The geomorphological and ecological functioning of the Silala River

Abstract Perennial rivers in desert regions are relevant environments that tend to concentrate most ecosystem services and values, but are not as studied as much as intermittent and ephemeral rivers. This article reports on the main morphological and ecological features of the Silala River, a narrow permanent river in the arid region of Antofagasta, in the north of Chile. The study was motivated by the dispute between Chile and Bolivia concerning the status of the Silala as an international watercourse. Field surveys of sediment transport using traps and marked sediments (colored and tagged clasts) revealed that finer sediments are moved in higher percentages and for longer distances than coarser sediment fractions, which corroborates the size‐selective nature of sediment dynamics in the river. The stream features the typical step/pool‐plane bed morphology that is to be expected in an alluvial river with the given boundary conditions of slope, grain size of sediments, and lateral confinement. Furthermore, the Morphological Quality Index (MQI) classifies the river as featuring overall good morphological conditions and the river hosts an abundant population of rainbow trout ( Oncorhynchus mykiss ). Although this is a non‐native species, their presence shows that the general conditions of the river (availability of food and presence of aquatic habitats) are able to sustain a population of resident fish. Overall, the morphological forms, geomorphic processes, and ecological features of the Silala River are typical of an alluvial stream with a permanent flow regime. This article is categorized under: Science of Water > Water and Environmental Change Human Water > Rights to Water Science of Water > Hydrological Processes Water and Life > Nature of Freshwater Ecosystems