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Who will use the Catchment Classification framework? 
Federal and State Government agencies.
Local governments, and the Australian Local Government Association.
Environmental groups, e.g. Australian Conservation Foundation.
Catchment Management Committees in all States.
Scientific community, e.g. CSIRO.
Industry councils and agricultural groups, e.g. National Farmers' Federation and National Association of Forest Industries.
How will the framework be used? Public funds and resources must be targeted to areas where they can be most effective. Through regional planning processes, the MDBC Salinity Strategy and the National Action Plan, priorities are being set for regional outcomes to be achieved within a given time frame. These define the criteria for ranking catchments for further investigations, salinity funding, and implementation of changes in land use and water management. Modelling results show that to control salinity, a reduction in the rate of recharge of 30-90% may be required to control salinity. The level of recharge reduction attained at a catchment scale is affected by: 1. The level of uptake of any management option 2. The level of recharge reduction attained where-ever the changed management occurs 3. The placement of the change in land management If there is 50% uptake of a land use or land management that reduces recharge by 50%, the net result is a 25% recharge reduction. This can be enhanced to a limited extent by targeting recharge reduction to areas of higher recharge. Nonetheless, most of the land surface overlying the groundwater system will need to have some form of changed land management to control salinity. The target of 50% recharge reduction at a regional scale would require enormous resources and hence difficult to see it being feasible within a short time frame. It is more easily envisaged that such a level of reduction can be achieved at a local catchment scale. We need to avoid recharge reduction being at too low a level to have a perceivable impact because of the need to cover a large area. Intense effort in a smaller number of catchments may enable threshold values of recharge reduction to be attained in areas where it is important to do so. This supports the notion of targeted actions in priority catchments. The MDBC Salinity Audit, MDBC Salt Trends Report and National Land and Water Resource Audit have provided information on what may happen in future under the status quo or 'no change' scenario. Unfortunately, the catchments for which salinity is likely to be the worst are not necessarily those for which it is easiest to control salinity. In fact it is often the opposite. For this reason, results from these studies do not form a good basis for ranking catchments. This section discusses how the Groundwater Flow Systems (GFS) approach may be useful for this purpose. There are a number of key reasons why groundwater factors are important in the ranking process: 1. Groundwater can be slow to respond to land use change depending on the type of GFS. 2. The magnitude of the change in recharge required to meet a target will depend on hydrogeological characteristics, salt stores and connection of the groundwater system to these salt stores and the stream. A large reduction in recharge will be more difficult. 3. For larger groundwater systems, the number of landholders required to meet a required level of recharge control increases substantially and generally so do the time lags. 4. The type of GFS is often correlated with other factors such as soils, land use and rainfall which affect the recharge. 5. The feasibility of engineering options to protect assets will depend on groundwater characteristics of the aquifer as well as other factors such as the topography and appropriate outfall site. These issues suggest that the type of groundwater flow system must be used explicitly in any ranking exercise. Using the Groundwater Flow System as a sieve As was seen in a previous section, once we understand groundwater characteristics of a catchment, there are methods available for assessing the impact of any management option on salinity. Unfortunately, these characteristics are not generally known over a large area. The GFS breaks up the landscape into areas with similar properties and hence in principle could extend results from catchments for which characteristics are understood. In reality, there are probably less than 50 catchments around Australia in which the characteristics are understood well enough for prediction and have been interpreted as such. One approach would be to transfer the results from the case study to all areas within the same GFS. Problems associated with this include: 1. The GFS classes are different at different scales and hence there are many more GFS classes than the fifteen at the national scale 2. Not all GFS classes will have a corresponding case study. 3. There is generally too much variation within a class at a national scale for management to be assumed to be the same across the whole class. The definition of regional GFSs should be similar enough for transfer from case/demonstration catchment studies. 4. Some management options will always require site specific information A second approach is to use the GFS as a sieve. This recognises that for specific management options to be defined, further work may be required. Nonetheless from the GFS definition, we know the scale of the groundwater flow-path and geology and this may allow us to divide options as to those that are extremely unlikely, those that are improbable and those that are probable (i.e. low, medium or high likelihood of success). This provides a first sieve for management options and provides some guidance as to where to direct resources and further investigations. This is illustrated using the example of a regional unconfined sedimentary basin. The ratio of recharge to discharge capacity, G, is high for these systems and hence there will need to be a very large change in water balance (>90%) to restore a water balance over the whole groundwater system. The longer-term control of salinity would thus require both a farming system that will sufficiently reduce recharge, and almost 100% uptake over a large area. The response time for lowering the discharge to original levels can be greater than 100 years and could be up to 1000 years and hence there is likely be a long lag time for benefits to accrue. Hence, the practical capacity of biological recharge reduction for restoring the original system within a time frame is limited. Certainly small areas of land use change will be ineffective. In the meantime, there may be a need to protect assets from salinity. The high transmissivity of many sedimentary aquifers means that engineering options for lowering water tables in the vicinity of the asset is perhaps feasible. Also, biological recharge reduction in the vicinity of the asset may slow the rate of salinisation. This can be confirmed with further field work and modelling. This style of ranking has been done with regional groups under the NDSP TOOLS project. From a general understanding of the groundwater characteristics, the options are ranked according to probability of success. Further field work, modelling and economic studies can then be targeted in those areas likely to have the most impact in order to constrain the range of options further. Support for the ranking process come from both the modelling work shown earlier in the report and case studies. |
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