We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Limited effect of the confluence angle and tributary gradient on Alpine confluence morphodynamics under intense sediment loads.
- Authors
Ostrander, Théo St. Pierre; Kraus, Thomé; Mazzorana, Bruno; Holzner, Johannes; Andreoli, Andrea; Comiti, Francesco; Gems, Bernhard
- Abstract
Confluences are dynamic morphological nodes in all river networks. In mountain regions, they are influenced by hydraulic and sedimentary processes occurring in steep channels during extreme events in small watersheds. Sediment transport in the tributary channel and aggradation in the confluence can be massive, potentially causing overbank flooding and sedimentation into adjacent settlement areas. Previous works dealing with confluences have been mainly focused on lowland regions, or if focused on mountain areas, the sediment concentrations and channel gradients were largely under-representative of mountain river conditions. The presented work contributes to filling this research gap with 45 experiments using a large-scale physical model. Geometric model parameters, applied grain size distribution, and the considered discharges represent the conditions at 135 confluences in South Tyrol (Italy) and Tyrol (Austria). The experimental program allowed for a comprehensive analysis of the effects of (i) the confluence angle, (ii) the tributary gradient, (iii) the channel discharges, and (iv) the tributary sediment concentration. Results indicate, in contrast to most research dealing with confluences, that in the presence of intense tributary sediment supply and a small tributary to main channel discharge ratio (0.1), the confluence angle does not have a decisive effect on confluence morphology. Adjustments to the tributary channel gradient yielded the same results. A reoccurring range of depositional geomorphic units was observed where a deposition cone transitioned to a bank-attached bar. The confluence morphology and tributary channel gradient rapidly adjusted, tending towards an equilibrium state to accommodate both water discharges and the sediment load from the tributary. Statistical analyses demonstrated that confluence morphology was controlled by the combined channel discharge and the depositional or erosional extents by the sediment concentration. Applying the conclusions drawn from lowland confluence dynamics could misrepresent depositional and erosional patterns and the related flood hazard at mountain river confluences.
- Subjects
SEDIMENTATION &; deposition; PARTICLE size distribution; SEDIMENTS; EVIDENCE gaps; SEDIMENT transport; AGGRADATION &; degradation; ANALYSIS of river sediments; FLOOD damage prevention
- Publication
Natural Hazards & Earth System Sciences Discussions, 2023, p1
- ISSN
2195-9269
- Publication type
Article
- DOI
10.5194/egusphere-2023-2432