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5.1.3 Linear dunes sub-dominant (Lowan salt valley, Antwerp)

Around Peppers Plains (west of Jeparit) and also buffering the western side of the Wimmera River, a regular series of northnorth- west to south-south-east trending ridges upon which east-west dunes are superimposed represents margin (transition) between what was known as the Northern Wimmera and Southern Mallee. These ridges are separated by distances of 800 m to in excess of 1500 m (Rowan & Downes 1963) and represent stranded beach ridges from the marine regression during the later Pliocene. The later forming dunes are weakly developed and occupy little of the landscape with relief across these landforms typically less than 10 m. Woven between ridges are gentle to level slopes that support gilgaied cracking clays. Gilgaied clay soils (Vertosols) predominate on the inter-ridge plains and on lower ridge slopes. Medium-textured Calcarosols tend to occupy middle and upper ridge slopes where the native vegetation is mainly mallee. The heavier soils of the lower positions have stands of big mallee. Reddish yellow sands predominate on these superimposed east-west dunes, with compact subsoils.

Native vegetation dominated by mallee except on dune crests where mallee savannah occurs (Rowan & Downes 1963). Vegetation includes woodlands, mallee and shrubland. Some of the more prevalent vegetation communities include Low Rises Woodland, Lowan Sand Mallee, Sandstone Ridge Shrubland, Ridged Plains Mallee, Parilla Mallee, Red Swale Mallee, Woorinen Mallee, Ridged Plains Mallee, Plains Woodland, Lignum Swampy Woodland, Shallow Sands Woodland and Plains Savannah. Overall, remnant vegetation is small mallee with porcupine grass understorey. Pine and belah woodlands occur widely on high ridges where grasslands are also common. In these areas the soils are mostly red brown medium-textured calcarosols.

The land is mostly devoted to agriculture. The overall erosion hazards of the landscapes are reduced by the lower proportion of dunes and by the widespread clay soils. However, the salinity hazard is severe in the southern Mallee where the rainfall is higher. Water seeps from the dunes perched on clay layers of low permeability, raising the watertable beneath the swales where soluble salt contents are high (Rowan 1971). Evaporation produces saline surfaces. Reclamation involves reducing seepage withdeep-rooted species on the dunes. Yields are also reduced by the inherent salinity of the clay soils, particularly on gilgai puffs. In addition, sodicity at the surface of puffs impairs tilth.

Soil-landform unit	Unit description	Area (km2)
Dimboola rises	Gently undulating rises	166
Hopetoun rises and swales	Undulating rises	329
Horsham lake and lunettes	Lake and lunette	3
Horsham lake-lunette cluster	Lake-lunette cluster	2
Kiata rises	Gently undulating rises	64
Lowan Salt Valley	Valley plain	349
Murra Warra West gentle rises	Gentle rises	9
Nhill lake and lunettes	Lake-lunette	13
Perenna undulating sand plains and rises	Gently undulating sand plains	85
Quantong dunes and swales	Dune and swale	4
Vectis undulating rises and low hills	Undulating rises and low hills	119
Werrap lake-lunettes	Lake-lunette complex	4

Figure 12 Sequence of lakes and lunettes (gypseous) north-east of Gerang Gerung on the western side of the Wimmera River