Delta (Da)

	Area: 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.	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 <10°C (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 USE	Mostly 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- cs

A 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
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) 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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