Department of Environment and Resource Management - Parliamentary Briefing Note To Minister Robertson Prepared for Parliamentary sittings 5 -7 October 2010 WIVENHOE DAM SPILLING - the likelihood of Wivenhoe Dam spilling and safety KEY POINTS • On the 1 October 2010, Wivenhoe Dam reached 100 per cent for the first time since 2001. c • After the weekend's weather, the dam reached 101 per cent on Monday. • On Monday 4 October, Seqwater commenced controlled increased releases from Wivenhoe Dam through the hydro- electric plant in the dam wall. • Even with substantial rain, Wivenhoe Dam's flood capacity is equal to 3 times Sydney harbour - or - 1.45 million megalitres. • Releases from Somerset Dam into Wivenhoe Dam via the cone valves ceased over the weekend. • Seqwater has a Dam Safety Management Program and a Flood Control Centre. The program ensures that each of its dams is operated and maintained in a manner that is both safe and minimises the risks associated with a dam failure and flood events, including working with local councils and emergency services. Contact: Dan Spiller Approved: Mike Lyons, Director, SEQ Water Grid Comms Telephone: Approved: [Insert title of ADG or DOG] Date: 4 October 2010 Approved: Director-General CTS No. 17669/10 1 RESPONSE • On the 1 October 2010 Wivenhoe Dam reached 100 per cent for the first time since 2001. • After the weekend's weather, the dam reached 101 per cent on Monday 4 October 2010. • The trigger level for full gate releases for Wivenhoe Dam is 102.5 per cent. • Also on Monday 4 October, Seqwater commenced controlled C increased release from Wivenhoe Dam through the hydro- electric plant in the dam wall. • The released water passes through the dam's hydro-electric generator before being sent to Mt Crosby Water Treatment Plant as part of the Grid's water supply. • These releases will continue for roughly 10 days, depending on further inflows and weather. • Seqwater expects to have released between 10,000 and C' 12,000 megalitres to reduce Wivenhoe Dam to just below the Full Supply Level. • There is no impact downstream as a result of these releases. • The hydro-electric plant, owned by Stanwell Energy Corporation, is built into the dam wall. • Water is fed through a turbine in the hydro-electric plant to generate renewable energy. Contact: Dan Spiller Approved: Mike Lyons, Director, SEQ Water Grid Comms Telephone: Approved: [Insert title of ADG or DOG] Date: 4 October 2010 Approved: Director-General CTS No. 17669/10 2 • Water supplied for consumption is always released through the hydro-electric plant. SEQ Water Grid flood preparation • Wivenhoe has enormous flood capacity - almost the equivalent of three times Sydney Harbour (1.45 million megalitres). To put this in context, Wivenhoe has received 376,000 megalitres in c flows for the year to date. • As well as the protection of flood storages, Seqwater has a Dam Safety Management Program. The program ensures that each of its dams are operated and maintained in a manner that is both safe and minimises the risks associated with a dam failure and flood events, including working with local councils and emergency services. • The program has been endorsed and approved by the Dam C \ Safety Regulator. • The Flood Control Centre will mobilise during a flood event at North Pine, Somerset or Wivenhoe dams. It operates 24 hours a day with teams of operators at each dam 24 hours a day managing releases. Benefits of the Grid Contact: Dan Spiller Approved: Mike Lyons, Director, SEQ Water Grid Comms Telephone: Approved: [Insert title of ADG or DOG1 Date: 4 October 2010 Approved: Director-General CTS No. 17669/10 3 • The Grid enables us to choose the water use - meaning that it is the most secure water supply in Australia, in drought and when the dams are full. • Heavy rain often causes water quality issues. It drags nutrients and other compounds from the catchments into our water supplies. • With the Grid, we are better prepared for these events than ever before. We can isolate, or blend water from multiples c sources. Wivenhoe Dam operating level • Investigations have commenced into the extent to which the full supply level of Wivenhoe Dam could be raised, without raising the dam wall and while maintaining acceptable risk levels at the dam itself and inundated areas. • We will not take risks with flood safety. C, • The investigation will involve detailed investigations associated with upstream and downstream flooding, environmental considerations, impacts on infrastructure and lease resumptions. • Until the raising of the full supply level is fully assessed, flood waters will be cleared to the existing Full Supply Level in accordance with the existing Flood Operations Manual Contact: Dan Spiller Approved: Mike Lyons, Director, SEQ Water Grid Comms Telephone: Approved: [Insert title of ADG or DOG] Date: 4 October 2010 Approved: Director-General CTS No. 17669/10 4 developed by Seqwater and approved by the Dam Safety Regulator, to ensure public safety is maintained. BACKGROUND Hydro Electric Plant at JNjvenhoe Dam • Wivenhoe Dam hOlY"; a pumped-storage, hydro-electric generating facility. This power station is situ8lc,j between Splityard Creek Dam and Lake Wivenhoe. • During the pumping phase in the operating cycle the generator will operate as an electric motor driving ~,.~ pump to lift water from Lake Wivenhoe to the upper storage of Splityard Creek L< .. :. When peak electricity demand occurs the flow of water is c reversed, flowing frcm the upper to the lower storage and driving the turbine generator to generat,,· 'ectricity. • The pumped storag'.; , Jwer station consists of two circular concrete silos, each of about 32 metres int,rnal diameter. Each of the silos house a 250MW turbine generator and pump ~. • The power station is l';"T1anned and is controlled remotely from the central operating centre for the Que" and power grid system. All aspects of the operation are monitored by competE":> within the centre. Twin 275KV transmission lines connect the power station to Hl" State's grid system Contact: Dan Spiller Approved: Mike Lyons, Director, SEQ Water Grid Comms Telephone: Approved: [Insert title of ADG or DOG] Date: 4 October 2010 Approved: Director·General CTS No. 17669110 5 Department of Environment and Resource Management - Parliamentary Briefing Note To Minister Robertson Prepared for Parliamentary sittings 26 2S Osteber23-25 November 2010 73 WIVENHOE DAM SPILLING - likelihood of spilling and safety KEY POINTS • On the 1 October 2010, Wivenhoe Dam reached 100 per cent for the first time since 2001. • On Saturday 9 October, Seqwater commenced releases from C the Wivenhoe Dam spillway. • Releases continued until 19 October 2010, which included a phased shutdown of the spillway gates. • At the time the Wivenhoe gates were closed on 19th October, small baseflows, supplemented by occasional rainfall, continued to flow into Somerset and Wivenhoe Dams and resulted in both dams rising above Full Supply Level. • Under Flood Manual rules, Seqwater is required to maintain the C flood storage component and return the dams to Full Supply Level. • To date, 15,000 megalitres have been released from Somerset and 72,000 megalitres have been released from Wivenhoe since the gates were closed on 19 October 2010. • No releases are currenty being made from Somerset Dam and a normal operating release of 319 megalitres per day is being maintained from Wivenhoe Dam. Contact: Dan Spiller Approved: Barry Dennien, CEO Water Grid Manager Telephone: Approved: Chris Robson, AlDeputy Director-General Date: 18 October 2010 Approved: CTS No.1 8687/1 0 6 • Wivenhoe Dam's flood capacity is equal to three times Sydney harbour - or - 1.45 million Megalitresmegalitres. • Seqwater has a Dam Safety Management Program approved by the State's Dam Safety Regulator, as well as a Flood Control Centre. • The program ensures that each of its dams is operated and maintained in a manner that is both safe and minimises the C dam failure risks associated with flood events, including developing and implementing working arrangements with local councils and emergency management groups. RESPONSE • On the 1 October 2010 Wivenhoe Dam reached 100 per cent for the first time since 2001. • On Saturday 9 October 2010, Seqwater began releasing water C from Wivenhoe Dam over and above that required for consumption, as a result of flood inflows. • This action is in accordance with the Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam, which is approved by the State's Dam Safety Regulator in accordance with the Water Supply Act 2008. • The current flood release manual was reviewed during 2009 and finalised in January 2010. Seqwater is required to provide Contact: Dan Spiller Approved Barry Dennien, CEO Water Grid Manager Telephone: Approved Chris Robson, NDeputy Director~General Date: 18 October 2010 Approved CTS No. 18687110 7 relevant catchment councils with a copy of the flood manual and this occurred. Councils provided with copies include Somerset Regional Council, Ipswich City Council and Brisbane City Council. • Flood water releases through the dam's spillway gates continued until the morning of 19 October 2010, including a 48 hour phased shutdown. • The phased shutdown allows Seqwater to control the water C through a systematic closure of the gates to discharge stored floodwater to provide for further flood events and to allow Councils to reopen river crossings. • The phased shutdown also aims to minimise adverse environmental impacts on the river system by copying the natural regression of the flood event. • Seqwater released 655,000 megalitres to bring Wivenhoe Dam back Full Supply Level. e . At the time the Wivenhoe gates were closed on 19th October, small baseflows, supplemented by occasional rainfall, continued to flow into Somerset and Wivenhoe Dams and resulted in both dams rising above Full Supply Level.