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Timbarra (Ta)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Timbarra- geoArea: 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 <10C (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- csA 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
    Form
    Susceptibility of components
    Incidence with components
    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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