Soil/Landform Unit 81

Dissection of the remnant ferruginised plateau (Unit 336) has lead to development of steep slopes and extensive drainage development

Area:

17 566 ha

1.32% of CMA region

Tomahawk Creek and its tributaries have dissected out deep valleys with characteristic north-north-west and south-south-east oriented parallel ridges and spurs. Small remnants of ferruginised plateau on the high parts of the landscape are bounded by scarps of which ferricrete outcrops. Neogene sand is often exposed in a narrow band below these scarps, and springs are often present at this level. Silt and clay are the more common parent materials on long straight slopes leading down to the valley floor. Small dissected terraces are found along the wider valleys with defined drainage. The terrain to the south and east of Tomahawk Creek shows a lower local relief than the area to the north and west. Areas of ferruginised plateau are often wider and surrounding slopes are shorter and more gentle. Site drainage is affected by the more subdued relief. Woodlands and low woodlands appear to have been more common in this area, with open forests to the north and west. Most of this unit has been cleared as part of the Heytesbury Soldier Settlement Scheme, and dairy farming is the main land use. Subsoils on many slopes are dispersible and gully and tunnel erosion is quite active. Some landslips have occurred, particularly below springs emerging at the base of scarps.

Dissected valleys near the Saddlecloth Plain
	Pine and blue gum plantations are common on this landscape and the neighbouring Kennedys Creek landsystem (soil-landform unit 87)

Component	1	2	3	4	5	6
Proportion of soil-landform unit	15%	6%	10%	50%	9%	10%
CLIMATE Rainfall (mm)	Annual: 850-1050, lowest January (40), highest August (125)
Temperature (^oC)	Annual: 13, lowest July (8), highest February (19)
Seasonal growth limitations	Temperature: less than 10^oC (av.) June-August Precipitation: less than potential evapotranspiration November-March
GEOLOGY Age and lithology	Pliocene ferruginised sand and clay			Miocene unconsolidated marine marl sand, silt and clay
Geomorphology	3.3.1 Dissected low hills plateaux of the Southern Uplands and 6.2.2 Dissected plains, rises and low hills of the Sedimentary Western Plains
LANDUSE	Cleared areas: Mainly dairy farming; some beef cattle grazing Uncleared areas: Hardwood forestry for sawlogs, some posts and poles; gravel extraction; nature conservation
TOPOGRAPHY Landscape	Deep valley dissected out from lateritic plateaux
Elevation range (m)	50-160
Local relief (m)	70
Drainage pattern	Trellis predominantly, some dendritic areas
Drainage density (km/km²)	2.5
Landform	Plateaux remnants		Scarp		Valley floor
Landform element	-	Upper slope	Upper slope	Mid slope	Lower slope
Slope and range (%)	1 (0-3)	28 (13-40)	13 (8-18)	12 (8-20)	5 (1-8)	0 (0-2)
Slope shape	Straight	Concave	Straight	Straight	Straight	Concave
NATIVE VEGETATION Structure	Open forest	Open forest	Woodland	Open forest	Low woodland	Woodland
Dominant species	E. obliqua, E. baxteri	E. obliqua, occasionally E. viminalis	E. radiata, E. baxteri, E. viminalis	E. ovata, E. obliqua, E. radiata, E. baxteri	E. radiata, E. ovata	E. viminalis, E. ovata
SOIL Parent material	Lateritic remnants	Colluvial lateritic ironstone	Siliceous sand	Sandy clay (in situ)	Colluvial/alluvial and over sandy clay	Sand clay alluvium
Description (Corangamite Soil Group)	Mottled brown, grey, yellow and red gradational soils with ironstone (7)	Stony red gradational soils (7)	Grey sand soils (29)	Yellow-brown gradational soils, structure (22, 7)	Grey sand soils, structured grey underlay (22, 8)	Grey gradational soils (34)
Soil type sites	MM238, OTR741	-	OTR742	OTR750	OTR737	OTR733
Surface texture	Sandy loam	Gravelly sandy loam	Coase sandy loam	Sandy loam	Sandy loam	Sandy loam
Permeability	Moderate	Very high	Very high	Low	Very low	Very low
Depth (m)	1.6	1.0	>2	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Low ineherent fertility and phosphorus fixation lead to nutrient decline. Leaching of salts leads to increased salinity of drainage waters.	Steep slopes with weakly structured surfaces of low water holding capacity are prone to sheet erosion. Low inherent fertility and high permeability lead to nutrient decline.	Emergence of springs from these perennial aquifers leads to seasonal waterlogging and soil compaction. Permeable soils of low inherent fertility are prone to nutrient decline.	Highly dispersible clay subsoils of low permeability receiving seepage water are prone to gully and tunnel erosion and to landslips and slumping.	Dispersible soils of low permeability receiving seepage water are prone to gully and tunnel erosion, waterlogging and surface compaction. Permeable surfaces of low inherent fertility are prone to nutrient decline.	Dispersible clay subsoils of low permeability receiving rapid runoff from surrounding hills are prone to gully erosion. Rising watertables and low permeabilities lead to seasonal waterlogging and soil compaction.

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