Do the morphological characteristics of Chilean gravel-bed rivers exhibit latitudinal patterns?

Abstract

Gravel-bed rivers exhibit remarkable dynamics and distinctive morphological patterns which influence the biological processes, as well as the river ecosystem resilience to human impacts. Classifications of river ecosystems into groups with morphologically distinct patterns are therefore of paramount importance for a better understanding of their dynamics, their management and conservation.Investigations on fluvial morphology and the related dynamics in Chilean gravel-bed rivers are still scarce, and, so far, no efforts have been made to identify latitudinal patterns of their morphological characteristics that may serve as a basis for further classification purposes. In fact, the great variability in bio-geographic, climatic, geologic and geomorphologic settings of the country offer an almost unique opportunity to study how the morphological characteristics of gravel-bed rivers may vary within extremely heterogeneous environments.We performed a regional analysis of nineteen Chilean gravel-bed rivers, from semi-arid Mediterranean to rainy temperate conditions (latitude ranging from 32° S to 39° S). Planform characteristics within these reaches were identified through interpretation of satellite images. Topographic features of the river basins were derived from open source digital elevation models and water discharge values were obtained from available national databases.We addressed the following research questions: a) can these 19 rivers be grouped into clusters considering their distinct planform characteristics of the river channel and basin features, as related to latitudinal gradients?, b) do river morphological characteristics vary along the analyzed latitudinal gradient?, c) does the distribution of specific geomorphic units (i.e. islands) follow a longitudinal pattern?, and finally, d) are these units associated to specific hidrogeomorfic characteristics?We generated a clustering which reflects latitudinal and morphological gradients in Chilean gravel-bed rivers, with the northernmost and southernmost rivers grouped according to their distinctive hydro-morphological characteristics and geomorphic units. We also observed a general tendency of an increase in the proportion of fluvial islands relative to the active channel area from the 33° Latitude in southward direction.