Redgum 1 (R1)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- geo

Area: 857 sq. km (4.2%)

Redgum 1 is the most extensive land system in the drier parts of the Eastern lowlands. It occurs on the gently sloping to undulating plains of the earlier Pleistocene terrace and of the more distal parts of the Tertiary flood plain deposits.

Dissection is firmly established and integrated drainage has developed, with broad shallow erosional basins holding the main streams. Most of the original land surface has now been removed. Near the southern bank of the Mitchell River flood plain, sink holes have developed where Miocene limestones occur close to the surface. Where sandy rises of Barrier or Perry land systems block the natural drainage, there are poorly drained depressions. Geology and climate are similar to those in Westbury 1 land system but Redgum 1 has lower relief.

The very gentle slopes and the well-developed duplex soils are major factors in the general stability of the area. However, the clayey subsoils are commonly sodic and any sheet erosion near the dissected edges of the plain and near the incised drainage ways could be followed by gully erosion.

The upper horizons are sometimes thick and sandy due to wind-blown accretions. The soils are similar to those in Redgum 2 land system but appear to lack gilgai micro-relief. Seasonal waterlogging occurs on the flatter slopes. The native vegetation, probably mainly an E. tereticornis grassy open forest II, has mostly been cleared.

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- image

Dissection of the early Pleistocene terraces has often resulted in steep slopes along the drainage channels with gently sloping and undulating terrain adjacent. This dissection distinguishes Redgum 1 from Redgum 2 land system.

CLIMATE Rainfall, mean (mm) Temperature, mean (°C) Seasonal growth limitations	Annual 500 - 800; lowest July or August (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 terrace and some more distal parts of Tertiary floodplain deposits; gravels, sands, silts and clays; unexposed marine limestone
PHYSIOGRAPHY Landscape Elevation range (m) Relative relief (m) Drainage pattern Drainage density (km/km²)	Gently sloping to gently undulating plains with shallow but definite dissection 20 - 160 0 - 20 Dendritic 0.3
PRESENT LAND USE	Mostly cleared: grazing of cattle and sheep; some cropping Minor proportion uncleared: bush grazing of cattle; timber (minor products and some firewood)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- cs

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Redgum1- graph

LAND COMPONENT Percentage of land system Diagnostic features	1 64 Slopes	2 20 Almost flat areas	3 10 Drainage depressions	4 5 Slightly depressed, poorly drained areas on the flats	5 1 Sink-holes
PHYSIOGRAPHY Slope %, typical and (range) Slope shape	3, (1 - 10) Straight	1, (0 - 2) Straight	1, (0 - 5) Concave	<1, (0 - 2) Concave	Variable, (0 - 10) Concave
SOIL
Parent material	Unconsolidated clay, silt, sand and gravel (often stratified, in places cemented or dense)				Colluvium from components 1 - 3 and/or marine limestone
Description	Very dark grey to very dark greyish brown loamy sand to sandy loam topsoil, grading into greyish brown in places deep, similarly textured subsurface soil; abrupt change to strongly mottled yellowish brown, blocky clay subsoil. Commonly very gravelly		No observations — probably undifferentiated medium textured gravelly soils	Similar to component 1 and 2, but mottling often extending into topsoil; clay subsoil may have columnar structure	Limited observations — greyish brown ^to slightly reddish brown clay loam to light clay, mottled to near the surface
Classification	Mostly Solodized Solonetz and Solodic Soils, some Soloths and Yellow Podzolic Soils Dy3.22, Dy5.22, Dy5.21, Dy3.31, Dy3.33, Dy3.23, Db2.31		-	Soloths, Yellow Podzolic Soils Dy3.41, Db2.41	Brown Earths Um6.21, Uf6.13
Surface texture	Loamy sand to sandy loam		-	Sandy loam	Clay loam
Surface consistence	Soft to slightly hard when dry		-	Friable to very firm when moist	Very firm when moist
Depth (m)	>2.0		>2.0	>2.0	>2.0
Nutrient status	Low to moderately low		-	Low	Moderately low
Available soil water capacity	Low		-	Moderately low	Moderately low
Perviousness to water	Slow		-	Slow	Slow
Drainage	Mostly somewhat poor		-	Very poor to poor	Somewhat poor
Exposed stone (%)	0		-	0	0
Sampled profile number	68	-	-	-	-
NATIVE VEGETATION Structure of vegetation and characteristic species of dominant stratum (+ Predominant species)	Grassy open forest II: Mainly E. tereticornis+ E. bridgesiana, E. polyanthemos associated On better drained slopes E. bosistoana or E. globoidea occasionally predominant			Mainly open forest I, II, often shrubby: E. tereticornis+ sometimes with E. ovata and occasionally E. cephalocarpa. Understorey often with Melaleuca ericifolia Closed scrub of M ericifolia in poor drained areas	As for components 1, 2 and 3

Disturbance	Affected process and trend	Primary resultant deterioration			Casual activities	Primary off-site process
Disturbance	Affected process and trend	Form	Susceptibility of components	Incidence with components	Casual 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 winter/spring water table	Nutrient loss Waterlogging	Not determined 2; low 3,4,5; moderate	Not determined Not determined	Removal of trees Reduced plant-water use in catchment	Increased movement of water to groundwater; increased base-flow of streams Increased run-on and ponding of water in low-lying areas
Increased exposure of surface soil	Increased overland flow and soil detachment	Sheet and rill erosion	1,3,4; low 2,5; very low	Uncommon: isolated occurrence on cleared land	Clearing, overgrazing, road building and other earth-moving activities, rabbit burrowing, trafficking by stock and vehicles.	Increased flash flows and sediment load.
Increased physical pressure on soil	Increased compaction With Reduced infiltration	Structure decline Sheet and rill erosion	1,2,3; low 4,5; moderate 1,3,4; low 2,5; very low	Uncommon Uncommon: isolated occurrence on cleared land	Increased trafficking and cultivation, overgrazing, export of organic matter As for sheet and rill erosion above	- Increased flash flows
Increased soil disruption	Increased soil break-up	Gully erosion	3; moderate 1; low - moderate 2,4,5; very low	Uncommon: but can be severe in incised drainage channels	As for sheet and rill erosion above	Increased sediment load
Comments: -

Page top