rating curves were constructed to transform microwave signal from TRMM, AMSR-E, AMRS-2, and GPM satellites into river discharge. The first rating curves were based on numerical discharge estimates from a global Water Balance Model (WBM); the second were obtained from the relationship between satellite signal and measured river discharge at ground gauging stations at nearby locations. Determination coefficients (R 2) between observed versus satellite-derived daily discharge data range from 0.38 to 0.57 in the upper basin, whereas in the middle of the basin R 2 values vary between 0.47 and 0.64. In the lower basin, observed R 2 values are lower and range from 0.32 to 0.4. Once time lags between the microwave satellite signal and river discharge from either WBM estimates or ground-based gauging stations are taken into account, the R 2 values increase considerably.