Soil/Landform Unit - Drung alluvial plains

Wimmera River upstream of Glenorchy

Area: 34 948 ha

1.49% of CMA region

The Wimmera River from Greens Creek to Natimuk is defined as the Drung

plains. These plains form part of the plains without leveed channels of the Older Alluvial Plains geomorphology sequence within the region. Alluvial plains are characterised by backplains with flats, slopes and stream channels while the modern drainage system has prominent stream banks, channels and drainage lines. Soils of these backplains and modern drainage systems comprise sodic grey texture contrast soils (

Sodosols

) and cracking clay soils (

Vertosols

) depending upon landform component and topographic position. Woodlands are the dominant vegetation type, including communities such as Riverine Chenopod Woodland, Plains Grassy Woodland, Sand Ridge Woodland and Shallow Sands Woodland. Wetlands also occur and are found in creeklines and swampy areas. Land use on these alluvial plains includes dryland cropping, pasture production (including lucerne), residential development and recreational activities (especially around Horsham).

Alluvial floodplain of the Wimmera River at Campbells Bridge
	Wimmera River at Glenorchy

Component	1	2	3	4	5
Proportion of soil-landform unit	50%	30%	5%	5%	10%
CLIMATE Rainfall (mm)	Annual: 495
CLIMATE Rainfall (mm)	Annual: 495
Temperature (^oC)	Minimum 8, Maximum 21
Precipitation less than potential evapotranspiration	September–April
GEOLOGY Age and lithology	Quaternary fluvial silt, sand and minor gravel (Shepparton Formation); Quaternary fluvial gravel, sand and silt; Neogene fluvial gravel, sand and silt; Cambrian marine sandstone, siltstone and biotite schist (St Arnaud Group)
GEOLOGY Age and lithology
Geomorphology	4.2.2 Plains without leveed channels of the Older Alluvial Plains
LANDUSE	Uncleared areas: water supply; nature conservation Cleared areas: dryland cropping; lucerne; sheep and beef cattle grazing; dairy farming; water supply
LANDUSE
TOPOGRAPHY Landscape	Alluvial floodplain
TOPOGRAPHY Landscape	Alluvial floodplain
Elevation range (m)	114–229
Local relief (m)	2
Drainage pattern	Dendritic
Drainage density (km/km²)	1.2
Landform	Backplains		Drainage systems
Landform element	Flat	Gentle slope	Stream channel	Bank	Drainage line
Slope and range (%)	0 (0-1)	1 (0-3)	1 (0-1)	1(0-2)	1 (0-3)
Slope shape	Straight	Straight	Straight	Convex	Concave
NATIVE VEGETATION Ecological Vegetation Class	Plains Woodland (39.6%), Riverine Chenopod Woodland (17.8%), Riparian Woodland (17.5%), Other (25.2%)
NATIVE VEGETATION Ecological Vegetation Class
SOIL Parent material	Fluvial gravel, sand and silt	Sandstone, siltstone, greenstone and biotite schist	Fluvial gravel, sand and silt	Fluvial gravel, sand and silt	Fluvial gravel, sand and silt
SOIL Parent material	Fluvial gravel, sand and silt	Sandstone, siltstone, greenstone and biotite schist	Fluvial gravel, sand and silt	Fluvial gravel, sand and silt	Fluvial gravel, sand and silt
Description (Corangamite Soil Group)	Cracking clay soils (22)	Sodic red texture contrast soils (25)	Sodic grey texture contrast soils (21)	Sodic grey texture contrast soils (21) and cracking clay soils (22)	Sodic grey texture contrast soils (21) and cracking clay soils (22)
Soil type sites	WIA22	WIA16, WIA14, WLRA105	WIA20	WIA20, WIA22	WIA20, WIA22
Surface texture	Medium clay	Fine sandy loam	Sandy clay loam	Sandy clay loam to medium clay	Sandy clay loam to medium clay
Permeability	Very slow	Slow	Slow	Slow	Slow
Depth (m)	> 2	> 2	> 3	> 3	> 3
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS Critical land features, processes, forms	Flat areas susceptible to inundation and waterlogging, but can be variable locally due to micro relief (gilgai). Slightly susceptible to gully erosion where dispersive subsoils are exposed. Surface soils are susceptible to compaction (less structure) at relevant moisture contents.	Hardsetting soil slightly susceptible to sheet and rill erosion. Soils are prone to compaction at critical moisture contents. Subsoil susceptible to gully erosion when exposed due to dispersive (sodic) nature. Slight susceptibility to acidification of surface soil.	Depressions are susceptible to seasonal inundation and waterlogging. Soil compaction can occur at critical moisture contents.	Banks are vulnerable to erosion from significant stream flows and flood events. Here sodic subsoils and hardsetting surface soils are extremely susceptible to stream and overbank erosion.	Depressions are susceptible to seasonal inundation and waterlogging. Soil compaction can occur at critical moisture contents.

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