Publication Name: A re-evaluation of groundwater discharge from the Burdekin floodplain aquifer using geochemical tracers
Date: December 2011
High water tables following an extensive wet season provided a unique opportunity to evaluate groundwater baseflow to rivers and coastal zones from the Burdekin River Delta aquifer. This region is one of the largest irrigation districts in Australia and relies, in part, on groundwater extraction. However, because of the complex nature of the aquifer, it is difficult to evaluate groundwater discharge to rivers and coastal zones using traditional hydraulic techniques. In 2003-04, Cook et al. (2004) evaluated groundwater baseflow to rivers in the Burdekin region using radon. In addition, they evaluated submarine groundwater discharge to Bowling Green Bay, an important outlet for the Burdekin aquifer, using radon and the radium quartet (223Ra, 224Ra, 226Ra, 228Ra). Radon and radium are naturally occurring radioisotopes that tend to be enriched in groundwater relative to receiving surface waters. This property makes them ideal tracers to quantify groundwater discharge.
In this study, the sampling survey by Cook et al. (2004) was repeated to compare groundwater discharge to surface water and the marine environment from the Burdekin aquifer at the end of the 2004 and 2011 wet seasons. This included an extensive field campaign from 9 – 12 May 2011 to collect longitudinal river profiles for radon from the Burdekin and Haughton rivers and from Plantation and Barratta creeks. In addition, radon and radium surveys were conducted in Bowling Green Bay. An effort was made to better characterize the radon and radium signatures for key water sources, such as radon activity in hyporheic water, radium activity at river mouths, and radium activity in the more saline sections of the Burdekin aquifer. Building on knowledge gained since the 2004 studies, the radon and the radium data from 2004 and 2011 were interpreted with modified models. For rivers, the potential contribution of hyporheic exchange to the river radon budget was quantified. For Bowling Green Bay, a different model was used that explicitly incorporated the effects of changes in bathymetry in the bay.
Cook, PG, Lamontagne, S, Stieglitz, T, Cranswick, R, Hancock, G 2011, ‘A re-evaluation of groundwater discharge from the Burdekin Floodplain aquifer using geochemical tracers', National Centre for Groundwater Research and Training Report, p 105.