Soil/Landform Unit - Natimuk-Douglas valley

Landform Unit Description

Swamp, lunettes and lakes litter the plains of the Natimuk-Douglas valley

Area: 29 326 ha

1.25% of CMA region

Also known as the

White Lake

unit from the Kowree report (1956) and the

Lowan

unit from soil-landform mapping of the Natimuk 1:100 000 mapsheet (1990), the Natimuk-Douglas valley consists of a valley running north-south with slopes that rise gradually to the east and west. The depression is sharply defined by the Kowree unit to the west and is most likely an extension of the Lowan Salt Valley unit to the north. Blackburn and Gibbons (1956) believed it to be ‘very probable that the unit occupies the site of an old valley through which the Glenelg River or an adjacent stream flowed north before this was captured by dissection extending along the present course of the Glenelg River’. Another theory suggests the Murray River may have once flowed south along the valley and then down the Glenelg River. Today’s landscape is characterised by valley slopes,

alluvial

plains and valley floor with

sodic

brown, yellow and grey texture contrast soils (

Sodosols

) dominant. Compaction is again a major soil degradation issue due to the

hardsetting

nature of the soils. Land use is mainly dryland cereal cropping with grazing intermixed. Vegetation communities include a number of woodland and wetland associations including Heathy Woodland, Low Rises Woodland, Riverine Chenopod Woodland and Seasonally Inundated Shrubby Woodland.

Looking east across Natimuk-Douglas valley towards the uplands
	Looking north along the Natimuk-Douglas valley towards Mt Arapiles

Component	1	2	3	4	5	6	7
Proportion of soil-landform unit	10%	25%	35%	15%	5%	7%	3%
CLIMATE Rainfall (mm)	Annual: 460
CLIMATE Rainfall (mm)	Annual: 460
Temperature (^oC)	Minimum 8, Maximum 21
Precipitation less than potential evapotranspiration	October–April
GEOLOGY Age and lithology	Quaternary aeolian dune sand (Lowan Sand); Quaternary paludal silt and clay
GEOLOGY Age and lithology
Geomorphology	5.3.3 Salt lake depression of the North West Dunefields and Plains
LANDUSE	Uncleared areas: nature conservation Cleared areas: dryland cropping; sheep grazing; gypsum extraction
LANDUSE
TOPOGRAPHY Landscape	Shallow depression to valley
TOPOGRAPHY Landscape	Shallow depression to valley
Elevation range (m)	105–174
Local relief (m)	15
Drainage pattern	Centripetal–deranged
Drainage density (km/km²)	0.7
Landform	Valley slopes		Alluvial plains and valley floors			Swamp complex
Landform element	Upper slope	Lower slope	Gentle plain	Flat	Lunette	Freshwater swamp bed	Saltwater swamp bed
Slope and range (%)	6 (3-12)	3 (2-10)	1 (0-5)	0 (0-2)	4 (2-12)	0 (0-1)	0 (0-1)
Slope shape	Convex	Concave	Straight	Straight	Convex	Straight	Straight
NATIVE VEGETATION Ecological Vegetation Class	Plains Woodland (37.3%), Shallow Sands Woodland (13.8%), Salt Paperbark Woodland (5.3%), Ridged Plains Mallee (5.1%), Other (34.3%)
NATIVE VEGETATION Ecological Vegetation Class
SOIL Parent material	Marine silt and clay, aeolian dune sand	Marine silt and clay, aeolian dune sand	Marine silt and clay, fluvial silt and sand	Fluvial silt and clay, minor alluvial gravels, sand and silt	Aeolian and alluvial dune sand and silt	Swamp and alluvial silt and clay	Swamp silt and clay, evaporites and aeolianites
SOIL Parent material	Marine silt and clay, aeolian dune sand	Marine silt and clay, aeolian dune sand	Marine silt and clay, fluvial silt and sand		Aeolian and alluvial dune sand and silt	Swamp and alluvial silt and clay	Swamp silt and clay, evaporites and aeolianites
Description (Corangamite Soil Group)	Sodic red texture contrast soils (39)	Sodic brown, yellow and grey texture contrast soils (38)	Sodic brown, yellow and grey texture contrast soils (38)	Grey and brown cracking clay soils (37)	Grey and brown cracking clay soils (37)	Seasonally wet soils: sodic yellow and grey texture contrast soils (33)	Seasonally wet soils: sodic yellow and grey texture contrast soils (33)
Soil type sites	NA174	LSWW11, LSWW17, LSWW13	LSWW11, LSWW17, LSWW13	LS3, LSWW9, LSWW5	LS3, LSWW9, LSWW5	NA171, NA141, NA178	NA171, NA141, NA178
Surface texture	Sandy loam	Loamy sand	Loamy sand	Medium clay	Medium clay	Sand	Sand
Permeability	Moderate	Moderate	Moderate to slow	Slow	Slow	Very slow	Very slow
Depth (m)	> 1.2	1.3	1.3	> 2	> 2	> 1.5	> 1.5
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS Critical land features, processes, forms	Hardsetting soil surface susceptible to sheet and rill erosion along with wind erosion when exposed. Dispersive and deep subsoils susceptible to gully erosion on steeper slopes. Compaction of upper soil variable depending on soil depth and moisture content. Upper soil is susceptible to acidification.	Susceptible to wind and sheet erosion where exposed and surfaces have little organic matter. Susceptible to compaction where hardsetting and restricted drainage. Upper soil is susceptible to acidification.	Susceptible to wind and sheet erosion where exposed and surfaces have little organic matter. Susceptible to compaction where hardsetting and restricted drainage. Upper soil is susceptible to acidification.	Susceptible to inundation and waterlogging in lower areas, but can be variable due to micro relief (gilgai). Slightly susceptible to surface sheet erosion where soils are exposed. Surface soils friable and only slightly susceptible to wind erosion. Soils susceptible to compaction at critical moisture contents.	Slightly susceptible to surface sheet erosion where soils are exposed. Surface soils are friable and only slightly susceptible to wind erosion. Soils susceptible to compaction at critical moisture contents.	Susceptible to seasonal inundation and waterlogging. Upper soils susceptible to sheet erosion and wind erosion when exposed.	Susceptible to seasonal inundation, waterlogging and ultimately soil salinity. Upper soils susceptible to sheet erosion and wind erosion when exposed.

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