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Seacombe (Sm)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Seacombe - geoArea: 85 sq. km (0.4%)

Seacombe land system occurs on parts of the prior and inner barriers. Where the inner barrier is still intact there is an undulating sand sheet, produced by a series of broad but closely spaced beach ridges parallel to the coastline. The formation is of Pleistocene age, but more recent aeolian disturbance producing an incipient dune-like surface has occurred in areas like Sperm Whale Head. More severe, peripheral, aeolian attack of these beach ridges has created larger, mostly parabolic dunes; these dunes are mapped in Banksia land system.

In other areas, the inner and prior barriers suffered partial dissection during the last major sea level fall and have since undergone lacustrine re-working to produce beach ridges of lower relief. The orientation of the beach ridges varies with the orientation of the paleo-lacustrine shores, rather than being parallel to the coastline. Often the beach ridges are no longer distinct and a sand sheet with an uneven surface occurs. Where there has been significant aeolian disruption of these lower ridges, the water table has been excavated and dunes with swampy cores occur.
A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Seacombe - image
Very low sand ridges form a large uneven sand plain typical of Seacombe land system

The sands may originally have contained shell fragments and carbonates, but now the soils are leached, infertile and strongly acidic, particularly in the topsoil. They also generally appear to have developed iron-indurated pans (
coffee-rock) mostly at greater depths (deeper than 1.5 m) than in similar soils elsewhere in the region. Being of sandy texture throughout, the soils are droughty and susceptible to wind erosion. There is a moderate salinity hazard because of a saline, ground-water table close to the surface of the swales and low-lying areas.

The vegetation is mainly a heathy open woodland of E. nitida and Banksia serrata. It is replaced by an open woodland of E. viminalis var. racemosa and B. serrata with Pteridium esculentum on lower moister site

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

    Annual 500 - 800; lowest January (30 - 50), highest October (40 - 70)

    Annual 12 - 14; lowest July (9 - 10), highest February (19 - 20)
    Temperature <10C (av.): No months
    Rainfall < potential evapotranspiration: November – March
GEOLOGY
Age, lithology
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)

    Marine and lacustrine sand sheets formed from a series of relict beach ridges

    0 - 20
    0 - 5
    Nil
    0
PRESENT LAND USE
    Mostly uncleared: within the Gippsland Lakes Coastal Park, The Lakes National Park and Blond Bay State Game Reserve; apiculture; bush grazing of cattle (very
    limited)
    Minor cleared areas: grazing of sheep and cattle

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

LAND COMPONENT
Percentage of land system
Diagnostic features
1
40
Closely spaced beach ridges forming gently
undulating surface
2
8
Swales
3
52
Sand sheets of low and uneven relief.
Occasional swamps in low-lying areas
PHYSIOGRAPHY
Slope %, typical and (range)
Slope shape
Variable, (0 - 20)
Convex and concave
<1, (0 - 2)
concave
1- 2, (0 - 5)
Straight but uneven
SOIL
Parent material
Marine and lacustrine sand, locally redistributed by wind
Description
Limited observations — leached acidic sand, black or dark grey at the surface, pale brown or whitish in the subsurface often over contrasting
dark yellowish brown sand or coffee rock; light yellowish coloured sandy subsoil. Depth to coffee rock or the dark yellowish brown sand
variable, probably between 1 and 2 m
Classification
Podzols, Siliceous Sands
Uc4.31, Uc2.32, probably also Uc4.2-, Uc2.2- and Uc1.21
Surface texture
Sand
Surface consistence
Loose or soft when dry
Depth (m)
>2.0
Nutrient status
Very low
Available soil water capacity
Very low
Perviousness to water
Very rapid
Drainage
Somewhat excessive
Exposed stone (%)
0
Sampled profile number
Nicholson (1978), profile 755
-
NATIVE VEGETATION
Structure of vegetation and
characteristic species of
dominant stratum
(+ Predominant species)
Mainly heathy open woodland I:
E. nitida, Banksia serrata (either predominant)
Understorey dominated mostly by Leptospermum myrsinoides or Thryptomene micrantha
On moister sites, ferny open woodland I:
E. viminalis var. racemosa+, B. serrata, Pteridium esculentum
Mainly open woodland I:
E. viminalis var. racemosa+ with Pteridium
esculentum
Swamps with Gahnia spp. or Juncus maritimus and/or Lepidosperma longitudinale and usually with fringe of Melaleuca ericifolia or M. squarrosa

    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 and leaching

    b) raised groundwater
    table



    Nutrient loss




    Salting



    1,2,3; high




    2,3; low


    Not
    determined





    Uncommon: isolated occurrences



    Removal of trees




    Reduced plant water use in the catchment



    Increased movement of water to groundwater



    Raised groundwater table

    Increased exposure of surface soil
    Increased wind velocity over soil and increased detachment of sand
    Wave erosion


    Wind erosion
    2,3; moderate


    1,2,3; high
    Uncommon


    Uncommon: but locally severe
    Clearing, burning, overgrazing, road building and other earth-moving activities, trafficking by stock and vehicles.
    Increased turbidity of water

    Encroachment by sand
    Increased physical pressure on soil
    Increased compaction
    Structure decline
    1; low
    2,3; low
    Uncommon
    Increased trafficking, overgrazing, export of organic matter
    -
    Increased soil disruption
    Increased loosening of sand
    Wind erosion


    Wave erosion
    1,2,3; high


    2,3; moderate
    Uncommon: locally severe

    Uncommon
    As for wind erosion above

    As for wave erosion above
    Encroachment by sand


    Increased turbidity of water
    Comments: Regeneration of vegetative cover poor in areas exposed to wind and wave erosion and expensive remedial works may be required. An area of salting occurs just south east of Lake Wellington.
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