Chowilla Business Case

PIKE INVESTMENT PROPOSAL

“The large divergence between required numbers of juveniles for population maintenance and observed numbers of juvenile trees on the Pike floodplain implies that the tree community is not currently sustainable. Action management intervention (e.g. managed flooding) is required to increase germination and recruitment in addition to ensuring the survival of existing trees” (Wallace, 2009).

Pike Investment Proposal

January 2010

Report prepared by: The SA MDB NRM Board.

CITATION: This report can be cited as follows: Hollis, B.A. 2010. Pike Investment Proposal. Report prepared for DWLBC.

DISCLAIMER: Although reasonable care has been taken in preparing the information contained in this publication, neither the South Australian Murray-Darling Basin Natural Resources Management Board nor the contributing authors accept any responsibility or liability for any losses of whatever kind arising form the interpretation or use of the information set out in this publication.

For further information please contact:

SA Murray-Darling Basin Natural Resources Management Board Wade St, Berri SA 5343 Phone: (08) 8582 4477 Fax: (08) 8582 4488 Email: [email protected] www.samdbnrm.sa.gov.au

CONTENTS Executive Summary 1

1. Introduction 6 1.1 Vision, Objectives and Targets 6 1.1.1 Vision 6 1.1.2 Objectives and Ecological Assets 6 1.2 Urgency of Action 7 1.2.1 Declining health of the Pike floodplain 7 1.2.2 Flow requirements to achieve ecological objectives 7 1.2.3 Flow requirements for vegetation targets 8 1.2.4 Maintenance of Water Supply & Water Quality on the Pike Floodplain 8 1.2.5 Reducing Groundwater Impacts to the Pike River Floodplains and River. 9 2. Background 9 2.1 Overview of Ecological Values and Treats 9 2.2.1 Indigenous 10 2.3 Major threats to Environmental Values 11 2.3.1 Altered flow regime 11 2.3.2 Altered groundwater regime 12 3. Potential Management Options 13 3.1 Management Options Assessed 13 3.1.1 Do Nothing 13 3.1.2 Increase flow from Mundic Creek to Lock 4 via Creeks 14 3.1.3 Weir pool raising at Lock 5 14 3.1.4 Permanent pumping infrastructure 14 3.1.5 Gravity watering wetland sites 14 3.1.6 Irrigation infrastructure 15 3.1.7 Environmental regulating structures at Col Col and on Tanyacka Creek. 15 3.1.8 Seasonally raise and lower water levels in the upper Pike-Mundic 15 3.1.9 Seasonally raise water levels in Tanyaca Creek 15 3.1.10 Raise and Lower Lock 4 16 3.1.11 Fish Passage 16 3.1.12 Regulate Individual Wetlands 16 3.1.13 Improve Flow Paths 16 3.1.14 Alternative maximum elevations for downstream regulating structures (15.8mAHD- 16.8mAHD) 17 3.1.15 Potential ecological benefits associated with the maximum extent (16.8mAHD) 24 3.1.16 Potential ecological impacts and risks associated with the maximum extent (16.8mAHD) 24 3.2 Summary of Options 25

4. Preferred Long-term Management Option 27 4.1 New environmental regulators in Tanyaca Creek, Col Col, and at Deep Creek and Margaret Dowling Creek 27 4.1.1 Proposed Works 30 4.1.2 Approvals 31 4.1.3 Timeframe 32 4.1.4 Costs 32 4.1.5 Ecological Benefits 33 4.1.6 Potential Ecological Risks 34 4.1.7 Ecological tradeoffs 36 4.1.8 Salinity Impacts 37

4.1.9 Potential Operating Regime 37 4.1.10 Water Requirement 40 5. Ecological Monitoring 43 5.1 Capacity for monitoring of floodplain condition and the effectiveness of intervention programs. 43

6. Complementary Management Actions 43

7. Sustainable Water Supply 44 7.1 Irrigation 44 7.2 Development and Water License Controls 46 7.3 Setting Sustainable Diversion Limits 46 7.4 Water Supply Options For Extractors 46 7.4.1 Alternative Supply from the River Murray Channel via pipelines 47 7.4.2 Gravity Pipeline bypassing Mundic Creek and Pike Lagoon 48 7.4.3 Re-lift Weir at Pike Lagoon Outlet 49 7.4.4 Summary of Water Supply Options Assessed 50 8. The Pike Salt Interception Scheme (SIS) 51 8.1 Pike SIS and the Basin Salinity Management Strategy (BSMS) 51 8.2 The Pike SIS Concept Design 52 8.3 Future Work for the Pike SIS 52

9. The Next Steps for the PIP Program 53 9.1 Investigations proposed for 2010 and beyond 53

10. Management Roles and Responsibilities 57

11. Summary 58

12. References 58

List of Tables

Table 1 Hydrological regime requirements for all vegetation target areas in the lower Murray ...... 8

Table 2 Flooding extent, frequency, and duration under natural and current conditions at Pike (Ecological Associates and AWE, 2008)...... 12

Table 3 Summary of anticipated benefits, risks and possible mitigation strategies associated with the Pike inundation options ...... 22

Table 4 Summary of potential surface water management options for the Pike anabranch and floodplain complex ...... 26

Table 5 Cost per hectare assessment of proposed landscape scale intervention activities throughout the Murray-Darling Basin...... 27

Table 6 Modelled inundation coverage for elevations with and without environmental regulators on the Pike floodplain...... 28

Table 7 Mean monthly pan evaporation rates at Lock 5 (DHI 2006)...... 41

Table 8 Mean water volume that needs to be delivered to SA for full regulator operation in addition to the modelled current flows to SA over the 1891-2006 period. Each event assumes a 120 day operational period for the regulator (based on MDBC modelling)...... 41

Table 9 Water volume that needs to be delivered to SA in excess of entitlement flows, in the event that minimum inflows of 10,000ML/day are required for the entire 120 day operational period for the Pike environmental regulators ...... 42

Table 10 Water requirements for operation of the Pike environmental regulators ...... 43

Table 11 Costs associated with various Pike pipeline options...... 47

Table 12 Summary of Water Supply Options ...... 51

Table 13 Proposed cost sharing arrangement between the MDBA and the Government of South Australia for the Pike SIS ...... 52

Table 14 Investigations proposed for 2010 and beyond ...... 54

List of Figures

Figure 1a. Inundation coverage of the Pike floodplain at low flows (10,000ML/day flow to SA), without (left) and with (right) environmental regulating structures operating upstream of Col Col and Tanyaca Creek...... 3

Figure 1. Inundation of the Pike floodplain under “current” conditions i.e. no environmental regulators...... 18

Figure 2. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 15.80mAHD as generated by the Pike DTM, which assumes no gradient on the river...... 19

Figure 3. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 16.30mAHD as generated by the Pike DTM, which assumes no gradient on the river...... 20

Figure 4. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 16.80mAHD as generated by the Pike DTM, which assumes no gradient on the river...... 21

Figure 5. Optimal elevation of environment regulators on the Pike floodplain of 16.4mAHD...... 29

Figure 6. Summary of estimated total construction costs for proposed floodplain infrastructure ...... 33

Figure 7. Hydrograph of modelled current flows from 1890-1919, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007) ...... 38

Figure 8. Hydrograph of modelled current flows from 1920-1949, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007) ...... 39

Figure 9. Hydrograph of modelled current flows from 1950-1979, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007) ...... 39

Figure 10. Hydrograph of modelled current flows from 1980-2006, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007) ...... 39

Figure 11. Hydraulic conditions of the highly modified Pike anabranch system...... 45

Figure 12. Example of the crude structures that currently exist throughout the Pike anabranch complex in order to divert the majority of flow down Mundic Creek, the upper and lower Pike River for extraction...... 45

Figure 13. Pipeline route to provide extractors on the Upper and Lower Pike with an alternative water supply from the River Murray Channel...... 48

Figure 14. Pipeline option to eliminate extraction from Mundic Creek and Pike Lagoon ...... 49

Executive Summary

This document presents a case for investing in the Pike floodplain and strives to clearly highlight that the proposal represents the only practical way of curbing the rapid and widespread ecological decline currently being experienced on the Pike floodplain.

Modifications to existing infrastructure, as well as development of new infrastructure is regarded as the most effective way of achieving (or at least approaching) the ecological objectives for the Pike floodplain. Wise use of environmental regulators could maintain and enhance the conservation value of as much as 25% of the Pike floodplain.

However, substantial investigation remains to be undertaken to confirm the viability of environmental regulators on the Pike floodplain; and to inform potential operating regimes to ensure infrastructure is operated in such a way as to maximise ecological benefit and minimise risk and impact. Further hydraulic, groundwater and vegetation modelling is required to understand flow behaviour, salinity impacts and potential benefits to tree health under a range of scenarios. Investment in detailed design is also required to confirm design and operating range of new and modified infrastructure (regulators, ancillary banks and fishways). In addition, it will be necessary to continue to undertake a scientifically robust and defensible ecological monitoring program focused on tree health, understorey vegetation, water quality, groundwater, fish, birds and frogs.

To delay or withdraw continued investment at this stage of the project and to „do nothing‟ will be contrary to strong, informed community and scientific support. Significantly, failing to provide sufficient funding for critical investigations on the Pike floodplain has the potential to jeopardise the considerable work and momentum gained to date; potentially undermining the confidence community members have in the current project team and the process being undertaken to identify and implement the preferred suite of short and long term management actions for the Pike floodplain. Members of the Pike community remain committed to working with the Pike project team to improve the ecological condition of this important national, state and local asset. Delays in funding will also inevitably lead to a further deterioration of floodplain condition.

The proposal outlined in this document is based on detailed technical information relating to the Pike floodplain and is supported by the Pike Implementation Plan (PIP) Reference Committee, Pike Floodplain Steering Committee, Pike Sustainable Water Supply Steering Committee, Pike River Land Management Group and the Pike-Mundic Association. Importantly, the proposal has also received support from community, scientific, agency and Indigenous groups.

Pike Floodplain Ecological Objectives

The Pike vision is "To achieve a healthy mosaic of floodplain communities which is representative of the communities which would be expected under „natural‟ conditions and which ensure that indigenous plant and animal species and communities survive and flourish throughout the site."

From this vision, the following overall objectives have been identified: • To improve the condition of existing vegetation; • To improve key aquatic riparian and terrestrial habitats required by native flora and fauna, including waterbirds, fish, reptiles, mammals and frogs; • To achieve a sustainable balance between the needs of the various users of the floodplain; and • To recognise and, where possible, respond to the needs of the existing productive users of the floodplain.

In support of these objectives, the Pike Floodplain has been divided into eight ecological assets: Flowing watercourses; Permanent wetlands; Temporary wetlands; Red Gum woodlands; Lignum shrublands;

Chenopod Shrublands / Grasslands; Black Box woodlands; and Dunes.

The assets each correspond to a different hydrological regime and together they comprise all of the terrestrial and aquatic habitats present on the Pike floodplain. The assets were selected on a hydrological basis to identify and classify hydrological and other threats and to link management options directly to the assets.

These objectives and ecological assets underpin this investment proposal and reflect the intention to maintain and improve existing habitats.

Do Nothing Scenario

Under a “Do Nothing” scenario the health of the Pike floodplain will continue to decline. Tree health modelling undertaken by CSIRO has predicted that under the current water regime, approximately 2700ha (90%) of all trees (River Red Gums, Black box and River Coobah), will die or seriously decline on the Pike floodplain within the next 30 years. The “do nothing” approach is clearly unacceptable and it is recognised that a pragmatic solution must therefore be sought using small flows to best effect.

Preferred Management Option

The long term management option which provides the greatest potential to achieve the objectives for the site involves the construction of a new network of environmental regulating structures at Col Col and Tanyaca Creek. Smaller ancillary structures on bypass flow routes would also be required. The proposal has been costed at $38m (URS, 2010), which includes replacement of the Deep Creek and Margaret Dowling Creek inlet regulating structures, as well as Col Col and Tanyacka Creek environmental regulators, fishways, ancillary by-pass regulators, blocking banks and other works. These costs are similar to the proposed “Katfish” project costs which inundates approximately 1000ha of high value floodplain (the Pike environmental regulators concept inundates approximately 1466ha, whilst influencing a far greater area through lateral groundwater recharge).

The new environmental regulators could enable water level variation within the Pike floodplain between 14.35mAHD, representing normal upper pool level at Col Col and 16.40mAHD, representing 100mm above the “normal” upper pool level at Lock and Weir No. 5. Thus the new regulating structures across the Pike anabranch system would be used to regulate water levels within the upper Pike floodplain over a maximum range of approximately 2.05m. The regulator will be operable under flows ranging from entitlement conditions up to 50,000 ML/day, although flows of at least 10,000 ML/day would be optimal to operate to the maximum possible extent; whilst minimizing potential ecological risks.

A range of alternative management actions and regulator sizes has been considered. Options considered included pumping, channel forming and gravity watering, and weir pool raising. Most of these options are being further investigated at a small scale as potential complementary actions, largely to bring benefits to areas outside the area of impact of the new regulating structures.

Short-term solutions such as pumping onto high value wetland sites continues to be effective at the local scale (less than 5% of the Pike floodplain can be watered in this way), but is only considered as supporting the longer-term environmental regulating structures solution. Pumping is not considered a viable approach for broader floodplain management.

Benefits

The environmental regulating structures (if deemed viable) could provide much needed water to a significant area of the Pike floodplain and reverse the severe ecological decline that has been observed over a number of years. The regulating structures could enable the inundation of at least 1450ha, or 25% of the floodplain and influence an even larger area through lateral groundwater freshening. This could enable the maintenance and improvement of the Red Gum, Black Box and River Coobah. It could also inundate large areas of other

floodplain habitats including wetlands, woodlands, shrublands and grasslands. The area inundated during a 10,000ML/day event with the proposed environmental regulators operating at 16.40mAHD would be similar to a natural 65,000ML/day flood. However, the inundation extent caused by the regulator would be slightly greater in the upper section of the floodplain and reduced in the lower section.

In addition to the vegetation benefits, the proposed regulators could provide a number of environmental benefits within the inundated area. These include increased connectivity between riverine and floodplain habitats, freshening of groundwater systems, improved soil condition, rejuvenation of existing wetland habitats, establishment of new floodplain and wetland plant communities, enhanced regional biodiversity, increased zooplankton abundance, increased habitat and breeding opportunities for water birds and frogs, and additional habitat for small native fish.

Risks

Engineered solutions to ecological problems are not without risk. A detailed ecological risk assessment process will need to be undertaken for a number of issues that have been identified as potential risks. These include the potential for cyanobacterial blooms, invasion by weeds, reduced lotic or flowing water habitats, interrupted fish passage, decrease in large-bodied native fish populations and increases in populations of common carp.

The scale and mitigation of these risks is discussed in detail in this proposal and is fundamentally related to the operating regime introduced. It is intended that the regulators (if deemed viable) would be operated to maximise ecological benefits and minimise negative impacts. It is recognised that most risks can be mitigated to a satisfactory level by avoiding frequent operation of the regulators under low flow conditions. An adaptive management approach will be applied in the development and refinement of the operating regime(s).

Most risks, including the risk of reducing high velocity fish habitat and increasing river salinity can be avoided or mitigated in several ways including: avoiding frequent and/or prolonged operation the regulator at times of low flow (<10,000ML/day QSA); operating at lower than the maximum regulator height during periods of low flow; and reducing the duration of operation during periods of low flow. Ecological risks are significantly reduced or eliminated when the regulator is operated at above entitlement flows (>10,000ML/day QSA).

Following operation of the Pike environmental regulators, a small downstream salinity increase will occur. It is expected that salt will flow off the surface of the floodplain at the commencement of floodplain inundation, whilst salt from groundwater can be expected to enter the anabranch on recession. Groundwater modelling is required to confirm peak salinity increases under a range of managed inundation scenarios. The post inundation salinity impact will be influenced by the operating regime (recession rate) and flow in the River Murray. Potential therefore exists to minimise risks and impacts to downstream users. Assessment of salinity impact over the MDBC 1975-2000 benchmark, as measured at Morgan remains to be determined; as

does the salinity impact immediately downstream in Lyrup post operation of environmental regulators. Confirming the likely salinity impact under a range of scenarios will need to be the focus of considerable assessment to develop an intimate understanding of groundwater processes and to quantify salinity and vegetation condition impacts.

Major salt accessions from the Pike floodplain tend to occur following very large floods. The proposed environmental regulating structures cannot be used during the highest flows (>50,000ML/day flow to SA because they would be overtopped) nor can it replicate the same inundation extent as experienced during a large natural flood; thus major salt accessions are not expected to result from operation of the proposed environmental regulating structures. Salinity inflow to the River Murray and Pike anabranch system is not regarded as posing any risk ecologically, or to downstream water users. Real time salinity impacts, particularly to extractors within and immediately downstream of the Pike anabranch remains to be assessed.

Operation of the regulators will also result in elevated groundwater levels under certain sections of the floodplain and may increase salt accumulation in non-flooded areas. This process also occurs during natural high flow conditions but may contribute to tree health decline in small sections of floodplain.

Operating Regime

To maintain floodplain vegetation health, an operating frequency of approximately one operation every three years is likely to be necessary. Initially however, in the continual absence of natural floods, it may be necessary to operate the Pike environmental regulating structures in 2 or 3 successive years to return the floodplain to a condition capable of withstanding 2-3 years without wide scale watering (this is one of the key findings from past Red Gum watering projects). To meet the requirements of floodplain vegetation over the 115yr (1891-2006) modelled “current” flow to SA hydrograph, a total of 38 operating events (of different magnitude) would be required. The optimal ecological time for watering would be in spring to early summer. Use of the regulating structures to maximum elevation (16.40mAHD) is likely to occur during periods when flow to South Australia is at least 10,000ML/day. This will help ensure ecological risks are minimised.

Water Requirement

The water requirements for Pike comprise of the volume that is consumed through seepage and evapo- transpiration during (or following) operation of the regulator and is not returned to the river.

The volume of water used during operation of the Pike environmental regulators, being operated to 16.40mAHD and the raising of Lock 5 to 16.80mAHD, under a flow to SA of 10,000ML/day for 120 days has been calculated at 16.94GL (Watertech, 2009). Further hydraulic modelling is proposed to quantify volumes (in the River Murray channel, the anabranch creeks, and on the floodplain) under a range of “regulator” and “no-regulator” scenarios, including the 30,000ML/day and 50,000ML/day scenarios using the same hypothetical operating regime as that used to calculate losses associated with the 10,000ML/day scenario.

The total volume of water that will be used by the environment during any given operation of the regulating infrastructure is dependant on the prevailing flow conditions and the height of the regulating structures. Water volume figures will be reduced if the environmental regulator is operated at less than its maximum height.

Complementary Works and Measures

Although the principle of a managed inundation regime which incorporates components of a natural hydrological regime via a range of surface water regulating infrastructure has been endorsed by various high level committees as being the preferred long term management option (in terms of it‟s potential to achieve ecological objectives) for the Pike floodplain; opportunities to complement the structures and further improve floodplain condition need to be further assessed, particularly in areas where limited floodplain inundation is expected under the regulating structures scenarios. Options may include the provision of permanent pumping infrastructure; lowering of sill heights to enable gravity inflow; and/or any other

measures that are deemed suitable to provide fresh water; particularly to the lower section of the Pike floodplain.

The Pike floodplain has long been recognised as a major contributor of salt to the River Murray. In addition, rising saline groundwater and soil salinisation (combined with reduced flooding frequency) has led to severe degradation of floodplain ecosystems.

Further investigation is required regarding a potential groundwater management scheme; focused on improving ecological condition on the floodplain, as opposed to the proposed SIS for the Pike, which targets interception of saline water from the highland. If deemed viable, such a scheme would provide additional protection to the floodplain ecology; particularly during extended dry periods.

Approval requirements

An EPBC referral will need to be submitted to the Australian Government (Department of Environment and Water) prior to the installation of any new regulating infrastructure on the Pike floodplain.

Planning SA, the relevant planning authority in South Australia has advised that: “The establishment of structures on watercourses and the floodplain for hydrological manipulation purposes is not a prescribed activity that requires development approval under the Development Act 1993 (nor a Major Development declaration). Thus, the proposed regulating structures and levee banks do not need development approval. The management of any potential environmental, social and economic impacts can be adequately addressed by the SA MDB NRM Board‟s internal assessment and decision-making processes (including the Cabinet Submission process)”.

Sustainable Water Supply

A complementary suite of water supply investigations have been undertaken and supported by the Pike Sustainable Water Supply Steering Committee; being led by DWLBC to ensure access, water supply and water quality issues for domestic and irrigation extractors are not adversely impacted by potential floodplain actions.

Many potential issues particularly in relation to flow, water levels and water quality (including potential salinity impacts) require further robust assessment to ensure any potential risks to extractors are minimised and/or mitigated. Numerous options have been investigated to enable floodplain restoration actions to be maximised whilst maintaining a sustainable water supply for extractors reliant on the Pike anabranch complex, including the potential of providing the current extractors with an alternative water supply from the River Murray channel via pipelines. Numerous routes and pipeline configurations have been assessed. All major pipeline options to provide an alternative water supply from the River Murray channel in isolation provide no ecological benefit to the floodplain. They are also considered cost prohibitive and as such will not be investigated further as part of this project. Additional funds will be required however in order to modify existing pump off-takes to ensure extractors are not adversely affected by a future lowering event.

Summary

Key stakeholders have been consulted prior to the submission of the Investment Proposal and have had direct input to the development of the Pike Floodplain Management Plan. Community forums and field tours have also been held to provide updates and gain feedback from targeted stakeholders and the wider community about the proposed Pike environmental regulating structures.

1. Introduction

The overall intent of the Pike Project is to enhance and where possible, restore the environmental values of the Pike by delivering ecological benefits to the floodplain and its wetlands. The SA MDB NRM Board and its predecessors have placed a high priority upon floodplain protection and rehabilitation in combination with attempts to attract increased environmental flows.

Although Pike is currently experiencing a significant decline in health, the floodplain still retains significant ecological character and attributes. It supports a high diversity of both terrestrial and aquatic habitats, including populations of rare, endangered and nationally threatened species. The floodplain also contains many sites of European and Indigenous cultural heritage significance.

There are a number of processes that are compromising the ecological integrity of the Pike floodplain. The key threats to the site are altered flow regimes, elevated highly saline groundwater, obstructions to fish passage, grazing pressure, and pest plants and animals. Flow regulation in particular has reduced flooding frequencies and duration, and has resulted in saline groundwater levels increasing by up to 3m higher than under natural or pre-regulation conditions. This is having a significant impact on the native fauna and flora. The outlook for aquatic and terrestrial ecosystems looks bleak unless there is more frequent, more extensive flooding. In the absence of a major increase in environmental flows and engineering intervention, it is evident that this decline will continue.

Within the SA reach of the River Murray there are six major weirs, of which three (Locks 4, 5 and 6) provide a unique opportunity for broadscale floodplain inundation (by taking advantage of the 3m hydraulic gradient that has been created by the difference between upper and lower pools). The Pike system, which straddles Lock 5, is one of those opportunities.

1.1 VISION, OBJECTIVES AND TARGETS 1.1.1 Vision

1.1.2 OBJECTIVES AND ECOLOGICAL ASSETS

In support of these objectives, the Pike Floodplain has been divided into eight ecological assets: Flowing watercourses; Permanent wetlands; Temporary wetlands; Red Gum woodlands; Lignum shrublands; Chenopod Shrublands / Grasslands; Black Box woodlands; and Dunes.

These objectives and ecological assets underpin this investment proposal and reflect the intention to maintain and improve existing habitats.

1.2 URGENCY OF ACTION 1.2.1 Declining health of the Pike floodplain

The Pike floodplain contains approximately 1257ha of River red gum forest and woodland, and 1540ha of Black box woodland. To maintain these areas in a healthy condition, flooding is generally required every 2-3 years for River red gums and every 4-8 years for Black box. Under natural conditions, a flood event of 80,000 ML/day occurred on average every 2-3 years and would provide water to the majority of the River red gum communities on the Pike floodplain. An event of this magnitude has not been experienced since 1993. This lack of flooding, in conjunction with ongoing salt accumulation in the floodplain soils has resulted in widespread decline in the health of trees throughout the Pike floodplain.

An assessment of floristic vegetation and tree health mapping throughout the River Murray Floodplain, including at Pike was undertaken in 2002 (Smith & Kenny, 2005). More recently (2009), the Murray-Darling Freshwater Research Centre (Wallis, 2009) were engaged to develop a statistically robust monitoring framework for the Pike floodplain that will be able to detect change in tree condition that may occur due to future management actions, unmanaged floods or uncontrollable events (e.g. fire). The assessment of tree condition by the MDFRC was undertaken using the core parameters that have been established for assessment of tree condition at the Living Murray Icon Sites (2009). This was a different approach to that undertaken by Smith and Kenny in 2002 where the tree condition (referred to as “health”) was assessed on a scale of 0-5. Ten trees were assessed in each sampling quadrat. These scores were averaged for each species at a site. In order to utilise this data for mapping of tree condition, Smith and Kenny (2005) reduced the number of categories to three: rating 0 was converted to “dead”, ratings 1, 2 and 3 were combined to a single value of “unhealthy” and ratings of 4 and 5 were combined into a single value of “healthy”

Due to the different approach to assessment of tree condition undertaken in the assessments, the capacity for direct comparison of condition as assessed in 2002 and 2009 is limited.

Direct comparisons should therefore be made with caution, however it is of note that numerous River Red Gum and Black box transects located within regions previously mapped in 2002 as being in “healthy” condition, were assessed as being “stressed” in 2009.

The distribution of healthy River red gums is such that virtually no healthy trees remain in areas of the floodplain that are located away from permanent watercourses. Even trees along permanent watercourses are in decline as a result of decreasing soil moisture and saline groundwater in the root zone due to lack of flooding in the last 16 years.

The salt and moisture-stress damage at Pike is predicted to get worse in the continual absence of inundation events. CSIRO WINDS vegetation modelling has predicted that based on the continuation of flows typical of the last 15 years that dead trees (River Red Gum, Black Box and River Coobah) will increase from 39% currently to 49% of the floodplain area by 2035.

While the lower River Murray has experienced prolonged drought events in the past, the combination of reduced flooding (frequency and duration) and elevated saline groundwater at Pike is inducing a major death event. This rapid and ongoing decline in tree health observed at Pike has the potential to significantly compromise the achievement of ecological objectives for the site unless an inundation regime to promote widespread recovery and recruitment is reinstated as a matter of urgency.

1.2.2 Flow requirements to achieve ecological objectives

A flow to SA of 65,000ML/day for 90 days (which is required to inundate approximately 25% of the Pike floodplain) requires a total volume of 5850GL. This would be sufficient to prevent the accumulation of salt in the floodplain, or to achieve a salt balance. The likelihood of recovering nearly 6000GL/year to maintain floodplain ecology is low.

Under current circumstances, it is acknowledged that it will not be possible to achieve the flow required to maintain whole of floodplain health in the short term (or perhaps even in the long term). A solution to maintain floodplain health must therefore be sought using low flows.

1.2.3 Flow requirements for vegetation targets

Table 1 outlines the flow required to maintain and/or enhance specific vegetation communities. These regimes assume current operating conditions and that no other management intervention has been undertaken.

The flow regime requirements were developed using results from the CSIRO WINDS modelling. The flow regimes outlined in table 1 are the minimum flows required by each of the vegetation communities to stop salt accumulation in the soil and maintain suitable soil moisture.

Table 1 Hydrological regime requirements for all vegetation target areas in the lower Murray Source: CSIRO, 2005.

Flow band to SA Majority of target Average flow regime Timing (preferred) (ML/day) vegetation in flow band required 5000 – 40,000 River red gum forest, 3 months, 61 years in Late winter/spring/ summer herbland 100 40,000 – 50,000 River red gum forest, Tea 3 months, 53 years in Late winter/spring/ summer tree, herbland, Lignum, 100 Coobah 50,000 – 60,000 River red gum woodland, 3 months, 45 years in Late winter/spring/ summer Black box, Coobah, Tea 100 tree, grassland, Lignum, Chenopod, herbland 60,000– 70,000 River red gum woodland, 3 months, 32 years in Late winter/spring/ summer Black box, Coobah, 100 grassland, Lignum, Chenopod, herbland 70,000– 80,000 Black box, Lignum, 3 months, 28 years in Late winter/spring/ summer Chenopod, Samphire, 100 herbland 80,000– 90,000 Black box 3 months, 24 years in Late winter/spring/ summer 100 90,000– 140,000 Black box 3 months, 12 years in Late winter/spring/ summer 100

These flow volumes and frequencies are clearly unattainable under current conditions.

The delivery of additional water to the floodplain and the reduction of salt accumulation will be reliant on complementary engineering intervention.

1.2.4 Maintenance of Water Supply & Water Quality on the Pike Floodplain

The Pike Floodplain including the Lower and Upper Pike River, Pike Lagoon and Upper Mundic system are important sources of water for local communities.

Currently, approximately 41 irrigators utilise the water for primarily irrigation but also domestic use.

The key immediate threat to maintenance of water supply for irrigation and domestic use is declining water quality. Water quality, in particular salinity levels have declined since the 1960‟s. Increased levels of sedimentation of water supplies and diminishing flows are also significant issues.

Any future management actions need to ensure the maintenance of water quality and sufficient water flows. Water quality needs to be within salinity tolerances for crops of almonds, grapes and citrus.

In addition, there is a requirement to ensure that pumps can continue to access water at key points within the floodplain.

1.2.5 Reducing Groundwater Impacts to the Pike River Floodplains and River.

The Pike irrigated area in the highlands adjacent to the Pike floodplain is considered a high impact zone of salinity discharge with significant discharge to the Pike floodplain and ultimately the river.

Excess irrigation drainage water has led to localised groundwater level rise and mounding which has created a groundwater gradient between the highland areas and the nearby floodplain aquifers. Saline groundwater from the highland area now flows to the floodplain aquifer at rates much higher than previously.

This has led to significant salinisation to the Pike floodplain and river as the floodplain aquifer is hydrologically connected to the Pike surface water system which allows for discharge of saline groundwater into the Pike anabranch complex.

Numerical groundwater modelling estimates that the 160 t/day is currently entering the River Murray.

The significant groundwater discharge to the floodplain and ultimately the river is a significant underlying cause of floodplain and river salinity with associated ecological, social and economic costs. From a regional perspective the Pike Floodplain and river has the highest level of salinity input than any other floodplain area within South Australia.

2. Background 2.1 OVERVIEW OF ECOLOGICAL VALUES AND TREATS

The information contained in this section is extracted from the Pike River Floodplain Management Plan (Ecological Associates and AWE, 2008) and all references contained are within the primary document.

The Pike River floodplain provides a diverse range of aquatic and floodplain habitats and a correspondingly diverse flora and fauna. Many of the habitat features of the Pike River floodplain have been degraded elsewhere, and the system provides the potential to preserve an important complex of inter-related habitats at one location.

Although isolated from the River Murray by a series of barriers, Mundic Creek provides a deep, permanent water body which supports a diverse fish population and a healthy macroinvertebrate community. Other watercourses and wetlands provide an extensive network of aquatic habitats which include shallow water and mudflats for waterbirds, extensive reed beds used by a number of shy waterbirds for shelter, and open water habitats which are used by fish-eating birds such as Pelican and Cormorant and by dabbling ducks such as Teal.

The lowest-lying parts of the floodplain are located near the banks of the River Murray. These areas support relatively healthy Red Gum woodland communities, which in places have a diverse understorey of native grasses and herbs. Red Gums provide habitat for a number of hollow-dwelling bats, birds, mammals and reptiles. The food provided by flowers and vegetation in the understorey and the canopy sustains high levels of ecosystem productivity, particularly after floods.

Lignum shrublands occur in less frequently flooded areas. Between flood events Lignum shrublands are relatively simple plant communities with low species diversity. They provide shelter for kangaroos during the day and nesting sites for some bush birds. During floods, the shrublands and adjacent chenopod shrublands provide very productive habitats. Macroinvertebrates and zooplankton quickly populate vegetated and open water areas. Fish graze on decaying plant matter and spawn in the flooded vegetation.

Lignum, which is relatively dormant during dry periods, grows new shoots and provides nesting platforms for waterbirds such as Ibis.

Black Box woodland occupies the most infrequently flooded parts of the floodplain. Like Red Gum, Black Box provides habitat for hollow-dependent animals. The understorey comprises grasses, chenopods, some low shrubs and herbs. This vegetation is generally intolerant of flooding, but provides a valuable habitat for aquatic fauna as it decays when flooded. The flowers and new shoots provided by Black Box trees after flooding supports a food web based on nectar and sap-eating insects and birds; and their predators.

Despite these values, there are significant threats to these values in the Pike River floodplain. Extensive areas of the floodplain are degraded by salinisation which occurs through groundwater discharge and the evaporative concentration of salts in floodplain soils. Salinity threatens habitat values in watercourses and threatens the health of vegetation over extensive areas of the floodplain.

Floods are essential to many important conservation values of the floodplain, but have become less frequent as a result of the storage and diversion of water upstream. Insufficient flooding has led to low productivity on the floodplain, poor vegetation health and low rates of germination and recruitment of floodplain trees.

Significant areas of the floodplain are grazed by stock, feral animals and kangaroos. Grazing has exacerbated the vegetation impacts associated with salt and flooding and has completely degraded vegetation in some areas.

The free movement of fish between the floodplain and the river is important to successful breeding, dispersal and migration. There are several blockages to fish passage which reduce the habitat value of the floodplain.

Watercourses and wetlands in the Pike River floodplain are becoming filled with sediment. Siltation has resulted from increased sediment in water entering the system from the River Murray upstream, from the impoundment of water in the Pike-Mundic pool and the Lock 4 weir pool and by the loss of frequent floods which used to scour watercourses and wetlands and maintain their shape.

2.2.1 Indigenous

There is much historical documentation of the use of the local environments by Aboriginal people and the descriptions tend to reflect the varied nature of food and other resources provided by the river and surrounding floodplain and highland environments.

The following detailed review and presentation of this material was prepared by Pring (2006) for the upgrade of the Pike River Land and Water Management Plan.

Aboriginal occupation along the River Murray system dates back more than 30,000 years at Lake Mungo to the east. The Dreaming story of Ngurunderi, tells of the creation of the River Murray, from the junction of the Darling and Murray to the Murray Mouth and Coorong. According to Tindale (1974) the local Aboriginal peoples around Renmark were known as Erawirung and Ngintait, sub-groups of the Meru (men).

The most detailed description of Aboriginal interaction with the local environment is sourced from Edward John Eyre (1845). The following paragraphs are provided as a sample of the ways in which Aboriginal people interacted with and depended on the environmental resources of the district: „Fish are procured in different ways, eg „weirs or dams, large seines (nets) made of string manufactured from the rush, and buoyed up with dry reeds, bound into bundles, and weighted by stones tied to the bottom.‟

Watercress was collected from the borders of lagoons at the Murray. The tops, leaves and stalks were steamed in a ground oven, providing a favourite and inexhaustible supply of food.

„...the bulbous roots of a reed called the belillah (probably bulrush), certain kinds of fungi dug out of

the ground, fresh-water mussels …‟ were eaten.

„Fresh water turtles, varying in weight from three to twelve pounds‟ were caught similarly to fish.

Small individual hooped nets were used by the group as well to scoop fish. Other types of nets and fish traps were also used seasonally „catching fish weighing from twenty to seventy pounds‟. As a group between 5 and 40 men dived to spear fish when the water levels were low.

At flood time, spearing of fish was practiced from canoes made from the bark of the gum tree. The spears were made from native pine. Freshwater lobsters weighing from two to four pounds are also speared, sometimes ten to sixteen in an hour or two.

Frogs, rats, lizards and other reptiles are eaten as well as grubs from trees and the ground.

The roots of various plants are eaten including the „flag‟ or cooper‟s reed „which grows in marshes or alluvial soils that are subject to periodical inundations. It is used all year but best after floods. The root is roasted in hot ashes. The „belillah‟ is another, about the size of a walnut, hard and oily and roasted and pounded into a thin cake. „Immense tracts of country are covered with this plant on the flats of the Murray …‟

A small berry or currant, called by the natives of Moorunde „eertapko‟, coloured red and an agreeable acid flavour, growing upon a low creeping tap-rooted plant, of a „salsolaceous‟ character, found in the alluvial flats of the Murray, among the polygonum bushes and other places.

When hunting possum up in a smooth trunked tree, a stone hatchet or strong sharp-pointed stick is used to make notches in the bark for toe holds.

Swans and brolga (native companions) were speared or killed with clubs. Swans were caught easily in the waterholes or lakes when mounting, as they are then unable to fly.

Birds are killed with clubs, by spearing, snaring, by noosing and by netting.

Nets for netting birds are as large as thirty to sixty feet broad and from twenty to forty deep, formed from lacing together pieces of old fishing nets.

There are recordings of burial places in the Cobdogla area so it could be assumed that this would be the case along the river to the east. Burials are often in sand, rather than clay, for ease of digging.

There are many sites of cultural significance along the River Murray and consideration must be given to these when developing environmental management options.

2.3 MAJOR THREATS TO ENVIRONMENTAL VALUES 2.3.1 Altered flow regime

The natural flow regime of the River Murray has been significantly modified by basin wide flow regulation, which has included the construction and operation of a series of locks and weirs and a number of upstream storages.

River regulation has resulted in greatly modified frequency, magnitude and duration of flow events including large flood events. These changes have altered the hydrology and ecology of floodplain environments, which are strongly influenced by variability. This flow alteration represents a major threat to ecosystem productivity and diversity as it disrupts many river-floodplain processes. In addition, restrictions to flow have also been caused by the construction of levee banks and blockages on anabranch creeks and other channels. Consequently, there has been a loss of connectivity between the river and its floodplain habitats.

The construction of Lock 5 was completed in 1930 on the River Murray near the upstream end of the Pike

floodplain, resulting in permanently higher water levels on the adjacent floodplain area, higher groundwater levels, and the continuous flows of water through the Pike floodplain anabranch system. A 3m head now drives flow through the anabranch. Water levels in the lower section of the Pike anabranch are also maintained by the presence of Lock 4 further downstream.

Under natural conditions flow was highly variable and frequently reached levels which inundate the floodplain (Table 2). River flow exceeded 30,000 ML/d almost every year and events of 70,000 ML/d occurred in 50% of years. Events of 120,000 ML/d, which would inundate most of the Pike River floodplain including Black Box woodlands, occurred on average one year in four.

River regulation and diversions have severely reduced the frequency and duration of peaks in river flow. The frequency of flow peaks between 20,000 and 40,000 ML/d have been reduced by approximately 50% while the duration of these events has been reduced by approximately 30%. Higher flow peaks have been reduced more significantly with the frequency of 100,000 ML/day events, which inundate most of the floodplain, reduced from 37 per 100 years to 11. The duration of these events has been reduced by one third.

Some of the ecological impacts of the altered hydrological regime include: Loss of ephemeral habitats through no natural summer drying, loss of in-stream habitat diversity, and a reduced range of bank habitats; Loss of long lived terrestrial vegetation and transition to arid or drought tolerant understorey species; Loss of flow dependent native fauna eg. Freshwater mussels (Alathyria jacksoni), Murray crayfish (Euastacus armatus) and River snails (Notopala hanleyi); Reduced exchange of organic material, carbon, nutrients and sediment between the floodplain and the river; Degradation of natural low flow channel shape; Thermal stratification, favouring cyanobacteria; Reduced diversity and biomass of invertebrates in annually flooded areas; and Reduced diversity of waterbirds and terrestrial native fauna.

Table 2 Flooding extent, frequency, and duration under natural and current conditions at Pike (Ecological Associates and AWE, 2008).

River Murray flow Return period Duration to SA (ML/day) (Number of times peak flows occur in (Number of months flow is exceeded) 100 years) Natural Current Natural Current 5000 100 100 11.8 11.9 10,000 100 94 10.1 4.6 20,000 99 63 7.8 4.6 30,000 96 51 6.4 3.9 40,000 91 40 4.9 3.3 50,000 79 30 3.9 2.7 60,000 59 21 3.9 2.5 70,000 49 15 3.6 2.9 80,000 45 12 3.2 2.6 90,000 37 11 3.1 2.1 100,000 32 9 2.9 2.0 120,000 23 5 2.2 2.8 150,000 12 4 2.2 1.5

2.3.2 Altered groundwater regime

There are many sections of the River Murray floodplain, such as Pike, that are areas of natural discharge of saline groundwater. The discharge of the highly saline groundwater into the River Murray is a serious

concern to downstream river users, especially following major flood events. Since the construction of the locks and the operation of weirs, groundwater levels have been elevated and the surface soil layers of some sections of the floodplain have accumulated additional salt. Significant areas of the floodplain are currently affected by soil salinisation and this is expected to increase.

The primary cause of soil salinisation is increased evapo-transpiration (and hence movement of salt up into the plant root zone), due to reduced flooding frequency and elevated groundwater (Overton and Jolly, 2003). In some sections of the Pike floodplain, the groundwater is about 2-3m higher than it was under natural conditions, thus increasing the rate of accumulation. The combination of a semi-arid climate with surface clay soils of low permeability means that, generally, there is little leaching of salt between floods.

Regular inundation events are important because they recharge the soil and groundwater, and flush salt that has accumulated through the dry period from the tree root zones. Flushing of salt from the floodplain soils now occurs less frequently as a consequence of the reduction of flooding.

Salinisation of floodplain soils is a major factor in the decline of the health of floodplain trees and in many areas it has caused extensive vegetation death. Dieback is clearly evident on the Pike floodplain, which is a function of the combined effects of river regulation and rising saline groundwater. These effects are being significantly exacerbated by the current drought.

3. Potential Management Options

3.1 MANAGEMENT OPTIONS ASSESSED

There are a number of potential management options for the Pike floodplain involving the modification and improved operation of existing infrastructure as well as the construction of new infrastructure. Investigations have been undertaken to assess the range of management options to determine how best to achieve the objectives for the Pike floodplain. AWE, Ecological Associates, Water Technology, URS, DEH, DWLBC, and the SA MDB NRM Board have been involved in assessing a range of potential management options in terms of cost, salinity impact, contribution to environmental objectives, and water use. These options are discussed below.

3.1.1 Do Nothing

This management option has been assessed and assumes no further intervention on the Pike floodplain. Under this scenario, the current vegetation on the Pike floodplain will continue to decline to a point where communities will not be able to recover. They will instead transition to a more salt tolerant community (such as samphire); causing a permanent ecological shift on the Pike floodplain which will severely compromise the integrity of the site (as is already being observed in some locations on the floodplain).

Although the river has experienced an unprecedented period of low flows in recent years, the degradation of the system was already underway. It can be argued that the capacity of the system to accommodate the drought was reduced by historic management.

The key processes which will continue to degrade the ecosystem are: the intensification and spread of soil salinisation, particularly in low-lying floodplain areas near the north of Mundic Creek and along the Upper and Lower Pike River; floodplain inundation insufficient for the survival of floodplain Black Box, Lignum and Red Gum and insufficient to maintain the primary productivity on which floodplain fauna depend; insufficient soil moisture to maintain tree health except along the flushed zone of the River Murray and the zone immediately adjacent to permanent watercourses; and depletion of native vegetation through grazing.

recruitment in addition to ensuring the survival of existing trees” (Wallace, 2009).

Under the “do-nothing” scenario, there is a risk that potentially water from the system could become unusable for irrigation due to increasing salinity levels, high levels of sedimentation or due to water levels altering thereby blocking the capacity to extract water using the current infrastructure.

This would have unacceptable consequences to the local community and local economy. There is a need to undertake sufficient management actions to secure water supplies for existing users.

3.1.2 Increase flow from Mundic Creek to Lock 4 via Creeks

Flowing water habitat required by fish could be provided in the channel between Mundic Creek and Tanyaca Creek. The flow and velocity of water passing could be increased by modifying the structures which control outflows from Mundic Creek. To achieve significant benefits, flows from the River Murray into Mundic would need to be increased and the distribution of flow out of Mundic between Tanyaca Creek and Pike River be controlled.

On its own, this option has a positive impact but on a relatively small scale. Thus, this is a proposed long- term management action that could be achieved with the operation of the proposed environmental regulators at Col Col and Tanyaca Ck.

3.1.3 Weir pool raising at Lock 5

This management option involves the raising of the Lock and Weir No.5 upper pool level from its normal level of 16.30mAHD up to a maximum level of 16.80mAHD, representing the physical top of weir structure. The effect of raising the Lock and Weir No.5 upper pool level by 500mm (maximum) is to increase flows into the Pike anabranch through the numerous existing bank and weir structures and increase the area of floodplain inundated.

3.1.4 Permanent pumping infrastructure

This management option involves long-term pumping into wetland areas and other suitable areas that are currently stressed as a result of river regulation and continued low flow conditions. This option enables the regular watering of a limited area, but is not suitable for watering larger and/or water shedding areas of the floodplain. This option does not result in a connection and subsequent transfer of carbon and nutrients between the river and the floodplain without further intervention.

This is not considered a viable long-term option. However, permanent pumping infrastructure may be considered in high priority areas that are beyond the influence of the proposed Pike environmental regulators. This management option would require investment in permanent banks and regulators at selected wetlands.

3.1.5 Gravity watering wetland sites

This management technique involves the construction of new blocking banks and regulator structures, and the excavation of new drainage channels to connect low-lying areas, which are considered suitable for watering via gravity feed. There are only a small number of sites where this option is viable; as such this option has limited scope for action on the Pike floodplain.

3.1.6 Irrigation infrastructure

This management option seeks to essentially address the requirements of Black box trees, which are generally located in the more elevated sections of the floodplain. Flow events of 80,000ML/day (flow to SA) or more are needed to reach most of the significant areas, which are located above the zone of influence of all but the major flooding events throughout the floodplain.

This technique is considered to be cost prohibitive ($1.6m establishment cost, for only 70ha) (URS 2006) and does not cater for other ecological benefits associated with an inundation event. These include increased connectivity between riverine and floodplain habitats, freshening of groundwater systems, improved soil condition, rejuvenation of existing wetland habitats, establishment of new floodplain and wetland plant communities, enhanced regional biodiversity, increased zooplankton abundance, increased habitat and breeding opportunities for water birds and frogs.

This is not considered a viable long-term management option.

3.1.7 Environmental regulating structures at Col Col and on Tanyacka Creek.

This management option would involve construction of a new network of environmental regulating structures at Col Col and on Tanyacka Creek, fishways, ancillary by-pass regulators, blocking banks and other works.

The new regulators could enable water level variation within the Pike floodplain between 14.35mAHD, representing normal upper pool level at Col Col and 16.40mAHD, representing the top of piers at Lock and Weir No. 5. Thus the new regulating structures across the Pike anabranch system could be used to regulate water levels within the upper Pike floodplain over a maximum range of approximately 2.05m. The regulators could be operable under flows ranging from entitlement conditions up to 50,000 ML/day, although flows of at least 10,000 ML/day would be optimal to operate to the maximum possible extent.

This is a proposed long-term management action and is discussed in detail in the following chapter.

3.1.8 Seasonally raise and lower water levels in the upper Pike-Mundic

A proposal to vary water levels annually over a 1.5m range has been assessed. Under this option, water levels could be raised annually by 0.5m and lowered by 1.0m. This proposal affects a smaller extent of floodplain woodland communities but allows for their recovery on the wetland fringes which are currently permanently inundated.

3.1.9 Seasonally raise water levels in Tanyaca Creek

Tanyaca Creek provides a wetland/watercourse/floodplain system where water levels can be manipulated independently of the Pike-Mundic system and without disruption to diverters.

A scenario to seasonally raise water levels by 0.5m and to lower water levels by 1.0m has been assessed. Inflow points from Mundic Creek would need to be modified with structures which allow more control of inflow and provide fish passage. Regulated levees, which provide for fish passage, would need to be required to control inflows from the River Murray on Wood Duck Creek and Swift Creek. A regulated levee would also be required on Tanyaca Creek just upstream of the junction with Rumpagunyah Creek to control outflows at this point.

By regulating the connection between Tanyaca Creek and the River Murray level, the structures would allow the water level to be lowered and raised.

3.1.10 Raise and Lower Lock 4

There is no scope to achieve significant floodplain benefit by raising Lock 4 water levels. Weir manipulation has the greatest effect immediately upstream of the weir and raising Lock 4 would only marginally raise water levels in the lower Pike.

3.1.11 Fish Passage

Upstream fish passage is completely blocked at all regulating structures except Col Col embankment where the rock weir provides some scope for crude fish movement. In addition, the Lock 5 Road crossings represent an unfavourable environment for migrating fish.

Fish passage should be incorporated in the design of new regulating structures. An overall plan of future works is required to identify the sites where fish passage is most important. Structures cannot be modified for fish passage until the functionality of the structure (maximum and minimum regulating level) is determined.

On its own, this option has a positive impact but on a relatively small scale. Thus, this is a proposed long- term management action that could be achieved with refurbishment of infrastructure required for the proposed environmental regulators at Col Col and Tanyaca Ck.

3.1.12 Regulate Individual Wetlands

There are a number of wetlands within the Pike River Floodplain which could be individually regulated to introduce seasonal wetting and drying regimes. Water levels could be raised by capturing water during high river levels or by pumping. Water levels could be lowered by releasing water or through losses to evaporation and seepage.

Works at individual wetlands would only be appropriate if the sites could not benefit from one of the larger scale water manipulation proposals outlined above. Potential sites for manipulation include: • Woodcutters Wetland • Lower Snake Creek Wetland; • Letton's Homestead Wetland; • Letton's Flat Wetland; • Swift Creek Wetland; and • Rumpagunyah Flood Runner.

3.1.13 Improve Flow Paths

Salt accumulates in the dead-end creek on the Lower Pike floodplain as water is drawn into the channel from Lower Pike River by evaporation. There is scope to increase the frequency of flushing flows by lowering the sill of the channel near the River Murray. It would be possible to lower the sill to a level where only minor

peaks in river flow would pass through the creek and saline water would be exported.

3.1.14 Alternative maximum elevations for downstream regulating structures (15.8mAHD- 16.8mAHD)

As part of an ongoing assessment process of flow management options on the Pike floodplain, a summary assessment of the potential ecological impacts, risks and benefits associated with managed inundation regimes at a range of different elevations has also been undertaken (Hollis, 2009a). The elevations assessed included 15.8mAHD, 16.0mAHD-16.4mAHD and 16.8mAHD to confirm an optimal regulating height concept.

Modelling undertaken to date demonstrates that increasing the elevation extent of regulating structures at Pike to 16.80mAHD (equivalent to top of piers at Lock 5), has the potential to increase the area of floodplain inundation from approximately 1227ha under the 15.8mAHD scenario (Figure 2) to 2140ha (Figure 4). For completeness, the 16.3mAHD scenario is also presented (Figure 3). This additional area of inundation has the potential to significantly enhance the ecological benefits likely to be generated by a managed inundation regime. These ecological benefits include increased connectivity between riverine and floodplain habitats, improved soil condition, rejuvenation of existing vegetation, establishment of new floodplain and wetland plant communities, enhanced regional biodiversity, increased zooplankton abundance, and additional habitat for small native fish.

Figure 1. Inundation of the Pike floodplain under “current” conditions i.e. no environmental regulators.

Figure 2. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 15.80mAHD as generated by the Pike DTM, which assumes no gradient on the river.

Figure 3. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 16.30mAHD as generated by the Pike DTM, which assumes no gradient on the river.

Figure 4. Potential inundation extent generated by operating the proposed Pike regulators up to a maximum height of 16.80mAHD as generated by the Pike DTM, which assumes no gradient on the river.

However, as mentioned, operation of these regulating structures at the higher elevation levels would not be without risks and potential impacts. The potential ecological risks associated with increasing the regulating height are similar to those risks (an increased potential for cyanobacterial blooms, invasion by weeds, reduced lotic or flowing water habitats, interrupted fish passage, and increases in populations of common carp) that have been identified and investigated under the reduced elevation scenarios. They are however exacerbated under the maximum elevation scenario, as maintaining the critical flow velocity during operation of the regulators becomes much more difficult. As the regulator height increases, the natural river gradient decreases, reducing the flow velocity throughout the entire anabranch complex. Mitigating and/or managing these potential impacts also become much more problematic under the maximum elevation scenario.

In addition, substantially more blocking bank material would be required in order to manage water behind the structures under the 16.8mAHD scenario (5.9km of banking compared to 1.3km under the 15.8mAHD scenario and 2.7km under the 16.4mAHD scenario). How this influences the hydraulics of a natural flood also needs to be considered and requires further assessment.

The likely generation of higher salt loads (being mobilised up to 2 years post inundation); and the increased water volume requirements (8.99GL, 16.23GL and 27.0GL required for operation at 15.80mAHD, 16.3mAHD and 16.8mAHD respectively), as well as potentially higher border flows required to operate the regulators to maximum capacity need to be considered as part of the 16.8mAHD scenario. Previous advice suggests border flows >30,000ML/day may be required to mitigate potential water quality impacts under the maximum elevation scenario. Please note this advice was in relation to mitigating of potential impacts to large bodied native fish at Chowilla. No Murray Cod have been detected in the Pike anabranch system to date, so there may be scope to operate the structures at Pike under reduced border inflows (QSA 10,000ML/day -20,000ML/day) with minimal risk. Again, further assessment and monitoring is required.

Under the maximum elevation scenario, significant inundation would be occurring in locations of the floodplain that are highly salinised and where vegetation condition is reduced (many long lived trees are highly stressed and/or dead).

The debate needs to be had in regards to targeting locations of the floodplain that are still currently intact to further maintain and improve existing habitats versus the value of providing water to areas of the floodplain that are currently not ecologically functional, but which may have the capacity to reinstate important ecological processes in response to long term management intervention.

The risks and potential ecological impacts associated with any potential future operation of regulating structures under this maximum elevation concept (up to 16.8mAHD) are likely to be heightened (particularly in regards to water quality). Table 3 provides this summary.

Table 3 Summary of anticipated benefits, risks and possible mitigation strategies associated with the Pike inundation options

Issue Benefit Risk 16.4mAHD 16.8mAHD Ecological Soil moisture Increased; critical   for vegetation Connectivity Flux of nutrients   (C, N, P) to river Nutrient transport Stimulate   productivity

Aquatic-terrestrial Resource input.   connectivity Support aquatic- terrestrial invertebrates Phytoplankton Phytoplankton   growth increased

Cyanobacteria Favoured by calm   water in pools- potential to deoxygenate water and cause fish deaths Changed hydrology More extensive   watering Increased blocking Potentially changing   bank the dynamics of natural flood events (different flow paths, increased flow velocity, different area of inundation etc), which is likely to increase the potential for major geomorphological disturbance (scouring, erosion, bank slumping, sedimentation etc); creating habitat disruption etc. Vegetation Floodplain   vegetation watered Biodiversity Increased in all   watered areas Groundwater salinity Increased soil   moisture Fish migration   Fish habitat Increase lentic   habitat Fish food Increased   abundance of zooplankton and macroinvertebrates Fish spawning Benefit small   species Carp abundance  

Potential for   geomorphological disturbance Potentially higher   larval fish mortality rates Miscellaneous Water volume   Amount of fill required   to construct banks Cost   Redesigning access   roads Red ticks are in relation to potential risks and impacts, black ticks are in relation to potential benefits.

3.1.15 Potential ecological benefits associated with the maximum extent (16.8mAHD)

As discussed, the additional area of inundation under the 16.8mAHD scenario has the potential to further enhance the ecological benefits likely to be generated under the reduced elevation concepts. These potential benefits include: Generating more widespread improvement in vegetation condition The establishment of new floodplain and wetland plant communities Enhanced regional biodiversity Increased zooplankton abundance Additional habitat for small and medium-bodied native fish Depths in specific wetlands and flow paths may increase, providing more migration opportunities for native fish to move from permanent creeks to ephemeral wetlands (and back again). This increase in water depth may also improve the opportunities for some frog and macroinvertebrate species to complete their life cycle; as well as providing breeding opportunities for some bird species such as the Sacred Ibis There will be greater river-floodplain connectivity (the return flow of floodplain water and nutrients to the river will be improved). The extent of these aforementioned ecological benefits has the potential to influence most of the upper Pike floodplain (Figure 4), leading to a potential rejuvenation of broader ecological condition in areas that would otherwise continue to deteriorate

3.1.16 Potential ecological impacts and risks associated with the maximum extent (16.8mAHD)

Potential impacts and/or issues of increasing the maximum height of regulating structures at Pike up to a maximum height of 16.8mAHD include: A far more extensive network of blocking banks may be required (there are implications with this aesthetically as well as in terms of potentially changing the dynamics of natural flood events (different flow paths, increased flow velocity, different area of inundation etc), which is likely to increase the potential for geomorphological disturbance (scouring, erosion, bank slumping, sedimentation etc); creating habitat disruption etc. Maintaining critical flow velocity through the faster flowing creek systems, which create habitat diversity and are preferred by medium and large bodied native fish, will be much harder to manage (the potential for decreasing flow velocity increases as the flow gradient decreases). The implications of which may include a long-term reduction in large and medium bodied native fish populations. It will also take longer to fill the system, which will result in longer periods of low flow velocity. Potentially higher larval fish mortality rates with an increase in “head height” across the downstream regulating structures.

Potential difficulty for fish movement as longer (possibly less efficient) fish passage will be required at the proposed floodplain regulating structures

3.1.17 Setting Sustainable Diversion Limits.

Setting sustainable diversion limits has been accepted by the community and government as an acceptable solution to improve security of future supplies and ensure environmental objectives are not compromised. It is proposed as a long term action and described in detail in future sections.

3.1.18 Flexible Water Extraction

This option involves modifying and/or moving pumps that extract water from the Pike system. This will ensure that water flows can be maintained to irrigation properties whilst the floodplain can be hydraulically managed to increase environmental benefits. This option has been endorsed by the Sustainable Water Management committee and is recommended as a long term option.

3.2 SUMMARY OF OPTIONS

Whilst any additional water available to Pike will provide benefits, modelling has demonstrated that the benefits of recovered “environmental” water will be limited without complementary structural and operational change. A flow to SA of 65,000ML/day (which is required to inundate 25% of the floodplain) for 90 days requires a total volume of 5850GL. The likelihood of recovering nearly 6000GL to be used every 2 years to maintain floodplain ecology is low. A solution to maintain floodplain health must therefore be sought using low flows.

As a result of the assessment undertaken, it is clear that the only option that comes close to achieving the ecological objectives for the Pike floodplain is the construction of environmental regulators in Tanyaca Creek and at Col Col, coupled with ancillary works at the existing mid pool embankment (Banks B, C, E, D, F, F1, H G and Coombs Bridge). Upgrading the two inlets upstream of Lock 5 (Margaret Dowling and Deep Creek) would also be required to improve inflows coming in to the anabranch complex as well as provide fish passage. Collectively, these works will enable a range of ecological objectives to be achieved as identified in the Pike Management Plan (Table 4).

Table 4 Summary of potential surface water management options for the Pike anabranch and floodplain complex

Management Option Potential for Potential for Potential for Potential for Potential for Potential for Nutrient Area Capacity to increased increased increased increased increased increased transfer from influenced achieve tree benefits understorey bird benefits fish benefits frog benefits water quality the floodplain ecological vegetation benefits to the River objectives benefits Do Nothing Low Weir pool raising at        <5% of the Low Lock 5 floodplain Permanent pumping      <5% of the Low infrastructure floodplain Gravity watering        <5% of the Low wetland sites floodplain Irrigation  <5% of the Low infrastructure floodplain Environmental        >30% of the High regulating structures at floodplain Col Col and on Tanyaca Creek up to 16.4mAHD Seasonally raise and      <5% of the Low lower water levels in floodplain the upper Pike-Mundic Seasonally raise water      <5% of the Low levels in Tanyaca Creek floodplain Raise and Lower Lock Low 4 Upgrade structures to  Low provide Fish Passage Regulate Individual        <5% of the Low Wetlands floodplain Improve Flow Paths   Low Alternative elevations        <30% Moderate and locations for downstream regulating structures

The costs associated with the environmental regulators are considered to be commensurate with the potential ecological benefit these works will bring. When considered with other major landscape scale intervention activities around the Murray-Darling Basin, such as the works being proposed at the Living Murray Icon Sites, the environmental regulators proposed for the Pike floodplain provide a similar “cost per hectare” benefit (see Table 5).

The management of local salinity impacts will require further assessment, and clarity is also required regarding salinity accountability.

Table 5 Cost per hectare assessment of proposed landscape scale intervention activities throughout the Murray-Darling Basin.

Site Proposed Works Area Inundated Cost ($m) Cost per hectare (ha) Pike Environmental 1460 $35 $24,000 regulators and ancillary structures Chowilla# Environmental 5580 $46.4 $8,300 regulator and ancillary structures “Katfish Reach”~ Environmental 1042 $30 $28,800 regulator and ancillary structures Koondrook- Channel and ancillary 5700 $59.5 $10,400 Pericoota# structures Hattah Lakes#^ Pumping station and 2950 $28.8 $9,800 ancillary structures Gunbower#* Channel and ancillary 4400 $24.4 $5,500 structures Mulcra# Environmental 800 $7.3 $9,125 regulator and ancillary structures ^ Excludes annual costs associated with pumping. * Concept is poorly developed; it is therefore subject to significant variance. # Source: MDBA (pers.comm. Jones 2009) ~ Source: (URS, 2008)

4. Preferred Long-term Management Option

4.1 NEW ENVIRONMENTAL REGULATORS IN TANYACA CREEK, COL COL, AND AT DEEP CREEK AND MARGARET DOWLING CREEK

It is recognised that the construction of new environmental regulators will achieve the most significant ecological benefits for the Pike floodplain; albeit further investigation is required to confirm viability. Operation of the proposed structures at Tanyaca Creek and Col Col to 16.40mAHD at low flows (10,000ML/day flow to SA) will inundate approximately 25% (1466ha) of the Pike floodplain (Watertech 2009). As flows to SA increase up to 50,000ML/day (just before Lock 5 is stripped and flow management is lost) significant increase in area inundated would not be expected. This is because of the physical constraints of the two inlet creeks- it would not be sensible to send more than 1000ML/day (combined) down these inlets to due risks associated with geomorphological disturbance. The close location of the inlets in relation to Lock 5 also means that very modest benefit would be generated from the “back water curve” upstream of Lock 5 generated at higher flows. Whilst the total area inundated is similar in size to a natural event (65,000ML/day), it is far greater in the upper Pike and non-existent in the lower Pike floodplain under the regulators scenario.

As part of the assessment process, a series of inundation extents have been modelled assuming the environmental regulators were in place (Figures 2-4). The area influenced by watering will be greater than the area actually inundated, as fresh water will recharge soils and the groundwater system beyond the water line, as has been evidenced in recent watering initiatives throughout SA and the Murray-Darling Basin. Therefore, the areas presented should be regarded as conservative.

Table 6 Modelled inundation coverage for elevations with and without environmental regulators on the Pike floodplain.

Flow to SA Area Extra % of Area of Red Area of Black Natural flow inundated area floodplain Gum box required to (ha) inundated inundated inundated inundated inundate (ha) (ha) (ha) equivalent area (ML/day) 10,000ML/day 814 0 11.5% 0 0 <30,000 (Without environmental regulators) 10,000ML/day 1817 1003 28.5% 244 370 70,000 (with environmental regulator operated at 16.4mAHD)

Figure 5. Optimal elevation of environment regulators on the Pike floodplain of 16.4mAHD.

4.1.1 Proposed Works

Concept designs undertaken to date have identified the following suite of works required for the Pike environmental regulators option: New minor regulators at Banks B and B2 New minor regulator on the road from Bank B to Bank C Remove existing Bank C and replace with new ancillary regulator Remove existing Bank E and replace with new ancillary regulator Major new regulator required with fishway at Tanyaca Creek Replace Banks D and F with new ancillary regulators Replace Bank F1 with fishway exit to Mundic Lagoon Replace Bank G and Coombs Bridge with new ancillary regulators (the latter to provide vehicle passage New minor regulators at outlets from Snake Creek New minor regulators placed strategically at key locations with the embankments to prove additions outlets during an E-flows event. Replace Deep Creek and Margaret Dowling Creek inlet structures (fishways provided for both structures) Major new regulator required with fishway at Col Col 2.7km of embankment constructed to a crest height of 16.6mAHD (200mm above the proposed maximum elevation of regulating structures (16.4mAHD)

Pike Environmental Regulators URS (2010) have developed a concept design for the proposed regulators with an operating water level range of 0m to 2.05m. This design was chosen, as it is best suited to the Pike floodplain area as: The design criterion requires the regulator be an overshot structure. Stoplogs are low technology. The concrete footings, piers, stoplogs and bridge decks are low maintenance. Stoplogs can be manipulated to control water level raises and falls to a resolution of 1 to 2 cm per day. A regulator using concrete piers and stoplogs is robust and resistant to vandalism. The regulator need not be permanently manned, but rather inspected and maintained.

Design features of the Pike environmental regulators (and ancillary structures) are still being refined.

Blocking Line/Banks The blocking line has been determined (Figure 5) to ensure that during environmental flow watering events, water levels within Pike can be held, and flows out of Pike controlled. The blocking line determines the downstream limit of environmental flow watering across the Pike floodplain up to a 50,000ML/day environmental flow event. Along the blocking line, blocking banks are proposed where the ground elevation is less than 16.4mAHD, or the optimal upper elevation of regulating infrastructure, in order to contain water up to that level, with appropriate freeboard (200mm).

The blocking alignment has been optimally positioned to maximize potential area of floodplain inundation, while minimising earthworks material required for blocking bank construction, and minimizing impact on the environment. The crest level of the blocking banks is set at 16.60mAHD. By setting the blocking bank crest level at 16.60mAHD this provides a blocking bank freeboard distance of 200mm above a maximum environmental flows water level of 16.40mAHD, while not restricting floodplain inundation.

The final locations of the ancillary regulators were selected to minimise the size and the amount of fill material required, whilst also maximising the extent of floodplain inundation. The design of the ancillary regulators is such that flow will not be impeded during natural flood events.

Fishway Designs: Concept designs have been prepared for a vertical slot fishway to be provided at Deep Creek and Margaret Dowling Creek inlets, as well as at Col Col environmental regulator. A fish lock has been proposed for Tanyaca Creek and Col Col (the Col Col fishway consists of a vertical slot with integrated fish lock). URS (2010) teamed with Dr Martin Mallen-Cooper from Fishway Consulting Services to prepare these designs. Rock groins are also proposed at key locations on Tanyaca Creek to optimize fish passage.

The passage requirements for the site have been described as: Passing small-bodied fish 20-90mm in length (eg. Flyspecked hardyhead, carp gudgeons [native species] and Australian smelt). Passing medium-bodied fish 90-500mm in length (eg. sub-adult and adult silver perch, callop, bony herring, catfish, carp and sub-adult Murray cod) Passing large bodied fish 500-1000mm (only adult Murray cod in this category, although large callop up to 650mm have been recorded elsewhere in the River Murray)

The above fish passage facilities would be operable at “normal” flow conditions as well as during an E-Flow environmental watering events.

Further Work Required: It is required that a full geotechnical investigation be undertaken at the site of the proposed new and modified infrastructure as part of detailed design in order to develop strategies and plans for: Groundwater control during construction Control of under-seepage post construction Understand the strength of the foundations

A detailed elevation survey of the blocking line is also proposed to confirm the location and inform the designs of the blocking banks.

4.1.2 Approvals

Development Planning SA has formally advised that: “The establishment of structures on watercourses and the floodplain for hydrological manipulation purposes is not a prescribed activity that requires development approval under the Development Act 1993 (nor a Major Development declaration).”

EPBC: An EPBC submission needs to be submitted to the Australian Government prior to constructing proposed environmental regulators for the Pike floodplain.

Native Title Native Title has been extinguished on the Pike floodplain

SA Constructing Agent Review SA Water is expected to be the constructing agents for all new and modified infrastructure on the Pike floodplain. An ongoing operation and maintenance budget should be provided such that SA Water can appropriately resource the requirements of the proposed new infrastructure. Previously, the Pike-Mundic Association have operated, owned and maintained all infrastructure on the Pike floodplain (principally for irrigation outcomes). SA Water is represented on the PIP Reference Committee and on the Pike Floodplain Steering Committee and is expected to provide technical reviews for all concept and detailed designs.

Fish Passage Task Force (FPTF) The concept designs for all the proposed fishways should be reviewed and endorsed by the FPTF.

PIP Reference Committee: The PIP Reference Committee will be involved in reviewing and endorsing all new and modified infrastructure for the Pike floodplain. This Committee has also been involved in reviewing and endorsing this investment proposal for the Pike floodplain.

Pike Floodplain Steering Committee: The Pike Floodplain Steering Committee will be involved in reviewing and endorsing all new and modified infrastructure for the Pike floodplain. This Committee has also been involved in reviewing and endorsing this investment proposal for the Pike floodplain.

4.1.3 Timeframe

It is anticipated that the construction of all new and modified infrastructure on the Pike floodplain, could commence in 2013, subject to approval requirements, and may take up to two years to complete. Detailed design could commence in 2011-12 and be completed within 12 months.

Following approval to proceed to detailed design, the management arrangements may change. The responsibility for the project management of the detailed design and construction may transfer to SA Water (an Agent of the SA Constructing Authority) overseen through an agreement with DWLBC and the SA MDB NRM Board. SA Water will still however report to the PIP Reference Committee. The PIP Reference Committee will retain responsibility for the integrated project.

Following detailed design, the Constructing Agent (SA Water) will conduct a comprehensive review of the cost estimate. Following this review, the final designs and cost estimates will be re-submitted to potential investors for endorsement. Prior to construction tenders being let, DWLBC and the SA MDB NRM Board will remain the project proponent and the design and construction delivery will be managed through a MoU between DWLBC, the SA MDB NRM Board and SA Water.

The construction of all new regulating infrastructure will be subject to an open and competitive tender process managed by SA Water. The actual cost of construction will not be known until the project is completed however the scope for variation beyond the tender is reduced.

Construction Risks The risks specific to this investment have been identified as low. The main risks relevant to this investment include: Delays on receipt of approvals for works- this is dependant on relevant bodies responding within appropriate and acceptable timelines to ensure that construction can commence as soon as design and planning have been completed. Availability of contractors. Floods or significant rain events. Considerable time and cost associated with undertaking Environmental Impact Statements (if required) in order to gain necessary approvals.

A comprehensive risk management strategy will need to be prepared for the project. This will form a part of the construction plan.

4.1.4 Costs

The construction cost estimates are currently being prepared by Currie and Brown (quantity surveyors). Final costs total approximately $35m for the floodplain infrastructure.

Figure 6. Summary of estimated total construction costs for proposed floodplain infrastructure

4.1.5 Ecological Benefits

Of all management options considered, the proposed environmental regulators are the only option that approaches the achievement of ecological objectives for the Pike floodplain.

The proposed environmental regulators will inundate approximately 244ha or River Red Gums and 370ha of Black Box at low flows, significantly improving the condition of existing trees as well as creating an environment which will be suitable to establish and sustain new emergent trees.

In comparison, all other management options considered barely even maintain current levels of River Red gum and Black box condition. The environmental regulators are the only option that influences the majority of the various habitats and land units on the floodplain. Various regulator options were investigated at different elevations (up to a maximum elevation of 16.8mAHD). These are discussed in detail in section 3. Whilst there is little doubt ecological benefit could be attained under the maximum elevation (16.8mAHD), it is also clear that significant risk is likely and would be difficult to mitigate and/or manage; hence the current concept (up to a maximum elevation of 16.40mAHD) is the preferred long-term management action for the Pike floodplain.

Operation of the environmental regulators will improve vegetation condition on the Pike floodplain through the introduction of a flooding regime that will improve soil-water availability, freshen the saline groundwater and reverse the accumulation of salt in the floodplain soils. Modelling completed to date indicates that operation of the environmental regulators at low flows (i.e. 10,000ML/day) will inundate a high number of ephemeral creeks and wetlands, providing an improved water regime to significant areas of River red gum forest, Black box woodlands and Coobah woodlands on Pike. Non-tree vegetation will also benefit, with operation of the proposed environmental regulators capable of delivering an improved water regime to the

lignum flats, the grassland/sedgeland areas, and the herbland areas. This predicted improvement in vegetation condition is supported by understorey data collected by SARDI following numerous watering initiatives as undertaken on lower Murray floodplains. Nicol and Wheedon (2007) conclude that floodplain inundation results (in most cases) in significant increases in the abundance of native flood dependent herbs and grasses).

Experience from the watering projects in SA demonstrates that the forest/woodland area that will benefit from the improved water regime will substantially exceed the area actually inundated. Results from watering projects indicate that the condition of trees up to 50m away from the water line improve via lateral freshening of the saline groundwater.

4.1.6 Potential Ecological Risks

Whilst the proposed environmental regulators could provide a number of substantial environmental benefits to the Pike floodplain, operation of the environmental regulators would not be without risks that require management. Possible negative impacts associated with operation of the environmental regulators include an increased potential for cyanobacterial blooms, blackwater events, invasion by weeds, reduced lotic or flowing water habitats, interrupted fish passage, decrease in large-bodied native fish populations and increases in populations of common carp.

A considerable effort has been put into the further assessment of risk for each of the risks identified. Projects have been undertaken to better quantify risks to fish, water quality and weed invasion. These projects have been undertaken by leaders in the various fields and have been used to inform operational strategies for the proposed Chowilla Creek environmental regulator to maximise ecological benefit and mitigate or minimise the various risks where they exist. Risks assessments and mitigation strategies as they relate to the Chowilla floodplain are transferable to Pike, as they apply to all lower Murray floodplains where environmental regulators are proposed to create broad scale floodplain inundation. The impacts and risks aren‟t unique only to the Chowilla floodplain.

4.1.6.1 Fish Most species of fish present in the Pike are expected to benefit from operation of the environmental regulators. Pike is similar to Chowilla in that it provides a fish-habitat mosaic that is rare in SA and supports a diverse native fish community. Within the Pike anabranch system, no Murray Cod have been caught by SARDI researchers, so the potential risks, impacts and mitigation strategies as they relate to Murray Cod in Chowilla are not considered as significant for the Pike floodplain (given the relative paucity of Murray cod present within the Pike anabranch). However, other risks still need to be addressed; particularly as Golden Perch, Freshwater catfish and Silver perch (the latter two are State listed) were found in the Pike anabranch complex.

It is believed that these species are present in the Pike system principally due to the high velocity creek systems that have become a permanent artifact at Pike since the construction and operation of Lock and Weir 5. Mallen-Cooper et. al (2007) advises it is important to maintain these fast flowing creek systems during operation of the proposed environmental regulators in order to avoid impacting on these high value species. The report concludes that most of the potential negative impacts of a managed inundation event can be mitigated if the regulators are used in a way that maintains the mosaic of fast-and slow flowing habitats that currently exist.

The proposed regulators provide the operational flexibility required to maintain preferred minimum flow velocity (0.18m/s) under a range of scenarios. This can be achieved by operating the regulators to a reduced elevation in order to maintain a sufficient hydraulic gradient to retain faster flowing habitats. If the higher velocity habitats are preserved during regulator operation the risks to Golden perch, Silver Perch and Freshwater catfish will be reduced; and the diversity and dynamics of fast and slow-flowing habitats will be maintained, which may be important in the survival of larvae of these species (Mallen-Cooper et al. 2007).

Further hydraulic modeling is required to determine the optimal (maintaining preferred minimum flow velocity in the faster flowing creeks of the anabranch system) regulating height for the Pike regulators and

Lock 5 under a range of flow conditions.

The authors also felt that adding variability to a managed inundation event would also be an important process in moving food resources for some fish species into channels leading to and from the floodplain (Mallen-Cooper et al. 2007).

The risk of increasing populations of common carp through floodplain inundation (which is a likely artifact of both natural and managed flooding) remains a concern.

Manipulation of flood levels to expose and kill carp eggs, is not considered viable. Unfortunately, the variability in water depths for spawning is too wide to easily be manipulated on the Pike floodplain. Therefore, mitigation of this risk remains extremely difficult. However, the authors did feel that maintaining preferred minimum flow velocity through the anabranch and floodplain during inundation may minimise the increase of common carp which favor shallow, low flow velocity habitat.

When the proposed Pike environmental regulators are not in use, there will be no restriction to fish passage and the head loss across the structures will be limited to a maximum of 50mm. However, when the Pike regulators are in operation there exists potential for fish passage to be reduced. As such, concept designs for the regulators have been prepared (URS, 2009 and SKM 2009) for vertical slot fishways at Deep Creek and Margaret Dowling Creek inlets, as well at the proposed Tanyaca Creek and Col Col regulators. Rock baffling is also proposed for Tanyaca Ck to improve fish passage. There will also be a vertical slot fishway and a fishlock built at Lock 5. The proposed fishways have been designed by Dr Martin Mallen-Cooper to accommodate the passage of small, medium and large bodied fish for a wide range of flows, as well as for a wide range of head and tail water levels. These fish passage concept designs will be available to be reviewed by the Fish Passage Task Force prior to the commencement of detailed design if necessary.

4.1.6.2 Cyanobacteria and Blackwater The return of nutrients and carbon from the floodplain to the main river channel is an important part of the function of a healthy low-land river. It is clear from wetland watering undertaken as part of current watering initiatives throughout SA that the Pike floodplain would produce a pulse of nutrients and carbon on inundation (as it would naturally during flooding). There is subsequently a risk of cyanobacteria occurring in the Pike floodplain with the operation of the proposed environmental regulators.

As a result of this risk, an expert team comprising Dr Justin Brookes (University of Adelaide), Mike Burch (Australian Water Quality Centre), Dr Darren Baldwin (Murray-Darling Freshwater Research Centre) and Dr Todd Wallace (Murray-Darling Freshwater Research Centre) were assembled to investigate the potential for the operation of the proposed Chowilla Creek regulator to increase the likelihood of blackwater events and cyanobacteria blooms (as compared to natural floods of a similar inundation extent and duration) in the Chowilla floodplain. The advice from this expert assessment is relevant also for the managed inundation regime being proposed for the Pike floodplain- it does not apply only to the Chowilla floodplain.

A combination of lower than normal flow in the river and higher than average temperatures would provide the worst-case scenario for persistent stratification (Brookes, et al. 2007). Under low flows (<10,000ML/day), the authors felt it would be unwise to operate the regulator to maximum extent, due to the heightened risk of algal blooms in the River Murray channel downstream of the floodplain. However, operation of the regulator (to maximum elevation) under a minimum of 10,000ML/day QSA would significantly reduce the risk of cyanobacteria posing a major problem (Brookes et al 2007). This advice needs to be applied when considering operation of the proposed Pike regulating structures.

As far as the risk of blackwater events is concerned, or more specifically the impacts of deoxygenation resulting from a blackwater event, there does not appear to be a substantial risk of a significant blackwater (deoxygenation) event in those areas that are either deep (>1m) flooded or have good rates of water exchange (Brookes et al 2007). With the exception of the areas dominated by Red Gums, the concentration of leaf litter on the floodplain at Pike is currently quite low and reflects the generally poor state of the vegetation; which inturn reflects on both the lack of flooding (to maintain soil-moisture) and the historical grazing of the floodplain.

Nutrient and carbon pulses from the floodplain occur naturally and are an important function for supplying energy and nutrients to the river. Under “natural” conditions, the vegetation on Pike would have been in substantially better condition than it currently is, which would have been reflected in higher levels of standing leaf litter, and hence a higher likelihood of supplying nutrients to sustain algal blooms and carbon to create blackwater events. Therefore, the risk of cyanobacteria blooms and de-oxygenations of water bodies caused by blackwater events would have been higher historically than exists currently (Brookes et. al 2007).

Decreasing the frequency of flooding on the Pike floodplain has no doubt significantly harmed the ecological condition of the floodplain itself but also the River Murray. The risk of algal blooms and blackwater events appears to be tightly coupled to the ability to maintain flow (both volume and velocity) within both the inundated area and the River Murray channel (Brookes et. al 2007). Further, the authors recommend that inundation be managed to create a relatively rapid rise in water levels and flow at the start of the intervention to dilute the concentration of nutrients and carbon leached from standing litter (Brookes et. al 2007). In conclusion, the authors feel that the risk of algal blooms or blackwater events should be relatively easy to manage.

4.1.6.3 Weed Proliferation

The operation of the regulator is expected to improve the condition of and create recruitment opportunities for most floodplain trees. Similarly, is also expected to improve the recruitment of floodplain herbs and grasses. As native species improve in condition and recruit, pest plant species (exotic and native) are also expected to recruit or expand their distribution and abundance as a result of operation of the regulators.

Under the current situation, much of the Pike floodplain is subjected to dry conditions with low soil moisture (due to a lack of floodplain inundation). Consequently, the floodplain is dominated by terrestrial species, which will remain dominant in the absence of flooding. Whilst most of these species are native to the region, it is doubtful that they were present in such high numbers historically when the floodplain would have been inundated more regularly.

Dr Jason Nicol (SARDI) was engaged to investigate the potential invasion of weeds associated with operation of the proposed Chowilla Creek regulator. Dr Nicol concluded that whether water is delivered to the floodplain by a natural or engineered flood is of little consequence to plants unless the natural flood has sufficient flow velocity to physically damage or uproot plants. Plants (whether they are native or exotic species) that are adapted to the hydraulic regime implemented will recruit; therefore, the risk of invasion of pest plants as a result of the operation of the regulator is no greater than that of a natural flood with the same inundation extent and duration (Nicol 2007).

The advice from this expert assessment is relevant also for the managed inundation regime being proposed for the Pike floodplain- it does not apply only to the Chowilla floodplain.

Monitoring following operation of the regulator will be required to inform managers of any weed expansions and new infestations in order to control pest plants.

4.1.7 Ecological tradeoffs

Tradeoffs are inherent in any attempt to maintain and/or restore floodplain ecosystems without fully restoring a natural flow regime. This is reflected in the proposed floodplain infrastructure, which target only the upper part of the floodplain; not the floodplain in its entirety. Similarly, no practical engineering based solution for Pike can be expected to fully replicate natural flooding and provide all the benefits of natural floods. This issue is well recognised and significant effort has been put into identifying and quantifying the risks and benefits associated with the long and short-term operation of environmental regulating structures (particularly at Chowilla). This summary presents the key findings of that work and it is clear that the floodplain regulating structures proposed for Pike can provide potentially significant ecological benefits compared to all other options; but is not without risk.

The risk assessment undertaken has indicated that most risk can be removed or reduced by avoiding operating at maximum capacity under low flow conditions and/or by reducing the duration or frequency of such events. Reducing flooding duration or extent will impact on many aspects of floodplain ecology such as vegetation condition, frog and water bird breeding, river and floodplain connectivity, habitat availability, and soil salinisation. These factors will need to be considered to make informed operating decisions. Further hydraulic modelling is proposed to determine potential changes to algal risk, high velocity habitat reduction and vegetation condition in order to optimise the operation of any new environmental regulators and ancillary structures. This work will enable a more quantitative presentation of tradeoffs and inform the development of more detailed operating rules.

It is recognised that ecological risks need to be managed and decisions will need to be guided by principals agreed by all stakeholders. These principals should include operation of Pike regulating structures: To achieve ecological objectives and targets Based on best available scientific information and informed by a robust monitoring program To maximise ecological benefit while minimising ecological risk

4.1.8 Salinity Impacts

4.1.8.1 In-stream Salinity Levels The Pike floodplain is a natural discharge area for the regional groundwater system. The flux to the floodplain from the surrounding mallee country remains to be quantified. The introduction of managed floodplain inundation through the periodic operation of the Pike regulators will result in post flood salt load increases in the River Murray. As previously discussed, use of the regulator will enable flooding over an area equivalent to a 65,000ML/day flow event. The salt load following a 65,000ML/day natural event (and equivalent managed events) can be predicted based on historical post flood accessions. This work remains to be done.

To quantify the salt load and resultant salinity impact (within the Pike anabranch system, immediately downstream at Lyrup, and as measured at Morgan) over a short and long time period, complex surface water and groundwater modelling is required.

4.1.8.2 Elevated Saline Groundwater Levels on Pike The issue of elevated groundwater levels and potential increased floodplain salinisation resulting from the operation of the regulator requires further investigation.

4.1.9 Potential Operating Regime

Additional work remains to be done in developing an operating regime for the Pike environmental regulators. Operation will be determined by the antecedent conditions, prevailing inflows (QSA), the ecological requirements of the floodplain, and the level of risk that the resource managers are willing to take. The Pike environmental regulators have deliberately been designed to allow them to be operated over a wide range of heights and flow conditions (up to 50,000ML/day QSA). Above entitlement flows (10,000ML/day QSA) will provide conditions most optimal for regulator operation, making it possible to gain maximum ecological benefit (operating the regulator to its maximum elevation) whilst minimising ecological risk. With lower inflows and in the absence of releasing water from upstream storages, trade-offs will inevitably have to be made in order to manage risks, such as: Inundating less floodplain, but maintaining preferred minimum flow velocity through the anabranch system. The regulator can be operated to an elevation less than its maximum capacity, in order to maintain a sufficient hydraulic gradient (and velocity) through the anabranch system under lower flow conditions. Lock 5 can also be raised to top of piers (16.8mAHD, which is 500mm above the “normal‟ Lock 5 upper pool) whilst operating the downstream environmental regulators to a maximum elevation of 16.4mAHD to maintain preferred minimum flow velocity in faster flowing creeks. Operating the regulator to an elevation less than its maximum capacity (16.4mAHD) will however result in less floodplain inundation and therefore a reduction in ecological benefit. Inundating more floodplain, but potentially reducing flow velocity (below the preferred minimum)

by operating the regulator to a higher elevation which may create disruptions to some native fish species (see section 4.1.6.1). Potentially delaying operation of the regulator until higher inflows can be utilised (the condition of the floodplain is likely to ultimately influence the frequency of operation, more so than relying on the arrival of optimal natural flow conditions). Potentially reducing the duration of operation to minimise water quality risks.

The following hypothetical operating regime has been developed based on the principles of trying to mitigate and/or manage ecological risks identified for algae, blackwater, fish and weeds. It takes into account modelled “current” flow to SA over the last 115 years (1891-2006) and the hydrological requirements necessary to achieve the MDBMC vegetation objectives for Pike (which are based on CSIRO modelling 2005): 40,000ML/day (flow to SA) for 3 months 1 in 2 yrs (on average). Operating the Pike environmental regulators to 16.0mAHD under inflows of 10,000ML/day can generate an equivalent inundation extent. 60,000ML/day (flow to SA) for 3 months 1 in 3 yrs (on average). Operating the Pike environmental regulators to 16.4mAHD under inflows of 10,000ML/day can generate an equivalent inundation extent. 80,000 ML/day (flow to SA) for 3 months 1 in 4 yrs (on average). Under “natural” flood conditions, these flows inundate significant areas of high elevation Black box vegetation. Operating the Pike environmental regulators under inflows of 10,000-50,000ML/day can inundate an equivalent area of high elevation Black box vegetation (~370ha).

It would not be desirable to operate the Pike environmental regulators at every possible opportunity; this has been reflected in the hydrograph (Figures 7-10), where a natural sequence of wet years has deliberately resulted in no out of channel operation of the Pike regulators. To achieve the desired 60,000 ML/day and 80,000 ML/day inundation extent it will be necessary to operate the regulator to full height. The regulator would be operated below full height to achieve the flood extent equivalent to a 40,000 ML/day event.

Figure 7. Hydrograph of modelled current flows from 1890-1919, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007)

Figure 8. Hydrograph of modelled current flows from 1920-1949, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007)

Figure 9. Hydrograph of modelled current flows from 1950-1979, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007)

Figure 10. Hydrograph of modelled current flows from 1980-2006, including potential operation (highlighted in red) of the proposed Pike environmental regulators (MDBC, 2007)

The following factors were considered to determine when the Pike environmental regulators were operated (and to what inundation extent) in the 115yr modelled current hydrograph (1891-2006) and presented in figures 7 to 10: Inflows to SA needed to be between 10GL/day and 50GL/day The floodplain required inundation according to the CSIRO vegetation requirements

Future operation of the Pike environmental regulators will obviously need to be based on the immediate floodplain requirements. There also exists the possibility that the future 115yr hydrograph may be reduced compared to the previous 115yr hydrograph. In addition, there exists the opportunity to operate the regulators when inflows are less than 10,000ML/day, under a range of heights, to maximise ecological benefit and minimise risk. As such, the frequency of operation into the future may need to occur on average 1 year in 3. Initially however, in the continual absence of natural floods, it may be necessary to operate the environmental regulators in 2 or 3 successive years to return the floodplain to a condition capable of withstanding 2-3 years without wide scale watering. The optimal time for watering would be in spring and early summer.

In order to maximise ecological benefit and minimise the potential for adverse effects, the operation of the regulators will be undertaken in an adaptive management framework which includes a robust monitoring program, that not just determines the change of condition of the floodplain, particularly the floodplain vegetation, but also assesses the impacts and benefits of the manufactured flood to floodplain soil condition, groundwater, receiving water in the Murray River and other important biota (Brookes et. al 2007).

The regulator would be operated to mimic a natural hydrograph, as in the following low flow, 120-day scenario: At 10,000ML/day (QSA), up to 1000ML/day could be diverted into the anabranch. Stop-logs would be added progressively to the bays of the regulators, raising water levels immediately upstream of the regulators by up to 10cm/day. 10 days will be required to increase water levels upstream of Col Col from 14.35mAHD to 16.4mAHD. The intention is to raise the water levels at the start of the intervention relatively rapidly in order to dilute the concentration of nutrients and carbon leached from standing litter; hence minimising the potential for blackwater events. With 1000ML/day flowing into the anabranch, at least 500ML/day would be allowed to flow over the Tanyaca and Col Col regulating structures and return to the Murray, maintaining sufficient flow velocity through the system to reduce risks of disturbance to large bodied fish habitat and the occurrence of blackwater events. With a retention rate of 500ML/day, the impoundment could attain full capacity (16GL) in approximately 32 days, assuming it is filled to full capacity. Impounded water levels would be fluctuated for 40 days (by increasing or decreasing anabranch inflows and/or removing and reinstating stop logs at downstream regulators) during the “holding” phase of the operation, mimicking normal variations in flood levels; moving food resources for some fish species into channels leading to and from wetlands and minimising the risk of poor water quality developing. If signs of poor water quality are detected, a reserve of water in upstream storages may need to be called upon. Levels then would be lowered gradually to river pool level. A head of 2m at Col Col will be drawn down over 20 days, would lower the water at about 10cm per day at the regulator. During this draining phase and for approximately 3 weeks post inundation, high inflows (1000ML/day) into the anabranch and high discharge downstream of the Col Col and Tanyaca Creek regulators, coupled with moderate flows (9000ML/day) immediately downstream of Lock 5 will be employed for dilution purposes to improve the response capacity and minimise adverse impacts to water quality.

4.1.10 Water Requirement

The water requirements to operate the Pike environmental regulators are comprised of two components: 1) Water losses, that is the volume that is lost through seepage and evapo-transpiration during (or following) operation of the regulator and is not returned to the river; and 2) Water delivery, that is the volume required to increase flow in the River Murray to a level suitable for operation of the regulator. The delivery volume remains available for downstream use.

4.1.10.1 Water losses

Volumes lost (defined as not returned downstream post inundation) per event of the Pike environmental regulators are influenced by a number of factors including inflows, regulator height, flow impounded on the floodplain compared to discharge downstream of the regulators during operation, the hydrograph employed, whether dilution flows are implemented etc. Numerous operational scenarios continue to be assessed using the Pike hydrodynamic model. Water is “consumed” on the floodplain during inundation events as a result of infiltration and evapo-transpiration.

Infiltration rates are greatest in sandy areas and when the clay-based areas of the floodplain are dry and cracked. Infiltration may reduce significantly following some wetting as the clay soils in some areas expand and cracks seal. Although typical infiltration rates are low, standing water in large wetlands may infiltrate over a period of months making the total volumes that have infiltrated significant. Infiltration throughout the floodplain needs to be modeled to gain a better understanding of the daily infiltration rates associated with

operating the Pike environmental regulators.

During periods of inundation, evaporative and evapo-transpiration losses are likely to be significantly larger than losses due to infiltration. This is particularly the case when large wetlands are filled, such as Marshall‟s Blackbox Depression. The infiltration loss in Marshall‟s Blackbox Depression is estimated as 1mm/day. The annual mean pan evaporation rate is approximately 4mm/day (based on Lock 5 observations). During the month of January, evaporation rates may regularly exceed 10mm/day. Annual variation of evaporation at the site (based on Lock 5 observations) is described in Table 7.

The modeled water losses attributed to evaporation and infiltration respectively should be viewed as best estimates only, as these losses will vary in time and space.

Table 7 Mean monthly pan evaporation rates at Lock 5 (DHI 2006)

The volume of water used during operation of the Pike environmental regulators, being operated to 16.40mAHD and the raising of Lock 5 to 16.80mAHD, under a flow to SA of 10,000ML/day for 120 days has been calculated at 12.40 (Watertech, 2009). Further hydraulic modelling is proposed to quantify volumes (in the River Murray channel, the anabranch creeks, and on the floodplain) under a range of “regulator” and “no-regulator” scenarios.

4.1.10.2 Water delivery The MDBC has modelled the mean flow volume to be delivered to SA, in addition to the current modelled flows to SA (table 8), for all 38 operating events of the regulator (over the 115 year modelled “current” flow sequence). The mean delivery volumes are approximately 93GL per event to create inundation extents equivalent in area inundated during a 40,000ML/day and 60,000ML/day natural flood.

The volumes presented in table 8 will be available downstream to be used at other high priority wetland or floodplain sites; and/or other water users post operation. The figures should be considered the average volume of water that will need to be delivered to SA, in the event that natural inflows are insufficient to maintain a “desirable” operational regime for the pike environmental regulators. The modelling assumes that stated minimum inflows (10,000ML/day) are required for the entire 120 day operational period. This won‟t necessarily be the case as operation of the regulators will not be dependent on such a restricted minimum inflow regime, as the structure has deliberately been designed to allow it to be operated in an ecologically sensitive fashion over a wide range of heights and flow conditions, as previously explained.

Operational regime Times regulator Mean water volume required in addition to operated in last 115 current modelled flow to SA year hydrograph (GL/120 day operation)

Minimum inflows of 8 93.0 10,000ML/day for 120 days (to generate the 40,000ML/day equivalent inundation extent) Minimum inflows of 30 10,000ML/day for 120 days (to generate the 65,000ML/day equivalent inundation extent)

The flow volumes presented in table 8 should be viewed as preliminary numbers only and are likely to be further refined as the MDBC incorporate other proposed Icon Site structures within the TLM water delivery model that has been developed (which is a modification of MSM-BigMod). As an extension of this modelling, the MDBC will also be investigating the use of dilution flows and “unregulated” flows, which are likely to further reduce the volumes listed in the table above.

Hypothetically, if the Pike environmental regulators were to be operated, using a minimum inflow of 10,000ML/day for the entire 120 day operational period (from September 1 to December 29), and in the event that no more than entitlement flow to SA was available, then an additional 511.5GL would have to be delivered to SA (table 9 provides explanation of this calculation). This is a highly unlikely operational scenario. A more likely regime under entitlement flow conditions would be either no operation of the regulators, operating the regulators to a reduced height, or operating the regulators for a reduced duration. These operational tradeoffs have been previously explained within this section.

It is highly likely that Pike will be able to “piggy-back” on water provided to SA for other landscape scale managed inundation events, such as those proposed for Chowilla and Katarapko; thereby preventing the need to fully account for the entire required volume of delivery, as it will have been accounted (at least partially) by one of other SA high priority floodplain sites (and/or the Lower Lakes Coorong and Murray Mouth- SA‟s other Icon Site in addition to Chowilla).

Month Days during month Entitlement flow Monthly total (ML/day) (GL/month) September 30 4500 135 October 31 5500 170.5 November 30 6000 180 December 29 7000 203 TOTAL 688.5 Month Days during month Additional water Monthly total (GL) September 30 5500 165 October 31 4500 139.5 November 30 4000 120 December 29 3000 87 TOTAL 511.5

4.1.10.3 Total Water Requirements As previously discussed, the total volume of water that will be consumed by the environment during any given operation of the environmental regulators is dependant on the prevailing flow conditions and the height of the regulating structures. Water volume figures (table 10) will be reduced if the Pike environmental

regulators are operated at less than their maximum height.

Table 10 Water requirements for operation of the Pike environmental regulators

Operating Regime Mean delivery volume (GL) Water losses per event (GL) Minimum inflows of 93 12.4 10,000ML/day for 120 days (to generate the 40,000ML/day and 60,000ML/day equivalent inundation extents)

5. Ecological Monitoring

5.1 CAPACITY FOR MONITORING OF FLOODPLAIN CONDITION AND THE EFFECTIVENESS OF INTERVENTION PROGRAMS.

Knowledge generated from undertaking scientifically defensible monitoring programs, as well as establishing ongoing monitoring frameworks for trees, understorey vegetation, fish and in-stream habitat has already proved effective in assessing the existing condition of the Pike floodplain; and is designed to ensure detailed assessment of the Pike environmental regulators. The knowledge generated is also being used to prioritise future interventions projects. For example, in the floodplain monitoring program, 21 permanent tree condition transects (incorporating 630 mature trees) have been established. The information generated from routine assessment of these transects provides capacity to report against the tree specific targets, and the effectiveness of the existing intervention (e.g. red gum watering) projects in improving tree condition on the Pike floodplain.

Permanent transects have also been established for monitoring the condition of understorey vegetation across the Pike floodplain to encompass all soil types, vegetation associations, grazing regimes and hydrological regimes above normal pool level. Sites have been selected on a stratified basis to ensure each management action has an appropriate number of sites to ensure sufficient statistical power to detect differences before and after management intervention. A collaborative project with SARDI Aquatic Sciences and the Murray- Darling Freshwater Research Centre is providing the necessary information for reporting against the condition of the native fish populations in the Pike anabranch.

Knowledge generated from existing groundwater and surface water monitoring programs managed by DWLBC is delivering the information required to assess the impacts of on-ground actions such as watering projects, and to inform the design and assessment of proposed groundwater and surface water management options. For example, data generated from ongoing investigations into surface water flow in the anabranch has been used in the development of the Pike hydrodynamic model (Water Technology, 2009). In addition to assessing water delivery options, this model is currently being utilised to assess the impact of operation on flow through the anabranch and the subsequent influence on lotic (flowing water) aquatic habitats, which are important for large-bodied native fish.

6. Complementary Management Actions

To maximise the potential benefit of the new environmental regulators for the Pike floodplain, it will be necessary to operate some of the structures in conjunction with weir pool raising at Lock 5. Margaret Dowling Creek and Deep Creek regulators in particular, will be used to ensure delivery of flow into the anabranch and to control the rate of water level rise and fall. These structures will be important for managing flows through the anabranch, increasing in-stream variability, and delivering ecological benefits on a local scale. This will include the ability to deliver pulse flows down Margaret Dowling and Deep Creeks in order to generate native fish movement and spawning cues and provide benefits to fringing riparian vegetation.

Operation of the environmental regulators has only a limited influence in the lower Pike floodplain. Additional investigations will need to be initiated to identify and assess a range of surface water management options to introduce an inundation regime and improve the ecological condition of this section of the

floodplain; further complementing the proposed Pike environmental regulators.

It is recognised that flow management options may not be sufficient to achieve all objectives and targets for the Pike floodplain. Some areas are beyond the extent of influence for surface water management options, or are more likely to respond to groundwater management. Therefore, as part of the options assessment process groundwater management should also be thoroughly investigated and assessed.

Artificially high saline groundwater levels and increased rate of salt accumulation in the floodplain soils are contributing to the ecological decline of the Pike floodplain. It is therefore considered necessary for the long- term management needs of the Pike floodplain to investigate the role and application of groundwater management in dealing holistically with the ecological needs of the floodplain. Groundwater management may provide significant floodplain benefit to areas beyond the influence of surface water management and may provide additional floodplain protection during times when proposed new surface water infrastructure will not be in operation.

A salt interception scheme (SIS) concept of groundwater wells intercepting saline groundwater along the edge of the highland adjoining the Pike floodplain is well developed and is progressing to the detailed design stage of the scheme during 2009-10. It is proposed that significant investigation be undertaken to determine the viability of extending the current SIS scheme to include groundwater wells on the floodplain and hence provide a capacity to reduce groundwater levels and the rate of floodplain salinisation in order to provide ecological benefits.

7. Sustainable Water Supply

7.1 IRRIGATION

The Pike River irrigation area extends on the south bank of the anabranch system from the Gurra Gurra Lakes complex in the south to Paringa in the north. The majority of the irrigated agriculture closely follows the highland cliffs. There are also small areas of irrigation on the floodplain however most of the floodplain irrigation was discontinued in the mid to late 1900‟s due to soil salinisation. There remain many signs of previous irrigation, particularly in the form of abandoned flood irrigation bays.

The majority of highland irrigation development occurred in the 1960s and since then the Pike irrigation area has grown to encompass 2,088 ha of irrigated crops. The main crops grown are wine grapes, citrus, almonds and stone fruit. Most crops are irrigated either by drip or under canopy systems.

The horticultural value of the area is highlighted by figures which show that the district produced 29% of the Riverland‟s stone fruit, 16% of its nuts and almost 10% of its citrus in the 2003/04 season. The annual average Gross Value of Production (GVP) for the Pike Irrigation area is approximately $18m (2007).

There is currently 22.5GL of allocation allocated against 41 licenses extracted from the Pike River System. The allocation types include stock, domestic and irrigation, although irrigation accounts for 99% of the allocated volume. There are also 5 approved “Prior Commitment” allocations in the Pike irrigation area with a total volume of 14.8GL.

In a general entitlement flow year extraction from the Pike anabranch system accounts for some 7% of the inflow with 89% returned to the River Murray through the Lower Pike. In peak summer months, extraction accounts for 29% of inflow, with 64% returned to the River (AWE, 2008a).

For approximately 60 years (Pers.Comm. R. Frahn, 2009) modifications have been made to creeks, wetlands and other flows paths in order to maintain a constant and reliable water supply and water level for extractors (domestic and irrigation) within the upper Pike-Mundic anabranch complex. The following structures have been “owned, maintained and operated” by the Pike-Mundic Association since the 1940‟s (Figure 11): Margaret Dowling Creek inlet Deep Creek inlet Coombs Bridge

Banks B, C, D, E, F, F1, G, H and Col Col

At present, most structures provide no fish passage and cannot be flexibly operated to manage flow. There is also significant head loss across most structures (up to 1.41m); some have culverts that have been set above the bed of the waterway (increasing their “commence to flow” threshold); and many downstream conditions have become significantly silted and infested with typha and phragmites due to low flows and lack of hydraulic variability (Figure 12). The Pike-Mundic Association (comprising members of the Pike irrigation community upstream of Col Col) also regularly (biannually) undertake dredging to deepen creeks, remove typha and de-silt channels.

Figure 11. Hydraulic conditions of the highly modified Pike anabranch system.

Figure 12. Example of the crude structures that currently exist throughout the Pike anabranch complex in

order to divert the majority of flow down Mundic Creek, the upper and lower Pike River for extraction.

Water at many irrigation off-takes is shallow and irrigators prefer to take water from close to the waters surface (deeper water is generally more saline due to the lack of flow and hence mixing potential). Off-takes can therefore be susceptible to small changes in water level. The siltation of water bodies and invasive growth of typha and phragmites around off-takes may also be affecting the operation of many irrigators.

7.2 DEVELOPMENT AND WATER LICENSE CONTROLS

The information contained in this section is extracted from the Pike River Water Supply and Floodplain Management Stage 2 – Sustainable Water Supply (AWE, 2008) and all references contained are within the primary document.

MDBA/DWLBC controls the movement of extraction licenses, the policy is explained in Fact Sheet “River Murray Salinity Zoning”. The Pike area is in a High Salinity Impact Zone (HSIZ) and there are strict controls over movement of water allocations into the area. Key aspects of the policy are:

o A grower may change crop type if the water demand of the new crop is lower; the freed-up water may be used to expand area under irrigation or sold. If water demand is higher water must be transferred in accordance with the Policy,

o Similarly, a grower may introduce irrigation efficiency measures and use water freed-up as in the dot point above,

o A grower may establish new areas under irrigation but must obtain any additional water required in accordance with the policy,

o Water may be transferred between HSIZs without need for salinity credit adjustments as long as they are transferred with their salinity offset,

o Water may be transferred into the Pike HSIZ as part of an approved “Prior Commitment” and the state will provide the required EC salinity credits, if they are available.

o For water transferred into Pike from a low salinity impact zone or from interstate that is not covered by a prior commitment, the transferee is responsible for obtaining appropriate EC salinity credits or implementing approved salinity offset measures.

7.3 SETTING SUSTAINABLE DIVERSION LIMITS

Evidence indicates that setting sustainable diversion limits is required to secure future water supplies for irrigation and reduce adverse ecological impacts in key locations of the floodplain.

This involves undertaking initial detailed modelling of the Pike system and its components to develop appropriate sustainable diversion limits in specific localities of the anabranch complex. Studies show that the Upper Pike region appears to be the most sensitive to increased levels of extraction both from a water quality, flow and ecological perspective.

It is proposed to get specific diversion limits endorsed by the Sustainable Water Committee representing irrigators in the region and then ensure that these limits are written in the new River Murray Water Allocation Plan. The new WAP enables restrictions of water entitlement/allocations based on locality due to an unbundling environment.

7.4 WATER SUPPLY OPTIONS FOR EXTRACTORS

A complementary suite of water supply investigations have been undertaken and supported by the Sustainable Water Supply Steering Committee; being led by DWLBC to ensure access, water supply and

water quality issues for domestic and irrigation extractors are not adversely impacted by potential floodplain actions.

Many potential issues highlighted in section 4.1.6 and 4.1.8, particularly in relation to flow, water levels and water quality (including potential salinity impacts) require further robust assessment to ensure any potential risks to extractors are minimised and/or mitigated. Numerous options have been investigated to enable floodplain restoration actions to be maximised whilst maintaining a sustainable water supply for extractors reliant on the Pike anabranch complex.

7.4.1 Alternative Supply from the River Murray Channel via pipelines

The information contained in this section is extracted from the Sustainable Water Supply and Floodplain Planning Joint Project Assessment of Joint Project Options (AWE and Ecological Association, 2008) and all references contained are within the primary document.

Considerable investigation has been undertaken to assess the viability of providing the current extractors with an alternative water supply from the River Murray channel via pipelines. Numerous routes and pipeline configurations have been assessed. A key concern for growers in considering any alternative water supply option was that water would need to be available for extraction whenever it‟s required (as is the case currently for the Pike extractors). Accordingly, concepts were investigated to enable the pipeline systems to be able to supply up to 18 hours of pumping each day (from grower surveys and discussions, most major irrigators would expect to use pumping infrastructure at least 18 hours per day, every day during peak irrigation weeks). The scheme therefore needed to be designed to be able to pump 24 hours per day, to allow for a safety margin to be built in should breakdowns occur at critical times. Another significant consideration in the various pipeline designs was that no irrigator was to be negatively impacted, irrespective of whether other growers further upstream extracted at a rate above the maximum rate negotiated. As such, robust designs were developed to accommodate the irrigator requests. Table 11 shows the costs associated with various pipeline concepts, taking into account current allocation, alternative peaking factors (ratio between peak demand and average annual demand and thus links peak demand to allocations) and prior commitment.

Table 11 Costs associated with various Pike pipeline options.

Key assumptions in the design and costing of the pipeline options were as follows (AWE and Ecological Associates, 2008): High pressure pipeline with minimum 40m pressure head in the pipeline at each outlet. Assuming a loss of 5m through off-take and metering, this leaves 35m for the grower. This is considered the best overall solution, although some growers may need to change on-farm systems (i.e. larger pipes) or provide booster pumping. At final concept design, supply pressure would need to be confirmed in consultation with the irrigation community; A pipe friction based on Hazen Williams factor of C=120 which is considered to be conservative and allows for friction losses in fittings along the route; Pipeline will be buried and is assumed to follow the main road. Outlet are assumed to be in the road reserve near existing irrigator pipelines;

Pipe sizes have been optimised by balancing operating and capital costs. Unit costs for supply and installation have been chosen from a combination from recent project costs and updated pipe supply quotes; Pumping station costs have been based on a heuristic formula developed on kilowatt capacity of the pump station; and Outlets based on estimated size required for each scenario. Outlets include two isolation valves, a normally open remotely controlled valve, a magnetic flow meter and telemetry for real time monitoring.

Figure 13. Pipeline route to provide extractors on the Upper and Lower Pike with an alternative water supply from the River Murray Channel.

Pipeline options to provide extractors on the Upper and Lower Pike with an alternative water supply from the River Murray Channel have been ruled out by all high level program committees as in isolation they provide no ecological benefit to the floodplain. They are also considered cost prohibitive.

7.4.2 Gravity Pipeline bypassing Mundic Creek and Pike Lagoon

A pipeline from the River to the outlet of Pike Lagoon would mean Mundic Creek and Pike Lagoon were no longer used for a water supply for domestic and irrigation extraction, and could instead employ a much more variable hydraulic regime without potentially impacting on water users within the anabranch complex. A preliminary concept was developed and a possible route is shown in Figure 14. The pipeline needs to be 2.5m in diameter and at a cost of $30m this option was comparable in cost to the Upper Pike pipeline but has only a small portion of the benefits and was not considered in further detail.

Figure 14. Pipeline option to eliminate extraction from Mundic Creek and Pike Lagoon

A gravity pipeline bypassing Mundic Creek and Pike Lagoon has been ruled out by all high level program committees as in isolation it provides no ecological benefit to the floodplain. It is also considered cost prohibitive.

7.4.3 Re-lift Weir at Pike Lagoon Outlet

The construction of a re-lift weir at the outlet of Pike Lagoon would enable water levels in Mundic and Pike Lagoon to be lowered, whilst maintaining current water levels on the downstream side of the weir. The extent of lowering achievable depends on the hydraulic capacity of the creek between Mundic and Pike lagoon which needs to be further investigated. Such a reduction in water levels (up to 0.7m in Mundic Creek) represents a significant challenge for those extracting from the system and lowering of water levels cannot commence until water can be extracted unimpeded during lowering events. This is particularly the case for irrigators who cannot accommodate water storage to the extent of a domestic user. A follow up project is required to identify the changes required for each extraction point affected by lowering and the cost of these changes to pumps and sumps.

This project should allow the high level committees of the Pike program to make informed decisions about expenditure for pump modifications and potentially relocations for the lowering scenarios outlined in the Mundic Tributary Pump Survey Report (Rural Solutions 2008).

The objectives of the pump modification project are: Utilising the existing pump survey and scenarios contained within the Pike & Mundic Tributary Pump Survey Report to provide detailed designs and costings for either; a) Minor alterations to pumps. b) Major alterations to pumps. c) Relocation of pumps.

Identify areas with current water quality concerns where lowering is likely to exacerbate existing conditions (for example high salinity, high nutrient levels, sedimentation problems etc). In such areas alternative water sources will need to be identified.

$80,000 is required to undertake detailed design of pump modifications upstream from Pike Lagoon.

Under the re-lift weir concept, growers and domestic users with off-takes from Mundic Creek and Pike Lagoon may need to be supplied with a small pipeline direct from the River Murray.

A weir and associated small pipeline is expected to cost in the range $5m to $7m (about 10-15% of the cost of a full pipeline option).

The ecological benefits (and potential risks) of a re-lift weir require further investigation to determine if this option is viable. $30,000 is required to undertake this additional ecological evaluation.

7.4.4 Summary of Water Supply Options Assessed

Table 12 provides a summary of the water supply options assessed. The high level committees of the PIP Program have agreed that further investigation is required to determine if the re-lift weir is a viable concept to enable a much more variable hydraulic regime (including a lowering of water levels up to 0.7m) to be implemented for the ecological benefit of the upper section of the floodplain. In addition, funds to undertake detailed design are being sought as part of this Investment Proposal, to ensure extractors are not adversely affected by a future lowering event. It is also proposed that Sustainable Diversion Limits on Upper, Mid and Lower Pike extractors be determined and set. These should be enforced through the new River Murray Water Allocation Plan (WAP). Setting Sustainable Diversion Limits has the potential to reduce the stress of water dependent components of the ecosystems; particularly during periods of low flow to ensure that sufficient water flows through the system.

All major pipeline options to provide an alternative water supply from the River Murray channel in isolation provide no ecological benefit to the floodplain. They are also considered cost prohibitive and as such will not be investigated further as part of this project.

Table 12 Summary of Water Supply Options

8. The Pike Salt Interception Scheme (SIS)

The information contained in this section is extracted from the Pike Salt Interception Scheme Approval Submission (DWLBC, 2009b) and all references contained are within the primary document.

An „Approval Submission‟ has been forwarded to the Murray-Darling Basin Authority (MDBA) for consideration and approval to design and construct the Pike Salt Interception Scheme (SIS). The proposed Pike SIS is estimated to intercept approximately 167.6 tonnes per day (t/day) as averaged over the 30-year MDBA accountability period, and achieve a salinity benefit of 35.4 EC per annum at Morgan over the same period.

The area of interest for the Pike SIS includes the Pike floodplain and the adjacent highland where there is irrigated horticulture. The floodplain is a discharge zone for high salinity regional groundwater. Downward percolation of excess irrigation water to the underlying aquifer system has led to groundwater level rise and mounding, creating steeper groundwater gradients between the highland irrigated areas and the nearby floodplain aquifer. Saline groundwater now flows into the floodplain aquifer at rates greater than prior to irrigation development.

The floodplain aquifer is considered to be hydraulically connected to the Pike surface water system, which allows for the discharge of saline groundwater into the Pike River where groundwater levels are higher than surface water levels. The Pike River then delivers the salt it has collected to the River Murray.

Groundwater modelling indicates that approximately 160t/day of salt entering the River Murray from the Pike area. This is estimated to continue to rise to approximately 251t/day in 2104 if there is no interception of saline regional groundwater.

8.1 PIKE SIS AND THE BASIN SALINITY MANAGEMENT STRATEGY (BSMS)

The Basin Salinity Management Strategy (BSMS) recognises that salinity management is a long term challenge that will extend well beyond the life of the Strategy (2015). The Mid Term Review concludes it is

essential that ongoing implementation of the BSMS is maintained to build on the solid progress to date. It also recommends a new program be established to offset anticipated increases in River salinity (provisionally seeking benefits to be in the order of 40 EC).

The proposed Pike SIS can contribute to the intended outcomes of the BSMS by: providing a salinity benefit at Morgan of 35.4 EC or 167.6 t/day of salt (based on a 30 year average over 2008 – 2037); delivering the most cost effective scheme to date within the entire Murray-Darling Basin on behalf of the partner Governments (benefit to cost ratio of 2.31); and providing EC credits that will contribute to each jurisdiction‟s credit balance, as required under Schedule B of the Murray-Darling Basin Agreement.

8.2 THE PIKE SIS CONCEPT DESIGN

The Pike SIS concept design incorporates: 59 interception wells between Paringa and Lyrup, all on the edge of the highland; 28.5 kms of trunk main pipeline and 13.0 kms of spur main with sizes ranging from 450 mm down to 63 mm diameter, all running along the highland; and transfer of intercepted saline groundwater to the Noora Basin at a rate of 93 L/sec averaged over the next 30 years.

The estimated total capital cost of the Pike SIS is $25.321 million. Annual operation and maintenance (O&M) costs are estimated at $847,000 per year, with an additional $403,000 required every seventh year for pump replacement. Table 13 shows the proposed cost sharing arrangement between the MDBA and the Government of South Australia for the Pike SIS, based on the proportion of pre- and post-1988 salts loads during the 30-year SIS accountability period.

Table 13 Proposed cost sharing arrangement between the MDBA and the Government of South Australia for the Pike SIS

8.3 FUTURE WORK FOR THE PIKE SIS

Upon approval to proceed to the construction phase, it is proposed that SA Water, in partnership with DWLBC and the SA MDB NRM Board establish a project steering committee (PSC) and identify the key service providers required during the preliminary and final design stages. Once these providers are procured, project management, planning and risk assessment requirements will be refined and undertaken.

In the earliest project stages, hydrogeological field-based programs will be planned and undertaken to enable detailed bore field designs to be finalised and assessed. Concurrent with these technical investigations, all possible regulatory approvals and landholder access negotiations will be initiated. These approvals and negotiations will be refined and finalised after the project delivers a construction-ready final design. Key hold points will be established throughout the entire project life to enable the PSC to review project progress

and objectives and keep key stakeholders suitably informed.

The design and construction of the Pike SIS could be undertaken over an elapsed period of under four years and could be commissioned in December 2013. This assumes that approval for detailed design and construction is given in 2010.

9. The Next Steps for the PIP Program

The proposed management actions will need to be thoroughly assessed (environmentally, economically and socially) and will need to receive ongoing support from the appropriate community, scientific, agency and Indigenous groups. Further, where potential risks are identified, mitigation strategies will need to be developed to ensure any impacts are minimal, and are far outweighed by the accompanying benefits associated with the proposed actions.

It should be noted that delays in undertaking the required level of investigation to confirm the suite of surface water, groundwater, land management and community management actions; and their ultimate implementation will lead to a further deterioration of floodplain condition; just as the Pike floodplain has continued to deteriorate significantly since 2006 when the Pike River Land Managers Group worked with the Renmark to the Border Local Action Planning Association to produce the Pike River Land and Water Management Plan. The Plan highlighted grower concern for the increasing salinity levels in the Pike River and wetlands; the poor flow rates and the declining health of the floodplain and requested assistance to address these issues.

9.1 INVESTIGATIONS PROPOSED FOR 2010 AND BEYOND This proposal seeks ongoing investment in the Pike floodplain to confirm the viability of potential environmental regulating structures and to inform potential operating regimes to ensure any new and modified infrastructure is operated in such a way as to maximise ecological benefit and minimise risk and impact. The following investigations are proposed for 2010: Further hydraulic, groundwater and vegetation modelling is required to understand flow behaviour, salinity impacts and potential benefits to tree health under a range of scenarios. Investment in detailed design is also required to confirm design and operating range of new and modified infrastructure (regulators, ancillary banks and fishways). In addition, it will be necessary to continue to undertake a scientifically robust and defensible ecological monitoring program focused on tree health, understorey vegetation, water quality, groundwater, fish, birds and frogs.

Conceptual designs have been developed for the upgrade of the two inlets to the Pike anabranch system upstream of Lock 5 (Margaret Dowling and Deep Creek) to: provide fish passage and to improve the operational flexibility of structures Seasonally manipulate wetland and creek water levels Maximise flowing habitat

Conceptual designs have also been developed for a new network of environmental infrastructure, which includes the Col Col and Tanyaca Creek environmental regulators, fishways, ancillary by-pass regulators, blocking banks and other works.

The new environmental regulators could enable water level variation within the Pike floodplain between 14.35mAHD, representing normal upper pool level at Col Col and 16.40mAHD, representing 100mm above the “normal” upper pool level at Lock and Weir No. 5. Thus the new regulating structures across the Pike anabranch system could be used to regulate water levels within the upper Pike floodplain over a maximum range of approximately 2.05m. The regulator could be operable under flows ranging from entitlement conditions up to 50,000 ML/day, although flows of at least 10,000 ML/day would be optimal to operate to the maximum possible extent.

Investment of $1.078m is being sought immediately to undertake critical investigations required to confirm the viability of proposed long term management options and to maintain the momentum of the Pike

floodplain program. It is proposed to run detailed design concurrent with further ecological monitoring, modelling and investments to inform potential operating regimes, ensuring that any new or modified infrastructure is operated in such a way as to maximise ecological benefit and minimise risk and impact.

Table 14 Investigations proposed for 2010 and beyond

Project Objectives Timeframe Cost (excluding GST) Groundwater To develop an 12 months $280,000 (SKM, 2009a) investigations: understanding of Validation of groundwater processes AEM, and to quantify salinity Development of and vegetation condition groundwater impacts associated with a model, range of surface water Calibration and management regimes. validation of WINDS vegetation model Groundwater modelling Investigate the viability The work proposed in 12 months $150,000 (SKMa, 2009) of a complementary these investigations will Groundwater provide a sound basis for Management Scheme assessment of the (GMS) feasibility and business case for the GMS for the Pike floodplain. There are two primary objectives for the GMS; off-set salinity impacts from flow management; and provide further benefits to floodplain vegetation health.

Hydraulic modelling To identify and answer 12 months $100,000 (Water key questions relating to Technology, 2009) flow management and planning on the Pike Floodplain.

Specifically, hydraulic modelling will: - Improve understanding of potential risks and their management including salinity/ groundwater impacts, water quality change, fish passage impacts, and changes to fish habitat. Further assessment of the volume of water used during operation of new and modified infrastructure is also required.

- Inform preferred operation of new structures that will enable enhanced inundation of high value floodplain and wetlands, enhance fish passage and complement other floodplain restoration activities

Establishment and The broad objectives of 12 months $200,000 (DWLBC, 2009) management of a robust the surface water surface water monitoring monitoring program will program be to: - Define key locations within the anabranch system to collect flow and salinity data with respect to objectives of salinity, environmental flows, extraction and operational interests.

- Establish and maintain surface water monitoring network within the Pike anabranch system.

- Using the network, determine flows and salt loads through different parts of the system over a range of flows and inundation regimes.

Ecological Risk To develop an operating 8 months $100,000 assessment and regime for all new and operational strategy modified infrastructure development for new and on the Pike floodplain. existing infrastructure. Operation will be determined by the antecedent conditions, prevailing inflows (QSA), the ecological requirements of the floodplain, and the level of risk that the resource managers are willing to take.

Operational strategies will need to be designed to maximise ecological benefit whilst minimising potential risks and impacts. Sodic soil investigation To map areas on the Pike 6 months $50,000 floodplain where sodic and severely salinised soils exist.

To develop a remediation strategy to rehabilitate these soils to improve ecological functionality.

Scientifically Robust Statistically robust and 12 months $100,000 Ecological Monitoring scientifically defensible monitoring programs are required to assess the impacts of management actions such as removal of livestock grazing and hydrological manipulation. Quantitative baseline information and ongoing monitoring is required to compare future data collected to investigate changes through time and in response to management actions. The assessment of management actions will determine level of success and whether the actions are appropriate or need to be changed in the future (adaptive management). Project Management 98,000 (10% of total Costs project costs) TOTAL $1,078,000

10. Management Roles and Responsibilities

Management of the Pike floodplain is the key responsibility of government agencies in South Australia. The South Australian Murray-Darling Basin Natural Resources Management Board (SA MDB NRM Board) has taken the lead role since September 2009 as floodplain manager. Prior to this, DWLBC coordinated the PIP project. The SA MDB NRM Board has responsibility for developing the Floodplain Management Plan and coordinating the Pike integrated floodplain project. DWLBC maintains carriage of the SIS and the Sustainable Water Supply components of the PIP project. The PIP project involves various committees and groups that contribute to planning and the integration of management actions at the site. They include: PIP Reference Committee Pike Floodplain Steering Committee Pike Sustainable Water Supply Steering Committee Pike Integrated Floodplain Salinity Steering Committee

It is highly likely that SA Water will be the Constructing Agency for the site and will ultimately be responsible for the operation of new flow management structures on the Pike floodplain, including the proposed Pike environmental regulators.

The Department for Environment and Heritage (DEH) is the landowner for the majority of the Pike floodplain and manager for the Pike River Conservation Park. DEH provides biodiversity and land management support to the PIP project. The Pike River Conservation Park is managed in accordance with

the National Parks and Wildlife Act 1972 and park management plan (1994). DEH also has primary responsibility for the management of natural, historical and cultural features as well as visitors. The Pike floodplain has numerous existing leases over the property, which provides for certain land management activities. The management of pest plants and animals is the responsibility of both DEH and the lessees.

11. Summary

A significant and ongoing investment in the Pike floodplain is required to confirm the suite of surface water, groundwater, land management and community management actions. In particular intensive investigation is required for the Pike environmental regulators prior to it being proposed as the main intervention activity. The aim of the Pike environmental regulators is to restore a sequence of flooding to the Pike floodplain that more closely resembles the natural conditions under which the plants and animals have evolved. The environmental regulators will need to be designed and operated specifically for environmental management and would only be operational for small periods, typically for three months, on average one year in three. It would maximise flooding from low flows and would not be operated during large natural flood events (>50,000ML/day). The designs will include sophisticated fishways to enable fish passage for large, medium and small-bodied native fish. What the regulators could provide is much needed water to the floodplain to address the severe ecological decline that has been observed over a number of years, largely due to reduced flooding and elevated saline water tables. The combined impacts of over-allocation of water from the River Murray system and prolonged drought across the Murray-Darling Basin have resulted in an acceleration of this decline over the past few years.

The proposal to maintain ongoing investigations to confirm the viability of the Pike environmental regulators has been strongly supported by the PIP Reference Committee, the Pike Floodplain Steering Committee, the Pike River Land and Water Management Group, local Indigenous groups and by the broader community in numerous public forums.

To combat the mobilisation of salt that is currently discharged to the outer anabranch creeks, and reduce salt accumulation over a significant area of floodplain, the construction of a complementary groundwater management scheme should also be investigated. If this is proven to be viable, it will provide additional benefit to the stressed floodplain community and will also provide a significant salinity benefit for the irrigation extracting from the Pike anabranch system, as well as downstream of Pike.

Unfortunately, unless action is taken to reintroduce flooding on the Pike floodplain, this local, state and national ecological asset will become dominated with samphire and saltbush communities, as opposed to River red gums and Black box. The construction of environmental regulators (if deemed viable) will be the most effective means of achieving much needed inundation to the floodplain and to „do nothing‟ will be contrary to strong, informed community and scientific support.

Key stakeholders have been consulted prior to the submission of this Investment Proposal and have had direct input to the development of the Management Plan. Community forums and field tours have also been held to provide updates and gain feedback from targeted stakeholders and the wider community about the Pike environmental regulators.

12. References

AWE (2008) Pike River Water Supply and Floodplain Management Stage 2 – Sustainable Water Supply. Report prepared for the Department of Water, Land and Biodiversity Conservation.

AWE and Ecological Association (2008) Sustainable Water Supply and Floodplain Planning Joint Project Assessment of Joint Project Options. Report prepared for the South Australian Murray-Darling Basin Natural Resources Management Board, Berri.

Brookes, J.D., Baldwin, D., Wallace, T., Burch, M. (2007) Ecological evaluation of proposed flow control structure at Chowilla significant ecological asset. Report prepared for the Department of Water, Land and Biodiversity Conservation.

CSIRO (2005). Flood Extent, Groundwater Recharge and Vegetation Response from the Operation of a Potential weir in Chowilla Creek, South Australia. CSIRO Land and Water.

CSIRO (2007). Pike WINDS vegetation modelling. Report prepared for the Department of Water, Land and Biodiversity Conservation.

DHI (2006). Chowilla Floodplain Hydrodynamic Model- Final Report: Data Review and Model Development Report. DHI Water and Environment, Sydney.

DWLBC (2009). Pike Mundic Surface Water Monitoring Requirements. Proposal prepared for the SA MDB NRM Board.

DWLBC (2009b). Pike Salt Interception Approval Submission.

Ecological Associates and Australian Water Environments (2008). Pike River Floodplain Management Plan. Report AQ006-1-B prepared for the South Australian Murray-Darling Basin Natural Resources Management Board, Berri.

Hollis, B.A., Herbert, T. and Mollison, D. (2008). Chowilla Creek Environmental Regulator: Investment Proposal. Report prepared for the SA MDB NRM Board.

Hollis, B.A. 2009. Potential Benefits and Risks of Managed Inundation Extents on the Pike Floodplain. Summary Report prepared for the SA MDB NRM Board.

MDBC (2007). Hydrograph of modelled natural and current flows from 1891-2006. Murray-Darling Basin Commission.

Nicol, J. (2007). Risk of pest plant recruitment as a result of the operation of Chowilla environmental regulator. South Australian Research and Development Institute (Aquatic Sciences), Adelaide.

Nicol, J.M. and Weedon J.T. (2007) Understorey vegetation monitoring of the Chowilla river red gum watering trials. SARDI Aquatic Sciences, Adelaide.

Mallen-Cooper, M., Koehn, J., King A., Stuart I., Zampatti B. (2007) Risk assessment of the proposed Chowilla regulator and managed flood regimes on fish. Sydney

Overton, I.C. and Jolly, I.D. (2003) Investigation of Floodplain and Groundwater Interactions at Chowilla. CSIRO and Department for Water Land and Biodiversity Conservation.

Pers.Comm. (2009). Michael Jones, Project Coordinator (Environmental Works and Measures Program) Murray-Darling Basin Authority.

SKM (2009a) Margaret Dowling Creek and Deep Creek Inlet Regulating Structures: Concept Designs. Report prepared for the SA MDB NRM Board.

SKM (2009b) Pike Groundwater Investigations. Proposal prepared for the SA MDB NRM Board.

Smith F.M. and Kenny (2005) Floristic Vegetation and Tree Health Mapping, River Murray Floodplain, South Australia. Report for the Department of Environment and Heritage.

Wallace, T.A. (2009) An Assessment of Tree Condition at the Pike Floodplain (SA). A report prepared by the Murray-Darling Freshwater Research Centre for the South Australian Murray-Darling Basin Natural Resources Management Board.

Water Technology (2009). Hydrodynamic modeling of the Pike floodplain. Report prepared for the SA MDB NRM Board.

URS (2006). Chowilla Management Options. Report prepared for the Department of Water, Land and Biodiversity Conservation.

URS (2008). Concept Designs for the Katfish Reach Hydrological and Fish Passage Structures. Report Prepared for DEH.

URS (2010). Conceptual Designs for Surface Water Management Infrastructure for the Pike Floodplain. Report prepared for the SA MDB NRM Board.