A Froude‐scaled model of a bedrock‐alluvial channel reach: 2. Sediment cover. Issue 9 (16th September 2016)

• Record Type: Journal Article
• Authors: Hodge, Rebecca A.; Hoey, Trevor B.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016)
• Page Start: 1597
• Page End: 1618
• Publication Date: 2016-09-16
• Subjects: bedrock‐alluvial channel -- flume experiments -- sediment cover; Geomorphology -- Periodicals; 551.3
• DOI: 10.1002/2015JF003709
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Previous research into sediment cover in bedrock‐alluvial channels has focussed on total sediment cover, rather than the spatial distribution of cover within the channel. The latter is important because it determines the bedrock areas that are protected from erosion and the start and end of sediment transport pathways. We use a 1:10 Froude‐scaled model of an 18 by 9 m reach of a bedrock‐alluvial channel to study the production and erosion of sediment patches and hence the spatial relationships between flow, bed topography, and sediment dynamics. The hydraulic data from this bed are presented in the companion paper. In these experiments specified volumes of sediment were supplied at the upstream edge of the model reach as single inputs, at each of a range of discharges. This sediment formed patches, and once these stabilized, flow was steadily increased to erode the patches. In summary: (1) patches tend to initiate in the lowest areas of the bed, but areas of topographically induced high flow velocity can inhibit patch development; (2) at low sediment inputs the extent of sediment patches is determined by the bed topography and can be insensitive to the exact volume of sediment supplied; and (3) at higher sediment inputs more extensive patches are produced, stabilized by grain‐grain and grain‐flow interactions and less influenced by the bed topography. Bedrock topography can therefore be an important constraint on sediment patch dynamics, and topographic metrics are required that incorporate its within‐reach variability. The magnitude and timing of sediment input events controls reach‐scale sediment cover. Key Points: Sediment patches tend to form in low‐elevation, sheltered areas, but high flow velocities can override this At lower sediment supply, bed topography determines patch stability and patches are relatively insensitive to sediment supply At higher sediment supply, sediment patches stabilize by grain‐grain and grain‐flow interactions