Mineral Resources Tasmania Tasmanian Geological Survey Tasmania DEPARTMENT of INFRASTRUCTURE, Record 2003/02 ENERGY and RESOURCES Tasmanian Groundwater Flow Systems for Dryland Salinity Planning by M. Latinovic, W. L. Matthews, C. Bastick, S. Lynch, P. Dyson and E. Humphries Contents Groundwater Flow Systems ………………………………………………………………… 3 Options for salinity management …………………………………………………………… 5 Recharge management …………………………………………………………………… 5 Engineering — water table management …………………………………………………… 6 Managing saline resources — discharge areas ………………………………………………… 7 Tasmanian Groundwater Flow Systems ……………………………………………………… 8 1. Local flow systems in Quaternary sedimentary rocks (talus and till) …………………………… 10 2. Local to intermediate flow systems in Quaternary sedimentary rocks …………………………… 11 3. Local to intermediate flow systems in undifferentiated Quaternary to Tertiary sedimentary rocks ……………………………………………………………… 12 4. Local flow systems in high-relief Jurassic dolerite …………………………………………… 13 5. Local flow systems in high-relief Permian and Triassic sedimentary rocks ……………………… 14 6. Local flow systems in granites …………………………………………………………… 16 7. Local flow systems in high-relief folded and fractured Proterozoic and Palaeozoic rocks …………… 17 8. Intermediate flow systems in Tertiary sedimentary rocks……………………………………… 18 9. Intermediate to local flow systems in Tertiary basalt ………………………………………… 20 10. Intermediate to local flow systems in low-relief Jurassic dolerite ……………………………… 21 11. Intermediate flow systems in low-relief Permian and Triassic sedimentary rocks ………………… 23 12. Intermediate flow systems in low-relief folded and fractured Proterozoic and Palaeozoic rocks …… 25 13. Regional and local flow systems in Tertiary sedimentary rocks ……………………………… 26 References ………………………………………………………………………………… 28 Appendix 1: Characterisation attributes……………………………………………………… 29 Appendix 2: Methodology used in map production ………………………………………… 30 Tasmanian Geological Survey Record 2003/02 1 Introduction A workshop on defining Tasmanian groundwater flow systems as a strategic framework for managing dryland salinity was held from 25 to 27 July 2001. The workshop was convened by the Department of Primary Industries, Water and Environment and Mineral Resources Tasmania, and was attended by 23 people interested in groundwater and the management of salinity. Phil Dyson, Consulting Hydrogeologist, conducted the workshop. Phil Dyson was a joint author of the report Australian Ground Water Flow Systems Contributing to Dryland Salinity and has run similar workshops in other Australian States. Those who attended part or the entire workshop were: 0 Phil Dyson, Consulting Hydrogeologist (workshop facilitator and technical consultant); 0 Colin Bastick, Regional Land Management Officer, DPIWE (Convenor); 0 Loyd Matthews, formerly geologist and groundwater specialist, Mineral Resources Tasmania; 0 Miladin Latinovic, geologist and groundwater specialist, MRT; 0 Simon Lynch, GIS Land Resources, DPIWE (map preparation); 0 Adrian Waite, Senior Geologist, MRT; 0 Mike Walker, Project Officer Salinity, DPIWE; 0 Esta Kokoris, Project Officer Salinity Modelling, DPIWE; 0 Chris Grose, Senior Land Resource Management Officer, DPIWE; 0 Jacqui Knee, Project Officer Sustainability, DPIWE; 0 Liz Bond, Resource Assessment Officer Sustainability; 0 John Maynard, Davey and Maynard, Agricultural Consultant; 0 David Armstrong, Armstrong Agricultural Services; 0 Astrid Ketellar, Armstrong Agricultural Services, Agricultural Consultant; 0 David Wright, Catchment Officer, DPIWE; 0 Michael Hart, Food Agriculture Fisheries, DPIWE; 0 Sven Meyer, Hydrologist, Forestry Tasmania; 0 Bill Cotching, Regional Land Management Officer, DPIWE; 0 Geoff Peters, Honours student, University of Tasmania; 0 Robert Phillips, Principal Water Management Officer; 0 Sebastian Burgess, Greening Australia; 0 Louise Gilfedder, Nature Conservation Branch, DPIWE; 0 Kristin Jaehne, Bushcare Officer. The following discussion is to be used for the development of the Tasmanian Salinity Strategy and describes the process of defining a set of Tasmanian groundwater flow systems, and sets out some of the basic assumptions that underpin that definition. Tasmanian Geological Survey Record 2003/02 2 Groundwater Flow Systems A groundwater flow system is a landscape entity that increase is a shift in the overall distribution of recharge includes all aspects of a single groundwater flow path. towards higher rates. A new equilibrium state is It is a fundamental unit that needs to be considered attained once the new recharge distribution is when management options for dryland salinity established over time. The period of time for this new control are being selected. Groundwater flow systems state to be attained is termed the equilibrium response (GFS) characterise similar landscapes in which similar time, and is assumed to be of the order of decades for groundwater processes contribute to similar salinity local flow systems, and upwards of hundreds of years issues, and where similar salinity management for regional flow systems. options apply. The concept of response time is important for A groundwater system starts at the recharge area, and designing management and monitoring systems, finishes at a discharge area — it fully describes all because we ideally need to know how close the system elements of a flow path. The boundary around a GFS is is to reaching a new equilibrium before setting the point where no subsurface flow occurs. management objectives and performance indicators. If the system is close to equilibrating, management Groundwater flow systems are not land management objectives can be identified on the basis of a units, but rather they are part of the layers that describe more-or-less stable salinity with a given level of such units. For example, when salt export rates are overlaid on the GFS distribution, it might be evident degradation. If the system is tens or hundreds of years that two catchments in the same GFS have widely away from equilibrating, the extent and impacts of different salt export rates, and it would be prudent to dryland salinity are likely to worsen considerably in manage them differently. Similarly, when soil that period, with major implications for what landscape data are combined with GFS distribution, management objectives may be feasible and what different management options will become evident. monitoring approaches are appropriate. The fundamental property of a groundwater flow Attributes that define a system is its ability to respond to change. Response Groundwater Flow System refers to the time taken to achieve a balance between the amount of water flowing into, and out of, the Groundwater Flow Systems can be defined by a series groundwater system. Under constant recharge of attributes that describe how they will respond to conditions, a balance is maintained between the inflow different recharge regimes, and that describe how they and outflow volumes. If these conditions change (for will express any imbalance in their water budget. example, from land use change or climatic variability), These attributes include information about the the balance is disturbed. A rise in groundwater levels hydraulic properties of the aquifer, as well as indicates recharge increases and it is theorised that this information on their landscape expression. The Water Cycle and Dryland Salinity Rainfall A cleared catchment increases A healthy tree cover infiltration which in turn raises uses groundwater the water table. A minimal amount reserves and of moisture is transpired while evapotranspiration an increase is experienced in keeps the water table surface runoff at a safe depth Saline seepage occurs where the ground surface intercepts the water table, usually on footslopes and in drainage depressions A vegetative cover Decreased vegetative together with minimal cover predispose the runoff ensures ground surface to surface stability erosion A rising water table brings natural salts Land degraded by towards the surface, saline seepage and A low water table The lower slopes of killing the existing affected by a high does not bring Surface streams become a well timbered vegetative cover water table severely catchment permit a salts to the surface saline through runoff limits productive from saline seepages range of productive agricultural activity agricultural land uses and interception of the water table Tasmanian Geological Survey Record 2003/02 3 Attributes such as the hydrogeology and the slope can problem, and in yet other cases, an adaptation to be used to spatially define the various flow systems salinity will be required. Within this broad framework using available catchment information. Other it is important to interpret the landscape within the attributes can be used to describe the likely success or context of groundwater flow systems, and to target otherwise of management options. A complete listing management options such that the broad objectives are of the attributes, and their rankings and explanations, achieved. is given in the tables for each flow system. Integration with other issues Limitation of current knowledge Dryland salinity is not the sole degradation issue In the process of defining the groundwater flow facing Australian landscapes. With this in mind, it is systems some obvious knowledge gaps regarding key critical to ensure that the integration issues associated processes have been defined. These processes related with the implementation of management options are to the way in which