Walnut (Wt)

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

Area: 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 <10°C (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- cs

A 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
Disturbance	Affected process and trend	Form	Susceptibility of components	Incidence within components	Causal activities	Primary off-site process
Alteration of vegetation: — reduction in leaf area, rooting depth and/or perenniality	Reduced transpiration, resulting in increased deep percolation	Nutrient loss	Not determined	Not determined	Removal of trees	Increased movement of water to groundwater; increased base-flow of streams'
Increased exposure of surface soil	Increased overland flow and soil detachment	Sheet and rill erosion	1,2; low 3; moderate	Uncommon	Clearing, 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 soil	Increased compaction	Structure decline	1,2; low - moderate 3; low	Uncommon	Increased trafficking, cultivation, overgrazing, export of organic matter	-
Increased soil disruption	Increased soil break-up	Gully 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

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