Salinity conference

Brief review of the draft review report
Dr Brian Spies

Brian Spies is a Chief Research Scientist in CSIRO Exploration and Mining, recently completing a 3-year secondment to ANSTO as Director of Physics. He holds a BSc from the University of NSW and a PhD from Macquarie, and has held research and management positions in the petroleum and minerals industries in Australia and the USA. His contributions to exploration geophysics include the early development of electromagnetic prospecting methods while employed with the Bureau of Mineral Resources. He was Director of the CRC for Australian Mineral Exploration Technologies, which developed and commercialised the TEMPEST airborne electromagnetic mapping system. Brian is an active promoter of the science and profession of geophysics and holds numerous editorial and honorary positions. He was elected a fellow of the Australian Academy of Technological Sciences and Engineering in 1998, is a recipient of the Centenary Medal, and is currently first Vice-President of the Society of Exploration Geophysicists.

What I would like to do is give a very brief overview about the structure of the report. I know you have all read the report, so I don't need to dwell on this too much.

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It became clear, I think, as we started looking at these mapping techniques, that originally the thought was that there are dozens and dozens of techniques for mapping salinity. It turns out, when you look at them in detail, that they don't map salinity, they map something else, and there is a step of interpretation or inference to get from the measurement into the salinity detection. So we have grouped these techniques into direct techniques or methods and indirect methods. There were really only two direct methods, and a whole range of indirect methods, which in the report we have laid in terms of the depth that they look to: surface, root zone, regolith and a range of depths. So that is how we have described the different techniques in the report.

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We have put pictures in here of some of the techniques and results. There are techniques that operate from the air and can measure to different depths.

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There is a map here, just as an example – I am sure a lot of you have seen this. If you had an aerial photograph or a Landsat image of this area, Lake Toolibin, in Western Australia, you would see the surface, you would see the lake here in the middle, but then you start to look at some of the imaging techniques. We have got magnetics on the left, and there we are able to see beneath the surface. These lineaments are faults and dykes and so forth in the subsurface which control the groundwater flow. So we can start to use these techniques and work out where the water is moving, where the salt is being mobilised to.

This image on the right is airborne electromagnetics, and the red shows high conductivity, which was related to high salinity. We can see here where the salinity is being moved down in this direction. Where these barriers and these faults are, there is actually a concentration of salt and it comes through this.

So this really helps in the understanding of where the groundwater is moving, where salinity is and the risk, and the management techniques for that.

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In the User Friendly Guide we have placed a summary of techniques in this form. These are just two of the techniques, based at different scales: Field and Laboratory, then Surface-Based, Airborne and Satellite. We have got 'Mapping method' on the left, 'Application to Hazard Mapping' – understanding salt as a hazard – then 'Contribution to Risk Assessment', an idea of the cost, and some comments on the right. This is a very broad, high-level summary. It is meant to be easy to read by the landowner or the non-expert.

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This is an idea of some of the other techniques that they can use: digital elevation models, on the left, to get an idea of where the surface flow might be, and on the right is radiometrics, to measure various types of decays.

 

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We have got 19 different types of mapping methods in the report. I won't go through all these in detail, but it ranges from laboratory measurements, field measurements, going down into shallow-probing electromagnetics, into deeper-probing, other ground systems, borehole techniques, techniques based from the air – air photo, airborne radar, multi-spectral imagery – going up into satellite techniques as well.

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That is a satellite image on the top, for a perspective view. You can see the land use and the topography, and there are various parameters you can get out of satellite imagery as well, to do with the vegetation, to do with the soils.

Right underneath that is the airborne electromagnetic image at one particular frequency, which is the sum of the conductivity down to a certain depth under the ground. You can see there the red areas of conductivity, which then you can compare and look at both of these maps.

So there are 19 different classes that Peter spoke about. In some of those classes there are at least eight or nine different instruments out there. We did have a think about whether to include the names of instruments or not. There was a bit of a debate about that. I think the argument swayed towards including those that we knew about, because in a lot of the peer reviewed literature, and even in the titles of references, there are instruments named that are in some ways in common use, like M31/M38, and if you are going to name one instrument then you need to name the other vendors and other instruments as well. So what we would like to do is put the different instruments and vendors in there, to make that as up to date as possible now – if there are any that are missing, please let us know – and we need to also have a think about how this can be updated periodically, or whether some agency is going to help with that aspect.

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The key conclusions of the study: Peter talked about the risk and the hazard definition. These I guess are the high-level conclusions we could think of. There is no one mapping technique that you can use by itself. There is no one mapping technique that can map salinity. You have got to use a combination of approaches. You have really got to understand the landscape and hydrological processes in three dimensions, not just measure what is at the surface – you have got to understand what is happening in the subsurface, and using a range of these techniques together you can paint a picture of what is happening under the ground and how salinity may be mobilised and moved.

Ground truth and calibration from surface, borehole and underground measurements are very important for all techniques. You really need to do a calibration for each technique. The interpretation of that data depends on the type of soil, the types of rocks, the type of hydrology where you are, so that ground truthing is a very important part. Also, effective use of these techniques requires trained personnel with specialised knowledge. I think there is a real need in Australia for a lot more training and education. These aren't techniques that you can get a map and say, 'Therefore this map means such-and-such.' In the interpretation of that data I suppose I would like to draw an analogy with going to the doctor's and getting an X-ray or an MRI scan. We can look at those images and say, 'Oh yes, that's the brain, and there's this and there's that.' But it takes a trained physician, a trained surgeon, with a huge range of experience in the physiology of the body, to understand what those images mean. It is very much the same with these mapping techniques. We are making an image of the ground. It takes a lot of understanding of the way the processes work in the ground, in order to interpret that.

The next steps, as Peter said before, will be finalising the Technical Report and the User Friendly Guide, based on the input from today and the people here. The documents are out there. We have asked for comments by next Wednesday – I know that is very short, but there is a very tight timeframe. If you think you need a bit longer, talk to Peter and me and we will work out if it is possible. There are going to be proceedings of the public forum today that the two Academies will be publishing, as well.

I would like to acknowledge the steering committee, in particular Sharon, Richard and Mirko, and the 30 organisations and individuals who have made those two and a half thousand pages of submissions. A lot of work went into that. We know it was a very short timeframe and appreciate that very much.

I acknowledge also Land and Water Australia, Richard Price and Melanie King; our advisers to the project, Simon Veitch and Annette Bleys; and Jane Inall, down at the CRC for Spatial Information, for all her work in the background, making sure things got where they needed to very quickly.

Thank you.