Morphodynamics of Colombian Deltas under Changing Sediment Supply: Scenario-based projections using BQART

Abstract

Fluvial sediment flux plays an important role in shaping the morphology of river deltas. Deltas are facing increasing threats to their sediment flux as a result of climate change, sea-level rise, and anthropogenic activities. Understanding the effects of changing sediment fluxes under different climate and socio-economic pathways will improve insight into the delta’s future morphological evolution. This study assesses future changes in fluvial sediment flux and subsequent morphological evolution of six major Colombian river deltas: the Magdalena, Sinu, Atrato, San Juan, Patia, and Mira. Sediment flux projections were made using the BQART equation under the climate and socio-economic pathways of SSP-RCP 1-2.6, SSP-RCP 3-7.0, and SSP-RCP 5-8.5 between 1960 and 2100. In turn, these projections were combined with the quantitative Galloway classification to assess relative changes in process dominance. Across all projections, sediment flux is the highest under the conditions of SSP585, and the lowest under the conditions of SSP126. However, the results vary significantly as a result of differing combined effects of climate change and anthropogenic activities. The fluvial sediment fluxes of the Magdalena, Sinu, and Patia are projected to decrease under all pathways, largely driven by reservoir construction and land-use change. Increased sediment fluxes are projected for the Atrato, San Juan, and Mira deltas, primarily in response to rising temperatures. These changes in sediment supply lead to increased wave and tidal dominance under reduced fluvial sediment flux, and enhanced fluvial dominance where sediment fluxes increase. The largest changes in process dominance are projected for the Magdalena and Sinu deltas. In contrast, the strong present-day fluvial dominance of the Atrato and tidal dominance of the San Juan, Patia, and Mira result in comparatively limited shifts in their morphological regimes. Despite inherent uncertainties, the applied combination of the BQART and Galloway diagram using global datasets provides a valuable comparative framework for assessing fluvial sediment flux and morphological evolution under different climate and socio-economic pathways. The results indicate that differences in vulnerability to climate change can inform coastal planning and catchment-wide policy development under different climate and socio-economic pathways by accounting for geomorphologic consequences.