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 (R-2 = 0.82). 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.