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Avon (Av)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Avon - geoArea: 247 sq. km (1.2%)

Low hills and gentle slopes occur on Carboniferous sediments at relatively low elevations close to the southern margin of the East Victorian Uplands and along some of the major river valleys. These areas are mapped in Avon land system. Ridge crests are generally rounded and slopes are short. Structural control of slope gradient and shape is often evident and some rock outcrop occurs on crests and ledges. Red-bed shales can sometimes be observed in road cuttings. Avon is similar to Glenmaggie land system but has lower relief and gentler slopes.

Rocks, which weather to clays, silts and sands on relatively gentle slopes with moderate rainfall, enhance the formation of duplex soils. The alkaline nature of some subsoils may increase the risk of gully erosion.

The vegetation is mainly shrubby open forest II, with some open forest III on protected hillslopes and valley floors. Scattered pockets of closed forest II occur in narrow, steep-sided gullies.
A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Avon - image
A shrubby open forest, with leaf litter forming a relatively large proportion of the ground cover, typical of this 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: December – February
GEOLOGY
Age, lithology

Lower
Carboniferous freshwater siltstones, minor sandstones, conglomerates, often red (Snowy Plains Formation) with alternating quartzose and feldspathic sandstones and 'red-bed' siltstones
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)

Low rounded hills and undulating terrain

60 - 520
20 - 140
Dendritic
0.7
PRESENT LAND USEMostly uncleared: hardwood forestry (minor timber products); apiculture; bush grazing (limited); small area in Glenaladale National Park
Minor proportion cleared: grazing of beef cattle and sheep

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

LAND COMPONENT
Percentage of land system
Diagnostic features
1
40
Exposed slopes and narrow, often rocky crests
2
30
Broad, often gently
undulating crests
3
20
Protected slopes
4
5
Flats in major
drainage corridors
5
5
Fans and
associated minor drainage
depressions
PHYSIOGRAPHY
Slope %, typical and (range)
    Slope shape
15-20,(10-50)
Straight or concave
5-10,(0-20)
Convex
15-20,(10-50)
Concave
2.(0-5)
Straight but uneven
2 - 5.(0-10)
Straight
SOIL
Parent material
Siltstone, quartzose and feldspathic sandstone; some conglomerate
Alluvium of variable texture
Colluvium and local alluvium
Description
Dark greyish brown, dark grey or dark brown sandy loam to clay loam topsoil abruptly overlying yellowish brown or reddish brown clay subsoil, mostly acidic and whole coloured; subsoils sometimes alkaline. Brown or greyish brown uniform loamy sand, in places shallow on or near quartzose sandstone.
Limited observations – mainly undifferentiated brown sand and loam
Duplex with yellowish brown mottled clay subsoil (on colluvium) and brown loam (on colluvium)
Classification
Yellow and Red Podzolic Soils, Solodic Soils, some Earthy Sands
Dy2.21, Dy2.33, Dy3.43, Dy3.61, Dr2.11, Dr2.21, Dr3.21, Uc4.13, Uc4.24
Alluvial Soils
Uc1.24
Yellow Podzolic Soils
Dy2.22, Um1.44
Surface texture
Sandy loams (mainly) to clay loams
-
Sandy loams to clay loams
Surface consistence
Variable: soft to hard when dry, friable to firm when moist
-
Variable
Depth (m)
Variable: 0.8-1.5
>2.0
>2.0
Nutrient status
Low to moderate
Low to moderate
Low to moderate
Available soil water capacity
Low (sandy soils) to moderate
Low to moderate
Low to moderate
Perviousness to water
Slow to moderate
Moderate to rapid
Slow to moderate
Drainage
Mainly good
-
Very poor to somewhat poor
Exposed stone (%)
<10
0
0
Sampled profile number
-
56
-
-
-
NATIVE VEGETATION
Structure of vegetation and
characteristic species of
dominant stratum
(+ Predominant species)
Open forest I. II. Often shrubby:
E. macrorhyncha+.
E. polyanthemos+,
E. tereticornis+ or E. sieberi+;
and E. baxteri often
Open forest II:
E. melliodora+,
E. cypellocarpa
associated
Open forest II, III, often shrubby:
Composition variable —
E. cypellocarpa,
E. globoidea, E. sieberi
or E. tereticornis
usually predominant;
E. muellerana,
E. sideroxylon and
E. baxteri associated
Limited data — probably mainly open forest II, III, often shrubby of
E. melliodora+,
E. viminalis+ or
E. radiata+
Rarely closed forest II
of Acmena smithii,
climbers, ferns and epiphytes
Mostly open forest II with composition variable and
Including, E. bridgesiana.
E. radiata,, E. viminalis
Occasionally closed scrub
of Melaleuca ericifolia or
closed forest as for component 4

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 and leachingNutrient lossNot determinedNot determined
    Removal of trees
Increased movement of water to groundwater; increased base-flow of streams
Increased exposure of surface soilIncreased overland flow and soil detachmentSheet and rill erosion1,3; moderate
2; low
Uncommon
    Clearing, logging, burning, 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 soilIncreased compaction

with





reduced infiltration
Structure decline







Sheet and rill erosion
1,2,3; low - moderate
4; low


5; moderate



1,3: moderate
2; low
Uncommon



Uncommon
    Increased trafficking and cultivation, overgrazing, export of organic matter.

    As for sheet and rill erosion above
-



Increased flash flows
Increased soil disruptionIncreased soil break-upGully erosion



Scour erosion


Streambank erosion
1,3,5; moderate
2; low


4; moderate


4; high
Uncommon



Uncommon


Uncommon
    As for sheet and rill erosion above.


    As for sheet and rill erosion above.

    As for sheet and rill erosion above
Increased sediment load.


Increased sediment load

Increased sediments load and turbidity
Comments: -
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