Soil/Landform Unit 78

Undulating plains and rises outh-east of Colac

Area:

18 458 ha

1.38% of CMA region

An extensive ferruginised plateau to the north of the Otway Range has been dissected by the Barwon River and its tributaries. There are several plateau remnants separated by the

alluvial

plains of the Barwon River. In general, flat or gently undulating plains occupy the highest parts of the landscape, and these are surrounded by gentle slopes leading to slightly lower surfaces or by steep scarps falling away to the alluvial plains. The area to the west of the Barwon River is more dissected, with generally steeper slopes. The soils on the highest levels have been strongly ferruginised, with ferricrete throughout the profile and concentrated in discontinuous layers at about 1.2 m depth. Similar soils without ferricrete are found on lower levels, while the gentle slopes between these levels possess heavier textured soils with coarse

blocky

structures in the subsoils. Clearing has been widespread and the land is used for sheep and beef cattle grazing as well as some dairying. Soil salting has occurred in some areas, and major problems have arisen due to gully and tunnel erosion. The more dissected areas to the west of the Barwon River are the most susceptible, and damage has been widespread.

Undulating rises at Deans Marsh
	Scarp and remnant plateau bordering the Barwon River

Component	1	2	3	4	5	6
Proportion of soil-landform unit	40%	15%	20%	10%	7%	8%
CLIMATE Rainfall (mm)	Annual: 650-700, lowest January (30), highest August (85)
Temperature (^oC)	Annual: 13, lowest July (8), highest February (9)
Seasonal growth limitations	Temperature: less than 10^oC (av.) June-August Precipitation: less than potential evapotranspiration early October-late April
GEOLOGY Age and lithology	Neogene marine marl and calcarenite, and fluvio-marine sand, Recent clay, sand and gravel, Paleogene fluvial sand
Geomorphology	3.3.1 Dissected low hills plateaux of the Southern Uplands
LANDUSE	Cleared areas: Sheep and beef cattle grazing; cash and row cropping; dairy farming
TOPOGRAPHY Landscape	Undulating plain inalnd of the Otway Range
Elevation range (m)	120-190
Local relief (m)	40
Drainage pattern	Dendritic
Drainage density (km/km²)	1.5
Landform	Hills			High level terraces	Drainage lines	Scarps
Landform element	Broad crest	Gentle upper slope	Gentle broad slope	-	-	-
Slope and range (%)	1 (0-2)	5 (2-10)	3 (0-7)		0 (0-1)	35 (10-50)
Slope shape	Linear	Linear	Convex linear		Concave	Linear, convex
NATIVE VEGETATION Structure	Open forest	Open forest	Open forest	Woodland	Closed scrub	Open forest
Dominant species	E. viminalis, E. obliqua, E. radiata	E. viminalis, E. ovata	E. obliqua, E. viminalis, E. ovata, E. radiata	E. viminalis, E. obliqua, E. ovata	Leptospermum juniperinum, Melaleuca squarrosa	E. obliqua, E. viminalis
SOIL Parent material	Ferruginised sediments	Clay	Clay, silt and sand	Alluvial clay, silt and sand	Alluvial clay, silt and sand	Clay, silt and sand
Description (Corangamite Soil Group)	Mottled brown, grey, yellow and red texture contrast soils with ironstone (13)	Yellow-brown sodic texture contrast soils, coarse structure (19/20)	Mottled brown, grey, yellow and red texture contrast soils (13)	Yellow-grown calcareous sodic soils coarse structure (19/20)	Grey gradational soils (34)	Brown, grey and yellow sodic texture contrast soils (32)
Soil type sites	OTR601, CLRA3, SW67	MM97, SW77, OTR743	OTR492, OTR744, SW67	SW80	OTR733	OTR734
Surface texture	Sandy loam	Fine sandy loam	Sandy loam	Fine sandy loam	Fine sandy clay loam	Sandy loam
Permeability	Moderate	Low	Moderate	Low	Very low	Moderate
Depth (m)	1-2	>2	>2	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Low inherent fertility, phosphate fixation, and permeable surface soils lead to nutrient decline.	Dispersible clay subsoils of low permeability are prone to gully and tunnel erosion. Sodic subsoils of low permeability receiving saline seepage are prone to soil salting.	Low inherent fertility, phosphate fixation and permeable surface soils lead to nutrient decline.	Dispersible clay subsoils of low permeability are prone to gully and tunnel erosion and soil salting.	High seasonal watertable leads to waterlogging, soil compaction and soil salting. Dispersible clay subsoils are prone to gully and tunnel erosion.	Dispersible soils on steep slopes subject to periodic saturation are prone to landslips and sheet erosion.

Page top