Groundwater hydrogeology of the Peake, Roby and Sherlock Prescribed Wells Area (PRS PWA)

  • Fact sheet
  • August 2015

There are two main aquifer systems in the PRS PWA:

Most groundwater for irrigation, stock and domestic purposes is extracted from the Buccleuch Formation (known locally as the coral).

Unconfined aquifer

There is high groundwater salinity below the Coastal Plain, but low salinity groundwater beneath the Mallee Highlands only a few kilometres to the east. This is used for stock and domestic purposes. Due to the deep water table in the Highlands, stock and domestic groundwater users generally set pumps at depths of 50-100m.

The unconfined aquifer is recharged:

The timing of the recharge varies with depth. Rapid recharge can occur beneath the Coastal Plain where the water table averages about 5m below ground level. However beneath the Mallee Highland areas, where the water table can be as deep as 50m, recharge could take several decades to reach the water table.

Confined aquifer

The confined aquifer sits within the Buccleuch and Renmark Group formations. The Buccleuch Formation is comprised of bryozoal limestone or ‘coral’. In the Peake area, the coral layer begins to merge with the more extensive Renmark Group. The Renmark Group is made up of sands and clays.

Unlike the unconfined aquifer, the confined aquifer is not recharged by local rainfall in the PRS PWA. The main recharge source is from groundwater that flows through the aquifer from south-western Victoria.

On the coastal plain, most of the water for stock, domestic and irrigation use is sourced from the Buccleuch Formation. There is generally low groundwater salinity and good well yields near the township of Peake, which lends itself to irrigation commercial and recreational uses. 

Groundwater pressure trends

A network of 34 observation bores monitor groundwater pressure levels and salinity from both the unconfined aquifer (11 bores) and confined aquifer (23 bores). Between 2002 and 2007, the maximum decline in groundwater pressures was up to 12 metres.

Hydrographs for the observation bores show that since 2002, aquifer pressures measured each year have not recovered to pre-development levels, indicating that the aquifer is not recovering completely after each irrigation season.

Groundwater extraction and demand

Groundwater extraction in the PRS PWA was historically limited to minor extraction for stock, domestic use, town water supply, crop spraying and irrigation of recreational areas.

Before the area was prescribed, the groundwater resource was open to unregulated and unrestricted groundwater extraction.

Until November 2003, there had not been much groundwater extraction in the PRS PWA, however irrigation expanded near the town of Peake, and irrigation in this area is now the largest user of groundwater in the area.

Irrigation is expected to be the largest growing water user, however irrigation potential may be limited, particularly towards the west where groundwater salinity in the confined aquifer is higher.

Therefore, irrigation development will tend to concentrate near Peake, where there is good quality water and high groundwater yields. A Water Allocation Plan for the PRS PWA was released in 2011, creating legislation to manage the groundwater resources to ensure:

More information

See the WAP 2011, and other detailed information on the PRS PWA water planning page of our website.

We have also developed a range of factsheets about water allocation planning and licensing to assist you with managing your water resources. Refer to the related links below.

Related links