Relationship between morphology and sediment transport in a canyon river channel, Southern Brazil

PurposeMountain rivers differ from alluvial rivers due to their morphology and hydraulic characteristics. Within various types of mountain rivers, the canyon rivers are those under the direct or indirect influence of canyon landscapes. Studies involving canyons are extensive in the literature. However, there is a lack of knowledge to establish a relationship between morphology, topography, local sediments, and river channel characteristics. This study aims to understand the relationship between morphology, topography, and local sediments in a canyon river in Southern Brazil.MethodsTopobathymetric data were obtained during a field survey using a total station and an RTK-GPS device for three reaches (canyon landscape (CL), transition landscape (TL), and floodplain landscape (PL)) in the canyon river. Features such as bankfull width, depth, channel slope, and floodplain width were obtained. Geomorphic patterns of the reaches were evaluated in terms of their classification and similarity level through cluster analysis. Sediment size was surveyed using the zig-zag pebble-count procedure.ResultsResults suggest that sediment supply is an essential characteristic of the canyon's influence on river morphology. This condition improves the heterogeneity observed in the Geomorphic Unit Tool and topographical results. The thalweg lines are more complex in CL than the TL and PL reaches. Three grain-size-distribution curves presented similar sediment size and mean diameters. Sediments larger than d(80) remain immobile or, at least, need fractioning for transporting or depositing somewhere. Alternatively, these sediments may be transported during debris flow events or discharges with a high return period.ConclusionThe influence of the canyon on river characteristics weaken from upstream, close to the gorge, to downstream toward the floodplain. The valley shape can affect sediment transport since the entrenchment caused by the canyon walls influences the water level and the hydraulic conditions for incipient motion conditions.

Automated summary

This study aims to understand the relationship between morphology, topography, and local sediments in a canyon river in Southern Brazil. Topobathymetric data were obtained during a field survey, and the results suggest that sediment supply is an essential characteristic of the canyon's influence on river morphology. The study also found that the influence of the canyon on river characteristics weaken from upstream to downstream.