Home

user guide - CRC for Spatial Information

1. Soil samples can be taken at the surface as well as in the root zone or greater depths through augering or trenching Field procedures involve the use of saturated paste extracts of soil samples and soil solution extracts from which analytic procedures e g cation analysis and anion analysis can be performed Similar techniques can be used for groundwater and water extracted from soil Complete analyses of multiple chemical species can be obtained from analytical testing at commercial laboratories 2 Total soluble salts measuring EC of soil pastes and extracts in the field Total salt concentration can be estimated using a range of in situ or remote sensors including Il aqueous extracts of soil samples I samples of water obtained from the soil or in boreholes and I through the use of buried porous salinity sensors that imbibe soil water and measure its electrical conductivity Other techniques include remote measurements of the electrical conductivity of bulk soil using four electrode galvanic sensors or more commonly electromagnetic EM induction conductivity meters see pp 33 APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 1 LABORATORY ANALYSIS The most rigorous method Basic knowledge of the Standard water set of Laborious days or weeks needed of quantitatively amount and type of salt basic anions and cations to obtain results Salinity often evaluating soil salinity is an important param
2. Variations in the salinity profile with depth increasing uniform or decreasing can be determined by comparing vertical with horizontal orientations of ground EM conductivity tools from borehole EM logs or from inversion of broadband wide frequency or time range EM data The term inversion is used to describe the general process usually computer based of deriving a geologically plausible model of the subsurface that is consistent with observed data EC measurements in dryland soils are best made during the time of the year when soils are sufficiently moist to conduct electricity It is inappropriate to try to infer salinity from measurements of EC made on dry or nearly dry soil and also to include salinity analyses of such soils in the data used to establish EC versus EC calibrations The salinity of soil water the water that is accessible to plants may be much lower than that estimated from EC This is because salts will often be present in the saturation extract that would not be in solution under actual field conditions Additionally salts contained within the fine pores of aggregates will contribute to the EC value although it is doubtful that significant amounts of such salts are absorbed by plant roots or affect the availability of most of the water extracted by the plant which is primarily that present in the larger pores Shallow electromagnetic conductivity profiling with EM31 ENN gt 2 Bl ss eii S A
3. to process it Has the ability to map the terrain surface digital elevation models at fine resolution over large areas very accurately 29 SURFACE MAPPING 0 10 cm DEPTH 9 12 Airborne and satellite imaging spectrometry Imaging spectroscopy measures reflected sunlight in the visible to short wave infrared 0 4 to 2 5 microns in wavelength and emitted blackbody radiation in the thermal infrared 8 to 12 microns in wavelength regions of the electromagnetic spectrum to create images of the surface of the Earth Such measurements can be made from aircraft or satellites and can cover large areas at high resolution By measuring this complex spectra of signals it is possible to map vegetation types and infer effects of stress particularly patches of vegetation that are adversely affected by the presence of dryland salinity in the root zone Also under ideal conditions it is also possible to infer mineralogy of iron oxides sulphate hydroxyl and carbonate mineral assemblages and by association surface salinity However ground control and local knowledge are important for interpretation of spectrometry data and images that are affected by drought bushfire damage green flush such as spring rains and occur on black soils leads to mapping confusion can be misleading or confusing Satellite and airborne systems can now resolve areas of just a few metres square in size on the surface of the Earth They can cover tens of thousa
4. 4 i a T i q 5 y A lt Y t NE sunshaded 10m L 4 APPLICATION TO HAZARD CONTRIBUTION TO RISK MAPPING SURFACE MAPPING 0 10 cm DEPTH 7 amp 8 Airborne and satellite radar Radar techniques measure the complex reflectance of the Earth from electromagnetic radiation in the microwave 5 7 to 68 cm or 5 3 to 430 MHz range by transmitting an active pulse from an aircraft or satellite platform Radar signals are affected by moisture content and surface electrical conductivity and to a lesser extent the chemical composition of the soil Airborne and satellite radar has been used in research trials for salinity mapping Most radar systems give very little penetration of the surface and generally do not see into the root zone They require relatively moist ground conditions across the area to be mapped and the radar signal can be confused by the overstorey vegetation Airborne and satellite based radar systems can also produce digital elevation models of high quality over large areas The NASA Shuttle based mapping systems known as the Shuttle Radar Topography Mission used the Space Shuttle Endeavour to acquire radar data over 80 of the Earth s surface in February 2000 The conversion of these data into a DEM are now virtually complete and the data will be released by NASA The on ground resolution of the data are 30 m by 30 m pixels and the vertical accuracy is about 16 m COST COMMENTS ASSESSMENT 7 AIRBORNE R
5. a new and significant observing salt scalds or contribution as imagery 42 km x 30 km for improvement in technology indirectly mapping stressed can also map vegetation approximately 3000 cf multispectral sensors Requires vegetation Experimental type streams terrain and Cost 5 to 50 ha substantial research before it only at this stage Offers land use including processing develops proven applications potentially greater mapping Likely to have broader applications accuracy than the than the multispectral instruments multispectral instruments Price set by vendors will in part Applicable to the surface determine the degree of uptake by and indirect root zones users False colour 2 5 m resolution SPOT5 image near Boorowa NSW November 2003 CNES 2003 mo gt O A e e E Hi YE Image courtesy Spot and Raytheon 32 SURFACE MAPPING 0 10 cm DEPTH 13 Airborne and ground gamma ray spectrometry radiometrics Gamma ray spectrometry commonly known as radiometrics is based on measurement of naturally occurring gamma rays emanating from potassium uranium and thorium bearing materials at the Earth s surface Gamma ray spectrometry is widely used for soil mapping and can be measured either from aircraft or more rarely from vehicles on the ground Since surface salinity is often correlated with soil type and landscape characteristics radiometrics is sometimes used as a tool for ver
6. all stages of survey design acquisition processing interpretation and ground calibration to maximise the utility of AEM XIII XIV 20 Many mapping methods are used in combination and some are acquired Dl simultaneously The skill base in each technique is highly specialised and there are few users who are expert at more than two or three methods Some vendors claims that their techniques directly detect salinity are unsubstantiated e g some radiometric and remote sensing proponents claiming direct detection of salinity It is good practice for potential users to seek independent advice on claims made by vendors Photo Pauline English CSIRO 2005 Reproduced with permission 1 INTRODUCTION Salinity mapping methods in the Australian context the user guide and book provides up to date information about ways to map dryland salinity and strategies for making investment decisions for salinity management The user guide provides a broad overview that is directed towards a general readership The companion book contains an expanded description of techniques for salinity mapping prediction and monitoring as well as strategies for risk management The book also contains references to published literature case studies and extensive appendices with details of specific mapping techniques How can the user guide help The user guide will let you know more about how to map the current extent of dryland salinity haz
7. at the next level of detail each time targeted to answer specific questions This staged approach draws on the best elements of each available mapping technique and permits the best use of existing information It will help target or prioritise the areas that require new mapping information RECOMMENDATIONS u To map the extent of areas affected by dryland salinity the most straightforward methods are API air photo interpretation and satellite imagery combined with visual inspection and electrical conductivity EC mapping using a ground induction conductivity meter u To map the presence of salt at depth gt 2 m we recommend AEM constrained by borehole logging and point EC sampling u To investigate hydrological factors affecting the transportation of salt by groundwater aeromagnetics and AEM are the key techniques 23 24 5 MAPPING METHODS Techniques listed in the following pages are mainly used for hazard mapping although some useful data may be acquired at the same time for input into salinity risk assessment Many of the techniques may only have marginal use for mapping the salt itself but they may be essential for generating landscape hydrological pathway and soil maps from which salinity risk and management information can be derived Types of mapping are categorised by their depths of investigation into the subsurface Salt content salt load and salt hazard The terms salt content salt load a
8. common indirect method and that most closely related to salinity is electromagnetic conductivity see box p 16 for further detail Electrical conductivity EC depends on the type of solute clay content and moisture levels EC meters operate at a variety of scales from portable conductivity meters to deeper probing surface based and airborne methods Other indirect techniques are in effect extensions of visual inspection where large areas are investigated from aircraft or satellites These methods based on measurement of electromagnetic or other radiation at various wavelengths and include photographs multispectral and hyperspectral scanning and measurement of gamma radiation 13 14 A SYSTEMATIC APPROACH TO RISK MANAGEMENT Mapping projects should always be designed to achieve the intended outcomes in the most cost effective manner We need to u decide the types of risk to be considered e g arising from increasing salinity u identify the assets to be protected e g farms forests water supplies biodiversity residential areas and whether they are diffuse targets e g forests or single points e g specific buildings u identify the decision makers and those people who may be affected either inside or outside the area covered by the investigation e g farmers local residents regional authorities u decide the time frame of interest e g now or in 10 20 or 50 years and Il remember that assets at risk from d
9. lt pe q 7 i fit t Me A r a s ef x 2 dl O A a r oI Photo Kate Wilkinson 18 4 MAPPING SALINITY An intimate relationship exists between the landscape its geological and climatic history weathered and transported soil types groundwater and the hazard posed by the salt load in the soil Combinations of mapping techniques can be used to provide enhanced information on the operation of natural systems and to derive the geological and hydrological properties of the landscape including soils salt content and subsurface flow pathways The term salinity mapping in its broadest sense encompasses a range of procedures that can be used to delineate the surface expression of salinity give insight into how the salinity processes take place inferring water flow and resolve patterns of salt store Integrated landscape mapping involves detailed regolith studies and palaeogeographic reconstruction to delineate the subsurface geology regolith architecture and salt distribution This multidisciplinary geological systems approach can be used to generate a three dimensional picture of the subsurface and associated saline groundwater salt stores and flow systems that deliver salts to the discharge site see box Detailed studies of the regolith using airborne geophysics and borehole investigations demonstrate that the subsurface has much greater variability than can be inferred from surface
10. measurements At catchment and subcatchment scale the effects of variability in the regolith are likely to be particularly significant in influencing salt store and local groundwater flow MULTIDISCIPLINARY APPROACH TO MAPPING Airborne geophysical techniques can be used to map regolith units to give insight into the geological and hydrological processes For example aeromagnetics and airborne electromagnetics AEM can be used to map regolith units without considering conductivity or salt store Although a magnetic map is predominantly an image of magnetic mineral concentrations in the subsurface aeromagnetics is rarely commissioned to determine the quantities of magnetic minerals present Instead spatial patterns in magnetic minerals in the subsurface are used to delineate boundaries of geological units see Figure 2a The patterns from such imagery reveal the watercourses on the surface and buried palaeochannels where these coincide with appreciable amounts of magnetic mineral accumulation Similarly AEM is often used to map regolith units through analysis of spatial patterns see Figure 2b This image of the same area shows buried channels A a distinct sub basin B upland areas with thin regolith cover C and an east west break in pattern D without the need to consider the possibility of salt stores Figure 2 a Greyscale magnetic image first vertical derivative of total magnetic intensity and b colour conductivi
11. primary naturally occurring salinity or secondary due to land use impacts by people Secondary salinity can be divided further into dryland and irrigation salinity These categories relate to its cause rather than its chemical or physical character and the same techniques are used to measure and map salinity irrespective of its origin natural dryland or irrigation The main difference between dryland and irrigation salinity is in the management options available to address the salinity risk CAUSES OF DRYLAND SALINITY Dryland salinity is caused by rising watertables and the concentration of salt in locations where it poses a problem for people or the environment The watertable rises when water enters the ground at a greater rate than it can drain away horizontally or vertically Salt is either concentrated at the surface by evaporation or discharged into adjacent land drainage systems or surface water bodies Another type of salinity known as dry saline land is not hydrologically connected to a saline watertable and often occurs in upland winter rainfall zones such as semi arid regions of New South Wales Western Australia and South Australia Dry saline land can occur as high levels of salinity at the surface or deeper in the root zone or subsoil 0 3 to 1 0 m with salinity trends increasing from the surface into the subsoil Dry saline land can exist as either primary or secondary salinity SALINITY IN THE MURRAY DARLING B
12. project was overseen by a steering committee selected by the Operations Committee of the National Dryland Salinity Program The Australian Academy of Science and the Australian Academy of Technological Sciences and Engineering were invited by the Australian Government on behalf of the Programs Committee to review the outcome reports In order to fulfil their review function the joint academies undertook a number of activities u They first convened a workshop at the Academy of Science office in Canberra in September 2003 where 24 leading scientists were invited to critically examine the first working draft of the review and to offer advice on its further revision The workshop was hosted by Dr Jim Peacock President of the Australian Academy of Science and opened by the Secretary of the Department of Environment and Heritage of the Australian Government Mr Roger Beale It had as its guest Lord May of Oxford President of the Royal Society The day was chaired by Professor Brian Kennett of the Research School of Earth Sciences at the Australian National University u The academies then facilitated the involvement of leading scientists in the examination of specific issues as they arose in the re drafting and we are grateful to the people who reviewed without prejudice relevant sections of the text of the draft reports as they were prepared u The academies then hosted a public forum at the Shine Dome Canberra on 17 October 2003 The public f
13. the ground and 1 square mm is equivalent to 0 001 ha This is a useful scale for representing paddock level information 1 50 000 1 mm on the map is equivalent to 50 m on the ground and 1 square mm is equivalent to 0 25 ha This is a useful scale for representing subcatchment level information 1 100 000 1 mm on the map is equivalent to 100 m on the ground and 1 square mm is equivalent to 1 ha This is a useful scale for representing subcatchment and catchment level information 1 250 000 1 mm on the map is equivalent to 250 m on the ground and 1 square mm is equivalent to 6 25 ha This is a useful scale for regional representations 1 500 000 1 mm on the map is equivalent to 500 m on the ground and 1 square mm is equivalent to 25 ha This is a useful scale for regional and State Territory representations 1 1 000 000 1 mm on the map is equivalent to 1 km on the ground and 1 square mm is equivalent to 100 ha This is a useful scale for State representations Forty one 1 1 000 OOO map sheets are required to cover Y Australia The larger the scale the closer one gets to the real life object Thus 1 10 000 is considered to be large scale in relation to 1 1 OOO OOO which is considered to be small scale Expressions of local regional and national scales are also commonly used INVESTMENT DECISIONS COSTS AND BENEFITS OF MAPPING AND MANAGING SALINITY The relative costs and benefits associated with obtaining new information is a ce
14. them together In which initiatives should Australian governments invest to generate the best outcomes in relation to sustainability and profitability Saline discharge in the Goondoola Basin south west OLD Photo Kate Wilkinson Overall At all scales the user needs to consider whether the existing information or knowledge base is adequate to address the hazard risk and management responses Additional questions a user might ask are u Am I sure of the cause of the salinity u Will additional knowledge increase my capacity to more effectively manage the risk u Is new mapping modelling or research and development required and how much does it add to what do I have access to now u Can I conduct this mapping myself or is other expertise needed u What are the relative costs and benefits u Who will bear the cost and who will gain the benefit These questions are more complex for statutory land managers since they need to I understand salinity hazard and risk at all scales I balance competing interest groups and E use available funds to generate maximum return for public investment The key stakeholder is identified as the one who has the capacity and responsibility to study and manage the problem MAPPING SCALE Scale is the ratio of the dimensions of objectives in real life as represented on maps They are mainly expressed as the following simple ratios 1 10 000 1 mm on the map is equivalent to 10 m on
15. A new technology still in the observing salt scalds or contribution as imagery new acquisitions at a research phase resolving ability indirectly mapping stressed can also map vegetation scale of 1 25 OOO higher than multispectral imagery vegetation May also infer type streams terrain and including analysis Even salt by known association land use small areas will cost with specific mineralogies 1000s due to the cost of Applicable to the top few acquiring the imagery and centimetres and indirect the software required to root zone process it one off cost 11 SATELLITE IMAGING MULTISPECTROMETRY e g LANDSAT SPOT IKONOS EARTHWATCH Suitable through directly Substantial potential Usually much less than Proven technique for near surface observing salt scalds or contribution as imagery one cent per hectare salinity hazard mapping in the indirectly mapping stressed can also map vegetation Minimum area purchases hands of skilled interpreters in vegetation May also infer type streams terrain and usually apply so costs some regions Well developed for salt by known association land use can typically run to 100s its contribution to risk assessment with specific mineralogies plus processing and e g Western Australia Land Applicable to the surface interpretation Monitor and indirect root zones 12 SATELLITE IMAGING HYPERSPECTROMETRY e g HYPERION Suitable through directly Substantial potential Minimum purchase of Represents
16. ADAR e g AIRSAR Suitable through indirectly mapping surface electrical conductivity for radar wavelengths greater than 6 cm Applicable from the surface to several metres Around 5 15 ha Even small areas may cost 1000s due to the cost of acquiring the imagery and the software required to process it one off cost Radar has the ability to map very accurately the terrain surface DEM at fine resolution over large areas Largely an experimental technique at present with potential application for salinity mapping Has potential to be used as a tool for creating DEM which could therefore contribute to risk assessments 8 SATELLITE RADAR e g SIR C amp D JERS 1 SRTM Possibly useful through indirectly mapping electrical conductivity of surface and subsurface where radar wavelengths exceed 6 cm Applicable to between 10s and 100s of centimetres only Satellite radar has no proven operational use for salinity hazard mapping at present although it does offer potential However it will make a solid contribution to the mapping of topography which helps understanding of risk assessment NASA will be releasing over the next couple of years the Shuttle Radar Topographic Mission mapping that will produce a worldwide DEM and topographic maps for the first time Not meaningful to quote cost per hectare Even small areas will cost 1000s due to the cost of acquiring the imagery and the software required
17. ASIN Dryland salinity in the Murray Darling Basin has arisen from changes in the water balance following removal of native vegetation and introduction of European agricultural practices most significantly the adoption of shallow rooted annual crops and pastures Native vegetation has a great capacity to optimise water use Its extensive root systems draw water from deep within soils during dry times serving to increase the soil water deficit and provide room for the next season s rainfall Figure 1 This reduces the tendency for waterlogging Figure 1 The salinisation process in a dryland catchment The native deep rooted vegetation keeps watertables low when the land is cleared the watertable rises and mobilises salt Drawing Salt Action NSW AN SS A HIR SO ASE wy WANS Saa ON AAN aiiai i khi q p SA sh N A RN Sa A AE 10 SALINITY HAZARD RISK AND IMPACT Do I have a salinity hazard Do I have salt in the landscape somewhere on or under the land that may pose a risk to assets and if so can the risk be managed Salt is a natural part of the Australian landscape It becomes a hazard when it has the potential to move to a location where it can threaten an asset Salt moves in the landscape when it is dissolved and transported by water A dryland salinity hazard is the combination of salt with the potential for movement by surface water and groundwater Mapping salinity hazard involves describing the extent
18. Brian Spies and Peter Woodgate SALINITY MAPPING METHODS IN THE AUSTRALIAN CONTEXT PREPARED FOR THE NATURAL RESOURCE MANAGEMENT MINISTERIAL COUNCIL X AN vs LA sath at l R ae Labs Oy ont mn AS A am EA PED d vie TN N AX By IN it Brian Spies Brian Spies 30 years experience in research and management has been in fields as diverse as mining petroleum nuclear and environmental sciences and in industry government and academia He has worked in mineral and geothermal exploration non destructive testing and monitoring deep petroleum reservoirs Brian has held senior positions at CSIRO and the Australian Nuclear Science and Technology Organisation and was director of the CRC for Australian Mineral Exploration Technologies Brian is an active promoter of the science and profession of geoscience and has held numerous editorial and honorary positions He was elected a fellow of the Australian Academy of Technological Sciences and Engineering in 1998 and is a recipient of the Australian Centenary Medal Brian is science manager at the Sydney Catchment Authority and is responsible for research and science outcomes relating to drinking water catchment and environmental management He was formerly with CSIRO Exploration and Mining where the current study was initiated He lives with his family in Sydney and is a keen kayaker Sydney Catchment Authority PO Box 323 Penrith NSW 2750 email brian spies s
19. Land and Water Australia and the National Dryland Salinity Program Commonwealth of Australia 2005 This document has been prepared for Programs Committee of Natural Resource Management Ministerial Council through Land and Water Australia and the National Dryland Salinity Program Published by the Department of the Environment and Heritage and Agriculture Fisheries and Forestry June 2005 ISBN 0 642 55096 4 This report is available on the internet at www nrm gov au For additional copies please call the Natural Resource Management freecall line 1800 552 008 This work is copyright Apart from any use as permitted under the Copyright Act 1968 no part may be reproduced by any process without prior written permission from the Commonwealth available from the Department of Communications Information Technology and the Arts Requests and inquiries concerning reproduction and rights should be addressed to the Commonwealth Copyright Administration Intellectual Property Branch Department of Communications Information Technology and the Arts GPO Box 2154 Canberra ACT 2601 or at www dcita gov au cca References made to individual systems do not represent endorsement of those systems and are used for illustrative purposes only While reasonable efforts have been made to ensure that the contents of this publication are factually correct the Australian Government does not accept responsibility for the accuracy or completeness of the
20. RIAL PHOTO INTERPRETATION Directly maps salt scalds Substantial contribution as Each air photo costs A well established technique Can Indirectly maps stressed can also map vegetation around 50 An be slow to cover large areas but vegetation Applicable to type streams experienced interpreter can very reliable for surface mapping both surface and indirect terrain land use map 3 to 6 photos per day Digital photography is emerging as root zones Cost is approximately a replacement for traditional film 1 ha assumes existing at cost per frame from 20 to 50 air photos and minimum purchase often applies interpretation at a scale of approximately 2000 around 1 25 OOO New digital photography costs 5 to 20 ha scale at 1 25 OOO scale including analysis 5 AIRBORNE VIDEO Applicable although still Potential contribution as Cost 10 to 50 ha Competes with the multispectral only experimental can also map vegetation assuming new acquisitions instruments for applications Applicable to the surface type streams terrain and at a scale of 1 25 000 and indirect root zones land use including analysis Aerial photo of saline land near Williams Creek NSW a Photo courtesy DIPNR NSW 27 28 SURFACE MAPPING 0 10 cm DEPTH 6 Digital elevation models DEM Digital elevation models DEM with accuracies of tens of centimetres can be derived from air photos by automated photogrammetric techniques Altern
21. RICAL DEPTH SOUNDING ELECTRICAL RESISTIVITY PROBING e g ABEM TERRAMETER GEOMETRICS OHMMAPPER Capable of resolving Useful for detailed vertical and horizontal variations in conductivity from surface to bedrock Applicable from the surface to the bedrock topography mapping of groundwater pathways and bedrock 1400 for several km profiling per day Resistivity imaging 1 to several line km per day 3000 to 5000 per processed line km Assuming line spacing of 200 to 400 m gives a cost of 60 to 250 ha Requires use of grounded electrodes and towed arrays Robust automated inversion software available to produce conductivity depth section Higher resolution than deep EM 35 36 MAPPING BELOW THE ROOT ZONE gt 2 m DEPTH 17 Borehole conductivity logging Borehole conductivity meters operate on the same principle as surface based conductivity meters Output units are in mS m Borehole conductivity logging provides excellent ground truth of the true conductivity of the ground versus depth and should always be used to calibrate airborne electromagnetic soundings and surface based electromagnetic and electrical depth soundings APPLICATION TO HAZARD CONTRIBUTION TO RISK COST MAPPING ASSESSMENT 17 BOREHOLE CONDUCTIVITY LOGGING e g GEONICS EM39 Ideal method for Useful for understanding Usually charged on daily measuring conductivity changes with depth basis most instruments versus depth
22. and salinity in relation to assets being considered A risk map has higher inherent value and is more likely to be acted upon if it is targeted at the particular asset for which management decisions need to be made Modelling techniques are normally used to forecast risk see p 43 Hazard maps and risk assessments can be prepared for immediate use by land managers Confidence in the assessment will be directly influenced by knowledge of the scale of the processes driving the hazard or risk and this knowledge will be determined largely by the scale quality and quantity of the data available People making these decisions need to understand the level of confidence that is associated with their decisions Electromagnetic conductivity profiling using a 4 wheel bike Seed a wry le 1 r 4 AMI mi a ae g yy r J f a a ri 4 x 1 N y Photo Courtesy Geoforce MEASURING SOIL SALINITY Ideally we need to know the concentrations of individual salts in the soil under the entire range of field water and land use conditions particularly when soil sodicity a measure of the sodium content that affects soil structure or toxicity of specific components are to be assessed This is direct measurement of soil salinity Very few mapping techniques measure salt directly Direct measurements include visual inspection analysis of total soluble salts and laboratory analysis of soil samples Salinity maps can be constructed based on c
23. ards or predict the risk of dryland salinity It examines the information needs of ul the farmer at paddock level Iu the community at subcatchment level I regional catchment planning authorities and u State Territory and national authorities The user guide explains the difference between salinity hazard and risk and briefly describes the origins of dryland salinity It provides detailed information about methods to map dryland salinity and the geological and hydrological processes that control its development The guide also covers investment decisions and the cost skill level applicability and limitations of each method The guide will help identify optimal approaches to obtaining information about salinity problems and help people make better decisions about management options It is useful for informed practitioners of mapping techniques as well as experienced land managers and or their advisors Both these groups should be involved in any decision to proceed with new mapping and in any subsequent decisions affecting land management Such involvement will help ensure a high standard of mapping and the acquisition of the most reliable information If you want to know more More detailed information on all the salinity mapping methods detailed in the user guide can be found in the book available both in paper form and on CD The book also contains a bibliography and case studies for further reading Further information
24. atively more accurate technologies for mapping topography such as airborne laser scanning ALS and the Airborne Laser Terrain Mapper ALTM are fast gaining acceptance APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 6 DIGITAL ELEVATION MODELS DEM FROM AIR PHOTOS STEREO MULTISPECTRAL IMAGERY AIRBORNE LASER RADAR Not relevant as DEM do Substantial contribution Costs vary substantially The landscape context to spatial not directly detect salt or Can infer drainage and depending on scale and salinity patterns is invaluable in groundwater Applicable seepage patterns level of detail being able to enhance the final to the surface only Large surveys lt 0 3 ha mapping quality and as a very important aid to follow up management DEM data is normally acquired simultaneously with airborne electromagnetics and with aeromagnetics Digital elevation model of part of the Toolibin Catchment WA The data have a accuracy of 10 m horizontally and 1 to 2 m in elevation The image has been enhanced using virtual illumination from a north easterly direction The relative relief displayed by this grey scale image is approximately 50 m with Lake Toolibin 300 ha visible as a circular feature in the south west corner Image courtesy Dr Richard George WA Dept Agriculture ot O lt E Sa O Se e oa Y gt va gt DU A ee ee y h ai z a Y 4 Lh O HE YE very Ca 3 C Mr A NY t f f
25. ause harm to an asset Salt is only a hazard if it has the potential to move into a location where it can threaten an asset through mobilisation by surface and groundwater A salinity hazard map defines the spatial location both vertically and horizontally and concentration of salt that can potentially be mobilised by water Water is the main agent that moves salt in the landscape Mapping has important roles in delineating the location and extent of salt in the ground as well as identifying the hydrological pathways through which it is transported In order to determine whether salinity has the potential to harm an asset the suite of mapping systems must include those capable of collecting information about the factors that govern the hydrogeology of the area Risk is the likelihood that a hazard will cause harm to an asset at some defined place and time in the future Risk is classically defined as an impact usually an unwanted impact multiplied by its likelihood of occurrence at some given time in the future Assets include agriculture water resources built infrastructure and environmental attributes such as biodiversity Salinity risk maps should identify the actual class of asset under threat the timing of the impact of that threat the level of anticipated impact should it occur and the geographic location of both the risk and the asset Preliminary analyses for hazard assessment should first use existing data sets to develop an ov
26. be preliminary in nature followed by analysis then a second targeted mapping survey concentrating on key areas Mapping should be undertaken in a systematic manner with techniques that operate at the appropriate scale Regional investigation using airborne surveys for example should be followed with ground survey in areas of particular interest or concern KEY FEATURES OF AIRBORNE AND SATELLITE TECHNIQUES Airborne electromagnetics is the only airborne technique that can map salt stored below the root zone lt can detect but not resolve salt stored within the root zone Airborne magnetics help us to understand and map the gross structures faults dykes and basement highs below the soil layer that contribute to the movement of groundwater Radiometrics gamma ray spectrometry is useful for mapping soil type Multiple airborne techniques can be combined in a single survey at considerable cost savings to flying surveys individually AEM surveys usually include aeromagnetics and an approximate DEM digital elevation model is a by product of most modern airborne surveys Emerging techniques such as airborne and satellite hyperspectral imaging and radar imaging are yet to be implemented operationally As costs decrease and improvements in image analysis occur airborne radar has increasing potential for operational use Hyperspectral imagery requires further research before its operational potential can be further evaluated Ground
27. by the flying height and speed thus aerial photos may be used for mapping at 1 5000 scale with centimetre resolution whereas airborne radiometrics and electromagnetics have footprints spatial resolution of tens of metres while I satellite products have pixel spatial resolution sizes ranging from 1 m to greater than 10 m Maps have traditionally been presented on paper Over the last decade the increasingly wide availability of computers and geographic information systems GIS has meant that high quality maps are easy to generate and distribute in electronic form Map provenance Maps should include all or most of the following information I Informative heading or title I Prominent statement indicating the status of the map typically draft published or restricted internal use u Technical description of the technique or techniques used to generate data for the map and assumptions underlying the presentation used Data source and processing history including processing parameters and software used u Statement indicating the original purpose of the map and warnings about appropriate use and limitations may include statements of accuracy 1 Acknowledgment of the owner of the data and the owner of the map 19 Ii Scale north point date of creation legend I Name and contact details of those responsible for the map 20 Choice of method The choice of mapping methods depends on scale ground conditions the probl
28. ca nsw gov au Peter Woodgate Peter Woodgate is the Chief Executive Officer of the Cooperative Research Centre for Spatial Information involving over 50 partners from industry government and university sectors Prior to taking up this role Peter was the Chief Executive Officer of the Geospatial Science Initiative at RMIT University where he helped create their first spin off company Spatial Vision Innovations Pty Ltd as well as the Risk amp Community Safety Research Centre and the Global Sustainability Institute Peter has worked for many years in the Victorian public service leading development of various business units in natural resource management and spatial information He has a long standing interest in forest management salinity research the greenhouse effect and use of remote sensing for monitoring natural resources Peter lives in Melbourne with his family and he and his wife Janet are keen supporters of their children s various sporting interests including cricket equestrian eventing basketball and netball Cooperative Research Centre for Spatial Information 723 Swanston St Melbourne VIC email pwoodgate crcsi com au Brian Spies and Peter Woodgate SALINITY MAPPING METHODS IN THE AUSTRALIAN CONTEXT Results of a review facilitated by the Academy of Science and the Academy of Technological Sciences and Engineering for the Programs Committee of the Natural Resource Management Ministerial Council through
29. clays The measured EC of soil may be greater or less than the conductivity of the pore water In soils with low salt content the effect of clays usually dominates and the conductivity of a clay rich soil can be an order of magnitude higher than the conductivity of the pore water Conversely in soils with high salt content the contribution to conductivity from the salt concentration generally outweighs that from its cation exchange capacity and is relatively independent of the clay content EM tools have been shown to be effective in mapping all salinity types including dry saline land where salinity is present above the watertable Other studies in Australia have shown that between 75 and 90 of EC values can be usually explained by total soluble salt content Conversion of soil electrical conductivity to salinity calibration The success of deriving salinity values from EC measurements depends on the establishment of empirical equations that relate depth profiles of soil electrical conductivity of a saturated paste extract EC_ or soil water extract EC to bulk electrical conductivity EC_ obtained from EM measurements Numerous studies in Australia have derived calibration equations that work reasonably well in particular areas under constant hydrological conditions However it should be noted that the volume of earth sampled by EC measurements on soil samples is much smaller than EC measurements from EM measurements
30. contents and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of or reliance on the contents of this publication Editor Robin Jean Graphic design Themeda Printing Elect Printing Cover photographs Pauline English CSIRO 2005 reproduced with permission David Allen Fugro Airborne Surveys DIPNR NSW FOREWORD Our ability to effectively manage dryland salinity depends upon our understanding of its causes location and behaviour in any landscape Accurate mapping of the saline landscape and the hydrogeological pathways that control the movement of water and dissolved salt is critical if we are to understand its causes and develop measures for remediation This user guide and its accompanying book describe the various methods that can be used in Australian environments to acquire and present information about dryland salinity The user guide contains a summary description of each method and is designed to help the potential user determine how their mapping needs can be best met The user guide and accompanying book arose from a review of mapping methods that was commissioned by the Programs Committee of the Natural Resource Management Ministerial Council on the recommendation of its Science and Information Working Group Following a public call for submissions 36 organisations and individuals took the opportunity to make a contribution providing over 3000 pages of material The
31. coordination storage and management in order to maximise their value Such coordination can ensure the appropriate application of standards as well as help to identify properly credentialed specialists CONCLUSIONS ON SPECIFIC MAPPING SYSTEMS 14 15 16 17 16 19 The 26 mapping methods covered in this review can be used in some way to map salinity hazard and or risk The optimal choice of methods depends on the scale of mapping the vertical and horizontal resolution required availability of finances pre existing knowledge and complementary data sets Two techniques laboratory measurements and measurements of soil paste extracts are useful as analytical point measurement techniques of salt content Eleven techniques visual inspection satellite e g Landsat and SPOT and airborne remote sensing air photos and digital elevation models DEM can be used for surface mapping in the O to 10 cm depth range Some of these methods give direct information about salt at the surface while others give indirect information on salinity in the root zone through interpretation of vegetation stress Others such as radiometrics are useful for soil mapping Visual inspection air photo and DEM interpretation multispectral satellite imagery and ground electromagnetics EM are well developed operationally Ground electromagnetic conductivity mapping and ground penetrating radar can be used to probe to several metres into the Eart
32. ctivity and thickness of an electrically thin conductive layer 33 ROOT ZONE MAPPING 10 cm 2 m DEPTH DC direct current electrical 4 electrode measurements Electrical conductivity or more correctly its reciprocal resistivity can be also measured with DC electrode devices that require galvanic electrical contact with the ground Although DC resistivity measurements are slower than those made with inductive conductivity devices they are capable of improved depth resolution if measurements are made at a variety of electrode spacings 14 SHALLOW ELECTROMAGNETIC CONDUCTIVITY MAPPING e g GEONICS EM31 EM38 Strong correlation with Useful in mapping Starts at approximately Some depth information from salinity A popular near surface variability 1500 per day Coverage varying coil orientation Moisture inexpensive method for and salt load is between 50 ha day variations and clay content are mapping spatial variations detailed grid to second order effects Should be in conductivity in the root 500 ha day gt 100 m calibrated at key locations zone at farm scale lines at roughly Applicable to the root zone 1 to 30 ha only Shallow conductivity measurements with EM38 Photo Kate Wilkinson 34 MAPPING BELOW THE ROOT ZONE gt 2 m DEPTH 15 amp 16 Surface based electromagnetic and electrical depth sounding A large number of instruments for measuring electrical conductivity at depths greater tha
33. depth and concentration of salt as well as hydrological features that may affect water movement in the landscape Mapping systems either directly detect salt in the landscape e g chemical analysis of soil at the surface or in boreholes or indirectly infer its presence through its effect on vegetation or by observing changes to electromagnetic conductivity signals Mapping techniques can also be used to give insights on pathways for groundwater movement Is the land area that I manage and the assets that I value at risk of being adversely affected by dryland salinity at some time in the future The question of risk implies more serious consequences than hazard Risk assessment is far more complicated than salt hazard mapping because it requires an understanding of the factors that govern the movement of salt to locations where assets may be damaged Risk implies a prediction about the severity of the damage and when it will occur Evaluation of risk involves estimating both the likelihood of salt affecting an asset within a certain time frame and the impact or degree of severity on the assets should the event occur Assets at risk are often located at great distances from the source of the land use that may have caused the salinity The combination of salt and water is critical Areas with low concentration of salt when combined with high flow and high evaporation rates can result in a higher hazard and risk than areas with higher salt load but
34. em at hand the available expertise and budget The optimal choice and combination of methods should be targeted at the specific problem to be addressed discussed with experienced practitioners and include detailed discussion of the optimum suite of methods ground control processing and interpretation Many methods can be used to collect information that is useful in assessing risk Air photos and multispectral imagery from aircraft or satellites for example can map a number of useful parameters at the surface that affect our ability to predict groundwater movement including vegetation type streams terrain and land use However images of landscapes affected by drought bushfire damage green flush brought on by spring rains on black soils can be misleading or confusing Ground verification of mapping is essential and may include visual inspection local soil sampling and borehole logging Ideally a multi stage and or multi phase approach starting with preliminary analysis using existing datasets for hazard and risk assessment as a scene setting exercise should be used before undertaking detailed mapping Existing data gathered over large areas multiple catchment or at State Territory level can be examined to help prioritise key areas for more detailed investigations Thus a multi stage multi phase approach may involve more than one phase of mapping over the area of interest The first phase may involve one or more techniques and
35. er samples extracted from soil EC Il larger volumes of soil either from the ground or air EC Units A variety of units are used for measures of salinity and EC The international standard SI unit for conductivity is siemens per metre S m and EM instruments are commonly calibrated to read milli siemens per metre mS m EC units are commonly quoted in dS m decisiemens per metre or uS cm microsiemens per metre This guide uses mS m 100 mS m 1 dS m 1000 uS cm Other units include parts per thousand parts per million ppm milligrams per litre mg L osmotic potential OP and percentage total soluble salts in a 1 5 mix Various approximate factors exist for relating salinity measures but are based on assumptions on salt and soil type As a rough guide water with 15 OOO mg L TDS total dissolved solids have EC values of approximately 2300 mS m TDS in mg L 6 4 EC in mS m Factors affecting soil electrical conductivity The EC of soil is controlled by how an electrical current passes through the soil matrix and influenced by a number of factors Hl porosity the shape and volume of pores Hl permeability the interconnectedness of pores through which fluids can flow il moisture content the extent to which pores are filled with water il ionic species chemical composition of pore water Hl temperature and phase state liquid gas of the pore water and Il the amount and composition of colloids such as
36. erview of the landscape and to identify priority areas for detailed mapping Such an approach can also be used over large areas multiple catchments or State Territory level Salinity risk management should endeavour to prioritise areas information needs and mapping methods for appropriate levels of detailed investigation A sieving approach moving from general overview to specific detail based on progressive investigation and analysis can identify priority areas for appropriate types of mapping xi XII 10 11 LZ 13 An integrated geoscience or systems methodology employing three dimensional mapping of landscape salinity and groundwater elements will increasingly provide valuable insight into salinity processes and salt store distribution It builds upon the groundwater flow systems approach which to date has mainly been applied at regional scale and in most cases is limited to two dimensional models Both techniques can be applied at any scale where three dimensional information is available All mapping techniques should be ground truthed and calibrated through field inspection prior to the finalisation of the mapping program and in many cases before a mapping program is commenced Field measurements including soil sample measurements and borehole logging should be an integral part of any mapping campaign and take into account the three dimensional nature of the earth and statistical spatial variations with
37. eter 100 200 per sample varies substantially laterally and vertically so samples may not be representative of a larger area unless sampling density is high Salinity may also vary over time 2 TOTAL SOLUBLE SALTS MEASURING EC OF SOIL PASTES AND EXTRACTS IN THE FIELD A common and useful Useful as an adjunct to Around 10 per sample Needs to be calibrated for solute field procedure but other techniques for EC and pH type laboratory analyses Not all ignores soil moisture salt measured on paste extracts content and mobility affects vegetation or is readily of salt mobilised 25 26 SURFACE MAPPING 0 10 cm DEPTH 3 Visual inspection Visual inspection identifies salt scalds and salt pans where salinity impact reach the ground surface The presence of deeper salinity can sometimes be inferred from study of vegetation type and health Note that vegetation can also be stressed by waterlogging soil factors sodicity pH and land use over grazing Visual inspection is an essential component of the calibration and validation process of other broadacre mapping techniques and should also be included in any initial survey design APPLICATION TO HAZARD CONTRIBUTION TO RISK COST MAPPING ASSESSMENT 3 VISUAL INSPECTION Directly observes salt Provides spot checks for Subject to the cost of scalds and stressed some attributes required labour vegetation for risk assessment Applicable to both surface e g
38. ey use the quality of the understanding of the complex interactions of the factors of the landscape and the strength of the decision rules that are applied to drive the model Groundwater flow direction inferred from watertable levels courtesy Pauline English CSIRO a ES 5965000 Ios P N ig N i OON _ gt 5960000 N 5955000 se N ka i yw watertable i r rechargs pa N A A 5950000 A 5945000 5940000 Groundwater elevation 1 20 m AHD 5935000 Flow direction L i Caniambo Hills 10 km Euroa 5930000 355000 365000 375000 385000 395000 19 16 ELECTRICAL CONDUCTIVITY EC Electrical conductivity is an easily measured and practical index of the total concentration of ionised solutes in the sample and is the most common technique for inferring salinity in soils Many techniques for measuring the electrical conductivity of soils have been developed The most common techniques are EC extracts of paste water samples and the measurement of bulk electrical conductivity of soil EC_ with portable terrain conductivity meters Borehole and airborne sensors are also used depending on the level of detail scale required Measurements of electrical conductivity include those made on Il soil samples extracts of a saturated soil paste sample EC or solutions of that paste Il wat
39. g the survey including height corrections geometric corrections and primary field corrections conversion to a conductivity depth image CDI a mathematically complex procedure with many approaches each with its own assumptions advantages and disadvantages e g LEI which assumes a fixed number of distinct horizontal layers smooth model inversion where the conductivity is assumed to vary smoothly with depth conductance maps and interval conductivity that give the average conductivity over a depth range and approximate CDI sections interpretation with geological constraints involving converting conductivity depth data to more relevant parameters e g salt content as a function of depth and lateral position in addition to structural interpretation of depth to bedrock and identification of stratigraphic and structural features Interpretation requires sound knowledge of the local geomorphological and landscape properties constrained by ground and borehole observations AEM conductivity data draped on topography with depth slices Helicopter mounted AEM system for higher resolution surveys Image courtesy Fugro Airborne Surveys Photo Fugro Airborne Surveys MAPPING BELOW THE ROOT ZONE gt 2 m DEPTH Recommendations for users of AEM The following questions should be asked in the process of contracting an AEM survey and processing Have the target parameters lateral extent depth and conductivity
40. h to give information on salt load and or moisture content Of these electromagnetic conductivity mapping using instruments such as the EM38 is the most cost efficient technique and has wide utility at farm community and subcatchment scale Eight methods can be used to probe deeper than 2 m into the subsurface and map at high resolution These include deep EM such as EM31 and electrical probing methods borehole conductivity logging and stream sampling all of which give information on salt load Several methods ground magnetics seismic can be used to help delineate palaeochannels and barriers to subsurface flow Two methods nuclear magnetic resonance and seismo electric show promise for groundwater detection but are expensive and only used in research mode at present Airborne electromagnetics and airborne magnetic methods can be used for deep probing greater than 2 to 5 m on a subcatchment to regional scale Only one system airborne electromagnetics AEM offers a proven approach to broad area mapping of salt store below the root zone using a range of airborne platforms Although relatively expensive AEM has been used in dozens of studies over the past decade It has some limitations at shallow depths less than 5 m below surface that are now being addressed through applied research AEM also has limitations in areas where there are complex variations in vertical patterns of salt store and geology Careful attention should be paid to
41. icteric tee iio a 45 VII vili ABBREVIATIONS AEM ALS ALTM API CDI CRG LEME DC DEM dS EC EM GIS GPR HEM km LEI mg MHz mS us NDSP NMR OP ppm PRISM 5 SI TDS TEM airborne electromagnetics airborne laser scanning Airborne Laser Terrain Mapper air photo interpretation conductivity depth image Cooperative Research Centre for Landscape Environments and Mineral Exploration direct current digital elevation models decisiemens electrical conductivity electromagnetics geographic information system ground penetrating radar helicopter electromagnetics kilometre litre layered earth inversion metre milligrams megahertz millisiemens microsiemens National Dryland Salinity Program nuclear magnetic resonance osmotic potential parts per million Practical Guide of Salinity Models siemens international standard total dissolved solids transient electromagnetics see also electromagnetic definitions p 33 PREFACE Salt is a hazard when it has the potential to be moved to where it can threaten assets such as agriculture infrastructure water resources and biodiversity Salt stored in the ground may be mobilised by water and transported vertically and horizontally Australia s growing problem of dryland salinity cannot be reliably assessed without a thorough three dimensional understanding of the landscape and the hydrological processes that operate within it At least 26
42. ilities and interpretation products The main requirements of an AEM mapping system are broad bandwidth and accurate calibrated data over the entire range of frequencies or sample times A number of current research projects are directed at improving the near surface resolution of AEM Interpretation or mapping products include apparent conductivity maps at each frequency or sample time approximate conductivity depth image CDI sections or depth slices and layered earth inversion LEI and conductance maps Care should be taken with the application of rapid imaging routines for processing and visualising AEM data especially with inferred depth values Estimates of accuracy and errors should always be given Ground truthing through borehole induction logging or ground EM or electrical depth sounding should always be used to calibrate AEM data Inversion and processing of airborne electromagnetics Processing and interpretation of geophysical surveys especially airborne electromagnetics is complex because the signal originates from a range of depths The conversion of raw data to a final depth image involves a number of steps each having specific mathematical and physical assumptions la acquisition calibration of parameters such as transmitted waveform filter settings amplifier characteristics and the geometric relationship between source and receiver basic processing correcting for variations in acquisition parameters durin
43. iltered EM31 scaled i O 10000 20000 30000 40000 50000 Distance m 10 EM31 EM31 filtered EM31 scaled 10000 10500 11000 11500 12000 12500 13000 13500 14000 14500 15000 Distance m Conductivity mS m a Conductivity mS m eee EM31 filtered EM31 scaled 11500 11600 11700 11800 11900 12000 12100 12200 12300 12400 12500 Distance m A STAGED APPROACH TO MAPPING Before investing in a mapping project it is important to first ensure that maximum use is made of existing information ranging from local knowledge existing maps and the regional context A multi phase and or multi stage approach where mapping alternates with eround truth and interpretation ensures that best use is made of the existing and new information and that data are progressively transformed into useful information and then into knowledge of salinity and landscape processes One effective mapping design may be to use an initial sampling approach that determines the likely location of salt in the study e g field inspection stream sampling followed by techniques that map salinity on the surface air photos airborne imaging and or satellites plus deeper probing techniques e g AEM At each stage field observation ground truthing should be used as an essential tool for calibration and interpretation with borehole measurements as required The final stage is some form of post hazard mapping The cycle is then repeated
44. in situ for owned by consultants or salt store versus depth government agencies Applicable below the Approximately 2000 per root zone day for up to 10 bores per day Down hole electromagnetic conductivity logging using the EM39 pa ADA TIAS ELE 9 e 0 hi e Pe COMMENTS Boreholes should be logged as a matter of routine Important to map salinity profile and for calibration of surface and airborne systems Photo Pauline English CSIRO 2005 Reproduced with permission MAPPING BELOW THE ROOT ZONE gt 2 m DEPTH 18 Airborne electromagnetics e g Tempest Dighem Resolve Of all the airborne geophysical techniques aeromagnetics radiometrics and electromagnetics only electromagnetics EM has a signature closely related to salt stored below the subsurface Airborne EM systems can be used from fixed wing aircraft or helicopters AEM or HEM and are similar in many respects to the eround EM systems Fixed wing surveys AEM are generally preferred for larger areas and deeper depth penetration while HEM surveys offer finer spatial resolution Magnetic and digital terrain data are usually obtained at the same time as AEM The depth of investigation varies with ground conductivity at best it is around one skin depth or diffusion depth but it can be less depending on signal and noise levels The footprint or lateral averaging of HEM systems is smaller than that of fixed
45. in the subsurface As a general rule it is advisable to plan to undertake independent assessments of the veracity of all major mapping programs at the conclusion of mapping Such validations provide sound justification for the subsequent decision making phase by confirming the accuracy and uncertainty associated with the mapping products They are also a valuable learning tool Most mapping systems require a high level of expertise for their sound use Prior experience and a proven track record in understanding the acquisition processing and interpretation phases is highly desirable Users are advised to seek specialist advice before committing resources to mapping programs A balance needs to be struck between the need for data at fine resolution at paddock scale and the broader benefits that are possible when data are combined to produce a bigger picture at catchment State Territory and national levels Some of the systems reviewed e g radiometrics and electromagnetics can be used at both an overview and detailed scale The technologies that are suitable for mapping dryland salinity risk and hazard are evolving rapidly Australia is particularly fortunate to have an excellent science community that supports the development and deployment of new mapping methods as they continue to evolve Substantial investments have been made and will continue to be made in the collection of data for salinity management These data require systematic
46. is the ability of material to conduct electrical current Units are siemens per metre S m or more commonly millisiemens per metre mS m Resistivity is the reciprocal of conductivity Resistivity units in ohm m is commonly measured with direct current DC electrical probing devices Apparent conductivity EC_ is the conductivity of a uniform earth averaged to the depth of investigation that would give the same EM response as that measured Apparent resistivity p is the reciprocal of apparent conductivity Skin depth describes the attenuation of electromagnetic fields as they diffuse into a conductive earth It is defined the depth at which an electromagnetic field is attenuated to 37 of its value at the surface of the earth Skin depth is given by the expression 500 a f where A is the resistivity of the earth equal to 1 EC and f is the operating frequency Lower frequencies penetrate to greater depth Diffusion depth at time t is analogous to skin depth in the time domain replacing f in the expression by 7 t Later sample times penetrate to greater depths Low induction number EM instruments operate over a certain range of transmitter receiver coil separation and frequency parameters where the depth of investigation is controlled mainly by the separation between the transmitter and receiver coils rather than the operating frequency Also known as conductivity meters e g EM31 EM38 Conductance is the product of condu
47. ise the areas that require new mapping information and recognises that the most effective mapping design uses sequential field observation analysis of existing data hypothesis setting and testing with new mapping data APPLICATION TO HAZARD CONTRIBUTION TO RISK COST MAPPING ASSESSMENT 26 MULTI STAGE AND MULTI PHASE MAPPING Suitable Methods include Useful Risk data sources Variable depending on mapping of surface salt and systems could include size of area to be and the deeper subsurface GIS based hydro geology covered resolution of followed by post hazard and geoscience data mapping and mapping verification natural resource data combination of systems land use data groundwater used flow systems Flowtube and DEM A towed conductivity streamer on a canal COMMENTS A combination approach should always to be considered particularly after reviewing existing data Photo David Allen METHODS FOR PREDICTING SALINITY RISK Most methods for predicting the risk to an asset from an increasing salinity hazard are based on statistical techniques or hydrological models Examples of risk assessments using landscape modelling are provided in catchment case studies carried out for the National Land and Water Resources Audit These studies were set in the context where the most appropriate data for answering the questions of stakeholders were not readily available and the methods used were adapted for the best available da
48. location Applicable to depending on road access flow into streams Continuous indirect surface and and density of streams profile can also be made in streams subsurface and rivers with towed EC arrays The method is easily applied by land managers and community groups 21 NUCLEAR MAGNETIC RESONANCE NMR Detects water content in May be useful in 3000 per day for 5 to 8 Also known as magnetic resonance soil profile versus depth specialised studies when soundings at specific imaging One sounding per hour Applicable to the top 10s detailed knowledge of locations Cost per hectare alternative to drilling and flow to 100s of metres hydrology is required not meaningful testing stratigraphic layers 22 SEISMIC REFRACTION AND REFLECTION Maps subsurface May be useful in 2000 day for 1 3 km Common tool in engineering and stratigraphy Applicable specialised studies to profile Refraction geotechnical studies Not to the surface to map soil thickness 10 spreads day around recommended for general use for sub bedrock palaeochannels flow 100 m each 3000 per salinity studies paths barriers etc processed line km Cost per hectare not meaningful APPLICATION TO HAZARD MAPPING 23 SEISMO ELECTRIC Detects hydraulic conductivity moveable pore water in sediments Applicable to the top 10s of metres 24 GROUND MAGNETICS Used for geological mapping especially through soil cover Applicable from the surface through t
49. lower flow and evaporation rates Photo Pauline English CSIRO 2005 Reproduced with permission Many factors affect the rate location and destination of surface water and groundwater Climate is the long term cycle of droughts and rains evaporation and precipitation It moderates the water cycle through time Weather is the local affect of rain and sunshine and determines the water cycle over shorter periods Land use and land management tree clearing and replacement agricultural practices borehole water use and the installation of drains are the most powerful human activities affecting the water cycle and hence dryland salinity Terrain includes the steepness of the land location of streams and rivers and break of slope The combination of terrain and gravity drives water through the landscape Different soils have different permeability to water flow and different susceptibilities to the development of salinity Regolith is the unconsolidated material between the surface and bedrock It varies in its ability to allow water to permeate and move elsewhere and may contain preferential pathways for water movement Structural features in the bedrock can act as barriers or carriers to the passage of water Ancestral or prior river and stream systems are known as palaeochannels These buried ancient stream or river systems can preferentially promote the passage of groundwater Geological faults and dykes may a
50. ls water and salt and nutrient loads that define the environment and assist in the development of sustainable land management practices Saline land affects a wide range of stakeholders 45 46 UNITS A variety of units are used for measures of salinity and electrical conductivity The international standard Sl unit for conductivity is S m and common EM instruments are calibrated to read mS m EC units are commonly quoted in dS m or yuS cm For this report the unit mS m will be used 100 mS m 1 dS m 1000 uS cm Salinity is reported in a variety of units such as parts per thousand o parts per million ppm milligrams per litre mg L osmotic potential OP and percentage total soluble salts in a 1 5 mix TSS 1 5 Various approximate factors exist for relating salinity measures but are based on assumptions about salt and soil type As a rough guide water with 15 OOO mg L TDS total dissolved solids has EC values around 2300 mS m TDS in mg L 6 4 EC in mS m ema rp ahh OSS ea Pe a ARS
51. lso act either as underground channels that encourage the movement of water or act as barriers Plant roots take up water from the ground Different vegetation types of varying ages and densities use different amounts of water They also have differing abilities to tolerate salt in the soil The salt content of groundwater and its rate of movement varies with location depth and soil type HAZARD AND RISK Hazard refers to anything that can potentially cause harm to an asset Salt becomes a hazard when it has the potential to move into a position where it has the ability to threaten an asset Water is the main agent that moves salt in the landscape A dryland salinity hazard results from the combination of salt and the potential for movement by surface or groundwater Risk is the chance that a hazard will cause harm to an asset at some defined time in the future Risk is classically defined as an adverse impact multiplied by its likelihood of occurrence at some given time in the future In effect it is a way of weighting possible unwanted events by their likelihood So a highly unlikely but serious impact may be regarded as presenting the same risk as a likely but minor impact 11 12 In order to predict salinity risks the behaviour of each of these factors needs to be understood and described Their combined interpretation can then be used to prepare maps of salinity risk that show the extent severity and timing of the threat of dryl
52. magic bullet for salinity mapping or prediction Effective use of mapping methods requires expert knowledge or access to trained personnel This user guide describes and assesses methods for mapping dryland salinity and addresses their applicability for assessing salinity hazard and risk It is best read in conjunction with the accompanying book available also on CD which contains more detailed descriptions of ways to map predict and monitor salinity and risk management The book contains case studies that demonstrate applications of mapping techniques as well as appendices with details of specific mapping techniques and a comprehensive list of references Brian Spies FTSE Peter Woodgate IX Manager Science Chief Executive Officer Sydney Catchment Authority Cooperative Research Centre for lt brian spies sca nsw gov au gt Spatial Information lt pwoodgate crcsi com au gt SUMMARY MAPPING HAZARD AND RISK OF DRYLAND SALINITY L Dryland salinity is the salinisation of land and water resources caused by the clearing of native vegetation for agriculture particularly in dryland areas This land use change results in a rising of watertables and movement of salt to locations where it poses a problem for people or the environment Assets at risk from dryland salinity include agriculture water resources built infrastructure and the environment In the context of dryland salinity a salinity hazard is salt that can potentially c
53. mimics the lateral sampling of the AEM measurements over several hundred metres in dark blue The AEM and averaged EM31 measurements agree fairly well for all profile lengths At broader scales represented by the 5 and 50 km profiles the AEM predictions correlate moderately well with the trends in the raw EM31 measurements However over profile lengths that are little more than the horizontal resolution of the AEM system e g 1 km shown in the bottom panel the broad averaging involved in the AEM measurements is unable to capture the local variability detected using an EM31 instrument The AEM conductivity predictions and the raw EM31 apparent conductivity values would show very low correlation at this local scale Similar issues arise when comparing other types of measurements that sample different volumes for example soil samples extracts borehole measurements surface and airborne measurements Figure 3 Profiles of apparent conductivity measured using an EM31 instrument in vertical dipole mode light blue line filtered EM31 apparent conductivity dark blue line and conductivity predictions for O to 5 m depth from TEMPEST AEM data red line a 50 km profile b 5 km profile and c 1 km profile Profiles prepared by Richard Lane CRC LEME Geoscience Australia from data provided by the Queensland Department of Natural Resources and Mines CRC LEME and the Bureau of Rural Sciences 50 km profile Conductivity mS m EM31 f
54. n 2 m are available ranging from larger spacing terrain conductivity meters through transient electromagnetic TEM to DC resistivity 4 electrode or array devices Only a few of these have been used in Australia for groundwater and salinity investigations Many of these techniques are eminently suitable for mapping salinity and landscape variations within the regolith and can penetrate to depths of tens or hundreds of metres Mapping products include sections or maps of apparent resistivity at a particular sample time frequency or electrode spacing Automated computer inversion routines can be used to produce depth sections and profiles of conductivity or resistivity APPLICATION TO HAZARD CONTRIBUTION TO RISK MAPPING ASSESSMENT COST COMMENTS 15 SURFACE BASED ELECTROMAGNETIC AND ELECTRICAL DEPTH SOUNDING DEEPER PROBING EM e g GEONICS EM31 EM34 3 PROTEM SMARTEM TINYTEM Useful in mapping salt stores beneath root zone to the regolith scales Also to map Can be used at broader groundwater pathways and bedrock topography More expensive than shallow mapping 2000 per day for 30 to 40 soundings Profiling 20 to 30 line km per day processed data 300 per line km Assuming a line spacing of 200 to 400 m gives a cost of 6 to 15 ha Cannot resolve conductivity changes in root zone with exception of EM31 Use in conjunction with shallow probing EM 16 SURFACE BASED ELECTROMAGNETIC AND ELECT
55. nd salt hazard are often used interchangeably Strictly speaking salt content refers to the percentage by weight of salts contained in a sample of soil Salt load is normally used in the context of the total amount of salt in the soil profile that can be potentially mobilised by water Salt hazard refers to salt that can be moved to threaten an asset Costs Mapping costs usually comprise H cost of initial survey design I cost of data acquisition for ground and airborne surveys includes mobilisation demobilisation and sometimes a standby cost in the event of bad weather I costs of data preliminary processing ground truthing and field calibration final processing and interpretation and I cost of data verification to confirm the quality of the results The cost of mapping using various techniques included in the tables on the following pages relate to acquisition costs and in some cases preliminary processing Total survey costs including survey design calibration and ground truthing and interpretation can often double these indicated costs Mention of a specific vendor or instrument in the following tables does not represent endorsement Sampling groundwater for laboratory analysis Photo Pauline English CSIRO 2005 Reproduced with permission ANALYTICAL AND POINT MEASUREMENT 1 Laboratory analysis Soil sampling followed by chemical analysis in the laboratory determines solute type and concentrations
56. nds of square kilometres in a single pass and repeat that pass every day APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 9 AIRBORNE IMAGING MULTISPECTROMETRY e g CASI Suitable through directly Substantial potential 10 to 50 ha assuming Little used due to the substantial observing salt scalds or contribution as imagery new acquisitions at a cost of acquiring the imagery and indirectly mapping stressed can also map vegetation scale of 1 25 OOO processing it to produce maps Has vegetation Applicable to type streams terrain and including analysis Even potential the top few centimetres land use small areas will cost and the indirect root zone 1000s due to the cost of acquiring the imagery and the software required to process it one off cost False colour hyperspectral HyMap image of part of the Coleambally Irrigation Area NSW vegetated paddocks are red stubble is white bare soils are green Water and Cooperative Research Centre for Sustainable Rice Hyperspectral Task of the CSIRO Earth Observation Centre Source Courtesy Tim McVicar and Tom Van Niel CSIRO Land and Production The acquisition of the HyMap image was supported by the SURFACE MAPPING 0 10 cm DEPTH APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 10 AIRBORNE IMAGING HYPERSPECTROMETRY e g HYMAP AVIRIS Suitable through directly Substantial potential 10 to 50 ha assuming
57. ns costs and benefits of mapping and managing SS ANU so ators sta e Por UE A 8 lt A A eg Cue ee ney ae ee en ee eee ere 9 What is dryland salinity snancsreceotenstoaaertercacncaeeacratacsantsaanieetecstecant 9 Causes of dryland salinity ca dsasadedvccmeaventetsanewntuesesacesqenrnaieeonsnieeceaes 9 Salinity hazard risk and IMpact ccccccccnnnncccccnccnnannnnnnnanonananannannns 10 Measuring soil salinity ssssssresesrsrnsnrrnrnrrrrnrrnrrrrnrrrrrrrrrrnrrnrrrne 13 A systematic approach to risk management 0cccccccccnnnnnnnncnnnnnannano 14 The role of modelno escanea pira i 15 A MAPPING SALINITY caeeipeonatnebprenceseyyeccneus eteersreseceteurescqneees i 18 A staged approach to Mapping ccccccnnccccccccconananannnnnnonannnnnnnnnnnnas 23 Recommendations ssssssssssssssrssrreernnenurerunrennrnennsrnnernnernnerunene 23 De MAPPING METODOS octetos iodo 24 Analytical and point MeasureMenNt ccccccccccccnnnnnnnnnnnnnnnnannnnnnnnnnanas 25 Surface mapping O 10 cm depth ccccccseeeeeeeeeeeeeseueeeneeeees 26 Root zone mapping 10 cm 2 m depth c cece cece eeeeeeeeeeeeeees 33 Mapping below the root zone gt 2 m depth occcccccccnccccnccccnannanos 35 Other ground based subsurface mapping methods cccccoonnacccccooo 40 Multi stage and multi phase MappinQ ccccccccccccnnnnnnnnncnnonanannnnannos 42 Methods for predicting Salinity riSk cccceceeeeeeeeeseeeeeeeeeeeeeegennns 43 6 CONCLUDING REMARK S
58. nt decisions might be expressed in terms of an investment framework of where is it best to invest funds to maximise benefit e g into mapping modelling new research and development or into on ground interception works Other dryland salinity management scales such as the expanse of the Murray Darling Basin also exist State Territory and national levels State Territory and Australian governments have responsibilities and roles in managing dryland salinity Questions at these levels include How much salinity is present what is the distribution both in land and rivers and what are the trends e g mg L of salt hectares affected or depth to watertable What is the impact likely to be on various classes of assets and what are the priorities for management What are the management options e g where to locate interception schemes to achieve a target of a certain concentration measured in mg L at Morgan Which environmental asset is of greatest priority is at greatest risk and can be viably managed What will the impact be on other areas if funds are insufficient for management What resource sharing is required for investments outside the asset to manage the long term ecological function and use of the asset What are the overall effects of management options on whole communities through time What are the priorities for management of other forms of land degradation and the opportunities for synergies for actions to tackle
59. ntral consideration for land managers wanting to know about dryland salinity on their land A simple five step plan addresses this issue Five step plan for assessing the need for new information Steps 1 to 4 will produce a prioritised list of areas for which new mapping is likely to yield useful information the costs of doing so and the value of the assets to be mapped or affected by salinity Step 5 considers the likely cost of possible management actions following acquisition of new information and the likely benefit of undertaking these management actions Step 1 Determine the value of the assets potentially at risk A number of categories of assets are at risk from dryland salinity including agricultural productivity infrastructure e g roads townships water resources and biodiversity Maps showing the location and value of these assets can help target areas and concentrate the effort required to collect new information and undertake any land use actions Step 2 Assess the current level of knowledge about dryland salinity in the area of interest Areas where we currently have a poor level of knowledge of the natural environment may be more likely to benefit from new information Existing information should always be compiled and assessed to gain maximum understanding of landscape and hydrological processes before additional mapping is undertaken State Territory governments often have geoscience spatial information freely available
60. o bedrock 25 GRAVITY Maps variation in bulk density of soil and rock in the subsurface OTHER GROUND BASED SUBSURFACE MAPPING METHODS CONTRIBUTION TO RISK ASSESSMENT Potential for research tool such as when detailed knowledge of hydrology is required Can be used to map features in the landscape e g faults dykes and basement highs that influence groundwater movement Can be used to map features e g faults dykes and basement highs that influence groundwater movement COST COMMENTS Research mode costs 2000 to 3000 day Cost per hectare not meaningful Very much experimental and not recommended for routine use Ground variant of common airborne technique Can be carried or mounted on 4 wheel bike with EM31 Reasonably inexpensive up to 1500 day or 10 to 200 ha depending on line spacing Rental plus operator 100 200 day 15 to 20 km per day Moderately expensive at 20 m spacing microgravity 100 stations cost 2000 1000s ha For specialist use only 41 42 MULTI STAGE AND MULTI PHASE MAPPING 26 Multi stage and multi phase mapping A multi phase or multi stage approach where mapping alternates with ground truth and interpretation ensures that best use is made of the existing and new information This staged approach draws on the best elements of each available mapping technique and permits the best use of existing information It will help target or priorit
61. o to prevent us making it worse for our neighbours Depending on their location within the landscape some individuals in the community will find that their salinity problem will become worse while others find that the problem will lessen as a result of the remedial action taken by themselves and or their neighbours This can raise the shared issues of equity and cost Community participation in salinity mapping Photo Pauline English CSIRO 2005 Reproduced with permission Catchment management groups The operating area for regional level planning for dryland salinity is the catchment level where one or more catchment management groups have overall responsibility for developing an integrated management plan The Australian Government is working with State and Territory governments and catchment management groups to achieve effective action to manage salinity In such regions typical questions are u What is the overall level of the problem in the region u How do managers get that right mix of actions that tackle prevention recovery containment and adaptation Where are the best locations to put in salinity management options e g drainage revegetation works salt interception schemes that will deliver the salinity target e g mg L of salt being exported to the river or lowered watertable in the most cost effective fashion What information is needed to make sound investment decisions at this level Investme
62. of Technological Sciences and Engineering ACKNOWLEDGMENTS The authors would like to thank the 36 organisations and individuals who responded so willingly to the call for public submissions to the review and to the many individuals involved in the review The submissions and reviews comprised over 3000 pages of reports and papers in addition to the maps and CDs that are summarised in the appendices to the book An extensive list of acknowledgments and references is contained in the book The authors are grateful for the assistance of the Project Steering Committee of Dr Sharon Davis Chair Dr Richard George for his insight and extraordinary support in so many ways and Dr Mirko Stauffacher the Australian Academy of Science and the Australian Academy of Technological Sciences and Engineering the Operations Committee of the National Dryland Salinity Program and Mr Simon Veitch and Ms Annette Bleys VI CONTENTS FOREWORD trote lil ACKNOWLEDGMENTS acotstevecsusstancutennsdatassiantasonerimacsenttcenantadmestedn casei v ABBREVIATIONS scccstcavcaateaorsvortacteostuetarensiecarveottaatnteateetontedtesanesnteas viii PREFACE eere ae a cdas IX UNNAR siria alado tin iia xi Mapping hazard and risk of dryland salinity ccccceeeseeeeeueeeeees xi Conclusions on specific MAPPING SYSTEMS cceeeeeeeeeeeeeeeeeeneeees xiii a INTRODUCTION tdi cease eeraa a il eii 1 A NEEDS A PE ER E A 3 Classes Of USE oe Eaa 3 Investment decisio
63. ompilation of individual point measurements However the collection of direct information may be very costly and these measurements are usually restricted to laboratory studies of small samples from specific points locations at a specific time In practice and over large areas indirect mapping techniques are used to infer the likely presence of salt Indirect techniques include those that measure the declining health of salt affected vegetation and methods that respond to the electrical conductivity of salt loads beneath the surface They include I aerial photos measuring optical reflectance at visible wavelengths I satellite imaging that can see changes in the health of vegetation and I airborne and ground electromagnetics measuring electrical conductivity which is closely related to salt content Some of the same mapping techniques can also be applied to mapping groundwater variations in moisture content Radiometrics gamma ray spectrometry is widely used for identification of soil type Rapid indirect techniques based on electrical conductivity measurements are now the preferred method for inferring salinity in the root zone DIRECT VERSUS INDIRECT MEASUREMENT Direct methods of salinity measurements are based on laboratory analyses of soil samples with care taken to preserve water content and identify specific ion concentrations Indirect methods infer the level of salinity and several techniques are used The most
64. on salinity mapping and risk assessment can also be gained by contacting the National Dryland Salinity Program NDSP lt www ndsp gov au gt The NDSP published a summary of its ten years of knowledge in its Managing Dryland Salinity in Australia suite of publications in July 2004 Other information on dryland salinity is also available from the National Land and Water Resources Audit website lt www nlwra gov au gt Additional specialist expertise and knowledge of mapping systems can be obtained from government and industry sources in particular I Cooperative Research Centre for Landscape Environments and Mineral Exploration CRC LEME lt www crcleme org au gt I Geoscience Australia lt www ga gov au gt and I other relevant State Territory and Australian Government natural resource management agencies Photo Pauline English CSIRO 2005 Reproduced with permission Photo Pauline English CSIRO 2005 Reproduced with permission 2 USER NEEDS CLASSES OF USERS Many individuals and organisations have an interest in salinity and a need to understand the presence and extent of current salinity They may need to assess potential risks and management options arising from changes in salinity Users range from individual farmers to communities catchment groups and regional authorities Questions related to salinity depend to a large extent on the needs and budget of the user Answers to these questions help user
65. orum was chaired by Dr Phil McFadden Chief Scientist of Geoscience Australia Over 70 participants spent the day reviewing the modified draft reports in a series of sessions that were guided by presentations from leading scientists in their field The full transcript of the forum is available through the Academy of Science website at lt www science org au conferences salinity gt A panel of five scientists chosen by the joint academies undertook a final review of the reports The panel members were Professor Kurt Lambeck Chair Dr Andy Green Dr John Ive Professor John Lovering and Dr Ian Rae The panel was pleased with its positive interaction with the authors of the review reports The resulting user guide and book represent a thorough process of consultation public examination and scientific review that will contribute to our ability to better map dryland salinity and its associated risks and hazards The Academy of Science and the Academy of Technological Sciences and Engineering are pleased to have facilitated the review and contributed to its successful completion through our consultative processes We expect that the reports of the Review of Salinity Mapping Methods in the Australian Context will be an invaluable resource for a wide range of natural resource managers Dr Jim Peacock AG FAA FRS FISE President Australian Academy of Science On NN Dr John Zillman AO FTSE FAIP FAIM FEIA President Australian Academy
66. pping mapping especially map gross features factors that contribute to better through soil cover such as palaeochannels risk assessment well proven in Applicable from the surface faults dykes and most landscapes Requires through to bedrock basements highs in the specialist interpretation Cost landscape that strongly effective contribution to risk influence groundwater assessment and salinity movement management 39 40 OTHER GROUND BASED SUBSURFACE MAPPING METHODS 20 25 Other ground based subsurface mapping methods A range of other methods have application in specific circumstances Conductivity measurements on samples of water in streams and rivers can indicate locations of sources of salinity seeping into the watercourse from adjacent land Ground probing radar GPR nuclear magnetic resonance NMR seismic reflection and refraction seismo electric and ground magnetics all have specialist application see table and have use in research programs but are not widely employed APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 20 STREAM SAMPLING Provides an indication of Provides evidence of An EC meter 100 to This method is an indirect salt stores that have mobilisation of salt 2000 Thousands of indication of land salinity but entered the catchment hectares can be covered provides a useful trace back upstream of the sampling relatively quickly mechanism to salt store and lateral
67. range been defined Has the survey been designed to answer the question at hand using the most appropriate system and acquisition parameters Does the budget include the full cost of the survey including pre survey planning data acquisition preliminary processing ground truthing final processing and interpretation Has the client clearly specified what is expected of the contractor Are these spelt out in a tender specification sheet such as issued by Geoscience Australia for its mapping surveys Does the client have access to staff with sufficient expertise to ensure that the survey and processing specifications are met Are the mapping products clearly labelled with processing parameters error estimates and details of the calibration process if any 19 Airborne magnetics Airborne magnetics is an inexpensive technique normally acquired with other airborne data such as radiometrics or flown expressly for geological mapping It is useful in mapping geological structures such as faults dykes and basement highs below the soil layer that contribute to the movement of groundwater Aeromagnetics can also be used to map buried channels palaeochannels if the sediments contain magnetic minerals above background levels see Figure 2 p 18 APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 19 AIRBORNE MAGNETICS Used for geological Useful for its ability to Less than a 1 ha Excellent method for ma
68. ryland salinity are often located some distance from the human activity that causes dryland salinity and that non agricultural interests are also at risk A plan that identifies options and actions to intercept the water that moves the salt may also be required A risk management strategy also requires ongoing monitoring and review to determine any significant change from predictions and any notable failure or success of the risk reduction actions taken However the impact of remediation actions may not be visible for many years Dryland salinity in south western Victoria T a en ca ET PENN ieee mirar oi E Y Photo Baden Williams THE ROLE OF MODELLING Modelling techniques can be applied to predict salinity movement for example eroundwater flow system models build on a suite of fourteen factors including landform aquifer transmissivity temporal and spatial distribution of recharge and responsiveness to options in land management Other modelling systems produce a two dimensional picture of the rate of flow of groundwater down through the catchment through specific locations Modelling requires knowledge of the hydraulic gradients surface drainage features and permeability of the regolith and soil and other factors Combining modelling systems from different scales enables planners to better predict the likely location of dryland salinity These predictive models are only as good as the data that th
69. s to make better management decisions Farm scale Farmers have immediate personal and business related interests in salinity and while some may know about salinity indicators others may not Farmers usually focus on obtaining useful information at the paddock scale Key questions the farmer is likely to ask are u Are there any indicators of salinity on my land u If so how much more salinity am I likely to get and when u Are my land management activities contributing to the problem ul Is this salinity currently damaging any of my assets u If not are there risks to any of my assets in the future u What can I do to stop it Farmers often consider the cause of the salinity to be of secondary importance except in the context of how the salinity can be best managed and the desire to be a good community or catchment citizen by minimising impacts to others VZ LMA PPOs y 2 as 34 Qs y 36 j af 478 id Local community A local community may consist of between 10 and 20 neighbouring farms that may have similar soils and hydrological flow system located within a subcatchment Their questions are likely to be similar to those asked at the farm scale but with a greater community orientation How much salinity are we likely to get and when How serious is it now and how serious will it be in the future What can we do to stop it Is there anything we need our neighbours to do to stop it Is there anything we can d
70. satellite airborne and ground mapping techniques are available for mapping and delineating soils landforms water flow and pathways through the subsurface I Some can be used to detect or infer the presence of salt at the Earth s surface or contained in the soil profile I Satellite and airborne remote sensing techniques can reveal existing surface salinity and can track changes over time I Airborne geophysical techniques combined with ground and borehole control are important tools in understanding salinity and hydrology at depth at a variety of scales 1 Only borehole sampling and electromagnetics EM techniques can detect and resolve salinity in the subsurface at depths in and below the root zone EM techniques can also give complementary information on palaeochannels and structures which often control groundwater flow Salinity risk is a measure of the chance that the salt hazard will cause harm to an asset at some time in the future Cost benefit analyses in salinity management should take into consideration total cost and total benefit in context with the value of all assets The optimum strategy for mapping salinity hazard and risk depends on the scale farm community or catchment and resources available to the user Users need to make best use of existing information and then integrate a range of the available mapping methods so that they best address their specific problem No single method has primacy nor is there a
71. soils vegetation and indirect root zones type geology and land use COMMENTS Useful technique for mapping small areas paddocks Essential for checking maps prepared from satellites aircraft or systematic vehicle based EM surveys Ensures that the extensive local knowledge of landholders is used e g changes of salinity outbreaks through time as well as observations of causes effects e g wet seasons floods Inspecting salt scalding at the base of steep cleared bedrock slope Boho VIC Photo Pauline English CSIRO 2005 Reproduced with permission SURFACE MAPPING 0 10 cm DEPTH 4 Aerial photo interpretation API Aerial photo interpretation is the oldest remote sensing technique for broadacre mapping It involves the systematic acquisition of photos from precision cameras mounted on aircraft Salinity related mapping usually involves the detection of visible salt on the surface or the identification of vegetation patterns or water bodies that might infer salinity API mapping can also delineate drainage lines hydrology landform geology or geomorphology to help with an understanding of landscape processes for risk assessment Images that are affected by drought bushfire damage green flush such as spring rains can be misleading 5 Airborne video Airborne video largely experimental is an extension of aerial photographs and useful for examining flight paths for specific features 4 AE
72. ta and optimal approach A review of modelling systems used in dryland salinity risk assessment and management forecasting was undertaken by NDSP The Practical Guide of Salinity Models PRISM study released on CD reviewed over 300 tools models and frameworks see lt www ndsp gov au gt Methods for estimating dryland salinity risk vary with the level of sophistication and data requirements and include composite index methods strongly inverse methods and trend based methods Composite index methods rely on user experience strongly inverse methods rely on statistical relationships and trend based incorporate objective data on temporal changes All of the methods can be applied in a spatial framework using GIS and used to prepare maps of areas predicted or hypothesised to be at risk of dryland salinity However confidence in outputs of the methods varies considerably with trend based methods generally providing the highest confidence 43 44 Mapping methods available in Australia and their relative level and type of use Method Use in Use in Use in Paddock Farm Catchment Regional mapping mapping mapping scale scale scale scale dryland salt store regolith salinity hydrology SURFACE Visual XX E kk Laboratory EN Radiometrics ground ii Radiometrics airborne w Air photo interpretation io ii DEM Z LX Multi spect CASI etc Hyperspectral airborne 2 _ Video z _ E Sa
73. tellite imagery kai ME Hyperspectral satellite z _ ROOT ZONE lt 2 m Shallow EM Ex ARK E Resistivity Wenner etc _ Field drilling etc ER RR Airborne radar _ Satellite radar DEEPER gt 2 m MAL Ti Deeper EM31 34 etc Elect resist probing o Stream sampling kk GPR NMR seismo electric Magnetics kk Gravity _ Borehole logging gt AEM EX k EX commonly used 7 less often used some use not applicable 1 Based on a table prepared by Richard George WA Department of Agriculture Photo Pauline English CSIRO 2005 Reproduced with permission 6 CONCLUDING REMARKS This user guide presents a broad overview of methods for mapping salinity in the landscape and assessing salinity hazard and risk The concepts and techniques described here are covered in much greater detail in the accompanying book The report also contains case studies that show examples of the use of multiple mapping techniques for mapping salinity in Australia at various scales An extensive reference list and detailed appendices that describe the capabilities and limitations of each technique are also included in the book Dryland salinity is but one expression of the impact of human endeavour on the environment Mapping techniques such as those described in the user guide and book can help unravel the complexity and interaction of landscape features soi
74. that may be of assistance in understanding dryland salinity Step 3 Consider whether the mapping techniques you are proposing to use are suitable for the specific environment Not all mapping techniques are applicable in all environments some may be better suited to specific problems or be more cost effective Sequential or combined use of two or more methods may provide the most cost effective and timely information Step 4 Identify areas where no useful remedial action is possible In saline areas where no remedial action is likely to be available or new data is unlikely to improve or support remedial action the acquisition of new information may have limited merit unless it assists in the understanding of salinity changes in a regional sense or serves to assure stakeholders that the optimum course of action is already being followed Step 5 Apply the benefits of this approach Evaluate the benefits and costs of the mapping and interpretation proposal The budget should include costs of pre survey design data acquisition ground truthing and calibration with borehole control and interpretation 3 SALINITY WHAT IS DRYLAND SALINITY Soil salinity refers to the presence of salt in solution plus readily dissolvable salts in the soil Soils naturally contain a broad range of solutes the most common being sodium chloride but lesser amounts of other salts such as potassium and sulphates are also common Soil salinity is either
75. ty image interval conductivity for 10 to 15 m below surface where the warmer colours red and magenta indicate higher conductivity values courtesy Richard Lane Geoscience Australia b Map quality and interpretation Mapping methods and their interpretations form the basis of products that expand the knowledge base of non experts managers and policy makers They should be assessed in the context of economic considerations assets at risk cost of data acquisition cost of monitoring consequence of doing nothing in order to produce a salinity management plan Maps that have greater data input will be more complete Mapping of larger areas will result in lower costs per hectare Technological advances will also affect the suite of optimal techniques to provide each product Each mapping technique can be used for different purposes and end products and a skilled interpreter will always combine as many different types of measurement as possible to produce an interpretation or mapping product The user should also bear in mind the scale at which the data were acquired and their accuracy and the inherent spatial resolution of the technique Il ground measurements provide a more accurate measurement at one point in space and at one time but may not reflect the inherent geological variability unless measurements are taken at a high spatial density I airborne methods measure the average response over a footprint controlled
76. verification is essential Comparison of airborne and ground methods When comparing airborne ground and borehole results it is important to note that each technique has its own specific depth of investigation horizontal footprint and vertical and horizontal resolution Differences in the volume of investigation and horizontal and vertical resolution thus affect the correlation of different techniques see box next page The very accurate measure of soil properties such as salt content on small samples may be misleading when natural spatial lateral and vertical variations are considered Techniques such as EM that are sensitive to large volumes of ground may not be as accurate or precise as point measurements but will give a truer representation of average earth properties over a larger area Sampling groundwater a Bi en y Airborne mapping with combined magnetics and radiometrics Photo Mark Glover CSIRO 2005 Reproduced with permission Photo Fugro Airborne Surveys 2 1 22 DIFFERENCES IN HORIZONTAL RESOLUTION example from St George in Queensland The following example shows differences in horizontal resolution as measured with ground EM31 and airborne TEMPEST systems over profiles of length 50 km 5 km and 1 km Raw EM31 measurements are plotted in light blue TEMPEST AEM conductivity predictions for O to 5 m below surface in red and EM31 measurements filtered with a rolling average that
77. vertical coils from which some information can be obtained of variation in conductivity with depth e g increasing decreasing or constant through the root zone Since single measurements with conductivity meters have a relatively fixed depth of investigation some users have devised 4 wheel bike or vehicle mounted semi automated systems that employ a combination of coil configurations or systems with different coil spacings to provide better depth information and more rapid coverage of larger areas The systems are also used in time lapse mode to determine soil salinity changes for salinity risk or remediation applications They have been used in many areas of Australia to determine large scale root zone soil salinity classes Electrical conductivity is strongly correlated with salinity however other factors such as soil moisture content soil texture and composition in particular the amount and type of clays and temperature can also affect the readings and corrections should be made for these parameters ELECTROMAGNETIC DEFINITIONS Frequency domain systems are those that transmit a continuous sinusoidal waveform and measure the phase and amplitude or in phase and quadrature components of the resultant signal Time domain systems transmit a square or half sine wave pulse and measure the amplitude of the resultant decaying or transient signal at various times after cessation of the transmitter pulse Conductivity electrical
78. wing TEM airborne systems especially in the shallow subsurface The fundamental limitations of resolution of inductive electromagnetic techniques related to the volume of ground that contributes to each measurement means that AEM systems can detect but usually not resolve conductivity distribution in the top 5 to 10 m APPLICATION TO HAZARD CONTRIBUTION TO RISK COST COMMENTS MAPPING ASSESSMENT 18 AIRBORNE ELECTROMAGNETICS AEM is the only regional technique that maps salinity through the regolith and can also map total salt store Applicable from the root zone through to bedrock Useful for mapping From less than 1 ha Cannot resolve vertical variations palaeochannels basement to more than 10 ha within the root zone Depth range topography and other depending on line depends on ground conductivity pathways for spacing size and Must be calibrated with ground and groundwater flow location of area borehole data Care must be taken with processing and interpretation products Thickness of clay unit in Riverland SA inferred from a bore holes and b helicopter electromagnetics The detailed structure of clays and buried sand dunes is evident from the helicopter data from Case Study 2 in accompanying book a Clay thickness from bore logs b Clay thickness from constrained inversion of helicopter EM data 37 Distance km O 15 e 38 MAPPING BELOW THE ROOT ZONE gt 2 m DEPTH AEM capab
79. y indirect mapping of surface salinity and recharge properties especially when combined with DEM APPLICATION TO HAZARD CONTRIBUTION TO RISK COST MAPPING ASSESSMENT 13 AIRBORNE AND GROUND GAMMA RAY SPECTROMETRY RADIOMETRICS Provides mapping of soil Able to produce quality Airborne lt 1 ha types that sometimes soil mapping depending on area correlate with salinity Ground 10 to 20 ha Applicable to the top 10s of centimetres only High resolution acquisition of airborne magnetic and radiometric data WA b n i w Ske COMMENTS Airborne or ground A demonstrated technique for broad area soil mapping that is showing great promise operationally especially when combined with DEM Requires specialist analysts for interpretation Claims about its ability to directly map near surface salinity do not have scientific foundation Photo Fugro Airborne Surveys ROOT ZONE MAPPING 10 cm 2 m DEPTH 14 Shallow electromagnetic conductivity mapping Lightweight portable ground conductivity meters have achieved widespread acceptance for salinity mapping in the root zone and are now an important part of land and water management These instruments are designed for ease of use and provide a direct readout of electrical conductivity They have a focused depth range extending over the root zone to depths of several metres The instruments can be used in two measurement configurations horizontal and

user guide - CRC for Spatial Information

Contents

Download Pdf Manuals

Related Search

Related Contents