Your gateway to a wide range of natural resources information and associated maps

Victorian Resources Online

Walnut (Wt)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Walnut- geoArea: 82 sq. km (0.4%)

Walnut land system is mapped on the larger alluvial floors at low elevations in the East Victorian Uplands. Fluvial dynamics have been complex and a number of terraces and encroaching colluvial deposits are characteristic. Most occurrences are in the eastern half of the Uplands and they are commonly associated with areas of Dargo land system. Here they contain stored alluvium held back by resistant rock bars which form local stream base levels. Many of the major streams have levees and alluvial flats, too small to map at the scales used, but these are essentially part of the Walnut land system.

Soils occurring on the younger terraces still receive sediments during floods and little soil development has taken place beyond darkening of topsoils by organic matter accumulation and some surface structural development. Subsoils still show stratification of the alluvial sediments. Due to good internal drainage, subsoils are brown and not mottled. Glistening mica flakes can often be observed and are indicative of good reserves of potash. Minor swampy areas that have soils of low permeability are associated with these younger terraces. Limited observations indicate that the older terraces have variable soils, possibly reflecting differences in age, texture and mineralogy of parent materials. Textures may become more clayey with depth as a result of soil-forming processes. Duplex and gradational soils have been observed as well as soils with little textural differentiation. On most of the older terraces, subsoils tend to be brightly coloured, ranging from yellowish brown to reddish brown and may or may not show structural development.

The original vegetation, now largely cleared, appears to have been mainly open forest II and III, with closed sedgeland in swampy places.
A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Walnut- image
An alluvial terrace with relict stream channels, large enough to be mapped in Walnut land system, is surrounded by the partly cleared slopes of Wonnangatta land system. The forested slopes are in Talbotville land system.

CLIMATE
Rainfall, mean (mm)
Temperature, mean (C)
Seasonal growth limitations

    Annual 600 - 900; lowest July (40 - 70), highest October (60 - 90)

    Annual 12 - 14; lowest July (8 - 10), highest February (19 - 21)
    Temperature <10C (av.): May - September
    Rainfall < potential evapotranspiration: November – March
GEOLOGY
Age, lithology

    Holocene fluviatile deposits of sands, silts, some clays and gravels
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)

    Terraced alluvial floors at low elevations in the highlands

    100 - 900
    0 - 10
    Sinuous channel
    1.7
PRESENT LAND USE
    Mostly cleared: grazing of beef cattle on improved and native pastures; occasional cropping

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Walnut- csA study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Walnut- graph

LAND COMPONENT
Percentage of land system
Diagnostic features
1
50
Younger lower terraces, with
fluviatile forms preserved,
subject to flooding
2
30
Older higher terraces, now
erosional, not flood prone
3
10
Minor fan deposits
adjacent to higher land
4
10
Main channel, often slightly
braided
PHYSIOGRAPHY
Slope %, typical and (range)
Slope shape
1 - 2, (0 - 5)
Straight but uneven
1 - 2, (0 - 5)
Straight but uneven
15 - 25, (10 - 30)
Slightly concave
<1, (0 - 2)
Concave
SOIL
Parent material
Alluvial sand, silt and some clay and gravel often stratified at depth
Colluvium of variable texture
-
Description
Very dark greyish brown loamy
sand to silty clay loam topsoil
over structureless brown subsoil
Very dark greyish brown loamy
sand to sandy clay loam topsoil
over brown or reddish brown
subsoil with variable texture
and structure
Limited observations — probably
mainly dark greyish brown loamy
topsoil grading into or resting
on yellowish brown clay subsoil,
with some gravel
No soils; often gravelly
bed loads
Classification
Alluvial Soils, minor Humic Gleys
Uc5.21, Um5.52, Um6.22, Uc1.23,
Uc1.43, Uml.44
Non-calcic Brown Soils, Earthy
Sands, Solodic Soils, Red-brown
Earths
Uc5.21, Um4.25, Um4.31, Gn3.26,
Dr2.23
Alluvial Soils
Uc1.4-, Um1.4-
-
Surface texture
Variable; sand to clayey sand
Loamy sand to sandy clay loam
Sandy and loamy textures
-
Surface consistence
Loose to friable when moist
Slightly hard to very hard when
dry
Slightly hard to hard when dry
-
Depth (m)
>2.0
>2.0
>2.0
-
Nutrient status
Low for sands, otherwise moderate
Low to moderate
Low to moderate
-
Available soil water capacity
Low for sands, otherwise moderate
Low to moderate
Low to moderate
-
Perviousness to water
Moderate to rapid
Variable; slow to rapid
Slow
-
Drainage
Good
Good
Moderately good to good
-
Exposed stone (%)
0
0
Probably <10
-
Sampled profile number
18, 22
21
-
-
NATIVE VEGETATION
Structure of vegetation and
characteristic species of
dominant stratum
(+Predominant species)
Open forest II, III:
E. melliodora+ and/or E. viminalis+ or occasionally E. elata+; understorey often includes Melaleuca ericifolia, Leptospermum spp., Callistemon spp.
Occasional swamps with closed sedgeland, usually of Carex appressa
Mainly open forest II, III:
E. melliodora and/or E. viminalis predominant; E. radiata. E. ovata (in wetter areas) or E. stellulata (at higher elevations) sometimes associated
Fringing vegetation similar to component 1

Disturbance
Affected process and trend
Primary resultant deterioration
Causal activities
Primary off-site process
Form
Susceptibility of
components
Incidence within
components
Alteration of vegetation:
— reduction in leaf area, rooting depth and/or perenniality
Reduced transpiration,
resulting in increased deep percolation
Nutrient lossNot determinedNot determinedRemoval of treesIncreased movement of water to groundwater; increased base-flow of streams'
Increased exposure of surface soilIncreased overland flow and soil detachmentSheet and rill erosion1,2; low
3; moderate
UncommonClearing, cultivation, overgrazing, road and dam building and other earth-moving activities, trafficking by stock and vehicles.Increased sediment load and stream flow
Increased physical pressure on soilIncreased compactionStructure decline1,2; low - moderate
3; low
UncommonIncreased trafficking, cultivation, overgrazing, export of organic matter-
Increased soil disruptionIncreased soil break-upGully erosion


Scour erosion

Streambank erosion
3; moderate


1; high

1; high
Uncommon


Common: locally severe

Common: partly a natural process
As for sheet and rill erosion above

As for sheet and rill erosion above

As for sheet and rill erosion above
Increased sediment load and streamflow

Increased sediment load and streamflow

Increased sediment load and streamflow
Comments: Regeneration of vegetative cover is usually rapid because of high soil fertility and high moisture availability. However, engineering works may be required to help restore vegetation on eroded streambanks
Page top