Human Impacts on Sediment and Morphodynamics of Large Tropical Rivers

Abstract

A significant number of studies have been done on several tropical rivers in the last few decades focusing on hydrogeomorphic processes, morphodynamics, soil erosion and sediment fluxes, environmental flow assessment, river responses to climate change, and human interventions on the rivers and basins. However, many rivers in the tropics are still understudied or are barely known to the global scientific audience. This is particularly sensitive because the environmental pressure on tropical rivers has increased rampantly during the last two decades. Eight of the ten largest rivers of the world in water discharge or “megarivers” are in tropical regions. This group of tropical megarivers includes some of the remaining less human-impacted rivers of the world (e.g., the Japura-Caquetá) and also some of the most hydrophysically impacted and polluted systems (e.g., Ganges). We provide an update on the geomorphology research on rivers in the wet and tropical wet-dry regions and identify how geomorphology can contribute to tropical rivers’ ongoing and future environmental challenges. The geotectonic and climate settings, the hydrosedimentological regime, the geomorphological diversity, and the human pressures suffered by tropical rivers in the Anthropocene are discussed. We conclude that a past-present understanding of these fluvial systems and the production of first-hand knowledge of historical human-nature interactions is essential. Otherwise, if relying too strongly on modeling and generalizations that do not consider a deep regional knowledge of nature and human-nature dimension, we will fall short in understanding the evolution and morphodynamics of these systems, in predicting their response to global change, and in effectively contributing to societies and the decision-making chain beyond endemic discussions in academic circles.