There are no direct measurements of surface water – groundwater interactions in the Gloucester subregion. Estimates are made using observed stream and aquifer water levels and quality.
The direction of exchange is implied by comparing local groundwater levels to stream stage. The relative exchange between surface water and local groundwater is inferred from geochemistry data, principally stream and aquifer water salinity. A degree of validation is provided through groundwater modelling by Parsons Brinckerhoff (2013b). Using a simplified five-layer groundwater model, they provide long-term mean groundwater flow between near-surface layers, particularly between the alluvial aquifer carrying rivers and streams and the shallow weathered rock layer. These pieces of evidence indicate that streams are net gaining.
Using ratios of electrical conductivity, the baseflow contribution is estimated to be 3.0 to 4.5% in the Gloucester River, and 13 to 14% in the Avon River.
There are no direct observations or measurements of interactions between water in the river network and underlying aquifers in the Gloucester subregion. An assessment of the magnitude and direction of surface water – groundwater interactions can be made based on groundwater level measurements and the chemistry of stream and aquifer water. Details of these data are provided in Section 2.1.5.1 about observed data.
No statistical analyses have been undertaken as part of the bioregional assessment (BA) of the Gloucester subregion. Interpretation of the available data and analyses undertaken by Parsons Brinckerhoff (2013a, 2013b) are used to determine whether streams are gaining or losing, and the contribution from groundwater to stream flow (i.e. baseflow). This is reported in Section 2.1.5.2 about statistical analysis and interpretation.
