Valencia (Va)

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

Area: 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 <10°C (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- 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
Disturbance	Affected process and trend	Form	Susceptibility of components	Incidence within components	Causal activities	Primary off-site process
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 soil	Increased overland flow and soil detachment	Sheet and rill erosion	2; low - moderate 3; low	Uncommon	Clearing, 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 soil	Increased 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 disruption	Increased soil break-up	Gully erosion	2,3; low	Uncommon	As 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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