GEOMORPHOLOGY REPORT - CRC LEME

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EXECUTIVE SUMMARY In early 2007, an airborne electromagnetic (AEM) survey was acquired along a 450 km reach of the River Murray Corridor (RMC) in SE Australia. This aim of this survey, carried out under the auspices of the Australian Government’s Community Stream Sampling and Salinity Mapping Project (CSSSMP), and managed by the Bureau of Rural Sciences (BRS), is to provide information vital for addressing salinity, land management and groundwater resource issues. The study area stretches from where the Murray River crosses the South Australian border eastwards and south along the Murray River to Torrumbarry Weir. A total of 24,000 line km of AEM data were acquired. The survey area encompasses iconic wetland areas, national and state forest parks, and areas of irrigation and dryland farming. Within the Lindsay-Wallpolla and Lake Victoria-Darling Anabranch project area key land management questions include: 1) What is the potential for salt mobilisation during Living Murray inundation actions? 2) How is salt delivered to the river? 3) How are the drivers of floodplain health with respect to groundwater processes to be understood? 4) How are the high recharge areas in the floodplain to be indentified? 5) What is the extent and thickness of the Blanchetown Clay and the Coonambidgal Formation? 6) Where is salt stored in the unsaturated zone? To address many of these questions, maps of the distribution of salt stores, saline and fresh groundwater and the hydraulic properties of soil and regolith materials in the shallow subsurface are required. These are required to provide a 3-D understanding of how salt stores and saline groundwaters connect to the surface waterways and land surface. Sub-surface interpretations in the survey areas are hampered by a low density of useful borehole data in the floodplain in particular, and by a paucity of soil and landscape surface mapping at appropriate scales throughout the project area. New maps of surface materials, and a new geomorphic understanding of the RMC project area is required to constrain the interpretation of the AEM surveys, and address the land management questions. This report documents the results of new surface materials mapping in the Lindsay-Wallpolla and Lake Victoria-Darling Anabranch survey area, the methodology used to produce the maps, and supporting analyses. These data inform interpretation of the surface layer of the AEM products and provide an understanding of the geomorphic evolution of the landscape. The Murray River in the Lindsay-Wallpolla Islands reach runs though a valley incised through a Late Cainozoic succession consisting of the Blanchetown and Loxton-Parilla Formations. These are mantled by Pleistocene aeolian sands of the Woorinen Formation. The modern floodplain consists of three distinct generations of meander belt sediments with scroll bars and oxbow billabongs. A conventional fine-grained floodplain is absent because of the meander belt sediments extend across the full width of the floodplain within the confines of the incised valley. However, older meander deposits are draped by floodplain silty clays with the thicknesses increasing to more than a metre on the oldest deposits. The oldest floodplain deposits also show distinctively longer meander wavelengths and wide channels than the modern channel, indicating a diminished flow over time. The soils vary markedly in salinity and pH, with a general trend of increasing pH and salinity with increasing age. An extensive terrace occurs along both sides of the incised valley of the Murray River. The terrace is mantled by aeolian silts and sands and have local outlying dunes of the Woorinen Formation. Ghosts of channels and billabongs are visible in satellite imagery suggesting an environment similar to from that which formed the modern floodplain. The soils are potassic, alkaline, and moderately saline. iii
Lindsay and Wallpolla Creeks are sinuous fixed-channel anastomosing channels. While these channels may partly follow abandoned channels of the Murray River, they are incised into the floodplain and are inferred to be related to drainage during high water levels. These channels and the oxbow billabongs from abandoned meander loops of the Murray River are clay-lined, with water flow either non-existent or very slow. It is these channels that are flooded during the artificial watering process. Distal to the river are several clay pans with associated lunettes. The largest of these is Lake Victoria, followed by Lake Wallawalla. These abut the rise forming the edge of the incised valley or against the terrace. In their natural state, they are several metres lower than the rest of the floodplain, forming evaporation basins for water draining off the proximal floodplains along the fixed channels. Engineering works have resulted in Lake Victoria being used for permanent water storage and Lake Wallawalla for temporary storage. Both lakes are interpreted as modified meander loops of the Murray River. Ken Lawrie Project Leader iv
Page 1 and 2: CRCLEME Cooperative Research Centre
Page 3: This report (CRC LEME Open File Rep
Page 7 and 8: TABLE OF CONTENTS _Toc224538156 1 I
Page 9 and 10: List of Tables Table 1. Association
Page 11 and 12: The main objective of the studies r
Page 13 and 14: 4. Identification of the high recha
Page 15 and 16: The SRTM was used as to provide the
Page 17 and 18: Figure 6. Compartmentalisation of t
Page 19 and 20: Dune on terrace Alluvial terrace Yo
Page 21 and 22: Intermediate floodplain Modern floo
Page 23 and 24: Locations of sample sites are given
Page 25 and 26: 6.1 Granulometry 6.1.1 Methodology
Page 27 and 28: Table 2). Mean pH and EC profiles a
Page 29 and 30: when sampling. This is also reflect
Page 31 and 32: Figure 12. SPOT image of Wallpolla
Page 33 and 34: REFERENCES Bowler, J.M. and Harford
Page 35 and 36: APPENDIX 1. ASTER data and interpre
Page 37 and 38: APPENDIX 2. SPOT Data and interpret
Page 39 and 40: APPENDIX 3. DEM data and interpreta
Page 41 and 42: APPENDIX 4. Gamma-ray data 500000 (
Page 43 and 44: APPENDIX 6. Site Descriptions and D
Page 45 and 46: Site 3 South Settlement road, ~20 m
Page 47 and 48: Site 5 Western end of Keera Road, s
Page 49 and 50: Site 7 Eastern end of Old Mail Rd t
Page 51 and 52: Site 12 Further to west along Old M
Page 53 and 54: Site 14 Dedmens drive, across aband
Page 55 and 56:
Site 16 Same area as previous sampl
Page 57 and 58:
Site 18 Same location as 17, interm
Page 59 and 60:
Site 20 Adjacent to previous site C
Page 61 and 62:
Site 22 2 km east of Finnegans brid
Page 64 and 65:
APPENDIX 7: Analytical Results Appe
Page 66 and 67:
Appendix 7.2: Lindsay-Wallpolla Las
Page 68 and 69:
Appendix 7.3: Lindsay-Wallpolla XRF
Page 70 and 71:
16 200709 1929587 20-30 Fm1 7 0.611
Page 72 and 73:
Site Number Depth LEME ID Sample #
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