Timbarra (Ta)

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

Area: 195 sq. km (1.0%)

This land system is mapped on hills with plutonic and gneissic rocks, a ridge-and-ravine topography and moderately long steep slopes with outcropping rock and stone. Levees and alluvial flats similar to, but smaller than, those mapped in Walnut land system occur along a few major streams, notably the Timbarra River. The land system is found mainly in the Swifts Creek-Ensay area and near Timbarra, frequently on the higher peaks within areas of Dargo land system. It is similar to Blomford land system but has lower relief and shorter growing seasons. It is also similar in geology and topography to Tanjil land system but the climate is much drier.

In this moderately-high rainfall environment, the granitic rocks tend to weather relatively rapidly. On steep upper slopes the soil is continually mixed by natural erosion and by disturbances such as tree throw so that the soils are little differentiated and leached, acidic, sandy, structureless, red earths have developed. The incomplete weathering of clay-forming minerals may also have contributed to the lack of profile differentiation. On more-gentle lower slopes, blocky clay subsoils are common. These subsoils tend to be neutral to slightly alkaline and are probably prone to gullying, particularly in drainage lines and valley floors. Topsoils are susceptible to sheet erosion.

Shrubby open forest I or II is predominant, and open forest III often occurs in drainage corridors.

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Timbarra- image

Timbarra land system is similar to Blomford land system except that relief is lower and the slopes are less steep, generally with slightly deeper soils. As a result greater proportion of Timbarra land system (foreground) has been cleared.

CLIMATE Rainfall, mean (mm) Temperature, mean (°C) Seasonal growth limitations	Annual 700 - 1200; lowest January or February (40 - 80), highest October (100 - 150) Annual 8 - 12; lowest July (3 - 7), highest February (16 - 20) Temperature <10°C (av.): May - September Rainfall < potential evapotranspiration: November – March
GEOLOGY Age, lithology	Palaeozoic granites, granodiorites, diorites and coarsely crystalline gneisses
PHYSIOGRAPHY Landscape Elevation range (m) Relative relief (m) Drainage pattern Drainage density (km/km²)	Steep hills will ridge-and-ravine topography 60 - 720 80 - 260 Dendritic 1.5
PRESENT LAND USE	Approximately half the area uncleared: hardwood forestry (mostly minor timber products); bush grazing of cattle (limited); apiculture Cleared portion: grazing of beef cattle and sheep

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Timbarra- cs

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

LAND COMPONENT Percentage of land system Diagnostic features	1 95 Slopes with stony soils and dry forest	2 ⁵ Isolated terraces and fans along major drainage corridors
PHYSIOGRAPHY Slope %, typical and (range) Slope shape	20 - 30, (10 - 50) Straight	<2, (0 - 10) Straight but uneven
SOIL
Parent material	Granite, granodiorite, diorite and gneissic rock	Alluvium
Description	Dark greyish brown sandy loam topsoil grading into reddish brown sandy loam to coarse sand (mostly steep upper slopes); dark greyish brown sandy loam to clay loam over yellowish brown or brown mottled clay subsoil (mostly mid- and lower slopes)	Limited observations — variable soils; mainly brown or slightly reddish brown sandy loam to sandy clay loam over stratified alluvium
Classification	Red Earths, Yellow Podzolic Soils, Solodic Soils Uc4.12, Uc5.21; Gn2.86, Dy3.41, Dy5.11	Alluvial Soils, Solodic Soils Uml.44, Uc5.21, Ddl.23
Surface texture	Sandy loam to clay loam	Sandy loam to sandy clay loam
Surface consistence	Slightly hard when dry, firm when moist	Variable
Depth (m)	Mostly 0.8 - 1.2	>2.0
Nutrient status	Moderate	Low to moderate
Available soil water capacity	Low to moderate	Low to moderate
Perviousness to water	Slow to moderate	Slow to moderate
Drainage	Good	Good
Exposed stone (%)	<5, mostly 0	0
Sampled profile number	-	-
NATIVE VEGETATION Structure of vegetation and characteristic species of dominant stratum (+ Predominant species)	Mainly open forest I or II, occasionally III: Mixed forests — including E. albens (Tambo River catchment) E. goniocalyx, E. globulus, E. globoidea (one of which is usually predominant), E. rubida and E. sideroxylon (occasionally)	Limited data — probably open forest II, III : E. viminalis+ with or without E. radiata+; E. melliodora and E. ovata also sometimes predominant

Disturbance	Affected process and trend	Primary resultant deterioration			Casual activities	Primary off-site process
Disturbance	Affected process and trend	Form	Susceptibility of components	Incidence with components	Casual 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 Increased wind velocity over soil and increased detachment of sand	Sheet and rill erosion Wind erosion	1; high 1; low - moderate	Common Uncommon; local occurrences on exposed slopes at high elevation	Clearing, overgrazing, road and dam building and other earth-moving activities, rabbit burrowing, trafficking by stock and vehicles.	Increased flash flows and sediment load. -
Increased physical pressure on soil	Increased compaction With Reduced infiltration	Structure decline Sheet and rill erosion	1,2; low 1; high	Uncommon Common	Increased trafficking, overgrazing, export of organic matter As for wind, sheet and rill erosion above	Increased flash flows Increased flash flows
Increased soil disruption	Increased soil break-up Increased loss of topsoil cohesion	Gully erosion Streambank erosion Wind erosion	1; high 2; high 1; low - moderate	Common Uncommon As for wind erosion above	As for wind sheet and rill erosion above As for wind, sheet and rill erosion above Trafficking, overgrazing, rabbit burrowing, earthmoving activities	Increased sediment load. Increased sediment load Increased sediment load
Comments: Occurrences of wind erosion have been observed in the Ensay/Swifts Creek area. Gully erosion can start on any sloping surface and will work back from creeks across flat areas: the process is aided by the low cohesion of the topsoil and a dispersive subsoil.

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