5.1.5 Hummocky dunes sub-dominant (Hopetoun, Peppers Plains)

Across the north-west corner of the WCMA region (running from Yellangip to Wilkur South) are plains on which there are scattered low hummocks. Known from previous reports as the Culgoa landsystem (Rowan & Downes 1963), the scattered low hummocky dunes tend to occur in cluster ranging up to some 3 km across. Unlike unit 5.1.3, subdued ridges with superimposed recent dunes are absent from surface expression within this landscape. As a result, relative relief across these landforms is much lower than neighbouring landforms of landscapes to the north.

The eastern boundary is irregular but clearly defined from riverine plains of the Richardson and Avoca rivers. In the south-west this unit abuts the Lowan Salt Valley which is readily defined through its entrenched nature as evident in Digital Elevation Models (DEM). To the south the boundary is regarded as a transition and notes the heralded change from the Wimmera to the Mallee. Further refinement using suitable imagery and detailed field work are needed to locate the boundary accurately.

The plains on which the dunes occur are generally subdued. Slopes are gently to very gently inclined with gentle rises, undulating plains and level plains being the dominant landscape features. Drainage systems are few and far between with lake and lunette clusters found north-west of Donald.

Hummocks are more evident where superimposed on rises further north where underlying stranded beach ridges give a more pronounced affect to the landscape. The Yarriambiack and Dunnmunckle creeks run northwards through these calcareous dunefields where they have dissected the clay plains leaving the well defined stream channels that are less apparent further north. Woorineen Formation aeolain sands and silts are the primary source for these hummocks.