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Leading policy and reform in sustainable water management

Review of water management during the 2010 flood events in the Tumut River and Murrumbidgee River

Publisher

NSW Office of Water

Level 18, 227 Elizabeth Street GPO Box 3889 Sydney NSW 2001

T 02 8281 7777 F 02 8281 7799

[email protected]

www.water.nsw.gov.au

The NSW Office of Water manages the policy and regulatory frameworks for the state’s surface water and groundwater resources to provide a secure and sustainable water supply for all users. The Office of Water also supports water utilities in the provision of water and sewerage services throughout New South Wales.


August 2011

ISBN 978 1 74263 187 5

© State of New South Wales through the Department of Trade and Investment, Regional Infrastructure and Services, 2011

This material may be reproduced in whole or in part for educational and non-commercial use, providing the meaning is unchanged and its source, publisher and authorship are clearly and correctly acknowledged.

Disclaimer: While every reasonable effort has been made to ensure that this document is correct at the time of publication, the State of New South Wales, its agents and employees, disclaim any and all liability to any person in respect of anything or the consequences of anything done or omitted to be done in reliance upon the whole or any part of this document.

NOW 11_207


Contents

1 Executive summary..................................................................................................................... 2 1.1. State of the catchment and dam inflows............................................................................. 2 1.2. Agencies involved in flood operations ................................................................................ 2 1.3. State Water’s requirements ................................................................................................ 2 1.4. Snowy Hydro’s requirements .............................................................................................. 2 1.5. What action was taken to mitigate flooding ........................................................................ 3

2 Background and terms of reference ......................................................................................... 4 2.1. Glossary of terms................................................................................................................ 5

3 The Murrumbidgee and Tumut River Catchments................................................................... 7 3.1. Description of the catchment .............................................................................................. 7 3.2. Rainfall, inflows and flooding .............................................................................................. 8 3.3. Water infrastructure in the catchment............................................................................... 13

4 Administrative and legislative framework .............................................................................. 20 4.1. Overview ........................................................................................................................... 20 4.2. Blowering Dam operational requirements......................................................................... 22 4.3. Burrinjuck Dam operational requirements ........................................................................ 23 4.4. Snowy Hydro Limited ........................................................................................................ 27

5 Operational decisions............................................................................................................... 31 5.1. The Snowy Scheme.......................................................................................................... 31 5.2. Blowering Dam operations and Tumut flooding................................................................ 32 5.3. Burrinjuck Dam operations and flooding at Gundagai and Wagga Wagga ...................... 35

Conclusion ......................................................................................................................................... 38

i | NSW Office of Water, August 2011


Minister’s foreword Water is critical to our economy and the environment. Too little can be devastating to communities,

however too much can cause serious damage to property and infrastructure, and at its worst can lead to tragic loss of life.

Australia has a highly variable climate and dams are critical to ensuring that there is a reliable water

supply available to our cities and towns and agricultural and industrial water users. Dams can also help mitigate floods. There is however tension between the water supply role of dams and the flood mitigation role. The flood mitigation role is maximised if the dam is not full. However the reduced water storage this

requires may reduce the reliability of the water supply.

The floods in the Tumut and Murrumbidgee rivers in October and December 2010, coming as they did on the back of a long period of drought caused significant community concern. People were concerned

that the activities of Snowy Hydro Limited may have exacerbated the flooding and that maintaining the releases at a high level for extended period may have worsened erosion.

In response to these concerns I asked the NSW Office of Water to conduct a detailed review of water

management in the lead up to the floods and responses by the relevant agencies to the floods. The purpose of the review was to clearly describe the framework for flood management in this area and ascertain whether agencies implemented this framework.

The review describes a number of actions that have been taken since the flood event but does not make any recommendations as to whether inland dams should play an increased flood mitigation role. While this is an important question, it cannot be answered in a review of a single flood event.

By describing the water management rules in the Murrumbidgee and Tumut rivers this report will hopefully enable the community to engage with these broader questions and ensure that our rivers are managed in the best interests of the community, industry and the environment into the future.

The Hon Katrina Hodgkinson MP Minister for Primary Industries

1 | NSW Office of Water, August 2011



1 Executive summary

1.1. State of the catchment and dam inflows • Following eight years of drought the period from 1 July to 31 December 2010 was the wettest on

record in many parts of NSW including parts of the Tumut River and Upper Murrumbidgee River and flooding occurred in Tumut, Gundagai and Wagga Wagga (Part 3.2).

• During December 2010 the Snowy Scheme, Blowering Dam and Burrinjuck Dam experienced the greatest inflows on record for that month (see Part 3.2).

1.2. Agencies involved in flood operations • Six agencies have primary responsibility for water management and, in particular, flood

management in NSW: the NSW Office of Water, State Water Corporation (State Water), Snowy

Hydro Limited (Snowy Hydro), State Emergency Service (SES), Bureau of Meteorology (BOM) and Dams Safety Committee

• State Water and Snowy Hydro operate the main water infrastructure in the review area and are responsible for authorising releases from dams under their control (Part 3.3).

1.3. State Water’s requirements • State Water is responsible for operation of Burrinjuck and Blowering Dams (see Part 4).

• There are flood mitigation requirements, channel capacity constraints and airspace requirements set out in the Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003 for

both Blowering and Burrinjuck Dams. These requirements are binding on State Water through its operating licence (see Part 4).

• State Water made releases from Blowering Dam that exceeded the Tumut River channel capacity requirements from 14 to 27 December 2010 in order to reduce the surcharge in the dam. The water sharing plan notes these channel capacity requirements but does not require compliance

with them.

• The primary purpose of the dams is water supply and State Water is required to operate the dams

to achieve a full supply level at the end of the flood event (Parts 4.2 and 4.3).

• Airspace in Blowering Dam for electricity generation purposes is at the discretion of Snowy Hydro.

At the time of the floods this had been set at 50 GL (Part 4.2 and 4.4).

• State Water can make releases from Burrinjuck Dam to create airspace but only to the extent that

this will be refilled by forecast inflows prior to there being requirements for water by downstream licence holders (Part 4.3).

• State Water has operating procedures in place for Burrinjuck and Blowering Dams as well as training programs for these procedures. The procedures are not binding however appear to have generally been complied with (Parts 4 and 5).

• The notification procedures for Blowering Dam should be reviewed and clarified where necessary in consultation with the SES and other stakeholders. State Water notified the SES and the

Gundagai Flood Warning Association in accordance with the procedures but relied on the SES to undertake other notifications (Part 4.2).

1.4. Snowy Hydro’s requirements • Snowy Hydro is required to pass no more than natural inflows when Blowering Dam is spilling and

the Tumut River has exceeded its channel capacity immediately downstream of Blowering Dam. It

complied with these obligations (Part 4.4).

• Although over the water year Snowy Hydro was compelled to make releases to meet annual

release requirements as a result of its licence requirements, this annual requirement did not


require releases on any particular day. The releases it did make complied with its licence obligations (Part 4.4).

• Snowy Hydro did transfer water to the Tumut catchment during this period from Tooma Dam. While this may have impacted the ability to buffer natural inflows it was consistent with their licence (Part 5.1).

• Snowy Hydro did generate electricity during this period. This is unavoidable when water is being released through the Snowy Scheme’s turbines. The releases complied with Snowy Hydro’s

licence obligations (Part 5.1).

• Subsequent to the December flooding Snowy Hydro’s required annual release requirements were

reduced for the 2010/11 water year.

1.5. What action was taken to mitigate flooding • The operation of both Burrinjuck and Blowering dams provided flood mitigation by reducing and

delaying peak outflows (see Parts 5.2 and 5.3).

• Significant reductions in releases from Blowering Dam between 12 and 25 October 2010 reduced the volume of water at Tumut while floodwaters from the unregulated Goobarragandra River were peaking (Part 5.2).

• On three occasions during October and November releases were reduced from the Snowy Scheme and Blowering Dam in response to Bureau of Meteorology weather forecasts of

significant rainfall that did not occur. If significant rainfall had occurred this decision would have reduced the impact of downstream tributary inflows (Part 5.2).

• There was some reduction in releases from the Snowy Scheme immediately prior to the December flood event. However the capacity to take action was limited as at that stage the Blowering Dam was already surcharged and the rainfall that occurred was significantly greater

than predicted (Part 5.2).

• State Water made releases from Burrinjuck Dam to create airspace in response to forecasts of

significant rainfall (see Part 5.3).

• During October and December 2010 flood events peak releases made from the Burrinjuck Dam

were less than the peak inflows to the dam and accordingly peak flows at Gundagai were reduced and delayed (Part 5.3).

• State Water made four releases from Burrinjuck Dam to create airspace in response to forecasts of significant rainfall and likelihood of increased inflows during late October and November 2010. These reduced the storage level before these inflows arrived and the increased inflows until early

December 2010. The actual rainfall in the first December flood event in Burrinjuck Dam was substantially greater than forecast (Part 5.3).

• Bureau of Meteorology weather forecasts for 8, 9 and 10 December informed State Water’s decision to evacuate the surcharge from Burrinjuck Dam as quickly as possible after the first December flood so as to create airspace in the dam to mitigate the second flood (Part 5.3).

• There were inadequate arrangements in place in relation to obtaining data from gauging stations within the ACT which may have impacted on flood mitigation by Burrinjuck Dam during the first

December 2010 flood event (see Parts 3.3.1 and 5.3).




2 Background and terms of reference Following eight years of serious drought, the second half of 2010 brought significant rainfalls to much of

NSW and, in particular, the Murrumbidgee Valley. Inflows to Burrinjuck and Blowering Dams in this period were significantly higher than normal and by the end of October both dams were full and passing inflows.

In Gundagai this led to minor flooding in October and major flooding in December 2010. Tumut experienced moderate flooding in both October and December. Wagga Wagga experienced minor flooding in October and major flooding in December. 1

At the time of the December floods reductions in the height of Lake Eucumbene were observed and this led to concerns that Snowy Hydro Limited may have exacerbated the flooding in the Tumut River through its operation of the Snowy Scheme.

Community concern about the releases by Snowy Hydro into the Tumut River potentially exacerbating flooding, management of water from Lake Eucumbene and management of the Tumut River2 led to the Minister for Primary Industries announcing a review of these flood events in accordance with the

following terms of reference:

1. What was the state of the catchment for the Tumut River and the Murrumbidgee River between Burrinjuck Dam and Wagga Wagga (the “review area”) in the period from 1 June

2010 to 31 December 2010 including:

o the capacity over time of Eucumbene, Talbingo, Jounama, Blowering and Burrinjuck

Dams (the “relevant dams”)

o releases from the relevant dams

o natural inflows to the review area?

2. What action was taken to manage and mitigate flooding in the review area during the period 1 October 2010 to 31 December 2010 (“the review period”) including in relation to the operation of the relevant dams?

3. What was the volume and timing of releases from Eucumbene Dam to the Tumut River upstream of Blowering Dam in the review period?

4. Did releases from the relevant dams exacerbate flooding in the review area during the review period?

5. Who was responsible for authorising the releases from the relevant dams during the review period?

6. Did Bureau of Meteorology weather forecasts inform dam management decisions during the review period? If so, how?

7. What licences, approvals, policies, procedures or protocols were in place in relation to the volumes released from the relevant dams and works in the review area during the review

period?

8. To what extent, if any, did the actions of the dam managers contravene the requirements,

licences or approvals under the Snowy Hydro Corporatisation Act 1997 (including the Snowy Water Inquiry Outcomes Implementation Deed), State Water Corporation Act 2004, Water Act 1912 or Water Management Act 2000 during the review period in the review

area?

1 The SES categorises flooding as minor, moderate or major by reference to river heights at specified gauges. The term minor is not intended to downplay the very real impacts these events can have on individuals and the community. 2 For example see comments by the Tumut River Landholders Association reported in the Gundagai Independent 20 April 2011 page 1.


The review was undertaken by the Legal Branch within the NSW Office of Water. The Legal Branch had no involvement in the October or December flood management operations and was instructed to prepare an independent assessment of what occurred. The review was based on:

• analysis of primary documents and hydrometric data provided by State Water, Snowy Hydro and NSW Office of Water staff

• interviews with staff from State Water, Snowy Hydro and NSW Office of Water

• information obtained from the State Emergency Services, Bureau of Meteorology and the Tumut

Shire Council.

The primary focus of the review is to identify whether the actions taken by relevant State agencies and Snowy Hydro in the October and December 2010 flood events were consistent with their statutory

obligations. The review does not address what flood mitigation role the dams should play and the extent to which the current flood mitigation policies are appropriate. While these are important questions, changing the balance between capturing water for consumptive purposes and flood mitigation is likely to

impact on the volume and reliability of water available to downstream users, may trigger compensation requirements and is beyond the scope of this review.

The review has three key components:

Part 3 describes the “Murrumbidgee and Tumut river catchments” at the time of the flooding and in particular considers:

• the river systems in the catchment including both regulated (below dams) and unregulated (free

flowing) rivers

• the climatic conditions in the period, the nature of the inflows and the flood events that occurred

• the works that are relevant to the management of the Murrumbidgee and Tumut Rivers, including dams and pipelines.

Part 4 describes the “Administrative and legislative frameworks” relevant to flood management and in particular:

• the responsibilities of the various agencies such as the NSW Office of Water, State Water

Corporation, Snowy Hydro Limited, the State Emergency Services and the Bureau of Meteorology

• the specific rules that regulate the operation of Blowering Dam, Burrinjuck Dam and the Snowy

Scheme.

Part 5 describes the “Operational decisions” that were made during this period and the extent to which these were consistent with the administrative and legislative frameworks set out in Part 4.

2.1. Glossary of terms Water management and dam operations are quite technical. The following technical terms and abbreviations are used in this report:

ACTEW ACTEW Corporation Limited. ACTEW is a public company owned by the Australian Capital Territory Government with assets and investments in water, wastewater, electricity, gas and telecommunications

Airspace the space (volume) in a dam below the full supply level which can store future inflows. It is the gross storage capacity of the dam at spillway crest level minus the actual gross storage volume

AWOP Annual Water Operating Plan

BOM The Bureau of Meteorology

Channel capacity The maximum rate of flow that can occur in a stream before the water level rises above the stream banks

Confluence where two rivers join together

DISV Dry inflow sequence volume



Flood mitigation the difference between the peak inflow into a storage and the peak outflow from the storage in a given period

Full supply level the storage level considered to be the limit for the purposes of storage of water,

except during flood operations

Gauging station facilities and instruments located on streams used to measure and record water levels

Gigalitre (GL): 1GL = 1,000 ML

Maximum induced surcharge level the maximum level, above the full supply level, that the storage can be allowed to reach while the gates are controlling water levels. It is the maximum temporary increase in the storage level that can be generated by the action of not operating the spillway gates (e.g.

lowering the spillway gates in a sector gate storage).

MDBA Murray Darling Basin Authority

Megalitre (ML) 1ML = 1,000,000 litres

Percentile is the percentage amount of time that a volume or flow of water in a river occurs or is exceeded. For example, the 95th percentile (95%ile) is the flow that occurs or is exceeded 95 percent of the time, which is a very low flow

RAR Required annual release

SES State Emergency Service

Snowy Hydro Snowy Hydro Limited

State Water State Water Corporation

Spill the uncontrolled discharge of water from a storage when the storage level rises above the full supply level

Surcharge the temporary storage level increase above the full supply level during a flood

WAMC Water Administration Ministerial Corporation

Water year for Snowy Hydro, means a year commencing 1 May. For other licence holders the water

year commences on 1 July

WSP water sharing plan



3 The Murrumbidgee and Tumut River Catchments

3.1. Description of the catchment The Murrumbidgee River rises on the Monaro Plateau. The river initially flows southeast then turns north near Cooma and swings north-northwest through the ACT before entering Burrinjuck Dam near Yass.

Burrinjuck Dam has a total catchment area of 13,100 square kilometres. Within the ACT are a number of other dams and gauging stations that are under the control of ACTEW.

From Burrinjuck Dam, the Murrumbidgee River is joined by Jugiong and Muttama Creeks from the north

and the Tumut River from the south, before emerging onto the western plains near Gundagai. On its route flowing west to Wagga Wagga, it is joined by other streams including Adelong, Billabong, Hillas, Tarcutta and Kyeamba Creeks.

The Tumut River is the largest tributary of the Murrumbidgee, rising in the Snowy Mountains. Within its headwaters are works that form part of the Snowy Mountains Hydro-electric Scheme including Tumut Ponds, Talbingo Dam and Jounama Pondage.

Blowering Dam is located on the Tumut River just upstream of Tumut. It is outside of the Snowy Scheme and is operated by State Water Corporation. The major tributaries of the Tumut River below Blowering Dam are Gilmore, Brungle and Adjungbilly Creeks and the Goobarragandra River. The Tumut River joins

the Murrumbidgee River just upstream of Gundagai.

The Murrumbidgee Regulated River Water Source is the largest regulated river system in NSW, outside of the Murray River, and more water is used in this system than any other in NSW. Irrigation is the main

water use, with supplies from the Murrumbidgee River supporting the Murrumbidgee Irrigation Area, the Coleambally Irrigation Area, and many hundreds of private irrigators who pump directly from the river. Many towns along the Murrumbidgee and Tumut Rivers also receive supplies of water from Burrinjuck

and Blowering Dams. On average the two dams together supply approximately 2,000 GL per annum for various purposes, including irrigation, environmental flows, town water supply and stock watering right through to the confluence of the Murrumbidgee and Murray Rivers.

To manage the supply of water to downstream water users, inflows to Burrinjuck and Blowering Dam are conserved in the storage, typically during the winter and spring period, and supplied to licensed water users during the warmer months. In general, the majority of inflows to Burrinjuck and Blowering

(including from the Snowy Scheme) occur during the winter and spring, with dam storage levels peaking in late spring ahead of releases to meet the needs of licensed water users downstream.

A map of the area showing key dams and towns is set out in Figure 1.



Figure 1: Area map showing key dams and towns

3.2. Rainfall, inflows and flooding From June 2010 the rainfall in the catchment was significantly above average and rainfall in many parts

of the catchment in December 2010 was the highest on record. Figure 2 shows that the rainfall percentiles for the period 1 July 2010 to 31 December 2010 were the highest on record in many parts of NSW but in particular in the Tumut River and Murrumbidgee River catchments.

Figure 2: NSW rainfall percentiles for the period 1 July to 31 December 2010

Source: Australian Bureau of Meteorology




The most comprehensive indicator of the potential for flooding in the catchment is dam inflows. Figure 3 shows the monthly inflows for Blowering Dam and Burrinjuck Dam in the period July 2010 to December 2010 and the relevant percentile for each month. A percentile of 20 per cent means that only

20 per cent of historically recorded inflows in that month have been higher. Inflows in December 2010 were the highest ever recorded for December and this came on top of a series of very wet months.

Figure 3: Blowering and Burrinjuck Dam inflow volumes and percentiles

Blowering Natural Inflow (below T1) Burrinjuck Inflows

July 48,529 45% wet 115,112 43% wet

August 87,741 34% wet 183,328 32% wet

September 135,867 13% wet 295,804 14% wet

October 116,197 13% wet 259,426 15% wet

November 86,805 11% wet 191,815 17% wet

December 123,992 0% (max ever) 752,144 0% (max ever)

Note: All volumes in megalitres and percentiles of time.

The significance of the wet conditions in the catchment is two-fold. First, the run-off from the rain events in October and December 2010 was greater than normal as the catchment was already soaked. Second, widespread rain meant there had been little need for irrigators to order water from State Water as their

water needs were being supplied by rainfall and Blowering and Burrinjuck dams were therefore fuller than they would have been in a drier year.

The flooding that occurred in Tumut, Gundagai and Wagga Wagga is discussed below. There are a

number of things to keep in mind about the graphical information presented in this report:

• Information is provided in terms of both flow rate and river height. Flow rate is important as this is how discharges from the dams are measured. River height is important as this determines the

impact on the communities. The relationship between flow rate and river height is determined by the river channel and flood plain profile. A doubling in flow rate will not result in a doubling in river height.

• There are major unregulated tributaries to the Tumut and Murrumbidgee rivers downstream of the dams. While these are uncontrolled the flood peaks downstream of the confluence can be

influenced by ensuring peak flows from the dams do not coincide with peak flows from the tributaries.

• Even though more water generally enters the main branch of the Murrumbidgee as you move downstream towards Wagga Wagga,3 this does not necessarily mean that flow rates or flood peaks are higher. While the total volume of water passing a given point will often be greater, the

spread of water over floodplains may mean that there is a lower peak that lasts for a longer period (known as attenuation).

• Flooding is classified as either minor, moderate or major depending on the flood peak. These categories are specified in the NSW State Flooding Sub-Plan and summarised in Figure 4. A minor or moderate flood impact does not detract from the fact that individuals may still be

significantly affected.

3 Downstream of Wagga Wagga this becomes more complex.



Figure 4: Flood classifications

Flood classification levels in metres

Minor Moderate Major

Gundagai 6.1 7.6 8.5

Tumut 2 2.6 3.7

Wagga Wagga 7.3 9 9.6

3.2.1. Tumut flooding

Figure 5 shows the river heights at Gundagai, Tumut and Wagga Wagga in the period 1 October to 31

December 2010. Tumut experienced moderate flooding in October and December 2010 with flood peaks of 3.25 m and 2.82 m respectively. By comparison the highest peak since the construction of Blowering Dam was 3.38 m in August 1970. The Tumut River has exceeded two metres at Tumut 11 times in the

43 years since 1968. 4

Figure 5: River heights at Gundagai, Tumut and Wagga Wagga

NSW Office of Water01/10/2010 - 31/12/2010

0

2

4

6

8

10

12

1/10/2010

11/10/2010

21/10/2010

31/10/2010

10/11/2010

20/11/2010

30/11/2010

10/12/2010

20/12/2010

30/12/2010

Date

Riv

er H

eig

hts

(m

)

410004 - MURRUMBIDGEE @ GUNDAGAI

410001 MURRUMBIDGEE RIVER @WAGGA WAGGA

410006 TUMUT RIVER @ TUMUT

Max.ht=10.19m @Gundagai 4/12/2010

Max.ht = 9.66m @Wagga 6/12/2010

Max ht.= 3.25m @Tumut 15/10/2010

Max.ht = 2.82m @Tumut 9/12/2010

Max.ht = 8.69m

@Wagga 17/10/2010 Max.ht=7.04m

@Gundagai 17/10/2010

Figure 6 shows flows as measured at gauging stations at Oddy’s Bridge, at Tumut, and at Lacmalac on the Goobarragandra River from 1 October to 31 December 2010. The Oddy’s Bridge gauging station is

just below Blowering Dam and provides a measure of the rate of releases from the dam. The Goobarragandra River is a tributary that joins the Tumut River just upstream of Tumut.

This shows, in relation to the October flooding, both that releases from Blowering Dam were severely

reduced in anticipation of downstream inflows and that the primary cause of flooding in Tumut were flows in the unregulated Goobarragandra River. Blowering releases were not the cause of, nor a material contributor to, the October floods. The flood peak measured at Lacmalac is prior to the peak at Tumut as

the Lacmalac gauging station is upstream of the Tumut gauging station.

4 Tumut Local Flood Plan Annexure A p4.


Figure 6: October 2010 river flows: Tumut

NSW Office of Water01/10/2010 to 30/12/2010

0

5000

10000

15000

20000

25000

30000

35000

40000

1/10/20100:00

11/10/20100:00

21/10/20100:00

31/10/20100:00

10/11/20100:00

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20/12/20100:00

30/12/20100:00

Date

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char

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(ML

/d)

410006 - TUMUT RIVER @ TUMUT

410057 - GOOBARRAGANDRA RIVER ATLACMALAC

410073 -BLOWERINGRELEASES(TUMUT@ ODDYS BDGE)

Hydstra Output 23/06/2011

Figure 7 provides the same data but in more detail for the December 2010 floods. It shows that flows from Blowering Dam were a significant contributor to the Tumut flooding in December. However, the flows from Blowering Dam peaked after the flood peak at Tumut, indicating that the peak itself was

primarily caused by inflows from the Goobarragandra River. While the releases from Blowering Dam clearly contributed to the river flows, by this time Blowering Dam was spilling and little could be done to further mitigate these impacts.

Figure 7: December 2010 river flows: Tumut

NSW Office of Water01/12/2010 to 18/12/2010

0

5000

10000

15000

20000

25000

1/12/2010 0:00 3/12/2010 0:00 5/12/2010 0:00 7/12/2010 0:00 9/12/2010 0:00 11/12/20100:00

13/12/20100:00

15/12/20100:00

17/12/20100:00

Date

Dis

char

ge

(ML

/d)

410006 - TUMUT RIVER @TUMUT

410057 - GOOBARRAGANDRARIVER AT LACMALAC

410073 - BLOWERING RELEASES(TUMUT@ ODDYS BDGE)

Hydstra Output 23/06/2011



3.2.2. Gundagai and Wagga Wagga flooding

Figure 5 shows the river heights at Gundagai and Wagga Wagga in the period 1 October to 31 December 2010. This shows that the Murrumbidgee River at Gundagai had a peak of 7.04 m on 17 October 2010 and a subsequent peak of 10.19 m on 4 December 2010. To put this in context only 12

floods have exceeded 9.5 m in the last 125 years. Five of these 12 (including 2010) occurred since 1968 when Blowering Dam was completed (Burrinjuck was already in place at this time). The largest flood on record was the 1852 flood which peaked at 12.34 metres.

The Murrumbidgee River at Wagga Wagga had a peak of 8.69 m on 17 October 2010 and a subsequent peak of 9.66 m on 6 December 2010. To put this in context there were three floods in the previous century higher than this:

• May 1925 11.278

• August 1974 11.010

• March 1950 10.439

Historical records suggest that larger floods occurred in mid 1800s with the 1852 flood estimated to have peaked at 12.34 metres.

Figure 8 shows the flow rate peaking at Wagga Wagga in October before the flood peak at Gundagai. As Wagga Wagga is downstream of Gundagai this can only happen if the bulk of the flood waters at Wagga

Wagga enter the river downstream of Gundagai. This also shows the discharges from each of Blowering and Burrinjuck Dams. Discharges from Blowering Dam were not a contributor to this flood event.

Figure 8: October 2010 river flows: Gundagai and Wagga Wagga

Murrumbidgee Flows at Wagga & Gundagai 01/10/2010 - 25/10/2010

0

20,000

40,000

60,000

80,000

100,000

1/10/2010 6/10/2010 11/10/2010 16/10/2010 21/10/2010

Date

Dis

ch

arg

e (M

L/d

)

410004 MURRUMBIDGEE @ GUNDAGAI

410001 MURRUMBIDGEE @WAGGA WAGGA

Burrinjuck Releases

410073 Tumut R @ Oddys Bridge

Hydstra Data 23/06/2011

In contrast Figure 9 shows two flood peaks in December. In each case the peak in Gundagai occurs

approximately 3 days before moving through to Wagga Wagga. This is a more regular scenario for significant flood events where the flooding is caused by water in the main channel passing through both Blowering and Burrinjuck dams. Discharges from Blowering Dam were a relatively minor contributor to

this flood event.



Figure 9: December 2010 river flows: Gundagai and Wagga Wagga

Murrumbidgee Flows at Wagga & Gundagai 01/12/2010 - 31/12/2010

0

50,000

100,000

150,000

200,000

250,000

300,000

1/12/2010 6/12/2010 11/12/2010 16/12/2010 21/12/2010 26/12/2010 31/12/2010

Date

Dis

char

ge

(ML

/d)

410004 MURRUMBIDGEE @ GUNDAGAI

410001 MURRUMBIDGEE @WAGGA WAGGA

Burrinjuck Releases

410073 Tumut R @ Oddys Bridge

Hydstra Data 23/06/2011

3.3. Water infrastructure in the catchment Water infrastructure in the catchment comprises dams, power stations, tunnels and gauging stations (used to measure flow rates). This infrastructure is operated by a number of agencies and companies:

• NSW Office of Water operates gauging stations in NSW outside of the Snowy Scheme.

• State Water Corporation (State Water) operates Blowering Dam and Burrinjuck Dam, and all

downstream weirs.

• Snowy Hydro Limited (Snowy Hydro) operates the works within the Snowy Scheme.

• ACTEW Corporation Limited (ACTEW) is responsible for the gauging stations and dams within the Australian Capital Territory.

3.3.1. Gauging stations

Water flows in rivers and streams are monitored through the use of flow gauging stations that are located at key points throughout NSW. Flow gauging stations operate by measuring the water level at a particular location which is converted into a flow rate using historical knowledge about the relationship

between river height and the flow volumes at each gauge location. The flow gauging stations in the Review Area operated by the NSW Office of Water, Snowy Hydro and ACTEW are marked on Figure 10.



Figure 10: Location of gauging stations

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NOW flow gauging stations and data sharing

The NSW Office of Water is responsible for 66 surface water monitoring sites located in the Tumut and Murrumbidgee rivers and their tributaries between Blowering and Burrinjuck dams and Wagga Wagga.

Water level is measured continuously and automatically through a sophisticated digital sensor every 15 minutes and recorded on a data logger. The data is transmitted via telemetry equipment to a central location from 43 sites, hourly during flood times or at shorter intervals as required. The remaining sites

consist mainly of visual water depth marker boards which provide advice on stream crossings and other local information needs.

The Office of Water maintains a hydrographic database and communications system using the

commercial products known as HYDSTRA and HydroTel. These databases include data from the Office of Water telemetry system and also data from flow, storage and weather stations that are operated by a number of other state and commercial agencies including South Australia, Victoria, the Australian Capital

Territory (ACT), Snowy Hydro, Manly Hydraulics Laboratory and State Water.

“Real-time” access to this data is provided via the Office of Water’s HydroTel web site to BOM, Murray-Darling Basin Authority, State Water, Snowy Hydro and to the SES. This data is also sent directly

through file transfer by this system to these same agencies. State Water has direct access to the Office of Water’s HYDSTRA database.

Data is also made available to the public in near real time through two internet sites managed by the

Office of Water:

• “WaterInfo” has daily flow data from gauging stations managed by the NSW Office of Water that is generally updated each day, with more regular updates available during flood events. This site

provides data extending back over at least the last 10 years, see http://waterinfo.nsw.gov.au

• “RealTimeData” has been developed more recently as a part of the Office of Water’s website to

meet an increasing range of needs requiring more timely data, see http://realtimedata.water.nsw.gov.au

Sharing of data from gauging stations is critical to both the Office of Water and State Water functions. Although the Service Level Agreement for the provision of this data between the Office of Water and State Water is no longer current, the Office of Water continues to provide the data to State Water in accordance with that agreement while a new agreement is being developed.

The NSW Office of Water gauging network as a whole operated well during the October and December 2010 flood events. The gauging station downstream of Burrinjuck Dam (410008) was destroyed by a landslide on 3 December 2010 and this caused some gaps in data. Other data losses were experienced

during the floods due to electronic communication issues and extreme weather conditions. These were addressed whenever possible during the floods.

ACTEW gauging stations and data sharing

ACTEW is responsible for the gauging stations within the ACT. These gauging stations are on the Murrumbidgee River and its tributaries and are therefore important indicators of impending inflows in Burrinjuck Dam.

Historically the Office of Water and its predecessor organisations had direct access to the ACTEW gauges by way of phone telemetry and hence were able to obtain data from the logger directly whenever data was required. For operational reason ACTEW removed phone access leaving the Office of Water

and State Water without direct access to ACTEW gauging station data.

At the time of the October and December 2010 floods there were no agreements in place between the Office of Water or State Water and ACTEW to ensure that State Water received timely access to

ACTEW hydrometric data or information.

When the floods occurred, Office of Water staff worked on establishing direct file transfer arrangements with ACTEW but notwithstanding these efforts ACTEW gauging station data was not available during the



first December flood event. By the time of the second December flood event ACTEW gauging station data was able to be loaded directly onto the Office of Water’s HYDSTRA database where it could be accessed by State Water.

Since the floods, data continues to be transferred into HYDSTRA by ACTEW pursuant to informal arrangements put in place during the floods. However, the current informal arrangements do not provide the Office of Water with the ability to obtain the real-time hydrometric data at the frequencies that may be

required during flood events.

3.3.2. Tumut river works

Snowy Hydro is responsible for operating the Snowy Scheme. In addition to the gauging stations marked on Figure 10, Snowy Hydro operates the following dams, tunnels and power stations that are relevant to

this review:

• Eucumbene Dam: This is the long term storage of the Snowy Scheme. From this dam releases can be made to the Eucumbene River and diversions can be made to Tumut Ponds on the

Snowy-Tumut Development and Island Bend on the Snowy-Murray Development. The storage has an active capacity of 4,300,000 ML.

• Tooma Dam: this is the only storage on the Tooma River, a tributary of the River Murray. Water is diverted from Tooma Dam to Tumut Ponds through the Tooma-Tumut Tunnel. Tooma Dam has an active capacity of 25,500 ML.

• Tumut Ponds: This is the first major storage on the Tumut River with an active storage capacity of 50,000 ML. As described below there is capacity to transfer water from the storage to Lake

Eucumbene, however below this point there is no ability to divert releases or natural inflows to Lake Eucumbene.

• Tumut 2 Dam is a small dam below Tumut Ponds whose primary purpose is to re-regulate water into a second underground power station, known as T2. It has an active storage of 1,500 ML. Tumut 2 Power Station discharges water into Talbingo Reservoir. It is not considered further in

this review.

• Talbingo Dam is a deep storage whose main purpose is to increase the height of water above the

T3 power station to improve power generation capacity. The dam has a gross capacity of 921,400 ML, however only the top 160,400 ML can be released to the T3 power station (referred to as “active storage”).

• T3 power station: This power station was designed, built and operated as a “last resort” facility that can generate significant amounts of electricity at short notice if needed. To maximise its

generation capacity it can release up to 100,000 ML per day. However this would cause significant flooding downstream and for this reason the down stream storages of Jounama Pondage and Blowering were built and are generally managed to ensure that there is some airspace that can

buffer these releases if necessary.

• Jounama Pondage is the storage below Talbingo Dam with a gross capacity of 43,500 ML and

an active capacity of 27,800 ML. Releases can be made downstream directly into Blowering Dam through large radial gates or, now, through the recently commissioned Jounama Mini Hydro Power Station. Alternatively water can be pumped back up to Talbingo for re-release through the T3

power station.

• Tooma-Tumut Tunnel: The Tooma River is a tributary of the Murray. There is no power

generation capability on the Tooma Dam. This tunnel allows Snowy Hydro to divert water from the Tooma River into Tumut Ponds. This water can then be used to either generate electricity through the Snowy-Tumut Development or diverted to Lake Eucumbene for storage and subsequent re-

diversion. The maximum capacity of this tunnel for Tooma Dam diversions (ie excluding intermediate intakes) is approximately 3,300ML/day when Tooma Dam is at Full Supply Level and




Tumut Ponds is at Minimum Operating Level. Unlike the Eucumbene-Tumut Tunnel this tunnel can only transfer water into Tumut Ponds.

• Eucumbene- Tumut Tunnel: This tunnel allows water to be transferred in either direction between these two dams. The capacity of this tunnel varies depending upon the active storage levels of Lake Eucumbene and Tumut Ponds. It has a maximum capacity of approximately 9,300

ML/day when Lake Eucumbene is at Full Supply Level and Tumut Ponds is at Minimum Operating Level.

The last dam on the Tumut River is Blowering Dam. This was completed in 1968, consists of a 112 metre high earth and rockfill structure with a central clay core, concrete chute spillway, four outlet valves and a 80MW hydro-electric power station. Releases are controlled by the four outlet valves and the Hydro-electric power station, which have a combined capacity of 23,000 ML per day. Blowering Dam’s

spillway has a capacity of 203,000 ML per day.

This storage is operated by State Water and has a capacity of 1,631,410 ML. It is immediately downstream of the Jounama Pondage (operated by Snowy Hydro) and 24 km upstream of Tumut. It is

operated primarily to supply water required for irrigation and town water supplies but also has power generation capability. Power is generated at the Blowering Power Station only when water is made available by State Water for water users and the environment.

Operation of the dam by State Water is subject to a number of regulatory instruments including the Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003; the works approval under the Water Management Act 2000 and the operating licence under the State Water Corporation Act

2004. These are considered further in Part 4.2 below.

The various dams, tunnels and power stations are illustrated in Figure 11.


Figure 11: The Snowy Hydro-electric Scheme

Source Snowy Hydro Limited



Operation of the dam is also subject to two agreements between State Water and Snowy Hydro:

• Blowering Works Operating Deed and Lease under which Snowy Hydro leases the power station

from State Water; and

• Blowering Airspace Deed which provides for the maintenance of airspace in the dam for power generation purposes.

The Airspace Deed and the other legislative arrangements that govern operation of Blowering Dam are described in more detail in Part 4.2 below.

3.3.3. Murrumbidgee river works

Burrinjuck Dam is located on the Murrumbidgee River and has a capacity of 1,028,000ML. It is operated by State Water to supply water required for irrigation, town water supplies and hydro power

generation by Eraring Energy. Inflows into Burrinjuck Dam comprise natural inflows, releases from upstream dams operated by ACTEW and releases from Tantangara Dam in the upper reaches of the Murrumbidgee River.

Operation of the dam by State Water is subject to a number of regulatory instruments including the Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003 and the water supply works approval under the Water Management Act 2000 and the operating licence under the State Water

Corporation Act 2004. These are considered further in Part 4.3 below.

Burrinjuck Dam has three sector gates and four low level outlets which are used to release water. Sector gates are operated by lowering the gates, thus increasing the spillway opening, and therefore the

discharge from the dam. When the dam is at full supply level it has a volume of 1,028,000 ML. The maximum induced surcharge volume is 1,097,000 ML, and the sector gates are fully lowered when the storage exceeds this volume.

Releases may also be made for the purposes of hydro power generation via two hydro-electric power generation valves which feed Eraring Energy’s hydro generators. These releases are made only when water is made available for water users or the environment and during flood operations.

3.3.4. ACT dams

The ACT has constructed a series of dams in the Burrinjuck catchment to meet the water supply needs of Canberra. This includes:

• Googong Dam (121,000 ML capacity), the major storage on the Googong River (a tributary of the

Molonglo River)

• Scrivener Dam on the Molonglo River (a tributary of the Murrumbidgee River) behind which lies

Lake Burley-Griffin in the centre of Canberra

• Bendora Dam (11,540 ML capacity), Corin Dam (70,900 ML capacity), and Cotter Dam (3,800

ML capacity, being enlarged to 78 GL), all of which are in the Cotter River catchment (a tributary of the Murrumbidgee River).

These dams are managed primarily for the supply of Canberra by ACTEW with the exception of Scrivener Dam which is operated by Sunwater. Canberra is supplied via a pipe network from these dams and only minimal releases are normally made downstream for environmental reasons.

The only storage with spillway gates is Scrivener Dam, and periods of high flows or flooding can force

ACTEW to make significant releases to ensure the safety of their dam and avoid surcharging the storage to levels that would cause local flooding.




4 Administrative and legislative framework

4.1. Overview Five agencies have primary responsibility for water management and, in particular flood management in NSW.

The NSW Office of Water is a part of the NSW Department of Trade and Investment, Regional Infrastructure and Services and administers the Water Management Act 2000 under the oversight of the Minister for Primary Industries. The Office of Water’s role in flood management is in relation to:

• developing and implementing the Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003 which sets the rules for how the Tumut River and the Murrumbidgee River and dams are managed, including, for example, rules in relation to flood mitigation, channel capacity

and dam airspace

• issuing works approvals to State Water that regulate the operation of its works, including

Burrinjuck and Blowering dams

• managing the gauging stations and ensuring that the data about flow rates and river heights is

made available to other organisations such as State Water and the SES

• administering Snowy Hydro’s water licence and advising the Minister in relation to proposed

amendments to that licence.

State Water Corporation is a state owned corporation established under the State Water Corporation Act 2004. Prior to its corporatisation in 2004 it was a part of the former NSW Department of Land and

Water Conservation. For this reason a number of documents that arose prior to 2004 are in the name of the Water Administration Ministerial Corporation even though they are now the responsibility of State Water. State Water owns and operates Blowering Dam and Burrinjuck Dam and is responsible for the

delivery of water from these dams to water licence holders on the Tumut and Murrumbidgee Rivers.

State Water’s dam operations are governed in a number of ways:

• Section 49 of the Water Management Act 2000 requires State Water to “have regard to” the

provisions of relevant water sharing plans “to the extent to which they apply” to State Water. Different rules apply to Blowering Dam and Burrinjuck Dam under the water sharing plan and these are considered below.

• State Water must comply with the provisions of its operating licence granted under s11 of the State Water Corporation Act 2004. The operating licence requires State Water to comply with

approvals or water sharing plans that may be issued by the NSW Office of Water and to implement flood planning and other operations instigated by the Dam Safety Committee.5

• State Water must comply with the water supply works approvals issued by the Office of Water in relation to its dams. The works approval requirements are consistent with the provisions of the water sharing plan in relation to flood mitigation, channel capacity and dam airspace. At the time

of the October and December 2010 floods the relevant works approval had not yet been issued by the Office of Water and State Water were relying on “deemed” works approval under clause 8 of schedule 4 to the State Water Corporation Act 2004.

Snowy Hydro Limited operates the Snowy Scheme and gauging stations within the Snowy Scheme area. This is relevant to this review as the Scheme contributes to inflows into Blowering Dam. The requirements of the Snowy Hydro Corporatisation Act 1997, the Snowy Water Licence and the Blowering

Airspace Deed are relevant to this review.

Bureau of Meteorology is established under the Meteorology Act 1955 (Cth). The BOM is responsible for issuing “Flood Watches” and “Flood Warnings”. A “Flood Watch” means that people living or working

along rivers and streams must monitor the latest weather forecasts and warnings and be ready to move

5 Clause 6.1 of the State Water Corporation Operating Licence 2008-2013



to higher ground should flooding develop.”6 A “Flood Warning” is a notice issued by the BOM when river heights at specified points are predicted to exceed the minor, moderate or major flood heights for that point.

The NSW State Flood Plan indicates that Flood Warnings with height predictions are provided by BOM for the Murrumbidgee at Gundagai and Wagga Wagga. There is no requirement to provide Flood Warnings for the Tumut River at Tumut. However local flood advices are provided by the SES. During

the October flood events Flood Warnings were in fact issued by the BOM for Tumut.

Flood Warnings are based on a combination of the predicted downstream impacts of river heights measured at upstream gauging points, recent rainfall measurements, weather forecasts and predicted

additional inflows. In the period 1 October 2010 to 31 December 2010 numerous flood watches and flood warnings were issued in relation to the Murrumbidgee and Tumut Rivers.

BOM short term weather forecasts are used during floods to inform dam management decisions. BOM

forecasts used for this purpose include descriptive forecasts, which indicate the type of conditions expected for a particular day or days (for example “isolated showers”), and quantitative precipitation forecasts, which indicate the expected quantum of precipitation for the next day or two. BOM weather

forecasts are taken into account by dam operators in deciding whether to make releases to create airspace in the dam, the rate at which surcharge should be evacuated from the dam, what inflows can be expected, whether releases should be delayed due to heavy rainfall forecasts downstream of the dam.

Descriptive forecasts are only of limited use for the purposes of flood operations as these forecasts do not indicate the quantity of precipitation. It is also important to remember that forecasts are just that. They provide no guarantees or certainties. There can be very substantial discrepancies between

forecast rainfall and actual rainfall. Such discrepancies occurred during both October and December 2010 flood events. Dam operational decisions which take into account BOM weather forecasts are reviewed and revised depending on the actual weather conditions. This is discussed further in Part 5.

State Emergency Service is established under the State Emergency Service Act 1989. Under section 8 of its Act the SES is the designated “combat agency for dealing with floods (including the establishment of flood warning systems) and to co-ordinate the evacuation and welfare of affected communities”. SES

is responsible for the State Flood Sub-Plan which is a subplan of the New South Wales Disaster Plan. The SES is also responsible for preparing the Local Flood Plans that are in place for each of Gundagai, Tumut and Wagga Wagga. The local flood plans address issues such as preparedness, response and

recovery. They also provide details on matters such as the flood threat, effects of flooding on the community, evacuation arrangements and dissemination of flood bulletins. The SES role is critical however it is not the focus of this review.

Dams Safety Committee is established under the Dams Safety Act 1978. It maintains a “list of prescribed dams, their consequence categories and an assessment of deficiencies and [provides] a new list to the SES State Headquarters whenever the Committee changes the status of a dam”.7 This is an

important role but is not relevant to this review.

6 BOM statement in issued Flood Watches. 7 NSW State Flood Sub-Plan p11.


4.2. Blowering Dam operational requirements Blowering Dam is not a gated dam and accordingly, unlike Burrinjuck Dam, it cannot mitigate floods by using the gates to surcharge the dam. However during a major flood event the dam will still surcharge if

inflows are greater than outflows over the spillway. There is still a significant degree of control over releases by use of the control valves.

The Blowering Dam Emergency Operations Procedures manual was written in 1990 and contains a

section dealing with procedures during flood. There is no legislative requirement to comply with the procedures. The procedures include:

• Contact requirements for key stakeholders including Tumut Caravan Park, SES, Tumut Police,

Ready-Mix Industries, and Gundagai Flood Warning Association.

• A statement that the operational object “is to balance the increasing spillway discharges by

reducing the controllable outlet works … so as not to exceed a predetermined (or variable) flows at various sites”.

• The specified maximum flow rates are 9000 ML at Oddy’s Bridge and 9500 ML at Tumut. The 9,500 ML/day flow requirement at Tumut is marginally more than the flow requirement in the water sharing plan and should be reviewed to ensure consistency.

Handwritten amendments have been made to the procedures manual extracts provided to the Office of Water in relation to contacts and contact phone numbers. State Water contacted the SES on 29 November 2010 and the Gundagai Flood Warning Association on 25 November 2010 and maintained

contact with those bodies throughout the December flood event. State Water has indicated that:

Ready-Mix Industries is no longer operating a dredge in the river, and there is no other business operating at that site.

The other bodies were not contacted as State Water was relying on the SES undertaking this role.

The flood response is coordinated by the SES in accordance with the relevant Local Flood Plans and the State Flood Sub plan. The notifications requirements of the Blowering Dam Emergency Operations

Procedures manual should be reviewed in consultation with relevant agencies and updated.

Significant changes in flow rates (including significant reductions) can increase erosion and for this reason the procedures manual states that “Due to fragile river banks changes are done in 500ML

increments every hour.” It appears that there may have been a slight breach of this procedure on 28 December 2010 when flows measured at Oddy’s Bridge between 10.30am and 11.30am dropped by 631 ML from 7744 ML to 7113 ML.

The water sharing plan has a number of provisions that affect flows in the rivers including flood mitigation requirements, airspace requirements, channel capacity requirements and environmental release requirements. The water sharing plan obligations are made enforceable through the operating licence

and the water supply works approvals. As the obligations are consistent through the various instruments only the obligations under the water sharing plan are specifically referred to below. The extent to which the water sharing plan requirements were complied with is considered at Part 5.2.

In order to provide water licence holders with certainty about their licensed entitlement the Water Management Act 2000 makes compensation payable in certain circumstances if water allocations are reduced as a result of changes to water sharing plans. If it was desired to increase the flood mitigation

role of Blowering Dam or Burrinjuck Dam it may be necessary to amend the water sharing plan. The impacts of such a proposal on water users and the environment would need to be considered prior to making such an amendment and this is beyond the scope of this review.

Flood mitigation requirements

The water sharing plan prescribes that the operation of the Blowering Dam water storage during times of flood and spilling of water must be undertaken to maintain the safety of the dam infrastructure and must




leave the storage full at the completion of the flood event, subject to airspace requirements.8 The full storage obligation reflects the dam’s primary purpose as a water storage dam.

The water sharing plan has no other flood mitigation requirements in relation to Blowering Dam.

Airspace requirements

Airspace operation of Blowering Dam for power generation purposes must be undertaken in accordance with the provisions of the Blowering Airspace Deed between the Water Administration Ministerial

Corporation and the Snowy Hydro Limited.9 This is considered in more detail in Part 5.2 below.

Channel capacity requirements

The water sharing plan provides for the determination and specifying of the maximum operating channel

capacity where required for the purposes of determining extraction rights, managing water releases and providing water under access licences.10 The water sharing plan notes the following constraints on maximum flows but does not require compliance with them:

• 9,000 ML/day in the Tumut River at Oddys Bridge

• 9,300 Ml/day in the Tumut River at Tumut.

The water supply works approval under the Water Management Act 2000 does make these requirements mandatory except in times of flood. However this approval was not issued by the Office of Water until April 2011.

Environmental release requirements.

Clause 15(2) of the water sharing plan imposes different release requirements depending on the inflows into Blowering Dam:

• When natural inflows are less than 560 ML per day then the release from Blowering Dam must be greater than or equal to natural inflows plus any water use (other than basic landholder rights use) expected to occur between the dam and the confluence with the Murrumbidgee River.

• When natural inflows are greater than 560 ML per day then the minimum release from Blowering Dam is 560 ML per day plus the volume of water use (other than basic landholder rights use)

expected to occur between the dam and the confluence with the Murrumbidgee River.

The release requirements are minor compared to the actual releases that were being made throughout the period 1 June to 31 December 2010 and in no way contributed to the October or December 2010

flood events.

4.3. Burrinjuck Dam operational requirements Both the statutory requirements and the non-binding operations manual are considered further below.

The extent to which these were complied with is considered in Part 5.3 below.

4.3.1. Statutory requirements

Flood mitigation requirements

The water sharing plan prescribes that the operation of the Burrinjuck Dam water storage during times of

flood and spilling of water must be undertaken to maintain the safety of the dam infrastructure and must leave the storage full at the completion of the flood event, subject to airspace requirements.11

Airspace requirements

The water sharing plan prescribes that airspace operation of Burrinjuck Dam storage is to be undertaken in accordance with the following principles:

8 Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003 cl 67 9 As above clause 68 10 As above, clause 65. 11 As above clause 67



• To assist in mitigating the impact of floods, a volume of airspace may be maintained which is no greater than that which will be refilled by storage inflows prior to a need to release from the storage to supply downstream requirements. In other words, the storage can be reduced to a level

that is sufficient for it to refill based on the minimum predicted inflows.

• Downstream impact must be considered before releases to obtain airspace are made, including

channel capacity constraints.12

Channel capacity requirements

The water sharing plan provides for the determination and specifying of the maximum operating channel

capacity where required for the purposes of determining extraction rights, managing water releases and providing water under access licences.13

The water sharing plan notes a constraint on maximum flows of 32,000 ML/day in the Murrumbidgee

River at Gundagai but does not require compliance with this. The water supply works approval under the Water Management Act 2000 does make this requirement mandatory except in times of flood. However this approval was not issued by the Office of Water until April 2011.

Environmental release requirements

Burrinjuck Dam has more complex environmental release requirements than Blowering Dam. For the purposes of this report it is not necessary to go into detail on these release requirements. The Office of

Water is satisfied that environmental releases were not a contributor to the October and December 2010 flood events. These floods resulted from the dam exceeding its full storage level and spilling, and not from deliberate discretionary releases for environmental purposes.

Figure 12 Flow downstream from Burrinjuck Dam, October 2010

12 Water Sharing Plan for the Murrumbidgee Regulated River Water Source 2003 clause 68 13 As above, clause 65


4.3.2. Operating procedures

Consistent with its statutory requirements State Water’s objectives in flood operations are to ensure the safety of the structure, mitigate the effect of the flood as far as possible and end the flood with the storage at target level, which is the full supply level.

During flood operations, the bulk of the releases from the dam are made via the three sector gates and the spillway. Sector gates are operated by lowering the gates, thus increasing the spillway opening, and therefore the discharge from the dam.

The Burrinjuck Dam Flood Operation Manual (the Manual) includes procedures for how the dam is to be operated and other information such as key contacts, information on average times of travel of flood peaks in Murrumbidgee and Tumut Rivers, minor, moderate and major flood heights and extent of

flooding by reference to gauge readings at various locations, as well as worked examples. The Manual had not undergone any significant reviews or amendments between 2000 and 2010 due to the drought conditions prevailing in NSW, however, it is still considered to be best practice. Minor changes are made

to the Manual from time to time to update various details such as key contact numbers, gauging station lists and critical flood levels.

The procedures in the Manual are based on the procedure developed by the US Corps of Engineers with

modifications to suit Burrinjuck Dam. The procedures take into account the relationship between gate opening and discharge, calculate the maximum allowable surcharge level and derive the release required based on the storage level (or volume) and the current inflow rate.

The Manual sets out detailed instructions for two types of operating procedures: emergency and forecast procedures. There is also a crisis operating procedure however this was not relied on the October or December flood event and is not considered further.

The Manual includes a list of 30 “downstream landholders and associations to warn of a flood release or impending flood situation following changes to Burrinjuck Dam discharge levels”. State Water has advised that everyone on the list was called on the following dates: 15, 16, 17, 27, and 28 October 2010;

2, 10, 16, 25, and 26 November 2010; and 1, 2, 9, and 14 December 2010.

Emergency procedure

The emergency procedure is a simple procedure designed to ensure the safety of the dam and provide

downstream flood mitigation in circumstances when communications with the dam are impaired, when there is no access to staff with expertise in the more complex forecast procedure or when there is insufficient information available to carry out the forecast procedure. The Burrinjuck Dam operators are

trained in this procedure at least annually.

As the emergency procedure relies on the assumption that the observed inflows are the peak of the flood event, it reduces the operator’s ability to mitigate the flood downstream of the dam in comparison to the

forecast method, which incorporates considerably more information. For this reason the emergency procedure is only used when the forecast procedure is not practical.

The key elements of the emergency procedure are as follows:

1. Inflows to the dam are calculated in accordance with procedures set out in the Manual. This

involves comparing the current storage volume with the storage volume at the last observation. The inflow over this period is the sum of the change in storage volume and the known releases since the last observation. For example, if the storage volume has gone up,

the inflows are equal to the additional volume in the dam plus the releases that were made since the last observation.

2. The inflow and the known storage level are then plotted on a graph (known as a nomogram) and this indicates the rate of release that should be made.

3. The nomogram is based on historical flood profiles and, in particular, knowledge of how the storage inflow will recede based on average conditions following the flood peak. The release rate indicated by the nomogram will result in the dam being at its maximum allowable level




at the point when the dam inflow equals the dam release rate assuming the dam follows the average inflow historical profile and assuming that the observed inflow is at its peak. Following this, the volume of water will start reducing with the intention to leave the storage

at its full supply level at the conclusion of the flood event.

4. The Manual then specifies the release gate settings that are required to achieve the

indicated release rates.

5. As the assumptions about inflow profile and inflows peaking are merely assumptions it is

necessary to regularly repeat the above process and adjust the release rates based on the latest observed data. The calculations are normally revised at one hourly intervals during a flood until the flood has peaked and this is subsequently reduced to two to three hourly

intervals and then six hourly intervals.14

Forecast procedure

The forecast procedure is the same as the emergency procedure except that rather than assuming that

the inflow measured at each observation is the peak inflow it incorporates data such as incoming upstream tributary flows and rainfall information to provide a more refined forecast of the probable peak flow. This forecast peak flow is then used in the same way as the emergency procedure to determine

release requirements that will maximise flood mitigation while ensuring the dam is fully surcharged at the end of the event.

As for the emergency procedure the forecast procedure is an iterative process where the incoming data

and the required releases are regularly reviewed and updated.

While the forecast procedure is more precise it is also considerably more complicated to implement. Prior to the 2010 floods there were three people within State Water and one person within the Office of

Water who were experienced in the use of this procedure. During the December flood event only one State Water officer with experience in this procedure was available, however the Office of Water officer also assisted. These officers were assisted by the State Water Flood Operation Team.

State Water Flood Operation Team

The group within State Water responsible for flood operation of State Water’s dams, including the Burrinjuck Dam, is the Water Delivery Unit. The Strategic Water Services Manager in this Unit directs

flood operations and is responsible for delivering training.

The Flood Operations Team is made up of technical staff from Dubbo and other locations (who would generally operate from State Water’s head office in Dubbo during floods) and who are trained in the

forecast procedure. Team members include engineers, former operators, hydrologists and other technical staff.

The Flood Operations Team works with the flood forecast group of the BOM in NSW and also maintains

close contact with the SES. The Flood Operations Team relies on the forecast information from the BOM and the hydrometric data from various gauging stations operated by the Office of Water and ACTEW. State Water does not itself estimate river heights under flood conditions or issue flood warnings.

When a flood occurs, the Manual directs the storage operators to contact the key personnel in the operations branch of State Water, that is, the Flood Operations Team. It is the Flood Operations Team that performs the calculations in accordance with the Manual to determine the inflows and decides how

the gates are to be operated to achieve the required releases. The Flood Operations Team consults with the BOM, the SES and storage staff and directs the storage staff on the dam operation.

If communication is lost with the Flood Operations Team, or if there is an emergency at the site, control

and decision making responsibility reverts to the storage staff and the Manual directs storage operators to rigidly apply the emergency procedure.

14 Burrinjuck Dam Flood Operation Manual



4.4. Snowy Hydro Limited Snowy Hydro Limited is a company limited by shares. Its shareholders are the Commonwealth Government (13%), New South Wales (58%) and Victoria (29%). Snowy Hydro’s business is managed

by or under the direction of the directors, except where the Corporations Act or the company’s Constitution provides for decisions of the shareholders.15 The directors have a number of legal duties to the shareholders including fiduciary duties.

Section 8 of the Snowy Hydro Corporatisation Act 1997 makes it clear that Snowy Hydro does not represent the State of New South Wales and in particular is not a public authority or an instrumentality or agency of the State.

While Snowy Hydro is not run by the Government its water operations are regulated by the NSW Government through the Snowy Water Licence. Section 34 of the Snowy Hydro Corporatisation Act 1997 makes it an offence for Snowy Hydro to contravene the licence. If Snowy Hydro is found, by a

Court, to have contravened the licence “each person who is a director of the corporation or who is concerned in the management of the corporation is taken to have contravened the same provision if the person knowingly authorised or permitted the contravention”. Under section 34 this carries a maximum

penalty of up to two years imprisonment.

The framework does not give Snowy Hydro ownership of the water in the dams. However under section 23 of the Act Snowy Hydro can exercise the following rights in accordance with the licence:

• the right to collect all water from the rivers, streams and lakes within the Snowy water catchment

• the right to divert that water

• the right to store that water

• the right to use that water to generate electricity, and for purposes that are incidental or related to the generation of electricity or to the management of that water in its works

• the right to release water from storage in accordance with the arrangements made by the licence for the release of that water.

Snowy Hydro is authorised by the licence to release water from the works “at the times and in the quantities that it sees fit” provided that:

• it complies with the water release requirements contained in schedule 4 to the licence and the increased flow requirements in schedule 3 to the licence

• does “all things reasonably necessary to operate the Snowy Scheme in accordance with the … Annual Water Operating Plan”.16

These are considered further below.

4.4.1. Annual Water Operating Plan 2010/11

The purpose of the Annual Water Operating Plan (“AWOP”) is to provide the Minister “with details as to how [Snowy Hydro] proposes to operate the Snowy Scheme during the relevant Water Year within the

parameters set by (1) the Increased Flow Requirements and (2) the Water Release Requirements.” The AWOP is approved in April for the “water year” that commences in May.

The AWOP sets out the following key parameters and the supporting accounting:

• projections of the Required Annual Release (RAR) volume and the Dry Inflow Sequence Volume (if any) under various inflow conditions through the water year

• Minimum quarterly release totals for each development

• Environmental releases to the Snowy River, and to the Snowy Montane Rivers nominated in the

Snowy Water Licence.

15 Snowy Hydro’s Constitution clause 17. 16 Licence clause 7.4.


Under the 2010-11 AWOP, Snowy Hydro was required (on a cumulative basis) to have released 101 GL from the Snowy-Tumut Development by the end of October 2010 and 151 GL by the end of January 2011. In the 2010-11 Water Year, these quarterly release requirements did not in any way compel any

releases during the flood events.

4.4.2. Required Annual Releases from the Snowy-Tumut development

For the purposes of water accounting and release requirements the Snowy Scheme is operated as two separate developments, “the Snowy-Tumut Development” and “the Snowy-Murray Development”. Only

the Snowy-Tumut Development is considered here.

The RAR for the Snowy-Tumut Development is a complex equation that is set out in clause 12.2 of schedule 4 of the Licence. It is recalculated monthly. In summary the RAR is 1026GL subject to

adjustments for a number of matters such as shortfalls in releases from the previous year, inter-valley transfers and the volume of water savings made from the Murrumbidgee catchment for the purposes of effecting environmental flows. 1026GL is the volume of water that could be supplied through the worst

drought on record at the time of when the licence was issued in 2002. At that time this was the 10 year drought between 1936 and 1946. The 1026 GL was set in 1957 and has been used since the start of the fully operational Snowy Scheme in the early 1970s.

As at 1 January 2011, the RAR was 1219 GL. This was made up of:

Snowy Tumut Development Nominal RAR: 1026 GL

Plus Dry Inflow Sequence Volume +481 GL

Minus Excess releases made previously -12 GL

Minus water savings allocated to Snowy Tumut -72 GL

Minus payback of “Borrowed Water” -204 GL

TOTAL RAR: 1219 GL

The dry inflow sequence volume (DISV) and the borrowed water payback are considered further below as these are significant components of the RAR figure and they also varied during the water year.

The DISV and the borrowed water payback are considered further below as these are significant components of the RAR figure and they also varied during the water year.

Dry Inflow Sequence Volume

In addition in recognition that the historic drought of record could be exceeded the licence contains a mechanism to ensure that the Required Annual Release can be reduced if necessary to stop the Snowy Scheme running out of water. This mechanism is the “Dry Inflow Sequence Volume”. The DISV is a

complex equation set out in clause 8 of schedule 4 to the licence. It is accounted continuously from the date that the storages were last “on target”. This last occurred in 1996 and the storages are still well below target levels.

In 2006/07 when the previous drought record was exceeded the DISV led to reductions in the RAR. Shortfalls continued in the subsequent years. In May 2010, at the beginning of the 2010/11 water year, the DISV was 1,223 GL. In the 2010/11 water year due to the increased inflows the DISV recovered to

the point where 481 GL needed to be released in addition to nominal RAR of 1,026 GL.

In April 2010 Snowy Hydro put a proposal to the NSW and Victorian Governments to correct the DISV anomaly. Negotiations on this proposal continued and on 15 June 2011 proposed amendments to

Snowy Hydro’s licence were placed on public exhibition. If these amendments are adopted following consideration of public submissions this will provide better management of water that accumulates in Snowy Hydro storages following an extreme drought period.



Borrowed water payback

The rainfall during 2010/11 also triggered repayment of water borrowed from the Snowy Scheme by irrigators in the Murrumbidgee Valley. This water was “borrowed” by individual irrigators, primarily in

2005, to supplement the very low allocations that were being experienced at that time. These borrow arrangements generally involved Snowy Hydro agreeing to release more than RAR, which was then allocated to the individual irrigation participants in that year. The “borrowed” water was to be repaid by

the participants to Snowy Hydro when certain allocation triggers were met.

In the Murrumbidgee Valley repayment was to commence when announced water allocations reached 50 per cent. The effect of these repayments is that the RAR for the Snowy-Tumut Development was

reduced by the volume of water repaid, which was ultimately the full outstanding balance of the borrows being 204 GL. General Security water allocations reached 100 per cent in the Murrumbidgee Valley on 15 December 2010 and it was only at that point that it became certain that the full amount of the

borrowed water would be repaid.

Variability in the required annual releases

By the end of November 2010 the releases made by Snowy Hydro for the purposes of meeting its RAR

requirements were 785 GL. This occurred over seven months at an average monthly release rate of 112.14 GL. As it was not possible at this time to assume full repayment of the borrowed water, the RAR for the full year was 1423 GL assuming full repayment of the DISV. This would mean a residual

requirement to make releases of 638 GL. If no releases were made towards the RAR in December the required average releases for each of the last four months of the water year would be 159.5 GL. Snowy Hydro’s assessment that making releases towards the RAR in December 2010 would have been

problematic is reasonable for the following reasons:

• The forecast was for continuing wet conditions in the beginning of the 2011 calendar year. For the reasons discussed in Part 4.4.3 this may have restricted Snowy Hydro’s abilities to make releases

from Jounama Dam.

• When Lake Eucumbene is at less than full capacity there are reductions in the capacity of the

Tumut Pondage – Eucumbene-Tumut Tunnel that may have hindered releases of the required quantum being made.

Clause 13 of the licence allows the Office of Water and Snowy Hydro to, in any water year, agree to a reduced RAR. As inflows increased from September, the Office of Water and Snowy Hydro commenced discussions to reduce the RAR for 2010/11 to enable releases through the Snowy-Tumut Development to be reduced. Following the flooding a limited reduction to the RAR was agreed on 23 December 2010.

4.4.3. Snowy Hydro’s flood obligations

Clause 12.4 of the licence states that “if at any time when Blowering Dam is spilling the flow immediately downstream of Blowering Dam exceeds the operating channel capacity of the Tumut River [Snowy Hydro] must not release water from Jounama Dam in a daily volume that exceeds the natural in-flow into

Jounama Dam.” Compliance with this requirement is considered in Part 5.1 below.

While Snowy Hydro has capacity to divert water from Tumut Ponds to Eucumbene to increase the ability of this storage to buffer natural inflows, it is under no obligation to do so. However Snowy Hydro is

required to operate its storages in such a way that it does not exacerbate the flooding by making releases above natural inflows when flooding is occurring downstream of Blowering Dam. Snowy Hydro’s releases in December:

• did not exacerbate the flooding at Tumut (see Part 5.1 below)

• were not in breach of its flood obligations (see Part 5.1 below).




4.4.4. Airspace in Blowering Dam

Blowering Dam is owned and operated by State Water.17 Blowering Power Station is part of the dam and this is leased by State Water to Snowy Hydro. Under the lease agreement State Water is obliged to use its “best endeavours to make water releases from the Blowering Dam in accordance with requests

from [Snowy Hydro]” however this is subject to:

• “the exercise by [State Water] of its obligations and responsibilities at Law”

• “the timing and length of any irrigation season along the Murrumbidgee River” and

• “climatic conditions affecting the Murrumbidgee River”.

Accordingly the lease does not override State Water’s broader dam management responsibilities.

In 2002 the Water Administration Ministerial Corporation (WAMC)18 and Snowy Hydro signed an agreement in relation to the management of airspace in Blowering Dam for power generation purposes.

Clause 68(2) of the water sharing plan requires that the airspace operation of Blowering Dam to be undertaken in accordance with the Blowering Airspace Deed. “Airspace” is defined in clause 5.1 of the Deed as the gross storage capacity of the dam at the spillway crest minus the actual gross storage

volume.

The Deed gives Snowy Hydro the right to specify the airspace in Blowering Dam for power generation purposes that is to be targeted by State Water, for which Snowy Hydro must maintain an equivalent

compensatory volume within the Above Target Water reserves in the Snowy Scheme. The current Deed does not specify an upper limit, but historically up to a maximum of 190 GL has been considered appropriate for Snowy Hydro’s generation needs.

The purpose of this airspace is to ensure Snowy Hydro has a buffer for any significant releases from Jounama Pondage as otherwise, spill from Blowering Dam could exceed the channel capacity of the Tumut River and cause flooding downstream from Blowering Dam. While there may be flood mitigation

benefits these are incidental only. The statement in the Tumut Local Flood Plan that “190,000 megalitres is available for flood storage to reduce flooding in downstream areas”19 is incorrect.

State Water is required to make pre-releases to achieve the airspace requirements. However it is not

required to make any pre-releases:

• at a rate that would exceed the operating channel capacity of the Tumut River at Oddy’s Bridge or Tumut, or

• when flooding is occurring on the Murrumbidgee River.

17 The lease is expressed to be between Snowy Hydro and WAMC as the lease was entered into in May 2002 before the corporatision of State Water in 2004. As part of corporatisation WAMC’s obligations under the deed were transferred to Snowy Hydro. 18 Now the responsibility of State Water as owner of the dam. 19 Annexure A p2


5 Operational decisions Flood operations are complex. They require balancing uncertain weather forecasts, dam storage levels,

delays in flow peaks moving downstream and variable tributary inflows. Flood mitigation involves minimising of the effect of a flood peak downstream of the dam by either minimising the peak outflow or delaying releases to allow for downstream tributaries to subside.

This means that decision making about releases must take into account river travel times between dams, gauging stations and flood susceptible towns and development, predicted inflows both into the dam and from downstream tributaries and weather forecasts. For example:

• If major downstream tributary inflows are predicted it may be possible to reduce releases from upstream storages to reduce the flood peak if there is storage capacity.

• If a major rainfall event is predicted in the dam catchment it may be prudent to make pre-releases to create storage capacity to buffer the predicted inflows.

• Where there are dams in parallel like Blowering and Burrinjuck it may be possible to coordinate their operation to temporarily reduce releases from one of the storages so that the peak below the confluence of the rivers is lessened.

Each of these scenarios occurred in the October and December floods.

5.1. The Snowy Scheme As discussed above if Blowering Dam is spilling and the operating channel capacity of the Tumut River is being exceeded Snowy Hydro must not release water from Jounama Dam in a daily volume that exceeds the natural in-flow into Jounama Dam. Blowering Dam started spilling on 30 November 2010

and the channel capacity of the Tumut River below the dam was exceeded on 9 December and this situation continued until 28 December 2010.

Figure 13 has been provided by Snowy Hydro and maps Jounama natural inflows against Jounama

releases. The accuracy of the data underlying this figure has been reviewed and confirmed by the Office of Water. This indicates that Snowy Hydro reduced the releases from Jounama pondage below the natural inflows on 8 December. This delayed inflows to Blowering Dam thus giving State Water an

additional buffer to delay releases.

Figure 13: Jounama natural releases

Daily Jounama Natural Inflows vs Daily Jounama Release (period 1 Dec 2010 - 20 Dec 2010)

0

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10000

15000

20000

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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Joun Rels




Transfers into Tumut Ponds which is the upper storage on the Tumut River can occur from either Tooma Dam (in the headwaters of the Murray River) or Eucumbene Dam (in the headwaters of the Snowy River). In the period of September to December there was a net transfer from Tumut Ponds to

Eucumbene of 41 GL. This was offset by significant transfers of water from Tooma Dam to Tumut Ponds. It should be noted that:

• Diversions into Tumut Ponds at the time of or in the lead up to the floods may have reduced the

ability of the Snowy Scheme to buffer natural inflows but this does not constitute a breach of Snowy Hydro’s obligations under its licence. Snowy Hydro has stated that these diversions were made to prevent spill of Tooma Dam and thus potentially avoided major flooding in the upper

Tooma River.

• Snowy Hydro complied with its obligations to restrict Jounama releases to natural inflows.

5.2. Blowering Dam operations and Tumut flooding Blowering Dam’s full storage level is 1,631,000 ML. Between 1 June and 30 September 2010 there was a significant improvement in storage levels due to significantly improved inflows. However the critical

period was October, November and December. October inflows were in the top 13 per cent of recorded inflows for that month while November was in the top 11 per cent. The December 2010 inflows were the highest ever recorded for that month.

Figures 6 and 7 (Part 3.2.1) show what occurred during the October and December flood events in the Tumut River. Figure 6 shows the Blowering release rates (as measured at Oddys Bridge) and the flows in the Tumut River and the Goobarragandra River. Figure 6 shows that prior to the major flooding in

October the releases from Blowering Dam were cut sharply and kept at this reduced level until 26 October, well after the flood event had passed. Figure 14 shows the Blowering Dam releases, inflows and storage levels. It demonstrates that during this period the inflows into Blowering Dam were

significant and that the reduced releases were an operational response specifically to mitigate downstream flooding caused by flows in the Goobarragandra River.

Following the October flood event Blowering Dam reached its full storage level on 29 October. From this

time releases largely reflected inflows with some exceptions on 31 October, 16 November and 30 November when releases were restricted in response to BOM forecasts of significant rainfalls. This can also be seen on Figure 6 where the sharp reductions in Blowering releases coincide with increases in

inflows from the Goobarragandra River.

At the time of the December flood event Figure 14 shows that the inflows to Blowering Dam were significantly greater than the releases with the result that the dam started to surcharge. On 10 and 11

December in particular the inflows into the dam were significantly greater than the spillway overflows. The ability to restrict overflows was limited as the dam was already above its full storage level. However the storage surcharge capacity delayed the overflows, allowing the peak in the flows from the

Goobarragandra River to pass and reduced the height of the flooding that would otherwise have occurred in Tumut.

The storage surcharge peaked at 103.8 per cent on 11 December 2010 and the spillway discharge also

peaked. From the 15 December 2010 until 27 December 2010 releases were maintained at levels above the inflow rate by passing water through the release valves while the dam was spilling. This release rate was in excess of the water sharing plan requirements that ensure, where possible, that flows at Tumut

do not exceed 9,300 ML/day which is the limit applicable in normal operating conditions. This decision was taken after consultation with SES and downstream landholders. It was considered necessary to balance the problems of on-going low level flooding with the benefits of more rapidly reducing the dam

surcharge and returning the storage to 100 per cent of capacity.


Figure 14 Storage levels in Blowering Dam October 2010 to December 2010

Blowering Dam1/10/2010 to 31/12/2010

0

10,000

20,000

30,000

40,000

50,000

01-Oct-10

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Full Supply Level Releases

Full Supply Level (1,631,000 ML)

The Dam provided clear flood mitigation benefit:The peak of the outflow from Blowering was approx. 50% lower than the peak of the inflow, meaning the average daily flow in the Tumut River was reduced by about 50%.



Figure 15 Storage levels in Burrinjuck Dam October 2010 to December 2010

Burrinjuck Dam1/10/2010 to 31/12/2010

0

50,000

100,000

150,000

200,000

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01-Oct-10

08-Oct-10

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Inflows Storage Volume

Full Supply Level Releases

Full Supply Level (1,028,000 ML)




5.3. Burrinjuck Dam operations and flooding at Gundagai and Wagga Wagga

Figure 8 shows that Blowering Dam’s contribution to flooding in Gundagai and Wagga Wagga was minimal and accordingly this analysis focuses on the operation of Burrinjuck Dam. Burrinjuck Dam has a full storage level of 1,028,000ML. On 1 July 2010 it was at 41 per cent of capacity and this rose to 100

per cent of capacity on 16 October 2010.

The analysis below is based on information provided by State Water and on information collected by the Office of Water gauging stations. As described above, the emergency and forecast operating procedures

are an iterative process requiring continual review and inputting of new data. The review did not examine the accuracy of each calculation or the specific inputs to each decision. However the hydrometric data is consistent with the application of the procedures and does demonstrate that operation of the dams

achieved flood mitigation.

5.3.1. Status of the dam prior to the floods

Figure 15 shows that a significant increase in inflows into the dam in the middle of October 2010. State Water has indicated that a significant rainfall event in the catchments (90mm over 5 days at the dam)

filled the dam by 16 October 2010. Storage inflows totalled 187,000 ML over 7 days, which is a volume equivalent to 18 per cent of capacity. Spillway releases were delayed as much as possible to allow downstream flows to recede before the peak releases from the spillway. The combined spillway releases

and tributary inflows caused minor flooding at Gundagai. Figure 15 illustrates that during the October flood event the peak inflows were substantially higher than the releases made from the dam at that time. This indicates that a significant degree of flood mitigation was achieved.

5.3.2. Airspace releases prior to the December floods

The dam was near full most of the time from mid October 2010 leading up to the to the December 2010 floods, as illustrated by Figure 15. State Water had to consider the approaching summer and likely increase in demand for irrigation, while creating airspace in the dam in accordance with the airspace

rules (see Part 4.3.1).

There was very limited opportunity for releases to be made from the dam for the purposes of increasing airspace in October and November 2010 due to high inflows into the dam coupled with Blowering spilling

and downstream tributaries contributing most of the Gundagai target flows.20 Generally, releases were continued at maximum permissible rates, that is, subject to Gundagai channel capacity constraints. These constraints effectively limit target flows at Gundagai to under 32,000 ML per day as anything

above that is likely to result in flooding.

Figure 15 shows four airspace releases between the end of October and the end of November 2010. Information from State Water indicates that these were made in response to BOM weather forecasts of

high likelihood of increased inflows.

Airspace releases were made in late November 2010 in response to the forecast of some rainfall in early December 2010. In particular, on the 28 November 2010 Burrinjuck storage was 97.9 per cent full at

1004 GL and experiencing inflows of 2,463 ML per day. At that time there was 24,000 ML of airspace available in the dam. The releases were set at 9,255 ML per day and were made primarily to create additional airspace in the dam. The release rate was restricted as a result of high downstream tributary

flows. The rain continued during this period, recording 38.0 mm on 29 November 2010, 23.2 mm on 30 November 2010 and 24.0 mm on 1 December 2010. During this period the releases were reduced due to increasing flows at Gundagai but were continued at maximum permissible rates.

20 Report on the Burrinjuck Flood Operations 2-6 December 2010 provided by State Water on 15 June 2011



Despite the additional airspace, the increased inflows filled the storage to its full supply level on 30 November 2010. Since the downstream tributaries were contributing large volume of water, which resulted in Gundagai getting to minor flood level, State Water’s initial strategy was to allow the storage to

spill. At that time the BOM was forecasting light rain for the next few days.21

5.3.3. The first December 2010 flood event

By 2 December 2010 Burrinjuck Dam was 103.7 per cent full and experiencing inflows of 39,069 ML per day. There was no longer any available airspace in the dam. Releases were increased to 21,115ML per

day due to increased flows over the fixed spillways. Minor flooding was occurring at Gundagai and river levels were increasing. BOM was forecasting rainfall of 10-20mm.

Burrinjuck Dam staff commenced emergency flood operations procedure (see Part 4.3.2) at 4pm on 2

December 2010. The Strategic Water Services Manager and the Flood Operations Team was briefed on the Burrinjuck flood at 10pm on 2 December 2010. At this point, data from the ACTEW gauging station upstream of the dam was not available and the Flood Operations Team made the decision to continue to

operate the dam in emergency procedure.

A total of 111 mm of rainfall was recorded at the dam for the 24 hours to 8am on 3 December 2010. There had been isolated falls up to 180 mm of rainfall in some parts of the catchment. At 2am on 3

December 2010 the rate of inflows into the dam was 147,170 ML per day and releases were increased to 77,000 ML per day in accordance with emergency procedure.

During the early morning hours of 3 December 2010 there were eight landslides, blocking roadway to the

office and to the gate operations control room. A part of the dam workshop and some of the vehicles parked near the workshop were crushed by the landslide. This also affected the operation of the Office of Water gauging station immediately downstream from Burrinjuck Dam.

As can be seen on Figure 15, during this period there were very large inflows into the storage. The inflows continued to increase rapidly during the morning resulting in increased releases. The inflows ultimately peaked at 11am on 3 December 2010 at 240,610 ML per day, which, in accordance with

emergency procedure, resulted in lowering of all three gates as the dam had reached its maximum induced surcharge level. The rate of releases from the dam at that point was 184,000 ML per day. This means that the peak outflow was reduced to 78 per cent of the peak inflow.

As all gates were now fully lowered, the Flood Operations Team could only monitor the situation and could not take any further flood mitigation action. The storage continued to increase even after lowering all three gates and the spilling continued to increase culminating in the storage reaching a peak at 107.2

per cent capacity at about 4pm on the same day. This means that the peak outflow was delayed by several hours.

Despite the reduction and delay of the peak outflow from the dam, the outflows combined with

downstream tributaries resulted in Gundagai experienced a major flood peaking at 277,000 ML per day.

From the morning of 3 December 2010 the State Water Strategic Water Services Manager was assisted and at times relieved by an Office of Water officer experienced in Burrinjuck flood operation procedures

as at that point the State Water Strategic Water Services Manager had been operating for prolonged periods of time with minimal breaks.

The dam returned to its maximum induced surcharge level at 8pm on 3 December 2010. The Flood

Operations Team decided to leave the sector gates lowered and therefore allow the excess water to leave the storage and the storage to return to its full supply level. This decision was made because at that time the BOM was forecasting heavy rainfall on 8, 9 and 10 December 2010 and airspace needed to

be created to allow for this. The Flood Operations Team also considered downstream impacts as the flood peak had passed and these flows would arrive after the flood peaking at Gundagai.

21 Report on the Burrinjuck Flood Operations 2-6 December 2010 provided by State Water on 15 June 2011



The decision to leave the gates lowered at this point is a departure from the emergency procedure, which dictates that the raising of the gates is to commence once the peak inflows go through and the dam reaches the maximum induced surcharge level, thereby ensuring that the excess water leaves the

dam as slowly as possible. However, the Manual also provides for the departure from this procedure once the consequences in regard to downstream flooding have been evaluated. The decision was therefore consistent with the Manual.

The storage level fell back to its full supply level on 5 December 2010 and the Flood Operations Team commenced raising the gates in order to reduce releases, while still aiming to achieve 30,000 ML of airspace in preparation for the forecasted rain event.

Airspace targets are set by the Flood Operations Team, taking into account the airspace rules outlined in Part 4.3.1. In particular, the Flood Operations Team considers the relevant inflow information, such as current inflows at the dam, upstream gauging stations, catchment wetness conditions and BOM

forecasts, and determines minimum inflows. The Flood Operations Team then assesses the relevant downstream information relating to likely demand for water, unregulated flows and likely Blowering releases / spills to determine the earliest date that releases may be required. The minimum inflow

volume that will occur before the requirement for releases becomes the airspace target volume.22

The target airspace of 30,000 ML was achieved on 7 December and releases were reduced to 12,700 ML per day. As illustrated by Figure 15, this meant that the storage was lowered to 96 per cent of capacity prior to the flood event that commenced on 8 December 2010.

5.3.4. The second December 2010 flood event

During the second December flood event, the Flood Operations Team was able to use the forecast procedure (see Part 4.3.2). From 9 December 2010 the Flood Operations Group used eight hourly

forecast data from the gauging stations Murrumbidgee River at Mt MacDonald, Molongolo River at Scrivener Dam, Yass River at Yass and Goodradigbee at Wee Jasper. As outlined in Part 3.3.1 data from Mt Macdonald and Scrivener Dam gauging stations was not available during the first December

flood event.

The use of the forecast procedure allowed for significantly lower releases in comparison to inflows. This is illustrated in Figure 15. During the second December flood event, inflows into the dam peaked at over

174,360ML per day on 9 December. However, the maximum outflows on that day were 68,000ML per day and were delayed by four hours. Therefore, the combination of the initial airspace and the use of the forecast procedure resulted in the peak outflow constituting only 39 per cent of the peak inflow and the

peak being delayed by four hours.

The forecast procedure was followed until 16 December 2010 and releases were progressively reduced in accordance with this forecast procedure between 11 December 2010 and 16 December 2010.

By 17 December 2010 Burrinjuck was 99.6 per cent full and the Flood Operations Team determined another target airspace and increased releases via the valves in order to achieve that airspace. Releases continued to be reduced and became steady by 21 December 2010 as variable airspace was

being achieved.

5.3.5. State Water’s internal review

State Water has conducted an internal review of the December 2010 flood operations. This review identified that the Burrinjuck flood operations procedure needs to be amended to clarify the

reinstatement of the gates after the maximum induced surcharge level has been exceeded. State Water has indicated that this will bring Burrinjuck’s procedures in line with the other gated storages and would maximise flood mitigation by maximising the volume and duration of flood surcharge below the maximum

induced surcharge level and provide for faster evacuation of the surcharge, that is the excess water to leave the storage, if required for a subsequent forecast event.

22 As per background information provided by State Water by email of 30 June 2011



Conclusion The key findings of this review are set out in the Executive summary. Overall the various agencies

worked effectively together to manage inflows and releases from dams that assisted in mitigating the height and extent of flooding downstream.

There is a degree of tension between the operation of dams for water supply, electricity generation and

flood mitigation:

• If the primary purpose is water supply then the goal is to keep the dams as full as possible.

• Electricity generation requires releases to be made from the dams.

• Flood mitigation can be maximised if there is airspace in the dams.

This review does not consider whether the current balance between these functions is the optimal balance. However in explaining the legislative framework it will hopefully enable an informed discussion of what the balance should be.

review of water management during the 2010 flood events in ...€¦ · t 02 8281 7777 f 02 8281...

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