Groundwater

This Draft of the Corangamite Regional Catchment Strategy is currently awaiting Ministerial approval and may be subject to change

Overview

Groundwater is sub-surface water contained in the pores, cracks and fractures within the sediments and rocks.  Surface water from rainfall or other water bodies percolates through the ground to the water table (recharge) where it is stored in aquifers (a layer of fractured rock, gravel, sand or limestone below the ground that is porous enough to hold groundwater, and allow it to flow). Groundwater moves laterally within and between aquifers with intervening aquitards retarding or restricting flow.  Aquifers can discharge to the surface and are often important components of river flow and water for wetlands and native vegetation. 

Diagram showing how ground water systems work
Groundwater processes (from Southern Rural Water 2011, South-West Victoria Groundwater Atlas)

The Corangamite region contains a variety of deep and shallow groundwater aquifers of varying water quality and yield. Most of the Corangamite region is covered by the deep Otway sedimentary basin containing up to 700 metres thickness of sand and gravel aquifers interlayered by clay dominated aquitards overlying a deep bedrock.  The basin is flanked to the south by the Otway Ranges covering Anglesea, Lorne, Forrest and Apollo Bay regions and to the north by the Great Dividing Range in the Ballarat, Meredith and Bunniyong regions.  Both of these flanking areas contain shallow bedrock aquifers.  More information on groundwater resources in the area can be found at:

In the Corangamite region, groundwater is valued by the community and shared by many users. The Corangamite CMA region’s low stream flows and lack of topography suitable for dams has led to a high reliance on groundwater. Groundwater provides drinking water for many towns in the region (including Geelong, Ballarat, Bellarine Peninsula and Surf Coast). It is also drawn on for the supply of stock and domestic purposes, especially during low rainfall or drought periods. Therefore, the quality of this water is important for many rural asset managers across the Region.

The Corangamite region has many groundwater dependent ecosystems (GDEs), with groundwater playing an important role in the health of most wetlands and rivers. Groundwater discharge plays a key role in sustaining terrestrial vegetation communities, cave ecosystems and both terrestrial and aquatic fauna.  There are two main types of groundwater dependent ecosystems in the region: 1) aquatic GDEs that rely on direct groundwater discharge such as wetlands, rivers and springs and 2) terrestrial GDEs that rely on vegetation drawing water from the watertable.

Groundwater resources in the Corangamite region are managed by Southern Rural Water, in line with the requirements of the Water Act 1989 and associated government policies. Southern Rural Water has delegated responsibility for licensing bore construction and the take and use of groundwater to groundwater diverters, and leads the development and implementation of groundwater management plans. Groundwater management plans take into account the potential impact of groundwater extraction on streams, springs, wetlands and other Groundwater Dependent Ecosystems. State policy and guidance on groundwater planning and licensing matters is provided by DELWP.

For major aquifers of the region, Groundwater Management Units are designated under the Water Act to ensure groundwater extraction remains sustainable.  Each Groundwater Management Unit has a designated Permissible Consumptive Volume (PCV) which caps the volume of groundwater licence entitlement for uses such as irrigation and town water supply.  The volume used for stock and domestic use is not counted as part of the PCV.  In the Corangamite region, there are nine Groundwater Management Units covering the following aquifers:

  • Cardigan and Bungaree GMUs – covering the shallow basalt aquifers in the Ballarat region
  • Colongulac and Warrion GMUs – covering shallow basalt aquifers in the Colac and Camperdown regions
  • Paaratte, Newlingrook, Gellibrand, Gerangamete and Jan Juc GMUs – covering the deep Dilwyn Formation and Eastern View Formation aquifers overlying bedrock in the Otway Basin stretching from Port Campbell in the west to Torquay in the east.