GEOMORPHOLOGY REPORT - CRC LEME

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7 IMPLICATIONS 7.1 Hydrogeological issues 7.1.1 Flow The geomorphological interpretation of the data suggests that shallow groundwater flow may be strongly compartmentalised along the Murray River between different aged floodplain units, and possibly between different sedimentary units within each of the three mapped floodplain units. At depth, where similar sandy units of different ages may be juxtaposed, cross flow between meander belts of different ages is possible. It also appears that materials filling the incised valley of the River Murray are inset within intermediate Murray basin units (in this reach the Blanchetown Clay, which is covered by dunes and slope deposits). Similarly, the Coonambigdal Formation is inset within the Rufus Formation (as suggested by Gill (1973), and shown in cross sections by Rogers and Gatehouse 1990). Modern, intermediate and oldest floodplain units and deposits compartmentalise the Coonambigdal Formation, as suggested above. Different ages of the units mean that they have different properties, especially in the amount of clay at the surface, which in turn has important implications for recharge (see below). These differences occur across the axis of the floodplain, because of poor interconnections between morphosedimentary units, and possibly down axis, within morpho-sedimentary units. 7.1.2 Recharge As a result of the points discussed in the last section, we predict the following recharge characteristics: • All but the youngest floodplain sediments are sealed by dispersive clays; hence there will be little or no recharge on intermediate floodplain and terrace units. • Active channels have sand bottoms, but once flow stops and they become inactive, they become clay-lined (Figure 12), with the result that there is no recharge via abandoned channels. Cracking clays are of limited extent, and only in abandoned channel. There is limited bypassing of surface clays by water in initial heavy rainfall events through these cracks. • The presence of sand dunes on the terrace means there is localised high infiltration, which in turn results in local perching of water on underlying floodplain clays. For the source bordering dunes on the older floodplain meander belts there may be a direct connection between the dunes and the underlying scroll bars, bypassing the clay drapes. However, the spatial extent of the dunes is insignificant. Width of vegetation zones also helps in the assessment of recharge: • Zones of healthy vegetation (red in ASTER images – Appendix 1) are widest on modern floodplain units where the scroll bars consist of exposed sand, suggesting extensive flushing of saline water from runoff, infiltration, and through flowing river waters. • These zones are much narrower in abandoned or inset channels (e.g. Wallpolla Creek), indicating less flushing, possibly due to isolation of water in channels from surrounding floodplain by the clay seal at the bottom. 21
Figure 12. SPOT image of Wallpolla Creek (containing water at time imaged) and clay-lined nature of dried up channel of Wallpolla Creek as seen at ground level. Width of image is ~10 km, north to top. 7.1.3 Relevance to land management questions The results of the study to date can be compared back against the six land management questions raised by Lawrie (2006). We make the following conclusions with respect to each. Question 1: What is the potential for salt mobilisation during Living Murray inundation actions? To answer this question will require integration of the surface data (LIDAR DEM, soil pits, and satellite imagery) with the results of the AEM survey and bore hole data. Integrated products relating to salt mobilisation potential are found in the GIS and Atlas, in particular the Flush Zone Thickness, Flush Zone Conductivities, Extent of Flush Zones, Groundwater Recharge, Conductive Groundwater, Conductive Soils, Surface Salinity, Salinity Hazard, and Salt Store maps. Question 2: Delivery of salt to the river To answer this question will likewise require integration of the surface data (LIDAR DEM, soil pits, and satellite imagery) with the results of the AEM survey and bore hole data to identify various potential pathways, in particular the channels along which surface and groundwater is most likely to flow. Integrated products relating to salt mobilisation potential are found in the GIS and Atlas again include the Flush Zone Thickness, Flush Zone Conductivities, Extent of Flush Zones, Groundwater Recharge, Conductive Groundwater, Conductive Soils, Surface Salinity, Salinity Hazard, and Salt Store maps. 22
Page 1 and 2: CRCLEME Cooperative Research Centre
Page 3 and 4: This report (CRC LEME Open File Rep
Page 5 and 6: Lindsay and Wallpolla Creeks are si
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: when sampling. This is also reflect
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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