Soil/Landform Unit - Woorak clay plains

Looking north over cultivated clay plains near Woorak

Area: 55 686 ha

2.38% of CMA region

The plains (including swales) and low rises consists of many linear occurrences north of the Little Desert, east and west of Nhill and south of the Big Desert. This low plain complex is part of the North West Dunefields and Plains. These plains of

Quaternary

lacustrine

and

aeolian

sediments are part of a NNW/SSE orientated terrain surrounded by associated rises/ridges and other ridge/depression units (Kiata, Diapur, Lorquon). There are three components including level plains, gently undulating plains and low gentle rises. Drainage is strongly aligned to the terrain with little surface expression apart from local depressions, including swamps and lakes. Soil types are predominantly grey cracking clay soils (

Vertosols

) on plains and in local depressions, and brown and red sodic texture contrast soils (

Sodosols

) on the gentle rises. Waterlogging may be an issue in the depressions and extensive flat areas during wet seasons. Soil compaction may occur on heavier soils with or without thin topsoils. This unit is used for dryland cropping and grazing (sheep, beef cattle). Plains Savannah, Ridged Plains Mallee and Low Rises Woodland dominate remnant vegetation.

Cropped clay plains near Gerang Gerang
	Plains with remnant bulloke

Component	1	2	3
Proportion of soil-landform unit	20%	50%	30%
CLIMATE Rainfall (mm)	Annual: 435
CLIMATE Rainfall (mm)	Annual: 435
Temperature (^oC)	Minimum 8, Maximum 22
Precipitation less than potential evapotranspiration	September–April
GEOLOGY Age and lithology	Quaternary paludal silt and clay; Neogene marine sand and silt (Parilla Sand); Quaternary aeolian dune sand (Lowan Sand)
GEOLOGY Age and lithology
Geomorphology	5.5.1 Prominent ridges and oriented swales of the North West Dunefields and Plains
LANDUSE	Uncleared areas: nature conservation Cleared areas: dryland cropping; sheep and beef cattle grazing
LANDUSE
TOPOGRAPHY Landscape	Clay plains
TOPOGRAPHY Landscape	Clay plains
Elevation range (m)	92–207
Local relief (m)	3
Drainage pattern	Dendritic
Drainage density (km/km²)	0.3
Landform	Plains
Landform element	Low gentle rise	Level plain	Gently undulating plain
Slope and range (%)	4 (1-7)	0 (0-1)	2 (1-5)
Slope shape	Convex	Straight	Straight
NATIVE VEGETATION Ecological Vegetation Class	Plains Savannah (29.5%), Ridged Plains Mallee (27.6%), Low Rises Woodland (14.8%), Lignum Swampy Woodland (10.0%), Other (16.0%)
NATIVE VEGETATION Ecological Vegetation Class
SOIL Parent material	Marine sand and silt, aeolian sand	Marine sand and silt	Marine sand and silt
SOIL Parent material	Marine sand and silt, aeolian sand	Marine sand and silt	Marine sand and silt
Description (Corangamite Soil Group)	Sodic red texture contrast soils (35)	Grey and brown cracking clay soils (37)	Grey and brown cracking clay soils (37)
Soil type sites	LS15, LS8, LS23	LS3, LSWW9, LSWW5	LS3, LSWW9, LSWW5
Surface texture	Sandy clay loam	Medium clay	Medium clay
Permeability	Moderate	Slow	Slow
Depth (m)	1.6	> 2	> 2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS Critical land features, processes, forms	Hardsetting soil surface susceptible to sheet and rill erosion, and wind erosion where exposed. Dispersive and deep subsoils susceptible to gully erosion on steeper slopes. Hardsetting soils are prone to compaction. Topsoil may be susceptible to acidification.	Susceptible to periodic inundation and waterlogging in lower areas, but can be variable due to micro relief (gilgai). Surface soils are often friable and only slightly susceptible to wind erosion. Soils susceptible to compaction at critical moisture contents.	Susceptible to periodic inundation and waterlogging in lower areas, but can be variable due to micro relief (gilgai). Surface soils are often friable and only slightly susceptible to wind erosion. Soils susceptible to compaction at critical moisture contents.

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