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Developing the groundwater flow systems approach Salt is a natural occurrence in Australian landscapes. These salts have a range of origins, but are mainly the result of salt in rainfall which is left behind after evaporation. Over thousands of years, considerable amounts of salts ended up stored in Australian sub-soils. The extensive land use changes introduced by European settlers in the last century resulted in increased recharge to groundwater systems due to the widespread replacement of deep-rooted native vegetation with shallow-rooted cropping systems which use much less water. Salts once stored deep in the landscape are now being remobilised by rising groundwaters and moved to the ground surface (dryland salinity) and into streams (stream salinity). This short summary illustrates why it is not possible to provide salinisation processes understanding and management without a thorough understanding of groundwater processes and dynamics. Despite the variation of geology and geomorphology across the continent, there are a number of landscape types (or hydrogeological provinces) that have similar hydrogeological characteristics contributing to dryland salinity. These characteristics include geology, landform and relief. The National Classification of Catchments for Land and River Salinity Control (NCC) discriminates between the different groundwater-based salinisation processes based on areal extent, geology, geomorphology and specific geological structure influencing groundwater flow. The NCC was the first step towards a national salinity assessment and management framework. It provides a groundwater-based salinisation processes understanding that was developed with extensive input from expert State hydrogeologists. The framework is now widely accepted and used in Australia. While each of the fifteen conceptual models in the National Classification have real world examples, these are almost impossible to map. These models were based on the best knowledge available at the time (1998) and are being continuously improved as new understanding becomes available. The conceptual groundwater and salinisation processes understanding developed in the NCC provided a common working platform across Australia. But without being able to map the location of these models, it was inadequate for prioritising work and funding. Further development of the NCC was carried out within the Dryland Salinity theme (Theme 2) of the National Land and Water Resources Audit (NLWRA). This has resulted in a new Groundwater Flow Systems framework. Hydrogeologists from around Australia provided input into the definition of rules for mapping the conceptual models of the National Classification. These rules were based on geological and geomorphological characteristics of the different conceptual models, and applied to digital geological and elevation layers in a GIS. The rules are based on slope classes derived from a digital elevation model and digital geological information. The maps can be produced at any scale provided reliable data is available. Applying the Groundwater Flow Systems classification The aim of this section is to give some sense of the way in which groundwater flow systems (GFS) can be used. In doing this, it is difficult to be too prescriptive as specific situations will need to handled individually. We now address the key questions that were asked in the first section and show how the GFS framework can add value to them. These questions include assessing our ability to make a significant impact on the salinity problem, prioritising areas, targeting management and 'operationalising' salinity management plans. These questions can be asked at a range of scales for a range of purposes, depending on the interests of individual catchment groups to regional planning to State and National policy settings. We see four key roles for the GFS approach: 1. Breaking up the landscape: As shown in the previous section, the underlying principle of the GFS framework is to systematically divide the landscape into sub-areas using consistent rules. This enables us to 'compare apples with apples, rather than with lemons'. Any classification system balances the need to be simple with the complexity that actually exists. It is important that the in-class variability in regard to any management is constantly monitored and the framework adapted accordingly at appropriate intervals. To be useful for management at any scale it is important that the classification is fairly simple or else it will lose its value as a communication tool or as a basis for implementing appropriate incentives. The corollary to this is that there needs to be some variability within each groundwater flow system. In some parts of the Murray-Darling Basin, the level of spatial information is currently coarse and any system will need to be reviewed as knowledge improves. 2. Bringing out the right information: A second key role of the GFS is to transfer information from case studies and generic understanding from the National Classification across the broader landscape in a way that is useful and appropriate for salinity management. This transfer of information may take the form of understanding of key processes, parameter ranges for key variables, modelling results or management recommendations. The appropriateness of doing this will depend on in-class variability, availability of on-ground information and the sensitivity of management to this variability. 3. Aggregation: A third key role is to enable us to aggregate information across the broader landscape. If we are interested in managing for targets for salinity, salt loads and base-flow at downstream points of a river or on total area at risk of salinity, we need to be able to add up the impacts of changes made on different types of groundwater systems in different rainfall zones and for different land use changes. This needs to be done in an environment where data is sparse and where there is limited understanding of the processes. The GFS provides a structured approach to the groundwater aspects of these aggregations. The accuracy of the outputs will depend on the availability of information. 4. Framework for further studies: An important part of the implementation of any salinity management plan is the gathering of further data, testing of assumptions, development and testing of innovative ideas and research techniques. The difficulty in the implementation of any of this lies in the variability in the landscape and whether something that works on one catchment will work well in others. What are the likely impacts of salinity management? Finally, the question needs to be asked: How much overall impact will be made if we match salinity management to different groundwater flow systems? It is clear at this stage that: 
even if suitable land use systems existed and could be quickly implemented, these alone will not attain many of the regional targets that have been set for 15 to 20 years.
for many areas, such systems need to be profitable in their own right as it is difficult to justify public expenditure in terms of public benefits.
the groundwater flow systems that require the largest level of recharge reduction and have the longest time delays are already extensive and currently contain much of Australia's saline land areas.
All of these points suggest that management of the overall salinity problem will be difficult and long-term. The groundwater flow systems approach is still in its infancy, but is providing a useful framework for salinity management. The strongest factor in this is its acceptance by most regions across the Murray-Darling Basin and the development of management assessment tools and communication packages based on this framework. No management assessment tools are yet operational. Click on the map of Australian Groundwater Flow Systems for a larger version. |
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| design & production by Talkin' Technical Communications | last updated: April 2002 |