Salinity in the Western Victorian Region

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For the purposes of this document, the Western Region of Victoria encompasses the Catchment Management Regions of Glenelg Hopkins, Corangamite and the western half of Port Phillip and Westernport. It therefore covers the western urban fringe of Melbourne through to the South Australian border and runs from the coast north to the top of the Great Dividing Range and includes the southern half of the Grampians and all of the Dundas Tablelands.

The region contains the bioregions, Otway Plain, Otway Ranges, Victorian Volcanic Plain, Central Victorian Uplands, Greater Grampians, Dundas Tablelands, Glenelg Plain and Warrnambool Plain. The Otway Ranges are generally free of salinity due to their high rainfall and freely drained soils. While the Grampians themselves are also non-saline, salinity can be found in the surrounding plains to the east, west and south (including the Victoria Valley) at the base of the sandy erosional apron surrounding the ranges. The Glenelg Plain in the far south-west is predominately low lying and flat but generally free of salt. Its swamps and depressions support waterlogging tolerant but salt sensitive plant species, such as the grasses; Swamp Wallaby Grass (Amphibromus spp.) and Australian Sweet-grass (Glyceria distans) and various sedges and rushes; Red-fruit Saw-sedge (Gahnia sieberiana), Bristle-rushes (Chorizandra spp.) and Pallid Rush (Juncus pallidus).

Primary salinity is a feature of the Victorian Volcanic Plain with its many brackish drainage lines (e.g. Mia Mia Creek), salt lakes (e.g. Lake Corangamite) and ephemeral swamps (e.g. Chinamans Swamp) but interspersed with fresh water bodies (e.g. Lake Colac) and streams (Emu Creek). Salinity was encountered here by the first settlers but it some parts appears to be increasing due to groundwater extraction affecting flow systems, alteration in surface drainage patterns and landuse change. Although Primary salinity sites tend to support a good variety of Australian native plant species, such as Creeping Brookwell (Samolus repens), Sea Rush (Juncus kraussii) and Lax Saltmarsh-grass (Puccinellia perlaxa), they almost always contain a range of introduced naturalised species such as Buck’s-horn Plantain (Plantago coronopus) and Borrer’s Saltmarsh Grass (Puccinellia fasciculata). As well as some Primary salinity sites becoming more saline over time (e.g. Woady Yallock Creek), some freshwater systems may show salinity in times of stress (e.g. Lake Bolac during the drought years of 2000-07). Species composition of the vegetation in or around such systems may reflect these changes.

Secondary salinity is prevalent but sporadic on the Otway Plain, the Warrnambool Plain, the lower slopes of the Central Victorian Uplands and in the Dundas Tablelands; although there is mounting evidence that suggests that some of these saline systems are actually Primary in nature (e.g. creek-lines of the Dundas Tablelands). Vegetation on Secondary saline sites generally has fewer Australian native species but this can be confused by the fact that some natives, such as the Blown-grasses (Lachnagrostis spp.), can readily invade.

Reference

Corangamite Saline Ecosystems Assessment Kit, C.S. Allen, Corangamite Catchment Management Authority, Colac, Australia, 2007.

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