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Delta (Da)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Delta- geoArea: 54 sq. km (0.3%)

All major river levees and deltas associated with the Gippsland Lakes are included in this land system. Depositional tracts with significant levee construction begin where the form of the stream alters from sinuous to relatively straight or broadly curved, usually 10 to 15 km upstream from the point at which the river enters the lake. The deltas are mostly cuspidate and in varying stages of erosional decline, although the Mitchell River delta is digitate. The deltas are formed essentially by extensions of the natural levees. The combination of land components varies from stream to stream and with position along the stream. Component 3 is similar to lands in the Morass land system.

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Delta- image
Elongated areas of low-lying land, bordered by rivers or lakes, are typical of the Delta land system. Land use is
mostly grazing or water-based recreation.

Soils have developed on fine sand, silt and clay parent materials and are characteristically young. In some areas, sedimentation has been slow enough to allow topsoils to accumulate organic matter and develop a crumb or tine blocky structure. This condition is found largely in component 1. On many levees the surface sediments are too young to show any alteration by soil-forming processes. Erosion hazards are minor, but soil structure in component 1 is sensitive to damage by trampling or trafficking, particularly when the soils are wet. Salinity hazard is high, due to shallow water tables and moderate to high groundwater salinities.

Prior to clearing, the vegetation was probably grassy open forest II with shrubby open forest II on river banks and closed scrub and sedgelands in swamps. River banks and swamps often have fringing stands of Phragmites

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

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

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

Holocene alluvium of tine sands, silts and minor clays
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)

River levees and cuspate or digitate deltas in lacustrine environments

0 - 20
0 - 5
Deranged
1.3
PRESENT LAND USEMostly cleared: grazing of beef and dairy cattle on improved pastures; cropping limited; some irrigation
Minor proportion uncleared: recreation — fishing and shooting; some areas in The Heart Morass, Clydebank Morass, Dowd Morass and Lake Coleman State Game Reserves

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

LAND COMPONENT
Percentage of land system
Diagnostic features
1
65
Levee slopes and deltaic plains
2
20
Levee crests and river banks
3
15
Estuarine swamps, freshwater and brackish
PHYSIOGRAPHY
Slope %, typical and (range)
Slope shape
1, (0 - 2)
Straight or concave
2, (0 - 3)
Convex
<1, (0 - 2)
Straight
SOIL
Parent material
Fine sand, silt and clay
Fine sand, silt and clay
Fine sand, silt, clay and peat
Description
Limited observations — commonly black, fine structured silty loam to sandy clay loam or heavier textured topsoil merging into greyish brown mottled stratified subsoil
Dark greyish brown massive or fine structured sand to sandy clay loam topsoil merging into greyish brown or dark brown subsoil of variable texture; stratified at depth
No observations — soils presumed similar to Morass land system components 1, 2. and 3: variable texture, surficial or buried peaty layers, permanently wet
Classification
Wiesenboden
Um6.21
Alluvial Soils
Uc1.44, Uc6.12, Um1.23, Um1.43, Um5.52
Humic Gleys, some Acid Peats
-
Surface texture
Silty loam or heavier texture
Sand to sandy clay loam
Organic silty loam probably common
Surface consistence
Slightly hard when dry, friable when moist
Loose to slightly hard when dry
Slightly plastic when wet
Depth (m)
>2.0
>2.0
>2.0
Nutrient status
Moderate
Moderate
Moderate
Available soil water capacity
Moderate to high
Low to moderate
High
Perviousness to water
Slow
Moderate to rapid
Slow to moderate
Drainage
Poor to somewhat poor
Good
Very poor
Exposed stone (%)
0
0
0
Sampled profile number
25
19
-
NATIVE VEGETATION
Structure of vegetation and characteristic species of dominant stratum
(+ Predominant species)
Grassy open forest II:
E. tereticornis+
Clearing has made it difficult to determine the species may also have been
Shrubby open forest II:
Mainly E. tereticornis+; E. bosistoana or
E. polyanthemos occasionally predominant.
Phragmites communis often on river banks composition of the original vegetation; other predominant or associated
Vegetation variable, similar to Morass land system

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) rising, saline groundwater table



    Nutrient loss


    Salting



    Not determined


    1; moderate
    3: high



    Not determined


    Uncommon; isolated occurrences in areas NE, S and SW of Lake Wellington



    Removal of trees


    Reduced water-use by plants within catchment



    Increased movement of water to groundwater

    Increased groundwater table and salting

    Increased exposure of surface soil
    Increased soil detachment
    Sheet and rill erosion





    Wave erosion
    1,2: low






    2; moderate
    Uncommon: occurs occasionally





    Common: severe on exposed lake shores
    Clearing, burning, overgrazing, road building and other earth-moving activities, rabbit burrowing, trafficking by stock and vehicles.

    Protection once afforded by Phragmites communis is reduced by increasing salinity of lake
    Increased flash flows and sediment load.





    Increased lake turbidity
    Increased physical pressure on soil
    Increased compaction

    With

    Reduced infiltration
    Structure decline



    Sheet and rill erosion
    1; moderate
    2; low


    1,2; low
    Not determined



    Uncommon: occurs occasionally
    Increased trafficking cultivation, overgrazing, export of organic matter

    As for sheet and rill erosion above
    -



    Increased run-on and/or ponding of water
    Increased soil disruption
    Increased soil break-up
    Scour erosion


    Streambank erosion

    Wave erosion
    1,2: low


    2: high


    2: moderate
    Uncommon: occurs occasionally

    Common: partly a natural process

    Common: severe on exposed lake shores
    As for sheet and rill erosion above

    As for sheet and rill erosion above

    As for wave erosion above
    Increased sediment load and turbidity of streams

    Increased sediment load and turbidity of streams

    Increased turbidity of
    lake water
    Comments: Streambank erosion is accelerated where stock have access to the stream, and by any disturbances within the catchment that increase river flow
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