This proposal will generate a new quantitative process-based understanding of bedform adjustment to unsteady flows using both laboratory and field measurements, and link these new data to the development and application of a new numerical model of flow-bedform-roughness response.

  1. Quantify the morphology, flow fields, concurrent sediment transport and topographic change over mobile beds in a laboratory flume under a range of unsteady flow conditions (pre-determined hydrographs of different temporal scales) and identify the dynamic interactions between flow, sediment transport and the bed morphology in response to change.
  2. Quantify, in the laboratory, turbulent flow fields over fixed bedforms (that are informed by scaling from 1) under a range of disequilibrium conditions to generate a high-resolution, quantitative hydraulic context from which to explain flow-form-flow interactions during unsteady flow.
  3. Derive and quantify, from the outputs of 1 and 2, the processes and implications of bed response to unsteady flow in terms of both form drag and bed roughness.
  1. Validate the experimental relationships determined from (1-3) at the field scale through repeat detailed field surveys of bathymetry and flow during the annual floods (April/May) and base-flow conditions (September/October) on the Mississippi River (north of St Louis).
  2. Develop a fully three-dimensional numerical model that predicts the forcing mechanisms to capture the dynamics of dune migration including the feedbacks between sediment transport, dune morphology and flow structure.
  3. Use the results derived from 5 to determine process-coupling parameterisation for inclusion of physically-based dynamic forcing mechanisms within generic morphodynamic models applied over large areas (>10 km2) and longer time periods (>full flood hydrographs).