Soil/Landform Unit 148

Looking north over the swamps, lunettes and plains of this unit

Area:

9735 ha

0.73% of CMA region

This unit consists of gently undulating plains,

and associated minor swamps that occur between Cressy and Colac. Located within the volcanic Western Plains, the relief of this unit is subdued having a masked affect upon agricultural performance and land versatility. This unit has a number of components, some (such as the low rises and undulating plain) that are erosional landforms while others (such as the swamps, flats and lunettes) are depositional. The unit is adjacent to lakes and basaltic (stony) rises and forms a north-south corridor between Cressy and Lake Colac. The remnant vegetation includes less than 1% Plains Grassy Woodland. The soils are black strongly

sodic

texture contrast soils on the plains (coarse structure,

hardsetting

) with black and red cracking

self-mulching

soils on the lunettes, and black and grey cracking soils in the swamps. Land use is generally grazing, with the capability of the unit varying with component composition. The shallower soils and strongly structured soils on the lunettes provide more use throughout the year than the wetter flats.

Lunettes typically have deep frable soils that can support a wide variety of land uses
	Undulating lunettes intermixed with stony rises

Component	1	2	3	4	5
Proportion of soil-landform unit	8%	17%	15%	50%	10%
CLIMATE Rainfall (mm)	Annual: 600
Temperature (^oC)	Minimum 8, Maximum 19
Precipitation less than potential evapotranspiration	October-March
GEOLOGY Age and lithology	Quaternary source bordering sand dunes, alluvium and minor basalt
Geomorphology	6.1.5 Alluvium, terraces, floodplains, lakes, swamps and lunettes of the Volcanic Western Plains
LANDUSE	Uncleared: Nature conservation; water supply Cleared: Cropping; beef cattle and sheep grazing; dairy
TOPOGRAPHY Landscape	Gently undulating plains with low rises and lunettes, swamps and lakes
Elevation range (m)	112-139
Local relief (m)	10
Drainage pattern	Centripetal
Drainage density (km/km²)	0.7
Landform	Low rises, hillocks		Lunettes	Plains with minor drainage depressions	Swamps and broad depressions
Landform element	Crests and upper slopes	Mid and lower slopes	Lunettes	Plains	Swamps
Slope and range (%)	3 (1-6)	5 (3-10)	2 (1-5)	1 (0-3)	2 (1-5)
Slope shape	Convex	Concave	Convex	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Plains Grassy Woodland (1%)
SOIL Parent material	In situ basalt	In situ basalt	Aeolian deposits	In situ basalt and associated colluvium	Alluvial clay; silt and sand
Description (Corangamite Soil Group)	Friable red gradational soils (40) and alkaline red self-mulching clays and some black self-mulching clays (39)	Alkaline red self-mulching clays (39) and friable red gradational soils (39)	Alkaline black and grey self-mulching clays (9)	Alkaline mottled black texture contrast soils, some not mottled (35)	Alkaline grey cracking clays (31)
Soil type sites	SW26, SFS2, SW103	SW101, BD10, CLRA46	SW87, SFS21, MM114	SW86, SFS20, CLRA49	SW37, CLRA48, CLRA15
Surface texture	Clay loam	Light clay	Medium clay	Fine sandy clay loam	Medium clay
Permeability	Moderate to high	Moderate	Moderate	Low	Very low
Depth (m)	<1.5	<2	>2	<2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Friable soils, some expansive clays. Gradational or uniform texture change with depth. Moderate to high permeability, moderate rapid site drainage. Moderate to high nutrient capacity.	Friable but expansive clays and other friable soils. Uniform or gradational texture change with depth. Moderate permeability, moderately rapid site drainage.	Friable but expansive clays, calcareous and often sodic at depth. High nutrient capacity.	Texture contrast, possible surface waterlogging and compaction	High seasonal watertable leads to soil compaction. High organic matter content, high clay content and expansive clays.

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