Preferential Erosion Zones in Mixed Bedrock-Alluvial Meandering Rivers
Abstract
Recent experiments conducted in the highly-sinuous Kinoshita Meandering Flume at the Ven Te Chow Hydrosystems Laboratory, University of Illinois at Urbana-Champaign, suggest that zones of preferential erosion in mixed bedrock-alluvial meandering rivers are a function of both, local curvature and sediment supply ratio (defined as the sediment transport rate divided by the sediment transport capacity). Results for seven experiments with below-capacity sediment supply ratios suggest that areas of preferential erosion are narrower in sections with higher curvature, and wider in sections with lower curvature. In addition, the areas of preferential erosion are closer to the inner bank for low sediment supply ratios and, as supply increases and the alluvial point bar grows, the areas of preferential erosion move towards the outer bank. These two factors contribute to the formation of inset channels and outer-bank bedrock benches. Both morphologies, commonly observed in the Shimanto River, in Kochi, Japan, differ from the typical cross section of a purely alluvial meander bend. In this study, we compare the experimental observations with the planform characteristics of an approximately 40 Km long reach of the Shimanto River. The analyses for both the field and laboratory data are based on image processing techniques. Data extracted includes the areas of preferential erosion, the centerline curvature signal and the width and location of the alluvial point bars and outer-bank bedrock benches. We present simple relations between the local curvature signal and the location and width of preferential erosion zones in the Shimanto River and the experimental conditions. We then discuss the path towards identifying general relations between channel centerline curvature, sediment supply ratios and the size and location of preferential erosion zones in mixed bedrock-alluvial meandering rivers.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP31A..06F
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1856 River channels;
- HYDROLOGYDE: 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS