As the Lockyer Valley is a major food bowl, a considerable amount of work has been conducted to study the interaction between surface water and groundwater (e.g. Zahawi, 1975; Shaw, 2007, Watkinson et al., 2013). In a 2012 survey of surface water chemistry, surface water electrical conductivities were measured at 25 sampling locations of 15 different streams (Raiber, unpublished data). The survey showed that the electrical conductivity of stream water in the Lockyer Valley is highly variable, ranging from very fresh (approximately 190 µS/cm) to saline (14,000 µS/cm). The freshest surface waters were associated with creeks that drain the Woogaroo Subgroup, which is generally characterised by fresh groundwaters (Section 184.108.40.206). Fresh surface waters were also associated with creeks that are deeply incised into the Main Range Volcanics (e.g. Laidley Creek) in their headwaters. In these areas, the alluvial valleys are typically v-shaped, and the alluvium is generally thin and consists primarily of coarse sediments such as boulders, gravels and sands. There is a strong degree of connectivity between the volcanic bedrock, the alluvium and the streams in these areas.
In contrast, the most saline surface waters were encountered in the upper reaches of streams where these directly overlie the Gatton Sandstone, the Koukandowie Formation and the Walloon Coal Measures, and where these streams have developed only thin and narrow alluvial systems.
Both the strong similarities in the salinities and chemistries (including isotopes) of these creeks and the underlying bedrock in the tributaries to the Lockyer Creek – and especially in their upper reaches – confirm that there is a strong degree of connectivity between the bedrock, the alluvium and the creeks.
In the lower reaches of the Lockyer Valley and, in particular, along the central drainage line of the Lockyer Creek, the nature of surface water – groundwater interactions is more complex and more variable. Sixteen recharge weirs on streams have been built throughout the Lockyer Valley in order to artificially enhance surface recharge to the alluvial aquifer (Cox and Raiber, 2013) as the rates of rainfall recharge in the Lockyer Valley are comparatively small due to the thick clay layer on top of the alluvial sequence. Part of this complexity is due to the irregular and episodic patterns of rainfall. A recent study by Watkinson et al. (2013) on surface water – groundwater interactions in the lower Lockyer Valley and Mid-Brisbane river basin confirmed that droughts and floods have significant influence on surface water – groundwater interactions in this area. For example, during the drought, there was insufficient baseflow to sustain perennial flow in the creeks of the lower part of the Lockyer Valley and the Mid-Brisbane river basin. Following the floods of early 2011, a significant increase in surface water salinities was observed in the Lockyer Valley and at a major regional water treatment plant near Brisbane. This change was attributed to the re-connection of the creeks with the underlying alluvium and bedrock, which generally contain brackish-to-saline groundwater.
Conversely, recent isotopic analysis of groundwater and surface water by Raiber (unpublished data) demonstrated that after the break of the drought and the flooding in 2012, surface water recharge to the alluvium replenished the depleted alluvial aquifer throughout much of the Lockyer Creek alluvium to pre-drought levels. This was accompanied by a decrease in salinity in some locations from up to approximately 25,000 µS/cm observed at the peak of the drought to approximately 500 to 3000 µS/cm after the floods (Section 220.127.116.11.1.3).
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- 1.1.1 Bioregion
- 1.1.2 Geography
- 1.1.3 Geology
- 1.1.4 Hydrogeology and groundwater quality
- 1.1.5 Surface water hydrology and surface water quality
- 1.1.6 Surface water – groundwater interactions
- 1.1.7 Ecology
- Contributors to the Technical Programme
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