Changes in the rates of floodplain and in-channel bench accretion in response to catchment disturbance, central Queensland, Australia

• Published in: Geomorphology (Amsterdam, Netherlands) Vol. 114; no. 3; pp. 338 - 347
• Main Authors: Hughes, Andrew O., Croke, Jacky C., Pietsch, Timothy J., Olley, Jon M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.01.2010; Elsevier
• Subjects: 137Cs depth profiles; Earth sciences; Earth, ocean, space; Exact sciences and technology; Floodplain sedimentation rate; Geomorphology, landform evolution; Great Barrier Reef; Human impact; Isotope geochemistry; Isotope geochemistry. Geochronology; Marine and continental quaternary; Optical dating; Sediment yield; Surficial geology; Coral Sea; Pacific Ocean; West Pacific; Queensland Australia; Australia; Great Barrier Reef; Human impact; Sediment yield; 137Cs depth profiles; Floodplain sedimentation rate; Optical dating; Great Barrier Reef; stream transport; gullies; Australasia; Cs depth profiles; sedimentation rates; human activity; settlement; accretion; drainage basins; dating; landscapes; rivers; models; Cs-137; OSL; climate; grains; erosion rates; floodplains; sediment yield; channels; prediction; landform evolution
• DOI: 10.1016/j.geomorph.2009.07.016
• ISSN: 0169-555X

Analysis of the changes in rates of catchment sediment storage can provide material evidence of the impact of landscape disturbance on catchment sediment flux. A number of studies have suggested increased sediment yields from the rivers draining to the Great Barrier Reef since European settlement in the mid-nineteenth century. Many of these predictions, which indicate increases between four to ten times the pre-disturbance estimates, are based on large-scale catchment modelling that make some critical assumptions about pre-disturbance erosion rates and/or sediment delivery ratios. In addition, the majority have not been validated by empirical data. This study uses single-grain OSL dating and 137Cs depth profiles to determine pre- and post-floodplain accretion rates in Theresa Creek, a subcatchment of the dry-tropical Fitzroy River basin. We demonstrate that floodplain accretion rates have increased by three to four times since European settlement ( ca. A.D. 1850). Decreased rates of floodplain accretion since the mid-twentieth century at sites contributed to by gullied terrain suggest a decrease in the supply of sediment derived from gully networks. In contrast, floodplain accretion rates from areas dominated by cultivation remain high. Widespread in-channel benches deposited since European settlement are stable and appear to be important stores of large volumes of sediment. Low magnitude increases in post-disturbance floodplain sedimentation rates (3 to 4 times), in comparison to those reported from mainly temperate climates (10 to 100 times), are attributed to the naturally high sediment loads typical of dry-tropical catchments. Consequently, previous predictions of large post-disturbance increases in sediment yields from large dry-tropical catchments draining to the Great Barrier Reef are likely to be overestimates.