Soil/Landform Unit 96

Estuary of the Gellibrand River with cliffs in the foreground at Prinectown

Area:

4492 ha

0.34% of CMA region

Many of the larger rivers in the wetter parts of the study area have extensive floodplains. Areas large enough to map exist on the Barham, Aire and Johanna rivers as well as the Gellibrand River and its tributaries. The landscape is generally flat, but irregular areas occur in the form of infilled meanders and minor terraces. In general, most areas are poorly drained, with stunted vegetation. However, closer to the drainage lines, the improved drainage often results in conditions more favourable for plant growth. Most of these

alluvial

flats have been cleared and provide valuable summer grazing for dairy farms along the valleys. Areas prone to waterlogging have been drained and improved pastures established. However, the remoteness of the valleys, set among very infertile surrounding land, has hampered agricultural development.

Alluvial terraces and plains near Princetown
	Meandering estuary and swamps of the Gellibrand River

Component	1	2	3
Proportion of soil-landform unit	60%	30%	10%
CLIMATE Rainfall (mm)	Annual: 950-1100, lowest January (45), highest August (135)
Temperature (^oC)	Annual: 13, lowest July (8), highest February (18)
Seasonal growth limitations	Temperature: less than 10^oC (av.) June-September; July only near the coast Precipitation: less than potential evapotranspiration early November-late March, December-January near coast
GEOLOGY Age and lithology	Cretaceous fluvio-volcanic sandstone and conglomerate Quaternary clay, sand and gravel, Neogene fluvio-marine sand
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	Cleared areas: Dairy farming and water supply beef cattle grazing on improved pastures row and fodder cropping Uncleared areas: Water supply nature conservation; hardwood forestry for sawlogs
TOPOGRAPHY Landscape	Alluvial floodplain of the Gellibrand, Aire and Barham Rivers
Elevation range (m)	0-100
Local relief (m)	3
Drainage pattern	Major meandering stream with deranged tributaries
Drainage density (km/km²)	3.9
Landform	Alluvial terraces		Streambanks, cut-off meanders, lower terraces
Landform element	Poorly drained lower reaches	Well drained upper reaches	-
Slope and range (%)	1 (0-2)	0 (0-1)	2 (0-5)
Slope shape	Linear	Linear	Convex
NATIVE VEGETATION Structure	Low woodland	Tall open forest	Tall open forest
Dominant species	E. obliqua, E. radiata, E. ovata	E. viminalis, E. obliqua, E. ovata, Acacia melanoxylon	E. viminalis, E. obliqua, Acacia melanoxylon
SOIL Parent material	Alluvial clay, silt and sand	Alluvial clay, silt and sand	Alluvial sand, silt and clay
Description (Corangamite Soil Group)	Grey gradational soils (34)	Brown gradational soils, weak structure (34, 41)	Brown sandy loam soils (34)
Soil type sites	OTR733	OTR607	-
Surface texture	Fine sandy loam	Fine sandy loam	Sandy loam
Permeability	Very low	Moderate	Very high
Depth (m)	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	High discharge rates along watercourses lead to flooding and siltation. High seasonal watertable and low permeabilities lead to seasonal waterlogging and soil compaction.	High discharge rates along watercourses lead to flooding and siltation. Weakly structured soils are prone to surface compaction.	High discharge rates along watercourses with weakly structured soils lead to stream bank erosion and siltration. High seasonal watertable in some areas leads to waterlogging.

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