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Soil/Landform Unit 65

Landform Unit Description

Unit 65 image a
Open forests of the landscape evident abutting cleared land on lower slopes
      Area: 3233 ha
      0.24% of CMA region

      North of the Gellibrand River, Cretaceous sandstones and mudstones outcrop in the valleys of Yahoo Creek, Gum Gully Creek and an unnamed creek to the west of Black Bridge Road. These sediments belong to the Moonlight Head Beds of the Otway Group. Slopes are steep and valleys are narrow, in sharp contrast to the rounded hills of adjacent Paleogene sediments. The soils are similar to those found on other outcrops of Cretaceous sediments in the Otway Range, with the exception that surface horizons contain appreciably more sand and the parent material is usually highly weathered. Open forests of Eucalyptus obliqua, E. ovata and E. aromaphloia are similar to those found on the drier slopes of soil-landform unit 63. Most parts of these valleys remain virtually uncleared and quite remote. Hardwood forestry is the main land use, although the rugged terrain makes access difficult. Some softwood plantations have been established in the catchment of Yahoo Creek. Landslips occur on these soils under native forest, and the incidence increases dramatically following clearing. Sheet erosion and gully erosion are also prone to occur.
Unit 65 geomorphology

Unit 65 image b
Cleared gentle lower slopes and swale
Unit65 cross section

Unit 65 graph

Unit 65 image c
Steep and rugged hills surrounding Yahoo Creek are
difficult to manage due to rapid regrowth of vegetation

Component
1
2
3
4
Proportion of soil-landform unit
35%
45%
15%
5%
CLIMATE
Rainfall (mm)

Annual: 850-1000, lowest January (40), highest August (130)
Temperature (oC)
Annual: 12, lowest July (7), highest February (18)
Seasonal growth limitations
Tempreature: less than 10oC (av.) June-September
Precipitation: less than potential evapotranspiration November-March
GEOLOGY
Age and lithology
Cretaceous highly feldspathic fluvio-volcanic sandstone and mudstone (Moonlight Head Beds); minor Paleogene marine glauconitic sand
Geomorphology
LANDUSE
Uncleared areas: Hardwood forestry for sawlogs, poles and posts; nature conservation; water supply
Minor cleared areas: Sheep and cattle grazing; water supply
TOPOGRAPHY
Landscape

Deeply dissected hills to the north of Gellibrand River
Elevation range (m)
60-270
Local relief (m)
110
Drainage pattern
Dendritic with small radial areas
Drainage density (km/km2)
2.4
Landform
Hills
Landform element
Steep slope
Crest and upper slope
Slope
Swale and gentle lower slope
Slope and range (%)
50 (20-70)
15 (2-30)
35 (15-45)
13 (1-25)
Slope shape
Linear
Linear
Linear
Concave
NATIVE VEGETATION
Structure

Open forest

Open forest

Open forest

Open forest
Dominant species
E. ovata, E. obliqua, E. radiata,
E. aromaphloia, E. viminalis
E. obliqua, E. ovata, E. aromapholia,
E. radiata
E. viminalis, E. obliqua
E. viminalis, E. obliqua, Acacia melanoxylong
SOIL
Parent material

In situ weathered sandstone and mudstone, colluvial rock

In situ deeply weathered sandstone and mudstone

In situ weathered sandstone and mudstone

Colluvium
Description
(Corangamite Soil Group)
Stony brown gradational soils (7)
Yellow-brown gradational soils, coarse structure (7)
Brown gradational soils (7)
Dark brown gradational soils (7)
Soil type sites
OTR732
OTR750
OTR414, OTR416, OTR736
OTR428, OTR736
Surface texture
Fine sandy loam
Sandy clay loam
Loam
Loam
Permeability
High
Low
Moderate
Moderate
Depth (m)
0.7
1.2
0.9
>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS
Stony shallow soils with weak structure and low water holding capacity on steep slopes are prone to sheet erosion and landslides.
Soils of low permeability on the steeper slopes are prone to sheet and rill erosion. Dispersible subsoils are prone to gully erosion.
Clay subsoils on steep slopes subject to periodic saturation are prone to landslips. Steep slopes are prone to sheet erosion.
Weakly structured soils receiving runoff from adjacent hills are prone to scour gullying siltation and flooding.
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