School of Geography - Theses
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ItemCauses of incision of Gippsland river channels during the period of European settlement, with particular reference to Bruthen Creek( 1987)Historical evidence shows that many of the Gippsland river channels which are now deeply incised were formerly shallow, meandering and swampy. The change has occurred within the historic period, beginning in most cases between 1870 and 1900. This thesis investigates the changes along Bruthen Creek, near Yarram, using a variety of historical sources, including early maps and air photos, and archival material from the Department of Crown Lands and Survey (now the Department of Conservation, Forests and Lands), Victorian Railways (now V-line) and the local Shire offices. Together these provide sufficient evidence to support a model of development of incision through headward migration of a series of five distinct erosion sequences, each of which originated in a different part of the channel system. Possible causes of instability are investigated. It is concluded that although there appears to have been a climatic change towards increased annual rainfall in the area, dating from the mid 1940s, as proposed for coastal New South Wales, there is no evidence that this is causally related to channel instability. Similarly, although there has been extensive deforestation of the catchment, it is argued that this has not had sufficient impact on run-off to have caused channel erosion. The thesis concludes that human interference has been the critical factor leading to incision, particularly the efforts to drain the riverain swamps by channelising flow within them, and limiting the extent and frequency of flooding. This hypothesis is presented for Bruthen Creek, and evaluated in the light of the author's studies of eroded channels in other parts of Gippsland. Many of these studies have already been published, and are presented with this thesis as supporting papers. Some evidence is also included from the preliminary studies by the author, not yet published, of channel instability in a group of tributaries of the Tarra River, the catchment of which adjoins that of Bruthen Creek. It is concluded that all the Gippsland channels which were shallow and poorly defined at the time of settlement and have subsequently incised have been subject to similar attempts to channelise flow. Much of the work was carried out on a small scale by individual farmers soon after land settlement, and the only record of their activities is in the original land selection records. Entrainment of flow to ensure that floodwaters passed under newly constructed road and rail bridges has been a contributory factor, but most of this, particularly in the case of roads, is only poorly documented. The importance of individual action, and the paucity of early road records, has meant that the extent of human interference has often been underestimated, because much of it took place long before the establishment of a government department with a specific interest in river management.