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Questions & Objectives

linking 3D particle-scale structures to the evolution of gravel bed morphology

Questions

The research will answer these questions:

  1. R1. In a natural river bed, how do the spatial patterns of sediment structure and critical shear stress respond to changes in flow and sediment supply?
  2. R2. How do 3D sediment structure and critical shear stress evolve in response to fine sediment supply and surface morphology?
  3. R3. To what extent do the spatial patterns of 3D sediment structure and critical shear stress control the morphological development of a channel?

Each question is addressed though a corresponding work package (WP). The research focusses on two scales, the grain-scale and the reach-scale.

Work Packages

  1. WP1. Quantify the reach-scale pattern of sediment structure in the field, and how it changes in response to external inputs.
  2. WP2. Flume experiments scaled with WP1 data will enable quantification of the grain-scale processes that produce the 3D sediment structure and thus determine critical shear stress.
  3. WP3. Numerical modelling will identify the extent to which the implementation of small-scale processes found in WP2 produces the reach-scale patterns and behaviours observed in WP1; WP3 thus combines two scales, and enables synthesis and scale up from the field site to other conditions (e.g. grainsize, channel slope etc.).

Objectives

Specific project objectives are to:

  1. O1. Instrument the field reach so that sediment structure, grain dynamics and channel morphology will be monitored before, during and after high flow events and undisturbed bed sediment samples retrieved (R1, WP1).
  2. O2. Perform a set of flume experiments designed to understand how bed structure varies in relation to:
    1. a) volume and calibre of fine sediment load and,
    2. b) in response to variable bed morphology (R2, WP2).
  3. O3. Quantify 3D bed sediment structure from objective 1 and 2 using large scale CT scanning and 3D image processing (R1 & R2, WP1 & WP2).
  4. O4. Develop relationships that are capable of replicating the feedback processes between sediment structure and critical shear stress observed in the field and flume (R3, WP3).
  5. O5. Use numerical modelling to synthesize and upscale the relationships developed in O4 to assess the impact of the findings at larger spatial and temporal scales (R3, WP3).

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