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Valencia (Va)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Valencia- geoArea: 158 sq. km (0.8%)

Sea level began to fall after deposition of the earliest Pleistocene terrace materials. A temporary cessation of this fall led to the formation of a less-extensive, lower Pleistocene terrace, remnants of which can be found along the flanks of most of the major river valleys. Valencia and Yinnar land systems are mapped on this terrace. Valencia land system occurs in the main rain-shadow area of the Eastern lowlands on almost flat plains similar to those of Redgum 2 land system but with traces of fluviatile land forms still evident and with more variable and generally younger soils. Yinnar land system occurs further to the west in a more humid climate on terraces derived from Cretaceous sediments.

Due to the stability of the very gently undulating to flat terrain, most soils have developed a duplex profile; further profile development has been limited by the clayey parent materials and rather poor drainage. The degree of mottling is variable but it usually occurs in the clay subsoils and frequently in the upper horizons as well. The topsoils are strongly to mildly acidic while the subsoils are mostly neutral to alkaline, probably caused by the presence of sodium. Erosion is generally minor but the sodic soils are susceptible to gully erosion along the margins of the terrace. The rain-shadow effect combined with poor internal drainage creates a low to moderate salinity hazard.

The native vegetation, almost entirely cleared, appears to have been mainly a grassy open forest II dominated by E. tereticornis, with closed rushland in wetter back swamps.
A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Valencia- image
An almost flat plain with a poorly drained depression of a relict back-swamp

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.): June - August
    Rainfall < potential evapotranspiration: November – March
GEOLOGY
Age, lithology

    Lower
    Pleistocene alluvium; gravels, sands, minor silts and clays
PHYSIOGRAPHY
Landscape
Elevation range (m)
Relative relief (m)
Drainage pattern
Drainage density (km/km2)

    Almost flat alluvial plains of the second-highest terrace level

    0 - 80
    0 - 10
    Dendritic
    0.8
PRESENT LAND USE
    Cleared: grazing of beef and dairy cattle on improved pastures; cropping (limited); apiculture; irrigation of some pastures and crops

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Valencia- geoA study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Valencia- graph

LAND COMPONENT
Percentage of land system
Diagnostic features
1
85
Broad almost flat plains
2
5
Sloping terrace margins
3
5
Drainage depressions of minor streams
4
5
Relict back-swamps, poorly drained
and possibly now functioning as
drainage areas
PHYSIOGRAPHY
Slope %, typical and (range)
Slope shape
1 - 2, (0 - 5)
Straight
Variable, (0 - 10)
Convex
<2
Concave
<1
Straight
SOIL
Parent material
Mostly clay and silt but also some sand and gravel
Description
Very dark and sometimes mottled
sandy loam to clay loam topsoil
changing abruptly to yellowish
brown clay subsoil with many grey
and brown mottles
Limited observations — probably
similar to component I but top-
soil free of mottles and subsoil
brown or reddish brown with
few or no mottles
Limited observations — probably
dark greyish brown loamy sand
typical; possibly some
black heavy soils
No observations — probably black
heavy soil, mottled at depth;
yellowish brown mottled duplex
soils have been observed in
similar situations in other land
systems
Classification
Solodic Soils
Dy3.42, Dy3.43, Dy3.33, Dy3.23
Db2.23, Dy3.32, Dy2.33
Red Podzolic Soils
Dr2.21
Alluvial Soils
Ucl.21, Ucl.23
Wiesenboden, Humic Gleys
-
Surface texture
Sandy loam to clay loam
Sandy loam to clay loam
Variable
Silty clay loam or heavier textures
Surface consistence
Friable to firm when moist
Friable to firm when moist
Soft to hard when dry
Firm when moist
Depth (m)
>2.0
>2.0
>2.0
>2.0
Nutrient status
Low to moderate
Low to moderate
Low to moderate
Moderate
Available soil water capacity
Low to moderate
Low to moderate
Low to moderate
Moderate
Perviousness to water
Slow
Slow
Slow to rapid
Very slow
Drainage
Poor to somewhat poor
Moderately good to good
Somewhat poor to good
Very poor to poor
Exposed stone (%)
0
0
0
0
Sampled profile number
59, 66
-
-
-
NATIVE VEGETATION
Structure of vegetation and
characteristic species of
dominant stratum
(+ Predominant species)
Grassy open forest II:
E. tereticornis
Closed rushland of Juncus spp. in wetter areas
Clearing has made it difficult to determine if any other predominant or associated tree species

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:

a) increased deep
percolation




b) raised watertable



Nutrient loss





Salting



Not determined





2,3; moderate



Not determined





Uncommon: isolated occurrences



Removal of trees





Reduced plant water-use in the catchment



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

Raised watertable

Increased exposure of surface soilIncreased overland flow and soil detachmentSheet and rill erosion2; low - moderate
3; low
UncommonClearing, cultivation, overgrazing, road and dam building and other earth-moving activities, rabbit burrowing, trafficking by stock and vehicles.Increased sedimentation and ponding in low-lying areas
Increased physical pressure on soilIncreased compaction

With

Reduced infiltration
Structure decline



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


2; low - moderate
3; low
Uncommon



Uncommon
Increased trafficking, overgrazing, export of organic matter

As for sheet and rill erosion above
-



Increased flash flows
Increased soil disruptionIncreased soil break-upGully erosion2,3; lowUncommonAs for sheet and rill
erosion above
Increased sediment load.
Comments: Disturbances on adjoining land systems cause localised sheet, rill and gully erosion problems in the Valencia land system
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