Understanding Groundwater Flow Systems and ...

Understanding Groundwater Flow Systems and processes causing salinity in the Southern Midlands and parts of the Clarence municipalities

October 2005 Hocking, M., Bastick, C., Hardie, M., Dyson, P. and Lynch, S.


Please cite this report as: Hocking, M., Bastick, C., Hardie M., Dyson P. and Lynch, S. 2005. Understanding Groundwater Flow Systems and processes causing salinity in the Southern Midlands and parts of the Clarence Municipalities NRM South and North and National Action Plan for Salinity and Water Quality Tasmania Report, published by Southern Midlands Council. This project attracted funding of $161 000 from the Australian and State Governments under the National Action Plan for Salinity and Water Quality (NAP). The project was managed by the Southern Midlands Council for the Southern and North Natural Resource Management Committees and support was provided by the Department of Primary Industries, Water and Environment and Mineral Resources Tasmania.

The Southern Midlands Council & the Crown in the right of the State of Tasmania does not accept responsibility for any loss or damage which may result to any person arising from reliance on all or any part of this information, whether or not that loss or damage has resulted from negligence or any other cause.

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Executive summary This project has developed a foundation for salinity management using the nationally accepted Groundwater Flow System (GFS) framework. Data collation, groundwater drilling, technical data review, and technical consultation has provided a basis for this report. The study area encompasses the National Action Plan (NAP) parts of the Southern Midlands and Clarence Municipalities where the GFS methodology for salinity classification has been applied. A GFS is a description of geological and geomorphic information that captures the essential understanding of landscape groundwater interactions, which is used to consider groundwater and salinity processes. Nine GFSs have been defined within the study area. Conceptual models have been developed and the GFSs have been mapped at 1:100 000. Each GFS has been classified according to scale and responsiveness. Based on the limited data available and the limited drilling done, of the 9 GFS all but one (the GFS in Colluvium) contain saline groundwater and significant salt stores. Upon the collation of information for each GFS, salinity management prioritisation was undertaken based upon scale and responsiveness, landscape attributes, quality of land and water quality. The three highest priority GFSs identified for future investment were; •

Local scale GFS on alluvial plains and slopes,

•

Local/Intermediate scale GFS in low relief layered fractured rock, and

•

Local/Intermediate scale GFS in low relief dolerite.

While the 5 other GFS are considered to be important for salinity management, improvements in the understanding of the processes and changes in land management when targeted at the above four GFS is likely to provide the greatest salinity benefit over the shortest timeframe with lesser cost. The current impact of salinity in the study area is reflected more as groundwater base flow into streams rather than via land salinisation. Land salinity in this region is less apparent than other parts of Tasmania, but surface water salinity is generally much higher than other parts of Tasmania. A review of groundwater monitoring information across the region suggests a rise in groundwater level, however these results have limited weight due to the very limited amount of groundwater monitoring that occurs. The establishment of an adequate groundwater monitoring network is crucial in setting future resource condition targets for the region and should be a high priority for future works For each of the nine GFS identified in the study area, a suite of salinity management options have been developed and fact sheets prepared. The management options to be most relevant are maintenance of perennial pasture, avoidance development on known saline land (including irrigated production), and monitoring of irrigation water quality and groundwater quality. Recommendations are made with regard to future work, monitoring and assessment of asset condition.

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Understanding Groundwater Flow Systems and processes causing salinity in the Southern Midlands and parts of the Clarence municipalities Contents Executive summary ........................................................................................ i 1 Introduction............................................................................................ 1 2 Groundwater Flow System framework and application .................... 4 2.1 2.2 2.3

Groundwater Flow System framework 4 A rationale for salinity management 5 Can salinity be managed by reducing groundwater recharge? 6 Local (small) scale Groundwater Flow Systems ...........................................................6 Intermediate (larger) scale Groundwater Flow Systems ...............................................7 Regional scale Groundwater Flow Systems .................................................................7 2.4 Management responses 8 2.5 Forms of intervention 9 2.6 Biological management (vegetation) of groundwater recharge 9 2.7 Engineering strategies 10 2.8 Saline enterprises (living with salinity) 12

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Physical characteristics of the Southern Midlands......................... 13 3.1

Geology 13 Igneous rocks .............................................................................................................13 Sedimentary rocks ......................................................................................................13 Unconsolidated rocks .................................................................................................13 3.2 Landscape development (geomorphology) of the Southern Midlands 14 3.3 Climate 15 Oatlands .....................................................................................................................15 Melton Mowbray .........................................................................................................17 Hobart.........................................................................................................................18 Summary ....................................................................................................................20

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Salinity in the Southern Midlands ..................................................... 21 4.1 4.2 4.3 4.4

Introduction 21 Landscapes and groundwater flow systems 21 Historical salinity 22 Current salinity 22 Land ...........................................................................................................................22 Groundwater...............................................................................................................23 Surface water .............................................................................................................23 Ecological assets........................................................................................................23 Infrastructure ..............................................................................................................23 4.5 Threatening processes 24 Land use change ........................................................................................................24 Climate .......................................................................................................................26

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Groundwater Flow Systems in the Southern Midlands................... 28 5.1 5.2 5.3

Introduction 28 Identifying and mapping Groundwater Flow Systems 31 Conceptual models 35 Local scale GFS on alluvial plains and slopes ............................................................36 Local scale GFS on current floodplain ........................................................................39 Local scale GFS in Dunes ..........................................................................................42 Local scale GFS in high relief dolerite (Jurassic) ........................................................44 Local/Intermediate scale GFS in low relief dolerite (Jurassic).....................................46 Local scale GFS in high relief layered fractured rock (Triassic-Permian) ....................48

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Local/Intermediate scale GFS in low relief layered fractured rocks (Triassic-Permian)50 Local scale GFS in colluvium (talus) ...........................................................................52 Local/intermediate scale GFS in fractured basalt........................................................54

6 Priority setting process for Groundwater Flow Systems in the Southern Midlands....................................................................................... 57 7 Management of salinity in the Southern Midlands .......................... 62 7.1

Overview of salinity management options 62 Conserving perennial vegetation ................................................................................63 Manage cropping and irrigation development .............................................................63 Trees and shrubs to reduce recharge .........................................................................63 Plant or improve perennial plants including lucerne....................................................63 Increasing irrigation efficiency.....................................................................................64 Increase water use efficiency (WUE) ..........................................................................64 Engineering options to reduce recharge .....................................................................64 Salt tolerant trees and shrubs to mitigate and adapt to saline areas...........................64 Salt tolerant pastures..................................................................................................64 Engineering options to improve discharge areas ........................................................64 Options for using saline waters...................................................................................65 7.2 GFS fact sheets (salinity management options) 65 APS-GFS - Local scale GFS on alluvial plains and slopes .........................................66 CFP-GFS - Local scale GFS on current floodplain .....................................................70 HRD-GFS - Local scale GFS in high relief dolerite .....................................................74 FB-GFS – Local/Intermediate scale GFS in fractured basalt ......................................78 DUNE-GFS - Local scale GFS in dunes .....................................................................83 HRLF-GFS - Local scale GFS in high relief layered fractured rocks ...........................87 LRD-GFS – Local/Intermediate scale GFS in low relief dolerite..................................91 LRLF-GFS – Local/Intermediate scale GFS in low relief, layered fractured rocks.......95 COL-GFS - Local scale GFS in Colluvium (Talus) ......................................................99 Summary 102

8.0 Field checking conceptual models.................................................. 104 8.1

Historical groundwater information 104 Previous salinity related studies within the Southern Midlands .................................104 8.2 Groundwater trends 105 MRT monitoring network...........................................................................................105 DPIWE monitoring network.......................................................................................106 8.3 Salinity 106 8.4 Stream EC survey 108 8.5 Groundwater drilling program 109 Design and application .............................................................................................110

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Evaluation of current groundwater monitoring ............................. 115 9.1

Current groundwater monitoring 115 DPIWE monitoring network.......................................................................................115 MRT monitoring network...........................................................................................115 GFS monitoring network ...........................................................................................116 10.2 Future groundwater monitoring recommendations 117 Regional groundwater flow systems .........................................................................119

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Conclusions ....................................................................................... 122 Groundwater Flow Systems

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122

Recommendations ............................................................................ 125 12.1 Monitoring 12.2 Research and investigation 12.3 Evaluation of salinity

125 125 126

References.................................................................................................. 127 Glossary and abbreviations...................................................................... 130 Acknowledgments ..................................................................................... 131 Appendix 1 – Richmond Transect............................................................ 132 iii


Richmond transect groundwater level and salinity data Site R1 – Local scale GFS in low relief dolerite Site R2 – Local scale GFS in low relief layered fractured rocks Site R3 – Local scale GFS in current floodplain

132 135 136 137

Appendix 2 – Kempton Transect.............................................................. 138 Site K1 – Low relief dolerite GFS Site K2 – Local/Intermediate scale GFS in low relief layered fractured rocks Site K3 – Local/Intermediate scale GFS in low relief layered fractured rocks Site K4 – Local/Intermediate scale GFS in low relief layered fractured rocks Site K5 – Local/Intermediate scale GFS in low relief layered fractured rocks Site K6 – Local/Intermediate scale GFS in low relief layered fractured rocks

141 142 143 144 145 146

Appendix 3 – Oatlands site ....................................................................... 147 Site O1 – Local/Intermediate scale GFS in low relief layered fractured rocks

148

Appendix 4 – Bore construction, drilling sampling and groundwater data collection ............................................................................................ 149

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List of Figures Figure 1 Location of the NAP parts of the Southern Midlands and Clarence municipalities, the “study area” ........................................................................... 2 Figure 2 Communication process of GFS project ..................................................... 5 Figure 3 Saline soils currently impacting on production (lower right) with limited options for eliminating by management .............................................................. 8 Figure 4 Saline scald adjacent to an ineffective surface drain installed for salinity management ..................................................................................................... 10 Figure 5 Geology of parts of the Southern Midlands & Clarence Municipalities ..... 13 Figure 6 Mean annual rainfall of the Southern Midlands......................................... 15 Figure 7 Monthly average rainfall and evaporation information at Oatlands (source: BOM 2004a)...................................................................................................... 16 Figure 8 Cumulative residual rainfall information at Oatlands (source: BOM 2004a) .......................................................................................................................... 16 Figure 9 Monthly average rainfall and evaporation information at Melton Mowbray (source BOM 2004b)......................................................................................... 17 Figure 10 Cumulative residual rainfall information at Melton Mowbray (source: BOM 2004b)............................................................................................................... 18 Figure 11 Monthly average rainfall and evaporation information at Hobart (source: BOM 2004c)...................................................................................................... 19 Figure 12 Cumulative residual rainfall information at Hobart (source: BOM 2004c)19 Figure 13 Land use of the study area as at February 2002 (source: BRS 2002).... 25 Figure 14 Land use area estimates of the study area as at February 2002 (source: BRS 2002) ........................................................................................................ 25 Figure 15 Simplified extent of local, intermediate and regional scale GFSs ........... 30 Figure 16 Statewide GFS layer developed by Latinovic et al. (2003) ..................... 32 Figure 17 Differing scale geology map sheets used in the development of the Southern Midlands GFS layer (k refers to 1 000) ............................................. 33 Figure 18 GFS layer of the Southern Midlands and Clarence municipal areas (refer to Lynch, Hocking and Brown, 2005 for a 1:100 000 GIS map of the GFS) ..... 34 Figure 19 Simplified cross-section of a local flow system in alluvial plains and slopes ............................................................................................................... 37 Figure 20 Groundwater discharge from the local scale GFS in alluvial plains and slopes (Upper Coal River catchment) ............................................................... 38 Figure 21 Simplified cross-section of a local flow system in the current floodplain. 39 Figure 22 Groundwater-surface water interaction in the current floodplain GFS .... 40 Figure 23 Current floodplain GFS of the Coal River at Richmond .......................... 41

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Figure 24 Simplified cross-section of a local flow system in the Quaternary dune local flow system............................................................................................... 42 Figure 25 Groundwater discharge from a local dune GFS (east of Oatlands) ........ 43 Figure 26 Local scale GFS in high relief dolerite .................................................... 44 Figure 27 High relief dolerite landscape near York Plains ...................................... 45 Figure 28 Local/Intermediate scale GFS in low relief dolerite................................. 46 Figure 29 Low relief dolerite GFS near Tunbridge .................................................. 47 Figure 30 Local scale GFS in high relief layered fractured rocks............................ 48 Figure 31 High relief layered fractured GFS below high relief dolerite and associated break of slope salinity ..................................................................... 49 Figure 32 Local/Intermediate scale GFS in low relief layered fractured rocks ........ 50 Figure 33 Low relief GFS in layered fractured rocks at Oatlands ........................... 51 Figure 34 Local scale GFS in colluvium.................................................................. 52 Figure 35 High relief GFS in colluvium.................................................................... 53 Figure 36 Local/intermediate scale GFSs in fractured basalt ................................. 55 Figure 37 Elevated variant fractured basalt GFS near Lemont............................... 56 Figure 38 Priority GFS from salinity management of the NAP parts of the Southern Midlands and Clarence municipalities............................................................... 61 Figure 39 Location of MRT and DPIWE bores and bores drilled in this project .... 107 Figure 40 Location of rapid stream EC survey sample points............................... 108 Figure 41 Air rotary drilling equipment after bore construction ............................. 110 Figure 42 Location of drilling sites as part of this project ....................................... 111 Figure 43 Location of Richmond transect ............................................................. 112 Figure 44 Location of Kempton transect ............................................................... 113 Figure 45 Location of Oatlands bore..................................................................... 114 Figure 46 Cost comparison of manual and automated logging of groundwater level ........................................................................................................................ 116 Figure 47 Elevation and depth to watertable of the Richmond transect................ 132 Figure 48 Generalised regolith profile of the Richmond transect ........................... 133 Figure 49 Groundwater and salinity information along the Richmond transect..... 133 Figure 50 Elevation and depth to watertable of the Kempton transect ................. 138 Figure 51 Groundwater and salinity information along the Kempton transect ...... 139 Figure 52 Generalised regolith profile of the Kempton transect............................. 140 Figure 53 Groundwater and salinity information at the Oatlands site ................... 147

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List of Tables Table 1 The geographical extent and response time of local, intermediate and regional scale GFSs.......................................................................................... 30 Table 2 Impact on land assets ................................................................................. 58 Table 3 Impact on surface and groundwater assets ................................................ 59 Table 4 Overall GFS prioritisation ............................................................................ 60 Table 5 Summary: Relevance of Management Option to Each GFS..................... 103 Table 6 Estimated likely area of salinity within each GFS unit (modified from Bastick & Walker 2000) ............................................................................................... 107 Table 7 Costs of groundwater monitoring ............................................................. 117 Table 8 Method of groundwater monitoring for Local GFS (from Coram, Dyson and Evans 2001).................................................................................................... 118 Table 9 Recomended bore distribution for GFS in the study area ........................ 121 Table 10 Depth to water level and groundwater salinity of the Richmond transect ........................................................................................................................ 133 Table 11 Depth to water level and groundwater salinity of the Kempton transect 140 Table 12 Depth to water level and groundwater salinity of the Oatlands site ....... 147

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1

Introduction

The project aimed to develop an understanding of the Groundwater Flow System (GFSs) and processes causing, or likely to cause, salinity within the National Action Plan for Salinity and Water Quality (NAP) parts of the Southern Midlands and Clarence municipalities (Figure 1). The key objectives were to: •

Advance the understanding of the groundwater processes driving salinity so the joint NAP working group can determine the priority locations and management options for investment of future funding and determine where research and development needs are required to better target investment.

•

Develop recommendations on where to establish target indicator reference sites, so that real environmental change can be measured.

•

Identify those assets (natural and economic) which are under threat from salinity

•

Identify potential management strategies to address the salinity issue.

The improved understanding is critical for prioritising and implementing strategic action to address salinity within the study area. There is currently a lack of detailed baseline information to prioritise action for addressing salinity degradation in Tasmania. Consequently, it is difficult to identify the locations where effective work must be done. Indeed, the National Land and Water Audit 2000 (Coram et al. 2001) established that in order to effectively manage salinity it is essential that the major GFSs involved in the salinisation process are identified, described and prioritised. A GFS is a landscape entity that includes all aspects of a single groundwater flow path. It is a fundamental unit that needs to be considered when management options for dryland salinity control are being selected. GFSs characterise similar landscapes in which similar groundwater processes contribute to similar salinity issues, and where similar management options apply. The GFSs classification approach is used as the analytical framework for salinity and water management strategies to determine the location, type and priority for investment in management of land, water, vegetation and infrastructure assets.

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Figure 1 Location of the NAP parts of the Southern Midlands and Clarence municipalities, the “study area”

The objectives of the project will be achieved through: •

Determining the range of GFSs operating within the study area.

•

Identifying the major GFS that is having the largest influence on salinity within the priority study area.

•

Developing conceptual models of the processes involved, based on the identified GFS and the land management systems operating in the study area.

•

Undertake strategic groundwater drilling to provide initial field checking of the ‘conceptual’ models.

•

Identify potential management (on-ground and planning) strategies.

The project will also collect baseline data and identify key groundwater reference sites within the priority area to assist with the establishment of resource condition targets and condition trend reporting.

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This priority action project was developed as a stand-alone 12-month project with ambitious outcomes. Whilst the project has developed and tested initial conceptual models of GFSs and processes operating in the study area, one of the outcomes will be an identification of future activities needed to: •

further develop and verify the conceptual models

•

assist the regional Natural Resource Management (NRM) committees to establish and monitor resource condition targets relating to salinity.

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2

Groundwater Flow System framework and application

2.1

Groundwater Flow System framework

The Groundwater Flow System (GFS) framework is simply a method of dividing regions into areas that have similar geological and geomorphic features that define similar groundwater systems. The approach allows for specific consideration of salinity issues and the options for their management on the basis of an understanding of local landscape and groundwater conditions. The application of the GFS framework to salinity management in parts of Southern Midlands and Clarence municipalities of Tasmania has involved a review of landscapes and groundwater systems occurring throughout the region. This was completed through a series of workshops and field visits that brought together a range of salinity and groundwater specialists that have worked throughout the region over many years (Figure 2). Increased understanding of the salinity processes occurring in each part of the region was realised through discussion and consensus among the expert group. This knowledge base was supported by: •

limited research and investigations conducted throughout the region to date

•

relevant knowledge established through similar work in other regions of south-eastern Australia

•

earlier efforts in developing the statewide scale GFS framework under the auspices of the Department of Primary Industry Water and Environment and Mineral Resources Tasmania (Latinovic, et al. 2003).

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Figure 2 Communication process of GFS project

2.2

A rationale for salinity management

Salinity management means different things to different people. In agricultural terms the main concern lies with sustaining production from soils and continued access to water of sufficient quality to maintain farm production.

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To water resource managers, salinity management focuses on protecting the quality of water resources and streams in order to maintain the beneficial uses of water for downstream users. For those concerned with attaining and sustaining biodiversity, salinity management is a matter of protecting natural ecosystems from salinity damage, and for those that manage assets in cities and towns it is a matter of avoiding damage to infrastructure. Salinity management, thus, focuses on the protection of four major assets: •

soils important to sustained agricultural production

•

water resources important to agricultural users and downstream catchment communities

•

ecosystems important in sustaining biodiversity (terrestrial and aquatic)

•

built infrastructure important to the quality of urban environments and the ability to service rural business and residents.

In most instances increasing salinity is not an easy issue to manage, and protection of the four major assets indicated above requires careful consideration. In most instances salinity results from changes in the water balance of catchments initiated more than a hundred years ago. Elevated groundwater established within most catchments over such long periods of time now feed salinity issues in the lower landscape. Saline groundwater discharge areas continue to be ‘fuelled’ by groundwater flow from higher levels in the catchment. The extent to which groundwater systems can be managed depends to great extent on the scale at which they operate. 2.3

Can salinity be managed by reducing groundwater recharge?

In short, the reduction of groundwater recharge over a catchment provides a long-term solution to salinity control. The timeframe between groundwater recharge reduction and salinity control/elimination is a function of the scale and responsiveness of the GFSs of the catchment. Local (small) scale Groundwater Flow Systems

Salinity can be managed through recharge reduction where the size of the catchment contributing saline groundwater to discharge is small (local groundwater systems) and the groundwater system is sufficiently transmissive to allow the watertable to recede via

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groundwater flow following treatment. The hydraulic head provided by elevated groundwater in the catchment must be sufficiently reduced before a salinity benefit will be realised. In most local scale GFSs the distance between areas of groundwater recharge and areas of groundwater discharge will not exceed five kilometres, and the size of the catchments will not exceed two thousand hectares. Where effective strategies can be implemented that realise sufficient recharge reduction, treatments may realise a salinity benefit within a timeframe of less than twenty years. Intermediate (larger) scale Groundwater Flow Systems

In larger systems groundwater may flow over distances ranging from five to fifty kilometres sustaining salinity lower in the catchment. The catchments of such groundwater systems may exceed twenty thousand hectares. Where salinity process occurs on this scale it is very unlikely that they can be managed by recharge reduction. The scale of change required to produce a shift in the water balance is extremely large, and established hydraulic conditions will prevail well into the future irrespective of intervention. Salinity management in intermediate scale GFSs will in most instances focus on engineering strategies to protect important assets and adaptation to saline conditions. Fortunately there are few areas in the Southern Midlands that have salinity driven by intermediate scale GFSs, although groundwater discharge from higher flatter areas of dolerite, basalt and fractured rocks may fall within this class. Regional scale Groundwater Flow Systems

In very large regional scale GFSs the distance between groundwater recharge and groundwater areas exceeds fifty kilometres. The catchments of such groundwater system are immense and there can be little opportunity to control existing or potential salinity issues through recharge management strategies. The most appropriate strategies will involve engineering approaches that focus on protecting high value assets, and adaptation to saline land. The only regional scale GFS in the study area of the Midlands is the large alluvial plains system in the Longford Basin located in the northern parts of the Southern Midlands, and has limited impacts on groundwater processes in this region, for further information refer to Hocking et al. (2005). 7


2.4

Management responses

It is clear from the previous discussion that salinity management will not always equate with salinity mitigation. That is, it is not always possible to implement local land management strategies that will overcome existing salinity issues within a reasonable timeframe, nor lessen the risk of salinity occurring in the future (Figure 3). In some regions, particularly those comprising larger groundwater systems, engineering approaches together with adaptation to salinity will be a more appropriate response to asset protection. Three potential outcomes are now recognised for saline land management in southern Australia, these are: •

Fix – An appropriate goal where salinity issues occur within small GFSs sufficiently responsive to realise restoration and protection of assets in a reasonable timeframe through manipulation of catchment water balances.

•

Avoid – Appropriate where salinity issues occur within groundwater systems not sufficiently responsive to realise the restoration of assets affected by salinity within a reasonable timeframe, but avoidance of the onset of future salinity may be possible through manipulation of catchment water balances.

•

Adapt – Appropriate within GFSs that are unlikely to be responsive within a reasonable timeframe, and where existing processes are likely to produce additional future salinity irrespective of any manipulation of catchment water balances.

Figure 3 Saline soils currently impacting on production (lower right) with limited options for eliminating by management

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2.5

Forms of intervention

Three forms of intervention apply in considering salinity management. Each of these need consideration in the context of the three outcomes outlined above. They include:

2.6

•

Biological management of groundwater recharge – Adoption of various forms of vegetation that allow for greater use of rainfall and irrigation water and allow less surface water to percolate beyond the root zone.

•

Engineering approaches to watertable management – Manipulation of the water balance by means other than vegetation, typically though drainage and groundwater pumping. This is most commonly applied where assets require immediate protection not afforded by other means, or where there are opportunities to realise groundwater for productive purposes.

•

Saline enterprises – Adoption of saline enterprises and ecosystems to realise benefits from otherwise degraded land.

Biological management (vegetation) of groundwater recharge

Biological management of groundwater recharge was commonly recommended for salinity management of land and water in Australia during the late 1980s. To a large extent plans focused on farming systems that delivered an increase in agricultural production through improvements in vegetative water use. This philosophy focused largely upon reduction of groundwater recharge. Realising salinity management through improved water use and at the same time increasing agricultural production seemed at the time to be almost too good to be true. Indeed more detailed research over recent years has demonstrated that the opportunities to achieve this are far more limited than previously understood. The difficulty with biological management of recharge in salinity management is that it is limited by both climate and the inherent nature of GFSs. Perennial vegetation in comparison to annual pastures, for example, afford little opportunity for recharge reduction where annual rainfall exceeds 600 mm in southern mainland Australia (Clifton and Taylor, 1996). Equally, in poorly permeable groundwater systems and large regional groundwater systems the time required for landscapes to equilibrate is so long that such strategies are unlikely to produce salinity benefits within a timeframe acceptable to most investors and stakeholders. Biological management of recharge provides the best option for salinity management in moderately permeable responsive local scale GFSs where average annual rainfall is less than

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600 mm. Above this annual rainfall, strategic tree planting is a better option either on distinct recharge areas, or over breaks-of-slope in perched groundwater where there are opportunities for groundwater interception may exist. Where cropping is practised, improved irrigation through continuous cropping with no fallow period will reduce recharge upon the site. Scheduling of irrigation under cropping is important to limit excess recharge. Conventional surface drainage is seldom an efficient option, however sub surface drainage may be a viable option. 2.7

Engineering strategies

Engineering strategies afford options for salinity management where either drainage or groundwater pumping can be deployed to lower the watertable. Surface drainage, however, is seldom an efficient option since in most instances the removal of excessive surface water alone is not sufficient to realise a significant salinity benefit (Figure 4).

Figure 4 Saline scald adjacent to an ineffective surface drain installed for salinity management

Groundwater pumping affords greater benefits for salinity management where the volume of water removed is significant in terms of the volume held within the catchment/groundwater system. Pumping may also be a favourable option where it promises the protection of high value assets, or where water abstracted is of sufficient quality to be used for productive purposes.

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Options for groundwater pumping are limited by the inherent properties of groundwater systems. Pumping is only an option where the groundwater system comprises an aquifer of sufficient permeability to afford the desired volume of groundwater extraction, and groundwater salinity is relatively low. Pumping rates do not have to be high if the catchment/groundwater system is local. In many local scale GFSs low volume groundwater pumping is often possible. Opportunities for high volume groundwater pumping for salinity mitigation in the Southern Midlands are fairly limited. Many local scale GFSs are comprised of moderately high salinity groundwater and fairly poor yielding aquifers. Here the water quality is not useful for irrigation but some waters maybe useful for stock watering.

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2.8

Saline enterprises (living with salinity)

The average rainfall over the agricultural areas of the Southern Midlands varies from less than 500 mm to over 800 mm per annum. The options for vegetating saline land in the wetter parts of the study area are many and varied, and include planting species such as Puccinellia, fescue grasses, strawberry clover, etc. Saline enterprises may also include the use of break-of-slope plantations in GFSs that comprise perched aquifers. These have yet to be used to any significant extent in Tasmania but there could be potential to use this technique. Saline enterprises may also include opportunities for realising production from saline groundwater. In general it would seem that there are opportunities for greater utilisation of the generally low salinity groundwater causing many of the current salinity problems. There appears to be much room for a more entrepreneurial approach to the development of saline enterprises.

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3

Physical characteristics of the Southern Midlands

3.1

Geology

The geology of the study area can be simplified and divided into a number of major geological units: Igneous rocks

• •

Tertiary basalt – in-filled valleys in areas such as Lemont and Campania Jurassic dolerite – intruded mainly into Triassic rocks

Sedimentary rocks

• •

Triassic rocks –exposed throughout the study area Permian rocks – mainly in the west, but throughout the study area

Unconsolidated rocks

•

Quaternary and Tertiary rocks – in-filled valleys

Figure 5 presents the simplified geology layer developed for the study area.

Figure 5 Geology of parts of the Southern Midlands & Clarence Municipalities

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3.2

Landscape development (geomorphology) of the Southern Midlands

Within the study area landscape forming processes have been complex with various stages of geological uplift, intrusion and dissection. It has involved periods of geological uplift, igneous rock intrusion, sedimentation over extensive areas, and at times considerable dissection. Scanlon, Fish and Yaxley (1990) provide a detailed description of the geological development of Tasmania. The oldest rocks in Tasmania are estimated to be up to 1 000 000 million years old. Permian/Triassic sandstone/mudstone geology was deposited throughout the majority of the region 200 million years ago. However, like areas to the north, considerable geological movement prior to 160 million years ago triggered widespread intrusion of dolerite. The intrusion of the dolerite into the landscape around 400 million years ago caused frequent and violent earthquakes with large horst/graben structures found between 200 and 150 million years in age (Leaman, 2002). Volcanic basalt flows occurred around 21-36 million years ago in numerous areas scattered throughout the region. The most extensive surface basalt features are apparent at Campania and Lemont. In the past 20 million years the landscape in the study area appears to have been relatively stable as there is little evidence of geomorphic activity of erosion and deposition. The degree of existing stream dissection suggests significant down cutting of river systems. Towards the lower parts of the Prosser and Little Swanport catchments limited/no floodplain has developed, however lower in the Jordan and Coal river valleys the floodplain is much more extensive. Some marine incursion (of up to 25 metres) into the lower Coal River valley may have occurred. Murray-Wallace & Goede (1995) suggest the lower reaches of the Coal River valley may have experienced a highly saline environment, and in doing so high salt stores within the strata are likely. Also the relatively low elevation of the lower Coal River would suggest a lower groundwater gradient between the area and sea level, and therefore an inherently ‘natural’ shallow watertable.

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3.3

Climate

The Southern Midlands region of Tasmania has a relativity consistent rainfall, but with considerable seasonality. Figure 6 presents mean annual rainfall over the Southern Midlands.

(mm)

Figure 6 Mean annual rainfall of the Southern Midlands

As the spatial distribution of rainfall varies, the amount of groundwater recharge also varies. The following sections present mean monthly rainfall, pan evaporation and monthly cumulative residual rainfall at Oatlands, Mowbray and Hobart. Oatlands

Rainfall information at Oatlands (Figure 7) shows monthly rainfall volumes are relatively consistent throughout the year. Pan evaporation, however, varies considerably across seasons. As a result between the months of May and August is the most likely period where groundwater recharge would occur in the area.

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Monthly rainfall

Monthly evaporation

250

Volume (mm)

200

150

100

Main groundwater recharge period

50

0 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

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Figure 7 Monthly average rainfall and evaporation information at Oatlands (source: BOM 2004a)

Cumulative residual rainfall information suggests there has been a strongly decreasing trend in monthly rainfall since 1977 at Oatlands. This overall reduction in monthly rainfall is likely to be reflected in an overall lowering of the watertable in the region. 1500

Rainfall (mm)

Oatlands

Residual rainfall (mm)

Volume (mm)

1000

500

Jan-05

Jan-04

Jan-03

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Jan-01

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0

-500

-1000

-1500

Figure 8 Cumulative residual rainfall information at Oatlands (source: BOM 2004a) 16


Melton Mowbray

Average monthly rainfall information at Melton Mowbray suggests little variation in rainfall throughout the year, but a significant variation in evaporation (Figure 9). This variation in evaporation would suggest the greatest potential for groundwater recharge to occur between the months of May to August. Monthly rainfall

Monthly evaporation

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Figure 9 Monthly average rainfall and evaporation information at Melton Mowbray (source BOM 2004b)

A slightly falling trend is apparent in the residual rainfall information (Figure 10), suggesting the average rainfall since 1977 has been slightly less than average.

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Figure 10 Cumulative residual rainfall information at Melton Mowbray (source: BOM 2004b) Hobart

Rainfall information at Hobart airport (Figure 11) shows monthly rainfall volumes are relatively consistent throughout the year. Pan evaporation varies considerably between the months of June and August, therefore this is the most likely period where groundwater recharge would occur. The cumulative residual rainfall information suggests there has been a decreasing trend in monthly rainfall since 1977 at Hobart (Figure 11). This overall reduction in monthly rainfall is likely to also reflect a slight lowering of the watertable in the region in this period.

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Figure 12 Cumulative residual rainfall information at Hobart (source: BOM 2004c)

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Summary

The majority of groundwater recharge within the Southern Midlands occurs between May and August where monthly rainfall volume is high and evaporation is low. While short-term high intensity rainfall events can result in groundwater recharge, annually the months of May to August would appear to contribute the greatest recharge volumes. Residual rainfall data at all three climate stations are falling to various degrees, which is likely to result in a net downward trend in groundwater levels to various degrees. On balance, the post 1977 shift toward a drier climate may have alleviated some salinity risk in the region. The rate of groundwater rise may have lessened and the extent to which saline groundwater discharge now occurs may be an artefact of this phenomenon. The lack of long term groundwater data, however, makes any firm conclusion somewhat problematic.

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4

Salinity in the Southern Midlands

4.1

Introduction

Salinity occurs throughout the study area (the NAP parts of Southern Midlands and Clarence municipalities) in the same way that it does throughout most of southern Australia. Some land salinity has occurred in the study area prior to European settlement (primary salinity), and some has become apparent following European settlement (secondary salinity), the area and dominance of primary versus secondary salinity is unclear. Primary salinity refers to salinity that occurred in the landscape prior to land clearance. The processes of secondary salinity occurs from a change in the water balance brought about by the removal of native vegetation, and the development of agriculture, urban and irrigation areas, this causes a rise in the watertable and salinity to occur or add to the area of primary salinity. A general decrease in the amount of water used by vegetation under agricultural and urban landscapes compared with native vegetation allows more seasonal rainfall to seep downward below the root zone of plants adding to the volume of the groundwater. Additional water may be added where irrigation (rural and urban watering) is practised. As the watertable rises groundwater flow down the landscape increases, causing an increase in groundwater discharge to streams and low lying areas. This process continues ultimately until the increase in groundwater recharge is offset by an equivalent increase in groundwater discharge. Rising groundwater can remobilise salt stores in the unsaturated zone, this increases the groundwater salinity. When the groundwater comes within the capillary zone at the soil surface (usually < 2 metres) evaporation draws water to the surface and concentrates salt. The salinity of the emerging groundwater alone is usually sufficiently high to cause new salinity, but in some instances concentration further by evaporation can also be a significant factor. 4.2

Landscapes and groundwater flow systems

Salinity can be described in generic terms as an increase in saline groundwater discharge occurring in response to an increase in groundwater recharge resulting from changes in land use and land management. In practice, however, the processes causing salinity vary from place to place in relation with the geology and geomorphology.

21


Geological and geomorphic factors govern: •

Where and how groundwater recharge will occur within a catchment or sub catchment.

•

The length of time for likely to elapse before salinity will occur following changes in land use or land management.

•

The mass of salt stored within the landscape and the salinity of groundwater.

•

The risk of future salinity occurring in the future.

•

The most appropriate options for treating salinity.

•

How quickly groundwater systems and salinity issues will respond to various treatment strategies.

4.3

Historical salinity

Historical salinity (also known as primary salinity) refers to salinity occurring in the landscape prior to European settlement. Several areas are known to have experienced primary salinity (pre-European), such as in the Tunbridge area which features a number of salt lakes and pans, several of which were harvested for salt for human use in the early days of European settlement. Today it is difficult to define primary versus secondary salinity as long term records are not available to indicate whether salinity has changed over time. 4.4

Current salinity

Land

The project area has an area of approximately 275 000 hectares (DPIWE 2003). Some 148 000 hectares of this has been developed for agriculture and urban uses, and approximately 4400 hectares (~3%) is currently thought to be affected by salinity (DPIWE 2003). The project area accounts for 40 % of the land thought to contain salinity in the Southern NRM (Natural Resource Management) region and 6% of the land thought to contain salinity in Tasmania. Within the project area the landscapes vary from mountain ranges and very hilly terrain to areas of flat arable land. Currently the main expressions of salinity are found on the flatter terrain and valley floors. As a result, the current impacts are generally within the most versatile and agriculturally valuable land (mostly land capability class 4). For example, Finnigan (1995)

22


found approximately 1640 hectares of saline land in the Coal River Valley Irrigation Area, the majority of which is dryland salinity on the flatter, better land in the valley. Within the project area, at present it is unclear whether the extent of salinity is increasing or decreasing. However, if salinity increases in the future it is likely that the majority will affect more agriculturally productive land. Groundwater

The National Land and Water Resources Audit (Bastick & Walker 2000) reports that much of the groundwater within the project area has elevated salinity. The same report suggests that there is insufficient quantitative information available to suggest whether this groundwater is rising or falling. While the understanding of groundwater processes have been improved in parts of the project area through studies by Dell (2000) and Grose (2003) and a current study by Clarence City Council (Lisson, Hardie & Khan, 2005 in prep), the understanding of broad scale processes is poorly understood. Surface water

The project area includes all or significant parts of the Coal River, Jordan River, and the Little Swanport River catchments. Elevated salinities have been reported for the Coal River and Jordan River (Wilson & Foley 2003) suggesting that many of the main rivers in the project area are either naturally high in salinity or have been impacted by secondary salinity. Ecological assets

Native vegetation flora, fauna, wetlands and water bodies can be potentially impacted by changes in salinity. The project area contains many rare, endangered and vulnerable species and ecosystems, as well as many aquatic and wetland ecosystems (including the Ramsar listed Pittwater-Orielton Lagoon in the estuary of the Coal River catchment). Little is known of the current impact of salinity on these assets. Infrastructure

Shallow saline groundwater is known to affect built infrastructure, particularly roads, building foundations, sporting and recreational facilities, and underground services. Some peri-urban areas within the project boundaries may contain areas with saline groundwater, saline seeps and

23


scalds. No studies are known which have tried to measure the current impacts and potential threats to infrastructure in the project area. 4.5

Threatening processes

Based on the current understanding of the extent of land and water salinity, large areas within the project area appear to have significant salt stores. This salt would comprise a significant threat if it were mobilised through changes in the water balance due to changes in climatic influences (periods of excessive rainfall) or through changes in land use or land management. Therefore, a significant salinity hazard exists within the project area. The extent to which it is realised, however, is likely to depend upon medium-term (perhaps decadal) climatic influences, and past and present changes in land management. Clearly, in the latter case, the shift from dryland agriculture to irrigated agriculture is one factor that might initiate sufficient change in the water balance to realise a salinity threat. This statement is not made with the intention of prohibiting future development—it simply underlines the need for adequate investment in the design of production systems that minimise the risk. Land use change

Since European settlement much of the study area has been converted from natural vegetation (forest, open woodland and native grassy plains) to agricultural (pasture production, cropping and irrigation) and urban land uses. Land use is currently dominated by agricultural uses and native pasture (Figure 13).

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Figure 13 Land use of the study area as at February 2002 (source: BRS 2002) 60 50

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Figure 14 Land use area estimates of the study area as at February 2002 (source: BRS 2002)

25


Over the last 25 years there has been an expansion in cropping and irrigation, but the amount of land used for cropping (which includes irrigated cropping) is still a small percentage of the overall land use. Not represented in these figures is the amount of native vegetation affected by tree decline, which is a significant issue within the project area. The main land use drivers that may be affecting the water balance are therefore likely to be conversion of land to grazing and tree decline. The extent of the impact of these changes is not well understood. Whilst the regional water balance may not be affected to any great extent by local changes in land use or land management, there is considerable potential for local salinity issues to occur in the immediate vicinity of areas in which a new water balance has been imposed through local changes in land use or management such as irrigated cropping. The extent to which land use change may impose salinity on the land of the Southern Midlands is by necessity implied from observations elsewhere in southern Australia. Little local/regional information is currently available to assert with any great confidence the water balance of agricultural landscapes. The extent to which the water balance has changed post-agricultural development also remains largely unknown. Climate

Consistent with other regions in southern Australia, it is apparent from climatic records that the region has experienced a decreasing rainfall trend over the past 20 years. The relationship between groundwater recharge and climate is not well understood. In common with most regions that experience cool wet winters of high rainfall together with hot dry summers, there are indications that recharge occurs in response to seasonal soil saturation in late winter. Whether this occurs under the normal seasonal climatic circumstances, or whether it is imposed episodically in years of higher than average winter rainfall remains largely unknown. The rainfall ranges from just over 800 mm of annual rainfall in the north to below 500 mm. In dryland land management systems the main input of water into the hydrological systems comes from the net effect of rainfall and evapotranspiration. If rainfall exceeds

26


evapotranspiration, soils become waterlogged and potentially there is excess water available to drain below the root zone and mobilise any salt stores present. Ultimately this mobilisation is expressed as increased saline discharge. In higher rainfall zones (above 800 mm) this deep drainage generally has already removed all salt stores and freshwater discharges are more the norm. In regions of below 800 mm annual rainfall there is potentially some deep drainage but depending on the type of vegetative cover (land use), salt accumulates to varying degrees in the soil and regolith. Changes in the type of vegetative cover affect the amount of deep drainage and the potential for changes in hydrological balance. Therefore most of the study area experiences a climate which has allowed net accumulation of salt but also a climate where disturbances in water balance can drive salinity. Analysis of the historical rainfall records areas in and around the study area (refer to page 15) indicates that that for Oatlands and Hobart rainfall since about 1977 has been declining while around Mowbray the rainfall has been relatively steady. This means that in the areas where rainfall has declined there has been a reduction in rainfall available to fuel deep drainage and possibly the salinisation process. Counterbalancing this decline in deep drainage potential however is a potential increase in deep drainage due to reduced water use as land has been converted to introduced pastures, cropping, irrigation and urban land uses. Modelling work is needed to determine the net effect of reducing rainfall and land use change. It is likely that in the Mowbray-Kempton area where rainfall has remained steady over the last 30 years, there is notable land use change and the greatest potential for the expression of salinity to increase in the short-term.

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5

Groundwater Flow Systems in the Southern Midlands

5.1

Introduction

Like many other regions across Australia, parts of the Southern Midlands & Clarence Municipalities comprise a number of differing geological and geomorphic conditions. Within the study area of this project nine GFSs have been defined. The GFS framework was initially developed under the National Land and Water Resources Audit during the late 1990s. GFSs are defined on the basis of geological and geomorphic criteria that capture the essential understanding of landscape-groundwater interactions functioning in each distinct hydrogeological province within a particular catchment or region. In most instances a GFS will include all parts of the groundwater catchment that contribute to a salinity issue. The spatial definition of the GFS will include all areas down the flow path from zones of groundwater recharge through to zones of groundwater discharge. GFSs are essentially areas that are alike in their geological and geomorphic character. This causes them to have similar groundwater systems and similar salinity issues. The similarity of salinity issues is likely to be greater where rainfall conditions are equivalent. In Tasmania there is ample evidence to indicate that the salinity of the groundwater in any one type of GFS is inversely related to the magnitude of the average yearly rainfall. This understanding affords the opportunity to disaggregate catchments into component landscape-groundwater entities on the basis of hydrogeological and geomorphic processes contributing to salinity. The close spatial variability of the geology in parts of Tasmania may enable sequential flow of groundwater from one GFS to another. Thus the groundwater of one system may inherit water characteristics of another and this water may flow into yet another GFS and so on. This understanding of landscape-groundwater interactions can be encapsulated within conceptual models and their distribution depicted spatially in the form of GFS maps. The resultant map base together with the understanding of hydrologic and hydrogeological function affords the opportunity for consideration of the most appropriate options for salinity management. Conceptual models of groundwater behaviour are defined through consideration of a wide range of knowledge and information. The fundamental understanding of groundwater systems 28


consistent with the geological and geomorphic make-up of landscapes is usually well known to most local scientists. These people are able to draw upon their previous investigations and experiences to support the development of the GFS framework. At the same time they are able to accommodate additional new knowledge realised from similar areas with similar GFSs found elsewhere in Australia. The technical process of defining conceptual models also requires the assembly of a database defining the key biophysical and hydrogeological attributes of each GFS. The attributes include the hydraulic characteristics of groundwater systems, the climate of the regions in which the GFS occurs, the spatial and temporal distribution of groundwater recharge, the geomorphic character of the land, the most common forms of land use and land management, the salinity of soils and groundwater, and so on. GFSs can be grouped according to scale into three units: local, intermediate and regional (Coram et. al. 2001) as depicted in Figure 15. The description of each GFS allows for consideration of salinity treatment options. In a broad sense this might include where in the landscape works should occur. For example this might extend to a consideration of whether hilltop or valley floor treatments are most appropriate. Equally consideration of appropriate management options will extend to what should be undertaken, for example, whether perennial vegetation, trees, drainage, or groundwater pumping might be appropriate. The construction of conceptual models of groundwater behaviour extends to consideration of the scale of groundwater flow. It is understood that the options available for salinity management will be different in the larger less responsive ‘regional’ groundwater systems compared with much smaller ‘local’ groundwater systems. In most instances the larger regional scale GFSs will continue to produce salinity in ‘down-basin’ areas irrespective of any recharge mitigation. In local scale GFSs the volume of groundwater held within the GFS is much smaller and there are opportunities for a watertable to recede in response to biological reduction of groundwater recharge. Even in some local scale GFSs, however, the time required to realise a salinity response from the implementation of recharge reduction works may be quite long. This is

29


certainly true where the GFS comprises ‘sluggish’ materials that have low hydraulic conductance. GFSs have been grouped into local, intermediate and regional classes on the basis of scale of groundwater flow (Table 1), and the consequential understanding of salinity responses. The GFS relief unit (high or low) attempts to describe the landscape of the unit. For example, a low relief GFS describes a relatively flat landscape, whereas a high relief GFS describes a moderate to steep landscape, located high in the landscape. Table 1 The geographical extent and response time of local, intermediate and regional scale GFSs

Category Local Intermediate Regional

Length of flow (km) 50

Response time (yr) 100

Local GFS 50 km

Figure 15 Simplified extent of local, intermediate and regional scale GFSs

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5.2

Identifying and mapping Groundwater Flow Systems

GFSs are identified on the basis of geological and geomorphic attributes, these together with soils, climate and vegetation define salinity provinces in which inherent catchment processes contribute to dryland salinity. The taxonomy ascribed to each GFS conveys a sense of the scale of flow, and a sense of the nature of the main aquifers and terrain types. The GFS classifications produced during this project builds on an earlier statewide assessment (Latinovic et al. 2003) (Figure 16). The most detailed scale geological data was used wherever possible to provide the greatest accuracy. Figure 17 illustrates the differing scales of geology mapping used for identifying the GFSs throughout the Southern Midlands. The scale of geological mapping varies from 1:25 000 to 1:250 000 with the most common maps presented at 1:50 000. This variation in scale within the available geological base prevented the development of a unique GFS classification valid at a unique scale. Geological information from all maps sheets was assessed and aggregated into representative geological units. The simplified geological classification was further classified on the basis of slope characteristics. Field inspections followed to ascertain relief classes for each GFS. Figure 18 presents the GFS layer developed for the Southern Midlands. For more a detailed GFS map at 1:100 000 refer to Lynch, Hocking and Brown (2005).

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Figure 16 Statewide GFS layer developed by Latinovic et al. (2003)

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Figure 17 Differing scale geology map sheets used in the development of the Southern Midlands GFS layer (k refers to 1 000)

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Figure 18 GFS layer of the Southern Midlands and Clarence municipal areas (refer to Lynch, Hocking and Brown, 2005 for a 1:100 000 GIS map of the GFS)

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5.3

Conceptual models

The development of the GFS classification within the study area was achieved through a number of technical workshops involving landscape experts from throughout Tasmania and achieved via process depicted by Figure 2. These people are identified in the acknowledgments section of this report. The technical group identified nine GFSs functioning throughout the region. This was achieved through consideration of the collective understanding of hydrogeological processes functioning within distinct geological and geomorphic provinces. Conceptual models of landscape-groundwater behaviour were defined on the basis of experience within Tasmania and elsewhere. The suite of landscape-groundwater models resulting from this process were then spatially defined (mapped) according to a rule based system applied within a geographic systems environment. GFS were, thus, defined using an ‘expert’ systems approach. The process was consistent with that used to define the GFS framework elsewhere in Australia. The scale of groundwater flow is represented by terms that include ‘local’, ‘intermediate’ and ‘regional’ (Coram et al. 2001). Each of these classes are broadly defined as follows: •

Local scale GFSs – function within local sub catchments over distances seldom greater than five kilometres.

•

Intermediate scale GFSs – function over larger (sub-regional) scales over distances that typically range from ten to fifty kilometres.

•

Regional scale GFSs – function at large scales over distances in excess of fifty kilometres.

The scale of groundwater flow is a measure of the capacity to intervene in salinity through biological mitigation of groundwater recharge. This option is generally restricted to responsive local systems.

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Local scale GFS on alluvial plains and slopes Overview

The alluvial plains and slopes GFS of the region comprise alluvial terraces and neighbouring low angle slopes. The areas of this GFS contain a complex combination of mapped geology comprising predominantly tertiary rocks plus some quaternary rocks. Some are deeply weathered, some comprise sand and gravel units, whilst others are largely clay based. The tertiary rocks are thought to contain much of the salt stores and some of these can be relatively elevated in the landscape in some locations. The Coal Valley areas are considered to be geologically different from polygons in the northern part of the study area. Tertiary rocks in the Coal Valley are predominantly clays whereas in northern river valleys, rocks are quaternary sands and contain less salt stores. The terraces and slopes and their geomorphic character are well known throughout the region largely because they define land systems that vary significantly in terms of soils, hydrology and agricultural production. The alluvial plains and slopes GFS represents the penultimate floodplain to the modern day floodplain. Variations in terrace geomorphology produce sympathetic differences in hydrogeological performance. The terraces present a suite of small groundwater systems, and each of these has a somewhat unique character in the context of inherent processes contributing to salinity. Prior streams existing beneath the land surface provide a mechanism for water transport and discharge into streams. This GFS is the most complex in the region. The complexity of this GFS means that some map polygons contain quaternary rocks, particularly in northern river valleys, that would be mapped as a different GFS if mapped at a finer scale. Within the southern region saline expression is most common observed on the alluvial plains.

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Typical locations

Coal Valley, Cambridge, Bridgewater, Tea Tree and Lower Jordan Valley

Figure 19 Simplified cross-section of a local flow system in alluvial plains and slopes Salinity processes

Groundwater processes within the alluvial plains and slopes GFS are considered to be predominantly localised but limited information is available to be definitive about intermediate distance drivers. Older geology (dolerite and Triassic rocks) neighbouring this GFS are a source of recharge water and salt that emanates at break of slope positions where water is discharging. Discharge sites and salinity in lower slope positions ie flatter areas, is driven by recharge from several sources including neighbouring older geology ,nearby low slopes and pockets of isolated topographic confinement. Salinity can occur in topographic depressions, high on ridges or on low topographic rises. Evaporation of low salinity groundwater in flat waterlogged areas causes soil salinity in numerous locations scatted throughout the landscape, particularly at the breakof-slope and in low-lying areas. Some drainage lines contain discharges of salt but others may not. In conjunction with the localised groundwater processes, the alluvial plains and slopes GFS may also receive groundwater from adjacent groundwater systems, such as where a steep groundwater gradient occurs from a hill to a valley floor. In this GFS groundwater discharge is likely to occur in the valley floor or at the break-of-slope (Figure 20). 37


Groundwater discharge

Figure 20 Groundwater discharge from the local scale GFS in alluvial plains and slopes (Upper Coal River catchment)

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Local scale GFS on current floodplain Overview

The GFS defined as current floodplain refers to the lowermost modern day floodplain adjacent to active rivers. The width and elevation of the GFS unit varies according to the size and position in the catchment. In general, the size of the current floodplain GFS increases downcatchment as flooding frequency and intensity is likely to increase. The geology is predominantly quaternary rocks. Changes in catchment hydrology influenced the form and composition of the GFS. A gradual decline in rainfall in the Quaternary period effectively choked the waterways of the region. The reduction in surface runoff has caused the narrowing of rivers by rock infilling. The composition of the in-filled rocks vary considerably depending on up-catchment rock source, and are generally composed of coarse gravels and sand. The current floodplain GFS provides a linkage between the large rivers of the region and groundwater. High hydraulic conductivity of the GFS provides a hydrologic buffer between surface and groundwater processes. The GFS is recharged by both regional groundwater movement and also by groundwater-surface water interactions, generally during times of high flow or flood. Typical locations

Coal River floodplain

Figure 21 Simplified cross-section of a local flow system in the current floodplain

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Salinity processes

The current floodplain GFS can provide a linkage between perennial rivers and groundwater. In other areas there are no groundwater surface water interactions. Groundwater recharge can be provided by groundwater inflow, direct rainfall or via the adjacent river during times of higher than ‘average’ flow. Dissected drainage lines allow water table draw-down from adjacent groundwater. Groundwater discharge is delivered to the adjacent river when the groundwater level is above the height of the river. There are some areas of local topographic depressions where surface water is retained resulting in poorly drained areas with elevated salinity. Likewise when the GFS water level is higher than the surrounding GFS (i.e. alluvial plains and slopes GFS) groundwater is discharged into the adjacent aquifer. The water level of the current floodplain GFS is generally defined by the height of the adjacent river, and visa versa (Figure 22). The occurrence of groundwater discharge at the soil surface on this GFS is unlikely as the relatively high hydraulic conductivity of the unit causes the watertable to be very flat. Groundwater discharge is likely to occur directly into streams rather than as land salinisation, this is an important GFS when attempting to reduce catchment salt load export. Figure 23 presents the Coal River at Richmond on the GFS.

Figure 22 Groundwater-surface water interaction in the current floodplain GFS 40


Figure 23 Current floodplain GFS of the Coal River at Richmond

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Local scale GFS in Dunes Overview

Irregular east to west trending windblown sand dunes in the Quaternary (eg. past 2 million years) developed during cyclically dry and cold periods. During these times vegetation growth was minimal and allowed aeolian (wind blown) erosion of sand from the broad alluvial valleys of the region. These dunes form localised perched groundwater systems (Figure 24). The scale of the dune system is large enough that this system is being used for irrigation cropping as it is inherently well drained. The wind blown sediments comprising these dunes often contain clays and silts. The dune sediments contain low to moderate levels of salt which can be rapidly mobilised due to high transmissivity of the sediments. Surface expression of salinity may occur where groundwater discharge occurs at the basal contact of the dune with neighbouring low permeability soils. This description does not relate to coastal dunes at Pittwater. Typical locations

Tunbridge, adjacent to Jordan River

Figure 24 Simplified cross-section of a local flow system in the Quaternary dune local flow system Salinity processes

Groundwater recharge occurs throughout the GFS, particularly where vegetation cover is limited. Recharged groundwater from these dunes is likely to move more laterally rather than vertically. This results in a localised responsive aquifer which discharges groundwater at base of the dunes or on clay lenses within dunes (Figure 25). Groundwater salinity progressively 42


increases with flow length and increases significantly more in areas of groundwater discharge where evaporation processes concentrate salinity. The high hydraulic conductivity of the GFS allows for relatively rapid groundwater movement, suggesting the aquifer will be fast to respond following recharge reduction.

Water movement

Groundwater discharge

Figure 25 Groundwater discharge from a local dune GFS (east of Oatlands)

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Local scale GFS in high relief dolerite (Jurassic) Overview

The high relief dolerite has highly variable rock hardness and weathering. The variation in rock fracturing and weathering results in inconsistent aquifer properties (Figure 26). Groundwater drilling has shown even though hard rock may be at the surface, weathered rock may lie beneath. Typical locations

Higher elevations in Tunbridge-Oatlands, Kempton, Campania

Figure 26 Local scale GFS in high relief dolerite Salinity processes

The GFS exhibits highly irregular fracturing and weathering. Groundwater movement and discharge occurrence is generally related to cracks and fractures within the dolerite (Figure 27). Salinity is not necessarily restricted to localised depressions in the landscape but also upon hill sides. The majority of salinity occurs where springs come to the surface, drainage lines, and at the breaks-of-slope which can be associated with fault lines or contact between lithology. In areas with higher rainfall (ie >600mm pa) groundwater salinity is expected to be low.

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Figure 27 High relief dolerite landscape near York Plains

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Local/Intermediate scale GFS in low relief dolerite (Jurassic) Overview

The low relief dolerite GFS (Figure 28) is also believed to be highly variable in its’ properties (eg. thickness, salinity, etc.), much like the high relief dolerite GFS. The low relief dolerite also appears to have residual salinity stored within it, that is, some slightly elevated terraces are composed primarily of laterite (highly weathered dolerite). These weathered surfaces have a very high salt store and subsequently high groundwater salinity, such as identified in the Tunbridge bore transect of the Northern Midlands GFS study (Hocking et al. 2005). Salinity occurs primarily in topographic depressions or flat areas which have clay rich soils. Many saline areas are former swamplands. In general, hydraulic conductivity of the GFS is low and salt store is high which results in a very sluggish saline GFS. Typical locations

Tunbridge, Lemont

Figure 28 Local/Intermediate scale GFS in low relief dolerite

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Salinity processes

Groundwater recharge to this GFS occurs via two sources, from local groundwater recharge and contribution flow from other GFS (such as high relief dolerite GFS). Contribution from high relief dolerite GFS occurs via lateral groundwater (and salinity) movement generally in fractured zones. The majority of groundwater movement in this aquifer is likely to be flow through the lower weathering zone of the aquifer, and less so via rock fractures. Similar to the high relief dolerite GFS, the greatest salt stores are found where depth of weathering is the greatest, followed by low points in the landscape where salinity occurs (Figure 29). For further information relating to this GFS refer to the Tunbridge transect within Hocking et al. (2005).

Figure 29 Low relief dolerite GFS near Tunbridge

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Local scale GFS in high relief layered fractured rock (Triassic-Permian) Overview

This GFS is highly complex in occurrence and nature (Figure 30). Hydraulic conductivity of this GFS is relatively high. Groundwater recharge to this aquifer occurs via direct rainfall or via leakage from the high relief dolerite GFS. Most salinity occurrences in this aquifer are with low-lying areas in the landscape. Salt store in the GFS is generally low due to the more porous nature of the aquifer. Groundwater salinity variation across regions can be attributed to rainfall, where high rainfall generally relates to relatively low groundwater salinity. Permian and Lower Triassic rocks generally have better water quality and so are likely to contain little salinity. Upper Triassic rocks tend to have higher salinity Typical locations

Kempton, east Colebrook

Figure 30 Local scale GFS in high relief layered fractured rocks

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Salinity processes

Salinity occurrence of this GFS within the Southern Midlands is limited and occurs within drainage lines, breaks of slope and at lithological boundaries (Figure 31), yet the aquifer is extensive. Groundwater salinity is generally brackish in this GFS and the watertable is generally deep. The occurrence of salinity is likely to be associated with specific topographic, land use, climate and geologic features. Groundwater flow is controlled by fracture patterns and bedding planes and recharge is contributed to by fractures within the dolerite. Salinity is generally observed along drainage lines and occasionally in locations with topographical confinement. Importantly it is thought that this GFS contributes substantial amounts of saline basal flow to waterways in the southern region.

Figure 31 High relief layered fractured GFS below high relief dolerite and associated break of slope salinity

49


Local/Intermediate scale GFS in low relief layered fractured rocks (Triassic-Permian) Overview

The Low Relief Layered Fractured Rocks GFS is similar to the Low Relief Dolerite GFS in that both flow systems are relatively flat, and consist of a moderately permeable material above less permeable basement rocks. The Low Relief Layered Fractured Rocks GFS occupies low-lying valley floors and flat, poorly drained basins. These visually local systems may be linked underground giving rise to intermediate characteristics. This GFS is highly complex in occurrence and nature (Figure 32). Hydraulic conductivity of this GFS is generally relatively high depending on the geological formation. The GFS is defined by Permian-Triassic and sedimentary rocks. To various degrees these rocks contain some primary permeability (pore spacing), but most groundwater is believed to occur via interconnected fracture systems. Low to moderate hydraulic conductivity provides some potential for low yielding groundwater pumping for stock and domestic supplies, depending on groundwater salinity. Typical locations

Oatlands, Tunnack, Runnymeade

Figure 32 Local/Intermediate scale GFS in low relief layered fractured rocks 50


Salinity processes

Saline expression results from the restriction of groundwater flow through either small or large scale topographic confinement and the slow permeability of rocks and rocks at shallow depths. Unlike the Alluvial Plains and Slopes GFS, groundwater flow in the Low Relief Layered Fractured rock GFS is impeded by a lack of prior streams or deeply incised drainage lines. Salinity occurrence of this GFS within the study area is limited and only occurs within drainage lines and low-lying areas. Groundwater salinity is generally low in this GFS and the watertable is generally deep. The occurrence of salinity is likely to be associated with specific topographic, climate, land use and geologic features. Groundwater recharge occurs throughout the GFS, where groundwater salinity remains relatively consistent within the GFS varying according to local groundwater conductivity and climate. Figure 33 shows the local/intermediate scale GFS in low relief layered fractured rocks at Oatlands.

Figure 33 Low relief GFS in layered fractured rocks at Oatlands

51


Local scale GFS in colluvium (talus) Overview

The development of colluvium on slopes of topographic highs can provide a significant aquifer (Figure 34). High hydraulic conductivity of the GFS allows the rapid movement of groundwater and limits the build-up of salt storage within the aquifer. Typical locations

Quoin Mountain

Figure 34 Local scale GFS in colluvium Salinity processes

Salt storage is generally low in this GFS. Salinity occurrence is likely to be a function of topographic and geologic features, and therefore salinity is likely to occur in drainage lines and at the break-of-slope. Soils are generally known to be highly sodic rather than saline. Colluvium derived from sedimentary rocks tends to have lower permeability and therefore elevated salinity storage. Dolerite colluvium tends to have greater hydraulic conductivity and lower salt store. Groundwater recharge to this GFS occurs via direct rainfall, where groundwater flows downgradient. Groundwater then either recharges into another GFS (such as the alluvial GFS) or discharges at the break-of-slope. Water salinity of this GFS is very low throughout and is unlikely to experience any significant salinity. Figure 35 shows the colluvium GFS. 52


Colluvial slope (Talus)

Figure 35 High relief GFS in colluvium

53


Local/intermediate scale GFS in fractured basalt Overview

The fractured basalt GFS (Figure 36) developed as long as 40 million years ago when lava flowed down the ancient valleys of the area. Basalt occurs in two landscape positions on elevated hills and valley basins. Elevated basalts discharge at lithological contacts. Groundwater quality tends to be better in areas of elevated basalt than basalts in basins. Since the eruption of basalt drainage lines have re-dissected the landscape and in some instances inverted the basalt geology from being in the lower parts of the landscape to being the topographic high of the area. Typical locations

Campania, Lemont Salinity processes

This GFS is not well understood. The description and groundwater processes of basalt has been described in to two parts, low relief and elevated basalt. Low relief variant fractured basalt The low relief variant fractured basalt predominantly occurs in the Lemont and Campania areas where lava flows have filled ancient valleys, creating broad flat plains. This GFS appears to be similar to the Low Relief Dolerite GFS, although the basalt is thought to have better primary porosity. Little is known of the salinity expression within this GFS although it is likely that saline expression occurs in the drainage lines and broad flat plains. Recharge occurs both within this GFS and from lateral flow from adjacent GFSs. Elevated variant fractured basalt Elevated basalts tend to discharge (Figure 37), whereas most recharge occurs via direct rainfall rather than from other GFSs. Groundwater movement in this GFS is relatively rapid, where the rapid movement of water prevents the build-up of salt in the GFS. The relatively flat nature of the GFS suggests broad areas of salinity are likely to occur in this GFS, and therefore any small area of salinity should be considered as an indicator of a broad flat watertable close to the ground surface. Waterlogging may also occur on this GFS, which should be distinguished from a shallow watertable.

54


Figure 36 Local/intermediate scale GFSs in fractured basalt

55


Valley in distance Basalt landscape

Figure 37 Elevated variant fractured basalt GFS near Lemont

56


6 Priority setting process for Groundwater Flow Systems in the Southern Midlands Following the development of the GFS framework the GFSs were ranked based upon an assessment of environmental factors and expert opinion, which has provided a priority for future investment. As the GFS prioritisation is a relative measure, qualitative measures such as high, medium and low were used to rank the GFSs. The key components of the priority setting process include: •

Quality of land Quality of land refers to the capability of the GFS to typically sustain high value farming. Agricultural land with a higher productivity capability was considered to reflect a higher potential agricultural loss if salinity was occur. Over many years DPIWE have undertaken various land capability surveys in an attempt to identify the potentially high value agricultural productivity land.

•

Water quality Water quality refers to the surface water quality on the GFS and the contrast in water quality between groundwater and surface water. For example, on a GFS where surface water quality is good, but groundwater quality is poor, the GFS is considered be of high priority for investigation. Information collected from this report was utilised in conjunction with detailed published information was considered to determine the GFS priority.

The prioritisation of GFS within the study area was undertaken in by a technical workshop. At the workshop technical experts ranked the relative priority of each GFS separately based upon land and water. Following the separate prioritisation, the two tables (Table 2 & Table 3) were amalgamated to achieve an overall NAP investment prioritisation table (Table 4). The highest priority GFS are the GFS where future investment in improving understanding of process, the impact of current and future land use and management and a groundwater monitoring should first occur.

57


Flow System

Table 2 Impact on land assets

Presence of salt stores in landscape

Potential for landuse change

$ value of production from land use (not land capability)

Overall rating (1 – 9)

Local scale GFS on alluvial plains & slopes

H

H

H

1

Local scale GFS on current floodplain

L

M

M

5

Local scale GFS in Dunes

L

L

M

8

Local scale GFS in high relief dolerite (Jurassic)

M

L

L

6

Local/Intermediate scale GFS in low relief dolerite (Jurassic)

M-H

H

M

2

Local scale GFS in high relief layered fractured rock (Triassic-Permian)

L-M

L

L

7

Local/Intermediate scale GFS in low relief layered fractured rock (Triassic-Permian)

M

M

M

3

Local scale GFS in colluvium (talus)

L

L

L

9

M-H

M

M

4

Groundwater Flow System

Local/Intermediate scale GFS in fractured basalt

Area affected

H

L

58


Table 3 Impact on surface and groundwater assets

– lower confidence in assessment compared with land assets Presence of salt stores in landscape

Current groundwat er salinity

Landuse change will degrade water quality

Rivers/streams affected

Overall rating 1-9

Local scale GFS on alluvial plains and slopes

H

H

H

H

2


L

L-M

M

7


L

L

L

L

8


M

L-M

?

?

5


M-H

H

M

4

Local scale GFS in high relief layered fractured rock (TriassicPermian)

L-M

H

H

1

Local/Intermediate scale GFS in low relief layered fractured rock (Triassic-Permian)

M

H

M

3


L

L

L

9

M-H

M

H

6



H

H

59


Table 4 Overall GFS prioritisation

– both land and water assets

Land priority rating

Water priority rating

Multiply (land x water)

Overall ranking

Top 3 priority GFS

Local scale GFS on alluvial plains & slopes

1

2

2

1

1


5

7

35

7


8

8

64

8


6

5

30

6


2

4

8

3

3

Local scale GFS in high relief layered fractured rock (Triassic-Permian)

7

1

7

2

2

Local/Intermediate scale GFS in low relief layered fractured rock (TriassicPermian)

3

3

9

4


9

9

81

9


4

6

24

5


Future investigations must include not only a GFS but also surrounding GFSs (rock types) that have associated impacts.

60


Figure 38 Priority GFS from salinity management of the NAP parts of the Southern Midlands and Clarence municipalities

61

7 Management of salinity in the Southern Midlands Previous sections have described the conceptual understanding and groundwater processes of each GFS within the NAP parts of the Southern Midlands and Clarence municipalities. This section provides a summary of groundwater and salinity processes, and option for managing for each GFS. These ‘best bet’ treatment options are based upon conceptual understandings, information gained from the few salinity treatment plantings in Tasmania, and experience gained from GFS treatments throughout Australia. The management options are based on the triage approach for salinity management—fix, avoid or adapt. Fixing – This is the treatment of a saline site to remove the area of groundwater discharge and salinity, an example of this may include the planting of salt tolerant vegetation at a saline site and the ongoing reduction of groundwater recharge. Avoiding – This refers to the prevention of salinity. This may be achieved by minimising any future land use change that would result in increases in recharge in into susceptible GFSs, It can also be achieved in some circumstances by applying broad scale land use changes to decrease groundwater recharge and planting vegetation (not necessarily salt tolerant) in low parts of the landscape. Adapting – This assumes groundwater discharge is occurring, and the scale of groundwater recharge reduction and/or discharge treatment is far greater than is practical and/or possible. Therefore, the approach attempts to make the most of a saline area, for example, by establishing salt tolerant vegetation species and living with the saline area. As part of this project, the impact of salinity on infrastructure was explored, however limited hydrogeological information prohibited a measure of salinity impact to be achieved. 7.1

Overview of salinity management options

Throughout Australia, and especially in Tasmania, the amount of research that has been undertaken to prove the effectiveness and the cost benefit of these options is quite limited and often absent all together. Therefore these options should be

62


applied with caution and only used as a guide to the best management practice. It is recommended that expert advice is sort before use. Conserving perennial vegetation

Experience of salinity is a result an imbalance between recharge and discharge in an environment where salt is present or salt is introduced. If recharge increases there is a potential over time and space for discharge to increase. The original vegetation cover (mostly perennial) through its use of rainfall established a balance between recharge and discharge. Removal of the native vegetation is one of the triggers may disturb the water balance and results in an increase in salinity expression. Therefore in areas of high salinity hazard, and where large enough areas of native vegetation remain, conserving of perennial vegetation should be considered as a means of maintaining the water balance and avoiding an increase in salinity. Manage cropping and irrigation development

The replacement of perennial pastures with cropping and irrigation generally reduces the annual amount of rainfall used by plants and increases the amount of water available for recharging groundwater. Therefore in high salinity hazard areas changes in land use to cropping and irrigated cropping should be avoided. However in Tasmania, currently the areas of high risk are not well defined. Therefore cropping and cropping and irrigation developments should only be considered following a salinity risk assessment. Trees and shrubs to reduce recharge

Introducing trees and shrubs into recharge areas will often reduce recharge. However unless the scale of planting is large relative to the scale of the recharge area and the transmissivity of the GFS is relatively high, the reduction in discharge rates will be low or take a long time to be expressed. Plant or improve perennial plants including lucerne

Where annual rainfall is less than 600 mm, mainland research has shown that replacing annual pastures with perennial pastures can significantly reduce recharge. Improving perennial pastures may increase water use and decrease groundwater to a minor degree. 63


Increasing irrigation efficiency

Irrigation water is used efficiently when the plants use a high proportion of the water applied. High irrigation efficiency will reduce the amount of water that is potentially available for recharge. The efficiency of irrigation can be improved through the use of irrigation scheduling and using dryland follow-on crops to use water left over from the period of irrigation. Increase water use efficiency (WUE)

Water balance research and modelling has shown that for some dryland crops fallow periods between crops may increase the potential for recharge. The use of opportunity cropping and shorter fallow periods may reduce this potential recharge. Engineering options to reduce recharge

Where conditions are suitable, surface and sub surface drainage and raised beds may reduce potential recharge by effectively increasing run-off and reducing the length of time that soils are waterlogged. Salt tolerant trees and shrubs to mitigate and adapt to saline areas

Some trees and shrubs are mildly to highly tolerant of saline and waterlogged conditions. They can be used depending on salinity tolerance, to intercept saline groundwater before it is discharged or concentrated. Some success has been achieved on mainland Australia by using trees and shrubs to lower watertables, reclaim soils and re-establish pastures between the rows of trees. Salt tolerant pastures

Some pasture species are more tolerant to salinity than others and can be used to grow productive pasture on moderately saline land. Engineering options to improve discharge areas

These are used to lower the height of the watertable relative to the land surface. The common ones used are groundwater pumping and sub surface drainage. Raised beds and mounding can be used to elevate plants above the surrounding land thereby improving the drainage and leaching of water and salt out of the raised area. Care must be taken with disposal of water either pumped or drained 64


and to identify any potential sodicity and toxicity problems before investing in these options. Options for using saline waters

Some waters which are too saline to use for domestic or irrigation, if not too saline, can be used for stock water. The National Dryland Salinity Program project “Options for the productive use of saline land” (see; www.lwa.gov.au/ndsp) identified many potential options for the productive use of saline water with salinity over a wide range of concentrations. They are based on the use of saline surface or pumped groundwater. 7.2

GFS fact sheets (salinity management options)

In this section all information collected and derived has been summarised into summary sheets.

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APS-GFS - Local scale GFS on alluvial plains and slopes (Approximately 21 900 ha) Local scale GFS occurs in the broad river valley flats of the region. Typical examples of where the GFS occurs includes the broad valleys for the Jordan and Coal rivers.

Physical attributes relevant to salinity Geology:

Clayey to sandy rocks (Dominantly Tertiary in Coal Valley & predominantly Quaternary rocks in north) Landform: Plains and low angle slopes Catchment size: Large – generally more than 20 000 ha Land use: Dryland grazing/cropping irrigation/horticulture Annual rainfall: Variable up to 700 mm Salinity occurrence: Within drainage lines, breaks of slope, springs on slopes at lithological/geological boundaries and in topographic depressions Aquifer: Alluvial rocks Transmissivity: Low to moderate generally less than 10 m2/day (Prior streams can have higher transmissivity) Approximate salinity area: 600 ha (≈ 3% of GFS) Typical soil association Richmond and Coal Groundwater salinity: 1 to 25 dS/cm (1000 to 25 000 μS/cm) Recharge (temporal) Seasonal Recharge (spatial) Throughout the GFS, and adjacent GFSs

Landscape processes causing salinity Groundwater enters and migrates from the upper Poor irrigation and cropping management may parts of the aquifer and the above GFS toward create groundwater highs beneath irrigation zones and lead to localised saline areas. valley floors, and sometimes through the underlying aquifer. In the latter situation groundwater pressures build-up under the GFS and salinity occurs in response to artesian conditions that develop in the valley floor. Groundwater recharge to the aquifer occurs via direct rainfall and via upward groundwater pressure. Groundwater salinity may be concentrated by evaporation.

16000 14000

Area (Hectares)

12000 10000 8000 6000 4000 2000

n an ta tio Pl

/D is tu rb ed

C ro pp in g

U rb an

Fo re st ry C on se rv at io n

Ve g iv e at

Pa st ur e

th er N O

at iv e N

D

ry la nd

pa st ur e

0

Land use summary of the GFS

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Management strategies Biological systems for managing recharge Salinity is expressed in different topographic locations within the alluvial plains and slopes GFS. Options for managing salinity within the GFS need to reflect the different groundwater processes leading to salinity in these locations. The nature and extent of saline discharge areas is strongly influenced by the presence or absence of prior streams (paleochannels). Recharge is likely to be uniform within the GFS and so options for biological control of recharge exist. Biological options for reducing or controlling recharge may exist in areas not currently developed for irrigated agriculture or horticulture. Biological options to reduce recharge include; (a) Tree planting along contours at breaks in slope to intercept shallow groundwater flow. (b) Displacement of annual crops and pasture with deep rooted perennial crops and pastures i.e. lucerne, on elevated plains or terraces. (c) Broad scale native tree planting is limited by uncertainty as to where recharge is occurring in the landscape and high value agricultural production on this GFS.

areas in lower valley rocks. Trees should be planted in belts above the primary salinity area, preferably in plantations at least 40 metres in width. Optimum conditions for groundwater interception are attained when the tree belts are planted above the saline area—at this position in the landscape groundwater salinity usually has a lower salinity.

A relatively flat watertable and moderate permeability in the sandy clay rocks afford some local opportunities for biological control of salinity where suitable farming and forestry systems are able to deliver a reduction in groundwater recharge. The landscape has sufficiently low transmissive capacity to lower groundwater levels locally following recharge reduction.

Under dryland cropping phasing out the fallow phase would markedly reduce recharge. Where possible inter-sowing with perennial vegetation would allow any excess water to be used rather than it seeping below the root zone to groundwater recharge.

Where the rainfall is high (>600 mm/year) and salinity is experienced, it is unlikely that perennial vegetation alone will not have a significant role in salinity mitigation. In these instances the most promising salinity mitigation strategies are most likely to involve a mix of saline tree/scrub planting for localised watertable control, perennial vegetation to improve farm productivity (helping offset the cost of tree establishment), engineering options and living with salt options. For tree selection guidance refer to Finnigan and Poulton (2005). Recharge reduction under irrigation can be achieved by water deficit irrigation scheduling and low application rate irrigation such as centre pivots.

Perennial vegetation afford opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 600 700 mm. Lucerne or similar perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits. Tree belts planted adjacent to areas of a shallow watertable afford the opportunity to intercept groundwater prior to it migrating into saline

Engineering systems to control watertable level Engineering options may be viable in the alluvial plains and slopes GFS. The effectiveness of groundwater pumping will depend on the presence and nature of prior streams. The majority of regolith materials within this GFS are heavy impermeable clay rocks with little potential for successful groundwater pumping. However, the presence of prior streams enables large amounts of groundwater to be extracted from sand and gravel layers. Water extracted from these prior streams is likely to be highly saline (2-8dS/m) preventing direct disposal to surface waterways.

67


Low volume groundwater pumping from the alluvial aquifer affords a level of salinity management. It may also be useful in augmenting farm water supplies, however high groundwater salinity levels will limit stock water consumption. Installation of sub surface drainage maybe viable dependent on economics.

Living with salt Living with salinity options are likely to be a necessity within the alluvial plains and slopes GFS. In saline discharge areas, establishment of salt tolerant pasture including Pucinellia, Tall Fescue, and Persian Clover are likely to produce increased production and environmental benefits from improved ground cover. The use of Tall Wheat Grass (TWS)– Dundas, will need to be assessed on a site by site basis, however, it is likely to be a viable option in saline areas not associated with drainage lines (ie break of slope and flat elevated plains) under strict grazing guidelines. Within drainage lines, revegetation with salt and waterlogging tolerant vegetation and hybrid trees may be viable.

Avoidance Agricultural developments should seek to avoid irrigation on saline and high risk areas within this GFS. High risk areas include soils with high salt storage, and areas with shallow saline watertables within approximately 5 meters of the soil surface.

Research Requirements •

Evaluation of the efficiencies and effectiveness of groundwater pumping and understanding the importance of prior streams to water extraction.

•

Rehabilitation of saline discharge areas using native species and field trials using both local and non-endemic species.

•

Development of simple techniques for farmers to monitor changes in soil salinity associated with irrigating with saline water.

•

Determine the effectiveness and cost benefit of establishing salt tolerant vegetation ie pastures, shrubs and trees.

•

Determine the effectiveness of perennial cropping systems to minimise leakage.

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Local scale GFS on alluvial plains and slopes Options Biological Management of Recharge

Treatment Perennial pasture Crop management Planting trees/ woody vegetation

Engineering Intervention

Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage

Productive Use of Saline Land and Water

Avoidance

Monitoring.

Irrigation management Salt tolerant pasture Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land See note for Recent Floodplain GFS Maintain remnant woody vegetation. Groundwater

Irrigation water Surface soil salinity

Relevance High. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. High. Opportunities exist to replace annual cropping and fallow periods with permanent horticulture or perennial crops ie lucerne. Low. High land value and uncertainty as to location of recharge areas within the GFS limit application. Break in slope plantings may be valuable. Moderate. Raised beds are used extensively for waterlogging control. Surface grading may help reduce direct recharge within the GFS. Moderate. Groundwater pumping may be viable where prior streams enable rapid extraction of large volumes of water. Acceptable means of disposing of leachate are required. High draw-down restricted by low soil permeability. May be used to protect crops and horticulture adjacent to discharge areas. Very High. Recharge likely to be reduced under irrigation areas through use of irrigation scheduling tools. High. Production and environmental benefits are expected, although suitable land area may be limited. Low. May be possible as high to moderate salinity groundwater is expected. High. Probably limited to isolated drainage lines rather than broad scale planting. Very High. Minimise or avoid development of saline land for high value production or irrigated agriculture. Low. Few large areas of remnant woody vegetation remain. Very High. Some groundwater monitoring exists, however long term trend data is required within this GFS, especially where recent landuse change (ie irrigation, cropping and urban development) has occurred or high value assets are at risk. Very High. Surface water within this GFS is often saline. Monitoring irrigation water salinity is important to prevent crop losses. Very High. Trends in soil salinity under saline irrigation are required.

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CFP-GFS - Local scale GFS on current floodplain (Approximately 3 200 ha) Local scale GFS occur in the river valley flats of the region. Typical examples of where the GFS occurs include the broad river valleys of the lower Jordan and Coal rivers.

Physical attributes relevant to salinity Geology: Landform: Land use: Annual rainfall: Salinity occurrence: Aquifer: Transmissivity: Approximate salinity area: Typical soil association Groundwater salinity: Recharge (temporal) Recharge (spatial)

Quaternary/Holocene clays to sands with some gravels Floodplain adjacent to rivers & streams; more than 100 ha Dryland grazing/cropping irrigation/horticulture Variable up to 600 mm Within drainage lines and low-lying areas Alluvial rocks High - generally around 500 m2/day 300 ha (≈13% of GFS) Churchill 0.2 to 10 dS/cm (200 to 10 000 μS/cm) Bank full flow times, rainfall Throughout the GFS rainfall, river flow, and neighbouring GFSs

Landscape processes causing salinity Groundwater migrates from the upper parts of Groundwater recharge to the aquifer occurs via the aquifer and the above GFS (and sometimes direct rainfall and upward groundwater pressure. through the underlying aquifer), toward the valley floors or adjacent river. In some places upward groundwater pressures build-up under the GFS and salinity occurs in response to high groundwater pressure in the valley floor. Groundwater within the GFS migrates down slope where it either discharges in a depression, or discharges into the adjacent river. 1400 1200

Area (Hectares)

1000 800 600 400 200

Pl an ta ti o n

C ro pp in g U rb an /D is tu rb ed


Ve g

re pa st u

th er N at iv e

O

N at iv e

D ry la nd

Pa st ur e

0


70


Management strategies Biological systems for managing recharge Recharge within the current floodplain GFS results from a dynamic balance between terrestrial recharge occurring from rainfall on land and recharge of the aquifer from local waterways. Little opportunity exists to control groundwater recharge through biological means due to the recharge from the local waterways. Access to surface water has resulted in small areas of crop and horticultural development adjacent to the Coal and Jordan rivers. Biological options to control recharge are limited by; (a) The current floodplain are principally a discharge region rather than a recharge region. (b) Recharge occurs on neighbouring GFS and the current floodplains.

Perennial vegetation afford opportunities for increased water use. Tree belts planted adjacent to areas of a shallow watertable afford the opportunity to intercept groundwater prior to it migrating into saline areas in lower valley rocks or into the adjacent tributary. Trees should be planted in belts above the primary salinity area, preferably in plantations at least 40 metres in width. Optimum conditions for groundwater interception are attained when the tree belts are planted above the saline area—at this position in the landscape groundwater salinity usually has a lower salinity. For tree selection guidance refer to Finnigan and Poulton (2005).

Where salinity is experienced, it is likely the perennial vegetation alone will have a significant In areas used for irrigated production and dryland cropping groundwater recharge may be role in salinity mitigation. reduced through increased crop perennially and displacement of annual pastures with perennial crops and pastures. A relatively flat watertable and moderate to high permeability in the clayey/sandy/river gravel rocks afford limited opportunities for biological control of salinity. The landscape has limited transmissive capacity to lower groundwater levels (over a number of years) following recharge reduction.

Engineering systems to control watertable level In places where shallow saline watertables threaten to come within 2 meters of the soil surface, groundwater pumping may be a viable means of lowering watertables. Surface and sub surface drainage are currently employed to overcome production issues associated with waterlogging within the GFS. Surface and sub surface drainage assists with the reclamation of salt affected land, however, recharge is not likely to be impacted by drainage options. Discharge of saline waters generated from groundwater pumping and subsoil drainage will need to be carefully considered. Discharge of saline waters into the already saline waterways such as the Coal River, may not be acceptable. Any plans to dispose of saline leachate into surface water must be referred to the Environment Division of the Department of Primary Industries Water and Environment. High volume groundwater pumping maybe possible from the aquifer and affords a level of salinity management. It may also be useful in augmenting farm water supplies, but moderate to high groundwater salinity levels will limit water extraction.

Living with salt In saline discharge areas, establishment of salt tolerant pasture including Pucinellia, Tall Fescue, and Persian Clover are likely to produce increased production and environmental benefits from improved ground cover. The use of Tall Wheat Grass (TWS), Dundas will need to be assessed on a site by site basis due to its weed risk potential. In general the use of TWG is not supported on the current floodplains GFS due to the proximity of saline discharge areas to waterways. Within drainage lines, revegetation with native salt and waterlogging tolerant vegetation or salt tolerant hybrid trees may be viable and offer additional biodiversity benefits.

71


Avoidance Agricultural developments should avoid irrigation on or adjacent to existing saline areas within this GFS. High risk areas include current discharge areas, and areas with either high soil salinity above watertables, or any areas with shallow saline (>1.5 dS/m) watertables (600 mm/year) and salinity is experienced, it is unlikely that perennial vegetation alone will have a significant role in salinity mitigation. In these instances the An undulating watertable surface and moderate most promising salinity mitigation strategies are most likely to involve a mix of saline tree permeability in the sandy clay geology afford planting for localised watertable control, and opportunities for biological control of salinity perennial vegetation to improve farm where suitable farming systems are able to productivity (helping offset the cost of tree deliver a reduction in groundwater recharge. The landscape has sufficiently low transmissive establishment). capacity to lower groundwater levels (within a reasonable timeframe) following recharge reduction. Perennial vegetation afford opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 600 – 700 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits.

Engineering systems to control watertable level Engineering options are not considered viable within this GFS, due to the low yielding and the ‘random’ nature of the fractured aquifer. The only possible exception would be to extract groundwater from known faults or areas of geological contact, where reasonable flow rates may be expected. Lower salinity water is expected to be found in higher rainfall areas and areas higher up the GFS. Low volume groundwater pumping from the GFS affords a level of local salinity management. It may also be useful in augmenting stock water supplies.

Living with salt Living with salinity options are generally not relevant within the high relief dolerite GFS. Salinity expression usually occurs in adjacent GFSs. The exception is where the rock fracture pattern brings saline groundwater to the soil surface. Where the scale of tree planting is significant, saline tolerant trees for farm forestry or productive pasture options may be considered.

Avoidance Thin soils, steep topography, exposure and a lack of surface water resources have prevented this GFS being developed for irrigated production. Efforts to avoid salinity and groundwater recharge should focus on protecting remnant woody vegetation and growing tress and perennial pastures.

75



Understanding the effects of tree decline on groundwater recharge

•

Determine effectiveness of tree plantations (native and exotic) and farm forestry on recharge control within the high relief dolerite GFS

•

Understand the contribution of recharge and salinity from the high relief dolerite to other GFSs.

76


Local scale GFS in high relief dolerite Options Biological Management of Recharge

Treatment Perennial pasture


Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage Irrigation management Salt tolerant pasture Saline aquiculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater

Productive Use of Saline Land and Water Avoidance

Monitoring

Crop management Planting trees/ woody vegetation

Irrigation water Surface soil salinity

Relevance Moderate. Pastures are predominantly native perennials and few opportunities exist to replace annual pasture. NA – Low. Cropping absent or very rare on this GFS. Moderate – High. Broad scale tree planting may reduce recharge, however, establishment will be limited by altitude, exposure and existing tree decline. NA. Cropping absent or very rare on this GFS N.A. Fractured aquifer makes drilling and pumping difficult. NA. Cropping absent or very rare on this GFS NA. Cropping absent or very rare on this GFS Low. May be appropriate for isolated springs or seeps. NA. Low. May be appropriate for isolated springs or seeps Low. Cropping absent or very rare on this GFS Very High. Protect remnant vegetation from clearing and tree decline. Low. May be required for understanding flow into adjacent GFSs NA. Cropping absent or very rare on this GFS NA. Cropping absent or very rare on this GFS

77


FB-GFS – Local/Intermediate scale GFS in fractured basalt

(Elevation & Low relief variations) (Approximately 3700 ha) Local/Intermediate scale GFS occurs in the ancient river valley of the Coal River and scattered throughout the region. Typical examples of where the GFS occurs include Campania and Lemont.

Physical attributes relevant to salinity Geology: Landform: Catchment size: Land use: Annual rainfall: Salinity occurrence:

Basalt Hill top plateau and valley basins Medium – generally less than 5 000 ha Dryland grazing/cropping & irrigation, limited horticulture, forestry Variable up to 600 mm Within drainage lines, breaks in slope and contacts with contrasting lithology Aquifer: Fractured & vesicular basalt Transmissivity: High generally more than 100 m2/day Approximate salinity area: Less than 300 ha (≈9% of GFS) Groundwater salinity: 0.5 to 10 dS/cm (500 to 10 000 μS/cm) Recharge (temporal) Seasonal Recharge (spatial) Direct rainfall on plateau, various in basins

Landscape processes causing salinity Local/Intermediate scale GFSs function to effect salinity within the basalt and into adjoining aquifers. Groundwater migrates from the upper parts of the GFS toward valley floors, and sometimes through the underlying aquifer. In the latter situation groundwater pressures build-up under the basalt and salinity occurs. Shallow perched groundwater within the basalt migrates down slope where it either discharges in a depression, or feeds a poorly defined thin basal aquifer. Groundwater recharge to the aquifer occurs via direct rainfall and via upward groundwater pressure. 2500

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Management strategies (elevation variant Basalt GFS) Biological systems for managing recharge Little is known about the presence of salinity within this GFS. Salinity is thought to occur where either the basalt fracture pattern allows groundwater to come to the surface (often along fault lines) or where the basalt comes into contact with other rock types of lower hydraulic conductivity. Biological Options for reducing recharge will be limited by the difficulty in establishing trees or woody vegetation in elevated exposed areas. Options need to be considered on a site by site basis taking into account local climatic and environmental factors. Potential options include, farm forestry plantations, protecting remanent vegetation, broad scale vegetation planting, and replacement of annual with perennial pastures. A relatively flat watertable and moderate permeability in the fractured basalt affords opportunities for biological control of salinity where suitable farming systems are able to deliver a reduction in groundwater recharge. The landscape has moderate transmissive capacity prohibiting the ability to lower groundwater levels (within a reasonable timeframe) following recharge reduction.

700 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits. Tree belts planted adjacent to areas of a shallow watertable afford a limited opportunity to intercept groundwater prior to it migrating into saline areas in lower valley rocks. Trees should be planted in belts above the primary salinity area, preferably in plantations at least 50 metres in width. Optimum conditions for groundwater interception are attained when the tree belts are planted above the saline area-at this position in the landscape groundwater salinity usually has a lower salinity and may approach within two metres of the land surface. For tree selection guidance refer to Finnigan and Poulton (2005).

Perennial vegetation afford opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 600 –

Engineering systems to control watertable level Engineering options may be possible due to the moderate primary porosity of the basalt. Disposal of moderately saline water may be an issue. High volume groundwater pumping from the aquifer affords a level of salinity management. It may also be useful in augmenting farm water supplies, and in places low groundwater salinity levels will allow stock water consumption.

Living with salt Living with salinity options are not considered to be relevant within this GFS due to the absence of known saline areas. Further investigation may identify the presence of saline areas on the flat plateaus associated with this GFS.

Avoidance Avoidance of high value irrigated agriculture is not considered to be relevant in this GFS. Thin soils, steep slopes, exposure and a lack of surface water resources have prevented this GFS being developed for irrigated agriculture.

Research Requirements • Determine if saline expression exists within this GFS. •

Determine GFS interaction with other GFSs.

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Local/Intermediate scale GFS in basalt (elevation variant) Options Biological Management of Recharge


Relevance Moderate. Maintain perennial native pastures where possible.



Surface drainage (raised beds and surface grading) Groundwater pumping

NA. Cropping unknown on this GFS. Moderate. Broad scale tree planting may reduce recharge, however, altitude, exposure and existing tree decline will limit establishment. NA. Cropping unknown on this GFS.


Avoidance

Monitoring.

Sub surface drainage Irrigation management Salt tolerant pasture Saline aquiculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Low. The aquifer characteristics may be suitable but application limited by low agricultural production and disposal issues. NA. Cropping unknown on this GFS. NA. Cropping unknown on this GFS. NA Saline expression not well understood on this GFS. NA. NA. Saline expression not well understood on this GFS. NA. Cropping unknown in this GFS. Moderate. Protect remnant vegetation from clearing and tree decline. Low NA. Saline expression not well understood on this GFS. NA Saline expression not well understood on this GFS.

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Management strategies (low relief variant Basalt GFS) Biological Control of Groundwater Recharge. Biological recharge options are possible through targeted establishment of perennial woody vegetation in elevated areas. Adoption of tree planting and farm forestry is likely to be restricted by the need to replace pasture based production systems and high value cropping and horticultural enterprises, especially in the Campania area.

Engineering Options. On broad flat areas, groundwater pumping may be a viable means to lower watertables. The effectiveness and efficiency of groundwater pumping will depend on the fracture patterns and permeability of the basalt. Disposal of saline groundwater into surface waterways is likely to be problematical, especially in the Little Swanport catchment, which has significant aquaculture developments in lower estuary. Land grading and surface drainage are likely to improve movement of surface water and minimise small scale water logging that currently allow water to evaporate and concentrate salts. Efforts to reduce recharge or leakage occurring under irrigated production (such as irrigation scheduling) are also recommended, especially where irrigation systems have been developed on, or adjacent to, saline discharge areas.

Living with salinity Living with salinity options may be applicable where salinity occurs on broad flat areas. The use of Tall Wheat Grass – Dundas, will need to be assessed on a site by site basis, however, it is unlikely to be a viable option due to its ‘weedy’ nature and proximity of saline areas to surface waterways. Given that grazing is the dominant land use in this GFS, salt tolerant pasture systems are likely to be more readily adopted by producers, as they will require minimal changes to current farming systems.

Avoidance Avoiding the development of irrigated production on, or adjacent to, saline discharge areas will be an important management strategy. Little remnant vegetation occurs within this GFS.


Occurrence of saline expression within this GFS.

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Site by site assessment of the viability of groundwater pumping options.

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The effect of cropping systems on groundwater recharge, salinity discharge and surface water quality.

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The effectiveness and cost benefit of establishing salt tolerant pasture systems.

•

Determine the groundwater interactions between the Basalt GFS and other GFSs

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Local/Intermediate scale GFS in basalt (low relief variant) Options Biological Management of Recharge


Productive Use of saline land and water

Avoidance

Monitoring.

Treatment Perennial pasture Crop Management Planting Trees/ Woody Vegetation Surface Drainage (raised beds and surface grading) Groundwater Pumping Sub surface drainage Irrigation Management Salt Tolerant Pasture Saline aquaculture & salt harvesting Salt Tolerant Trees – Farm Forestry Avoid Development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Relevance High. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. Moderate. Adoption of perennial crops such as lucerne in areas adjacent to saline discharge. Low. some options exist, however complicated by shift to irrigated production systems and on-site nature of recharge. Moderate. Land grading or improving surface drainage will reduce some surface soil salinity. Moderate. More needs to be known about aquifer permeability. Disposal of saline water will be an issue. Low –Moderate. Acceptable draw-down where soils are well structured. Disposal of saline water is a potential issue. High. Reduce recharge under current irrigation management systems through use of irrigation scheduling tools. Moderate - High. Establishment of salt tolerant pasture systems in saline discharge areas. NA. Moderate. Appropriate in smaller discharge areas where grazing is not viable. Very High. Minimise or avoid development of irrigated production systems on saline land. Moderate. Large areas of remnant woody vegetation are relatively rare within the GFS. Moderate. Relevant where land use change has occurred or high value agricultural production is at risk. Moderate. Potentially important, especially on low permeability clays. Moderate. Potentially important especially on low permeability clays.

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DUNE-GFS - Local scale GFS in dunes (Approximately 2800 ha) Local scale GFS occurs in the sand rises of the region. Typical examples of where the GFS occurs include north of Richmond, lower slopes near Kempton to Oatlands.

Physical attributes relevant to salinity Geology: Aeolian Fine sandy rocks (eg. Holocene) with some clay lenses Landform: Dunes Catchment size: Small – generally less than 40 ha Land use: Dryland grazing/cropping & irrigation/horticulture Annual rainfall: Variable up to 700mm Salinity occurrence: At contact of dune with neighbouring GFS and inter-dune swales Aquifer: Porous sands Transmissivity: Low to moderate generally less than 20 m2/day Approximate salinity area: 600 mm/year) and salinity is experienced, it is unlikely the perennial vegetation alone will have a significant role in salinity mitigation. In these instances the The relatively high - moderate permeability in most promising salinity mitigation strategies are the sand afford some opportunity for biological most likely to involve a mix of saline tree planting for localised watertable control, and control of salinity where suitable farming perennial vegetation to improve farm systems are able to deliver a reduction in groundwater recharge. The landscape has a high productivity (helping offset the cost of tree establishment). enough transmissive capacity to lower groundwater levels (within a reasonable timeframe) following recharge reduction. Perennial vegetation affords opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 600 – 700 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits. Tree belts planted adjacent to areas of a shallow watertable afford the opportunity to intercept groundwater prior to it migrating into saline areas in lower valley rocks.

Engineering systems to control watertable level Groundwater pumping is a potentially viable means of lowering watertables within the Dunes GFS. This is likely to have beneficial effects on the expression of salinity in adjacent GFSs. Groundwater quality is expected to vary from very good to average. Where groundwater quality is good (ie 600 mm/year) and (d) Deep groundwater. (e) Land within this GFS is currently valued for salinity is experienced, it is unlikely that perennial vegetation alone will have a significant pasture production. role in salinity mitigation. In these instances the most promising salinity mitigation strategies are An undulating watertable and moderate most likely to involve a mix of saline tree permeability in the clay to sand rocks afford planting for localised watertable control, and some opportunity for biological control of salinity where suitable farming systems are able perennial vegetation to improve farm to deliver a reduction in groundwater recharge. productivity (helping offset the cost of tree establishment). The landscape has a moderate to high transmissive capacity which will allow for localised watertable fall following recharge reduction. Perennial vegetation afford opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 700 600 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits.

Engineering systems to control watertable level Groundwater pumping for salinity control is not very feasible in this GFS due to the current depth of the watertable, elevated position in the landscape, and complex aquifer systems related to the variable porosity and storage capacity of the aquifer. This GFS supports almost no cropping so that surface and sub surface drainage systems are inappropriate in most areas. High volume groundwater pumping from the Permian aquifer affords a level of salinity management. It may also be useful in augmenting farm water supplies, and where low groundwater salinity levels will allow for stock water supplies.

Living with salt Living with salinity options are not particularly relevant for the High Relief Fractured Rocks GFS as salinity expression is not common. Where saline springs or confined areas occur, salt tolerant Eucalypt hybrids as farm forestry and salt tolerant pasture options could be considered. The areas affected are most often small to moderate. They occur in response to the discharge of moderate to high salinity groundwater in regions where seasonal rainfall is relatively high. The affected soils are wet in the winter months and quite dry (almost arid) in the summer months.

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Avoidance Poor soil quality and steep slopes usually prohibit irrigated development. Efforts to protect remnant vegetation are considered important to limit recharge.


Understanding the effects of groundwater flow on surface water salinity.

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Understanding the effects of pasture management on recharge.

•

Understanding of groundwater pathways and complexity of the aquifer system.

•

Determine management options to reduce discharge of saline water to waterways.

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Local scale GFS in high relief layered fractured rocks Options Biological Management of Recharge



Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage Irrigation management Salt tolerant pasture


Avoidance

Monitoring.


Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Relevance High. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. NA. Very few areas under cropping within the GFS. Moderate, Broad scale native tree planting may reduce recharge, however, establishment will be restricted by altitude, exposure, tree decline and value of current grazing based production systems. NA. Very few areas under cropping within the GFS. Low. Very little potential due to elevation and disposal difficulties. NA. Very few areas under cropping within the GFS. NA. Very few areas under cropping within the GFS. Low. Not generally applicable due to scarcity of saline expression within GFS. Low – Moderate. High salinity groundwater Low. Not generally applicable due to scarcity of saline expression within GFS. NA. Not applicable due to absence of saline expression within GFS & low suitability for intensive agricultural production. High. Remnant vegetation should be maintained wherever possible. Moderate. Potentially important for understanding effects of groundwater on surface water salinity. NA. Very few areas under cropping within the GFS. NA. Not applicable due to absence of saline expression within GFS.

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LRD-GFS – Local/Intermediate scale GFS in low relief dolerite (Approximately 9700 ha) Intermediate scale GFS occurs in the lower parts of the undulating landscape such as Tunnack and Kempton.

Physical attributes relevant to salinity Geology: Landform: Catchment size: Land use: Annual rainfall: Salinity occurrence: Aquifer: Transmissivity: Approximate salinity area: Groundwater salinity: Recharge (temporal) Recharge (spatial)

Jurassic dolerite Localised basins and flat to undulating landscapes Small – generally less than 500 ha Mainly dryland grazing & some irrigation cropping & pasture Variable up to 1200 mm Topographic confinement, basins, drained swamps Weathered dolerite and rock fractures Low to moderate generally less than 20 m2/day more than 20 ha (≈0.1% of GFS) 0.1 to 18 dS/cm (100 to 18 000 μS/cm) Seasonal Throughout the GFS

Landscape processes causing salinity Groundwater migrates from the upper parts of the aquifer and the above GFS (eg. high relief dolerite) toward valley floors. Shallow perched groundwater within the dolerite migrates down slope where it either discharges in a depression, or drainage line. Most groundwater flow appears to occur within the top 30 metres of the GFS, likewise the greatest salt store is within this zone. 6000

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Management strategies Biological systems for managing recharge Options for biological control of recharge include targeted tree planting, farm forestry and protection of remnant vegetation in recharge areas. The effectiveness of broad scale native replanting may be limited by direct recharge from rainfall occurring across the GFS. Options need to be considered on a site by site basis taking into account local climatic and environmental factors. It is likely that tree planting and farm forestry options will be restricted by the need to displace pasture based production systems and unfavourable establishment conditions including altitude, exposure and tree decline in some areas (especially in the south and west of the study area).

groundwater prior to it migrating into saline areas in lower valley rocks. Trees should be planted in belts above the primary salinity area, preferably in plantations at least 30 metres in width. Optimum conditions for groundwater interception are attained when the tree belts are planted above the saline area—at this position in the landscape groundwater salinity usually has a lower salinity and may approach within two metres of the land surface. For tree selection guidance refer to Finnigan and Poulton (2005).

Where the rainfall is high (>600 mm/year) and salinity is experienced, it is unlikely that perennial vegetation alone will have a significant A relatively flat watertable and low to moderate role in salinity mitigation. In these instances the most promising salinity mitigation strategies are permeability in the sandy-clay rocks afford most likely to involve a mix of saline tree opportunities for biological control of salinity planting for localised watertable control, and where suitable farming systems are able to perennial vegetation to improve farm deliver a reduction in groundwater recharge. productivity (helping offset the cost of tree The landscape has sufficient transmissive capacity to lower groundwater levels (within a establishment). reasonable timeframe) following recharge reduction. Perennial vegetation afford opportunities for increased water use, but will be less effective where the annual rainfall is in excess of 600 – 700 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with recharge reduction benefits. Tree belts planted adjacent to areas of a shallow watertable afford the opportunity to intercept

Engineering systems to control watertable level Groundwater pumping is unlikely to be a viable option within this GFS, due to the low hydraulic conductivity and the limited extent of land likely to be protected by pumping. Disposal of saline groundwater into surface waterways is also likely to be problematical, especially in the Little Swanport catchment, which has significant aquaculture developments in the lower estuary. Cropping on raised beds is likely to reduce the effects of waterlogging and may reduce direct recharge within the cropping areas. Given the flat nature of the land, surface drainage is likely to improve movement of surface water and minimise small scale topographical confinements that currently allow water to evaporate and concentrate salts. Efforts to reduce recharge or leakage under irrigated production (such as irrigation scheduling) are should be encouraged, especially where irrigation systems have been developed on, or adjacent to, saline discharge areas. Low volume groundwater pumping to augment farm water supplies, although moderate to high groundwater salinity levels will limit stock water consumption.

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Living with salt In saline discharge areas, establishment of salt tolerant pastures including Pucinellia, Tall Fescue, and Persian Clover are likely to produce increased production and environmental benefits from improved ground cover. The use of Tall Wheat Grass (TWG) – Dundas, will need to be assessed on a site by site basis. It is likely to be a viable option in saline areas not associated with drainage lines (i.e. breaks of slope and flat, elevated plains) with strict grazing guidelines. In the Little Swanport catchment use of tall wheat grass is not recommended due to the risk of escape and impact on aquaculture production in the lower estuary. Within drainage lines, revegetation with salt tolerant woody vegetation and salt tolerant hybrid trees may be viable depending on the levels of soil salinity and offer additional biodiversity benefits.

Avoidance The Low Relief Dolerite GFS is currently being targeted for irrigated expansion, particularly in the Little Swanport catchment. Avoiding the development of irrigated production on or adjacent to saline discharge areas will be an important management strategy to minimise the spread of salinity within the catchment. Maintenance of remnant vegetation may also be important especially where vegetation occurs adjacent saline areas.


Identification of potential saline discharge areas before irrigation production systems are developed.

•

Rehabilitation of saline discharge areas using native species and trials using both local and non-endemic species.

•

Development of the understanding of the relationship between groundwater flow and surface water quality is required in the Little Swanport catchment.

•

The effect of cropping systems on groundwater recharge, salinity discharge and surface water quality.

•

The effectiveness and cost benefit of establishing salt tolerant pastures.

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Local/Intermediate scale GFS in low relief dolerite Options Biological Management of Recharge



Avoidance

Monitoring.

Treatment Perennial pasture Crop management Planting trees/ woody vegetation Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage Irrigation management Salt tolerant pasture Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Relevance Moderate. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. High. Opportunities exist to replace annual cropping and fallow periods with permanent horticulture or perennial crops ie. lucerne. Moderate. Tree planting may be viable on soils not suited to irrigated production. High. Improved surface drainage will reduce soil salinity in some areas. Low. Aquifer permeability and issues associated with disposal of saline water limit application. Low-moderate. Draw down restricted by low soil permeability. Disposal of saline water is a potential issue. High. Recharge can be reduced under irrigation areas through use of irrigation scheduling tools. High. Salt affected areas could benefit from establishment of salt tolerant pastures. N.A. Moderate. May be appropriate in smaller discharge areas where grazing is not viable. Very High. Minimise or avoid development of irrigated production systems on saline land Low. Few large areas of remnant woody vegetation remain within this GFS. Moderate. No known groundwater monitoring exists. Groundwater is likely to respond rapidly following landuse change. Very High. Surface water within this GFS is often saline. Monitoring irrigation water salinity is important to prevent crop losses. Moderate. Prevent crop losses through salt accumulation associated with saline irrigation.

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LRLF-GFS – Local/Intermediate scale GFS in low relief, layered fractured rocks (Approximately 26 000 ha) Local/Intermediate scale GFS occur at the base of low and moderate slopes scattered throughout the region


Fractured Triassic/Permian sedimentary rocks Lower slopes and basins Small – generally less than 500 ha. Dryland pasture, cropping, native vegetation, forestry Variable up to 800 mm Low lying areas Fractured Triassic/Permian rocks Moderate, generally less than 100 m2/day more than 30 ha (≈ 0.1% of GFS) 0.1 to 14 dS/cm (100 to 14 000 μS/cm) Seasonal Throughout the GFS, plus adjacent high relief fractured rocks

Landscape processes causing salinity Groundwater migrates from the upper parts of the aquifer and the above aquifer (such as the high relief dolerite GFS) toward valley floors or via direct groundwater recharge. Groundwater within the GFS migrates down slope where it either discharges in a depression or flows beneath depressions down catchment.

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Management strategies Biological systems for managing recharge Broad scale native tree planting is likely be an effective means of reducing watertable level within the Low Relief Layered Fractured Rock GFS. In places the adoption and effectiveness of broad scale tree planting is likely to be restricted by the presence of tree decline throughout most of the GFS and the current value for pasture production. An undulating watertable and moderate permeability in the sandy to clay rocks afford limited opportunities for biological control of salinity where suitable farming systems are able to deliver a reduction in groundwater recharge. The landscape has a high transmissive capacity and therefore limited capacity to lower groundwater levels (within a reasonable timeframe) following recharge reduction.

Trees should be planted in belts above the primary salinity area, preferably in plantations at least 50 metres in width. Optimum conditions for groundwater interception are attained when the tree belts are planted above the saline area—at this position in the landscape groundwater salinity usually has a lower salinity and may approach within two metres of the land surface. For tree selection guidance refer to Finnigan and Poulton (2005).

Where the rainfall is high (>600 mm/year) and salinity is experienced, it is unlikely that perennial vegetation alone will have a significant role in salinity mitigation. In these instances the most promising salinity mitigation strategies are most likely to involve a mix of saline tree planting for localised watertable control, and perennial vegetation to improve farm productivity (helping offset the cost of tree Perennial vegetation affords limited opportunities for increased water use, but will be establishment). less effective where the annual rainfall is in excess of 600 – 700 mm. Lucerne or simular perennial vegetation may afford production opportunities in conjunction with limited recharge reduction benefits. Tree belts planted adjacent to areas of a shallow watertable afford the opportunity to intercept groundwater prior to it migrating into saline areas in lower valley rocks.

Engineering systems to control watertable level Groundwater pumping from the aquifer affords a level of salinity management. It may also be useful in augmenting farm water supplies, and low - moderate groundwater salinity levels is unlikely to prohibit stock water consumption. Other engineering options such as surface drainage, land grading and raised beds may be a suitable means of reducing the effects of waterlogging within this GFS. Surface drainage may also help to reduce the expression of salinity where salts have built up overtime through the evaporation of saline groundwater from shallow pools of standing water.

Living with salt Living with salinity options offer considerable potential within the Low Relief Layered Fractured Rock GFS. In areas with saline expression salt tolerant pasture systems such as Pucinellia, Tall Fescue, and Persian Clover are likely to produce increased production and environmental benefits from improved ground cover. The use of Tall Wheat Grass (TWG) – Dundas, will need to be assessed on a site by site basis, however, it is unlikely to be a viable option as most saline areas are associated with drainage lines or surface waterways. Given that grazing is the dominant landuse in this GFS, salt tolerant pasture systems are likely to be readily adopted by producers as they will require minimal changes to current farming systems. Planting on breaks of slopes and farm forestry may also be effective in some areas.

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Avoidance Areas within the GFS are being targeted for expansion of irrigated production, due to access to water resources and flat topography. Agricultural developments should seek to avoid irrigation on current or potential saline areas within this GFS. High risk areas include current discharge areas, areas with high salt storage in the soil profile and areas immediately up-slope of currently saline areas. Where possible remnant vegetation should be maintained, however, it is recognised that broad scale changes in vegetation management are probably required to reduce watertables in this GFS.


Determine the viability of groundwater pumping to reduce watertable height.

•

Understanding the effects of vegetation change and agricultural production on this GFS and long term expression of salinity.

•

Determine the location and extent of tree planting required to reduce watertable height to acceptable levels.

•

Determine the economic benefits of salt tolerant pasture systems.

•

Determine crop management systems that avoid or reduce leakage to the groundwater.

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Local/Intermediate scale GFS in low relief layered fractured rocks Options Biological Management of Recharge


Treatment Perennial pasture Crop management Planting trees/ woody vegetation Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage Irrigation management


Avoidance

Monitoring.

Salt tolerant pasture Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water

Surface soil salinity

Relevance High. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. High. Where cropping exists, opportunities may exist to replace annual cropping and fallow periods with perennial crops such as lucerne. Low - Moderate. Restricted due to land value and scale of replanting thought to be required to be effective. High. Raised beds, surface drainage will reduce waterlogging and reduce salt accumulation through evaporation of standing saline water. Low. Likely to be limited by slow permeability of upper aquifer and issues associated with disposal of saline water. High. Applicable where impermeable clay subsoils prevent drainage. Draw-down restricted by slow soil permeability. Low –Moderate. Use of irrigation scheduling tools may assist to reduce leakage, although slow permeability rocks will also help to reduce recharge. High. Production and environmental benefits are expected. Suitable land area likely to be of sufficient size to warrant investment. Low. May be possible, high to moderate salinity groundwater is expected. High. Probably limited to isolated areas due to dominance of grazing systems. Very High. Minimise or avoid development of saline land for high value production or irrigated agriculture. Low. Few large areas of remnant woody vegetation remain within the GFS. Very High. Long term trend data is required within this GFS, especially where recent landuse change (irrigation) has occurred or high value assets are at risk. Very High. Surface water within this GFS is often saline. Monitoring irrigation water salinity is important to prevent crop losses. Slow soil permeability will increase salt accumulation. Very High. Monitoring trends in soil salinity especially under saline irrigation is important.

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COL-GFS - Local scale GFS in Colluvium (Talus) (Approximately 5700 ha) Local scale GFS occurs scattered in the western parts of the study area, and the Western Tiers.


Colluvial sand, clay and boulders of various rock types Mid and foot slopes Small – generally less than 1000 ha Native vegetation, forestry, limited grazing & horticulture Variable up to 1600 mm At the break-of-slope Colluvial rocks and under ground streams Moderate generally less than 50 m2/day 40 ha (≈0.1% of GFS) 0.1 to 0.8 dS/cm (100 to 800 μS/cm) Seasonal Throughout the GFS, but more where soil cover is thin plus from neighbouring GFSs

Landscape processes causing salinity Local scale GFSs function to effect salinity within and below colluvium. Groundwater migrates from the upper parts of the aquifer towards the break-of-slope. Groundwater recharge to the aquifer occurs via direct rainfall. Groundwater discharge is most likely to occur at the break-of-slope where the watertable intersects with the base of a rise

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Management strategies Biological systems for managing recharge Biological control of recharge is difficult to Tree belts planted adjacent to areas of a shallow reduce due to the following factors: watertable afford the opportunity to intercept (a) Relatively small size of the GFS limits the groundwater prior to it migrating into saline influence recharge control planting would areas in lower valley rocks. Trees should be have on salinity expression in adjacent planted in belts above the primary salinity area, GFS. preferably in plantations at least 30 metres in (b) Unknown connections to deeper aquifers width. Optimum conditions for groundwater make targeting recharge planting’s difficult interception are attained when the tree belts are as recharge may also (or predominantly) planted above the discharge area. For tree occur in the adjacent Dolerite GFS. selection guidance refer to Finnigan and Poulton (c) Difficulty establishing plantations, (2005). especially at high elevations and on steep Perennial vegetation alone not will have a slopes. Areas with remnant vegetation on the Colluvium significant role in salinity mitigation. In these instances the most promising salinity mitigation GFS should be retained, especially where it strategies are most likely to involve a mix of exists beside larger stands of remanent vegetation on the High Relief Dolerite GFS or saline tree planting for localised watertable High Relief Fractured Rocks GFS. Occasionally control, and perennial vegetation to improve farm productivity (helping offset the cost of tree this GFS is used for horticultural production, establishment). including vineyards, due to the steep slopes assisting drainage and warmer temperatures on north facing slopes. A relatively steep watertable and moderate permeability in the sandy rocks afford opportunities for biological control of salinity where suitable farming or forestry systems are able to deliver a reduction in groundwater recharge. The landscape has a high transmissive capacity to lower groundwater levels (within a reasonable timeframe).

Engineering systems to control watertable level Where horticulture exists within this GFS sub surface drainage may assist to overcome the inherently low soil permeability. High volume groundwater pumping from the colluvial aquifer affords a level of salinity management. It may also be useful in augmenting farm water supplies, and low groundwater salinity levels will not limit stock water consumption.

Living with salt Where the rock fracture pattern brings saline groundwater to the soil surface, salt tolerant farm forestry or productive pasture options could be considered. The areas affected are most often small to moderate. They occur in response to the discharge of moderate to high salinity groundwater in regions where seasonal rainfall is relatively high. Treatment involves fencing out affected areas and the establishment of salt tolerant species such as Puccinellia, strawberry clover etc.

Avoidance Where large areas of remnant vegetation exist, (usually in association with the High Relief Dolerite GFS) efforts should be directed towards maintenance of the existing vegetation. Development of high value horticulture needs take into account soil sodicity and potential for salt accumulation within soil resulting from saline irrigation.

Research Requirements • •

Determine the effect of saline irrigation on soil salinity and recharge under perennial horticulture such as vineyards. Determine the impact the GFS has on other GFS in the region.

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Local scale GFS in Colluvium (Talus) Options Biological Management of Recharge



Surface drainage (raised beds and surface grading) Groundwater pumping Sub surface drainage


Irrigation management Productive Use of saline land and water

Salt tolerant pasture Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry

Avoidance

Avoid development of known saline land

Monitoring.

Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Relevance Moderate. Opportunities exist to replace annual pasture with perennial pasture or maintain native perennial pasture. NA. Very few areas with cropping within the GFS. Low - Moderate. Some options exist, however position in landscape and small size of GFS make effective recharge control unlikely. NA - Low. Very few areas with cropping within the GFS & steep slopes ensure good drainage. Mod. Some potential. NA - Low. Rare however sub surface drains may be installed under horticultural developments. Low. Deficit irrigation of vineyards and other horticulture occurs in some areas. Potential for recharge is low, however risk of salt accumulation with saline irrigation exists. Low. Generally not required. Isolated springs may benefit from salt tolerant vegetation including productive pasture and farm forestry. NA. Groundwater quality is high. Low. Generally not required. Isolated springs may benefit from salt tolerant vegetation including productive pasture and farm forestry. NA. Not generally applicable due to minimal saline expression. Horticultural developments should avoid tunnel prone soils. Moderate - High. Maintain remnant vegetation where it exists. Low. Limited land area, complex aquifer. Low. Limited to horticultural production. Moderate. Generally not required, however, soil monitoring is considered a high priority if saline irrigation water is applied to this GFS.

101


Summary Relevance scores in Table 5 indicate that the application of the proposed salinity management options are most relevant to the Alluvial Plains and Slopes GFS, Low Relief Fractured Rocks GFS, and Low Relief Dolerite. The lowest relevance for management option included the elevated Basalt, High Relief Dolerite, and Colluvium GFS. Of the 15 management options, maintenance of perennial pasture, avoiding development (including irrigated production) on known saline land, and monitoring of irrigation water quality and groundwater were found to have the highest relevance.

102


Basalt (Low)

Basalt (Elevated)

Score

Monitoring.

Colluvium

Avoidance

Dunes


Sub surface drainage Irrigation management Salt tolerant pasture Saline aquaculture & salt harvesting Salt tolerant trees – Farm forestry Avoid development of known saline land Maintain remnant woody vegetation. Groundwater Irrigation water Surface soil salinity

Low Relief Layered Fractured Rocks


High Relief Layered Fractured Rock

Perennial pasture Crop management Planting trees/ woody vegetation Surface drainage (raised beds and surface grading) Groundwater pumping

Low Relief Dolerite

Biological Management of Recharge

High Relief Dolerite

Treatment

Current Floodplains

Options

Alluvial Plains & Slopes

Table 5 Summary: Relevance of Management Option to Each GFS

H H

M L

M NA - L

M H

H NA

H H

H M

M NA

H M

M NA

25 14.5

L

L

M– H

M

M

L–M

M

L-M

L

M

16.5

M

M

NA

H

NA

H

L

NA - L

M

NA

13.5

M

L

NA

L

L

L

M– H

NA -L

M

L

12

H

H

NA

L-M

NA

H

NA

NA - L

L -M

NA

12.5

VH

H

NA

H

NA

L –M

H

L

H

NA

18.5

H

M

L

H

L

H

L

L

M- H

NA

17.5

L

L

NA

NA

L-M

L

NA

NA

NA

NA

4.5

H

M

L

M

L

H

L

L

M

NA

16

VH

VH

L

VH

NA

VH

L

NA

VH

NA

22

L

L

VH

L

H

L

M

M-H

M

M

19.5

VH VH

M VH

L NA

M VH

M NA

VH VH

L L-M

L L

M M

L NA

20 20.5

VH

M

NA

M

NA

VH

L

M

M

NA

17

40

22

14.5

30.5

8.5

Score 42 31 13 33.5 14.5 VH = Very High (4), H = High (3), M = Moderate (2), L = Low (1), NA = Not Applicable or None (0) * Highest score indicates highest relevence

103

8.0 Field checking conceptual models 8.1

Historical groundwater information

Within the Southern Midlands some investigations have provided insight to the hydrogeological environment and salinity issues of the region, this section attempts to summarise the key findings from reports published at the time of this project. Previous salinity related studies within the Southern Midlands Assessment, rehabilitation, management and monitoring of salt affected farmland in Tasmania (Finnigan 1998)

Finnigan investigated land salinity and the impact on vegetation. The project focused upon the treatment of salinity rather than the processes which caused it. As part of this work shallow groundwater bores were constructed and EM31 (electromagnetic induction) surveys were undertaken. Salinity treatment trials were established and recommended methods of vegetation planting documented. Extent and impacts of dryland salinity in Tasmania (Bastick & Walker 2000)

As part of the National Land and Water Resources Audit (NLWRA), Bastick and Walker made the first attempt to define the extent of salinity in Tasmania. The report used land system mapping as a basis for estimating salinity area within each land system unit in 2000. The salinity area was approximated to be in the order of 53 500 hectares with a possible increase of 9360 hectares by 2050 (Bastick & Walker 2000). Land degradation salinity risk project (Grose 2003)

Grose undertook an investigation of salinity risk at three locations across Tasmania. One, site was located in the Coal River Valley, within the study area of this project. The Grose study focused upon the salinity impact on soil attributes and therefore agricultural productivity. The study identified about 20% of the study area fell within the moderate to high salinity category with a distinct salt bulge between 75 and 150 centimetre depth. The report also suggested irrigation resulted in no groundwater fluctuation in the area (inferred to be groundwater recharge).

104


The report concluded the area has sodic soils and is at a clear salinity risk. Also, current irrigation practices do not appear to contribute groundwater recharge to the aquifer but further monitoring is required to determine long-term trends. 8.2

Groundwater trends

Two groundwater monitoring programs overlap the region: Mineral Resources Tasmania (MRT) and Department of Primary Industries, Water and Environment (DPIWE). MRT monitoring network

The MRT bore monitoring network extends throughout Tasmania, included as part of this network are 2 bores located within the Southern Midlands. The network was established with an emphasis on monitoring groundwater resources, namely groundwater level and water quality. Few reports relating to groundwater monitoring have been written—of note are Bacon and Latinovic (2003) and Ezzy (2004). A review of groundwater in Tasmania (Bacon & Latinovic 2003)

Bacon and Latinovic provided a good summary of groundwater prospectively and aquifer yields throughout Tasmania. An overview of the Mineral Resources Tasmania statewide groundwater monitoring network (Ezzy 2004)

To provide an overview of MRT statewide groundwater monitoring network, Ezzy scrutinised the network. The report identified considerable deficiencies in the monitoring network, which was initially installed for salinity and groundwater mapping projects. The majority of bores require significant maintenance for the sustainable management of Tasmania’s water resources (Ezzy 2004). Within the Southern Midlands, Ezzy commented on the two monitoring bores within the region, at Tunnack and Melton Mowbray. Tunnack

At Tunnack, the bore monitors Permian mudstone (Intermediate scale GFS in low relief layered fractured rocks) and indicates a rising trend of 0.11 metres/year based a upon linear regression. The bore has been identified as requiring decommissioning or redrilling. 105


Melton Mowbray

The Triassic sandstone aquifer is monitored by the MRT monitoring bore (intermediate scale GFS in low relief layered fractured rocks) at Melton, with a linear regression trend of 0.55 metres/year (overall groundwater trend likely to be ≈ 0.10 metres/year). The bore has also been identified as requiring decommissioning and/or redrilling due to non standard bore screen installation. DPIWE monitoring network

The DPIWE groundwater monitoring network was established to investigate salinity projects on a property scale. As a result the majority of groundwater monitoring bores are less than 5 metres deep and monitor the watertable only. Considerable effort has been put into the construction and monitoring of the groundwater bores. Bastick and Walker (2000) reviewed all DPIWE monitoring bores and estimated groundwater trends. At the time of data collection in this project, 12 monitoring bores existed in the study area. Groundwater trend summary

Bores in the DPIWE monitoring network were not interpreted for trends as evaporative processes lower the depth of watertable at the site, and therefore obscure any possible groundwater trend. The monitoring frequency and the benefit of the data collected requires review. 8.3

Salinity

The presence of salinity in the study area varies according to season and land use, in conjunction with the underlying hydrogeological setting. Area estimates of salinity for each land system (Bastick & Walker 2000) is the best available for determining the extent of salinity over the entire study area. Table 4 presents the percentage area of salinity within each land system unit and suggests the majority of salinity in the region is located upon the alluvial plains and slopes GFS.

106


Figure 39 Location of MRT and DPIWE bores and bores drilled in this project Table 6 Estimated likely area of salinity within each GFS unit (modified from Bastick & Walker 2000)

Groundwater Flow System (GFS)

Approximate area (ha)

Local scale GFS on alluvial plains and slopes

600

Local scale GFS in current floodplain

300

Local scale GFS in dunes

200

Local scale GFS in high relief dolerite

500


300

Local/Intermediate scale GFS in low relief dolerite

20

Local scale GFS in high relief layered fractured rocks

400

Local/Intermediate scale GFS in low relief layered fractured

30

rocks Local scale GFS in colluvium

40

* The above table provides an estimate of the likely salinity area, the actual salinity area is not known in the region

107


8.4

Stream EC survey

During April 2005 a rapid assessment stream salinity survey was undertaken at the majority of road-stream intersections of the Southern Midlands. The objective of the survey was to provide a snapshot of stream salinity base flow. Figure 40 presents the locations and water salinity at each sampling point. The EC meter used for this survey was a TDS 1200, with 7 metre lead and calibrated twice a day with 718 μS/cm conductivity standard. The sampling was undertaken at road crossings where possible, and the probe of the EC meter was generally lowered to a depth 20 centimetres from the base of the stream where the average EC was noted. EC readings were taken at the point of flow, this ensured the water was mobile, and hence the sample was representative of the area. EC readings were generally only taken where there was flowing (no sampling of stagnant water). The rapid rate at which the survey was carried out is important with respect to being an accurate ‘snapshot’ of the catchment, hence the technique of stream surveying relies upon consistent surveying throughout the catchment in a relatively short timeframe (1-3 days).

Figure 40 Location of rapid stream EC survey sample points 108


The lowest base flow groundwater salinity of 80 EC (0.08 dS/cm) was recorded upon the local scale high relief layered fractured rocks GFS, whereas the local scale GFS in alluvial plains and slopes had salinities of up to 7400 EC (7.4 dS/cm). Surface water salinity increased down catchment, particularly down the Coal River. The EC survey identified that there was little stream base flow in the upper parts of the Coal River and less in the Jordan River, while the Little Swanport and Prosser rivers had no base flow within the study area during the time of the sampling. This information suggests that in general, groundwater levels are relatively deep in the Little Swanport and Prosser catchment and the Jordan and Coal rivers have shallower watertable depths. Whereas the lower parts of the Coal River appears to have both the greatest base flow volume and salinity (excluding irrigation water). The dissected nature of the study area provides significant potential for relatively high base flow (groundwater) volumes into streams. This dissected landscape also allows the ‘natural’ drainage of the landscape, therefore limiting the land area affected by a shallow watertable. Broad flat areas such as on the alluvial plains and slopes and current floodplain would appear to have the greater area of shallow watertable. 8.5

Groundwater drilling program

Prior to this project some effort and resources (with a groundwater resource prospective) were focused on groundwater drilling upon agricultural lands within the Southern Midlands. Exploration drilling for high quality groundwater has resulted in some understanding of where potable aquifers are located, with some documentation of conceptual groundwater processes. Groundwater drilling as part of this project focuses on the processes which drive groundwater movement and therefore salinity, such as groundwater recharge and discharge pathways.

109


Figure 41 Air rotary drilling equipment after bore construction Design and application

In order to gain a greater understanding of groundwater processes and movement two bore transects (refer to Figure 42 for locations) were constructed and also a single bore was drilled at Oatlands for groundwater level monitoring. Drilling description of the drilling includes consideration of soil, regolith and hard rock.

110


Figure 42 Location of drilling sites as part of this project Richmond transect

The Richmond transect is positioned 2 kilometres upstream and perpendicular to the Coal River at Richmond. The primary objective of the transect was to determine the variations in watertable level, watertable salinity, groundwater pressure and soil salinity down slope to the Coal River upon the low relief layered fractured rocks GFS and onto the floodplain alluvium GFS. Drilling of the Richmond site ( and Kempton and Oatlands) confirmed that there are significant salt stores in most parts of the landscape and that the GFS do contain saline groundwater,. Therefore there is a potential for salinity to increase in the future if these GFS are destabilised but changes in recharge. All drilling stratigraphic records and aquifer data collected is presented in Appendix 1 – Richmond Transect

111


Figure 43 Location of Richmond transect Richmond - summary of drilling results

Groundwater drilling results shows a steep groundwater level gradient of 0.023 m/km from site R1 to R2 along the transect, the groundwater gradient then flattens out to 0.013 between bores R2 and R3. Information suggests the upper slopes of the dolerite geology provide notable groundwater to the Coal River Valley, this can be verified by further groundwater monitoring and subsequent recharge estimates. Limited drilling funds prohibited the locating of a deep bore adjacent to bore R3, therefore pressure heads gradients were not able to be determined. Appendix 1 – Richmond Transect provides further discussion of drilling results obtained along this transect. Kempton transect

The primary objective of installing piezometers along the Kempton transect was to determine the variations in watertable level, watertable salinity, groundwater pressure and soil salinity down slope upon the local/intermediate scale GFS in low relief layered fractured rocks All drilling stratigraphic records collected and aquifer data collected is presented in Appendix 2 – Kempton Transect.

112


Figure 44 Location of Kempton transect Kempton - summary of drilling results

Drilling along the Kempton transect identified discrepancies with geology mapping in the region. The transect identified a relatively flat groundwater gradient of 0.01 m/km along the transect and variable groundwater salinity along the transect which appears to reflect weathered depth. Appendix 2 – Kempton Transect discusses drilling results in greater detail. Oatlands bore

The Oatlands bore is positioned along Henrietta Street, south of the Oatlands township. The primary objective of installing the bore was to begin monitoring the intermediate scale GFS in low relief layered fractured rocks in the north to central parts of the catchment, as there is currently no groundwater monitoring in this area. Drilling the bore has also provided insight to the likely groundwater level and quality of the aquifer of the area. All drilling stratigraphic records collected and aquifer data collected is presented inAppendix 3 – Oatlands site.

113


Figure 45 Location of Oatlands bore Oatlands - summary of drilling results

Limited information is able to be drawn from the single bore drilled at Oatlands. Depth to water level is deeper than expected, but groundwater salinity is higher than expected. Appendix 3 – Oatlands site discusses drilling results in greater detail.

114


9

Evaluation of current groundwater monitoring

9.1

Current groundwater monitoring

Evaluation of environmental trends is crucial in determining the effectiveness of a natural resource management program. To monitor the long-term trends of salinity related features, a number of features can be monitored including: area of salinity, salt load export, groundwater levels and groundwater and surface water salinity. All of these features are impacted by local (eg. land use) and regional (eg. climate) factors, and for this reason commitment of long-term monitoring is required for accurate environmental trends to be determined. The following section examines the current monitoring status of both the DPIWE and MRT groundwater monitoring network within the study area. Upon review of the two monitoring networks it is apparent each differs. DPIWE monitoring network

The DPIWE groundwater monitoring network was established primarily to demonstrate the linkage between groundwater and salinity processes. For this reason most bores are located in areas of shallow watertable (i.e. 20 metres) could not be drilled adjacent to the shallow bore R3.

Figure 48 Generalised regolith profile of the Richmond transect 4.5

Groundwater salinity Depth to water level

0

4 2

3

4

2.5 6 2

1.5

8

Depth to water level (metres)

Groundwater salinity (dS/cm)

3.5

1 10 0.5

12 R3

R1

R2

0

Figure 49 Groundwater and salinity information along the Richmond

transect Table 10 Depth to water level and groundwater salinity of the Richmond transect

Site id R1

Bore depth (metres) 24

Depth to water level (metres) 7.85

Groundwater salinity (dS/cm) 2.12

R2

16

10.10

3.05

R3

7

3.39

4.03 133


Site R1 – Local scale GFS in low relief dolerite

0–2

Light clay with rock fragments up to 30 mm

2–4

Light clay with rock fragments up to 30 mm Light clay with rock fragments up to 10 mm Light clay with rock fragments up to 5 mm

4–6 6–8 8 – 10

Hard rock

Colour (wet)

Geology

pH soil/water 1:5 extract Moisture

Cream – light brown

Weathered Triassic sandstone

Dry

Cream – light brown Cream – light brown Cream – light brown Light grey

Weathered Triassic sandstone Weathered Triassic sandstone Weathered Triassic sandstone Weathered dolerite

Dry

0

2

4

6

8

10

EC soil/water 1:5 extract

12

14

0

0

Dry

0.5

1

1.5

0

5

5

Dry Moist

10 – 12

Hard rock

Light grey

Weathered dolerite

Wet

12 – 14

Hard rock

Light grey

Weathered dolerite

Wet

14 – 16

Hard rock

Light grey

Weathered dolerite

Wet

16 – 18

Hard rock

Light grey

Weathered dolerite

Wet

18 – 20

Hard rock

Light grey

Weathered dolerite

Wet

20 – 22

Hard rock

Light grey

Weathered dolerite

Wet

22 – 24

Hard rock

Light grey

Weathered dolerite

Wet

10

Depth (metres)

Texture

Depth (meters)

Depth (metres)

15

20

10

15

20

EC1:5 (dS/m) pH 25

Bore depth 24 metres

ECe/10 (dS/m) 25

This location contains significant salt stores above the watertable which could be mobilised if watertable rise or significant extra recharge occurs at this site.

135


Site R2 – Local scale GFS in low relief layered fractured rocks Texture

Colour (wet)

Geology

Cream – light brown Light brown cream

4–6

Fine sandy light clay

Light brown cream

Weathered Triassic sandstone Weathered Triassic sandstone Weathered Triassic sandstone

Dry

2–4

Medium clay with some rock fragments up to 10 mm Fine sandy light clay

Weathered Triassic sandstone Weathered Triassic sandstone Weathered Triassic sandstone Weathered Triassic sandstone

Dry

6–8

Some medium clay hard rock

Light brown cream

8 – 10

Some medium clay hard rock

Light brown cream

10 – 12

Medium clay

Light orange – light brown

12 – 14

Medium clay


14 – 16

Some medium clay in dolerite fragments


Weathered Triassic sandstone

2

4

6

8

10


12

14

0

0

2

Dry

0.2

0.4

0.6

0.8

0

2

Dry

4

Dry Moist Wet

4

6

Depth (metres)

0–2

Moisture

Depth (meters)

Depth (metres)

pH soil/water 1:5 extract 0

8

10

6

8

10

Wet

12

12

14

14

EC1:5 (dS/m) pH 16


ECe/10 (dS/m) 16

This location contains significant salt stores above the watertable which could be mobilised if watertable rise or significant extra recharge occurs at this site.

136


Site R3 – Local scale GFS in current floodplain Depth (metres) 0–2

Texture Clay with rounded quartz up to 10%, max 10 mm

Colour (wet) Light brown brown

Geology Quaternary rocks

pH soil/water 1:5 extract Moisture

0

2

4

6

8

10

12

EC soil/water 1:5 extract 14

0

0

Dry

2

6–8

Medium clay with angular quartz up to 40%, max 20 mm

Light brown – dark grey

Light orange light brown

Quaternary rocks

Quaternary rocks

Quaternary rocks

Moist

Wet

1.5

4

6

6

8

Depth (metres)


Light brown – dark grey

Depth (meters)

4–6


1

2

4

2–4

0.5

0

NOT SAMPLED 10

12

8

NOT SAMPLED 10

12

14

14

16

16

18

18

Wet

pH 20

EC1:5 (dS/m) ECe/10 (dS/m)

20


8 – 10


Light orange light brown

Quaternary rocks

Wet

137


Appendix 2 – Kempton Transect This section provides a discussion of drilling results obtained along the Kempton transect. The transect was selected based upon location and landscape, three GFSs were intersected upon the transect, the low relief layered fractured rocks, the high relief layered fractured rocks and the local scale GFS in alluvial plains and slopes. The Kempton transect also had good access perpendicular to the Jordan River, that is, there was adequate roadside access for construction of roadside bores without forgoing hydrogeological objectives of the transect Figure 44 presents the location of groundwater monitoring bores along the transect. A detailed topographic survey was undertaken to measure the elevation variation and the groundwater gradient, Figure 50 presents the elevation and depth to watertable along the transect and shows the depth to watertable is generally a subdued reflection of the elevation. 250

Elevation (metres) Watertable AHD (metres)

240 230

Elevation (metres)

220 210 200 190 180 170 160 150 0

500

1000

1500

2000 2500 Distance (metres)

3000

3500

4000

4500

Figure 50 Elevation and depth to watertable of the Kempton transect

Groundwater salinity and water level information of the nested sites is presented in Figure 51. Figure 51 shows groundwater salinity increases and depth to watertable decreases down slope along the transect. Data from the nested site K5 suggests a downward gradient of groundwater movement (eg. groundwater recharge site (Table 11). Variation in groundwater salinity information along the transect appears to increase down the transect, but salinity decreases upon the alluvial floodplain.

138


Low relief layered fractured rocks GFS


4.5

0

Alluvial plains and slopes GFS


4 3.5

5

10

3 2.5

15

High relief dolerite GFS

2

20 1.5


5

1 25 0.5 30 K6

K5

K4

K3

K2

K1

0

Figure 51 Groundwater and salinity information along the Kempton transect

Figure 51 suggests that the higher salinities are in the Local GFS in low relief layered fractured rocks with lower salinities in the GFS dolerite and alluvial plains.

139


Table 11 Depth to water level and groundwater salinity of the Kempton transect

Site id K1

Bore depth Depth to water Net pressure* (metres) level (metres) (metres) 30 28.32

Groundwater salinity (dS/cm) 0.52

K2

38

4.63

1.82

K3

22

8.90

3.65

K4

28

11.52

4.49

K5s

6

2.67

3.87

K5d

50

2.58

K6

48

5.38

-0.15

4.21 2.28

*+ indicates upward pressure, - indicates downward pressure Stratigraphic and water level information suggests one aquifer (Triassic/Permian geology) determines the depth to watertable along the transect, with a localised alluvium aquifer adjacent to the Jordan River. At the time of drilling, the floodplain alluvium aquifer had a downward pressure gradient to the underlying Triassic/Permian geology aquifer. This information suggests the Jordan River floodplain was recharging the Triassic/Permian geology aquifer in the area at the time of monitoring. It is expected that the Triassic/Permian aquifer is flushed from the overlying local floodplain alluvium aquifer as groundwater recharges the deeper aquifer. Localised variations in groundwater salinity is expected due to localised variances in hydraulic conductivity (i.e. higher hydraulic conductivity ≈ low groundwater salinity).

Figure 52 Generalised regolith profile of the Kempton transect

140


pH soil/water 1:5 extract

Site K1 – Low relief dolerite GFS Texture

Colour (wet)

Geology

0–2

Medium clay with rock fragments Rock fragments, medium clay

Weathered Triassic mudstone Weathered Triassic mudstone

Dry

2–4

Off white with orange mottles Light brown – off white

4–6

Rock fragments, medium clay

Off white – light brown

Dry

6–8


Light brown – off white

Weathered Triassic mudstone Weathered dolerite

8 – 10


Light grey – off white

Weathered dolerite

Dry

10 – 12

Rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand

Light grey

Weathered dolerite

Dry

Grey – dark blue

Dolerite

Dry

Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand Hard rock fragments, medium clayey fine sand

Grey – dark blue

Dolerite

Dry

Grey – dark blue

Dolerite

Dry

Grey – dark blue

Dolerite

Dry

Grey – dark blue

Dolerite

Dry

Grey – dark blue

Dolerite

Dry

Grey – dark blue

Dolerite

Moist

Grey – dark blue

Dolerite

Wet

Grey – dark blue

Dolerite

Wet

14 – 16 16 – 18 18 – 20 20 – 22 22 – 24 24 – 26 26 – 28 28 – 30

2

4

6

8

10


12

14

0

0

0.5

1

1.5

0

Dry

5

5

10

Dry

10

Depth (metres)

12 – 14

Moisture

Depth (meters)

Depth (metres)

0

15

15

20

20

25

25

EC1:5 (dS/m) pH 30

ECe/10 (dS/m) 30


141



Site K2 – Local/Intermediate scale GFS in low relief layered fractured rocks Geology

Moisture

Medium clay with 20% rock fragments

Light brown

Weathered mudstone Triassic

Dry

Weathered mudstone Triassic Weathered mudstone Triassic Weathered mudstone Triassic Weathered mudstone Triassic Weathered mudstone Triassic Triassic mudstone

Dry

2–4


Light brown – grey

4–6


Light brown – grey

6–8

Light clay with rock fragments

Light brown – light grey

8 – 10


Light grey

10 – 12


Light grey

12 – 14


Light grey

14 – 16

Light clay with rock fragments Light clay with rock fragments

Light grey

Very fine sandy clay

Light grey

16 – 18 18 –20 20 – 22

20 metres

Colour (wet)


Light grey

Light grey

4

6

8

10


12

14

0

5

10

Dry Dry Dry

Triassic mudstone Triassic mudstone

Dry

Triassic sandstone

Dry

Triassic sandstone

Dry

Dry

0.1

0.15

0.2

0.25

5

10

Dry Dry

0.05

0

15

Depth (metres)

0–2

Texture

2

0

Depth (meters)

Depth (metres)

0

20

25

15

20

25

30

30

35

35

EC1:5 (dS/m)

22 – 24


Light grey

Triassic sandstone

Dry

24 – 26


Light grey

Dry

26 – 28


Light grey

Triassic sandstone Triassic sandstone

28 – 30


Light grey

Dry

30 – 32


Light grey

32 – 34


Light grey

Triassic sandstone Triassic sandstone Triassic sandstone

34 – 36


Light grey

Wet

36 – 38

Light clay

Brown – marron

Triassic sandstone Triassic sandstone

pH 40

ECe/10 (dS/m) 40


Dry

Moist Wet

Wet

142


Site K3 – Local/Intermediate scale GFS in low relief layered fractured rocks Colour (wet)

Geology

Moisture

0–2

Medium clay with rock fragments


Geology mix, dolerite alluvium, Triassic

Dry

2–4


Light brown

Triassic siltstone

Dry

4–6


Light brown

Triassic siltstone

Dry

6–8


Light brown

Triassic siltstone

Dry

8 – 10


Light brown

Triassic siltstone

Dry

10 – 12


Light brown

Triassic siltstone

Dry

12 – 14


Light brown

Triassic siltstone

Moist

14 – 16


Light brown

Triassic sandstone

Wet

2

4

6

8

10


12

14

0

0

0.5

1

1.5

0

5

5

10

Depth (metres)

Texture

Depth (meters)

Depth (metres)

pH soil/water 1:5 extract 0

15

20

10

15

20

EC1:5 (dS/m) 16 – 18

18 – 20

20 – 22


Light brown

Hard rock

Light grey

Hard rock

Light grey

Triassic siltstone

Wet

Triassic sandstone

Wet

Triassic siltstone

Wet

pH 25

ECe/10 (dS/m) 25

Bore depths 22 metres

20 metres

143



Site K4 – Local/Intermediate scale GFS in low relief layered fractured rocks Texture

Colour (wet)

Geology

0–2

Medium clay

Light brown

Quaternary rocks

Dry

2–4

Medium clay

Yellow – light brown

Weathered mudstone

Dry

8

10


12

14

0

Weathered mudstone

Dry

6–8

Light clay

Light grey

Weathered mudstone

Dry

8 – 10

Light clay

Light brown

Weathered mudstone

Dry

10 – 12

Light clay

Light brown

Weathered mudstone

Dry

12 – 14

Light clay

Grey – blue

Weathered mudstone

Dry

14 – 16

Light clay

Grey – blue

Weathered mudstone

Dry

16 - 18

Light clay

Grey – blue

Weathered mudstone

Dry

18 – 20

Light clay

Grey – blue

Weathered mudstone

Dry

Weathered mudstone

Moist

0.5

1

1.5

0

5

10

Depth (metres)

Light brown

Grey – blue

6

5

Light clay

Light clay

4

Moisture

4–6

20 – 22

2

0

Depth (meters)

Depth (metres)

0

15

20

10

15

20

EC1:5 (dS/m) pH 25

22 – 24

Light clay

Grey – blue

Weathered mudstone

Wet

24 – 26

Light clay

Grey – blue

Weathered mudstone

Wet

26 – 28

Light clay

Grey – blue

Mudstone

Wet

ECe/10 (dS/m) 25


144



Site K5 – Local/Intermediate scale GFS in low relief layered fractured rocks Colour (wet)

Geology

0–2

Light clay

Light brown

2–4

Light brown

12 – 14 14 – 16

Light clay some gravel up to 5 mm Clayey fine sand some gravel up to 10 mm Medium sand some gravel up to 10 mm Sandy clay some gravel up to 10 mm Clayey fine sand some gravel to 5 mm Clayey fine sand Clayey fine sand

Quaternary rocks Quaternary rocks Quaternary rocks

16 – 18

4–6 6–8

Light brown

Dry

8

10


12

14

0

0.5

Moist

Wet

Light grey Light grey

Mudstone Mudstone

Wet Wet

Clayey fine sand

Light grey

Mudstone

Wet

18 – 20

Clayey fine sand

Light grey

Mudstone

Wet

20 – 22

Clayey fine sand

Light grey

Sandstone

Wet

22 – 24

Clayey fine sand

Light grey

Sandstone

Wet

24 – 26

Clayey fine sand

Light grey

Sandstone

Wet

26 – 28

Light grey black Light grey

Mudstone

Wet

28 – 30

Clayey fine sand some black coal Clayey fine sand

Mudstone

Wet

30 – 32

Clayey fine sand

Light grey

Mudstone

Wet

32 – 34

Clayey fine sand

Light grey

Mudstone

Wet

34 – 36

Black

Mudstone

Wet

36 – 38

Clayey fine sand some black coal Clayey fine sand

Black

Sandstone

Wet

38 – 40

Clayey fine sand

White

Sandstone

Wet

40 – 42

Clayey fine sand

Light grey

Mudstone

Wet

42 – 44

Clayey fine sand

Light grey

Mudstone

Wet

44 – 46

Clayey fine sand

Light grey

Mudstone

Wet

46 – 48

Clayey fine sand

Light grey

Mudstone

Wet

49 – 50

Clayey fine sand

Light grey

Mudstone

Wet

0.5

1

1.5

0

0.5

Dry

Quaternary rocks Quaternary rocks Mudstone

10 – 12

6

Moisture

Light brown grey Light brown grey Light grey

8 – 10

4

1

1

Wet

Wet

1.5

1.5

Depth (metres)

Texture

2

0

Depth (meters)

Depth (metres)

0

2

2.5

2

2.5

3

3

3.5

3.5

4

4

pH 4.5

NOT SAMPLED below 4 metres due to mud drilling

Bore depth 6 and 50 metres

EC1:5 (dS/m) ECe/10 (dS/m)

4.5

NOT SAMPLED below 4 metres due to mud drilling

145



Site K6 – Local/Intermediate scale GFS in low relief layered fractured rocks Texture

Colour (wet)

Geology

Light clay including rock fragments Light clay including rock fragments Light clay including rock fragments Light clay including rock fragments Light clay including rock fragments

Light brown

Dry

10 – 12

Light clay

Light grey

12 – 14

Light clay

Light grey

14 – 16

Light clay

Light grey

16 – 18

Light clay

Dark grey

18 – 20

Hard rock (clay)

Light grey

20 – 22

Hard rock (clay)

Light grey

22 – 24

Hard rock (clay)

Light grey

24 – 26

Hard rock (clay)

Light grey

Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone Weathered mudstone

26 – 28

Hard rock (clay)

Light grey

Dry

28 – 30

Hard rock (clay)

Light grey

30 – 32

Hard rock (clay)

Light grey

32 – 34

Hard rock (clay)

Light light grey

Weathered mudstone Weathered mudstone Weathered mudstone Sandstone

Dry

34 – 36

Hard rock (clay)

Light grey

Mudstone

Dry

36 – 38

Hard rock (clay)

Light grey

Mudstone

Moist

38 – 40

Hard rock (clay)

Light grey

Mudstone

Moist

40 – 42

Hard rock (clay)

Light grey

Sandstone

Moist

42 – 44

Hard rock (clay)

Light grey

Sandstone

Wet

44 – 46

Hard rock (clay)

Light grey

Sandstone

Wet

46 – 48

Hard rock (clay)

Light grey

Sandstone

Wet

2–4 4–6 6–8 8 – 10

Light brown Light brown Light brown Light brown

4

6

8

10


12

14

0

0.5

1

1.5

0

Moisture

5

5

10

10

15

15

Dry Dry Dry Dry Dry Dry Dry Dry Dry Dry

Depth (metres)

0–2

2

0

Depth (meters)

Depth (metres)

0

20

25

30

20

25

30

35

35

40

40

45

45

Dry Dry

EC1:5 (dS/m)

Dry Dry

pH 50

ECe/10 (dS/m) 50


32 metres

146


Appendix 3 – Oatlands site The single bore drilled at Oatlands was constructed in an attempt to begin to understand groundwater processes in the area, yet limited funds prohibited drilling at other locations. Topographic information of the Oatlands bore was measured to determine the elevation of the bore. Groundwater salinity and water level information of the site is presented in Figure 53. Table 12 shows groundwater salinity at the bore is slightly higher than expected and is likely to be as result of the bore being located in a highly weathered zone, which typically has a relatively high salt store. A watertable depth of 13 metres was recorded which suggests the site is unlikely to be impacted by salinity in the near future. A highly weathered zone was encountered while drilling in the first 25 metres, this zone had a relatively low hydraulic conductivity and thus caused the bore depth to be much greater than required due to uncertainty of the watertable while drilling. 0

3

2

2.5

4

2

6

1.5

8

1

10

0.5

12

0

14



O1


3.5

Figure 53 Groundwater and salinity information at the Oatlands site Table 12 Depth to water level and groundwater salinity of the Oatlands site

Site id O1d

Bore depth (metres) 34

Depth to water level (metres) 12.79

Groundwater salinity (dS/cm) 3.01 147



Site O1 – Local/Intermediate scale GFS in low relief layered fractured rocks Depth (metres)

Texture

Colour (wet)

Geology

0

2

4

6

8

10


12

14

0

0

Moisture

0–2

Clayey fine sand


Sandstone

Dry

2–4

Clayey fine sand

Off white – light grey

Sandstone

Dry

4–6

Clayey fine sand


Sandstone

Dry


Sandstone

5

Dry

8 – 10

Clayey fine sand


Sandstone

Dry

10 – 12

Clayey fine sand


Sandstone

Dry

12 – 14

Clayey fine sand


Sandstone

Dry

Off white – light grey Off white – light grey Off white – light grey Off white – light grey Off white – light grey Off white – light grey Off white – light grey

Sandstone

Dry

Sandstone

Dry

Sandstone

Dry

Sandstone

Dry

14 – 16

Clayey fine sand

16 – 18

Clayey fine sand

18 – 20

Clayey fine sand

20 – 22

Clayey fine sand

22 – 24

Clayey fine sand

Sandstone

Dry

24 – 26

Clayey fine sand

Sandstone

Dry

26 – 28

Clayey fine sand

Sandstone

Moist

28 – 30

Clayey fine sand


Sandstone

Wet

30 – 32

Clayey fine sand


Sandstone

Wet

32 – 34

Clayey fine sand


Sandstone

Wet

0.3

0.4

10

Depth (metres)

Clayey fine sand

0.2

5

10

Depth (meters)

6–8

0.1

0

15

20

15

20

25

25

30

30

EC1:5 (dS/m) pH 35

ECe/10 (dS/m) 35


32 metres

148


Appendix 4 – Bore construction, drilling sampling and groundwater data collection Piezometer construction involved auguring, air-rotary and mud-rotatory drilling methods to be employed. Augur drilling was the preferred method of drilling as stratigraphic samples were of the best quality in comparison to the other techniques. Auger drilling sites were limited to soft unconsolidated locations due to the limitations of the method and therefore all augur drilled holes were at a maximum depth of 10 metres. Air-rotary drilling produced poorer quality stratigraphic samples, but the drilling technique allowed for harder geology to be drilled (including hard rock with an air-hammer). In general, all holes drilled between 10 to 30 metres used the air-rotary drilling method. Mud drilling was limited to highly unconsolidated rocks (eg. gravel, sand). The method used water to drill the hole, which reduced rocks ‘caving into the hole’ while drilling. Stratigraphic samples were of poor quality using this technique, and the intersection with high yielding aquifers could not be confirmed while drilling. Following the drilling of the hole by the various methods placement of 50 or 100 millimetre PVC (100 mm casing if greater than 10 metres deep) was inserted into the hole. A 0.3 metre sump with a 1.5 metre slotted interval of PVC above was placed at the base of all holes. In holes with significant clay content, following the placement of the PVC piping the piezometer was flushed with water for approximately 10 minutes. This involved passing water from the inside of the PVC piping to the outer hole with the objective of removing the sludge accumulated during the drilling process. After flushing, approximately 10 litres of 2 mm gravel (dependent on diameter of hole) was poured down the outer rim of the hole, forming a gravel pack between the slotted interval and the substrate. Following this, approximately 400 millilitres of bentonite pellets (dependent on diameter of hole) were poured down the outer rim of the hole. The remaining void left on the outer rim of the hole was then filled with soil. The final task involved in the construction process was surging the piezometer with compressed air. An air hose was placed down to the slotted interval within the PVC piping and air surged for approximately 20 minutes. Stratigraphic drilling samples were taken at 1 metre intervals from 0 to 10 metres, and at 2 metre intervals at depths greater than 10 metres. Samples had colours and textures described (in the field) and were later analysed for soil EC and pH in the laboratory. Groundwater level and salinity measurement was undertaken following bore development.

149