Murray Mallee (Province 2)

This province extends from the coast in the south to the Murray River in the north and is bounded in the west by the escarpment of the Mt Lofty Ranges. Major landforms are the active dune system of the Coorong, Lakes Alexandrina and Albert into which the Murray River discharges, the Pleistocene consolidated dune complex inland of the coastal dunes, and beyond than an extensive rolling plain locally overlain by sand dunes. Notable areas of riverine landforms occur along the Murray River only in the north-east of the province.

The cool, relatively moist coastal climate in the south is characterized by a mean annual rainfall of about 500 mm. This gives way to a semi-arid steppe-like climate in the north, where mean annual rainfall declines to around 250 mm. Mean temperatures and seasonal and diurnal ranges increase with distance inland. Potential evaporation exceeds the median rainfall in every month of the year throughout the province.

The Murray Mallee has been largely cleared for pasture and cropland except for the large remnant of the Big Desert Scrub north-east of Keith, and the Billiat Conservation Park. Elsewhere only scattered remnants of the mallee remain.

Livestock grazing and cereal cultivation dominate the land use of the province but there are areas of irrigated horticulture and irrigated pasture cultivation along the Murray. Irrigation farming is practised in districts which receive about 250 mm of annual rainfall and have potential evaporation losses of approximately 2000 mm per annum; thus they require irrigation water form the Murray River in most months. The quality of the irrigation water is particularly important for horticultural purposes, and there is concern for the long-term quality of the Murray River water in the horticultural districts from Remark to Waikerie. Grapes, citrus and stone and pome fruits are the main products. Irrigation is mainly confined to the undulating plains and dunes above the riverine landforms. The plains consist of shallow red calcareous earths and the dunes of deep reddish sands. These soils are well drained but increasing salinity is an important problem.

The irrigated pasture lands of the lower Murray are located in areas with a slightly higher rainfall but which still suffer from very high potential evaporation. Here irrigation is confined largely to the floodplains which consist of poorly drained black clays with a high saline water table. Lucerne, which is more tolerant of dissolved salts in irrigation water than are fruit trees, is the major pasture species. Milk and fat lambs for the Adelaide metropolitan market are the major products.

Dryland cereal farming on the undulating plains includes wheat, barley and oats cultivated in rotation with improved pastures. Extensive grazing of native pastures occurs in areas not used for rotation farming towards the northern and north-western fringe of the province where rainfall is low and unreliable. There undulating plains have shallow, often stony red calcareous earths and deep sands on the dunes. The shallow stony earths have a low water-holding capacity which is a severe limitation for agriculture especially with decreasing rainfall to the north. Dune sands become unstable when cleared of vegetation and moderate wind erosion is common.

Four environmental regions are recognized within the province.

Murray Lakes (Environmental Region 2.1)

The Coorong dune system is one of the most active and scenic coastal landforms of Australia, extending as a massive dune ridge of white sand up to 50 m high over a length of 120 km. The extensive lagoon system on its landward side connects with Lakes Alexandrina and Albert which occupy a large depression. Barriers have been constructed at the lake outlets to prevent the inflow of sea water.

Northern Calcarenite Ridges and Plains (Environmental Region 2.2)

This region lies east of the Coorong. It consists of a series of older consolidated calcarenite dune ridges with intervening plains which represent the continuation of the stranded dune ridge complex of the South East Province. Unconsolidated dunes overlie large areas of these older dunes. North-east of there two regions is the extensive, undulating lower Murray plain, formed on limestone and other sedimentary rocks overlain by younger deposits, mainly sand and calcrete. The calcrete plain is frequently overlain by easterly trending sand dunes. The lower Murray plain is divided by a climatic boundary which is reflected in the distribution of the native vegetation and of certain soils types.

South-East Mallee Heathlands (Environmental Region 2.3)

This region is characterized by whitish to yellow dune sands with a natural cover of mallee with a broombush or heath understory.

Upper Murray Lands (Environmental Region 2.4)

This region is characterized by brown to red sands with a natural cover of mallee with a saltbush and bluebush or hummock grass understory.