Hydraulic resistance in mixed bedrock-alluvial meandering channels

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.

Automated summary

The experimental analysis showed that hydraulic resistance in a mixed bedrock-alluvial channel changes with the degree of alluviation, with greater resistance for bare-bedrock conditions but decreasing as sediment supply increases. Bedforms may lead to increased resistance due to form drag, and fluctuations in alluvial cover can result in instantaneous changes in hydraulic resistance.