Soil/Landform Unit 103

Rises of scoria and basalt near Irrewarra. These soils and a sufficient rainfall make this area extremely versatile for potential land uses

Area:

835 ha

0.06% of CMA region

The low hills and rises east of Irrewarra (near Colac) are derived from volcanic scoria and basalt that is evident in a cutting on the outskirts of Colac when heading towards Winchelsea. This volcanic eruption point on the Western Plains has nearly 45 m of local relief. The low hill has little remnant vegetation (less than 2%) with the major vegetation class being Grassy Woodland. These remnants occur mainly as sporadic stands across the landscape. The hills and rises have highly fertile side slopes and footslopes that have been used for cereal production and are currently under residential development. The basaltic rock and scoria support mottled texture contrast soils with shallow black cracking clays, though basalt floaters and outcrops make cultivation difficult on certain slopes. Slumping and nutrient decline are minor degradation issues of these low hills.

Volcanic derived low hills and rises located on this ner side of Colac

Component	1	2	3	4	5
Proportion of soil-landform unit	20%	15%	10%	40%	15%
CLIMATE Rainfall (mm)	Annual: 550
Temperature (^oC)	Minimum 9, Maximum 19
Precipitation less than potential evapotranspiration	November-March
GEOLOGY Age and lithology	Quaternary scoria and minor basalt, Neogene marine marl and fluvio-marine sand
Geomorphology	6.1.1 Eruption points of the Volcanic Western Plains
LANDUSE	Uncleared: Nature conservation Cleared: Sheep and beef cattle grazing; cropping (cereal)
TOPOGRAPHY Landscape	Undulating low hills and rises
Elevation range (m)	45-147
Local relief (m)	45
Drainage pattern	Centipetal
Drainage density (km/km²)	0.9
Landform
Landform element	Low hills and rises				Plains
Slope and range (%)	Broad low crests	Upper slopes	Mid slopes	Lower slopes	Long gentle slopes and plains
Slope shape	2 (1-5)	5 (3-10)	8 (5-15)	3 (1-8)	1 (0-5)
NATIVE VEGETATION Ecological Vegetation Class	Grassy Woodland 1.6%
SOIL Parent material	In situ basalt	In situ basalt	In situ basalt and colluvium	In situ basalt and colluvium	In situ basalt and colluvium
Description (Corangamite Soil Group)	Alkaline mottled brown, grey or yellow texture contrast soils (36)	Alkaline mottled brown, grey or yellow texture contrast soils (36)	Alkaline mottled brown, grey or yellow texture contrast soils (36)	Alkaline mottled brown, grey or yellow texture contrast soils (36)	Alkaline mottled brown, grey or yellow texture contrast soils (36)
Soil type sites	SFS6, MM5015, CLRA47	SFS6, MM5015, CLRA47	SFS6, MM5015, CLRA47	SFS6, MM5015, CLRA47	SFS6, SFS11, CLRA47
Surface texture	Fine sandy clay loam	Fine sandy clay loam	Fine sandy clay loam	Fine sandy clay loam	Fine sandy clay loam
Permeability	Low to moderate	Low to moderate	Low to moderate	Low	Low to very low
Depth (m)	<1.5	<1.5	<2	1.5-2.5	1.5-2.5
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Texture contrast shallow, low water holding capacity and moderate nutrient holding capacity in shallow surface and subsurface soils, higher in deep subsoil Yellow (brown) soils have low permeability. Strongly sodic subsoil. Moderately rapid site drainage.	Texture contrast soil, low water holding capcity and moderate nutrient holding capacity in shallow surface and subsurface soils, higher in deep subsoil. Yellow (brown) soils have low permeability. Strongly sodic subsoil. Moderately rapid to rapid site drainage.	Texture contrast soil, low water holding capacity and moderate nutrient holding capacity in shallow surface and subsurface soils, higher in deep subsoil. Yellow (brown) soils have low permeability. Strongly sodic subsoil. Moderately rapid to rapid site drainage.	Texture contrast soil, low water holding capacity and moderate nutrient holding capacity in shallow surface and subsoils soils, higher in deep subsoil. Yellow (brown) soils have low permeability. Strongly sodic subsoil. Slow site drainage.	Texture contrast soil, low water holding capacity and moderate nutrient holding capacity in shallow surface and subsurface soils, higher in deep subsoil. Yellow (brown) soils have low to very low permeability. Strongly sodic subsoil. Slow site drainage.

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