Soil/Landform Unit - Diapur ridge

Lawloit Ranges with defined drainage on the northern side of the Western Highway

Area: 95 961 ha

4.09% of CMA region

Undulating low hills are a pronounced NNW/SSE trending ridge with relief varying from 30–80 m that occur in the north-west of the region. The Diapur Ridge (known locally as the Lawloit Range) as a type site is composed of a number of landform components including broad crests, hillslopes, footslopes and defined drainage networks that occur on slopes. The parent material is chiefly Parilla Sand that has been strongly ferruginised, with a veneer of Woorinen

aeolian

clays present over much of the current surface. As a result, soils are quite variable and exhibit differing pH trends depending upon source material (Parilla Sand with

acidic

trends or Woorinen Formation with alkaline trends down profile).

Sodic

brown, yellow and grey texture contrast soils (

Sodosols

) are the dominant soil type, however cracking clays may be found on broad crests as well as topographically much lower drainage depressions. Soils are vulnerable to wind and sheet erosion where exposed and soils are inherently low in fertility. The main vegetation communities include Shallow Sands Woodland, Sandstone Ridge Shrubland, Ridged Plains Mallee and Low Rises Woodland. Smaller extents of Heathy Woodland, Lowan Sands Mallee, Dunefield Heathland, Plains Woodland and Plains Savannah have also been recorded.

Undulating rise in the distance of the Diapur Ridge
	Parilla Sand cutting at Lawloit

Component	1	2	3	4
Proportion of soil-landform unit	10%	50%	35%	5%
CLIMATE Rainfall (mm)	Annual: 470
CLIMATE Rainfall (mm)	Annual: 470
Temperature (^oC)	Minimum 8, Maximum 21
Precipitation less than potential evapotranspiration	October–April
GEOLOGY Age and lithology	Quaternary paludal silt and clay; Quaternary aeolian dune sand (Lowan Sand); Neogene marine sand and silt (Parilla Sand)
GEOLOGY Age and lithology
Geomorphology	5.5.1 Prominent ridges and orientated swales of the North West Dunefields and Plains
LANDUSE	Uncleared areas: nature conservation; gravel extraction Cleared areas: dryland cropping; sheep grazing; gravel extraction
LANDUSE
TOPOGRAPHY Landscape	Undulating stranded beach ridges
TOPOGRAPHY Landscape	Undulating stranded beach ridges
Elevation range (m)	108-224
Local relief (m)	35
Drainage pattern	Dendritic
Drainage density (km/km²)	0.2
Landform	Low rises (ridges) and plains
Landform element	Hill crest	Hillslope	Footslope	Drainage depression and drainage line
Slope and range (%)	4 (2-10)	6 (3-15)	2 (0-5)	3 (0-5)
Slope shape	Convex	Convex	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Low Rises Woodland (30.5%), Shallow Sands Woodland (24.9%), Sandstone Ridge Shrubland (18.8%), Ridged Plains Mallee (10.9%), Other (14.3%)
NATIVE VEGETATION Ecological Vegetation Class
SOIL Parent material	Marine sand and silt	Marine sand and silt	Marine sand and silt, aeolian dune sand	Swamp silt and clay
SOIL Parent material	Marine sand and silt	Marine sand and silt	Marine sand and silt, aeolian dune sand	Swamp silt and clay
Description (Corangamite Soil Group)	Sodic red texture contrast soils (35)	Sodic brown, yellow and grey texture contrast soils (36)	Sodic brown, yellow and grey texture contrast soils (36)	Grey and brown cracking clay soils (37)
Soil type sites	LS15, LS8, LS23	LS2, LS13, LS24, LS6, LS10, LS22	LS2, LS13, LS24, LS6, LS10, LS22	LS3, LSWW9, LSWW5
Surface texture	Sandy clay loam	Sandy clay loam	Sandy clay loam	Medium clay
Permeability	Moderate	Slow	Slow	Slow
Depth (m)	1.6	> 2	> 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. Compaction of soil dependent upon depth of force and moisture content.	Susceptible to wind and sheet erosion where exposed. Low inherent soil fertility in well drained surface soil abruptly over structured subsoil. Susceptible to compaction where Hardsetting with restricted drainage.	Susceptible to wind and sheet erosion where exposed. Low inherent soil fertility in well drained surface soil abruptly over structured subsoil. Susceptible to compaction where Hardsetting with restricted drainage.	Susceptible to waterlogging in lower areas, but can be variable due to micro relief (gilgai). Slightly susceptible to surface sheet erosion where soils are exposed. Gully erosion can occur where subsoils are dispersive and deep. Surface soils friable and only slightly susceptible to wind erosion. Soils susceptible to compaction at critical moisture contents.

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