Resource Management and Geography - Theses
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ItemRiver channel changes in Gippsland, Victoria( 1990)Channel changes during the period of European settlement on three streams in Gippsland, Victoria, the Thomson and Avon Rivers and Freestone Creek, were investigated on the basis of information contained in historical documentary sources including early maps and aerial photographs and the files and records of a number of Victorian government departments. Changes in channel position, planform characteristics, cross section, long profile and channel behaviour were analysed both qualitatively and quantitatively, revealing that river metamorphosis had occurred on parts of all three streams in the study area at different times during the period of European settlement. River metamorphosis in all cases involved changes in both channel morphology and channel behaviour; and on the Thomson River and Freestone Creek coincided with channel avulsion. A causal link between changes in the channel/floodplain relationship resulting from incision and river metamorphosis was identified. Incision associated with river metamorphosis was the result of both intrinsic geomorphological factors and human interference, the relative importance of which varied between streams. Changes in catchment-generated discharge regimes and sediment loads of sufficient magnitude to have caused river metamorphosis are considered unlikely except at the downstream end of the Avon River. Channel changes took place here in response to an increase in sediment load resulting from upstream channel changes and occurred in the absence of any major change in the channel/floodplain relationship. Since the explanation of the causes of river metamorphosis in terms of changes in the channel/floodplain relationship offered in this thesis cannot be accommodated by Schumm's (1969) widely accepted model, an alternative model of river metamorphosis is proposed. This model envisages channel morphology and behaviour as being controlled by an intrinsic sequence of channel and floodplain development, of which river metamorphosis is an inherent component. Extrinsic disturbances can cause river the intrinsic sequence and metamorphosis also even by short circuiting without this shortcircuiting. The occurrence of river metamorphosis in response to intrinsic controls and in the absence of changes in external inputs has serious implications for fluvial palaeohydrology. It means that climatic or other environmental changes cannot be validly inferred from alluvial evidence without independent supporting data.