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Groundwater and the environment in the South West

Groundwater and the environment in the South West

Groundwater interacts with the surface environment where it occurs at or near the surface. The upper aquifer across this region occur at or near the surface and so they interact most closely with surface water environments such as streams and lakes and other Groundwater Dependent Ecosystems (GDEs). The middle aquifers rise to the surface between Port Campbell and South Australia where they are thought to interact with waterways and wetlands. The lower aquifers rise to the surface near the Grampians and Otway Ranges and provide baseflow to the Glenelg, Gellibrand and Anglesea Rivers.

Where is groundwater most likely to interact with the environment?

To view on a map where groundwater is most likely to interact with the environment in this region visit the South West region map page and select the 'Environment' layer from the drop down box in the top right corner.

What do we know?

Western District lakes, wetlands and waterways

The Western District between Ballarat, Colac, Warrnambool and Hamilton is famous for its volcanic lakes and wetlands, many of which are of significant ecological value. These surface water features all interact with the Newer Volcanics basalt upper aquifer. Salinity levels in this aquifer vary significantly depending on the distance to old volcanoes. This in turn determines whether the lakes and wetlands are fresh or salty. Each lake and wetland has a different level of dependence on groundwater and surface water inflows. In addition, the depth of the lake affects how quickly water evaporates, how much the salinity levels change between wet and dry periods and whether the lake is permanent or seasonal.

Lake dynamics

Diagrams showing how the upper aquifers play an important role in supporting regional lakes such as Lake Murdeduke, Lake Weering, Lake Colac and Lake Wendouree.

These diagrams show how the upper aquifers play an important role in supporting regional lakes.  Lake Corangamite has similar dynamics to Lake Wendouree. Diagram: ©Spatial Vision Innovations Pty Ltd (2015)

Groundwater discharge to some of the region’s waterways along the edges of the Newer Volcanics aquifer. The most well-known example is Brucknell Creek near Terang. Here, the groundwater becomes surface water.

The highlands

In the highlands of the region, fractured rock aquifers provide baseflow to streams. These fractured rocks occur in the Grampians, around Ballarat and in the Otway Ranges. Rainfall leaks into the fractured rock and discharges to streams after moving a short distance in a local flow system. To find out more, visit our How does groundwater move page. This discharge can be from relatively permanent springs or be active for only a short time after rain. The headwaters of the Glenelg and Moorabool Rivers depend on this baseflow and it is an important interaction along the entire length of the Gellibrand River.

Far south west

In the far south west, the Glenelg River Estuary and Long Swamp are the most significant potential Groundwater Dependent Ecosystems. While the middle reaches of the Glenelg River are thought to interact with the lower aquifer which occurs at the surface in this area, the lower reaches and Long Swamp are more likely to interact with the middle aquifer. It is also likely that several smaller but high value wetlands to the west of Casterton interact with the upper aquifer.

Plantation forestry increased dramatically across the far south west during the 1990s. Since then a significant relationship has been shown to exist between tree plantations and baseflow to rivers. The dense planting of trees leads to changes in the water balance as the trees grow. The trees intercept rainfall that would otherwise recharge aquifers that occur close to the surface. As the tree roots extend deeper, they are also likely to “drink” groundwater directly as part of the evapotranspiration process. The combination of these two processes leads to declining groundwater levels and, in turn, declining baseflows. This is because the amount of groundwater discharge to any river (baseflow) depends on how high the groundwater level is in relation to the river bed – ie the higher the groundwater level, the greater the amount of baseflow.

Baseflow to Fitzroy River

This diagram shows the change in baseflow over time to the Fitzroy River near Heywood after the effect of reduced rainfall is removed.  This shows us that, in this case, changes in land use have a significant impact on baseflows.

How do we manage this?

When assessing licence applications for new entitlements and the trading of existing entitlements Southern Rural Water takes into account the needs of the environment. With licence applications for bore construction, no new bores are permitted immediately adjacent to streams or rivers.

Learn the basics

To find out about how groundwater supports surface water features such as lakes and rivers visit our How does groundwater interact with the environment page.

To find out about who manages groundwater visit our Who manages groundwater page.

Page last updated27th May 2015
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