Research Article 2014 WRR Burdekin sediment budget

PUBLICATIONS Water Resources Research RESEARCH ARTICLE 10.1002/2013WR014386 Key Points:  Catchment sediment budgets should incorporate sediment particle size  Large reservoir influences clay and fine silt transport in a tropical catchment  Annual sediment loads highly variable in seasonally dry tropical rivers Supporting Information: Readme  Bainbridge et al Auxiliary Material  Correspondence to: Z. T. Bainbridge, [email protected] Citation: Bainbridge, Z. T., S. E. Lewis, S. G. Smithers, P. M. Kuhnert, B. L. Henderson, and J. E. Brodie (2014), Fine-suspended sediment and water budgets for a large, seasonally dry tropical catchment: Burdekin River catchment, Queensland, Australia, Water Resour. Res., 50, 9067–9087, doi:10.1002/2013WR014386. Received 15 JUL 2013 Accepted 20 OCT 2014 Accepted article online 27 OCT 2014 Published online 24 NOV 2014 Fine-suspended sediment and water budgets for a large, seasonally dry tropical catchment: Burdekin River catchment, Queensland, Australia € T. Bainbridge 1,2,3 , Stephen E. Lewis 1 , Scott G. Smithers 1,2 , Petra M. Kuhnert 4 , Zo e Brent L. Henderson 5 , and Jon E. Brodie 1 1 Catchment to Reef Research Group, TropWATER, James Cook University, Townsville, Australia, 2 College of Marine and Environmental Sciences, James Cook University, Townsville, Australia, 3 CSIRO Land and Water Flagship, ATSIP, Townsville, Queensland, Australia, 4 CSIRO, Adelaide, South Australia, Australia, 5 CSIRO, Canberra, Australian Capital Territory, Australia Abstract The Burdekin River catchment (130,400 km 2 ) is a seasonally dry tropical catchment located in north-east Queensland, Australia. It is the single largest source of suspended sediment to the Great Barrier Reef (GBR). Fine sediments are a threat to ecosystems on the GBR where they contribute to elevated turbid- ity (reduced light), sedimentation stress, and potential impacts from the associated nutrients. Suspended sediment data collected over a 5 year period were used to construct a catchment-wide sediment source and transport budget. The Bowen River tributary was identified as the major source of end-of-river sus- pended sediment export, yielding an average of 530 t km 22 yr 21 during the study period. Sediment trap- ping within a large reservoir (1.86 million ML) and the preferential transport of clays and fine silts downstream of the structure were also examined. The data reveal that the highest clay and fine silt loads— which are of most interest to environmental managers of the GBR—are not always sourced from areas that yield the largest total suspended sediment load (i.e., all size fractions). Our results demonstrate the impor- tance of incorporating particle size into catchment sediment budget studies undertaken to inform manage- ment decisions to reduce downstream turbidity and sedimentation. Our data on sediment source, reservoir influence, and subcatchment and catchment yields will improve understandings of sediment dynamics in other tropical catchments, particularly those located in seasonally wet-dry tropical savannah/semiarid cli- mates. The influence of climatic variability (e.g., drought/wetter periods) on annual sediment loads within large seasonally dry tropical catchments is also demonstrated by our data. 1. Introduction Sediment budgets provide a structured framework for representing river catchment sediment sources, stor- age, and yields [Dunne and Leopold 1978; Walling and Collins, 2008], and provide an effective communica- tion tool for natural resource managers to understand sediment loads and transport [Slaymaker, 2003]. In particular, catchment-scale sediment budgets have been applied to identify changes in catchment sedi- ment loads and sources associated with anthropogenically modified land use, including both increases in loads driven by elevated erosion associated with land clearing, agriculture, and mining as well as declines in sediment load downstream of depositional areas such as reservoirs [Syvitski, 2003; Walling, 2006]. Although this approach is commonly adopted (see reviews by Walling and Collins [2008] and Koiter et al. [2013]), there have been few sediment-budget studies from tropical catchments (see reviews by Nagle et al. [1999] and Tooth [2000]). Further, detailed investigations on the transport of specific sediment-size fractions within tropical catchments are rare [e.g., Verbist et al., 2010]. This study addresses this knowledge gap by quantify- ing suspended sediment sources and yields for a large seasonally dry tropical river catchment with high interannual and intra-annual streamflow variability associated with the arrival and strength of the summer monsoon. We focused on the finer clay and silt sediment fractions (<16 mm) that are most likely to reach the downstream receiving environment, the Great Barrier Reef (GBR) lagoon, located on the north-eastern coast of Australia [Bainbridge et al., 2012]. The influence of anthropogenically increased sediment delivery on inshore GBR turbidity and resuspension regimes has been debated over the past few decades. Some studies suggest that turbidity levels on the BAINBRIDGE ET AL. C 2014. American Geophysical Union. All Rights Reserved. V 9067