Groundwater Resources

Victoria's Groundwater Resource

This information is derived from reports by Leonard (1992) - from assessments carried out of the groundwater resources of the Port Phillip region.

The groundwater regime in basalt is very complex. In general, the vertical permeability is via fracture and shrinkage cracks formed as the basalt cooled and is negligible compared to the horizontal permeability which is largely due to interflow spaces (i.e. within the region of contact between the various basalt flows). Aquifers may occur between flows or at the Tertiary sediment/basalt boundary.

The groundwater system is mainly recharged by direct infiltration of rainfall over the groundwater catchment. Only about 10% of the rainfall enters the groundwater system as most is lost to the atmosphere by evapotranspiration, and to surface streams via direct run-off. Most of this groundwater, estimated at between 88 and 97%, subsequently discharges into the surface water system, generally in the lower parts of the catchment where the groundwater surface is higher than the stream channel. Such discharge has been noted in the Skeleton creek by Sargeant (1993) and probably also occurs in the lower reaches of the Werribee River.

Skeleton Creek near Werribee

Yields from bores in this area range from 0.4 to 16.4 L/sec with yields of less than 1.2 L/sec typical. Larger yields are obtained from bores situated along pre-basaltic stream lines within the Brighton Group sediments. Salinities are in the range 2 000 to 6 000 mg/L total dissolved salts (Leonard, 1992). Chemical analyses from one bore on a larger property in the Municipality showed a salinity 0f 3 840 mg/L. Such water is only suitable for sheep, cattle and horses. It is not suitable for irrigation.

The Fyansford aquifer is of low permeability and is regarded as an aquitard, largely preventing leakage downwards from the overlying basalt system and leakage upwards from the underlying Werribee Formation. The groundwater in the Werribee Formation in this region is generally more saline than in the basalts.

Reference

Leonard, J.G. (1992). Port Phillip Region Groundwater Resources. Department of Water Resources, Victoria.

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