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Redwater Creek Land System

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In the southern parts of the Otway Range, gentle hill cappings of Tertiary quartzitic sands occur as remnants on the high parts of the landscape. Most creeks and rivers have dissected through these sands, exposing Cretaceous sandstone and mudstone on steep slopes leading down to the drainage lines.

The capping of sand overlies Cretaceous sediments at a fairly shallow and uniform depth. The native vegetation on the sands is not dissimilar from that on the surrounding brown gradational soils, consisting of tall open forests of Eucalyptus obliqua, E. cypellocarpa and E. regnans on the better sites. These tall trees apparently extract nutrients from underlying weathering Cretaceous rocks. Nutrient cycling by leaf fall and decay has built up the fertility of the sands, far above that normally encountered on such parent material.

Only minor parts of this land system have been cleared and it appears that a marked decline in soil fertility has resulted. Hardwood forestry is the main land use, together with a small industry in the cutting of tea-tree stakes.
A Study of land in the catchments of the Otway Range and adjacent plains - redwater creek

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

The higher parts of the landscape form undulating hills, with E. regnans
successfully competing with other trees on sand soils.

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


Area: 57 km
2
Component and its proportion of land system
1
5%
2
40%
3
5%
4
25%
5
25%
CLIMATE
Rainfall, mm

Annual
: 1,150 – 1,60, lowest January (60), highest August (160)
Temperature, 0oC
Annual: 12, lowest July (7), highest February (16)
Temperature: less than 10oC (av.) June – September
Precipitation: less than potential evapotranspiration December – mid February
GEOLOGY
Age, lithology

Paleocene unconsolidated quartz sand and gravel shallowly underlain by Lower Cretaceous sandstone and mudstone

Lower Cretaceous sandstone and mudstone
TOPOGRAPHY
Landscape

Deeply dissected hills with broad gently hill cappings in the southern parts of the Otway Range.
Elevation, m
15 – 370
Local relief, m
90
Drainage pattern
Dendritic with some radial areas
Drainage density, km/km2
3.7
Land form
Rise
Scarp
Land form element
Crest
Crest, upper slope
Swale
Crest, upper slope
Steep slope
Slope (and range), %
4 (1-7)
20 (3-35)
3 (1-5)
8 (3-15)
35 (10-60)
Slope shape
Linear
Convex
Concave
Irregular
Linear
NATIVE VEGETATION
Structure

Woodland

Tall open forest

Closed forest

Open forest

Tall open forest
Dominant species
E. nitida, E. baxteri
E. obliqua, E. cypellocarpa, E. regnans, E. viminalis
Leptospermum juniperinum
E. regnans, E. obliqua,
E. baxteri, occasionally
E. viminalis
E. obliqua, E. regnans,
E. cypellocarpa,
E. viminalis
SOIL
Parent material

Deep deposits of quartz sand

Shallow deposits of quartz sand

Alluvial sand and gravel, organic matter

Shallow deposits of quartz sand and gravel

In-situ weathered rock
Description
Grey sand soils with hardpans, uniform texture
Black sand soils, uniform texture
Black sand soils, uniform texture
White sand soils, uniform texture
Brown gradational soils
Surface texture
Loamy sand
Sandy6 loam
Silty loam
(Gravelly) loamy sand
Sandy clay loam
Permeability
Low
High
Moderate
Very high
Moderate
Depth, m
1.2
>2
>2
>2
1.4
LAND USE
Uncleared areas: Hardwood forestry for sawlogs and pulpwood; tea-tree stake harvesting; nature conservation; sand and gravel extraction.
Minor cleared areas: Beef cattle grazing on unimproved pastures.
SOIL DETERIORATION HAZARD
Critical land features, processes, forms
Hardpans restrict vertical drainage, leading to seasonal waterlogging. Very low inherent fertility with some leaching of permeable highly acidic surfaces leads to nutrient decline.
Soils of high permeability in high-rainfall areas are prone to nutrient decline. Steeper slopes with compacted soils (tracks, clear-felled areas) are prone to sheet and rill erosion.
High water tables lead to waterlogging. Run-off from adjacent hills lead to flooding and siltation.
Soils of very low inherent fertility, low nutrient – holding capacity and high permeability in high-rainfall areas are prone to nutrient decline.
Clay subsoils on steeper slopes are subject to periodic saturation and are prone to landslips. Steeper slopes are prone to sheet erosion.
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