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Wonga Land System

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Adjacent to the lateritic plateau around Simpson and at a similar elevation, a gently undulating plain without lateritic ironstone extends eastwards towards Barongarook. The parent material is mainly Tertiary sand and clay, with some minor redistribution on sand veneers in some parts and outcrops of deeply weathered Cretaceous sandstone along the sides of some of the drainage lines.

The soils exhibit similar mottling and deep weathering to those found in the Simpson land system, and are prone to nutrient deficiencies and phosphate fixation. Open forests of Eucalyptus obliqua occur over most of the landscape, although E. baxteri tends to dominate on the polygenetic soils with hardpans. Acacia mucronata acts as a strong indicator of the presence of Cretaceous outcrops.

Most areas remain uncleared and are selectively logged for hardwood timber, although most timber is of insufficient size to provide good sawlogs.
A Study of land in the catchments of the Otway Range and adjacent plains - wonga

A Study of land in the catchments of the Otway Range and adjacent plains - wonga

The cleared area in the foreground contrasts with the native
hardwood forests.

A Study of land in the catchments of the Otway Range and adjacent plains - wonga


Area: 72 km
2
Component and its proportion of land system
1
45%
2
7%
3
25%
4
15%
5
8%
CLIMATE
Rainfall, mm

Annual
: 850 – 950, lowest January (40), highest August (120)
Temperature, 0oC
Annual: 13, lowest July (8), highest February (18)
Temperature: less than 10oC (av.) June – August
Precipitation: less than potential evapotranspiration late October – March
GEOLOGY
Age, lithology

Paleocene marine unconsolidated clay, silt and sand

Lower Cretaceous feldspathic sandstone and siltstone
TOPOGRAPHY
Landscape

Undulating plain in the north part of the Gellibrand River catchment
Elevation, m
120 – 340
Local relief, m
30
Drainage pattern
Parallel and dendritic
Drainage density, km/km2
1.2
Land form
Undulating plain
Land form element
Crest, upper slope
Colluvial fan, depression
Slope
Lower slope
Lower slope, drainage line
Slope (and range), %
7 (0-12)
4 (0-7)
7 (1-16)
10 (4-14)
10 (4-14)
Slope shape
Convex
Concave
Convex
Linear
Linear
NATIVE VEGETATION
Structure

Open forest

Open woodland

Open forest

Open forest

Open forest
Dominant species
E. obliqua, E. radiata,
E. baxteri, occasionally
E. ovata, E. viminalis,
E. aromaphloia
E. baxteri, E. ovata,
E. nitida
E. baxteri, E. radiata,
E. ovata, E. obliqua, occasionally E. aromaphloia
E. obliqua, E. radiata,
E. ovata, E. baxteri
E. obliqua, E. ovata,
E. radiata, E. aromaphloia
SOIL
Parent material

Clay, silt and sand

Colluvial sand on sand, silt and clay

Colluvial sand on sand, silt and clay

Clay, silt and sand

In-situ weathered rock
Description
Mottled yellow and red gradational soils
Grey sand soils, weakly structured clay underlay
Grey sand soils, structured clay underlay
Yellow-brown gradational soils, coarse structure
Yellow-brown gradational soils, coarse structure
Surface texture
Sandy loam
Sandy loam
Sandy loam
Sandy loam
Fine sandy clay loam
Permeability
Moderate
Low
Low
Low
Low
Depth, m
>2
>2
>2
>2
1.5
LAND USE
Uncleared areas: Hardwood forestry for sawlogs, posts and poles; water supply; nature conservation; gravel extraction.
Minor cleared areas: Beef cattle grazing; dairy farming
SOIL DETERIORATION HAZARD
Critical land features, processes, forms
Low inherent fertility and phosphorus fixation lead to nutrient decline.
Low permeability and perched water tables lead to seasonal waterlogging and soil compaction.
Low inherent fertility and leaching of permeable surfaces lead to nutrient decline. Low permeabilities lead to seasonal waterlogging and soil compaction.
Dispersible clay subsoils of low permeability are prone to gully erosion. Steeper slopes are prone to sheet erosion.
Dispersible subsoils receiving run-off from adjacent areas are prone to gully erosion.
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