Soil/Landform Unit - Wimmera River

Wimmera River at Dimboola

Area: 19 743 ha

0.84% of CMA region

Alluvial plains and terrace plains of the Wimmera River extend from Horsham to Lake Hindmarsh and from Lake Hindmarsh to Lake Albacutya. Part of the Northern Riverine Plains modern floodplains (4.1), these plains sit within the older

alluvial

plain, dissecting the Little Desert and bound within the Lowan salt valley. There are five components, the plain being dominant and terrace plain subdominant. The other components are the terrace flats, drainage depressions and playas. Drainage consists of concentrating flow from the plains and the outwash slopes including seeps, which may be saline. Grey cracking clay soils (

Vertosols

) and sodic grey texture contrast soils occur on the flats. Seasonal inundation and waterlogging are the main land degradation susceptibilities of this relatively flat terrain. Land use includes grazing (sheep and cattle), dryland cropping, water supply, recreation, nature conservation, residential and hardwood forestry. Vegetation communities include a variety of woodland, mallee and shrubland vegetation such as Plains Woodland, Drainage-line Woodland, Freshwater Lignum Shrubland, Red Swale Mallee and Ridged Plains Mallee.

Looking north towards the junction of the Wimmera River and Datchak Creek
	River red gums lining the Wimmera River

Component	1	2	3	4	5
Proportion of soil-landform unit	40%	10%	35%	10%	5%
CLIMATE Rainfall (mm)	Annual: 410
CLIMATE Rainfall (mm)	Annual: 410
Temperature (^oC)	Minimum 8, Maximum 22
Precipitation less than potential evapotranspiration	September–April
GEOLOGY Age and lithology	Quaternary aeolian dune sand (Lowan Sand); Neogene marine sand and silt (Parilla Sand); Quaternary paludal silt and clay
GEOLOGY Age and lithology
Geomorphology	4.1.1 Meander belt below plain level of the Modern floodplain
LANDUSE	Uncleared areas: hardwood forestry for sawlogs, posts and poles; water supply; nature conservation Cleared areas: heep grazing; water supply; dryland cropping; residential development; recreational activities
LANDUSE
TOPOGRAPHY Landscape	River plain
TOPOGRAPHY Landscape	River plain
Elevation range (m)	74–137
Local relief (m)	1
Drainage pattern	Dendritic
Drainage density (km/km²)	2.0
Landform	Alluvial plains
Landform element	Plain	Terrace flat	Terrace plain	Drainage depression	Playa
Slope and range (%)	2 (1-3)	1 (0-2)	1 (0-2)	2 (0-3)	1 (0-2)
Slope shape	Straight	Straight	Straight	Concave	Concave
NATIVE VEGETATION Ecological Vegetation Class	Riverine Chenopod Woodland (28.9%), Intermittent Swampy Woodland/Riverine Grassy Woodland Complex (24.8%), Riparian Woodland (14.3%), Semi-arid Woodland (6.3%), Other (25.7%)
NATIVE VEGETATION Ecological Vegetation Class
SOIL Parent material	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Paludal silt and clay
SOIL Parent material	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Alluvial gravel, sand and silt	Paludal silt and clay
Description (Corangamite Soil Group)	Cracking clay soils (22)	Sodic grey texture contrast soils (21)	Sodic grey texture contrast soils (21) and cracking clay soils (22)	Cracking clay soils (22)	Cracking clay soils (22)
Soil type sites	WIA22	WIA20	WIA20, WIA22	WIA22	WIA22
Surface texture	Medium clay	Sandy clay loam	Sandy clay loam to medium clay	Medium clay	Medium clay
Permeability	Very slow	Slow	Very slow	Very slow	Very slow
Depth (m)	> 2	> 3	> 2	> 2	> 2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS Critical land features, processes, forms	Plains are susceptible to inundation, waterlogging and flood events. Surface soils are susceptible to compaction (less structure) where moisture content is critical.	Flat areas susceptible to inundation and waterlogging. Surface soils can be susceptible to sheet and rill erosion along with compaction at critical moisture contents. Slight susceptibility of surface soil to acidification.	Terrace plains are susceptible to inundation and waterlogging. Surface soils can be susceptible to sheet and rill erosion along with compaction at critical moisture contents. Slight susceptibility of surface soil to acidification.	Flat areas are subject to seasonal inundation, waterlogging and flooding. Subsoils are sodic and extremely vulnerable to gully erosion where exposed. Surface compaction occurs at critical moisture contents.	Playa plains are subject to seasonal inundation, waterlogging and flooding. Subsoils are sodic and extremely vulnerable to gully erosion where exposed. Surface compaction occurs at critical moisture contents.

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