2.1.5 Surface water – groundwater interactions


Surface water – groundwater interactions were mainly investigated using water quality and chemistry data. Additionally, the response of alluvial water levels to climate variability was also used to determine the hydraulic relationships between bedrock aquifers, alluvial aquifers and streams.

Due to the spatial and temporal variability of surface water – groundwater interactions and the likely variable influence of different bedrock units, these interactions are best investigated using a wide range of independent but complementary techniques. This section discusses how multiple data sources such as groundwater quality, groundwater hydrographs and surface water hydrographs have been integrated with a preliminary three-dimensional geological model to develop an improved understanding of the major drivers of the hydraulic connectivity between these systems in the Clarence-Moreton bioregion.

From this analysis, two principal categories of surface water – groundwater interactions have been identified: stream–aquifer interactions, and aquifer–wetland interactions.

The analysis of stream electrical conductivity (EC) data measured irregularly at more than 190 streamflow sampling points demonstrated considerable spatial and temporal variability. This variability is driven by climate controls in addition to the nature of the bedrock underlying the alluvial aquifer systems.

Three examples are presented of how groundwater levels and streambed elevations are used as indicators to infer the degree of hydraulic connectivity between streams and aquifers. The three examples from the Richmond river basin, the Lockyer Valley and the Bremer river basin highlight some characteristic differences in the responses of different surface water – groundwater systems to droughts, the break of drought and subsequent flooding, with the local geology, geomorphology (valley characteristics) and in particular the bedrock geology identified as major drivers of these differences.

In addition to this local analysis of surface water – groundwater interactions, there are also processes that are likely to be controlled by regional characteristics of the geological Clarence-Moreton Basin, such as the geometry of aquifers or the presence of faults. This preliminary analysis indicates that there are areas where the presence of wetlands can be linked to the abutment of bedrock aquifers at the basin margins.

Surface water quality and chemistry data were used to identify areas where surface water systems are in connection with aquifers. Surface water quality data (i.e. EC) were used to infer areas where groundwater baseflow to the streams occurs.

In addition to the use of groundwater and surface water chemistry to assess surface water –groundwater interactions, alluvial groundwater levels representing different climate periods (i.e. climax of drought in 2007, after the break of the drought in 2008 and after the floods of 2010–11) were imported into the preliminary three-dimensional geological model. From the three-dimensional geological model, cross-sections were developed for selected transects in different river basins to determine the spatial and temporal variability of the hydraulic relationships between bedrock aquifers, alluvial aquifers and streams.

Last updated:
8 January 2018
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