Soil/Landform Unit 18

The colluvial footslopes often provide deep sands or texture contrast soils that have higher water holding capacities than the steeper slopes with shallow soils of the neighbouring granite hills

Area:

1114 ha

0.08% of CMA region

The

alluvial

fan deposits and footslopes of this unit received most of their source material from the granitic hillslopes higher in the catchment. Neighbouring Unit

(

Devonian

granite) this unit is located south of Pittong in the north of the catchment within the Midlands of the Western Uplands. The footslopes and deposits are characterised by areas of gentle slopes graduating into prominent drainage depressions and drainage lines. The alluvial/colluvial source granitic material is characterised by deep

mottled

yellow/brown/grey

duplex

soils graduating into heavier clays in the minor drainage lines. Remnant vegetation includes only 0.1% Grassy Woodland with extensive clearing of the land. Land use is restricted to grazing and cropping due to the low available water holding capacity and ready leaching of nutrients from these soils. Gully erosion occurs to a minor extent and is easier to control than the steeper slopes and valleys of the granite hills due to the gently undulating nature of the slopes.

Long colluvial slopes and alluvial fans of these granite hills often have salinity expressed at the break-of-slopes
	Fan deposits that are derived mainly from the granitic colluvial slopes

Component	1	2
Proportion of soil-landform unit	80%	20%
CLIMATE Rainfall (mm)	Annual: 680
Temperature (^oC)	Minimum 7, Maximum 18
Precipitation less than potential evapotranspiration	October-March
GEOLOGY Age and lithology	Recent clay, sand and gravel and Devonian granite
Geomorphology	2.1.2 Dissected Western Uplands associated with granitic rocks and aureoles
LANDUSE	Uncleared: Nature conservation Cleared: Sheep grazing; limited cropping (cereal)
TOPOGRAPHY Landscape	Colluvial footslopes and fans from granite hills
Elevation range (m)	260-299
Local relief (m)	10
Drainage pattern	Dendritic
Drainage density (km/km²)	1.1
Landform	Footslopes	Colluvial fans
Landform element	Long gentle slops	Fans
Slope and range (%)	4 (1-7)	3 (1-6)
Slope shape	Irregular	Concave
NATIVE VEGETATION Ecological Vegetation Class	Grassy Woodland (01%)
SOIL Parent material	Granitic, colluvium; sand, clay and silt, in situ granite	Granitic colluvium; sand, clay and silt
Description (Corangamite Soil Group)	Mottled brown, yellow or grey texture contrast soils (1)	Mottled brown, yellow or grey texture contrast soils (1)
Soil type sites	MM237	MM237
Surface texture	Loamy sand	Loamy sand
Permeability	Slowly	Slowly
Depth (m)	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Large texture contrast between topsoil and subsoil, low water holding capacity and low to moderate nutrient holding capacity of subsurface and surface soils, higher in subsoil. Coarse sand component throughout profile. Hardsetting surface soil with some stone. Sodic soil, generally strongly. Deep soil. Very low permeability in heavy clay subsoil, high in upper soil. Moderately rapid site drainage. Variable susceptibility to sheet, rill, gully and tunnel erosion.	Large texture contrast between topsoil and subsoil, low water holding capacity and low to moderate nutrient holding capacity of subsurface and surface soils, higher in subsoil. Coarse sand component throughout profile. Hardsetting surface soil with some stone. Sodic soil, generally strongly. Deep to very deep soil. Very low permeability in heavy clay subsoil, high in upper soil. Moderate rapid site drainage. Variable susceptibility to sheet, rill, gully and tunnel erosion.

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