Identifying flood recharge and inter-aquifer connectivity using multiple isotopes in subtropical Australia

Abstract

Abstract. An understanding of hydrological processes is vital for the sustainable management of groundwater resources, especially in areas where an aquifer interacts with surface water systems or where aquifer interconnectivity occurs. This is particularly important in areas that are subjected to frequent drought/flood cycles, such as the Cressbrook Creek catchment in Southeast Queensland, Australia. In order to understand the hydrological response to flooding and to identify inter-aquifer connectivity, multiple isotopes (δ 2 H, δ 18 O, 87 Sr / 86 Sr, 3 H and 14 C) were used in this study in conjunction with a comprehensive hydrochemical assessment, based on data collected 6 months after severe flooding in 2011. The relatively depleted stable isotope signatures of the flood-generating rainfall (δ 2 H: −30.2 to −27.8 ‰, δ 18 O: −5.34 to −5.13 ‰ VSMOW) were evident in surface water samples (δ 2 H: −25.2 to −23.2 ‰, δ 18 O: −3.9 to −3.6 ‰ VSMOW), indicating that these extreme events were a major source of recharge to the dam in the catchment headwaters. Furthermore, stable isotopes confirmed that the flood generated significant recharge to the alluvium in the lower part of the catchment, particularly in areas where interactions between surface waters and groundwater were identified and where diffuse aquifer recharge is normally limited by a thick (approximately 10 m) and relatively impermeable unsaturated zone. However, in the upper parts of the catchment where recharge generally occurs more rapidly due to the dominance of coarse-grained sediments in the unsaturated zone, the stable isotope signature of groundwater resembles the longer-term average rainfall values (δ 2 H: −12.6, δ 18 O: −3.4 ‰ VSMOW), highlighting that recharge was sourced from smaller rainfall events that occurred subsequent to the flooding. Interactions between the bedrock aquifers and the alluvium were identified at several sites in the lower part of the catchment based on 87 Sr / 86 Sr ratios; this was also supported by the hydrochemical assessment, which included the modelling of evaporation trends and saturation indices. The integrated approach used in this study facilitated the identification of hydrological processes over different spatial and temporal scales, and the method can be applied to other complex geological settings with variable climatic conditions.

Assessment of groundwater–surface water interaction using long-term hydrochemical data and isotope hydrology: Headwaters of the Condamine River, Southeast Queensland, Australia

“…This confirms observations from other studies (e.g. Baskaran et al, 2009;Hughes and Crawford, 2013;King et al, 2015), which also observed that high precipitation rainfall events associated with east coast pressure systems in Australia can be isotopically more depleted and less influenced by evaporation. The time series of hydraulic data indicates that recharge of both alluvial and MRV occurs following Table 3 Summary of bore data used in the temporal analysis of hydraulic head and river stage elevations.…”

Time series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream

“…Second, more abrupt depletions of 2 H and 18 O occurred during significant precipitation events (Fig. 2c), as has been reported in other parts of eastern Australia (Hughes and Crawford, 2013;King et al, 2015). In streamwater, isotopic ratios were generally lower for S1 and S2 than for rainfall, which most likely reflects the predominant contribution of depleted rainfall to recharge (Duvert et al, 2015b).…”

2015 Disastrous Floods in Louisiana, USA, and Assam, India: Groundwater Impact on the Water Balance Estimation

“…Since floods are considered as solely a surface phenomenon, there still is the risk of making incorrect predictions concerning flood development. It is important to understand that the river basin (with underlying aquifers) is a system with a complex balance, and changes in one part can cause significant changes in remote parts [11]. Not taking into account floods caused by tsunamis or tornadoes, the main traditionally declared factor of flood emergence and development remains precipitation.…”