Soil/Landform Unit 202

Tidal swamps lie just inland from the coastal dunes and provide valuable habitats for wildlife

Area:

593 ha

0.04% of CMA region

Many of the outlets of creeks and rivers to the east of the Otway Range possess tidal swamps with braided channels and brackish lagoons. Thompson Creek and Painkalac Creek have such river mouths, although the most extensive swamp lies just outside the present study area, surrounding the mouth of the Barwon River. Only minor differences in height above mean tide level determine the differences between the land components. The marine terraces escape inundation in all but extremely rare combinations of floods and high tide, while most other tracts of land are flooded either regularly or irregularly. Halophytic shrubs and herbs colonise the grey and structureless silty clays found on these swamps. The structure and species of each community are strongly influenced by the height above mean tide level and the degree of salinity of the tidal water. Some parts of these areas have been drained or filled to provide for agriculture or recreational facilities. However, most parts remain in their natural state.

Swamp east of Torquay

Component	1	2	3	4	5
Proportion of soil-landform unit	30%	30%	10%	15%	15%
CLIMATE Rainfall (mm)	Annual: 625, lowest January (30), highest August (60)
Temperature (^oC)	Annual: 14, lowest July (10), highest February (18)
Seasonal growth limitations	Temperature: less than l 0^oC (av.) July Precipitation: less than potential evapotranspiration October–early April
GEOLOGY Age and lithology	Recent estuarine sand, silt, clay and plant remains				Veneer of aeolian sand
Geomorphology	6.2.5 Alluvium, alluvial terraces, floodplains and coastal plains of the Sedimentary Western Plains
LANDUSE	Cleared areas: Some of the higher areas cleared for grazing, cropping and recreational Uncleared areas: Nature conservation; refuse disposal facilities
TOPOGRAPHY Landscape	Flat estuarine lowlands with braided channels
Elevation range (m)	0–4
Local relief (m)	1
Drainage pattern	Deranged
Drainage density (km/km²)	4.6
Landform	Marine terraces	Swamps
Landform element	-	Upper surface occasionally inundated	Lower surface regularly inundated	Free water surface	Area adjacent to sand dune
Slope and range (%)	1 (0–2)	0 (0–1)	0		1 (0–2)
Slope shape	Convex	Linear	Linear		Irregular
NATIVE VEGETATION Structure	(Not known)	Low shrubland	Closed grassland	-	Sedgeland
Dominant species	-	Arthrocnemum arbusculum, Gahnia filum	Frankenia pauciflora, Samolus repens, Arthrocnemum arbusculum	-	Scirpus nodosus
SOIL Parent material	Estuarine clay, silt and sand	Estuarine clay, silt and plant remains	Estuarine clay, silt and plant remains	Estuarine clay, silt and plant remains	Aeolian sand, shell grit over estuarine clay, silt and plant remains
Description (Corangamite Soil Group)	Brown, grey or yellow sodic texture contrast soils (32)	Saline soils (12)	Saline soils (12)	Saline soils (12)	Grey sand soils, weakly structured clay underlay (12)
Soil type sites	OTR734	CLRA34, CLRA44	CLRA34, CLRA44	CLRA34, CLRA44	OTR737
Surface texture	Sandy loam	Silty clay loam	Silty clay	Silty clay	Sandy loam
Permeability	Moderate	Very low	Very low	Very low	Low
Depth (m)	>2	>2	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Sodic subsoils with high saline groundwater tables are prone to soil salting, surface compaction and sheet erosion.	Occasional influx of estuarine saline water on clays of low mechanical strength leads to soil salting and compaction.	Regular influx of estuarine saline water on clays of low mechanical strength leads to soil salting and compaction.	Minor hazards.	Sodic subsoils with low permeability and high saline groundwater tables are prone to surface compaction and soil salting.

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