Year

2013

Degree Name

Bachelor of Environmental Science (Honours)

ANZSRC / FoR Code

0502 ENVIRONMENTAL SCIENCE AND MANAGEMENT

Department

School of Earth & Environmental Science

Advisor(s)

Tim Cohen

Abstract

River response to large magnitude floods can vary significantly and a range of factors can influence this variation. Catchment and riparian vegetation represents a significant control over sediment supply and bank stability and yet is the control most vulnerable to human disturbance. Extensive vegetation clearing from the channel and floodplain in the period following European settlement has altered the hydrology and sediment regime of many Australian rivers, likely altering the geomorphic effectiveness of floods. Two major floods occurred in the Lockyer Valley, Queensland in January of 1974 and 2011. This study assessed the role of woody riparian vegetation in enhancing or inhibiting geomorphic change during these large floods.

Woody vegetation coverage in 1971, 1974, 2009 and 2011 was measured by classifying orthophotos. Changes in the spatial extent of woody vegetation between the two time periods were identified using a post classification change detection method. A combination of GIS methods and statistical analysis were used to assess the effect of this vegetation change on erosion and deposition occurring during the floods for three study reaches in contrasting valley settings. Analysis of geomorphic change occurring during the 1974 flood demonstrates the change occurring in lower reaches was much more significant in relation to the upper catchment. This study suggests that unvegetated banks in the 1974 flood were more susceptible to rapid geomorphic change. Furthermore, the results demonstrate that along the banks of two of the three reaches; woody vegetation was associated with more significant deposition and less erosion during the January 2011 flood. This was not consistent in the third reach, where significant erosion and deposition occurred in areas that were unvegetated or where vegetation was removed in the 2011 flood. This highlights that vegetation alone was not the only control on channel response to the large 2011 flood.

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