GEOMORPHOLOGY REPORT - CRC LEME

The main objective of the studies reported here is to provide information for constrained
inversion of AEM data as a first step in interpreting those data to provide answers to land use
questions posed by the Malee and Lower Murray-Darling Catchment Management
Authorities (CMAs) for the area. The studies also provide a materials framework within
which to assess the utility of the airborne electromagnetic (AEM) data to help answer the land
management questions.
2 PREVIOUS STUDIES
There has been a paucity of geomorphic studies undertaken on the Murray Floodplain
downstream Swan Hill. Those which have been undertaken relate largely to the geology and
its evolution in the region, and soils and pedogenesis (Brown and Stephenson 1991; Gill
1973; Macumber 1977; Hills 1975). However, a number of studies have been undertaken in
the Riverine Plain of Victoria and NSW, and extrapolated to the Murray floodplain region due
to similarities in their evolutionary histories (Bowler and Harford 1966; Butler et al. 1973;
Pels 1966). More recently, studies have focused on the ecological or vegetation health (Jolly
et al. 1993; Thoms et al. 1999) of the native vegetation. There have been few highly
integrated studies in which geology, geophysics, soils, and geomorphology have been used to
address questions of land management, with perhaps the study by Rowan and Downes (1963)
being a notable exception. This is particularly important given that the floodplain of the
Murray River in this region acts as an interface between the river and the regional
groundwater systems, with the potential to mobilise large stores of salt under altered
hydrological regimes.
The soils of the Murray Basin are closely related to the Quaternary geology. Grey and brown
soils of the Riverine Plain and solonised brown soils of the Mallee region predominate. The
grey and brown soils overlie mainly the fluvial Shepparton and Coonambidgal Formations,
while the solonised brown soils overlie a variety of aeolian units including the Woorinen
Formation (Brown and Stephenson 1991).
Previous geomorphological studies in the region have identified a number of terraces
(Kotsonis et al. 1999) in the Murray Floodplain. Thoms et al. (1999) recognise that the
present day channels and rivers in this region are inset within intermediate channel systems,
and are therefore associated with relict floodplain surfaces that contain numerous palaeochannels
and oxbow lakes. Gill (1973) named the oldest terrace the Rufus Formation.
While the Riverine Plain consists of thick lacustrine and fluvatile sediments deposited mainly
in the late Tertiary and Quaternary, the Mallee is a semi-arid region with extensive aeolian
deposits overlying Either the Pleistocene lacustrine Blanchetown Clay or intermediate
Cainozoic marine sands of the Loxton-Parilla Formation. The aeolian deposits occur in the
form of two types of dunes in the Mallee. The first is a regular series of linear dunes with an
east-west trend stabilised by vegetation except for the very local active sand patches. The
dunes generally have calcareous B horizons, with buried palaeosols. The material of which
the east-west dunes are composed of a pale to dark reddish-brown calcareous sand with some
clay fraction of the Woorinen Formation (Hills 1975). The second type of dune is a complex
set of parabolic and transverse dunes which are found outside of the study area.
On the New South Wales side of the river Lake Victoria is a giant oxbow system lying on an
anabranch formed by Frenchman’s Creek and the Rufus River, and has acted as sand trap to
form a large lunette on its eastern bank which has been emplaced and remodelled over 20 000
years (Gill 1973) of deflation. The river banks and sides of Lake Victoria are subjected to
erosion with extensive blowouts and sandfalls, while the lunette associated with the lake is
unusually wide with horizontal bedding (Gill 1973). Several salt pans exist in the vicinity of
Lake Victoria, which may be relicts of a former single large lake indicated by a shallow
gypsiferous layer above the Blanchetown Formation, with groundwater occurring within a
2