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The importance of case studies within Catchment Classification Much of our understanding of the processes leading to salinity and its management comes from intensive research and investigations in a number of case studies around Australia. Since these underpin the groundwater flow systems framework and more broadly decisions on salinity management, it is important that these are documented and analysed in a similar fashion and subsequently peer reviewed and circulated. It is also important that there is a range of case studies that reasonably cover the range of different groundwater flow systems. For historical reasons, this has not been the case. Through the National Land and Water Resources Audit (NLWRA) and the Murray-Darling Basin Commission D9004 grant, we have attempted to analyse a broad range of case studies using a consistent approach. The steps for each case study were: 1. Develop a conceptual groundwater model This involves: (a) collation of existing groundwater and other data relevant to salinity (b) collation of reports that interpret this data (c) critically analysing the data and reports (d) describing key processes and parameters 2. Develop a groundwater model Management of salinity involves understanding the implications of various actions including maintaining the status quo. This necessarily involves prediction and modelling, particularly groundwater modelling, of some sort even if this is mostly conceptual in nature. Within this project, we have numerically simulated the conceptual model developed in the first part, but have aimed to make this as simple as possible, while retaining the key processes. The FLOWTUBE model has been used for most of the studies. 3. Relating land use to recharge Much of the modelling is directed towards predicting the impacts of reducing recharge through land use changes. For the NLWRA case studies, we tried to use farm-scale models to compare deep drainage under different land uses. Unfortunately, for many of the case studies, the information needed to do this reliably was simply not available on an appropriate scale and this has been dropped for the remaining case studies. Further work on relating recharge to land use is occurring through the Landmark project and the NSW Dryland Salinity Initiative. 4. Relating recommended management to groundwater flow systems classification From the modelling predictions, we can suggest which management will not work well. For land use change, key criteria for this includes level of recharge reduction required to control salinity and time lags between implementation and impacts. Inevitably, not all groundwater flow systems will be covered by the current project. However, the approach is being applied in the NDSP project (Christopher Clarke) and by all states to other groundwater flow systems. It is also important to synthesise our understanding of how groundwater response is related to catchment characteristics. Being confident in doing this will aid in the transfer of understanding from the intensively studied catchments to the broader landscape. Case studies and modelling Groundwater processes and the manner in which distinctive processes lead to salinisation of the landscape and/or streams varies between groundwater flow systems (GFS). An understanding of hydrogeologic processes and their governing mechanisms in representative catchments for each of the GFS categories (Coram et al. 2000) is prerequisite before broad-scale solutions can be developed towards mitigation of salinity problems. Case studies from wide-ranging catchments across salinised parts of Australia are aimed at providing coherent information about key characteristics and processes operating within diverse hydrogeologic systems. These processes include recharge dynamics, groundwater redistribution, salt mobilisation, and eventual discharge to the land surface or to streams. This catchment case study information provides a basis for modelling the capacity of different groundwater systems to respond to land use changes or other recharge reduction measures over given spatial and temporal scales. Understanding the behaviour of these case studies (through field investigation, data collation and modelling) helps us to understand the way groundwater processes vary in different parts of the landscape. This understanding can then be used as a basis for more widely predicting behaviour. Nine catchment case studies representing diverse GFS categories are outlined here: Wanilla, Kamarooka, Billabong Creek, South Loddon Plains, Kyeamba Creek, Axe Creek, Brymaroo, Lake Warden, and Liverpool Plains. For each catchment, the extent or magnitude of the salinity problem, the fundamental hydrogeologic characteristics, modelling results and management recommendations are presented in overview. Next Pages: Transferabilty of Case Studies Case Studies Murray-Darling Basin Groundwater Flow Systems Stream Salinity and Water Yield Options for Managing Dryland Salinity Research |
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