Physical Modelling in Fluvial Geomorphology

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PHYSICAL MODELLING IN FLUVIAL GEOMORPHOLOGY 241 Figure 9.10 Schematic summary of observed modes of confluence movement and sedimentation in response to the migration of confluent anabranches. After Ashmore (1993) and reproduced by permission of the author and the Geological Society of London
242 SCIENTIFIC NATURE OF GEOMORPHOLOGY Figure 9.11 Chute cut-off in an established braided channel. (a) Point bar A begins to develop. (b) After a period of growth and increasing sinuosity, point bar A is cut off leaving portions of the original channel abandoned and developing a new point bar on the opposite bank. (c) Point bar at A is converted to a medial bar by a second chute cut-off. The elapsed time between successive photographs is 1 hour. Flow is from right to left. Interpretation and diagram after Ashmore (1991b, p. 331), reproduced with the permission of the author and the NRC Research Press distribution and had flow Reynolds and Froude numbers that were often transitional and supercritical, respectively (see Table 9.1 and the presence of oblique diagonal standing waves in many of Ashmore's photographs). However, these experiments clearly illustrate the full power and potential of an FSM and suggest that it is not always necessary to scale all parameters strictly to produce realistic predictive models. DISTORTED SCALE MODELLING (MOVABLE-BED MODELLING) For the study of large geomorphological scales, fine prototype sediments or precise modelling of sediment transport and deposition, models may have to be distorted. Geometrically distorted models have a small vertical:horizontal scale ratio in order to model large prototypes, whilst maintaining adequate model flow depth. Perhaps the most spectacular example of a distorted geometric model is that of the entire Mississippi basin by the US Corps of Engineers at a horizontal scale of 1:2000 and vertical scale of 1:100,
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Physical Modelling in Fluvial Geomorphology

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