Soil/Landform Unit 95

Upper Barwon River floodplain south of Birregurra

Area:

8436 ha

0.63% of CMA region

The floodplain of the Barwon River and its tributaries extend from the foothills of the northern side of the Otway Range to the basalt plains near Winchelsea and encompass a comparatively wide climatic variation. The vegetation reflects these changes, with tall open forests of

Eucalyptus viminalis

and

E. ovata

occurring in the south, and woodlands of

E. camaldulensis

dominating in the north. The soils also show a gradual transition from acid freely drained profiles (gradational soils) to heavier neutral soils as the influence of basalt derived alluvium increases towards the north.

Flooding and siltation are common on these plains. Waterlogging of soils is a problem, particularly on low-lying areas such as cut-off meanders and infilled swamps. Gully erosion and streambank erosion are also common.

Broad alluvial plains near Pennyroyal
	Introduced perennial pasture of the floodplain

Component	1	2	3
Proportion of soil-landform unit	5%	85%	10%
CLIMATE Rainfall (mm)	Annual: 600-1000, lowest January (30), highest August (80)
Temperature (^oC)	Annual: 13, lowest July (8), highest February (19)
Seasonal growth limitations	Temperature: less than 10^oC (av.) June-August (also September in higher rainfall areas) Precipitation: less than potential evapotranspiration October-April in lower rainfall areas, November-March in higher rainfall areas
GEOLOGY Age and lithology	Recent alluvium-sand, silt, clay and gravel
Geomorphology	3.3.3 Dissected low hills alluvial terraces and floodplains of the Southern Uplands and 6.2.5 Alluvium, alluvial terraces, floodplains and coastal plains of the Sedimentary Western Plains
LANDUSE	Dairy farming; cropping; sheep and beef cattle grazing
TOPOGRAPHY Landscape	Alluvial floodplain of the Barwon Rivr and its tributaries with numerous cut-off meanders
Elevation range (m)	90-150
Local relief (m)	3
Drainage pattern	Deranged with major meandering channel
Drainage density (km/km²)	3.7
Landform	Plains
Landform element	Rise	Flat plain	Streambank, infilled meanders
Slope and range (%)	4 (1-6)	1 (0-2)	2 (1-8)
Slope shape	Convex	Straight	Convex
NATIVE VEGETATION Structure	Woodland
Dominant species	E. ovata, E. viminalis, Acacia melanoxylon, in north E. camaldulensis
SOIL Parent material	Sandy alluvium	Clayey alluvium	Sandy alluvium
Description (Corangamite Soil Group)	Brown sandy loam soils (34)	Grey gradational soils (34)	Brown sandy loam soils (34)
Soil type sites	-	OTR733	-
Surface texture	Fine sandy loam	Fine sandy clay loam	Fine sandy loam
Permeability	Very high	Moderate	Very high
Depth (m)	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	High permeability and leaching lead to nutrient decline.	High seasonal watertable leads to waterlogging, soil compaction and salting. Dispersbile clay subsoils are prone to gully and tunnel erosion. High discharge rates along some watercourses lead to flooding and siltation.	High discharge rates and weakly structured soils lead to stream bank erosion and siltation. High seasonal watertables lead to waterlogging.

Page top