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Redgum 1 (R1)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- geoArea: 857 sq. km (4.2%)

Redgum 1 is the most extensive land system in the drier parts of the Eastern lowlands. It occurs on the gently sloping to undulating plains of the earlier Pleistocene terrace and of the more distal parts of the Tertiary flood plain deposits.

Dissection is firmly established and integrated drainage has developed, with broad shallow erosional basins holding the main streams. Most of the original land surface has now been removed. Near the southern bank of the Mitchell River flood plain, sink holes have developed where Miocene limestones occur close to the surface. Where sandy rises of Barrier or Perry land systems block the natural drainage, there are poorly drained depressions. Geology and climate are similar to those in Westbury 1 land system but Redgum 1 has lower relief.

The very gentle slopes and the well-developed duplex soils are major factors in the general stability of the area. However, the clayey subsoils are commonly sodic and any sheet erosion near the dissected edges of the plain and near the incised drainage ways could be followed by gully erosion.

The upper horizons are sometimes thick and sandy due to wind-blown accretions. The soils are similar to those in Redgum 2 land system but appear to lack gilgai micro-relief. Seasonal waterlogging occurs on the flatter slopes. The native vegetation, probably mainly an E. tereticornis grassy open forest II, has mostly been cleared.
A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- image
Dissection of the early Pleistocene terraces has often resulted in steep slopes along the drainage channels with gently sloping and undulating terrain adjacent. This dissection distinguishes Redgum 1 from Redgum 2 land system.

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

    Annual 500 - 800; lowest July or August (30 - 50), highest October (50 - 80)

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

    Lower
    Pleistocene terrace and some more distal parts of Tertiary floodplain deposits; gravels, sands, silts and clays; unexposed marine limestone
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)
    Gently sloping to gently undulating plains with shallow but definite dissection
    20 - 160
    0 - 20
    Dendritic
    0.3
PRESENT LAND USE
    Mostly cleared: grazing of cattle and sheep; some cropping
    Minor proportion uncleared: bush grazing of cattle; timber (minor products and some firewood)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- csA study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- graph

LAND COMPONENT
Percentage of land system
Diagnostic features
1
64
Slopes
2
20
Almost flat areas
3
10
Drainage depressions
4
5
Slightly depressed, poorly
drained areas on the flats
5
1
Sink-holes
PHYSIOGRAPHY
Slope %, typical and (range)
Slope shape
3, (1 - 10)
Straight
1, (0 - 2)
Straight
1, (0 - 5)
Concave
<1, (0 - 2)
Concave
Variable, (0 - 10)
Concave
SOIL
Parent material
Unconsolidated clay, silt, sand and gravel (often stratified, in places cemented or dense)
Colluvium from components
1 - 3 and/or marine limestone
Description
Very dark grey to very dark greyish brown loamy sand to
sandy loam topsoil, grading into greyish brown in places
deep, similarly textured subsurface soil; abrupt change
to strongly mottled yellowish brown, blocky clay
subsoil. Commonly very gravelly
No observations —
probably undifferentiated
medium textured gravelly
soils
Similar to component
1 and 2, but mottling often
extending into topsoil;
clay subsoil may have
columnar structure
Limited observations —
greyish brown to slightly
reddish brown clay loam to
light clay, mottled to near
the surface
Classification
Mostly Solodized Solonetz and Solodic Soils, some Soloths
and Yellow Podzolic Soils
Dy3.22, Dy5.22, Dy5.21, Dy3.31, Dy3.33, Dy3.23, Db2.31
-
Soloths, Yellow Podzolic
Soils
Dy3.41, Db2.41
Brown Earths
Um6.21, Uf6.13
Surface texture
Loamy sand to sandy loam
-
Sandy loam
Clay loam
Surface consistence
Soft to slightly hard when dry
-
Friable to very firm when
moist
Very firm when moist
Depth (m)
>2.0
>2.0
>2.0
>2.0
Nutrient status
Low to moderately low
-
Low
Moderately low
Available soil water capacity
Low
-
Moderately low
Moderately low
Perviousness to water
Slow
-
Slow
Slow
Drainage
Mostly somewhat poor
-
Very poor to poor
Somewhat poor
Exposed stone (%)
0
-
0
0
Sampled profile number
68
-
-
-
-
NATIVE VEGETATION
Structure of vegetation and
characteristic species of
dominant stratum
(+ Predominant species)
Grassy open forest II:
Mainly E. tereticornis+ E. bridgesiana, E. polyanthemos associated
On better drained slopes E. bosistoana or E. globoidea occasionally predominant
Mainly open forest I, II, often shrubby: E. tereticornis+ sometimes with E. ovata and occasionally E. cephalocarpa.
Understorey often with Melaleuca ericifolia Closed scrub of M ericifolia in poor drained areas
As for components 1, 2 and 3

    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:

    a) increased deep percolation

    b) raised winter/spring water table



    Nutrient loss


    Waterlogging



    Not determined


    2; low
    3,4,5; moderate



    Not determined


    Not determined



    Removal of trees


    Reduced plant-water use
    in catchment



    Increased movement of water to groundwater; increased base-flow of streams

    Increased run-on and ponding of water in low-lying areas

    Increased exposure of surface soil
    Increased overland flow and soil detachment
    Sheet and rill erosion
    1,3,4; low
    2,5; very low
    Uncommon: isolated occurrence on cleared land
    Clearing, overgrazing, road 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
    1,2,3; low
    4,5; moderate



    1,3,4; low
    2,5; very low
    Uncommon




    Uncommon: isolated occurrence on cleared land
    Increased trafficking and cultivation, overgrazing, export of organic matter

    As for sheet and rill erosion above
    -




    Increased flash flows
    Increased soil disruption
    Increased soil break-up
    Gully erosion
    3; moderate
    1; low - moderate
    2,4,5; very low
    Uncommon: but can be severe in incised drainage channels
    As for sheet and rill erosion above
    Increased sediment load
    Comments: -
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