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Simpson Land System

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Small remnants of flat lateritic plateaux near Simpson and extending towards Irrewillipe are evidence of former widespread lateritization. Most lateritic hill capping have been removed by dissection, and this set of north-nor’-west- and south-sou’-east-orientated ridges is the only significant remnant to the west of the Range.

The most common soils have gradational profiles containing lateritic ironstone. However, some profiles possess sand veneers in the surface horizons, with hardpans overlying mottled clays. Drainage of the landscape is poor, particularly where hardpans occur, and seasonal waterlogging is a problem.

The ridges have been extensively cleared as part of the Heytesbury Settlement Scheme and dairy farming is the main land use. There are problems arising from low soil fertility and exposure to wind. Only one small area of native vegetation remains in the study area.
A Study of land in the catchments of the Otway Range and adjacent plains - simpson

A Study of land in the catchments of the Otway Range and adjacent plains - simpson
Clearing of these flat lateritic plateau has been very thorough,
and little evidence remains of the former hardwood forests that covered them.

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


Area: 33 km
2
Component and its proportion of land system
1
65%
2
25%
3
10%
CLIMATE
Rainfall, mm

Annual
: 800 – 950, lowest January (35), highest August (110)
Temperature, 0oC
Annual: 13, lowest July (8), highest February (18)
Temperature: less than 10oC (av.) June – August
Precipitation: less than potential evapotranspiration late October – early April
GEOLOGY
Age, lithology

Pliocene lateritized sand and clay

Veneer of Quaternary sand
TOPOGRAPHY
Landscape

Very gently undulating plateau with north-west and south-east dissection
Elevation, m
150 – 170
Local relief, m
10
Drainage pattern
Parallel
Drainage density, km/km2
1.0
Land form
Plateau
Land form element
Middle and upper slopes, crest
Middle slope
Lower slope, depression
Slope (and range), %
4 (0-14)
0 (0-3)
5 (0-9)
Slope shape
Straight (some convex)
Straight
Concave
NATIVE VEGETATION
Structure

Open forest

Closed scrub

Open forest
Dominant species
E. obliqua, E. baxteri
Leptospermum juniperinum Melaleuca squarrosa, E. nitida, Casuarina littoralis
E. baxteri, E. ovata
SOIL
Parent material

Weathering lateritic remnants

Lateritic remnants covered by varying depths of sand

Alluvial sand and clay
Description
Mottled yellow and red gradational soils with ironstone
Grey sand soils, structured clay underlay
Yellow-brown gradational soils, coarse structure
Surface texture
Sandy loam
Sandy loam
Sandy loam
Permeability
Moderate
Low
Low
Depth, m
1.7
>2
>2
LAND USE
Cleared areas: Dairy farming; some beef cattle grazing
Minor cleared areas: Hardwood forestry production
SOIL DETERIORATION HAZARD
Critical land features, processes, forms
Low inherent fertility and phosphorus fixation lead to nutrient decline. Leaching of salts lead to increased salinity to drainage waters.
Low inherent fertility and leaching of permeable surface horizons lead to nutrient decline. Low permeabilities lead to seasonal waterlogging and soil compaction.
Low permeabilities and high seasonal watertables lead to seasonal waterlogging and soil compaction. Leaching of salts from landscape leads to increased salinity of drainage waters.
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