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Hydraulic resistance in mixed bedrock-alluvial meandering channels

Author(s): Roberto Fernandez; Marcelo H. Garcia; Gary Parker; Alejandro J. Vitale

Linked Author(s): Marcelo García, Gary Parker, Roberto Fernandez

Keywords: Lluvial cover; Bars; Bed roughness; Bedforms; Bedload; Hydraulic resistance; Meandering

Abstract: We present an experimental analysis of hydraulic roughness variations due to changes in alluvial cover in a mixed bedrock-alluvial meandering channel with larger bedrock roughness than alluvial roughness. Three sets of experiments were conducted in a highly sinuous flume: one with bare bedrock, and two with enough sediment to cover 21% and 78% of the bedrock respectively. We compare our results with data from experiments previously conducted in the same flume with flat- and smooth-bed, and data from experiments with fully alluvial conditions. Our results show that: (1) hydraulic resistance in a mixed bedrock-alluvial channel changes with the degree of alluviation; (2) hydraulic resistance is greater for bare-bedrock conditions, and decreases as sediment supply increases; (3) if bedforms appear, hydraulic resistance may be larger than for bare bedrock conditions due to form drag; (4) fluctuations in alluvial cover due to freely-migrating bars lead to instantaneous changes in hydraulic resistance.

DOI: https://doi.org/10.1080/00221686.2020.1780489

Year: 2021

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