Flow-substrate interactions in geophysical flows

On earth, and every solid planetary body studied in this solar system, geophysical flows sculpt the landscape in environments including rivers, glaciers, deserts, deltas, shallow seas and the deep oceans. A near ubiquitous feature of such flows is that sediment transport produces features such as ripples and dunes, i.e., bedforms. Bedforms are important because their presence strongly affects the character of any deposited sediment and influences the character of the overpassing flows. Thus, the mutual interaction of bedform and flow is a complex and poorly understood system and is the focus of intense study. Controlling factors include the shear of the overpassing flow and the characteristic grain size – commonly interpreted by bedform phase-space stability diagrams. However, flow-bed interaction is complicated by other variables, including: sediment grainsize distribution and abiotic and/or biotic inter-particle cohesive forces; short time scale variations in the flow conditions; rapid transition through bedform phase-space and inherited bedform conditions; long time scale changes in flow conditions and bedform preservation. Although the complete list of controls is too complex to systematically study experimentally, novel analytical and numerical bedform evolution models, calibrated to selected experimental data, offer a unique opportunity to investigate a key earth surface process.