Soil/Landform Unit 73

Steep rolling hills of the Pennyroyal landscape with softwood plantations in the foreground north-east of Deans Marsh

Area:

10 986 ha

0.82% of CMA region

Along the northern periphery of the Otway Range, flat-topped spurs and ridges form an irregular band of foothills from Wormbete Creek to Barwon Downs. The terrain is variable, with steep slopes leading away from these gentle hill crests to slopes upwards towards the Otway Range and becomes narrower as the local relief increases. The gentle parts of the landscape are formed on Paleogene clay, silt and sand. These sediments overlie

Cretaceous

sandstones and mudstones, which outcrop on steep slopes on the valley sides. Soil and vegetation reflect changes in the parent material, with the soils on the upper parts of the landscape being somewhat deeply weathered with sandy surface horizons in contrast to loam or clay loam soils on the Cretaceous outcrops. Clearing has been widespread and sheep and beef cattle grazing as well as dairy farming are the main land uses. Some hardwood is logged from forested areas, and softwood plantations have been established in the east. Poor management of these hills can lead to rapid surface runoff along the valleys creating problems of gully erosion, siltation and flooding further downstream.

Across slope with sands and bracken prominent on cleared land
	Extensive deep gully erosion along the valley floor of steep slopes

Component	1	2	3	4	5
Proportion of soil-landform unit	35%	15%	35%	12%	3%
CLIMATE Rainfall (mm)	Annual: 700-1050, lowest January (35), highest August (80)
Temperature (^oC)	Annual: 12, lowest July (8), highest February (18)
Seasonal growth liitations	Temperature: less than l0^oC (av.) June–September Precipitation: less than potential evapotranspiration November-March
GEOLOGY Age and lithology	Paleogene unconolidated fluvial clay, silt and sand Minor remnants of ferruginisation			Cretaceous fluvio-volcanic sandstone and mudstone	Recent alluvial clay, silt and sand
Geomorphology	3.2.2 Dissected upland ranges of the Southern Upland
LANDUSE	Cleared areas: Sheep and beef cattle grazing; dairy farming; water supply Uncleared areas: Hardwood forestry for some sawlogs, posts and poles; softwood plantations; nature conservation; water supply; gravel extraction; passive recreation
TOPOGRAPHY Landscape	Steep rolling hills on the northern periphery of the Otway RAnge
Elevation range (m)	135-300
Local relief (m)	65
Drainage pattern	Dendritic
Drainage density (km/km²)	2.2
Landform	Hills				Valley Floors
Landform element	Gentle crest	Upper slope and crest	Gentle upper slope	Steep lower slope	-
Slope and range (%)	3 (0-15)	7 (0-25)	15 (3-25)	30 (5-45)	1 (0-2)
Slope shape	Convex	Convex	Linear	Linear	Concave
NATIVE VEGETATION Structure	Open forest	Open forest	Open forest	Open forest	Tall open forest
Dominant species	E. obliqua, E. ovata, E. radiata, E. aromaphloia, E. nitida	E. obliqua, E. raidata, E. nitida, E. viminalis	E. obliqua, E. viminalis, E. radiata, E. ovata, Acacia melanoxylon	E. obliqua, E. radiata, E. cypellocarpa	E. obliqua, E. cypellocarpa, E. globulus
SOIL Parent material	Clay, silt and sand, often deeply weathered	Sand and clay	Clay, silt and sand	In situ weathered sandstone and mudstone	Alluvium
Description (Corangamite Soil Group)	Mottled brown, grey, yellow and red duplex soils (27)	Brown, grey or yellow gradation soils, weak structure (29)	Yellow-brown texture contrast soils, coarse structure (28, 15)	Brown texture contrast soils (6)	Grey gradational soils (34)
Soil type sites	CLRA14	CLRA13	SW32, OTR499	OTR424, OTR735, SW71	CLRA15, OTR733
Surface texture	Sandy loam	Loamy sand	Fine sandy loam	Loam	Sandy loam - clay loam
Permeability	Moderate	High	Low	Moderate	Low
Depth (m)	>2	>2	>2	0.8	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Low inherent fertility and phosphorus fixation lead to nutrient decline. Weakly structured surface soils on steeper slopes are prone to sheet erosion.	Low inherent fertility and high permeability lead to nutrient decline. Weakly structured soils on steepest slopes are prone to sheet erosion.	Dispersible clay subsoils on steep slopes are prone to gully erosion. Soils of low permeability on steep slopes are prone to sheet erosion.	Steep slopes lead to sheet erosion, particulary on dry aspects. Clay subsoils on steep slopes subject to periodic saturation are prone to landslips.	High seasonal watertable and low permeability lead to seasonal waterlogging soil compaction and soil salting. High discharge rates, Dispersible clay suboils and dispersible sandy clay parent material of low mechanical strength lead to gully and tunnel erosion.

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