Floodplain dynamics in space and time: the case of the Lockyer Valley south-east Queensland, Australia.

Abstract:

Twenty-two lives were lost in the Lockyer Creek floods in southeast Queensland (SEQ), Australia in the summer of 2011. The predicted average recurrence interval (ARI) for this event in the upper catchment was ~ 2000 yrs based on relatively short gauging station records (median 38 yrs in Eastern Australia). This study presents an assessment of the basin-scale (3000km²) spatial patterns of floodplain erosion, deposition, and net morphological change following the January 2011 using multitemporal Light Detection and Ranging (LiDAR) DEMs. Clear spatial patterns of floodplain deposition and erosion are evident reflecting high degrees of variability in channel capacity and floodplain inundation frequency. This data is then compared to a millennial-scale record of floodplain deposition from six key reaches of the Lockyer Valley determined using extensive stratigraphic and optically stimulated luminescence (OSL) dating. OSL samples were taken from both bedrock and alluvial reaches and from both floodplain and within-channel benches. This presentation discusses the resultant spatial and temporal dynamics of floodplain deposition in a catchment dominated by hydrological extremes. The results highlight some important considerations of preservation potential in floodplain reconstruction but also provide data to test key hypotheses with respect to flood reconstruction in south eastern Australia.