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Murrumbidgee reach reportConstraints Management Strategy

July 2015

Note: this is a summary of the information collected in the 2014 prefeasibility study. In 2015 a decision was made to reduce the upper flow limit being investigated from 7.15m at the Wagga gauge down to 6.31m.

Murrumbidgee reach report, Constraints Management Strategy

Published by the Murray‒Darling Basin Authority

Postal Address: GPO Box 1801, Canberra ACT 2601Telephone: (02) 6279 0100 international + 61 2 6279 0100Facsimile: (02) 6248 8053 international + 61 2 6248 8053Email: [email protected]: www.mdba.gov.au

ISBN (online): 978-1-925221-06-0

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Cover image: McKennas Lagoon near Carrathool in 2000 showing tall spike rush, water ribbons and other aquatic plants. Photo: James Maguire, NSW Office of Environment and Heritage.

Edited by Biotext, Canberra.

DisclaimerTo the extent permitted by law, the Murray‒Darling Basin Authority and the Commonwealth excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this report (in part or in whole) and any information or material contained within it.

AccessibilityAustralian Government departments and agencies are required by the Disability Discrimination Act 1992 (Cwlth) to ensure that information and services can be accessed by people with disabilities. If you encounter accessibility difficulties or the information you require is in a format that you cannot access, please contact us.

Acknowledgement of the Traditional Owners of the Murrumbidgee waterwaysMDBA acknowledges and pays its respects to the Wiradjuri, Nari Nari, Walgalu, Muthi Muthi and Wadi Wadi people as the Traditional Owners of the country downstream of Burrinjuck and Blowering dams to the Murrumbidgee’s junction with the Murray and the area influenced by the junction. MDBA recognises and acknowledges that the Traditional Owners and their Nations have a deep cultural, social, environmental, spiritual and economic connection to their lands and waters. MDBA understands the need for recognition of Traditional Owners’ knowledge and cultural values.

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ContentsSummary........................................................................................................................................1

The Constraints Management Strategy.............................................................................1

The Murrumbidgee............................................................................................................2

Next steps..........................................................................................................................5

What is the Constraints Management Strategy?........................................................................7

At a glance.........................................................................................................................7

What areas are affected....................................................................................................7

What could change............................................................................................................9

Background to the Strategy.............................................................................................11

Why is the Strategy important?.................................................................................................12

At a glance.......................................................................................................................12

Rivers before and after river regulation...........................................................................12

Connecting rivers to their floodplains..............................................................................14

Why the Strategy is important in the Murrumbidgee region............................................15

What is happening in the Murrumbidgee?................................................................................16

At a glance.......................................................................................................................16

Catchment characteristics...............................................................................................16

How the Murrumbidgee has changed..............................................................................20

How the Murrumbidgee is managed................................................................................24

Mapping flows and understanding effects.......................................................................26

What flows are being considered for the Murrumbidgee?......................................................28

At a glance.......................................................................................................................28

How these flows have been chosen................................................................................28

When and how often these flows would happen.............................................................29

What is not being considered..........................................................................................31

How would the flows be delivered...................................................................................31

What might be the effect of the proposed flows in the Murrumbidgee?...............................33

At a glance.......................................................................................................................33

Environmental effects......................................................................................................33

Community effects...........................................................................................................35

What does the community think?..............................................................................................38

At a glance.......................................................................................................................38

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Key Murrumbidgee community messages......................................................................38

What happens next?...................................................................................................................41

Timelines for the Constraints Management Strategy......................................................41

2014 Phase 1 — Pre-feasibility.................................................................................42

2015–16 Phase 2 — Feasibility....................................................................................42

2016–24 Phase 3 — Planning and implementation......................................................43

Post 2024 Higher managed flows will only be possible when packages of mitigation options are fully implemented..........................................................................................43

What is happening in the subreaches?.....................................................................................45

Blowering and Burrinjuck dams down to Wagga Wagga........................................................46

At a glance.......................................................................................................................46

Reach characteristics......................................................................................................46

What flows are being considered....................................................................................48

What these flows look like...............................................................................................50

What could be affected by these flows............................................................................51

What is the initial community reaction to the range of flows being suggested?..............54

Below Wagga Wagga to Hay......................................................................................................55

At a glance.......................................................................................................................55






Hay Weir to end of Murrumbidgee system...............................................................................65

At a glance.......................................................................................................................65






References...................................................................................................................................71

Appendix 1 Hydrographs at Darlington Point......................................................................73

Appendix 2 Flow footprint maps...........................................................................................75

General disclaimer for the maps in Table 23...................................................................75

Modelling disclaimer for the maps in Table 23................................................................75

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Sources for the maps in Table 23....................................................................................76

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SummaryFor the past century, the Murray–Darling Basin (the Basin) has been developed with a focus on delivering water for productive use. Large dams have been built to capture and store as much water as possible to be used later for consumption and irrigation. There have also been many rules put in place across the Basin around how the rivers and dams are managed.

These structures and practices are of great benefit to our industries and have greatly supported the building of our nation, our Basin communities and our economy. However, the changes we have made have affected how, when and where the Basin’s rivers flow and how healthy they are. Water that once flowed downstream is now often stored, and delivered in regular patterns at times that suits production, not necessarily in a more natural variable way that most benefits and supports the environment. Only when dams are full and spill over are there any significant overbank flows downstream.

For many floodplain areas of the Basin, the time between drinks is now too long for floodplain plants and animals. Small overbank flows that connect the river to its floodplain are vital to the environment. These overbank flows improve water and soil quality, recharge groundwater, and support native plant and animal species. Before rivers were regulated, these flows were far more common. The lack of these flows is affecting long-term river and floodplain health, and, ultimately, Basin communities and businesses who rely on healthy waterways.

Environmental watering has been successfully done for many years in some parts of the Basin, and is one way we can deliver water to benefit the environment. However, there would be many environmental benefits if we could deliver slightly higher flows in the future (mostly up to minor flood level) to reach the floodplains. So, the Basin governments requested that the Basin Plan include a Constraints Management Strategy (the Strategy) to explore how this might be done.

The Constraints Management StrategyThe Constraints Management Strategy is about ensuring that water can flow onto the lower floodplain, while mitigating any effects this water may have on property and people.

For the purpose of the Strategy, constraints are river rules, practices and structures that restrict or limit the volume and/or timing of regulated water delivery through the river system. The Strategy will support governments to operate our highly regulated rivers in smarter ways to increase the frequency and duration of small overbank flows to sustain and improve floodplain health.

Given consumption and irrigation needs, it is not possible, nor is it the goal, to return regulated rivers to their ‘natural’ or ‘without-development’ flows. The Strategy is also not trying to create or change how often damaging moderate and major floods occur. The idea is to make modest regulated releases from storages, generally when higher flows downstream would have occurred if dams were not there. That is, the small overbank flows being proposed will ‘top up’ natural rainfall or unregulated tributary flows, to increase either their peak or duration.

In 2014, we completed the first phase of work — the pre-feasibility phase — which involved looking at seven areas of the Basin in more detail. The Murray–Darling Basin Authority (MDBA) collected information about how small overbank flows, typically up to around minor flood level, affect the environment, and people who live and work along the Murrumbidgee River. We also

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collected information about how such flows can be managed and what sorts of protective measures are needed first.

This was released for public comment in November 2014. Since then, we have continued discussing constraints with the communities that might be affected by any changes. This final version contains some new information that communities thought should be included to tell a more complete story of constraints.

The Murrumbidgee The headwaters of the Murrumbidgee system are regulated by a number of dams, with Tantangara and Burrinjuck on the Murrumbidgee, and Talbingo and Blowering on the Tumut River being the main structures. These structures have greatly modified flows, and the remaining flows, which would once have filled our lagoons and anabranch streams, are no longer sufficient to water these areas. The health of these areas has therefore suffered.

The Sustainable Yields Project in the Murrumbidgee (CSIRO 2008) found that, after development, the frequency of flows of 28,600 ML/day at Narrandera had halved and the maximum period between flows of this size had more than tripled from 2.8 to 9.7 years. The 28,600 ML/day flow is equivalent to a flow of between 30,000 and 40,000 ML/day at Wagga Wagga.

The environmentThe Murrumbidgee region hosts a range of important environments. The area includes habitats critical to several fish species in the Murrumbidgee, and supports a range of species and communities listed as threatened under both Australian and state legislation. The Mid-Murrumbidgee River Wetlands are listed in the Directory of important wetlands of Australia (DoE 2014).

The health of the Mid-Murrumbidgee River Wetlands has declined significantly since the construction of Burrinjuck and Blowering dams. This decline was exacerbated by the Millennium Drought, which lasted from 2000 to 2009. However, our modelling shows that even during this drought, flows would have reached these wetlands if the dams weren’t present.

By providing connecting flows to these wetlands, we will help them to recover and reduce the likelihood of another similar decline in the future. This will provide habitat and food for a range of native species including fish, frogs, turtles, waterbirds and woodland birds.

At the higher flow being investigated of up to 48,500 ML/day (7.15 m) at Wagga Wagga, around 8,000 ha of wetland and 25,400 ha of floodplain vegetation is watered upstream of Hay, and a further 11,600 ha of wetland and 69,900 ha of floodplain is watered downstream.

The proposed flows will flush out organic matter from these inundated areas. This is an important process to reduce the severity of future blackwater events. The organic matter is also important in driving the food web of the river system, and is particularly important for providing food for fish larvae and juvenile fish.

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Proposed flowsNote: this is a summary of the information collected in the 2014 prefeasibility study. In 2015 a decision was made to reduce the upper flow limit being investigated from 7.15m at the Wagga gauge down to 6.31m.

We are investigating making regulated releases from storages to achieve a range of flows from 30,000 to 48,500 ML/day (5.22 to 7.15 m) at Wagga Wagga. The bottom of this range has been delivered before and is just below the level at which Mundarlo Bridge (a low-lying bridge between Gundagai and Wagga Wagga) is inundated. The top level is beneath the minor flow level at Wagga Wagga (7.3 m or 50,100 ML/day) with a small buffer.

The flow levels would generally be achieved by delivering water when tributaries below the dams were responding to rainfall. This would take advantage of natural triggers for native species to breed and grow, and reduce the volume of water needed to be delivered from Burrinjuck and Blowering dams.

Downstream of Wagga Wagga, the flow level would gradually decrease as water seeps into creekbeds and floodplains.

The flows would be delivered in winter and spring in line with when flows would naturally occur. The peak would generally be between three to five days at Wagga Wagga followed by a natural rate of recession. As the flow event moves down the river it attenuates. That is, it flattens out – the height of the flow decreases and its duration increases. For example, flows may have a peak of 40,000 ML/d at Wagga for 4 days. By the time the flow reaches Hay, it may only be 20,000 ML/d, but would remain this high for 8 days (Figure 1). Further work is required to determine the ideal frequency of flow delivery, but initial investigations suggest the range may be around three to four additional flows per decade.

Only limited investigations have been done to date on the Tumut River, an important tributary of the Murrumbidgee. Flows there are limited to 9,300 ML/day through Tumut township. Increasing this limit would improve the flexibility for managed flows; however, the Tumut is a smaller river than the Murrumbidgee and it is already passing unnaturally high flows because Snowy Mountains Hydro-electric Scheme contributions are routed through it. The current flow limit is already very close to bankfull, so any increase would be difficult to manage.

In the lower Murrumbidgee, the channel capacity decreases significantly. Flows above 8,000 to 9,000 ML/day spread across the extensive Lowbidgee Floodplain. Contributions to the Murray are therefore limited in the peak height they can provide. The Murrumbidgee’s value to the Murray is by providing longer duration flows that could provide a base for high flows in the Murray. Although work in the Nimmie–Caira system may allow some additional flows (up to 3,000 ML/day) through to the end of the system, the overall volume of the event, not the peak upstream, drives the flow that reaches the end of the system. The objective of higher peak flows in the Murrumbidgee is to be high enough in the river channel to start filling wetlands in the mid-Murrumbidgee, not to achieve significantly higher peaks at the end of system.

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Figure 1: Proposed changes to flow height and duration

The communityThis reach report reflects MDBA’s current knowledge base after preliminary technical work and after talking with people along the Murrumbidgee River.

Before publication on the MDBA website, an early draft of the report was shared with key stakeholders in the Murrumbidgee region. The report was published on the website on 11 November 2014, and was also emailed and/or posted to stakeholders that had been involved in previous conversations with MDBA about constraints throughout 2013–14.

Landholders perceive higher flows differently depending on how far down the river they are. In the western area, particularly downstream of Hay, inundation is generally seen as beneficial to the country and supports pasture growth. Higher up the river, where rainfall is more reliable, inundation can be disruptive to agricultural operations. Landholders have noted a number of concerns associated with higher flows including pasture damage, impacts on irrigated areas, impeded access, damage to fencing, the need to clean-up debris that accumulates on land following the recession of water, introduction of weed species (particularly lippia), and the need to move stock and pumps.

Councils have also noted issues with low-lying access roads and crossings. The major crossing affected is Mundarlo Bridge, but Mundowy Lane, which provides access to a bridge across the Murrumbidgee 30 km downstream of Wagga Wagga, would be closed at the higher flow ranges. There are also issues with stormwater drainage at Wagga Wagga, Narrandera and Darlington Point, with gates needing to close for some drains that go under the town levees as the river level rises. This poses a risk if there is heavy rain inside the levees while the gates are closed. Councils have used pumps to alleviate this risk during high flows.

Communities are also concerned about a number of other issues, including the effect of higher than expected tributary inflows coinciding with dam releases. However, this risk needs to be counterbalanced by the fact that deliveries will create airspace in dams, which reduces the risk of dam spills and larger floods while the airspace remains. River managers will need to be

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conscious of these risks during the planning and management of events, taking into account weather forecasts and catchment conditions. Another concern is tree fall and erosion occurring during high flows. It will be important to plan events so river levels can rise and fall at a natural rate to reduce this risk.

Irrigator representatives are concerned that delivery of higher flows may require more water to be delivered from Burrinjuck Dam than Blowering Dam due to flow restrictions in the Tumut River. Further work will need to be done to model any potential dam imbalance issues to ensure that the reliability of water entitlements would not be adversely affected.

Possible mitigation optionsMitigation measures can be put in place to address effects of these flows, but the community needs reassurance that the risks of unintended adverse consequences are being planned for and managed. Mitigation options could include:

upgrading roads bridges, and other infrastructure to keep roads and access routes open (e.g. raising Mundarlo Bridge)

installing pumps for stormwater systems where gates may have to close installing a regulator at the Yanco Creek Offtake so that high flows down the creek could

be controlled to avoid overbanking when it was not desired negotiating agreements with landholders for easements or other measures to allow low-

lying land to be wet raising pumps or improving their ability to be moved.

Another option that was considered was whether en-route storages, such as Lake Coolah or turkey-nest dams, could be used to provide a portion of the peak, thereby reducing the height of the flow needed upstream. However, an analysis of previous work done on this, particularly in GHD (2002), found that these options did not provide enough benefits for the costs.

Next stepsThis is the start of a 10-year process and Basin governments are only at the early stages of finding out what the issues and opportunities are, to support future decision making.

This reach report:

provides a context and background to the MDBA work on constraints, which seeks increased flexibility to connect rivers with their floodplains, as part of the implementation of the Basin Plan

outlines the types of changes needed to achieve the river flows being investigated reports on community feedback on possible changes to managed river flows.

The MDBA released the reach reports for all seven regions on our website through October–December 2014. Discussions with community on these reports continued until March 2015 to add to our knowledge base and refine our understanding of what flows mean for communities.

Information from all seven priority areas of the Basin was included in the annual report, which made recommendations to Basin governments about options for further investigations. The annual report was made available on the MDBA website in late 2014.

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In late 2014, Ministers decided to continue investigations in all of the seven priority areas. This means proceeding with the collection of more information, including technical and community studies, to better understand the feasibility of small overbank flows and the mitigation measures needed for delivering the proposed flows. In the Murrumbidgee we are looking at a target flow of 40,000 or 6.31 m at Wagga Wagga. We will also be investigating a buffer which would provide mitigations above this level. The 2014 decision was not a green light to build, do or change anything about how the river is managed.

The next decision, in 2016, is about whether to start putting mitigation measures in place, based on recommendations from the feasibility studies. Actions would take place between 2016 and 2024 to ensure mitigation measures are in place — such as formal arrangements with landholders, rule or management practice changes, asset protection, and infrastructure upgrades — before any managed overbank flows are delivered.

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What is the Constraints Management Strategy?

At a glanceThe Constraints Management Strategy looks at ways to allow rivers to connect to their floodplains more often to improve and maintain the environment, while avoiding, managing or mitigating effects on local communities and industries.

In a river, ‘constraints’ are the things that stop water from reaching some areas.

The constraints can be:

physical structures, such as bridges roads or outlet works river management practices.

The Constraints Management Strategy (the Strategy) is about ensuring that our rivers — and the environments they support — stay healthy and sustainable.

In particular, it is about investigating how to connect rivers with their floodplains more often, while avoiding, managing or mitigating effects to local communities and industries.

By carefully managing constraints, we can ensure that water continues to sustain our vital river environments and communities, both now and in the future.

What areas are affectedThe Strategy is looking at seven areas of the Murray–Darling Basin (the Basin) (Figure 2). These areas were chosen because we are likely to get the best environmental benefits by changing constraints to increase regulated flows in these areas. The areas are:

Hume to Yarrawonga Yarrawonga to Wakool junction Goulburn Murrumbidgee Lower Darling River Murray in South Australia Gwydir region.

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Figure 2: Areas in the Murray–Darling Basin affected by the Constraints Management Strategy

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What could change Current situation:

The current regulated operation of the river system provides flows within a range that is largely governed by irrigation requirements and minimum flow provisions.

Irrigation requirements generally follow crop demand patterns, so flows are higher in the summer irrigation season, and lower in the winter and spring than would naturally be the case.

Rivers are operated to maximise water availability to consumptive use and to limit flows on floodplains.

Releases from storages resulting in overbank flows are a consequence of managing storages when they are close to full or spilling over, rather than to meet environmental objectives.

Over time, such operations have led to a substantial decline in floodplain health. The Strategy is about identifying and enabling smarter ways to manage rivers so that water availability is still maximised and damage from large floods is limited, but also so that some of the smaller overbank flows that are essential for floodplain health are reinstated.

The environment is a relatively new ‘customer’ for regulated water delivery and has different water requirements — including timing and amounts — compared to crops. This is why the Murray–Darling Basin Authority (MDBA) is trying to determine if there are ways to increase flexibility in the range of regulated flows that can be delivered to meet the needs of this new customer.

Possible future situation:

Flows from unregulated tributaries may be topped up with regulated releases from storages. Together, these sources of water would combine to become a flow of sufficient size to result in small overbank flows downstream

Small overbank flows are designed to reach particular parts of the floodplain to achieve specific ecological outcomes.

The ability to do this relies on river managers having hydrological information that is accurate enough to enable them to plan, with confidence, when and when not to make regulated releases. It also relies on governments being able to understand and mitigate any impacts on private land and community assets along the entire flow path.

Mitigation measures must be in place before regulated overbank flows can be delivered. These include formal arrangements with landholders, rule or management practice changes, asset protection, and infrastructure upgrades. The Strategy is focusing on these types of activities during the next decade.

It is important to note that the Strategy should not increase how often damaging moderate and major floods occur. The Strategy is about delivering small overbank flows, which are far smaller than the damaging floods that Murrumbidgee residents vividly remember (e.g. 2010, 2012) (see ‘Small overbank flows’).

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Small overbank flows

In unregulated river systems, overbank flows occur frequently, wetting the floodplain areas around the river.

The changes being investigated in the Constraints Management Strategy aim to increase the frequency and duration of some of the small overbank flows, allowing water to reach particular parts of the landscape that haven’t been getting water as often as they need, such as creeks, billabongs and floodplain vegetation.

The flows being investigated are generally below or at the level defined as a ‘minor flood’ by the Bureau of Meteorology. Bureau of Meteorology flood warnings fall into three categories — minor, moderate and major. The official definition of a minor flood is a flow that causes inconvenience. Low-lying areas next to rivers and creeks start to get wet, requiring the removal of stock and equipment. Minor roads may be closed and low-level bridges or crossings submerged.

The Strategy is about delivering small overbank flows, which are below flood levels that are damaging (Figure 3).

Note: The descriptions of minor, moderate and major floods are the official definitions from the Bureau of Meteorology1.

Figure 3: The effects of minor floods compared with moderate and major floods

The small overbank flows would be created by ‘topping-up’ unregulated tributary flows with releases from storage to increase the peak or duration of a flow event, and so reinstate some of the flows that have been intercepted and stored by dams.

Although classified at around minor flood level, the Murray–Darling Basin Authority understands that some of the flows under investigation by the Constraints Management Strategy will affect businesses and the community, and that these effects need to be mitigated.

1 www.bom.gov.au/water/floods/floodWarningServices.shtml

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Background to the StrategyThe Strategy was developed in 2013 through technical assessments and many conversations with local communities and industries. It incorporated community views and suggestions from a public comment period in October 2013 (see ‘What does the community think?’ and the Constraints Management Strategy public feedback report2).

The Strategy is about giving effect to the Murray–Darling Basin Plan to make the best use of the water that has been recovered for the environment.

The Australian Government has committed $200 million to carry out approved mitigation works that are identified as priorities by the Basin states in the next 10 years.

2 www.mdba.gov.au/sites/default/files/CMS-Public-Feedback-Report.pdf

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Why is the Strategy important?

At a glanceConnecting rivers to their floodplains sustains the local environment and provides benefits to communities, such as improved water quality and floodplain grazing in western areas. River development and regulation have reduced the overbank flows that provide this connection. The Constraints Management Strategy aims to put some water back into the environment to boost riverine productivity, and increase health and resilience.

In the Murrumbidgee River, assessments have rated the current health of the environment as ‘poor’.

Rivers before and after river regulationIn unregulated river systems, there are no constraints to overbank flows caused by high rainfall and catchment run-off, which regularly spread out across the floodplain and reach floodplain creeks, wetlands and billabongs.

In regulated river systems, dams and weirs harvest and control high rainfall events, significantly reducing the flow downriver (Figure 4).

Figure 4: Rivers with pre-regulation and post-regulation flow

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This affects the behaviour of the river downstream. It reduces the height and duration of small overbank flows, and increases the time between overbank flows (Figure 5).

Figure 5: Changes to a river’s hydrology after river regulation (hypothetical flow curve used to demonstrate concept – actual flow graphs for the Murrumbidgee are at Figures 10, 11, 20, 21 and 22)

Regulated releases from storage are mostly restricted to in-channel flows (Figure 6). This reduces the water that reaches particular parts of the landscape — most notably the floodplain and its creek network, wetlands and billabongs. River water stimulates the ecology of many plant and animal species, and, without flows to trigger a range of ecological processes (feeding, breeding, moving), both the diversity of species and their individual numbers have declined.

Figure 6: Regulated releases from storage are mostly restricted to in-channel flows

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Connecting rivers to their floodplainsSmall overbank flows, which are being considered by the Constraints Management Strategy (the Strategy) are vital to the environment. Before river regulation, small overbank flows were common events and they deliver a range of benefits (Figure 7).

Overbank flows:

improve water quality, by– flushing out leaf litter and other organic matter from along riverbanks and floodplains

to reduce the build-up over time, thereby reducing the severity of future blackwater events

improve soil quality, by– moving carbon and nutrients between rivers and floodplains

support native species, by– triggering plants to seed or germinate– filling wetlands to create habitat– supporting habitat and breeding of aquatic bugs and insects (the primary source of the

river food chain) – stimulating animals like native fish to feed and breed — for example, golden perch need

high river flows to spawn, and floodplains make great nursery habitats to rear young fish– allowing plants and animals to move throughout river systems and colonise new areas.

Figure 7: The environmental effects of overbank flows

Constraints to delivering small overbank flows are damaging the river environment. It is important to recognise that this threatens not only the natural environment, but the communities that depend on it. For example, many floodplain graziers in the lower Murrumbidgee rely on overbank flows.

The proposed overbank flows will usually ‘top up’ existing flows, increasing either their peak (river height) or duration (Figure 8).

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Flows are important for many environmental processes, such as breeding and migration, and many species use weather conditions as triggers in anticipation of a large flow. Coordinating regulated water releases with rainfall events and catchment run-off makes use of natural ecological cues to improve environmental outcomes.

Figure 8: ‘Topping-up’ unregulated tributary flows with regulated releases to create small overbank flows

Why the Strategy is important in the Murrumbidgee regionOver time, the Murrumbidgee River has been modified and become highly managed. Burrinjuck and Blowering dams store and deliver water for irrigation and consumption, and also significantly alter the flow of the river. The operation of dams reverses the natural seasonal flow pattern. Under natural conditions, the river flows are highly variable and have high flows in winter and low flows in summer. Under regulated conditions, the river flows are less variable and have generally low flows in winter and high flows in summer.

Changing the seasonal flow pattern disrupts the natural cycles of feeding, growing and breeding for many plants and animals.

Many high in-channel flows and minor overbank flows are caught by the dams. These flows are important for connecting to the extensive system of anabranch creeks and lagoons that make up the Mid-Murrumbidgee River Wetlands. They also spread water out to floodplain grazing areas and wetlands in the lower Murrumbidgee. Without these flows, the health of these systems has declined.

There have been two recent comprehensive assessments of river ecosystem health — the Sustainable Rivers Audit 2008 and 2012 (MDBA 2008; 2012a). The audits rated the health of the Murrumbidgee as ‘very poor’ in 2004–07 and ‘poor’ in 2008–10.

See also ‘How the Murrumbidgee has changed’.

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What is happening in the Murrumbidgee?

At a glanceFlows that connect with floodplain creeks and billabongs, particularly in the mid-Murrumbidgee region, have become far fewer due to river regulation. The health of the Mid-Murrumbidgee River Wetlands has decreased accordingly. The reduction in small overbank flows also allows leaf litter and other organic matter to build up on the floodplain. This can lead to heavy loads of organic matter being brought into the river when an overbank flow eventually does occur, increasing the risk of low-oxygen blackwater events. Managed small overbank flows could help to flush out some of the organic matter before it builds up and also help to feed the food chains that support the river’s fish.

Catchment characteristicsThe Murrumbidgee River spans almost 1,600 km, from its headwaters in the Snowy Mountains to its junction with the River Murray downstream of Balranald (Figure 9).

Tantangara Dam regulates the upper section of the Murrumbidgee. Below Tantangara, the Murrumbidgee runs through upland areas and is then regulated by Burrinjuck Dam.

Downstream of Burrinjuck Dam, the Tumut River joins the Murrumbidgee. The junction is about 10 km above Gundagai. Flows in the Tumut River are heavily altered through regulation by the Talbingo and Blowering dams, and inflows from the Snowy Mountains Hydro-electric Scheme (Snowy Scheme).

The floodplain of the Murrumbidgee is confined by hills until the Malebo Range, downstream of Wagga Wagga. The floodplain is particularly narrow in the Murrumbidgee upstream of the confluence with the Tumut. Downstream from there the floodplain widens somewhat, and there are more lagoons and anabranch creeks. After the Malebo Range, the country flattens considerably and the floodplain spreads in many areas. There are more anabranch creeks, some of which are quite large, such as Beavers and Old Man creeks. West of Narrandera, Yanco Creek comes off the river and conducts water from the Murrumbidgee off to the south, eventually joining Billabong Creek and, subsequently, the Edward River in the Murray system at Moulamein.

The floodplain of the Murrumbidgee remains fairly wide until it reaches Carrathool (upstream of Hay). From there the floodplain narrows — often to less than a kilometre wide for all but the largest of floods. Downstream of Hay, around Maude, the channel capacity decreases and higher flows spread out into the extensive Lowbidgee Floodplain. Around Balranald, flows come back to a narrower floodplain. Downstream of Balranald, the Murrumbidgee joins the Murray. This area supports the Junction Wetlands, which are an extensive area of distributary creeks and other wetlands.

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Figure 9: Map of Murrumbidgee River features

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People and economyThe Murrumbidgee River sustains a large and productive irrigation industry, which produces rice and other cereals and oilseeds, stone and citrus fruits, grapes, fodder crops and, increasingly, cotton. The Murrumbidgee Irrigation Area (which supports the major town centres of Griffith and Leeton) and the Coleambally Irrigation Area are of particular importance. These areas are serviced by extensive networks of canals. Lower down the river, the Lowbidgee Flood Control and Irrigation District also has a network of canals. In addition to these areas, there are many producers who extract water directly from the river and its associated creeks, or have smaller systems of canals.

The Murrumbidgee and its tributaries also provide water for stock and domestic use, and for population centres, including the cities of Canberra and Wagga Wagga.

In the lower Murrumbidgee (particularly downstream of Hay), overbank flows from the Murrumbidgee help to support floodplain grazing.

The Murrumbidgee also supports important recreational activities such as fishing, camping and boating.

The Murrumbidgee and the Tumut rivers are also of central importance to the Traditional Owners in the region. The Wiradjuri, Nari Nari, Walgalu, Muthi Muthi and Wadi Wadi people have lived with and from the rivers for many thousands of years. Scar trees in the river country, such as in the following photograph, stand as evidence of the importance the river has played for many years. Today the river retains its importance to Traditional Owners, including through management of river country such as Toogimbie, near Hay.

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Scar tree, Hay. Photo: Paul Doyle, MDBA.

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EnvironmentThe Murrumbidgee River contains many native fish species, including Murray cod, trout cod and yellowbelly (golden) perch; crustaceans, including Murray crayfish; turtles; frogs; and platypus. It also sustains an extensive network of wetlands that are important to the survival of these and other species, particularly waterbirds.

The remains of former river channels on the extensive floodplains downstream of Gundagai and particularly of Wagga Wagga mean that there are a large number of natural lagoons and anabranch creeks on the mid-Murrumbidgee floodplain. Using satellite imagery of flood events between 1989 and 1997, approximately 1,600 floodplain wetlands were identified between Gundagai and Hay (Frazier 2001; Murray 2006 in MDBA 2012b), with most located between Wagga Wagga and Carrathool (Frazier & Page 2006). The Mid-Murrumbidgee River Wetlands are listed in the Directory of important wetlands of Australia (DoE 2014). The area includes habitats critical to several fish species in the Murrumbidgee (Gilligan 2005), and supports a range of species and communities listed as threatened under both Australian and state legislation (MDBA 2012b).

The Lowbidgee Floodplain Wetlands support a mosaic of red gum and black box woodlands, lignum shrublands, reed beds, aquatic sedgelands and open water habitat, including Yanga Lake. Around 200,000 ha of the Lowbidgee Floodplain Wetlands is listed in the Directory of important wetlands of Australia (DoE 2014). The wetlands support large colonial nesting waterbird breeding events, a variety of frog species (including the nationally vulnerable southern bell frog), and a variety of other native animals and plants.

Downstream of Balranald, the Junction Wetlands support black box and red gum woodlands, and a range of creek and open water habitats.

How the Murrumbidgee has changedThe regulation of the Murrumbidgee has significantly changed the way the river flows. As previously noted, the seasonality of river flows has changed, with low flows in winter and high flows in summer under regulated conditions. The frequency, duration and volume of higher flows has also changed.

Figures 10 and 11 show flows at Darlington Point, which has been chosen because it is downstream of the major irrigation offtakes and is also in an area where there is a high concentration of wetlands. The graphs compare flows that were measured at the river gauge, with estimates of what the flows would have been if there were no dams to hold back flows or extractions taking water from the river. It is called the ‘without-development flow’. The graphs are somewhat crowded, so only flows of up to 40,000 ML/day are shown and only about 20 years of flows are shown in each graph. Two time periods are shown: 1970 to 1990 in the first graph, and 1990 to 2009 (when the modelled data goes up to) in the second. Further time periods are included in Appendix 1.

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Figure 10: Flows at Darlington Point, 1970–90

Figure 11: Flows at Darlington Point, 1990–2009

Flows in the Darlington Point area begin to connect with low-lying wetlands as flow increases. This is particularly the case when flows reach 10,000–25,000 ML/day. The graphs show that many flows that would have reached wetlands without regulation have reduced in size and

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duration. This is less pronounced during wet periods such as the early 1990s, but during dry periods it is more noticeable. The Millennium Drought of 2000 to 2009 was particularly severe; however, there were still flows during this period that the modelling indicates would have connected and filled the wetlands in the 10,000 ML/day to 25,000 ML/day flow range, without regulation. In reality though, with regulation in place, only a portion of these flows got through, with one in 2005 connecting some of the low-lying wetlands, but not reaching the wetlands that required higher flows.

Effect of changesDams capture many natural higher flows, meaning there are fewer flows that are high enough to connect and fill lagoons and anabranch creeks on the lower floodplain. This is particularly important for the Mid-Murrumbidgee River Wetlands, which rely on these events to get water. Although the wetlands, and the plant and animal communities they support, are adapted to a cycle of wetting and drying, the ‘time between drinks’ is now too long and their condition is declining.

Extended dry periods of between 5 and 10 years has a dramatic effect on the vegetation communities the wetlands support. Some wetland plants, such as common spike rush, have rhizomes from which they can regenerate after several years of drying (Roberts & Marsten 2011), but these rhizomes dry and die during extended periods without water. The seed viability of aquatic plants reduces with extended periods in dry sediments (Roberts & Marsten 2011).

For longer-lived species like river red gums, their condition can be severely weakened and some may die. However, they are more resilient than the aquatic vegetation and, in some cases, may colonise what would normally be open water or aquatic plant habitats following minor flow events. Normally these gum saplings would be drowned out by subsequent flow events, but if the frequency of connecting flows is reduced, then this may not happen and they can take over these habitats. These types of changes not only significantly alter the floodplain ecology, but also have implications for the passage of future flood waters that may be impeded by this vegetation.

The health of the aquatic vegetation community of the Mid-Murrumbidgee River Wetlands has declined since 2000. The photographs below show McKennas Lagoon, near Carrathool, before and after the Millennium Drought, showing the loss of aquatic vegetation during this period. Two factors are believed to have played a part in this loss:

The reduced number of flows high enough to connect and fill the wetlands has, over time, led to a lack of viable rhizomes and a diminished seed bank. This was to the point where there were insufficient rhizomes remaining in the soil to effectively respond when higher flows did eventually occur in spring 2010.

Any vegetation that did establish following the spring flow was generally in poor condition and, consequently, vulnerable to the severe blackwater event associated with the December 2010 flood.

Blackwater occurs when organic matter, such as leaf litter, is picked up by high flows. These materials can stain the water a dark colour and when they break down they use up oxygen within the water. In severe cases they can effectively use up all the oxygen in the water and result in fish deaths. The dark staining can also block light to water plants. Blackwater occurs naturally, but the severity of the events is dependent on the period between high flows. The longer

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between flows, the more organic matter can build up. Reduced watering also stresses trees, causing them to drop a larger proportion of their canopy. In the case of the December 2010 flood, it had been a decade since there had been any significant overbank flows.

McKennas Lagoon near Carrathool in 2000 showing tall and short spike rush, and other aquatic plants. Photo: James Maguire, NSW Office of Environment and Heritage.

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McKennas Lagoon near Carrathool in 2011 showing lack of aquatic plants following an extended dry period. Photo: James Maguire, NSW Office of Environment and Heritage.

The way water passes through the Lowbidgee has also changed, particularly since the construction of engineering works in the Nimmie–Caira system. These works included channels, water storage dams and minor levees around paddocks to hold water for later cropping. The works appear to have affected flows to the River Murray reach between Wakool junction and Euston, especially during high flow periods. This change is evident from the differences in flow peaks observed at Euston versus Wakool junction, and the flow contribution from the Murrumbidgee River as recorded at Balranald gauge.

How the Murrumbidgee is managedThe Murrumbidgee and Tumut rivers are managed using a number of water storages and weirs to deliver orders.

Tantangara Dam stops water from the upper Murrumbidgee. Historically, 290 GL/year has been taken from Tantangara via tunnel to Lake Eucumbene (and subsequently to Blowering Dam), resulting in 99% of the average natural yearly stream flow at this site being diverted from the upper Murrumbidgee River. However, under the Snowy Initiative, up to 27 GL/year of the upper Murrumbidgee flow is now allowed to pass through Tantangara and continue along the Murrumbidgee (NSW Office of Water 2011).

The next major water storage down the Murrumbidgee is Burrinjuck Dam, which was built in 1928 and enlarged in 1957 to a capacity of 1,030 GL. The outlet capacity of Burrinjuck Dam is 29,100 ML/day, although this reduces as water levels become low.

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On the Tumut River, Blowering Dam was completed in 1968 with a capacity of 1,630 GL. As well as holding back water from the upper Tumut River, Blowering Dam also receives water from the Snowy Scheme. The water from the Snowy Scheme includes water that is redirected from the Murrumbidgee upstream of Tantangara Dam.

The outlet capacity of Blowering Dam is 21,300 ML/day. However, the Murrumbidgee water sharing plan (NSW Government 2003) limits managed releases from Blowering Dam to 9,000 ML/day to lessen the effects of inundation, waterlogging of low-lying areas and erosion along the Tumut River. The Goobarragandra River comes into the Tumut River upstream of Tumut township, where managed flows are limited to 9,300 ML/day. This means that when flows from the Goobarragandra River exceed 300 ML/day (which they often do), managed releases from Blowering Dam must be adjusted down to ensure the Tumut town limit is not exceeded.

There is a low-lying bridge at Mundarlo between Gundagai and Wagga Wagga. The Murrumbidgee water sharing plan (NSW Government 2003) set a limit on flows at Gundagai of 32,000 ML/day (which equated to 4.87 m under the old gauge height rating), because flows above 5 m were known to inundate the bridge.

Below Wagga Wagga, a proportion of flows diverts off to the south into Beavers Creek, which becomes Old Man Creek downstream of Beavers Creek. Old Man Creek returns to the Murrumbidgee upstream of Narrandera, but — if flows are high enough — they can divert from Old Man Creek into the ephemeral Sandy Creek. Flows into Beavers Creek are controlled by the Beavers Creek Weir, but this structure can only regulate flows of up to 20,000 ML/day (3.9 m at Wagga Wagga). Above this height, the weir is designed not to impede flows into the creek.

At Berembed Weir, flows are diverted off to the Murrumbidgee Irrigation Area via Bundidgerry Creek and then into the Murrumbidgee Irrigation Area Main Canal.

At Yanco Weir, a proportion of flows diverts off down Yanco Creek Cutting into Yanco Creek. The proportion of flows that diverts down Yanco Creek is regulated by adjusting the height of the Yanco Weir pool on the Murrumbidgee. Yanco Creek provides water for irrigation, and stock and domestic purposes, and conveys water through to the Murray system.

At Gogeldrie Weir, flows are diverted to the Coleambally Irrigation Area and Tombullen Storage via the Coleambally Main Canal and to the Murrumbidgee Irrigation Area via the Sturt Canal.

Releases can be made from Tombullen Storage, which has a capacity of 11,000 ML, to top up flows in the Murrumbidgee. The maximum release rate is dependent on how full the storage is, but at full level it can supply a maximum of around 1,700 ML/day (CEWO 2014).

Irrigators in the Hay area draw from Hay Weir.

At Maude Weir, flows are diverted to the Nimmie–Caira area of the Lowbidgee Floodplain via the Nimmie–Pollen Creek, and the North and South Caira channels. Downstream of Maude, Redbank Weir enables water to be delivered into the North Redbank system via the North Redbank Channel and the South Redbank system (which includes Yanga National Park).

Balranald Weir is the final weir in the Murrumbidgee, and provides water for Balranald and some limited irrigation.

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In the lower Murrumbidgee, the channel capacity decreases significantly. This is most noticeable at Chastons Choke, 15 km upstream of Balranald, which has a capacity of 8,000–9,000 ML/day. Flows above this spread across the extensive Lowbidgee Floodplain. The NSW Office of Water is undertaking a project in the Nimmie–Caira area to investigate the feasibility of allowing up to 3,000 ML/day to bypass Chastons Choke. If feasible, this could allow 11,000 to 12,000 ML/day to pass through to Balranald without major overbanking. Trying to deliver flows greater than this is very difficult, because flows tend to spread out across the floodplain.

Mapping flows and understanding effects ‘Flow footprint’ maps let you look at what areas of land are likely to get wet for different-sized flow rates. Mapping was done for two stretches of the river using different methods: from Burrinjuck Dam to Hay using modelled flows, and from Hay Weir to the Murray Junction using satellite imagery. In both cases, this mapping provides an indication of where flows of specific volumes are likely to spread to.

It is important to note that the relationship between a particular flow and the predicted extent of inundation are not consistent. Flows can shape and change the river and floodplain over time, and are also affected by regulation development, such as the construction of levee banks, weirs and regulators. In addition, the condition of the environment before a flow — in particular, how wet the soil is already — can affect the extent of inundation. Therefore, no two flow events are exactly alike.

Due to the numerous variables that influence the certainty around the models’ outputs, both modelling techniques have limitations for fine-scale analysis. However, these models were deemed suitable for the type of analysis required to support the pre-feasibility stage of the Constraints Management Strategy, as they were accurate enough for the scale of assessment required.

Burrinjuck Dam to Hay mappingThe hydraulic model used for the Murrumbidgee down to Hay was developed by State Water. The MIKE11 model used was primarily the CARM (computer-aided river management) river model developed by the Danish Hydraulics Institute, which was modified to suit the requirements of this study. Modifications included adding Beavers, Old Man, Sandy and upper Yanco creeks, and updating the main Murrumbidgee stem modelling to take into account recent changes to gauge ratings. Further information on the setup of the MIKE-11 model and assumptions is provided in a separate technical report on flow inundation mapping and impact analysis for the Constraints Management Strategy available on the MDBA webpage.

The model was run to establish what height the flow peak would be at particular points on the river. To then calculate how the water has spread, the ‘lay of the land’ between these points must be identified, and this is provided by an electronic contour map (digital elevation model) based on light detection and ranging (LIDAR) data and, where LIDAR data were not available, on less-accurate shuttle radar topography mission data. The Murray–Darling Basin Authority (MDBA), together with State Water, compared Landsat satellite images of flows events similar to those mapped to identify errors and omissions where possible. Information from landholders and publications on floodplain works, such as NSW Water Resources Commission (1979; 1983), has also been used to verify the maps where possible.

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Hay Weir to Murray Junction mappingFlow footprint maps were created by CSIRO. The mapping used Landsat satellite images from previous events to show how flows of different sizes move down the river and spread across the landscape. CSIRO then used a digital elevation model based on LIDAR to predict the height of the water surface across the landscape. Satellite images for every flow size were not available, so CSIRO interpolated between available flow images to calculate the area inundated for flows where no images exist. CSIRO mapped the Murrumbidgee from Hay Weir down to the junction with the Murray. They have also mapped much of the River Murray, so this Murray mapping is able to be used to look at how water spreads directly upstream and downstream of the junction. Further information on the CSIRO mapping is provided in the technical report on flow inundation mapping and impact analysis for the Constraints Management Strategy available on the MDBA webpage, and information about the maps used is in Appendix 2.

How MDBA is using the flow footprint mapsMDBA used the flow footprint maps to help determine how flows would affect native vegetation and wetlands on the floodplain, as well as agricultural land use, and roads, bridges and other structures.

Flow footprint maps can help us calculate the environmental benefits. In addition, by identifying what might be affected at different flow levels, we can also estimate what costs might be associated with mitigation to reduce effects. Mitigation can include:

negotiating easement agreements or other arrangements to allow flows on private land undertaking infrastructure works — for example, upgrades to roads and bridges.

These cost estimates are presented in the Constraints Management Strategy annual report, which is available on the MDBA website.

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What flows are being considered for the Murrumbidgee?

At a glanceFlows are based on the flow at Wagga Wagga, which is the point of highest average flow in the river. The flows being considered are 30,000, 40,000 and 48,500 ML/day at Wagga Wagga, which equate to 5.22, 6.31 and 7.15 m at Wagga Wagga. These flows diminish as you go downstream.

Generally flows would be delivered by ‘topping-up’ tributary events, so that less water is needed from dams to achieve the desired flow. Flows would generally be delivered in winter–spring. The peak of the flows would generally be from three to five days (or shorter for the higher flow levels) with a natural rate of recession following the peak. Further work is required to determine the likely frequency, but it is likely to be around three to four additional flows per decade.

Our work is looking at possible new ways to manage the Murrumbidgee River to improve both its long-term health and the health of the broader Basin to which it contributes. This work is also investigating any impacts that higher flows could have, and opportunities to avoid or minimise them.

We are continuing to collect information on flow patterns and behaviours, environmental effects, and community knowledge and opinions to understand what is and isn’t possible.

How these flows have been chosenThe lower flow level of 30,000 ML/day (5.22 m) at Wagga Wagga is in line with the size of previous environmental events in 1998, 2000, 2010 and 2011. Above this level, Mundarlo Bridge is closed (which limits regulated releases to below this level). In addition to the closure of Mundarlo Bridge, landholders in some areas also experience effects at this level, so it is important to investigate flows at this height to tease out what effects there may be. The minor flood level at Wagga Wagga is 7.3 m (50,100 ML/day). An upper flow of 48,500 ML/day (7.15 m) was chosen to give a buffer under this.

Flows upstream of Wagga Wagga do not need to be as high as the target flow at Wagga Wagga, because tributary inputs would provide some of the water.

Downstream of Wagga Wagga, the flow peak would reduce as the flow spreads out along the channel, and into anabranch creeks and billabongs. Historical flows were statistically analysed to determine what flows would be expected downstream of Wagga Wagga. Table 1 shows what flows are being investigated at major gauges along the river. Note that the flows are indicative only, and further work is being done to refine these values..

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Table 1: Flows being investigated including indicative flows at gauges downstream of Wagga Wagga

Location Lower flows Height (m)

Lower flows Flow

(ML/day)

Middle flows

Height (m)

Middle flows Flow

(ML/day)

Upper flows

Height (m)

Upper flows Flow

(ML/day)Gundagai 4.92 30,000 5.80 40,000 6.10 43,900Wagga Wagga 5.22 30,000 6.31 40,000 7.15 48,500

Narrandera 5.06 22,000 6.22 34,000 6.61 39,000Yanco Creek offtake 3.79 2,174 4.25 3,007 4.55 3,715

Darlington Point 4.59 17,500 5.64 27,000 5.98 30,500

Carrathool 5.00 15,800 6.50 25,000 6.65 28,000Hay 5.50 14,000 7.05 21,500 7.62 25,000Balranald 5.54 8,000 5.98 10,000 6.29 13,000

Flows at Tumut have been assumed to be at the water sharing plan limit of 9,300 ML/day. To ensure all possibilities are fairly considered, flows of up to 12,000 and 14,000 ML/day are being looked at in a preliminary way in the Tumut; however, increases above the current 9,300 ML/day limit are difficult. The Tumut River is a smaller river than the Murrumbidgee, and 9,300 ML/day at Tumut already represents a flow that is close to bankfull in many places.

When and how often these flows would happenThe timing of these flows would generally be in line with natural seasonality, which is in winter–spring. Figure 12 shows the month in which flows are modelled to have occurred under without-development conditions (i.e. without dams or water extractions). It shows that the seasonality of high flows is winter to spring (June to November) and, particularly, from July to September. Timing will usually be dictated by when natural tributary events occur.

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Figure 12: Month in which flow events of 30,000 to 48,500 ML/day at Wagga Wagga occurred. Flows are modelled without development, where the effects of dams and water extraction have been removed.

The duration of these flows is likely to be three to five days at peak flow level at Wagga Wagga. As the flow moves down the river, the duration would extend as the peak level reduces. The peak would be followed by a drop in flow in line with natural rates of fall, which are generally around 10–15% from the previous day. Flows at the higher end of the flows — more than 40,000 ML/day — are likely to only be held at peak for two or three days at Wagga Wagga, as these larger flows are reliant on tributary events that tend to be quite short and sharp, and often last only a few days. The tributary catchments are relatively small and they drain into a relatively short section of river from the dams to Wagga Wagga — a distance that equates to around two days of travel time for flows. Under natural conditions, these high-flow events would often be extended by flows coming through from the upper catchment, but these flows are now frequently held back by the dams.

Further work is being undertaken to determine how often flows would be delivered. An indication of the desired frequency of events can be taken from the Assessment of environmental water requirements for the proposed Basin Plan: Mid-Murrumbidgee River Wetlands (MDBA 2012b). This provided recommendations for flow frequencies for the Mid-Murrumbidgee River Wetlands. These recommendations were based on the flow at Narrandera, not Wagga Wagga, but some of the flows are comparable to those being investigated for this study. The relevant flows are provided in Table 2. Table 2 also gives the frequency these flows would occur without dams and extraction, and the frequency under current development conditions. Finally, the table gives the frequency of events that the assessment determined would be required to meet ecological targets and then, consequently, how many events would be needed to ‘fill the gap’. Note the flows from the MDBA (2012b) assessment are somewhat higher than the flow that would be expected at Narrandera from the flow levels we are looking at in this study. They are useful, however, in providing a rough indication of frequencies. Also note that the numbers given for events needed to fill the gap are not independent. Some events for the higher flows would fulfil the requirements of the lower flows. Given that some events will be covering the requirements of multiple flow thresholds, it is anticipated that around 20 to 25 additional events may be required per 100 years.

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Table 2: Environmental watering requirements for Mid-Murrumbidgee River Wetlands

Flow at Narrandera (ML/day)

Comparable flow from this study (Wagga

Wagga flow, ML/day)

Time at this height

at Narrandera

(days)

Proportion of years

event occurred

under modelled without-

development conditions

(%)

Proportion of years

event occurred

under modelled current

development conditions

(%)

Proportion of years

event required

to achieve ecological target with

high certainty

(%)

Proportion of years

when event

would be needed to

‘fill the gap’ (%)

26,850a 30,000 5 67 46 60 14

34,650a 40,000 5 57 29 40 11

44,000a 48,500 3 44 22 35 13*Note this flow is somewhat higher than the flow that is likely to result at Narrandera for the ‘comparable flow from this study’, so the results should only be taken as a rough indication of the flow frequencies likely. Source: MDBA (2012b).

This information may not provide the full picture, as there may also be shorter duration events that may be desirable to deliver. The Sustainable Yields Project for the Murrumbidgee (CSIRO 2008) noted that flows at Narrandera of 26,800 ML/day of any duration occurred about 250 times every 100 years under without-development conditions. Under current development conditions, the frequency has halved to about 125 times. The maximum period between events has more than tripled from 2.8 years for without-development conditions to 9.7 years for current development conditions (CSIRO 2008).

Although only a portion of the lost events would be ecologically critical, it indicates that there may be some shorter events that may be advantageous to reinstate, in addition to the longer duration events. To cover this eventuality, it is suggested that assessments should cover the possibility of 50% more events than those in Table 2 (noting that the additional events would be of shorter duration). This would bring the total number of events (allowing for the fact that there will be some duplication between flows) to a total number of additional flows of around 30 to 40 per 100 years, or three to four per decade.

As noted, these figures require further analysis and more work is being done to properly estimate the frequency.

What is not being consideredWe are not trying to create or change how often moderate and major floods occur. These are recognised as damaging and disruptive, and are outside the bounds of active river management.

How would the flows be deliveredGenerally, flows would be delivered when tributaries downstream of the dams are contributing significant flows due to a local rainfall event. This has two advantages: the tributary flows provide natural triggers that wildlife, such as fish, respond to, and it also reduces the contribution of water needed from Blowering and Burrinjuck dams to bring the flow to the desired levels. Further downstream, Tombullen Storage also provides some limited capacity to top up flows.

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It is important to note that the flow levels being investigated are the total flows — that is, the level achieved from dam deliveries and the tributary inflows combined. For example, if a flow of 40,000 ML/day is sought and tributary flows are providing 15,000 ML/day, then dam deliveries would be 25,000 ML/day.

Decisions on whether to target these higher flows in a particular year are made by environmental water holders (the NSW Office of Environment and Heritage, and the Commonwealth Environmental Water Holder) in consultation with the Murrumbidgee Environmental Water Advisory Group. In making these decisions, consideration would be given to the time since the wetlands were last connected to the river, the condition of the wetland communities, the amount of water available, any risks and what other priorities there are. Should it be decided that an event was desired in that year, the actual decision on when to deliver would be dependent on tributary events. A technical advisory group, including water holders, the river operator (NSW State Water Corporation), the NSW Office of Water and others as needed, would assess tributary flows from rainfall events to determine if the flows are large enough to provide a base for the target flow.

During an event, State Water would analyse the tributary inflows and calculate the volumes required from the dams to achieve the desired flow level downstream. State Water is rolling out a computer-aided river management system across the Murrumbidgee that will improve their ability to determine what release rates are required from the dams.

Regulated flows from Blowering Dam are limited to 9,000 ML/day and the flow at Tumut (which includes flows from the Goobarragandra River) is not able to exceed 9,300 ML/day. This means that the remaining flow to top up the tributary inflows must come from Burrinjuck Dam. As the outlet capacity of Burrinjuck Dam is limited to a maximum of 29,100 ML/day, this means that for flows above 38,000 ML/day, contributions from the tributaries are required. However, due to the desirability of natural cues, it is unlikely that any of the flows investigated in this study would occur without tributary contributions.

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What might be the effect of the proposed flows in the Murrumbidgee?

At a glanceDownstream of Hay, inundation of floodplains is generally seen as beneficial, wetting the soil to support the growth of native pasture. Higher up the river, inundation tends to disrupt agricultural operations, as it can damage improved pastures and lucerne crops. Other effects include impeded access, damage to fencing, distribution of debris across paddocks, the introduction of weed species (particularly lippia), and the need to move stock and pumps. Low-lying access roads and crossings, including Mundarlo Bridge, can also be submerged. There are also issues with stormwater drainage at townships.

The effect of the delivery of higher flows on the balance between levels in Burrinjuck and Blowering dams needs to be further investigated.

The flows would water substantial areas of wetland and floodplain vegetation, and will flush out organic matter from these areas. This flushing is an important process to reduce the severity of future blackwater events. The organic matter is also important in driving the food web of the river system.

Environmental effectsReconnecting the river to the lower floodplain, anabranch creeks and lagoons has multiple environmental benefits, including supporting the recovery, growth and reproduction of vegetation communities. The vegetation communities provide habitat and food for native animals, including fish, frogs, turtles, waterbirds and woodland birds. Higher flows also provide cues for animals such as fish to move and reproduce. ‘How the Murrumbidgee has changed’ describes the types of effects that reconnecting flows would be seeking to address.

InundationTable 3 shows the areas of wetlands and floodplain vegetation that are inundated by the flows being investigated. The figures for upstream of Hay and downstream of Hay have been given separately, as some of the areas downstream of Hay can be inundated without high flows through channels off Maude and Redbank weirs. The areas were determined using the flow footprint mapping discussed in a previous section, and should be treated as being indicative only at this stage.

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Table 3: Environmental benefits of different levels of change

Environmental benefits

Lower flows:

30,000 ML/d 5.22 m at Wagga Wagga

Middle flows:


Higher flows:


Wetlands (Australian National Aquatic Ecosystem)

Upstream of Hay: 6,013 ha

Downstream of Hay: 8,148 ha

Upstream of Hay: 7705 ha



Downstream Hay: 11,641 ha

Floodplain vegetation: river red gum, black box and shrublands (including lignum)







BlackwaterThe flows would flush out organic matter from inundated areas. This is an important process to reduce the severity of future blackwater events. If the period between events is prolonged, the volume of leaf litter and other organic matter can build up to a point where the next flood will cause a damaging low-oxygen blackwater event. This is akin to bushfire risk — if the fuel load in an area builds up and is not managed with fuel reduction burns, then the next fire can be highly destructive. So too for the organic matter that fuels blackwater events — managed flows to the lower floodplain can help to reduce the fuel load before the next flood and reduce the severity of any blackwater event.

FoodThe flows would direct organic matter to the river. In moderate amounts, the contribution of organic matter to rivers is beneficial and important in driving the food web of river systems, and is particularly important for providing food for fish larvae and juvenile fish. Organic matter is broken down by bacteria, which is then eaten by microcrustaceans such as copepods. These then provide food for fish larvae. Fish larvae have very small mouths and are only able to eat small prey. Without sufficient food of the appropriate size like copepods, fish larvae starve. Fish may successfully spawn, but without sufficient food, the fish larvae will not survive.

DownstreamThe higher flows are likely to have environmental benefits in areas of the lower Murrumbidgee as well. Some areas of the Lowbidgee Floodplain are able to be watered via channels from Maude and Redbank weirs. However, some areas are not and they require higher flows to be inundated. These areas are the floodplains upstream of Maude, north of the river from Maude to Redbank, and downstream of Balranald including the Junction Wetlands. In addition, even for those areas that can be watered from Maude and Redbank weirs, filling via higher flows is more beneficial because there is superior connectivity between the river and the wetlands during overbank flows. This allows fish and other wildlife, as well as plant seeds and propagules, to move into and out of

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the wetlands, allows for the exchange of nutrients and organic matter, and provides more natural cues for native species.

Flows from the Murrumbidgee also provide significant benefits to the Murray and Lower Murray, particularly in helping build higher flows that inundate adjacent billabongs, creeks and floodplains. The contribution to Murray flows from the Murrumbidgee is, however, limited by channel capacity in the Lowbidgee (as previously discussed). This factor, in conjunction with the high level of attenuation of flows (as they move down the Murrumbidgee), means the main driver of peak flows at Balranald is the total volume of an event, not the size of the peak in the upper Murrumbidgee. The objective of higher peak flows in the Murrumbidgee is, therefore, to drive connectivity with Mid-Murrumbidgee River Wetlands, not to achieve higher peaks at the end of system. High flows at the end of the system can be achieved by longer duration in-channel flows.

Community effectsEffects on the community differ as you move down the river. In the lower Murrumbidgee, particularly below Hay, where rainfall is lower, inundation is generally seen as beneficial, wetting the soil profile to support native pasture. Higher up the river, where rainfall is more reliable, inundation tends to disrupt agricultural operations, such as damaging improved pastures and, at higher flows rates, lucerne crops (which tend to be located higher on the floodplain). Higher flows can also impede access to areas. More detailed information on potential effects in each section of the river is outlined in ‘What is happening in the subreaches?’

The following list presents a summary of effects identified by the community through our constraints consultation. The community is already experienced at dealing with flows of this size and the accompanying effects. The managed flows being considered by the Constraints Management Strategy would, however, add to the frequency of flow events.

Inundation of low-lying land Pasture can benefit from short durations of flooding (several days), but longer periods will

damage or kill it. The length of time different species are able to cope with inundations varies. In the case of improved pastures, where extended inundation results in their death, pastures will need to be re-sown — this is an added cost. A period of stock exclusion is also required following the recession of water to allow pastures to recover. During this time, stock need to be grazed on higher areas of the farm, compromising the production of those areas. Alternatively, agistment or supplementary feeding could be required, both of which present additional costs.

As noted above, as you move west down the Murrumbidgee, increased inundation is viewed as beneficial, serving to support pasture growth. In wetland areas, growth of palatable wetland species, such as marsh grasses and sedges, also provides additional feed for stock.

Some areas, particularly in areas affected by the higher flow level, have irrigated lucerne and similar crops. Inundation of more than a few days can result in the loss of these high-value species. In cases where inundation is extended and the stand is killed, additional costs are also incurred associated with re-sowing and lost production time as stands are re-established. Landholders also noted that this affects their ability to fulfil production contracts and, consequently, maintain customers.

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Weeds, such as lippia, can be a problem following flooding and can significantly reduce carrying capacity and increase management costs.

In some areas, if flooding is deep and extended, soil compaction can be a problem. Nutrients can leach from the soils, particularly if they have been fertilised. Overbank flows

can, however, also provide benefits to the soil. Debris (e.g. tree branches) brought in by the flow often requires clearing afterwards,

particularly from fences.

Infrastructure Fencing can be damaged by flows and would require repairs or replacement. Farmers with pumps below the flow levels would need to move them. At Wagga Wagga, Narrandera and Darlington Point, the gates on some stormwater

drains under levees would need to be closed to prevent water backing up from the river into the drainage systems. This poses a risk if a downpour occurred inside the levees while the gates are closed. Councils have used pumps to alleviate this risk during high flows.

Roads and access A number of low-lying roads and crossings may be affected. These include the low-lying

Mundarlo Bridge across the Murrumbidgee (between Gundagai and Wagga Wagga) and Mundowy Lane (near Collingullie, 30 km west of Wagga Wagga), which provides access to a bridge across the Murrumbidgee River and a bridge across Beavers Creek. The closure of these access routes means substantial detours to the nearest other bridges at Gundagai (in the case of Mundarlo Bridge) and Wagga Wagga (in the case of Mundowy Lane).

Parts of people’s properties may become inaccessible and all stock may need to be moved, particularly if the period of impeded access is expected to be long. Mustering stock at short notice (the case for areas nearer the dams) can be difficult to manage. Having land unable to be used requires agistment or supplementary feeding if the property does not have suitable other land.

Tourism and recreation The highest flow level comes close to the evacuation point for the caravan park at Wagga

Wagga Beach (7.3 m or 50,100 ML/day) and also causes concern for the caravan park at Darlington Point (evacuation point is 6.5 m or 40,000 ML/d), although there is still a buffer to the upper flow level (upper flow level of 5.98 m or 30,500 ML/day). If there were higher flows in the Tumut River the Riverglade Caravan Park at Tumut Town could also be affected.

Access to beaches, camping and wood-gathering areas and boat ramps may be impeded, which may have an effect on tourism (although it should be noted that the proposed flows are well outside the major tourist seasons of summer and Easter).

Other effects There is concern about bank erosion and tree fall during high flows and their recession. It

will be necessary to ensure rates of flow recession are in line with natural rates to address the risk of bank slumping.

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In areas next to the river that have sand/gravel soil profiles, watertables can rise if the higher flows are of sufficient duration. This would be the case in parts of the Tumut valley. If the watertable rises into the root zone of plants for extended periods, this could damage or kill the plants.

A quarry near Mundarlo may be inundated for the higher flow range. This would cause lost production and would require pumping out and possibly remedial works.

Mitigation measures to address these issues are outlined in ‘What needs to be in place before environmental flows can happen’. Some of these mitigation measures may help the community during times of existing natural inundation (e.g. bridges that can be used throughout the year).

Mundarlo Bridge (also known as Tenandra or Poley Bridge) on Murrumbidgee River downstream of Gundagai. Photo: Paul Doyle, MDBA

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What does the community think?

At a glanceHow landholders perceive higher flows changes the further down the river they are. In the eastern part of the floodplain, upstream of Carrathool, inundation is generally seen as detrimental, with particular concerns about the higher flow level. In the western area, particularly downstream of Hay, inundation is generally seen as positive.

Communities have concerns about the effect of higher than expected tributary inflows coinciding with dam releases, and tree fall and erosion. Councils are also keen to see that issues with low-lying access roads and crossings, and stormwater drainage are addressed.

The effect of the delivery of higher flows on the balance between levels in Burrinjuck and Blowering dams needs to be further investigated.

Since 2013, the Murray–Darling Basin Authority has been talking with a number of landholders, councils and Indigenous community representatives, as well as the Murrumbidgee Environmental Water Advisory Group and the Murrumbidgee State Water Customer Services Committee. Consultation has concentrated on key areas where mapping indicates more of a spread of water onto low-lying areas. These areas are Collingullie, upper Yanco Creek, Darlington Point and the Lowbidgee (Hay to Balranald). In the feasibility stage, more extensive consultation will be conducted.

Key Murrumbidgee community messages

OpportunitiesAs noted in ‘Community effects’, in the western area of the floodplain, particularly downstream of Hay, inundation is generally seen as beneficial to the country and supports pasture growth.

If you send down the higher flow I’ll send you a box of chocolates — this country needs the water. Farmer west of Maude

There are also patches upstream of Hay where inundation could be beneficial. In some parts of the lower Yanco Creek system, higher flows would be welcomed for their benefits to the health of the low-lying country. In the Sandy Creek system, which comes off Old Man Creek near Galore, flows could provide benefits by pre-wetting the creek channel to reduce losses during the irrigation season. Parts of the Sandy Creek system are also thought to benefit from flooding.

During the good times there when the Buckingbong would fill up, the cattle would be wandering around there with marsh grass up to their bellies and they were the fattest cattle you’d ever see. Long-time farmer from the Sandy Creek/Old Man Creek area

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Some members of the Indigenous community saw the returning of some of the natural flows and the wetting of country as positive.

When I go down to the river country it is a bit like going to church for me — there’s something special about it. Getting the water to that country would be a good thing. Aboriginal elder in the mid-Murrumbidgee

ConcernsGenerally, however, inundation is perceived as detrimental in areas in the eastern part of the floodplain. In areas where significant portions of paddocks are inundated or cut off, there is concern about both the immediate and after-flow effects. Moving stock can be difficult at short notice, as would be the case in areas such as around and upstream of Wagga Wagga, which is approximately two days flow travel time from the dams. Additionally, newborn lambs and calves are not able to walk or be mustered easily.

Mustering stock in the wooded creek country can take a while. You sometimes have to go back a couple of times to get them all. Farmer near Collingullie

In isolated areas, stock can be difficult to manage, particularly if they are lambing or calving at the time. It is also a problem if shearing is planned and access to shearing sheds is cut. Duration of inundation is important — farmers need to check and manage stock regularly for fly strike and other pests and diseases.

Providing agistment, fodder or using a higher paddock to feed the stock all has costs.

Having to move livestock from low-lying land means that we often have to sacrifice a cereal crop or a pasture preserved for hay on our higher ground for feed. Farmer near Collingullie

Several farmers underlined that once the flow recedes, that is not necessarily the end of the story. Some areas are in depressions that can take a long time to dry out. It can also take a long time for pasture to recover or re-establish, and stock must be withheld until this has occurred. If inundated for too long, the plants will die and then the area will need to be re-sown which takes time and money. There will also be lost production for the time it takes the plants to re-establish.

For the improved-pasture Phalaris, it is relatively flood tolerant but more than a week of flooding will set it back or kill it — it takes 12 months before you can introduce stock to it. Farmer near Collingullie

For areas where lucerne is grown, farmers noted how difficult it was to maintain customers if you are not able to provide a regular supply of lucerne hay.

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The councils of Wagga Wagga, Narrandera and Darlington Point are concerned about their stormwater drainage systems. There are also concerns from councils about low-lying roads and recreational areas, such as boat ramps and camping areas.

Some landholders noted concerns about the risk of intense rainfall happening at the same time as a high flow, resulting in a higher flow than anticipated. This would be a concern where there are major tributaries — that is, upstream of Wagga Wagga. However, some of the ephemeral streams in the stretch directly below Wagga Wagga — notably Houlaghans Creek and Bullenbung Creek — can contribute substantial flows to the river on rare occasions.

Other landholders noted that the use of water early in the season to achieve a high flow would create airspace in Burrinjuck and Blowering dams, and reduce the risk of major flooding while the airspace remained.

The risk will need to be managed by river managers, taking into account the weather forecast for the delivery period. It should be noted that the time from delivery to where the major tributaries come in is relatively short in the Murrumbidgee — it is approximately two days from the dams to Wagga Wagga. Houlaghans Creek comes in directly below Wagga Wagga, and Bullenbung Creek is around an additional day downstream. These relatively short travel times should give river operators the opportunity to adjust releases should rain be forecast.

Irrigator representatives expressed concern that the delivery of higher flows may require more water to be delivered from Burrinjuck Dam than Blowering Dam due to flow restrictions in the Tumut River, therefore reducing the proportion of water available in Burrinjuck later to meet peak irrigation demands. Further work is being done to model any potential dam imbalance issues to ensure that the reliability of water entitlements would not be adversely affected.

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What happens next?

At a glance

The information we have collected since 2013 contributes to the development of the Constraints Management Strategy annual report. That report will make recommendations to Murray–Darling Basin governments about further work required to investigate key constraints.

In late 2014, Ministers decided to continue investigations in all of the seven priority areas. This means we will continue to collect more information including technical and community studies to better understand the feasibility of small overbank flows and the mitigation measures needed for delivering the proposed flows. The 2014 decision was not a green light to build, do or change anything about how the river is managed.

Further work will include the development of detailed proposals in preparation for implementing mitigation measures between 2016 and 2024. Mitigation measures have to be in place before overbank flows can be delivered. We will continue to collect information on flow patterns and behaviours, environmental effects, and community knowledge and opinions to understand what is and isn’t possible.

Timelines for the Constraints Management StrategyThe publication of this reach report and the development of recommendations in the annual report are just the start of a much longer process (Figure 13). There will be no change to current river operations in the Murrumbidgee River for some years to come, if at all.

Figure 13: Phases of the Constraints Management Strategy

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2014 Phase 1 — Pre-feasibilityPhase 1 of the Strategy has been about collecting information about the management and effects of higher flows. MDBA:

investigated options to modify constraints, looking at different potential flows assessed the effects of these changes, including talking to landholders and communities

about how different flows might affect them identified options to avoid or mitigate inundation effects (e.g. building bridges, upgrading

roads or buying easements).

Information for the Murrumbidgee was then drawn together with information from the six other areas into the Constraints Management Strategy annual report, which was published in late 2014. This report informed decisions by Basin ministers as to which areas will be the subject of more detailed investigation.

At the end of Phase 1, MDBA recommended to Basin governments that they continue to explore the potential to relax constraints in each of the seven key focus areas through the feasibility phase (2015 to June 2016).3

Basin ministers (state and federal) have agreed that detailed investigations should proceed for higher managed flows in all seven key focus areas as part of feasibility investigations. The flow rate under investigation for the Murrumbidgee is 40,000 (6.31 m) at Wagga Wagga. This is a commitment to undertake further studies, not a commitment to go ahead with planning and implementation of mitigation measures to allow higher managed flows.

2015–16 Phase 2 — FeasibilityThe Australian Government Department of the Environment has made funding available for the key focus areas to provide states with the resources needed to conduct detailed studies and prepare business cases.

In Phase 2 of the Strategy, MDBA and Basin states will need to:

do more detailed hydrologic analysis to determine the best flow rates to relax constraints to in each key focus area

assess inundation impacts and options to mitigate those impacts improve cost estimates undertake further community consultations.

Ministers have requested that further studies be done on constraint measures in all key focus areas. In the Murrumbidgee, further investigations will be carried out by the NSW Government with support from the MDBA.

Business cases for constraints projects will be finalised by November 2015. Information in the draft business cases will be available for community review before they are finalised.

2016–24 Phase 3 — Planning and implementationState and federal governments will decide by mid-2016 about whether to go ahead with easing constraints (planning and implementing mitigation measures that then allow higher managed 3 www.mdba.gov.au/media-pubs/publications/cms-annual-progress-report-to-ministers-2014

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http://www.mdba.gov.au/media-pubs/publications/cms-annual-progress-report-to-ministers-2014


flows). This decision will be based on the environmental gains, whether any effects on communities can be overcome, and the costs involved.

If constraint measures move ahead to planning and implementation (mid-2016 to 2024), it is likely the states will undertake this work.

To ease constraints, proponent states would need to negotiate and pay for land-based agreements with landholders, such as easements, to allow water to flow onto private land (for flows to reach an environmental asset or allow sufficient water to flow down a channel).

Post 2024 Higher managed flows will only be possible when packages of mitigation options are fully implementedIt is essential that measures are in place to mitigate the adverse effects on private landholders and community assets before environmental flows can be considered.

Options for mitigation could include:

building a new, higher Mundarlo Bridge upgrading other crossings and roads to keep them open or, for very low-lying roads that

cannot be kept open, improving and maintaining them so they are in good condition following events

installing pumps for stormwater systems where stormwater gates under levees may have to close during events

installing a regulator at the Yanco Creek Offtake so that high flows down the creek could be controlled to avoid overbanking when it was not desired

negotiating agreements with landholders for easements or other measures to allow low-lying land to be wet

improving farm pumping infrastructure so that it is above the planned flows or more easily moved

implementing erosion control measures improving notification systems so the community has the ability to move stock and

undertake other measures to manage for higher flows.

An option that was considered was whether en-route storages, such as Lake Coolah or turkey-nest dams, could be used to provide a portion of the peak, thereby reducing the height of the flow needed upstream of the en-route storage. However, analysis of previous work done on this, particularly in GHD (2002), found that these options had significant negative net cost–benefit outcomes.

Another measure could be to negotiate arrangements with irrigators to improve the outcome of flows. Higher flows are likely to include a component that is available to irrigators to use as part of ‘supplementary flow’ arrangements. There is an opportunity to work with irrigators to hold off taking this water (where it is not essential at that time) to preserve critical flows. The water could then be ‘paid-back’ later, often at a more opportune time for irrigators. This would be better environmentally as more of the natural flow would be maintained, and it would mean flows would not need to be as high upstream of the irrigation areas during the event to achieve the desired flow downstream. However, this measure is not simple — it requires an agreed method to determine how much water has been foregone and agreements to be negotiated with irrigators.

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As mentioned above, there are potential issues with the balance of levels between Blowering and Burrinjuck dams, because delivering higher flows may require Burrinjuck Dam to be drawn upon more than would otherwise be the case. An option to alleviate potential dam imbalance issues is to allow some Murrumbidgee water that is currently caught by Tantangara Dam to pass through Tantangara down the upper Murrumbidgee to Burrinjuck Dam. This would provide benefit to the upper Murrumbidgee, reduce some of the pressure on the Tumut River (which would otherwise have to pass the flow) and improve the reliability of Burrinjuck Dam. However, this option results in foregone electricity generation through the Snowy Mountains Hydro-electric Scheme because sending water via Burrinjuck produces significantly less hydroelectricity than sending it via Blowering. The cost of the foregone electricity generation is of the order of $100 per ML (in 2002 dollars, GHD 2002), meaning this option is unlikely to be feasible, especially for large volumes.

MDBA has commissioned independent consultants to develop a consistent and standardised methodology to cost mitigation activity. MDBA is concentrating on estimating the indicative costs of allowing small overbank flows on private land and what infrastructure upgrades are needed in the seven different regions of the Basin. However, these are not the only types of mitigation activity that may be needed. The cost estimates can be found in the Constraints Management Strategy 2014 annual report.

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What is happening in the subreaches?The river has been divided into three subreaches:

Burrinjuck Dam to Wagga Wagga Downstream of Wagga Wagga to Hay Hay Weir to the junction with the Murray.

We have analysed the possible impact of changed flows on these subreaches. This has included mapping of flow footprints and obtaining information from the community. We are continuing to collect information about the effect of small overbank flows in these reaches.

The following sections provide information on the current characteristics and possible future plans for each of the subreaches.

See also the subreach inundation maps, available for separate download on the Murray–Darling Basin Authority website.

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Blowering and Burrinjuck dams down to Wagga Wagga

At a glanceThe Murray–Darling Basin Authority is investigating flows from 30,000 to 48,500 ML/day (5.22 to 7.15 m) at Wagga and 30,000 to 43,900 ML/day (4.92 to 6.1 m) at Gundagai. Mapping shows that inundation in the Murrumbidgee upstream of where the Tumut River comes in is limited. Downstream of this, anabranch creeks, lagoons and some low-lying areas of the floodplain are inundated.

Generally, landholders did not see the flows as positive, and noted potential effects on fencing, pasture and, in some cases, lucerne; impeded access to parts of farms; the need to move pumps; and that Mundarlo Bridge and at least two public culverts across creeks would be closed. Several stormwater gates would also require closing at Wagga Wagga. Mitigation will need to address these issues.

Reach characteristicsThis river reach includes the Murrumbidgee River from Burrinjuck Dam down to the Gobbagombalin (Gobba) Bridge at Wagga Wagga and the Tumut River from Blowering Dam down to the junction with the Murrumbidgee (Figure 14). The reach is fed by releases from the two dams and inflows from tributaries, particularly the Goobarragandra River and Tarcutta Creek. Other creeks, including Gilmore, Brungle, Adjungbilly, Jugiong, Muttama, Adelong, Billabong (near Nangus), Hillas (Yaven) and Kyeamba, can also provide significant inflows.

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Figure 14: Burrinjuck and Blowering dams to Wagga Wagga

Wagga Wagga has been picked as the end point of this reach because it is downstream of the major tributaries. Wagga Wagga is the point of maximum average river flow (Page et al. 2005). Upstream of Wagga Wagga, the Murrumbidgee is a ‘gaining river’, with tributary inflows increasing the flow. Downstream of Wagga Wagga, the Murrumbidgee is a ‘losing river’, with the lack of significant tributaries and evaporation, seepage and uptake by natural wetlands leading to reduced flows. Wagga Wagga also represents a change in the catchment and the floodplain. Above Wagga Wagga, the country is hilly and the floodplain is confined by hills in many places. Below Wagga Wagga, plains start to dominate and the floodplain is less constrained.

There are a number of gauges along this river reach for tributaries, as well as the main regulated Murrumbidgee and Tumut channels. Flows for three gauges are shown below: Tumut town gauge on the Tumut River, and Gundagai and Wagga Wagga gauges on the Murrumbidgee River. These were shown because these are the major population centres and they are the only points on this stretch that have designated flood levels (minor, moderate and major flood levels).

TumutBlowering Dam is very effective at providing flood protection for those living downstream of the dam. For Tumut township, only one major flood has occurred since 1970. There have been 14 moderate and 12 minor floods in this period. Recent flood events are shown in Table 4.

Table 4: Recorded flood flows for Tumut River at Tumut township

Flood class Date Gauge height (m) — hourly reading

Flow (ML/day)

Major (3.7 m) 4 March 2012 3.84 96,297Moderate (2.6 m) 9 December 2010 2.81 23,326Minor (2.0 m) 1 December 2011 2.07 16,045

GundagaiGundagai has had 17 major floods since 1970, as well as 3 moderate floods and 14 minor floods. The largest (1974) and the two most recent major floods are shown in Table 5, as well as the most recent minor and moderate floods.

Table 5: Recorded flood flows for Murrumbidgee River at Gundagai

Flood class Date Gauge height (m) Flow (ML/day)

Major 30 August 1974 11.01 481,910Major 4 December 2010 10.20 219,580Major 5 March 2012 10.92 345,070Moderate 2 October 1996 7.50 75,500Minor 17 Oct 2010 7.05 57,430

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Wagga WaggaWagga Wagga has had 4 major floods since 1970 and these are shown in Table 6. There have also been 4 moderate and 16 minor floods, and the most recent of these are also shown.

Table 6: Recorded flood flows for Murrumbidgee River at Wagga Wagga


Major 30 August 1974 10.74 493,190Major 6 March 2012 10.60 312,760Major 15 July 1991 9.61 196,320Major 6 December 2010 9.69 144,670Moderate 16 August 1989 9.38 162,890Minor 17 October 2010 8.70 77,810

As an example of the variation in flows in this subreach, a hydrograph for Wagga Wagga from 1980 to 2013 is shown in Figure 15.

Figure 15: Flows in the Murrumbidgee River at the Wagga Wagga gauge, 1980–2013

What flows are being consideredThe Murray–Darling Basin Authority (MDBA) is collecting information about what effects river flows have at different places along the Murrumbidgee River system, but only up to around the minor flood level. Flows significantly higher than the minor flood level are not being considered as they are damaging and disruptive, and outside the bounds of active river management.

We are using Wagga Wagga as the reference gauge due to its position as the point of maximum average river flow (Table 7).

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Table 7: Comparison of flows and flood levels, Wagga Wagga gauge

Flow or flood level

Flow rates MDBA is

looking at (Wagga Wagga

gauge)

Flow rates MDBA is


gauge)

Flow rates MDBA is


gauge)

Minor flood levela

Moderate flood levela

Major flood levela

Flow rate (ML/day) 30,000 40,000 48,500 50,100 90,000 136,000

Gauge height (m) 5.22 6.31 7.15 7.30 9.00 9.60

MDBA = Murray–Darling Basin Authoritya Bureau of Meteorology definition

These flows equate to different flows along the river reach. As the flows being looked at would normally be delivered using natural tributary flow events, less flow would be required at upstream locations to achieve each of the flows at Wagga Wagga, because tributary inflows would provide some of the required flow. However, in most cases, to be conservative, it has been assumed that the full flow is required upstream (although in reality this would rarely, if ever, be the case). The exception to this is for the higher flow level at Gundagai, where flows are limited to 43,900 ML/day in line with the minor flood level at that gauge (Table 8). Flows above this level are not being investigated.

Table 8: Comparison of flows and flood levels, Gundagai gauge

Flow or flood level

Flow rates MDBA is

looking at (Gundagai

gauge)

Flow rates MDBA is


gauge)

Flow rates MDBA is


gauge)

Minor flood levela


Major flood levela

Flow rate (ML/day) 30,000 40,000 43,900 43,900 68,800 96,700

Gauge height (m) 4.92 5.80 6.10 6.10 7.60 8.50


Flows above Gundagai come from the Murrumbidgee River arm (Burrinjuck Dam and tributary inflows including Jugiong Creek and others) and the Tumut River arm (Blowering Dam releases plus tributary inflows including Goobarragandra River, Gilmore and Adjungbilly creeks, and others). Flows were mapped assuming the flow contributions from each arm in Table 9.

Table 9: Contribution from Tumut and Murrumbidgee to mapped flows at Gundagai

Gundagai flow (ML/day) Contribution from Murrumbidgee (ML/day)

Contribution from Tumut (ML/day)

30,000 20,500 9,50040,000 30,500 9,50043,900 34,400 9,500

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The Burrinjuck Dam valve capacity limit of 29,100 ML/day means that tributary inflows below the dam will be required to achieve the middle and higher flow level for the Murrumbidgee arm. For the highest flow level, this means tributary inflows of 5,300 ML/day would be required. This would require good flows from creeks such as Jugiong Creek. The hydrologic record shows it has had flows in excess of 5,000 ML/day on 62 occasions since 1970; however, some of these events have been of short duration (often one to two days), so it is likely that the highest flow level of 43,900 ML/day at Gundagai would only be able to be achieved for short durations at the peak height. If the flow of 43,900 ML/day is not achieved, it is still possible that tributary inflows below Gundagai could make up for any shortfall and the flow of 48,500 ML/day could still be achieved. Tarcutta Creek had flow events of more than 5,000 ML/day on 82 occasions since 1970 and flows of more than 10,000 ML/day on 34 occasions.

It was assumed for this initial phase of investigation that the flow contribution from the Tumut River was limited to 9,500 ML/day, which would be 9,300 ML/day through Tumut township; the remaining 200 ML/day would come from tributaries downstream of this. Flows downstream of Tumut township can exceed 9,300 ML/day due to tributary inputs below the township. It is likely that tributary inflows downstream of Tumut township could be greater than 200 ML/day and, where this was the case, it would reduce the amount required from the Murrumbidgee arm.

Although flows from the Tumut River have been assumed to be within the water sharing plan (2004) limit of 9,300 ML/day at Tumut township, higher flows at Tumut are being given some preliminary consideration. The minor flood level at Tumut township is 2 m, which equates to a flow of 15,300 ML/day. Flows of up to 12,000 and 14,000 ML/day (1.7 m and 1.89 m at Tumut) are being looked at; however, increases above the current 9,300 ML/day limit are difficult (see the section below on ‘What could be affected by these flows’ under the heading ‘Tumut’). The Tumut River is a smaller river than the Murrumbidgee and it is already passing unnaturally high levels of flows because Snowy Mountains Hydro-electric Scheme (Snowy Scheme) contributions are routed through it. The current flow limit is already very close to bankfull.

What these flows look like Flow footprint maps let you look at what is likely to get wet for different-sized river flows. The method used to produce the maps is outlined in ‘Mapping flows and understanding effects’ in the main report.

When interpreting the maps, it is important to bear in mind that they are from a model of a generalised event, not a real event. Therefore, some caution should be used when interpreting the ‘typical flow footprints’ presented in this report. They are not intended to mimic real flow events, but be an initial representation of what could get wet for a flow of a particular size at a broad scale. They are not necessarily accurate at a property scale.

The relevant flow footprint maps for this subreach are separately downloadable on the MDBA website under ‘Burrinjuck to Wagga Wagga maps’. They show the flow footprint for the 30,000, 40,000 and 48,500 ML/day flow at Wagga Wagga. Table 10 shows what the flow is for Gundagai and from Burrinjuck to the Tumut Junction for each of these flow levels.

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Table 10: Mapped flows in the subreach Burrinjuck Dam to Wagga Wagga

Wagga Wagga (ML/day) Burrinjuck to Tumut Junction (ML/day)

Gundagai (ML/day)

30,000 20,500 30,00040,000 30,500 40,00048,500 34,400 43,900

The Tumut River was not mapped for this exercise because it was assumed to have flows within the current limits of 9,300 ML/day at Tumut township. An initial trial showed that the methodology used for mapping in the Murrumbidgee is not yet appropriate for the Tumut valley due to the lack of light detection and ranging (LIDAR) elevation data for large sections of the river and the small number of cloud-free Landsat satellite images that exist for flow events in the valley. Further work is required to investigate how higher flows could affect the Tumut valley; however, as mentioned above, the Tumut is a smaller river than the Murrumbidgee and 9,300 ML/day is close to bankfull at Tumut township.

The Murrumbidgee maps show that the flows appear to be generally confined to or close to the channel in the Murrumbidgee above the confluence with the Tumut River. Downstream of the Tumut River through to Wagga Wagga, there are a number of anabranch (old river channel) creeks and lagoons that appear to connect up and fill. There are also low-lying areas of floodplain affected close to the river and billabongs.

Comparison of the modelled flow footprints with images from Landsat satellites taken during flow events showed that the footprints are generally in line with those images, with some local inaccuracies.

In the feasibility study stage, further work will be conducted to confirm if the mapping accords with the experiences of landholders and local councils in the area.

What could be affected by these flowsOnly limited consultation has taken place in this reach to date. More detailed consultation is being undertaken to better determine what the likely effects will be.

The following information about what might happen at different river levels is a guide only. Information has been sourced from limited community feedback, local flood guides of the State Emergency Services and council reports, where available.

Lower flow level: 30,000 ML/day at Wagga Wagga (5.22 m) and Gundagai (4.92 m), 20,500 ML/day in Murrumbidgee upstream of the Tumut Junction.

Flows of this size have been delivered for environmental watering in previous years.

At Gundagai, Morleys Creek begins to flow. Otway Street causeway on Morleys Creek is closed (alternative routes available), although the creek may benefit from flushing.

At 30,000 ML/day, Mundarlo Bridge has not historically been affected, as flows of greater than 5 m (30,800 ML/day by the current gauge rating) at Gundagai are required to inundate it.

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Landholders have at times managed their low-lying areas in the knowledge that no flow deliveries above the Mundarlo Bridge height could occur. This means that farmers have often planned around the possibility of flows up to that height, so that no or only very limited plantings of crops and improved pastures are expected in areas up to this height.

Initial feedback from landholders indicates that most pumps are above this level; however, there may be some low-lying pumps that need to be moved and some fences in low-lying areas that may be affected.

The mapping also indicates that some flood-runner creeks and lagoons begin to run and fill. This may lead to access issues for some farmers.

At Wagga Wagga City, gates on three of the stormwater pipes under the levee may need to be closed. There are 46 gates for stormwater pipes under the levees of North Wagga Wagga and Wagga Wagga City, and these need to be progressively closed as flow heights increase. When the gates are closed and intense local rainfall occurs, water draining to those stormwater gates can back up behind the levee and there is a risk of localised flooding inside the levee if mitigation measures such as pumps are not in place. The council has pumps on some structures and has used temporary pumps in the past during high flows.

Middle flow level: 40,000 ML/day at Wagga Wagga (6.31 m) and Gundagai (5.80 m), 30,500 ML/day in Murrumbidgee upstream of Tumut confluence.

At Gundagai, the Bereena Road Bridge across Adelong Creek is closed. There is an alternative route available, but the detour is approximately 8-km long, and it is not suitable for trucks from the nearby quarry.

At this flow, Mundarlo Bridge is inundated and would need to be closed for the duration of the flow. The alternative route via Gundagai is a significant detour. Following the flow, Gundagai Shire Council would need to clear debris from the bridge.

Further access issues are likely as more billabongs and flood-runner creeks begin to flow.

Sandy Beach campsite near Wantabadgery may have access closed by a lagoon that fills from the river. Some low-lying areas next to the river are inundated, affecting pasture and some sections of lucerne. Many pumps would need to be moved, which causes significant inconvenience for farmers.

At Wagga Wagga City, a total of five stormwater gates would need to be closed.

Upper flow level: 48,500 ML/day at Wagga Wagga (7.15 m), 43,900 ML/day at Gundagai (6.10 m), 34,400 ML/day in Murrumbidgee upstream of Tumut confluence.

This level submerges a bridge across Billabong Creek between two paddocks. Stock would need to be moved and any planted crops (e.g. lucerne) would be impacted. Damage to fencing is an issue if flows have high velocities.

More access issues occur as more billabongs and flood-runner creeks begin to flow.

Further low-lying areas next to the river are inundated, including pasture and lucerne, and a section of a turf farm paddock. A quarry may be inundated, causing lost production and requiring

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pumping out and potentially remedial works. More pumps would need to be moved. Access to the Common at Gumly Gumly is cut.

A total of five stormwater gates at Wagga Wagga City and three at North Wagga Wagga would need to be closed during the event.

The beach caravan park at Wagga Wagga is normally scheduled for evacuation with flows of 7.3 to 7.5 m; however, Wagga Wagga City Council staff have advised that they would need to consider evacuating the caravan park for a planned flow of 7.15 m. Vans need to be relocated and utilities closed if this occurs. However, the lease on the site will expire in 2019, before flows of this size could occur (if they proceed at all), and Wagga Wagga City Council decided in February 2014 not to renew the lease; rather, the area will be converted to a public recreational space. Nonetheless, issues may still remain with caravan parks in Wagga Wagga because a site for a caravan park is being considered at Wiradjuri Reserve, which is also low lying.

Tumut RiverAlthough higher flows in the Tumut River have only been given preliminary consideration, they are likely to be difficult. Potential effects of flows above 9,000 ML/day from Blowering Dam and 9,300 ML/day at Tumut include:

Inundation — as mentioned previously, the Tumut River is a smaller river than the Murrumbidgee and, in some areas, flows of 9,000 ML/day are close to bankfull. The photo below shows the river upstream of Tumut at a flow of around 4,000 ML/day. Flows greater than 9,000 to 10,000 ML/day can spread out of the banks onto pasture.

Fencing — flows in the Tumut River are relatively fast compared to the lower Murrumbidgee and damage to fencing may result if flows go out of channel.

Watertables — soils in the Tumut valley are often quite sandy (relative to other parts of the Murrumbidgee) and, therefore, water readily permeates to the groundwater system. As a result, the watertable near the river rises fairly quickly in response to river rises. Studies by the NSW Water Conservation and Irrigation Commission (1974) have shown that high flows during the irrigation season resulted in elevated watertables, with the degree of effect increasing with the duration of the high flow and proximity to the river. Elevated watertables can cause damage to crops like millet and corn, and deep-rooted perennials like lucerne. It is noted that the amount of cropping done in the Tumut valley has decreased during the past several decades, with grazing now dominating the area.

Access — when anabranch creeks and lagoons start to fill, access can be impeded. Erosion and tree fall — the banks of the Tumut River have experienced significant erosion

since the flows of the Snowy Scheme have been diverted through the river. Long-duration high flows in the irrigation season with relatively quick changes in water level when orders change are also understood to have exacerbated the situation. The river has widened significantly in many areas and altered its course in some places, cutting off meander bends and leaving sections of properties isolated from the remainder of the landholding. Much riparian vegetation has been lost. A program of rocking banks to protect against erosion in affected areas has been in place for some years and continues. Environmental flows would be delivered at elevated levels for shorter periods than those experienced during the irrigation season, and with slower rates of flow draw down that mimic natural rates of fall. However, the heavily affected riparian vegetation and weakened state of the riverbanks may mean that even ‘naturally shaped’ events may be damaging.

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Tourism — water enters the bottom end of Tumut Riverglade Caravan Park at 1.5 m (10,100 ML/d), but this depends on flow in Gilmore Creek. Flows of 2.35 m (18,700 ML/day) deliver water well into the caravan park, with only high spots remaining clear, but this is well above the heights being looked at.

Mitigation measures, which would be needed to address these issues, are outlined briefly in the main body of the report in ‘What needs to be in place before environmental flows can happen’.

Tumut River upstream of Tumut township and Goobarragandra River junction at a flow of around 4,000 ML/day. Photo: Paul Doyle, MDBA.

What is the initial community reaction to the range of flows being suggested?Generally, the flows being investigated were not seen as positive in this reach by landholders, and there would need to be significant mitigation measures put in place to make these flows acceptable to the riverside landholders.

‘Key Murrumbidgee community messages’ in the main report outlines how some of the impacts above are likely to affect landholders. An issue that was seen as particularly important to this reach was the need for timely notification due to the short flow travel times from the dams and related issues, such as only having short periods to move stock and pumps where necessary. Another issue is the potential for fencing damage due to higher flow velocities in parts of the subreach that have greater river gradients than further down the river.

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Below Wagga Wagga to Hay

At a glanceThe Murray–Darling Basin Authority is investigating flows from 30,000 to 48,500 ML/day (5.22 to 7.15 m) at Wagga Wagga. The flow reduces as it proceeds down the river and NSW State Water has mapped the footprint of these flows down to Hay. The mapping shows that the flow appears to spread to a number of anabranch creeks and lagoons, as well as low-lying areas, particularly around Beavers Creek/Old Man Creek, Upper Yanco Creek and Darlington Point. West of Carrathool, the floodplain narrows and the spread of water is more limited.

Generally, landholders did not see the flows as positive and noted the potential effects on pasture and, in some cases, lucerne; the impeded access to parts of farms; as well as problems with weeds, fencing and moving stock. There are also issues with stormwater drainage at Narrandera and Darlington Point. Mitigation will need to address these issues.

Reach characteristicsThis river reach includes the Murrumbidgee River from the Gobbagombalin (Gobba) Bridge at Wagga Wagga down to Hay, as well as its distributary creeks: Beavers Creek/Old Man Creek and the upper part of Yanco Creek (Figure 16). The reach has no major dams, but has weirs at Berembed, Yanco and Gogeldrie on the Murrumbidgee, and there is a weir on Beavers Creek. There is also an off-channel storage at Tombullen. The reach has some irregularly flowing tributaries, including Houlaghans Creek and Bullenbung Creek, but, due to the relative flatness and the lower rainfall of the area, the input from the tributaries is generally far less than from the tributaries higher upstream.

The reach contains important irrigation areas, including the Murrumbidgee Irrigation Area and the Coleambally Irrigation Area. It also contains the Mid-Murrumbidgee River Wetlands — a complex of many hundreds of billabongs and anabranch creeks listed in the Directory of important wetlands in Australia (DoE 2014).

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Figure 16: Wagga Wagga to Hay subreach

Wagga Wagga has been picked as the starting point of this reach because it is downstream of the major tributaries and, around Wagga Wagga, the country changes from generally hilly to relatively flat.

Hay was picked as the end point of this reach, because below Hay breakouts start to occur into creek systems such as Budgee Creek and then further down into the Lowbidgee Floodplain.

There are a number of gauges along this river reach. Records from three gauges are shown below: Narrandera, Darlington Point and Hay. These were shown because these are the population centres on the river and the only points on this stretch (apart from Carrathool, which is off the river) that have designated flood levels (minor, moderate and major flood levels). The Wagga Wagga gauge is shown in the preceding subreach chapter, ‘Blowering and Burrinjuck dams down to Wagga Wagga’.

NarranderaThere is a break in the records for this gauge from 1970 to 1973. The records from 1973 show that 8 minor floods, 12 moderate floods and 2 major floods occurred. Table 11 shows the 2 major floods, and the most recent moderate and minor floods.

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Table 11: Recorded flood flows for Murrumbidgee River at Narrandera gauge


Major 10 March 2012 8.95 255,520Major 4 September 1974 8.91 247,940Moderate 13 December 2010 8.02 95,480Minor 25 July 1995 6.96 44,230

As an example of the variation of flows in this subreach, a hydrograph showing flows at the Narrandera gauge from 1980 to 2013 is shown in Figure 17.

Figure 17: Flows in the Murrumbidgee River at the Narrandera gauge, 1980–2013

Darlington PointThe records from 1970 show that 22 minor floods, 4 moderate floods and 2 major floods occurred. Table 12 shows the 2 major floods, and the most recent moderate and minor floods.

Table 12: Recorded flood flows for Murrumbidgee River at Darlington Point gauge


Major 6 September 1974 7.66 115,200Major 13 March 2012 7.72 104,830Moderate 21 December 2010 7.14 64,200Minor 30 October 2010 6.08 32,190

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Hay WeirThe available records for this gauge start in 1982, and show that 12 minor floods, 2 moderate floods and 4 major floods occurred. Table 13 shows the most recent moderate and minor floods, and the 2 most recent major floods.

Table 13: Recorded flood flows for Murrumbidgee River at Hay Weir gauge


Major 21 March 2012 10.19 65,360Major 27 December 2010 9.80 53,246Moderate 9 September 1990 8.97 37,562Minor 8 November 2010 7.90 26,858

What flows are being consideredThe Murray–Darling Basin Authority (MDBA) is collecting information about what effects river flows have at different places along the Murrumbidgee River system, but only up to around the minor flood level. Flows significantly higher than the minor flood level are damaging and disruptive, and outside the bounds of active river management.

As mentioned above, we are looking at flows of 30,000, 40,000 and 48,500 ML/day, or 5.22 m, 6.31 m and 7.15 m, respectively, at Wagga Wagga.

These flows decrease as you move down the river due to attenuation, seepage, evaporation and wetland filling. We analysed historical flows to find what the flow levels in Wagga Wagga equate to downstream. Comparisons were made using winter flows to ensure that irrigation uptake during the event was minimal. The height that a flow from Wagga Wagga reaches as it travels down the river varies with each flow and depends on factors such as the duration of the peak and the wetness of the catchment. The indicative flows for the major downstream gauges of Narrandera, Darlington Point, Carrathool and Hay are given in Tables 14–17. Note the duration of the peak of the flow will also change as the event moves down the river. The duration will increase downstream of Wagga. Further work is being undertaken to determine the expected duration at each downstream gauge.

Table 14: Comparison of flows and floods, Narrandera gauge

Flow or flood level

Flow rates MDBA is

looking at (Narrandera

gauge)

Flow rates MDBA is


gauge)

Flow rates MDBA is


gauge)

Minor flood levela


Major flood levela

Flow rate (ML/day) 22,000 34,000 39,000 40,300 51,700 130,000

Gauge height (m)b 5.06 6.22 6.61 6.70 7.30 8.20

MDBA = Murray–Darling Basin Authoritya Bureau of Meteorology definitionb Note the gauge height to flow relationship has changed recently at Narrandera and new work will reflect this.

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Table 15: Comparison of flows and floods, Darlington Point gauge

Flow or flood level

Flow rates MDBA is looking at

(Darlington Point gauge)





Minor flood levela


Major flood levela

Flow rate (ML/day) 17,500 27,000 30,500 25,500 56,000 74,300

Gauge height (m)b 4.59 5.64 5.98 5.50 7.00 7.30

MDBA = Murray–Darling Basin Authoritya Bureau of Meteorology definitionb Note the gauge height to flow relationship has changed recently in Darlington Point and new work will reflect this.

Darlington Point is the only place on the Murrumbidgee River where any of the flows being investigated go into the minor flood category. Here the middle flow level (5.64 m) and the upper flow level (5.98 m) are above the minor flood level of 5.5 m, but below the moderate flood level of 7 m.

Table 16: Comparison of flows and floods, Carrathool gauge

Flow or flood level

Flow rates MDBA is looking at (Carrathool

gauge)


gauge)


gauge)

Minor flood levela


Major flood levela

Flow rate (ML/day) 15,800 25,000 28,000 36,100 50,000 86,900

Gauge height (m) 5.00 6.50 6.65 7.00 7.50 8.50


Table 17: Comparison of flows and floods, downstream Hay Weir gauge

Flow or flood level


(Hay Weir gauge)


(Hay Weir gauge)


(Hay Weir gauge)

Minor flood levela


Major flood levela

Flow rate (ML/day) 14,000 21,500 25,000 26,187 36,286 39,997

Gauge height (m) 5.50 7.05 7.62 7.80 8.90 9.20


What these flows look likeThe method used to produce the maps is outlined in ‘Mapping flows and understanding effects’ in the main part of this report.

Modelling and flow footprint mapping were undertaken for flows of 30,000, 40,000 and 48,500 ML/day at Wagga Wagga. As mentioned above, as this flow travels down the river, the peak reduces. We analysed historical flows to determine the flows this would correspond to at the

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main gauge points along the river system. Tables 14–17 (above) give the relevant flows for Narrandera, Darlington Point, Carrathool and Hay. Table 18 gives the indicative flows that were mapped for a number of other gauge points. The model assumed a constant rate of loss between each gauge point.

Table 18: Indicative flows mapped for gauges on Beavers, Old Man and upper Yanco creeks

Wagga Wagga

Flow (ML/day)

Beavers Creek at Mundowey

Flow (ML/day)

Beavers Creek at Mundowey

Height (m)

Old Man Creek at Kywong

Flow (ML/day)

Old Man Creek at Kywong

Height (m)

Yanco Creek at Offtake

Flow (ML/day)

Yanco Creek at Offtake

Height (m)

Yanco Creek at Morundah

Flow (ML/day)

Yanco Creek at Morundah

Height (m)

30,000 8,577 4.83 5,028 3.34 2,174 3.79 1,023 2.0540,000 12,429 5.51 6,759 3.93 3,007 4.25 1,364 2.2948,500 15,703 5.85 8,230 4.37 3,715 4.55 1,654 2.47

Again, when interpreting the maps, note that they are from a model of a generalised event, not a real event. Therefore, some caution should be used when interpreting the ‘typical flow footprints’ presented in this report.

The relevant flow footprint maps for this subreach are separately downloadable on the MDBA website under ‘Wagga to Hay maps’. The maps show that water spreads to a greater degree for this subreach than for above Wagga Wagga. This is because the landscape flattens out as you move west of Wagga Wagga. Notable areas include:

Beavers Creek, where there is a broad area of inundation in and around Berry Jerry Forest areas in the western part of Old Man Creek — levees confine the spread of inundation in

much of this area the lower part of Sandy Creek (which comes off Old Man Creek), particularly around

Buckingbong Swamp — this swamp can fill from water coming down Sandy Creek or directly from the Murrumbidgee River

areas east of Narrandera on the northern side of the river, including some of Narrandera Common, but also private land — comparisons with Landsat satellite images indicate that the maps are overestimating the degree of spread of inundation for the highest flow here; however, this needs further investigation using information from landholders

areas surrounding the upper part of Yanco Creek, although comments from landholders in this area and comparisons with Landsat satellite images indicate that there is some overestimation of the spread of flows in this area

numerous lagoons from Narrandera to Carrathool — many of these lagoons and some of the floodplain surrounding these appear to be inundated; comparison of this mapping with Landsat images and landholder feedback indicates that the spread of the lower flow level is being overestimated in some areas

downstream of Carrathool, where the immediate floodplain becomes narrow and hence the spread of inundation is more limited.

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What could be affected by these flowsThe following information about what might happen at different river levels is a guide only. Information has been sourced from community feedback, local flood guides of the State Emergency Services and council reports, where available.

Note: information for Wagga Wagga upstream of the Gobba Bridge is in the preceding subreach chapter ‘Burrinjuck and Blowering dams down to Wagga Wagga’.

Lower flow level: 30,000 ML/day at Wagga Wagga (5.22 m), 22,000 ML/day at Narrandera (5.06 m), 2,174 ML/day at Yanco Creek offtake (3.79 m), 17,500 ML/day at Darlington Point (4.59 m), 15,800 ML/day at Carrathool (5.00 m) and 14,000 ML/day at Hay (5.50 m).

Flows of this size have been delivered for environmental watering actions in previous years.

The map shows the general area of effects; some examples of effects are listed below.

Water from Beavers Creek flows into Little Beavers Creek near Collingullie and blocks the low-level culvert on Beavers Island Road, which is the sole public road across Little Beavers Creek. Landholders can no longer move machinery and stock across. This also blocks access to the Riverina Water County Council water bore, which supplies Collingullie (this is a problem if maintenance is required while access is blocked).

Flows inundate areas of private land on Beavers Creek, particularly around Berry Jerry Forest.

On the upper part of Yanco Creek, areas of private land are inundated and a number of minor flood-runner creeks start to flow, causing access issues.

At Darlington Point, flows cover the town beach and fill a number of lagoons, causing inundation of grazing land and access issues, including for Uri Creek crossings.

Middle flow level: 40,000 ML/day at Wagga Wagga (6.31 m), 34,000 ML/day at Narrandera (6.22 m), 3,007 ML/day at Yanco Creek offtake (4.25 m), 27,000 ML/day at Darlington Point (5.64 m), 25,000 ML/day at Carrathool (6.50 m) and 21,500 ML/day at Hay (7.05 m).

Flows close Mundowy Lane, which is the route to a bridge across the Murrumbidgee River and a bridge across Beavers Creek near Collingullie. The lane provides access between the Rock and Coolamon; alternative access is a significant detour via the Gobba Bridge at Wagga Wagga.

Water in flood-runner creeks and lagoons isolates some further areas like Mundowy Island near Collingullie.

Water flows from Old Man Creek into Sandy Creek, and also directly from the Murrumbidgee River into Buckingbong Swamp at the lower end of the Sandy Creek system.

Council closes the access road to Narrandera Common and shuts the stormwater gate on the town levee to stop river water backing up into the stormwater system.

For upper Yanco Creek, further access issues occur between paddocks for a number of properties and the area of inundation of low-lying paddocks increases.

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Around Darlington Point, water spreads out from some lagoons and there are access issues for some properties, with a property cut off at this height. There may also be restricted access to some national parks, state forests and other camping sites (some on private land). This would affect tourism/recreation, and stop woodcutters and firewood collection. Council closes some stormwater gates under the town levee and if this coincided with a local rainfall event, pumping would be required, causing noise pollution and additional costs.

At Hay, water reaches three stormwater gates. However, the river height would be below town levels, so there would be a head difference and stormwater would still flow out of the town.

Upper flow level: 48,500 ML/day at Wagga Wagga (7.15 m), 39,000 ML/day at Narrandera (6.61 m), 3,715 ML/day at Yanco Creek offtake (4.55 m), 30,500 ML/day at Darlington Point (5.98 m), 28,000 ML/day at Carrathool (6.65 m) and 25,000 at Hay (7.62 m).

Water begins to backup in Bullenbong Creek and can affect up to 100 ha of mostly wooded areas. Near Euberta, water travels up a drainage channel to inundate paddocks used to grow lucerne hay and other crops.

Wagga Wagga City Council closes O’Sheas Road near Euberta and a section of River Road near Wagga Wagga.

At Darlington Point, further stormwater gates are likely to need closing. Although the Darlington Point Caravan Park is not evacuated until 6.5 m (40,000 ML/day), the level of the top flow causes some concerns when it is at 5.98 m (30,500 ML/day). Some rural properties near Darlington Point may have additional access issues. In one case, around half of a low-lying property is inundated and the rest is cut off. There are concerns about fencing being inundated and subsequent corrosion to the fencing that may occur. One property estimated that water would touch around 7 km of fencing at this height. Sticks and branches can clutter the fences and the river water can accelerate rusting.

At Hay, water would reach another three stormwater gates. However, the river height is still believed to be below town levels, so there would be a head difference and stormwater would still flow out of the town.

What is the initial community reaction to the range of flows being suggested?Generally, the flows being investigated were not seen as positive in this reach by landholders and there would need to be significant mitigation measures put in place to make these flows acceptable to the riverside landholders. Landholders near Wagga Wagga, Euberta, Collingullie, the upper part of Yanco Creek and some areas near Darlington Point were particularly concerned. It should be remembered that only a small proportion of landholders have been contacted, so there are likely to be other areas of concern that will require assessment during the feasibility stage.

Issues that were seen as particularly important to this reach were the effects of inundation on pasture and lucerne. Landholders noted the extended period of the effects due to the time it takes pasture and lucerne to re-establish and the lost production cost that that entails. They also noted issues with moving, managing and feeding stock when access was cut to areas of the

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farm. These issues are covered along with other effects in ‘Key Murrumbidgee community messages’ in the main report. Other points that were prominent in this subreach included:

controlling weeds, particularly the introduced lippia (Phyla canescens), which is hard to manage and significantly reduces carrying capacity

managing the compaction of soils — in bad cases, deep ripping of the land may be required

the disruption to production making it difficult to maintain customers — for example, several farmers noted they lost lucerne sale contracts after the 2010 and 2012 major floods, which were then hard to win back.

There were also concerns about streambank erosion and tree fall into the watercourse. Examples were given of very old red gums falling into the river in recent years during high flows. It will be important to ensure that environmental flows are delivered with natural rates of recession to minimise the risk of bank slumping.

Slow rates of recession are also important for other reasons. For Yanco Creek, farmers mentioned that sheep can get stuck in muddy banks if the level drops too quickly and the sheep come down to the creek to drink.

However, the flows were seen as potentially positive in some instances and areas:

A late September flood can be beneficial for Phalaris and clover — but only for a few days. If it happens in October it would be no good. Farmer near Collingullie

Flows down Sandy Creek (which branches off Old Man Creek near Galore) would generally be viewed as positive, because the water would wet the area surrounding the creek, which would assist in pasture growth and reduce the transmission losses that farmers experience when water is delivered later in the year for irrigation. At the bottom end of Sandy Creek, water spreads to form the Buckingbong Swamp, where it is likely to be beneficial for fodder growth. Similarly, some farmers in the lower and middle part of the Yanco Creek system believed there could be benefits for their country.

Some landholders were concerned about heavy localised rainfall causing some of the few ephemeral (irregularly running) tributaries in the area to flow during an environmental flow event, causing a higher river than predicted or localised flooding when the tributary backed up. Other landholders noted that the use of water early in the season to achieve a high flow would create airspace in Burrinjuck and Blowering dams, and reduce the risk of major flooding while the airspace remained.

Gap Creek doesn’t run much but it can flood with intense local rainfall. If the river is up around 22 foot or more at the same time that the Gap Creek flows, then the water will not be able to flow out to the river and might back up onto properties here. Farmer near EubertaBullenbung Creek — with intense local rainfall this can make a difference. This might occur once every 8 to 10 years, but you need to watch for that. Long-time farmer on Old Man Creek/Sandy Creek

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As far as I am concerned the more water you use in winter and early spring the better — I’d like to see airspace in those dams. It’s the big floods I’m worried about. Farmer west of Wagga Wagga

Local councils and county councils also had concerns. As mentioned above, councils were concerned that issues with stormwater drainage needed to be addressed. Access to infrastructure, such as the water bore at Collingullie, will also need to be dealt with. Local councils also raised concerns about access to amenities such as town beaches, boat ramps, camp sites and recreational areas, such as national parks and reserves. This may have implications for tourism during the flow, although they also recognise that the flows are likely to occur during winter and early spring, and so are outside the main tourist season. They also are aware that the short-term problem of lack of access to some of these recreational areas is counterbalanced by the longer-term benefits that watering provides to the health of these areas. However, more frequent wetting of some amenities such as boat ramps may have implications for maintenance programs.

In terms of managing flows, some councils also mentioned that increased vegetation that has occurred in some areas of the lower floodplain during the past few decades was something that water managers needed to be mindful of.

The build-up of debris against the thicker forest growth can cause ‘beaver walls’ that restrict flows and may cause flows of 25,000 ML/day to be higher than they would otherwise be. Murrumbidgee Shire Councillor

Flow estimates will need to use flow versus height rating calculations that have been recently checked and updated.

Mitigation measures, which would be needed to address these issues, are outlined briefly in ‘What needs to be in place before environmental flows can happen’ in the main report. In addition to those outlined in that section, there will be other mitigations specific to this section. These might include measures such as the introduction of a regulator at the end of the Gap Creek drain to prevent water backing up into paddocks during high flows.

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Hay Weir to end of Murrumbidgee system

At a glanceThe Murray–Darling Basin Authority is investigating flows from 30,000 to 48,500 ML/day (5.22 to 7.15 m) at Wagga Wagga, which equate to around 15,000 to 25,000 ML/day (5.74 to 7.62 m) at Hay Weir. The flow reduces as it proceeds down the river and CSIRO has mapped the footprint of these flows down to Hay. The mapping shows that the flows spread widely through the Lowbidgee Floodplain.

Generally, landholders see the flows as positive, with significant benefits for floodplain grazing. There are some issues with impeded access to parts of farms, particularly near the junction with the Murray, and these may need to be mitigated.

Reach characteristicsThis river reach starts at Hay Weir (downstream of Hay Township) and includes the Lowbidgee, Balranald, the junction with the Murray and the Junction Wetlands (Figure 18). The reach has no public dams, but has weirs at Hay, Maude, Redbank and Balranald. The reach has no significant tributaries, but there are a number of distributary creeks including Coonoon Creek, Budgee Creek, Caira Creek, Nimmie/Pollen Creek and Fiddlers/Uara Creek. The Lachlan River meets the Murrumbidgee in the Lowbidgee region, but flows from the Lachlan are rare, only occurring during very large floods, which take a long time to travel down the Lachlan.

For the stretch from Hay to Maude, the Murrumbidgee River is generally confined to a narrow floodplain less than 1-km wide. There are some creeks that diverge from the channel in this stretch, including Coonoon Creek and Budgee Creek. Around Maude, the river enters the Lowbidgee region, which extends through to Balranald. In the Lowbidgee, the channel capacity is greatly reduced, being as low as 8,000 to 9,000 ML/day at Chastons Cutting (downstream of Redbank Weir). With the low channel capacity and flat topography of the region, flows spread across a wide area known as the Lowbidgee Floodplain. This provides important wetland habitat and also supports grazing in what is an otherwise relatively dry area. The Lowbidgee includes a number of lakes; Yanga Lake is the most prominent.

Near Balranald, the floodplain narrows again and the channel capacity increases so that moderate flows are more confined to the river and the floodplain immediately adjacent to it. However, closer to the junction with the Murray, there are a number of flood-runner creeks that connect into the Junction Wetlands. When the flow at Balranald exceeds 5,000 ML/day for more than a week and, simultaneously, the Murray River is flowing above 10,000 ML/day, these creeks can run and wet wetland areas near the junction (NSW Office of Environment and Heritage 2013).

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Figure 18: Hay to Murray subreach

There are a number of gauges along this river reach. Balranald is shown because it is the only sizeable population centre and the only point on this stretch that has designated flood levels (minor, moderate and major flood levels).

Balranald has had three minor floods since the gauge at Balranald Weir began operation in 1979. There were no moderate or major floods in this period. The minor floods since 1979 are shown in Table 19.

Table 19: Recorded flood flows for Murrumbidgee River at Downstream Balranald Weir gauge


Minor 26 April 2012 6.79 23,330Minor 26 September 1990 6.73 25,151Minor 25 May 1989 6.72 24,753

A hydrograph showing flows at the Balranald Weir gauge from 1980 to 2013 is shown in Figure 19.

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Figure 19: Flows in the Murrumbidgee River at the Downstream Balranald Weir gauge, 1980–2013

What flows are being consideredThe Murray–Darling Basin Authority (MDBA) is collecting information about what effects river flows have at different places along the Murrumbidgee River system, but only up to around the minor flood level. Flows significantly higher than the minor flood level are damaging and disruptive, and outside the bounds of active river management.

The flows are being investigated at three flow levels: 30,000, 40,000 and 48,500 ML/day at Wagga Wagga.

Statistical analysis of historical flows was undertaken to find what the flows at Wagga Wagga equate to downstream. Note that the height that a flow from Wagga Wagga reaches as it travels down the river varies with each flow, and depends on factors such as the duration of the peak and the wetness of the catchment. The indicative flows for Balranald are given in Table 20. Further work will be done to estimate the duration of the peak of the flows in this subreach. The duration of the peak would be five or less days at Wagga Wagga, but it likely to be at least twice that long in this subreach.

Table 20: Comparison of flows and floods, Balranald Weir gauge

Flow or flood level

Flow rates MDBA is

looking at (Balranald

Weir gauge)

Flow rates MDBA is


Weir gauge)

Flow rates MDBA is


Weir gauge)

Minor flood levela


Major flood levela

Flow rate (ML/day) 8,000 10,000 13,000 20,800 27,600 36,700

Gauge height (m) 5.54 5.98 6.29 6.70 6.90 7.10


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What these flows look likeThe method used to produce the maps is outlined in ‘Mapping flows and understanding effects’ in the main report.

The maps are based on a model using satellite imagery and every flood is different. Therefore, some caution should be used when interpreting the ‘typical flow footprints’ presented in this report.

The relevant flow footprint maps for this subreach are separately downloadable on the MDBA website under ‘Hay Weir to Murray Junction maps’. The mapped flows at Balranald were given in Table 20. Table 21 provides the flows that were mapped for a number of other gauge points. Indicative flows are based on the analysis of historical flows.

Table 21: Flows mapped at Hay, Maude and Redbank gauges for each Wagga Wagga flow

Wagga Wagga

Flow (ML/day)

Hay Weira

Flow (ML/day)

Hay Weira

Height (m)

Maudeb

Flow (ML/day)

Maudeb

Height (m)

Redbank Weir

Flow (ML/day)

Redbank Weir

Height (m)

30,000 15,000 5.74 13,000 3.34 9,000 5.6340,000 20,000 6.79 18,000 3.93 10,000 5.8948,500 25,000 7.62 22,000 4.37 11,000 6.11

a Flows values at Hay Weir were rounded from figures used in the upstream analysis from 14,000 to 15,000 ML/day for the lower flow level and from 21,500 to 20,000 ML/day for the middle flow level. The upper flow level remains unchanged.b These are estimates for Maude flows, but they were not used for the mapping, which was based on flows at Hay, Redbank and Balranald.

In addition to providing mapping for the Murrumbidgee, a zone of the Murray directly upstream of the Murrumbidgee junction was included in the map, as well as a zone of the Murray directly downstream. This was to check for interactions that may occur. To be conservative, high flows were assumed in the Murray, based on statistical analysis of flows that have previously coincided with high flows in the Murrumbidgee. The assumed flows in the Murray are in Table 22.

Table 22: Flows mapped in the Murray upstream and downstream of the Murrumbidgee junction

Balranald

Flow (ML/day)

Murray zone upstream of Junction (Murray Wakool gauge)

Flow (ML/day)

Murray zone upstream of Junction (Murray Wakool gauge)

Height (m)

Murray zone downstream of Junction (Murray Wakool gauge)a

Flow (ML/day)

Murray zone downstream of Junction (Murray Wakool gauge)a

Height (m)8,000 45,000 8.53 53,000 9.18

10,000 60,000 9.60 70,000 10.0013,000 70,000 10.00 83,000 10.33

a These flow estimates are derived by adding the Balranald flow to the flow from upstream of the Junction.

The maps show that water spreads to a far greater degree for this subreach than for the reaches upstream. This is because of the flatness of the landscape and the reduced channel capacity in the Lowbidgee area.

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Notable areas include:

the downstream section of Coonoon Creek and around Budgee Creek down to Maude for the higher flow level

large areas of the Lowbidgee, which are inundated for all flow levels; Lake Tala and Yanga Lake are filled in all scenarios. Note this mapping is based on what satellites have seen for flows of this size. This spread of water could be due to the overbank flows from the river or managed flows delivered from channels off Redbank and Maude weirs. Landholder feedback suggests that the majority of the inundation in the Redbank and Nimmie–Caira areas is due to active diversions through the weirs. There is no guarantee that these areas will continue to be watered in this pattern. This is particularly the case in the privately held North Redbank area where commercial decisions could reduce the diversion of water to ecological areas. However, in South Redbank and the Nimmie Caira environmental water managers control the watering infrastructure so diversions to ecological assets are likely to continue or improve.

The spread of water in the Lowbidgee during an event will be influenced by:o the duration of the high flow and the degree to which the flow exceeds the channel

capacity. For example, if the channel capacity is exceeded for 10 days by 2,000 ML/day then 20,000 ML/day will flow into the adjacent wetlands.

o the amount of diversion occurring from Maude and Redbank weirs. from Balranald and down to the Murrumbidgee Junction, where the spread is much reduced,

with inundation generally limited to billabongs and the floodplain immediately adjacent to the river

in the Murrumbidgee Junction area and along the Murray, where there is a lot of inundation that is being driven more by the far higher Murray flows than by the flows of the Murrumbidgee. However, the Murrumbidgee flows will be influential in the way water spreads around the junction itself and there is a wide spread of inundation along creeks such as Manie Creek.

What could be affected by these flowsThe following information about what might happen at different river levels is a guide only. Information has been sourced from community feedback.

By the time high flows arrive at this reach, the peak has reduced but the duration has increased. Much of the area is flood prone and can be inundated for extended periods, and infrastructure is generally built to take this into account. It does not appear that any public roads or crossings will need to be closed for any of the flows. However, large areas of private land are inundated. Due to the relatively dry climate in the area, wetting from the river is likely to be highly beneficial to the growth of fodder species, which are adapted to this floodplain environment.

An exception to this is where access to parts of properties is blocked by creek systems and this appears to be the case in parts of the Junction Wetlands. There are areas between the Murray and Manie Creek, as well as other flood-runner creeks that may be cut off when the Murrumbidgee flows occur during high Murray flows. When this occurs, access is blocked and landholders have difficulty managing stock. In at least one case, there is an irrigation block that becomes inaccessible. The landholder needs to boat or wade across the water in the creek to ensure pumps are running and to check stock.

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Additionally, although the wetting of paddocks is generally welcomed due to the improved fodder growth following the watering, there may be times when it does not fit with activities that may be taking place, such as timber cutting and collecting.

What is the initial community reaction to the range of flows being suggested?Initial feedback from landholders, local councils and Traditional Owners suggests that all flow levels being investigated would generally be welcomed.

‘Key Murrumbidgee community messages’ in the main report outlines the benefits and potential issues for farmers.

The benefits are fairly straightforward — improved pasture growth.

These flows would be welcomed with open arms down here. Balranald councillor and farmerThis country needs water. Spring watering is good but we’ll take it any old time. Lowbidgee grazier

Flows to the Junction Wetlands could cause access issues, although high flows in the Murrumbidgee alone are not enough to cause any concerns — a landholder noted that in the 2012 flood there was only enough water for the Manie Creek to run but not to spread out. When there are simultaneous high flows in the Murray and Murrumbidgee, though, there are issues managing the isolated country. Between Manie Creek and the Murray, there is some irrigated country. This requires frequent management so disrupted access makes things difficult. On one occasion, a landholder and his employee had to carry batteries and fuel across the creek floodplain area through mud. However, this landholder stated that there is benefit from watering if the spread across the floodplain is sufficient.

It is difficult to say if it was better to have the higher flows or not on my property as the access issues are very disruptive, but we appreciate the benefits of watering to the creek country. Farmer in the Murrumbidgee/Murray Junction region

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ReferencesCEWO (Commonwealth Environmental Water Office) 2014, Commonwealth environmental water use options 2014–15: Murrumbidgee River Valley, CEWO, Canberra.

CSIRO 2008, Water availability in the Murrumbidgee. A report to the Australian Government from the CSIRO Murray–Darling Basin Sustainable Yields Project, CSIRO.

DoE (Australian Government Department of the Environment) 2014, A directory of important wetlands in Australia, Australian wetlands database, accessed August 2014 at www.environment.gov.au/topics/water/water-our-environment/wetlands/australian-wetlands-database/directory-important.

Frazier, P 2001, River flow/wetland inundation relationships for the mid-Murrumbidgee River: Gundagai to Hay, Charles Sturt University, Riverina, NSW.

Frazier, P & Page, K 2006, The effect of river regulation on floodplain wetland inundation, Murrumbidgee River, Australia. Marine and Freshwater Research, vol. 57, pp. 133–41.

GHD 2002, Investigation of options for reducing high summer flows in the Tumut River — a scoping study, draft report for the NSW Department of Land and Water Conservation, Sydney.

Gilligan, DM 2005, Fish communities of the Murrumbidgee catchment: status and trends, report to the Murrumbidgee Catchment Management Authority, NSW Department of Primary Industries, Sydney.

Murray, PA 2006, ‘Wetlands of the Murrumbidgee River catchment, New South Wales’, in P Murray & I Taylor (eds), Wetlands of the Murrumbidgee River catchment — practical management in an altered environment, Fivebough and Tuckerbil Trust, Leeton, NSW, pp. 4–11.

MDBA (Murray–Darling Basin Authority) 2008, Sustainable Rivers Audit 2008, MDBA, Canberra.

MDBA (Murray–Darling Basin Authority) 2012a, Sustainable Rivers Audit 2012, MDBA, Canberra.

MDBA (Murray–Darling Basin Authority) 2012b, Assessment of environmental water requirements for the proposed Basin Plan: Mid-Murrumbidgee River Wetlands, MDBA, Canberra.

NSW Government 2003, Water Sharing Plan for the Murrumbidgee regulated river water source 2003, NSW Government, Sydney.

NSW Office of Environment and Heritage 2013, Murrumbidgee Valley annual environmental watering plan 2013–14, NSW Office of Environment and Heritage, Sydney.

NSW Office of Water 2011, Response to the Snowy Scientific Committee report on ‘The adequacy of environmental releases to the upper Murrumbidgee River’, NSW Office of Water, Sydney.

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NSW Water Conservation and Irrigation Commission 1974, Report on a proposal by the Snowy Mountains Council that the carrying capacity of the Tumut River be increased, NSW Water Conservation and Irrigation Commission, Sydney.

NSW Water Resources Commission 1979, Floodplain development: Old Man Creek, NSW Water Resources Commission, Sydney.

NSW Water Resources Commission 1983, Guidelines for Sandy and Poison Waterholes creeks floodplain development Kywong to Narrandera, NSW Water Resources Commission, Sydney.Page, KJ, Read, A, Frazier, P & Mount, N 2005, The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River, Australia. River Research and Applications, vol. 21, no. 5, pp. 567–78.

Roberts J & Marston F 2011, Water regime for wetland and floodplain plants: a source book for the Murray–Darling Basin, National Water Commission, Canberra.

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Appendix 1 Hydrographs at Darlington PointSee ‘How the Murrumbidgee has changed’ in the main report for description of the graphs.

Figure 20: Gauged flows and modelled ‘without-development’ flows at Darlington Point from the beginning of flow records for the gauge, 1914–29

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Figure 21: Gauged flows and modelled ‘without-development’ flows at Darlington Point, 1930–59

Figure 22: Gauged flows and modelled ‘without-development’ flows at Darlington Point, 1950–69

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Appendix 2 Flow footprint mapsDue to the size (A3 landscape) and number (16) of flow footprint maps for the Murrumbidgee reach, they have not been included in the main body of this report. Instead, they are provided as separate documents for downloading at the MDBA website.4 The maps are listed in Table 23.

Table 23: List of flow footprint maps

Subreach Part Individual map name

Burrinjuck to Wagga Wagga A Burrinjuck to Tumut JunctionBurrinjuck to Wagga Wagga B Gundagai to MundarloBurrinjuck to Wagga Wagga C Wantabadgery to Wagga WaggaWagga Wagga To Hay A Wagga Wagga to Berry JerryWagga Wagga To Hay B Galore to BuckingbongWagga Wagga To Hay C Narrandera to GogeldrieWagga Wagga To Hay C-1 Yanco CreekWagga Wagga To Hay D Darlington PointWagga Wagga To Hay E Upstream CarrathoolWagga Wagga To Hay F Carrathool to HayHay Weir to Murray Junction A Hay downstreamHay Weir to Murray Junction B Maude downstream northHay Weir to Murray Junction C Redbank Weir northHay Weir to Murray Junction D Maude downstream southHay Weir to Murray Junction E South Redbank and western Nimmie–CairaHay Weir to Murray Junction F Balranald

Due to limited space on the map sheets, each maps sheet directs readers to this document. The disclaimers and sources for the maps are listed below instead of on each map.

General disclaimer for the maps in Table 23The information in the maps is subject to change as the quality of information is improved and newer information becomes available. The inundation maps are a representation of a particular flow, accounting for many variables within the Murray–Darling system. Actual areas of inundation will depend on the variable conditions in the system at a particular point in time. The inundation maps are provided for consultation purposes only and should not be relied on for any other purpose. The Murray–Darling Basin Authority (MDBA) makes no claims, promises or guarantees in relation to the accuracy, completeness or adequacy of any information contained in these inundation maps.

Modelling disclaimer for the maps in Table 23Two methods of inundation modelling are shown within this series of maps. This includes RIM-FIM downstream of Hay, and MIKE11 upstream of Hay.

4 www.mdba.gov.au

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The RIM-FIM inundation modelling process was a technique developed by CSIRO to provide a broad-scale indication of inundation effects on floodplains at various flows. It is a point-in-time approach based on historic flows and inundation footprints of historic events. No hydrologic modelling has been undertaken to support RIM-FIM’s derived inundation models, although the flows presented are based on peak historic flows at relevant gauges matched with satellite images collected at that time.

MIKE-11 was developed by NSW State Water for the NSW Office of Environment and Heritage’s Upper Murrumbidgee Environmental Flows Enhancement Project. It is based on a steady-state simulation. The model was updated for MDBA’s purposes. The resulting flood inundation model is suitable for indicating broad-scale inundation patterns. The data are not necessarily suitable for individual property-level assessments.

The flow rates examined for this work do not indicate a commitment by MDBA to deliver flows at these rates.

Sources for the maps in Table 23 Geoscience Australia © Topo 1 million data (2001) Geoscience Australia © GEODATA 250K Series 3 (2008) Geoscience Australia © AusHydro V2.1 (2010) NSW Land and Property Information © Digital Topographic Database (2014) Commonwealth of Australia (ABARES) © National Parks (2003) Commonwealth of Australia (MDBA) © Flood inundation mapping SPOT IMAGE © SPOT imagery (2010)

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