An examination of the forms and processes associated with bed waves in gravel-bed rivers with special reference to the braided river type
| dc.contributor.author | Hoey, Trevor Bernard | |
| dc.date.accessioned | 2020-08-14T01:42:28Z | |
| dc.date.available | 2020-08-14T01:42:28Z | |
| dc.date.issued | 1989 | en |
| dc.description.abstract | A review of the literature leads to a classification of bed waves and bedload pulses in gravel-bed rivers, on the basis of their spatial and temporal scales. Mesoscale waves and pulses are associated with distinctly different processes from macro- and mega-scale features. Whether the sources of sediment for the wave / pulse are endogenous or exogenous to the river channel is used as a basis for sub-classification. Froude number scale modelling of gravel-bed streams was performed in order to elucidate the mechanisms responsible for the production of bed waves. Three experimental runs were conducted, in which sediment transport rates and channel morphology were monitored. This was augmented by investigation of two reaches of the Kowai River, New Zealand, involving surveys of sediment storage and channel morphology, and palaeohydrological reconstruction of the flows responsible for production of the recorded morphology. Measured fluctuations in the sediment output rates from the model streams were related to cycles of aggradation and degradation in the channels. The aggradational phases were associated with decreasing bed relief, and transfer of sediment from inactive to semi-active and active storages within the channel bed. Degradational phases were associated with inverse patterns. The switch between aggrading and degrading states was weakly dependent on stream power per unit bed area. The sediment transport rate was only close to that predicted by the Bagnold (1980) equation at times of channel stability, which occurred in about 40 % of locations. The equation overpredicted actual transport during aggradation and underpredicted during degradation. Even with constant water and sediment inputs to the channel, waves and pulses of different spatial and temporal scales were produced. The relationships developed between aggradation and degradation, channel morphology, and sediment transport rates were supplemented by observations of the evolution of bed waves in the modelling experiments. Field data supported these results and added information on the textural properties of deposits within a bed wave. There were no significant differences between bed waves produced by endogenous sediment and exogenous material delivered to the river reach from upstream. Descriptive models of bed morphology changes as a bed wave passes through a cross-section were developed for the laboratory and field situations. Introduction of dyed tracer sediment to one of the experimental runs showed that the input sediment was rapidly dispersed, but this wasn't indicative of bed wave attenuation. A stochastic model of sediment transfers between in-channel storage reservoirs illustrated the differences between aggrading, stable and degrading channel conditions. The times taken for sediment from different reservoirs to reach the downstream end of the experimental channel were equal under given conditions, implying the existence of a form of equilibrium. The results enable the classification of wave types to be refined with waves of exogenous material that behave similarly to endogenous ones being separated from other exogenously supplied forms. The latter group have distinctive modes of behaviour. Equilibrium conditions were infrequently encountered at the mesoscale, but can be identified when the data are aggregated in both space and time. Bed waves of endogenous types can thus be regarded as equilibrium forms which lie within the geomorphological regime of gravel-bed river systems. | en |
| dc.identifier.uri | https://hdl.handle.net/10092/100893 | |
| dc.identifier.uri | http://dx.doi.org/10.26021/1099 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.publisher | University of Canterbury | en |
| dc.rights | All Rights Reserved | en |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | en |
| dc.title | An examination of the forms and processes associated with bed waves in gravel-bed rivers with special reference to the braided river type | en |
| dc.type | Theses / Dissertations | en |
| thesis.degree.discipline | Geography | en |
| thesis.degree.grantor | University of Canterbury | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
| uc.bibnumber | 267490 | en |
| uc.college | Faculty of Science | en |