1 6 October 1992 Complete revision and re-issue November 1997 Complete revision and re-issue. 4 6 September 2002 Complete revision and re-issue

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2 Revision No. Date Amendment Details 0 27 October 1968 Original Issue 1 6 October 1992 Complete revision and re-issue 2 13 November 1997 Complete revision and re-issue 3 24 August 1998 Change to page September 2002 Complete revision and re-issue 5 4 October 2004 Complete revision 6 20 December 2004 Miscellaneous amendments and re-issue 7 November 2009 (approved by Gazette notice 22 January 2010) Complete revision 8 September 2011 Revision but no substantive alteration of objectives, strategies or operating practices 9 November 2011 Insertion of Section 8 and consequential amendments 10 October 2012 Revision but no substantive alteration of objectives, strategies or operating practices 11 November 2013 Revision to take account of changes to the Act and improve clarity, but no substantive alteration of objectives or strategies. Operating practices amended to exclude consideration of Twin Bridges and Savages Crossing following stakeholder input. 12 November 2014 Significant revision including changes from WSDOS investigations, legislative changes and a number of general improvements. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 1

3 TABLE OF CONTENTS Table of Contents Glossary... 6 Preamble The Dams and Catchment Introduction Purpose of the Manual Application Exclusions Role of Seqwater Legal Authority Document Control Significant Changes in this Revision Procedural Matters Preliminary Operational Arrangements Responsibilities of the Duty Senior Flood Operations Engineer Responsibilities of a Duty Flood Operations Engineer Responsibilities of Flood Officers Responsibilities of Dam Supervisors Responsibilities of Dam Operators Qualifications, Experience and Training of Flood Operations Staff Maintaining and Improving the FFS Maintenance of Communications Equipment Flood Mitigation Objectives General Structural Safety of the Dams Inundation of Property Inundation of River and Creek Crossings Retain the Lake Level at near FSL at the Conclusion of the Flood Event Minimise Environmental Impacts on River Bank Stability and Riparian Flora and Fauna Flood Operations Overview Introduction Flood Event Commencement and Ending Operational Strategy Selection and Release Plan Development Use of Forecast Rainfall Alternative Procedures Implementing the Release Plan Bridge Closure Advice Provision of Data to Agencies Wivenhoe Dam Flood Operations Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 2

4 TABLE OF CONTENTS 5.1 Splityard Creek Dam Flood Release Infrastructure Flood Mitigation Strategy Dam Safety Strategy Drain Down Strategy Modification to Flood Operating Procedures if a Subsequent Flood Event Occurs Prior to the Reconstruction of Triggered Fuse Plugs Radial Gate Operation Somerset Dam Flood Operations Flood Release Infrastructure Somerset Dam Strategy Regulator Valve, Sluice Gate and Crest Gate Operation Emergency Flood Operations Introduction Overtopping of Dams Structural Failure of the Dams During Flood Events Dam Operator Actions in the Event of Communications Failure Equipment Failure Failure of the FFS Declarations of Temporary Full Supply Levels for Flood Mitigation Glossary Purpose Application Procedures for Release of Water Stored Above the Temporary Full Supply Level at Wivenhoe Dam Procedures for Release of Water Stored Above the Temporary Full Supply Level at Somerset Dam Modifications to Strategies and Procedures When A Temporary FSL is in Force References Appendix A Control of the Manual Appendix B Somerset Dam Technical Data Appendix C Somerset Dam Auxiliary Equipment Appendix D Somerset Dam Plans, Maps and Photographs Appendix E Wivenhoe Dam Technical Data Appendix F Wivenhoe Dam Breached Fuse Plug Scenarios Appendix G Wivenhoe Dam Radial Gate Operating Considerations Appendix H Wivenhoe Dam Plans, Maps and Photographs Appendix I Key Reference Gauges Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 3

5 TABLE OF CONTENTS Appendix J Bridges and Dam Recreation Areas Impacted By Floods Appendix K Historical Floods Appendix L Flood Forecasting System (FFS) Appendix M Brisbane River Schematic Diagram Appendix N Alternative Procedures Communications Protocol Between the Regulator and Seqwater Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 4

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7 GLOSSARY Glossary In this Manual, save where a contrary definition appears Act means the Water Supply (Safety and Reliability) Act 2008 (Qld) including any subordinate legislation made under it and any legislation amending, consolidating or replacing it; Actual Lake Level means the Lake Level at the staff headwater gauge with reasonable adjustments (where possible made by an engineer) to take into account prevailing conditions; AEP means annual exceedance probability, the probability of a specified event being exceeded in any year; AHD means Australian Height Datum; "Alternative Procedure" has the meaning set out in Section 4.5; "Alternative Urban 3" is a potential operational option examined in WSDOS that the Queensland Government selected as its preferred optimised operational strategy for the Dams during Flood Events, as described in Section 1.6; "Authorisation Request Information" has the meaning set out in Section 4.5; BoM means the Bureau of Meteorology; Catchment inflows upstream of the Dams means the combination of the inflow to Somerset Dam from the catchment above Somerset Dam, and the inflow to Wivenhoe Dam from the catchment above Wivenhoe Dam, excluding any releases from Somerset Dam into Wivenhoe Dam; or the estimated inflow into Wivenhoe Dam if Somerset Dam was not constructed; CEO means the Chief Executive Officer of Seqwater; Chief Executive means the Director-General of DEWS; Controlled Document means a document subject to managerial control over its contents, distribution and storage; Dams means Wivenhoe Dam and Somerset Dam and Dam means either Wivenhoe Dam or Somerset Dam depending on the context used; Dam Crest Flood or DCF means the Flood Event which would result in the Lake Level just reaching the crest level of the Dam; Dam Operator means a person with the required qualifications, experience and training (set out in Section 2.8) who has been approved by Seqwater to fulfil the role of a Dam Operator under this Manual. Responsibilities of Dam Operators are outlined in Section 2.7; Dam Supervisor means the designated senior Dam Operator at Wivenhoe or Somerset Dam as the case may be. Responsibilities of the Dam Supervisor are outlined in Section 2.6; DEWS means the Queensland Department of Energy and Water Supply; DNRM means the Queensland Department of Natural Resources and Mines; "Downstream inflows" means the predicted inflow into the Brisbane River downstream of Wivenhoe Dam excluding releases from Wivenhoe Dam; DTMR means the Queensland Department of Transport and Main Roads; Duty Engineer means either the Duty Senior Flood Operations Engineer or a Duty Flood Operations Engineer; Duty Engineers means both the Duty Senior Flood Operations Engineer and a Duty Flood Operations Engineer; Duty Flood Operations Engineer means a Flood Operations Engineer (or Senior Flood Operations Engineer) who is on duty and, whilst on duty, has the responsibilities set out in Section 2.4 of this Manual. For the avoidance of doubt, more than one Duty Flood Operations Engineer may be on duty at any time; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 6

8 GLOSSARY Duty Senior Flood Operations Engineer means a Senior Flood Operations Engineer who is on duty and, whilst on duty, has the responsibilities set out in Section 2.3 of this Manual. For the avoidance of doubt, only one of the Senior Flood Operations Engineers will be the Duty Senior Flood Operations Engineer at any point in time (even though other persons who are Senior Flood Operations Engineers may be conducting flood operations at the same time); EL means elevation in metres Australian Height Datum; FFS means the Flood Forecasting System. The FFS is described in Appendix L; Flood Event means a flood event that commences in accordance with Section 4.2 or Sections 8.4c or 8.5b and ends in accordance with Section 4.2; Flood Officer means a person with the required qualifications, experience and training (set out in Section 2.8) who has been approved by Seqwater to fulfil the role of a Flood Officer under this Manual. Responsibilities of Flood Officers are outlined in Section 2.5. Flood Operations Centre means the Centre used by Flood Operations Engineers to manage Flood Events; Flood Operations Engineer means a person with the required qualifications, experience and training (set out in Section 2.8) who has been approved by Seqwater to fulfil the role of a Duty Flood Operations Engineer under this Manual; FSL or Full Supply Level means: the level specified in the Moreton ROP; or such other lower level in Wivenhoe Dam or Somerset Dam as shall apply pursuant to the Act or as shall apply under an interim program approved pursuant to the Moreton ROP; but in any case not exceeding EL 67.0 m for Wivenhoe Dam or EL 99.0 m for Somerset Dam; Gauging Station means a location at which rainfall and/or water level is measured. Water level is measured in metres, either in reference to a local datum or Australian Height Datum. Flow in cubic metres per second (m 3 /s) can be inferred using a water level versus discharge rating; judged likely or judges it likely means an event or circumstance being, in the professional engineering judgement of the Duty Engineer, sufficiently certain to occur given the likely consequences associated with any decision which depends upon the judgement; judged unlikely means an event or circumstance being, in the professional engineering judgement of the Duty Engineer, not sufficiently certain to occur given the likely consequences associated with any decision which depends upon the judgement; judged very likely means an event or circumstance being, in the professional engineering judgement of the Duty Engineer, certain or near certain to occur given the likely consequences associated with any decision which depends upon the judgement; Lake Level means the still water surface elevation in a dam and when used in this Manual, "Lake Level" shall mean the Actual Lake Level, unless specifically indicated to the contrary, such as by the use of the prefix "predicted"; Manual or Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam means the current version of this Manual; Monitoring Network means the network of rainfall and water level Gauging Stations which provides data in near real time and enables continuous monitoring of rainfall and stream levels within the Dams' catchments. The Monitoring Network is part of the FFS. Key Gauging Station locations are identified in Appendix I for reference purposes; Moreton ROP means the Moreton Resource Operations Plan; PMPDF means Probable Maximum Precipitation Design Flood; Power Station means the Wivenhoe pumped storage hydro-electric power station associated with Wivenhoe Dam and Splityard Creek Dam; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 7

9 GLOSSARY predicted means, unless the context requires otherwise, the prediction of an event or circumstance made by the Duty Engineer using the FFS in the manner set out in Section 4.3; Probable Maximum Flood or "PMF means the flood resulting from PMP and, where applicable, snowmelt, coupled with the worst flood-producing catchment conditions that can realistically be expected in the prevailing meteorological conditions; Probable Maximum Precipitation" or PMP means the theoretical greatest depth of precipitation for a given duration that is physically possible over a particular catchment area, based on generalised methods; "Release Plan" means a planned sequence of releases, within a strategy, from Wivenhoe and Somerset Dams over the following hours and days developed in accordance with the guidelines in this Manual; Senior Flood Operations Engineer means a person with the required qualifications, experience and training (set out in Section 2.8) who has been approved by Seqwater to fulfil the role of a Duty Senior Flood Operations Engineer under this Manual; Seqwater means the Queensland Bulk Water Supply Authority trading as Seqwater; WSDOS means the Wivenhoe and Somerset Dams Optimisation Study; WSDOS Report means the final DEWS Wivenhoe and Somerset Dams Optimisation Study Report (DEWS 2014). Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 8

10 PREAMBLE Preamble The Dams and Catchment Somerset Dam (on the Stanley River) and Wivenhoe Dam (on the Brisbane River) are located in the Brisbane River basin. The Dams are dual-purpose storages that provide water supply (including drinking water) to South East Queensland, as well as flood mitigation benefits to areas below Wivenhoe Dam potentially impacted by flood flows along the Brisbane River. Flood Events that impact the Dams are caused by rainfall events that vary in intensity, duration and distribution over a total catchment area exceeding 7,000 km² above the Dams. When making decisions about releasing water from the Dams during Flood Events, consideration is also given to rain falling in Brisbane River catchment areas not controlled by the Dams. These catchment areas, which include the Lockyer Creek and Bremer River catchments, cover an area in the order of 6,500 km² and rain falling in these catchments will also vary in intensity, duration and distribution. Maximum overall flood mitigation can be achieved by operating Wivenhoe Dam in conjunction with Somerset Dam. The capacity of the water supply compartment that relates to Wivenhoe Dam s FSL is 1,165,000 ML. The Dam can also store up to a maximum of 1,967,000 ML as temporary flood storage up to EL 80.0 m. For Somerset Dam, the capacity of the water supply compartment related to its FSL is 380,000 ML, with 721,000 ML volume available for use for temporary flood storage up to EL m. A schematic of the Dams, downstream locations and approximate travel times for water released from Wivenhoe Dam is provided in Appendix M. Further descriptions of the Dams are contained in Section 3.2 of this Manual, with more specific details about: Wivenhoe Dam also provided in Section 5.2, Appendix E and Appendix H; and Somerset Dam also provided in Section 6.1, Appendix B and Appendix D. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 9

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12 INTRODUCTION 1. Introduction 1.1 Purpose of the Manual Given the potential significant impact on downstream populations, it is imperative that Wivenhoe Dam and Somerset Dam be operated during Flood Events in accordance with clearly defined operational procedures to protect the structural safety of the Dams and minimise impacts to life and property. The purpose of this Manual is to provide sufficient information and guidance to suitably qualified and experienced professional engineers to allow those engineers to make appropriate decisions on how best to release floodwater from the Dams during Flood Events. Given the indefinitely large number of flood scenarios which can occur, it is not possible or appropriate to provide prescriptive procedures describing how decisions are to be made in all circumstances when managing Flood Events. Rather, the objectives and strategies contained in this Manual are designed to guide Flood Event decision making based on professional judgements by qualified engineers. The strategies and procedures in this Manual have been developed to meet the objectives in Section 3, but in full recognition of: the fact that flood forecasting involves estimation and judgement as there are limitations on being able to (amongst other things): o o accurately estimate flood run-off within the Brisbane River basin; and obtain accurate forecasts of rainfall during Flood Events; and the limitations on being able to: o o identify all potential flood hazards and their likelihood; and remove or reduce community vulnerability to flood hazards. 1.2 Application Exclusions The operational procedures in this Manual do not apply to operational releases made from the Dams. Those releases are governed by the Moreton Resource Operations Plan (Moreton ROP). 1.3 Role of Seqwater Seqwater owns and operates the Dams. During Flood Events, the Dams are managed in accordance with this Manual. Seqwater does not have responsibility under this Manual for: forecasting flood levels along the Brisbane River, Bremer River or Lockyer Creek during Flood Events (this being the responsibility of the Bureau of Meteorology (BoM)); interpreting forecast flood levels to provide local information on areas likely to be inundated or providing local flood warnings to residents (this being the responsibility of local governments and Local Disaster Management Groups); operating Splityard Creek Dam; the closure of roads and bridges. 1.4 Legal Authority This Manual has been prepared and approved as a Flood Mitigation Manual in accordance with Chapter 4 Part 2 of the Act. The operational procedures in this Manual must be used for the operation of the Dams during Flood Events. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 11

13 INTRODUCTION 1.5 Document Control Appendix A describes the document control procedures used for this Manual. Only the current version of the Manual is to be used in the direction of flood operations during Flood Events. 1.6 Significant Changes in this Revision As part of the process of continuous improvement, this Manual is reviewed and updated from time to time. Since Revision 11 of the Manual, a report has been released by the Queensland Government providing the results of the Wivenhoe and Somerset Dams Optimisation Study (WSDOS) (DEWS 2014). WSDOS was initiated in response to the Queensland Floods Commission of Inquiry (QFCOI) to investigate potential alternative operations of the existing Dams during floods. This study into possible improvements to the flood operations of the Dams is the most comprehensive review of operations since Wivenhoe Dam was commissioned in The WSDOS Report was the product of two years of cooperation and knowledge sharing between Queensland Government entities and the Brisbane River catchment councils (Brisbane City, Ipswich City, Lockyer Valley Regional and Somerset Regional councils). The cooperation and knowledge sharing between state and local government has ensured the assessments and findings of WSDOS are evidence based and informed by specialist studies. The purpose of WSDOS was to assess and present various operational options to enable the Queensland Government to make informed decisions on the future operation of Wivenhoe and Somerset Dams. The options have been assessed against competing objectives for Dam operations, in particular balancing water supply security, dam safety, flood inundation impacts downstream of Wivenhoe Dam and economic outcomes. Optimisation of the operation of Wivenhoe and Somerset Dams is particularly challenging because releases from these Dams must take into account flows emanating from downstream tributaries (which are not regulated by the Dams). Ultimately, trade-offs must be made between the key considerations of flood mitigation, water supply security and the structural safety of the Dams whilst having regard to the submergence of bridges, bank slumping, erosion and impacts on riparian flora and fauna. Following the initial release of the WSDOS Report, a community consultation program was undertaken to gather a wide range of views on the presented options. A range of additional investigations were undertaken to further examine the benefits, implications and practicalities of the various options. Following this consultation and investigation process, the Queensland Government has selected as its policy the option known as Alternative Urban 3 as the preferred optimised operational strategy for the Dams during flood events. Alternative Urban 3 bypasses the (Revision 11) Strategy WR, raises the dam safety trigger to EL 75m, and increases the (Revision 11) Strategy WU compartment size. The Department of Energy and Water Supply (DEWS) has thus requested the preparation of a flood mitigation manual for Wivenhoe and Somerset Dams that implements the Alternative Urban 3 operational strategy. Accordingly, the 2014 Manual has been updated to implement this decision, and also to include a number of other identified improvements. Significant changes made in this revision of the Manual are as follows: Changes to flood operation procedures in accordance with WSDOS Alternative Urban 3; Improved description of the Strategy selection and Release Plan development process, including the use of Forecast Rainfall; Additional guidance for emergency scenarios; Additional guidance on historical flood flow recession rates. A number of investigations related to flooding in the Brisbane River are underway, including the Brisbane River Catchment Flood Study (BRCFS) managed by the Department of Natural Resources and Mines (DNRM), and the Brisbane River Floodplain Management Study and the Brisbane River Floodplain Management Plan managed by the Department of State Development Infrastructure and Planning (DSDIP). This Manual will continue to be reviewed and updated on a regular basis, to include learnings from these and other relevant studies, from experience in flood operations and from advances in flood management. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 12

14 PROCEDURAL MATTERS 2. Procedural Matters 2.1 Preliminary This Section 2 identifies a number of procedural requirements regarding the management of Flood Events. 2.2 Operational Arrangements Seqwater must ensure that the following operational arrangements are undertaken: Periods Outside Flood Events: a log of rainfall and stream height Gauging Station availability is maintained; the Dams' radial gates, sluice gates and the regulator valves are kept in good working order at all times and are not to be removed from service for maintenance or any other reason without the specific permission of the Duty Senior Flood Operations Engineer; the Duty Senior Flood Operations Engineer is advised when the Dams radial gates, sluice gates and the regulator valves are returned to service (after being removed from service in accordance with the point above); a Senior Flood Operations Engineer is assigned to the role of Duty Senior Flood Operations Engineer, and at least one Flood Operations Engineer is assigned to the role of Duty Flood Operations Engineer; the Duty Engineers are on call at all times on a 24/7 basis; once a Flood Event is declared under Section 4.2, the Flood Operations Centre is mobilised within two hours. During a Flood Event: a Duty Engineer is on duty at all times in the Flood Operations Centre to direct flood operations at the Dams during Flood Events; at least one Flood Officer is on duty at all times in the Flood Operations Centre to assist the Duty Engineer/s during Flood Events; a Duty Senior Flood Operations Engineer is on call at all times during Flood Events, and able to travel to the Flood Operations Centre to assist with decision making within two hours of being called; at least two Dam Operators are available to operate each of the Dams during a Flood Event, one of which is designated the Dam Supervisor; unless communications are lost between the Flood Operations Centre and the Dams, release of water from the Dams during Flood Events is carried out under the direction of a Duty Engineer; when communications are lost between the Flood Operations Centre and the Dams, release of water from the Dams during Flood Events is to be carried out in accordance with Section 7.4; and records showing the performance of the FFS in predicting Lake Levels and stream flows are available at the conclusion of each Flood Event. 2.3 Responsibilities of the Duty Senior Flood Operations Engineer The responsibilities of the Duty Senior Flood Operations Engineer under this Manual are as follows: Periods Outside Flood Events: lead the on-call team in monitoring conditions and carrying out routine flood preparation activities; and monitor weather forecasts and catchment conditions, and, if the conditions in Section 4.2 are met, declare the commencement of a Flood Event and organise mobilisation to the Flood Operations Centre. During a Flood Event: lead the flood operations team on duty in carrying out Dam operations under this Manual; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 13

15 PROCEDURAL MATTERS set the overall strategy for management of the Flood Event in accordance with the objectives of this Manual and direct the operations of the Dams in accordance with this overall strategy; and seek authorisation from the Chief Executive to adopt Alternative Procedures and adopt Alternative Procedures as described in Section 4.5. An illustration of the key roles involved in operating the Dams in Flood Events is shown in Figure Figure Key Roles During Flood Events (for Wivenhoe, Somerset and North Pine Dam Flood Operations) 2.4 Responsibilities of a Duty Flood Operations Engineer The responsibilities of a Duty Flood Operations Engineer under this Manual are as follows: Periods Outside Flood Events: monitor weather forecasts and catchment conditions, and, if the conditions in Section 4.2 are met, declare the commencement of a Flood Event and organise mobilisation to the Flood Operations Centre. During a Flood Event: direct the operation of the Dams in accordance with the overall strategy determined by the Duty Senior Flood Operations Engineer; and follow any direction from the Duty Senior Flood Operations Engineer in relation to adopting Alternative Procedures, which have been authorised in accordance with Section 4.5. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 14

16 PROCEDURAL MATTERS A Duty Flood Operations Engineer is to follow this Manual in managing Flood Events and is not to adopt any Alternative Procedure unless directed by the Duty Senior Flood Operations Engineer or the Chief Executive. 2.5 Responsibilities of Flood Officers The responsibilities of a Flood Officer under this Manual are as follows: Periods Outside Flood Events: undertake routine flood preparation duties; During a Flood Event: assist the Duty Engineers in undertaking their responsibilities under this Manual. 2.6 Responsibilities of Dam Supervisors When rostered on duty during a Flood Event at a particular Dam, the responsibilities of a Dam Supervisor under this Manual are as follows: carry out operations at that Dam in accordance with directions from a Duty Engineer; and if difficulties are experienced in communications with the Flood Operations Centre, the Dam Supervisor should attempt to contact the Flood Operations Centre using the means listed in Section 7.4. In the event of communications loss between the Flood Operations Centre and the Dam, the Dam Supervisor is to assume responsibility for flood releases from the Dam, and apply the procedures set out in Section Responsibilities of Dam Operators When rostered on duty during a Flood Event at a particular Dam, the responsibilities of a Dam Operator (who is not the Dam Supervisor) under this Manual are as follows: assist the Dam Supervisor in undertaking their responsibilities under this Manual. 2.8 Qualifications, Experience and Training of Flood Operations Staff Qualifications and Experience of Flood Operations Engineers The Flood Operations Engineers (including the Senior Flood Operations Engineers) must hold a current Certificate of Registration as a Registered Professional Engineer of Queensland. Additionally, the Flood Operations Engineers (including the Senior Flood Operations Engineers) must have at least: knowledge of the principles related to the structural, geotechnical and hydraulic design of large dams; and a total of at least five years of suitable experience and demonstrated expertise in at least two of the following areas: o o o o investigation, design or construction of major dams; operation and maintenance of major dams; hydrology with particular reference to flooding, estimation of extreme storms, water management or meteorology; and applied hydrology with particular reference to flood forecasting and/or flood forecasting systems. The above qualification and experience requirements are to apply until they are either rescinded or varied by the Chief Executive. Summary of Requirements for Training of Flood Operations Engineers The Flood Operations Engineers (including the Senior Flood Operations Engineers) are to be trained and to achieve competency in the following areas relevant to the Dams: the requirements of this Manual; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 15

17 PROCEDURAL MATTERS the requirements of the Emergency Action Plans for the Dams; the duties and responsibilities of the Duty Senior Flood Operations Engineer and Duty Flood Operations Engineer roles; the procedures for mobilising the Flood Operations Centre; the procedures for operation of the Flood Operations Centre during Flood Events; any restrictions or limitations which may apply to flood operations at the Dams; the use and operation of the FFS; the requirements contained in Communications Protocol for Releases from Seqwater s Gated Dams. Summary of Requirements for Training of Flood Officers Flood Officers are to be trained to provide assistance to the Flood Operations Engineers during Flood Events and maintain the FFS outside Flood Events. The Flood Officers are to be trained and achieve competency in the following areas relevant to the Dams: the requirements of this Manual; the requirements of the Emergency Action Plans for the Dams; the procedures for operation of the Flood Operations Centre during Flood Events; the use and operation of the FFS; the requirements contained in the Communications Protocol for Releases from Seqwater s Gated Dams. Summary of Requirements for Training of Dam Operators The Dam Operators are to be trained and achieve competency in the following areas for each Dam they operate: the requirements of this Manual; the requirements of the Emergency Action Plans for the Dams; the operation and maintenance of the flood release infrastructure at the Dam; any restrictions on the operations of flood release infrastructure at the Dam; the requirements for dam safety monitoring and surveillance during Flood Events. Annual Briefings and Exercises Briefings and exercises are to be conducted annually in order to maintain and enhance the abilities of flood operations staff, including: an annual briefing prior to 1 October each year of all Flood Operations Engineers, Flood Officers and Dam Operators on the safety status of Dams including any operational restrictions that have been applied to the Dams, FFS updates and Spillway Adequacy Assessments; an annual flood exercise that simulates a Flood Event and tests the application of the Dam Safety Strategy for Wivenhoe Dam; Verification Verification that this Section 2.8 has been complied with is required, including: documenting the training activities and the areas of training covered; checking the registration of each Flood Operations Engineer; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 16

18 PROCEDURAL MATTERS verifying that each Flood Operations Engineer has the required qualifications, experience and competency; verifying that all training has been completed as required; verifying that annual briefings and exercises have been undertaken. A summary of the qualifications, experience and training of flood operations staff is to be included in the Annual Preparedness Report in accordance with the requirements of the Act. 2.9 Maintaining and Improving the FFS The Flood Forecasting System (FFS) is not a single component or model, but an integrated suite of tools used to support flood operations decision making. The components of the FFS are described in Appendix L. Seqwater must: maintain the FFS and have it available for use by the Duty Engineers during Flood Events. provide appropriate levels of backup to enable the FFS to continue to operate under reasonably foreseeable risks such as partial failure of power, communications or network services, improve the practical operation of the FFS by: o o o o implementing improvements identified during Flood Event reviews; improving model calibration as improved data becomes available; updating software in line with industry standards; and improving the coverage and reliability of the data collection network in conjunction with Agencies and the BoM. maintain a record of the performance of the Monitoring Network (being part of the FFS), including revised field calibrations and changes to the number, type and locations of rainfall and stream height gauges. maintain a record of the performance of the FFS and rectify any identified faults as soon as practicable. collect and catalogue all available data and documentation from each Flood Event for future use. provide any information collected that is relevant to the calibration of its Gauging Stations to the BoM and relevant Agencies Maintenance of Communications Equipment Seqwater must provide and maintain equipment to enable communication to exist at all times (as far as practicable) between the Seqwater Flood Operations Centre and Dam Operators at the Dams. This equipment shall include: landline telephone; mobile telephone; satellite telephone; Seqwater radio network; facsimile; and . Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 17

19 FLOOD MITIGATION OBJECTIVES 3. Flood Mitigation Objectives 3.1 General The primary objectives of the operational strategies in this Manual, listed in descending order of importance, are to: protect the structural safety of the Dams; minimise inundation of property; minimise inundation of river and creek crossings; retain the Dams at near FSL at the conclusion of a Flood Event; and minimise environmental impacts on river bank stability and riparian flora and fauna. Achieving these objectives is the aim of flood operations, but circumstances may occur when not all will be met. The balance between the objectives embodied in the strategies and procedures documented in this Manual has been developed over many years through a wide range of studies, extensive experience in historical events, periodic reviews of this Manual and consultation with the community and stakeholders. Most recently, government policy decisions following the release of the WSDOS study has further refined the balance between the objectives (as discussed in Section 1.6). This balance, and the strategies and procedures included in the Manual, are the subject of ongoing study and review. Sections 3.2 to 3.6 below provides additional detail on the five objectives listed above. 3.2 Structural Safety of the Dams The structural safety of the Dams is the primary objective in the operation of the Dams during Flood Events. Techniques for estimating extreme floods show that Flood Events that overtop both Dams are possible. Overtopping of the Dams may result in the failure of the Dams, producing catastrophic flooding consequences downstream and impacting on water supply security for an extended period. Wivenhoe Dam The structural safety of Wivenhoe Dam is of paramount importance. Structural failure of Wivenhoe Dam could have catastrophic consequences. Wivenhoe Dam is predominantly a central core zoned earthfill dam. Such dams are not resistant to overtopping and are susceptible to breaching should the dam overtop. Overtopping is considered a major threat to the security of Wivenhoe Dam. Wivenhoe Dam is overtopped by an event when the Lake Level exceeds EL 80.0 m (the crest level of the saddle dam). The Wivenhoe and Somerset Dam Optimisation Study Simulation of Alternative Flood Operations Options report (Seqwater April 2014) estimates the probability of an event reaching EL 80m is approximately 1 in 50,000 to 1 in 100,000 AEP. The Dam Safety Strategy in Section 5.4 provides the key procedures to protect the safety of Wivenhoe Dam. Section 7.2 provides some guidance on actions in the emergency situation where the maximum safe level is predicted to be exceeded. Somerset Dam The structural safety of Somerset Dam also is of paramount importance. Failure of Somerset Dam could have catastrophic consequences as it may also cause Wivenhoe Dam to fail due to the cascading effect produced when Somerset Dam fails. Whilst Wivenhoe Dam has the capacity to mitigate the flood effects of such a failure in the absence of any other flooding, if the failure were to occur during major flooding, Wivenhoe Dam could be overtopped and destroyed also. Somerset Dam is a mass concrete dam with a crest level of EL m. Concrete dams can generally withstand limited overtopping. Stability calculations have indicated that Somerset Dam can safely withstand being overtopped to a Lake Level of at least EL m, provided all crest gates are fully open. With all crest gates fully open, Lake Levels in Somerset Dam in excess of EL m could cause a dam failure that may occur suddenly and without warning. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 18

20 FLOOD MITIGATION OBJECTIVES The Wivenhoe and Somerset Dam Optimisation Study Simulation of Alternative Flood Operations Options report (Seqwater April 2014) estimates the probability of an event exceeding EL 109.7m is approximately 1 in 20,000 to 1 in 50,000 AEP. If the crest gates are closed, the forces on the dam wall increase. It is considered that Lake Levels in Somerset Dam in excess of approximately EL107.0 m could cause a dam failure that may occur suddenly and without warning. The Somerset Dam Strategy in Section 6 provides the key procedures to protect the safety of Somerset Dam. Section 7.2 provides some guidance on actions in the emergency situation where the maximum safe level is predicted to be exceeded. Closely Spaced Large Floods Historical records show that there is a significant probability of two or more flood producing rain systems occurring in the Brisbane River basin within a short time of each other. A study undertaken by DSITIA (An analysis of the time between closely spaced flood events in South-East Queensland, DSITIA 2013) indicates that the two main climate influences causing floods, namely the Madden - Julian Oscillation and East Coast Lows, can cause consecutive major rainfall events. The DSITIA study has estimated that there is an 8 to 11% chance that a second significant flow event into Wivenhoe Dam could occur in the seven days following an earlier significant flow event. To protect the safety of the Dams against the risk of a second closely spaced rainfall event, it is important that the flood storage is emptied soon after a rainfall event. However, draining the Dams to FSL too quickly may require release rates that increase downstream flooding. The procedures in the Drain Down Strategy in Section 5.5 have been developed to drain the Dams to FSLs in a period that is considered to provide an appropriate balance between the risks of downstream flooding and dam safety. 3.3 Inundation of Property The second objective is to reduce flooding of property on the flood plains below Wivenhoe Dam. Flooding of property (such as residences, personal belongings, commercial premises, industrial equipment, power and water utilities, schools, hospitals, etc.) causes significant financial damage and disruption to the community. Operation of the Dams in accordance with this Manual provides significant flood mitigation benefits to property on the flood plains below Wivenhoe Dam. In this Manual the objective to minimise inundation of property is achieved by procedures that target a flow at Moggill (See the Flood Mitigation Strategy in Section 5.3). Moggill is just downstream of where the last major tributary, the Bremer River, joins the Brisbane River. Accordingly, the flow at Moggill represents the aggregate of flows from the Lockyer Creek, the Bremer River, controlled releases from Wivenhoe Dam and the runoff from local areas between these locations. The flow at Moggill is an important indication of the potential for infrastructure and property inundation. Flooding impacts to infrastructure and property start at around a flow rate of 2000 m 3 /s at Moggill. As flows increase above 2,000 m 3 /s, impacts increase. A flow rate of 4000 m 3 /s at Moggill has been adopted as the threshold for significant over-floor flooding of residential and commercial premises. As flows increase above 4000 m 3 /s the impacts continue to increase. The damage to property may also be reduced by the additional lead time provided to flood warning agencies due to operation of the Dams. This increase in warning time allows residents, businesses and government agencies to take additional actions to manage the effects of flooding, reducing the damage that occurs. It is important to note that during Flood Events, the flow at Moggill (and other locations) is predicted by the Duty Engineer using the FFS. Flow is not measured during Flood Events directly and continuously in real time. Accordingly, references in this Manual to flow rates are references to predictions of such flow rates. 3.4 Inundation of River and Creek Crossings River and creek crossings in the Brisbane Valley will be impacted by flooding, both as a result of Dam operations and independent of Dam operations. Inundation of river and creek crossings in the Brisbane Valley can cause isolation and inconvenience to residents and businesses. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 19

21 FLOOD MITIGATION OBJECTIVES In areas upstream of the Dams, high Lake Levels can inundate river and creek crossings. Downstream of Wivenhoe Dam, river and creek crossings can be affected by a combination of downstream inflows and Wivenhoe Dam releases. For the purposes of this Manual, river crossings are categorised into two groups based on their importance: The Brisbane Valley Highway Bridge at Fernvale (Fernvale Bridge) and Mount Crosby Weir bridges are regionally important transport connections. These bridges have capacities in the order of 1,800-2,000 m 3 /s. In smaller Flood Events, flood operations will endeavour to maintain the trafficability of these two bridges, and hence the procedures in Section 5 and 6 explicitly consider the flow capacities of these bridges. Other bridges have lower usage, have alternative routes available, or have limited flow capacity. The flow capacities of other bridges are not explicitly included in the procedures in Section 5 and 6. Disruption to navigation in the Brisbane River may also be taken into account. This disruption is normally associated with high flood debris loads in the Brisbane River. In most circumstances, this consideration is secondary. 3.5 Retain the Lake Level at near FSL at the Conclusion of the Flood Event As the Dams are a major water supply for South East Queensland, it is important that all opportunities to fill the Dams are taken. The Dams must be near FSL following a Flood Event. However, it is permissible for the Dams to be drained below FSL before final gate closure if it is judged likely that continuing base flow will return the Lake Level to near FSL following gate closure. See the Drain Down Strategy in Section 5.5 for details of the procedures for declaring an event complete. 3.6 Minimise Environmental Impacts on River Bank Stability and Riparian Flora and Fauna Riverine and riparian flora and fauna and their supporting habitats, including river banks, will be impacted by flooding, both as a result of Dam operations and independent of Dam operations. Consideration is given to minimising environmental impacts on river bank stability and riparian flora and fauna and their supporting habitats. The causes of river bank instability are complex and are subject to ongoing research. As at the date of this Manual, scientific research has not identified any objective criteria which could be used to guide the development of Release Plans that aim to minimise environmental impacts on river bank stability. Until further research is available, gate closure sequences that mimic typical natural flood recessions are preferred, as indicated in the Drain Down Strategy in Section 5.5. Near the conclusion of a Flood Event, strategies aimed at minimising harm to fish populations in the vicinity of the Dams' structures are instigated, whilst not adversely impacting on other flood mitigation objectives. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 20

22 FLOOD OPERATIONS OVERVIEW 4. Flood Operations Overview 4.1 Introduction The sections below provide an overview of Dam operations during Flood Events. Section 4.2 provides the conditions for the declaration of a Flood Event and the conditions when a Flood Event may be declared over; Section 4.3 outlines the way in which operational strategies are selected and the operational procedures which apply in each strategy, including the development of Release Plans; Section 4.4 provides guidance on the use of forecast rainfall in developing the Release Plan; Section 4.5 specifies the process should the Duty Senior Flood Operations Engineer consider that an Alternative Procedure would best meet the objectives in Section 3; Section 4.6 provides advice on the implementation of Release Plans; Section 4.7 outlines the provision of advice on the predicted inundation of bridges downstream of Wivenhoe Dam; Section 4.8 outlines the provision of Lake Level and release data to specified agencies. 4.2 Flood Event Commencement and Ending The Duty Engineer will review weather forecasts and catchment conditions and will declare that a Flood Event has commenced when it is judged likely that either: the predicted Lake Level in Wivenhoe Dam will exceed the FSL and a release of water from the radial gates or from the auxiliary spillway will be required; or the predicted Lake Level in Somerset Dam will exceed EL m and a release of water from the sluice gates will be required. For the avoidance of doubt, such declaration may be made before the Actual Lake Level in either of the Dams exceeds the FSL(s). When a Flood Event is declared in accordance with the above, the strategy is set to the Flood Mitigation Strategy at Wivenhoe Dam and the Somerset Dam Strategy at Somerset Dam. Refer to Section 4.3 for guidance on operational strategy selection and the application of operational procedures to develop Release Plans after event commencement. The Duty Engineer will declare that a Flood Event has ended when the conditions listed in the Drain Down Strategy shown in Section 5.5 are met. 4.3 Operational Strategy Selection and Release Plan Development The selection of the operational strategy and the development of the Release Plan at any point in time during a Flood Event is a matter for the professional engineering judgement of the Duty Engineer, based on consideration of: The objectives set out in Section 3. The guidance and procedures set out in Section 4, 5 and 6. The information before the Duty Engineer in respect of: o o o Observed rainfall, observed stream heights and estimated flows (including in downstream tributaries), Actual Lake Levels in the Dams, and weather radar. Predicted stream flows (including in downstream tributaries) and predicted Lake Levels in the Dams. Forecast rainfall information provided by the BoM including qualitative and quantitative rainfall forecast products and weather warnings. The use of rainfall forecasts in the selection of a strategy and the development of the Release Plan is discussed in Section 4.4. A wide range of other factors, including, but not limited to: Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 21

23 FLOOD OPERATIONS OVERVIEW o o o Information from dam operators regarding dam safety, operability of gates, spillway performance, or any other matter for safe operation of the Dams and safety of operators. Information from emergency services, councils and others regarding safety of the public. Potential uncertainties and risks associated with the Dams and catchments, elements of the FFS, and with the strategies and procedures in this Manual. Figure provides an outline of the key steps undertaken in developing and reviewing a Release Plan. Figure Strategy Selection and Release Plan Process As outlined in Figure 4.3.1, the additional data and model results available through the FFS will be utilised in developing an updated Release Plan, after which the Release Plan is implemented. The strategy and Release Plan will change during Flood Events in response to changing rainfall and stream flow conditions. The Duty Engineer will review the Release Plan at a frequency appropriate to the circumstances of the Flood Event, but no less frequently than once per 12 hour shift. There are two strategies (Flood Mitigation Strategy, Dam Safety Strategy) for Wivenhoe Dam, one strategy (Somerset Dam Strategy) for Somerset Dam, and one strategy (Drain Down Strategy) that applies for both Dams. An overview of the strategies for Wivenhoe and Somerset Dam is provided in Figure Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 22

24 FLOOD OPERATIONS OVERVIEW Figure Overview of Strategies Details of the procedures in each Strategy are given in Sections 5 and 6. These procedures have been developed in order to provide an appropriate balance between the objectives in most situations. However, every flood event is different, and if the Duty Senior Flood Operations Engineer considers that an Alternative Procedure would provide an improved outcome in relation to the flood mitigation objectives listed in Section 3 given the circumstances being experienced in a particular Flood Event, the process in Section 4.5 may be applied. It is noted that rainfall and flood predictions are estimates only, and decisions taken in Flood Events are made in a timelimited and data-limited scenario. As the Flood Event progresses, it may be discovered that some earlier Release Plans Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 23

25 FLOOD OPERATIONS OVERVIEW did not have the intended effect as a result of variations in rainfall, routing or other factors. Experience from previous Release Plans may be used to assist in the formulation of the next Release Plan based on the latest information. Overall, the selection of release rates in the Release Plan is a matter for the professional engineering judgement, exercised in real time, by the Duty Engineer. 4.4 Use of Forecast Rainfall Forecast rainfall is useful in considering how a flood event may develop which assists in flood response and disaster management planning and also influences the direction of flood event decision making. However, because rainfall on the ground can take up to 24 hours to flow into the dams and releases from Wivenhoe Dam can take up to 24 hours to reach Brisbane, relying on forecast rainfall when developing release plans can have serious adverse consequences due to the high uncertainties it contains in terms of depth, spatial and temporal accuracy. Australia has a highly variable climate, one of the most variable in the world. The south-east region of Queensland is no exception to this, with a large variability in rainfall evident in the historical record both over space and time. For example, the highest daily rainfall recorded in Queensland occurred at Crohamhurst (located just north of the Brisbane River catchment) 907mm in a single 24 hour period in February Contrast this with the total annual rainfall at Wivenhoe Dam in the water year, 480mm, during the lowest point of the millennium drought (Source: BoM Website). Rainfall intensities in the Brisbane River catchment can vary rapidly from one hour to the next, and from one subcatchment to the next. This high spatial and temporal variability is a particular challenge for weather forecasters. The Bureau of Meteorology (BoM) is the Australian Government agency responsible for weather forecasting. The BoM provides a suite of forecasts and weather warnings over a variety of spatial and temporal scales that inform a range of industries including water supply, construction, power generation, mining, agriculture, tourism and flood management as well as the general public. The BoM forecasts and warnings provide an indication to the Duty Engineer of when an event may be likely and the potential further development of an active event. The Duty Engineer considers BoM weather predictions in making a number of decisions under this Manual, including the decision to mobilise to the Flood Operations Centre, to declare a Flood Event, in the development of a Release Plan, and in the decision to declare a Flood Event complete. As part of the range of forecasts and weather warnings, the BoM produces a number of quantitative rainfall products that provide numerical estimates of rainfall depths for various catchment areas over various timescales. These rainfall forecasts may be numerically included in the FFS to provide an indication of the potential development of a particular event. The Duty Engineer may evaluate a number of potential what-if scenarios based on the provided rainfall forecasts, to explore how Dam operations may be modified in response to possible future conditions. Such scenarios are a useful way for the Duty Engineer to explore the consequences of various operational strategies, although the time constraints of an active event limit the number of scenarios that may be examined. These quantitative forecasts have a high degree of uncertainty. The BoM has advised that the quantitative rainfall forecasts they issue are too unreliable to be used as a basis for predicting definitive future Lake Levels and river flows and making releases from the Dams. While there is often the ability to forecast the potential for a significant rain event to occur in the southeast Qld-northern NSW region, it is difficult (if not impossible) to predict the actual location of the heaviest rain, even with only a few hours notice. (Bergin M and Baddiley P (24 July 2006)), The Water Information Research and Development Alliance (WIRADA) report on the Assessment of the accuracy of NWP forecasts for significant rainfall events at the scales needed for hydrological prediction (Roux & Seed (Sept 2011)) provides an assessment of forecast accuracy, based on an assessment of eight case studies (four in South East Queensland) over It concluded that numerical weather model performance for predicting rainfall is highly variable and that none of the models were able to reproduce rapid changes in mean areal rainfall. Forecast accuracy decreased with lead time, with very little skill evident past day two. In August 2013 the BoM provided further advice reinforcing the uncertainties associated with forecast rainfall products, stating: On some occasions, the 7 day rainfall forecast may provide some indication of the flood-producing potential of systems, but models cannot be relied upon to capture the development of every rainfall event at that timescale. In particular, the models have less skill for higher rainfall intensities and while guidance may indicate that a heavy rainfall event is possible, it is only guidance and thus, should be used in that way. (Webb (30 Aug 2013)) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 24

26 FLOOD OPERATIONS OVERVIEW As described above, forecast rainfall has significant uncertainty associated with its depth, timing and spatial extent. Adverse consequences to flooding, water supply security and dam safety can arise from reliance on rainfall forecasts, for example: If releases are made on the basis of forecast rainfall, and the rain occurs later, in an adjacent catchment, or of less depth than in the forecast, unnecessary flooding may be caused downstream of Wivenhoe Dam. If releases are made on the basis of forecast rainfall on the dam catchments, and the rain actually falls on the downstream catchments, the releases may add to peak flows from downstream catchments, causing unnecessary flooding downstream of Wivenhoe Dam. If releases are made on the basis of forecast rainfall to draw down the dam below FSL, and the rain is less than forecast or occurs in an adjacent catchment, water supply security for South East Queensland may be impacted. If water is held back in the Dam because of forecast rainfall downstream of the Dam, and rain actually occurs upstream of the Dam, the risk of Dam failure or breaching the fuse plug embankment may be increased. The Duty Engineer must carefully consider potential adverse consequences if a Release Plan is developed based on predictions using forecast rainfall. The procedures in this Manual provide a robust method of developing Release Plans based on forecast floods using recorded rainfall, making dam operations responsive to flow predictions beyond the current point in time. The procedures are designed to position the Lake Levels appropriately to respond to future rainfall. Given the very large uncertainty inherent in the rainfall forecasts, the potential adverse consequences associated with implementing a Release Plan that significantly relies on forecast rainfall generally outweighs the potential benefit. Therefore, zero or minimal weight is usually given to the flow and Lake Levels predictions which have been derived from the FFS based on rainfall forecasts when selecting a strategy and developing a Release Plan (other than in the exceptional circumstance referred to below). The exceptional circumstance where weight may be given to predictions which have been derived from the FFS based on forecast rainfall is, if, due to the nature of the rainfall system or other circumstances, the BoM is able to provide a rainfall forecast with a very high probability of occurrence. As discussed in the WSDOS Report (DEWS 2014) Section , there may be scope in the future for the more direct use by Seqwater of BOM forecasts in the operations of the dams but this requires targeted research.... This process would need to be progressed subsequent to WSDOS, owing to the complexity and timelines required to develop processes that would be accepted by experts. In summary, owing to the large uncertainty in the spatial and temporal pattern and the depth of the forecast rainfall, it is not currently possible to define objective criteria for the use of forecast rainfall in the strategies and procedures of this Manual. Accordingly, the degree of weight to be given to the predictions which have been derived from the FFS based on forecast rainfall is always a matter for the professional engineering judgement of the Duty Engineer. 4.5 Alternative Procedures When this Section Applies This Section 4.5 applies if the Duty Senior Flood Operations Engineer reasonably considers that: an operating strategy or procedure set out in Sections 4 to 6 of this Manual does not provide or does not adequately provide for the Flood Event or an aspect of the Flood Event; and to achieve a flood mitigation objective set out in Section 3 of the Manual and respond effectively to the Flood Event it is necessary to: o o disregard an operating procedure set out in Sections 4 to 6 of this Manual (an existing procedure); and observe a different operational procedure (an Alternative Procedure). Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 25

27 FLOOD OPERATIONS OVERVIEW Seeking Authorisation from Chief Executive The Duty Senior Flood Operations Engineer must, on behalf of Seqwater, seek authorisation from the Chief Executive to observe an Alternative Procedure. When seeking authorisation from the Chief Executive, the Duty Senior Flood Operations Engineer must, as soon as practicable, give the Chief Executive the following information (the Authorisation Request Information); the grounds for considering that: o o an existing procedure does not provide or does not adequately provide for the Flood Event or an aspect of the Flood Event; and to achieve a flood mitigation objective set out in Section 3 of this Manual and respond effectively to the Flood Event it is necessary to disregard an existing procedure and observe an Alternative Procedure; the facts and circumstances that are the basis for the grounds; information to identify the existing procedure; details of the Alternative Procedure; the time by which Seqwater would need the Chief Executive to make a decision for Seqwater to be able to respond effectively to the Flood Event; and other information to enable the Chief Executive to make a decision whether or not to authorise the Duty Senior Flood Operations Engineer, on behalf of Seqwater, to disregard the existing procedure and observe the Alternative Procedure. To avoid any doubt, the Duty Senior Flood Operations Engineer can: seek authorisation for a number of Alternative Procedures from the Chief Executive at the one time (but the circumstances which would give rise to each Alternative Procedure being adopted must be identified and the Chief Executive will not decide, as between procedures, which is the most appropriate); and provide the Authorisation Request Information to the Chief Executive orally. If the Authorisation Request Information is provided to the Chief Executive orally, the Duty Senior Flood Operations Engineer must record the Authorisation Request Information provided to the Chief Executive in writing as soon as practicable after giving the Chief Executive the information orally. In making contact with the Chief Executive, the Duty Senior Flood Operations Engineer will use the Alternative Procedures Communications Protocol in Appendix N. Alternative Procedure cannot be adopted unless Authorised by Chief Executive After providing the Authorisation Request Information to the Chief Executive, the Duty Senior Flood Operations Engineer: must not adopt an Alternative Procedure until receiving the advice from the Chief Executive about whether or not the Alternative Procedure has been authorised; and after receiving the advice from the Chief Executive: o o is only authorised to adopt an Alternative Procedure if the Chief Executive gives advice that the Alternative Procedure is authorised; must not adopt the Alternative Procedure where the Chief Executive gives advice that the Alternative Procedure is not authorised; and must not adopt a different operational procedure other than the Alternative Procedure for which authorisation from the Chief Executive was sought. To avoid any doubt, the Duty Senior Flood Operations Engineer is not authorised to adopt an Alternative Procedure where the Chief Executive has been contacted and provided the Authorisation Request Information but is considering the Authorisation Request Information. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 26

28 FLOOD OPERATIONS OVERVIEW Alternative Procedure where the Chief Executive cannot be contacted If the Duty Senior Flood Operations Engineer: makes reasonable efforts to contact the Chief Executive to give the Chief Executive the Authorisation Request Information; but cannot contact the Chief Executive (using the contact methods referred to in Appendix N) within a reasonable time to respond effectively to the Flood Event, or, having made contact with the Chief Executive but before the Chief Executive makes a decision, loses contact with the Chief Executive and cannot re-establish contact by the time in which Seqwater would need a decision on the request; the Duty Senior Flood Operations Engineer: is authorised to adopt an Alternative Procedure considered necessary to respond effectively to the Flood Event; and must, as soon as practicable after failing (after reasonable efforts) to contact the Chief Executive, or losing contact with the Chief Executive, record the Authorisation Request Information in writing and give that information to the Chief Executive. 4.6 Implementing the Release Plan Once the Release Plan is determined, action is then taken to implement the plan. Typically this will include: Directing gate operations at the Dam, and carrying out those directions. Providing advice of predicted downstream bridge inundation to relevant Agencies as described in Section 4.7. Providing data to agencies as described in Section 4.8. Providing general information in respect of the Release Plan through regular Situation Reports, in accordance with the Communications Protocol for Releases from Seqwater s Gated Dams. Monitoring conditions at the Dam as the Release Plan is implemented, in particular any impact on the sidewalls of the plunge pool or unfavourable hydraulic conditions (see Section 5.7). 4.7 Bridge Closure Advice Prior to the public road bridges impacted by releases from Wivenhoe Dam listed in Appendix J being inundated due to releases of water from Wivenhoe Dam, the Duty Engineer should aim to ensure that the agency responsible for the closure of the bridge is notified. This notification should, where practicable, allow sufficient time for the agency responsible to close the bridge in a safe and orderly manner. Runoff from areas downstream of the Dam can inundate these bridges at short notice (independent of dam operations), and bridge flow capacities may change from time to time, so it will not always be possible for the Duty Engineer to provide advance notice of bridge inundation. 4.8 Provision of Data to Agencies At the commencement of a Flood Event, and whenever there is a significant change in flood release strategy, Seqwater shall provide the following organisations with the details of Actual Lake Levels and predicted Lake Levels at Somerset Dam and Wivenhoe Dam, and actual and predicted water releases from Wivenhoe Dam: BoM; DEWS; Brisbane City Council; Ipswich City Council; and Somerset Regional Council. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 27

29 FLOOD OPERATIONS OVERVIEW The contact information for relevant organisations and Agencies is contained in the Emergency Action Plans for the Dams, and communications protocols are contained in Communications Protocol for Releases from Seqwater s Gated Dams. 5. Wivenhoe Dam Flood Operations Wivenhoe Dam can be operated in a number of ways to reduce flooding in the Brisbane River downstream of the Dam. The methods of operation that are used will depend on the origin, magnitude and spatial extent of the rainfall occurring over the Brisbane River basin, an area of some 14,000 km 2. Flood mitigation benefits downstream of Wivenhoe Dam are achieved by operating Wivenhoe Dam in conjunction with Somerset Dam. 5.1 Splityard Creek Dam Splityard Creek is owned and operated by CS Energy. Splityard Creek Dam both pumps water from and discharges water into Wivenhoe Dam for hydro power generation. The full supply volume of Splityard Creek Dam is 28,700 ML (at a FSL of EL m). This volume can be emptied into Wivenhoe Dam within 12 hours and this water can affect the Lake Level in Wivenhoe Dam by up to 300 millimetres when Wivenhoe Dam is close to FSL. Operation of the power station and release of water from Splityard Creek Dam to Wivenhoe Dam is outside the direct control of Seqwater. The potential implications of Splityard Creek Dam operations should be considered when operating Wivenhoe Dam during Flood Events, especially when the Dam Safety Strategy is invoked. To assist with this, a communications protocol between the power station and Seqwater has been developed for use in Flood Events (Communication Protocol with Seqwater for Water Movements Between Splityard Creek Dam and Wivenhoe Dam WIV- COMMS-01). 5.2 Flood Release Infrastructure Radial gates and an auxiliary spillway are the primary infrastructure used to release water during Flood Events at Wivenhoe Dam. The arrangement of the radial gates is shown in Figure The hydro outlet and the regulator valve shown in the diagram can also be used to release water during Flood Events for low flow management purposes. The FSL for Wivenhoe Dam is EL 67.0 m, unless the Minister has declared a temporary full supply level as set out in Section 8. The auxiliary spillway was constructed at Wivenhoe Dam in 2005 as part of an upgrade to improve Wivenhoe Dam's ability to safely pass large floods. The auxiliary spillway consists of a three bay, fuse plug spillway located near the right abutment of the main dam embankment. In association with other works constructed at Wivenhoe Dam, this spillway gives the Dam Crest Flood an AEP of approximately 1 in 100,000. An additional spillway may be constructed at Saddle Dam Two in the future to allow the Dam to safely pass the Probable Maximum Flood. The arrangement of the auxiliary spillway is shown in Appendix E. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 28

30 WIVENHOE DAM FLOOD OPERATIONS Figure Wivenhoe Dam Radial Gates Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 29

31 WIVENHOE DAM FLOOD OPERATIONS 5.3 Flood Mitigation Strategy This strategy focuses on the objective of minimising inundation of property. The primary objective to protect the structural safety of the Dams is met by the strategy exit criteria. At the start of a Flood Event, the strategy for Wivenhoe Dam is set to the Flood Mitigation Strategy. This strategy may also be commenced according to the exit criteria in the other strategies. When in this strategy, the following procedures apply: ID Procedure 1. Determine a Release Plan a b c d At the commencement of an event, the Release Plan should initially aim to maintain Wivenhoe Dam within approximately 0.5m of FSL while: i. Maintaining releases under the predicted peak catchment inflows upstream of the Dams. ii. Maintaining the trafficability of the Mount Crosby Weir Bridge and Fernvale Bridge. iii. Maintaining the flow at Moggill under 2000 m 3 /s. iv. Observing the minimum gate operation intervals provided in Section 5.7. v. Considering issues associated with community safety and disruption to community activities, including the provision of reasonable warning of downstream bridge closures to responsible agencies. Once the above is no longer practical, determine a Release Plan as per 1b-d below. Select a target flow at Moggill to use in the development of a Release Plan. The permitted range for the target flow is between 1800 m 3 /s and 6000 m 3 /s. However, if the peak of the downstream inflows is judged likely to exceed 6000 m 3 /s, then the permitted range for the target flow is between 1800 m 3 /s and the predicted peak of the downstream inflows. Flood damage downstream of the Dam increases as flows at Moggill increase above 2000 m 3 /s, so increases in target flows above 2000 m 3 /s should only be made if the aim of this action is judged likely to mitigate the severity of the flooding downstream of Moggill. Therefore, within the requirements of this strategy, aim to maintain the target flow as low as possible and, where practicable, less than the predicted peak of the downstream inflows. To avoid doubt, the flow at Moggill includes contributions from downstream inflows and Wivenhoe Dam releases. Once a target flow at Moggill has been selected, apply the following principles in developing the Release Plan focussed on the selected target flow at Moggill 1 : i. The Release Plan should aim to maximise releases without exceeding the target flow at Moggill. ii. If downstream inflows are greater than the target flow, aim to minimise releases in periods when downstream inflows are predicted to exceed the target flow. iii. A Release Plan may be developed with the objective of keeping a bridge open if it is considered that this makes only a minor difference to the release rates chosen, or pursuant to procedures 1c(iv) or 5a below. iv. While the Lake Level is below FSL +3m, the Release Plan may be adjusted in order to maintain the trafficability of the Mount Crosby Weir Bridge and/or Fernvale Bridge. v. Observe the minimum gate operation intervals provided in Section 5.7. vi. Provided the above principles are applied, it is permissible for releases to exceed the predicted peak catchment inflows upstream of the Dams. Evaluate the Release Plan by reviewing the predicted peak Lake Level using Figure Adjust the target flow and Release Plan until the predicted peak Wivenhoe Lake Level is judged likely to be lower than the level indicated by Figure Check gate conditions a b In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to the gates being overtopped. In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to adverse turbulence or vibration. 3. Check Somerset Dam Procedures a Check consistency of the Release Plan with the procedures given for Somerset Dam in Section Note the Guidance on Uncertainties in Targeting a Flow at Moggill on the next page. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 30

32 WIVENHOE DAM FLOOD OPERATIONS 4. Check strategy exit criteria a b If the predicted Lake Level is judged very likely to reach EL 75m, the strategy must change to the Dam Safety Strategy. If the rainfall event is judged very likely to be complete or nearly complete, the inflow to the Dams is judged likely to be well understood, and the combined Dam storage volume has started to fall, the strategy must change to the Drain Down Strategy. 5. Consider if the rainfall event is complete or nearly complete a If the rainfall event is judged likely to be complete or nearly complete and it is anticipated that the Drain Down Strategy will be selected in the near future, it is permissible to reduce releases, target a lower flow at Moggill, and/or cease the inundation of additional bridges, even if the Lake Level exceeds the levels shown in Figure Figure Wivenhoe Dam Guide Curve for Flood Mitigation Note: If a temporary FSL is declared, adjust the guide curve in accordance with the guidance in Section 8.6. Uncertainties in Targeting a Flow at Moggill As noted in Section 4.3, Release Plans developed according to the procedures in this Manual may not always achieve the intended result due to a range of factors including: future rainfall on downstream catchments; river routing influences; uncertainty of flow estimates at gauges; modelling uncertainties. This is particularly relevant when aiming to achieve a target flow at Moggill. Water released from Wivenhoe Dam reaches Moggill between 12 to 20 hours or more after the time the release is made. Factors such as those listed above Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 31

33 WIVENHOE DAM FLOOD OPERATIONS may cause the flow at Moggill to exceed the target flow. As stated in Section 4.3 and 4.4 the allowance made for forecast rainfall and other uncertainties is a matter for professional judgement by the Duty Engineer. It is noted that the Wivenhoe Dam Guide Curve shown in Figure is solely a tool used in the development of the Release Plan at a particular time as described in the procedures for the Flood Mitigation Strategy. Should significant rain continue to fall past the time of development of a particular Release Plan, it is expected that Lake Levels will increase and consequently the Target Flow at Moggill will need to be increased. The Wivenhoe Dam Guide Curve is therefore not an applicable tool to evaluate flood mitigation performance based on actual Lake Levels and flow at Moggill post-event. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 32

34 WIVENHOE DAM FLOOD OPERATIONS 5.4 Dam Safety Strategy This strategy focuses on the objective of protecting the structural safety of the Dam. The Dam Safety Strategy may be commenced according to the exit criteria in other strategies. When in this strategy, the following procedures apply: ID Procedure 1. Endeavour to Inform the CEO and Chief Executive a Make reasonable attempts to inform the CEO and the Chief Executive if the Dam Safety Strategy is invoked. 2. Request the Cessation of Hydropower Releases from Splityard Creek Dam a Make reasonable attempts to contact CS Energy to request the cessation of hydropower releases from Splityard Creek Dam into Wivenhoe Dam. 3. Determine a Release Plan focused on Dam Safety a b c d e The primary guideline in developing the Release Plan is that all gates must be fully open before the first fuse plug trigger level is reached (see Appendix E) in order to protect the safety of the Dam. (See Section 5.6 for modifications to this requirement if fuse plug/s have previously breached and have not been reconstructed). Under this primary guideline, the Duty Engineer uses professional judgement to apply procedure 3b or 3c or a combination of both. Table may be used to guide releases from the Dam. If the release rate differs from the release rate in Table when this Strategy is invoked, a Release Plan may be developed using professional judgement and the general guidance provided by the table, and ensuring gates are fully open before the first fuse plug trigger level is reached. A Release Plan that aims to minimise the peak flow at Moggill while protecting the safety of the dam may be developed 2. The Release Plan must be developed so that it is capable of being altered to achieve fully open gates before the first fuse plug trigger level if the Lake Level starts to rise more rapidly than expected. There are no minimum gate opening interval timings in this strategy. As a lower priority to the other guidelines in this strategy, when developing the Release Plan, endeavour to limit very rapid increases in downstream flows. Provided the above principles are applied, it is permissible for releases to exceed the predicted peak catchment inflows upstream of the Dams. 4. Check gate conditions a b In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to the gates being overtopped. In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to adverse turbulence or vibration. 5. Check Somerset Dam Procedures a Check consistency of the Release Plan with the procedures given for Somerset Dam in Section Check strategy exit criteria a b If the Lake Level is judged unlikely to reach EL 75m, the strategy may change to the Flood Mitigation Strategy. If the rainfall event is judged very likely to be complete or nearly complete, the inflow to the Dams is judged likely to be well understood, and the combined Dam storage volume has started to fall, the strategy must change to the Drain Down Strategy. 7. Consider if the rainfall event is complete or nearly complete a If the rainfall event is judged likely to be complete or nearly complete, it is judged very likely that the Lake Level will not reach the fuse plug trigger level, and it is anticipated that the Drain Down Strategy will be selected in the near future, it is permissible to reduce releases to minimise the flow at Moggill. 2 - Developing a Release Plan in this situation is complex in real time. In hindsight the result achieved in applying this procedure may not be optimal. Note also the Guidance on Uncertainties in Targeting a Flow at Moggill under the Flood Mitigation Strategy. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 33

35 WIVENHOE DAM FLOOD OPERATIONS 5.5 Drain Down Strategy for Wivenhoe and Somerset Dams This strategy focuses on draining both Dams to near their FSLs within seven days, while aiming to minimise impacts on property, river crossings, bank stability and riparian flora and fauna. The Drain Down Strategy is commenced according to the exit criteria in other strategies. A single Drain Down Strategy is applied for both Wivenhoe and Somerset Dams. When in this strategy the following procedures apply: ID Procedure 1. Determine a Release Plan for drain down a b c d e The Release Plan should be determined with the aim of reducing impacts downstream as soon as reasonably possible, while returning both Dams to near their FSL within seven days of the commencement of this strategy. The Release Plan should be developed initially to return the Dams to near their FSL within seven days, observing the minimum gate operation intervals provided in Section 5.7 and Section 6.3. However, if a favourable weather outlook is available, the drain down period may be extended if such action: i. aims to reduce flood impacts downstream; and ii. does not extend the total drain down period beyond 14 days; and iii. does not pose significant additional risk to the structural safety of the Dam. Within the drain down period, the guidelines for developing the Release Plan are listed below in order of priority: i. Aim to avoid exceeding the actual peak flow of the flood event at Moggill. ii. Reduce the flow at Moggill to less than 4000 m 3 /s. iii. Reduce the flow at Moggill to a flow between 2000 and 4000 m 3 /s. iv. Reduce the flow at Moggill to less than 2000 m 3 /s. v. Reduce the flow to allow the Fernvale and Mount Crosby Weir Bridges to be opened. vi. Reduce the flow to allow Burtons Bridge to be opened. vii. Reduce the flow to allow Colleges Crossing to be opened. Somerset Dam should generally be drained down with the aim of equalising the percentage of flood mitigation storage used at both Dams. Provided a favourable weather outlook is present, consideration may be given to draining down the Dams at a faster or slower rate in order to reduce impacts on communities and river and creek crossings above Somerset and Wivenhoe Dams, while still achieving the drain down period requirement in procedure 1a and 1b. Relevant levels for upstream infrastructure are in Appendix J. Consideration may also be given to the following factors when developing the Release Plan: i. Minimising community disruption and limiting impacts on community safety. ii. Minimising the impacts on riparian flora and fauna. Appendix K provides some guidance on recession rates for flows below 2000 m 3 /s. iii. Limiting adverse water quality and other impacts on water supplies below Wivenhoe Dam. iv. Ceasing flood releases from Wivenhoe Dam in daylight to allow a safe and adequate fish recovery operation. v. The potential effect of tides and tidal anomalies. vi. The final Lake Levels at the end of the drain down period should be set so that it is judged likely that the Dams will return to near their FSLs taking account of ongoing baseflow from the Flood Event. 2. Check gate conditions a b In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to the gates being overtopped. In accordance with Section 5.7, adjust the Release Plan if it is judged likely that the gate settings in the plan may lead to adverse turbulence or vibration. 3. Check Strategy exit criteria a b During the drain down period, if it is judged likely that actual or forecast rain would mean that significant renewed rises in downstream flows would be required in order to meet the drain down period requirement, and an uncertain weather outlook does not allow procedure 1b to be applied, the Wivenhoe Dam Flood Mitigation Strategy and Somerset Dam Strategy may be recommenced. If both Dams have drained to a level that with consideration of ongoing baseflow, is judged likely to result in the Dams returning to near their FSLs, then the Flood Event may be declared at an end. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 34

36 WIVENHOE DAM FLOOD OPERATIONS 5.6 Modification to Flood Operating Procedures if a Subsequent Flood Event Occurs Prior to the Reconstruction of Triggered Fuse Plugs When one or more fuse plug embankments have been previously triggered, the discharge from the triggered fuse plug/s are to be taken into account when determining the Release Plan. Other than this, there is no change to the Flood Mitigation Strategy or the Drain Down Strategy. In the Dam Safety Strategy, Procedure 3a should be modified as follows when one or more fuse plug embankments have previously been triggered: If one or two fuse plugs have previously been breached and have not been reconstructed, all gates must be fully opened before the lowest fuse plug trigger level for the remaining intact fuse plug/s is reached. If all three fuse plugs have previously been breached and have not been reconstructed, all gates must be fully opened before the Lake Level reaches EL 76.78m. 5.7 Radial Gate Operation Radial Gate Opening and Closing Intervals Rapid opening or closing of the radial gates can cause rapid changes in downstream river levels. Accordingly, the aim in opening or closing radial gates is to operate the gates one at a time at intervals that will minimise adverse impacts. Examples of adverse impacts include: rapid increases at low downstream flow rates can increase downstream levels rapidly, causing risks to public safety. rapid decreases at low downstream flow rates can impact on bank stability and may cause fish to become stranded. long intervals between gate operations reduce the ability of the Dams to provide flood mitigation and adjust to changing circumstances. The following table shows the target minimum intervals for gate operations based on these considerations. The Duty Engineer may select a longer gate operations interval based on professional judgement. The Duty Engineer may reduce these target intervals as necessary in any of the following circumstances: the safety of Wivenhoe Dam is at risk; the radial gates are at risk of being overtopped; or there is a requirement to preserve stored water or to reduce downstream flooding. When directing gate operations at the Dam, the Duty Engineer will take into account the infrastructure and personnel related limitations involved in undertaking rapid gate movements under flood conditions. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 35

37 WIVENHOE DAM FLOOD OPERATIONS Table Target Minimum Intervals for Radial Gate Operations Estimated Flow at Fernvale Bridge Opening interval Closing interval (m 3 /s) 1 Up to minutes 45 minutes minutes 30 minutes minutes 20 minutes minutes 10 minutes (or in the Dam Safety Strategy) No minimum interval No minimum interval 1- The estimated flow downstream of the junction with Lockyer Creek prior to the gate operation. Radial Gate Operation Sequences Under normal operation, the following gate operation sequence should be adopted: The sequence shown in the table below is to be adopted up to all gates being open to five metres. Once all radial gates are open to five metres, gates are operated in the order of 3, 2, 4, 1, 5. Once all radial gates are open to ten metres, gates are generally opened 1m at a time. Once all radial gates are open to fifteen metres, the next opening on each gate generally fully opens that gate, to 17.5m opening. Variations are permitted at any time to reduce or prevent erosion adjacent to and downstream of the Wivenhoe Dam spillway. Any inoperable radial gates are to be dropped from the opening or closing sequences and under these circumstances flow in the spillway should be made as symmetrical as possible. Radial gate closure at Wivenhoe Dam, in usual circumstances, occurs in the reverse order to radial gate opening. During the initial opening or final closure sequences of gate operations, it is permissible to replace the discharge through a radial gate by discharge from the regulator valve or hydro outlet as this allows for greater control of low flows. Table Gate 1 Opening (m) Gate 2 Opening (m) Gate 3 Opening (m) Gate 4 Opening (m) Gate 5 Opening (m) Gate Operated Total Opening (m) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 36

38 WIVENHOE DAM FLOOD OPERATIONS Gate 1 Opening (m) Gate 2 Opening (m) Gate 3 Opening (m) Gate 4 Opening (m) Gate 5 Opening (m) Gate Operated Total Opening (m) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 37

39 WIVENHOE DAM FLOOD OPERATIONS Gate 1 Opening (m) Gate 2 Opening (m) Gate 3 Opening (m) Gate 4 Opening (m) Gate 5 Opening (m) Gate Operated Total Opening (m) Protection of the Spillway Walls The flip bucket spillway is designed to dissipate the energy of the discharge from Wivenhoe Dam. The flip throws the discharge clear of the concrete spillway structures and into a plunge pool where the energy is dissipated by turbulence. Under non-symmetric flow conditions, or when Gates 1 and 5 are not operating, the discharge jet may impinge on the walls of the plunge pool. As these walls have been excavated into erodible sandstone rock, this impingement may cause unpredictable erosion. Upstream migration of this erosion is to be avoided. This can be achieved by operating Gates 1 and 5 to deflect the discharge away from the walls of the plunge pool. Therefore in operating the spillway, the principles to be observed in order of priority are: the discharge jet into the plunge pool is not to impinge on the right or left walls of the plunge pool; and the flow in the spillway is to be as symmetrical as possible. Overtopping of the Gates When operating the Dam, care must be taken to ensure that the radial gates are not overtopped. Overtopping of the radial gates may result in damage that causes the gates to become inoperable. The top and bottom levels of the gates for various gate openings are shown in Appendix E, to enable consideration to be given to this possibility in developing the Release Plan. Additionally, if this condition is observed during flood operations, then the Release Plan should be adjusted to prevent overtopping of the gates. Lifting Radial Gates Clear of the Release Flow At large gate openings, having the bottom edge of a radial gate close to the downstream release flow surface may cause adverse turbulence or vibration that could adversely impact on the radial gates. Accordingly, if adverse turbulence or vibration is observed during flood operations, then the bottom edge of the radial gate should be lifted clear of the water surface. Lowering Radial Gates that have been Lifted Clear of the Release Flow Lowering a radial gate after the bottom edge of the gate has been lifted clear of the water surface may cause adverse turbulence or vibration that could adversely impact on the gate. Accordingly, if adverse turbulence or vibration is observed during flood operations, then the bottom edge of the radial gate should be lowered sufficiently to restore stable orifice flow through the spillway. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 38

40 SOMERSET DAM FLOOD OPERATIONS 6. Somerset Dam Flood Operations Somerset Dam is operated in conjunction with Wivenhoe Dam to maximise the flood mitigation benefits downstream of Wivenhoe Dam. In general terms, this is achieved by maximising the use of the combined flood storage compartments of both Dams. As Somerset Dam is the upstream Dam, decisions on flood releases from Somerset Dam must take into account the Wivenhoe Dam Lake Level. 6.1 Flood Release Infrastructure Crest gates, sluice gates and regulator valves are the primary infrastructure used to release water during Flood Events at Somerset Dam. The crest gates and sluice gates are normally operated either fully open or fully closed. The arrangement of this infrastructure is shown in the diagram below (Figure 6.1.1). The FSL for Somerset Dam is EL 99.0 m, unless the Minister has declared a temporary full supply level as set out in Section 8. Figure Somerset Dam Flood Release Infrastructure As shown in Figure and Figure 4 of Appendix E, at EL m floodwaters commence to flow over the dam crest. To account for this discharge, at Lake Levels above EL m the dam crest is assumed to operate as a broad crested weir with a spillway width of metres. See Appendix B for a list of significant levels at Somerset Dam and associated dam safety risks. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 39

41 SOMERSET DAM FLOOD OPERATIONS 6.2 Somerset Dam Strategy This strategy focuses on the objective of protecting the structural safety of both Dams while aiming to make the best use of the Dams flood storage volume to mitigate flooding downstream of Wivenhoe Dam. At the commencement of a Flood Event: the strategy for Somerset Dam is set to the Somerset Dam Strategy; and the crest gates are fully opened. When in this strategy, the following procedures apply: ID Procedure 1. Determine a Release Plan for Somerset Dam a b Figure provides the Somerset Dam Guide Curve. A Release Plan is to be developed with the objective of matching the predicted Lake Levels to the Somerset Dam Guide Curve at the peak of the Flood Event, observing the minimum gate operation intervals provided in Section 6.3. It is recognised that infrastructure restrictions and the minimum gate operation intervals mean that it will not always be possible to develop a Release Plan where the predicted peak Lake Levels plot close to the Somerset Dam Guide Curve. The Somerset Dam crest gates: i. Are opened at the start of the event, and generally remain open throughout the event. ii. Must be open if the Actual Lake Level of Somerset Dam is above EL m. iii. May be operationally tested under high flow conditions, if the following conditions are met: a. The Actual Lake Level of Somerset Dam is below EL m. b. Only one crest gate is tested at any time. c. Seqwater has provided the Chief Executive with information satisfactory to the Chief Executive which confirms that testing of the gates can be undertaken safely. These tests will provide important information to guide the use of the crest gates in future Flood Events. iv. May be closed with the objective of preventing a fuse plug initiation or protecting the safety of Wivenhoe Dam if the following conditions are met: a. The Actual Lake Level of Somerset Dam is below EL m. b. The potential benefits arising from closure of the crest gates are judged likely to outweigh the risks (both likelihood and consequences) associated with crest gate failure, Somerset Dam failure, Wivenhoe Dam failure and Wivenhoe Dam fuse plug initiation. c. Crest Gate I or Crest Gate P must be fully closed and fully opened under the prevailing flow conditions before proceeding with closure of the remaining crest gates. Closure of the remaining crest gates should only proceed if this initial operational test of a single crest gate is completed successfully. d. Seqwater has provided the Chief Executive with information satisfactory to the Chief Executive which confirms that closure of the gates can be undertaken safely. 2. Check Wivenhoe Dam Procedures a Check consistency of the Release Plan with the procedures given for Wivenhoe Dam in Section Check strategy exit criteria a If the rainfall event is judged very likely to be complete or nearly complete, the inflow to the Dams is judged likely to be well understood, and the combined dam storage volume has started to fall, the strategy must change to the Drain Down Strategy (see Section 5.5). 4. Consider if the rainfall event is complete or nearly complete a If the rainfall event is judged likely to be complete or nearly complete and it is anticipated that the Drain Down Strategy will be selected in the near future, it is permissible to reduce releases to produce an increasing divergence from the Somerset Dam Guide Curve, if it is judged very likely that this can be done without significant additional risk of triggering a fuse plug or to the safety of the Dams. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 40

42 SOMERSET DAM FLOOD OPERATIONS Figure Somerset Dam Guide Curve Note: If a temporary FSL is declared, adjust the guide curve in accordance with the guidance in Section 8.6. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 41

43 SOMERSET DAM FLOOD OPERATIONS Use of the Guide Curve It is noted that the Somerset Dam Guide Curve shown in Figure is solely a tool used in the development of the Release Plan at a particular time as described in the procedures for the Somerset Dam Strategy. Should significant rain continue to fall past the time of development of a particular Release Plan, it is expected that Lake Levels will increase and the Release Plan will need to be re-evaluated. The Somerset Dam Guide Curve is therefore not an applicable tool to evaluate flood mitigation performance based on actual Lake Levels post-event. 6.3 Regulator Valve, Sluice Gate and Crest Gate Operation Operating Intervals Releases from Somerset Dam flow directly into Wivenhoe Dam and therefore the downstream river impact considerations associated with radial gate operations at Wivenhoe Dam do not directly apply to Somerset Dam. The table below shows the target minimum intervals for operating regulator valves, sluice gates and crest gates at Somerset Dam for flood mitigation purposes. These intervals have been chosen to minimise any adverse impacts caused by Lake Level rises above the junction of the Stanley and Brisbane Rivers. The Duty Engineer may use professional judgment to select a longer gate operations interval. The Duty Engineer may reduce these target intervals to whatever value considered necessary in any of the following circumstances: the safety of either or both of the Dams is at risk; there is a need to quickly move towards the Somerset Dam Guide Curve; or there is a requirement to retain stored water or to reduce flooding. When directing gate operations at the Dam, the Duty Engineer will take into account the infrastructure and personnel related limitations involved in undertaking rapid gate movements under flood conditions. Table TARGET MINIMUM INTERVALS FOR FLOOD OPERATIONS Item Opening Closing Regulator valves 30 mins 60 mins Sluice gates (Lake Level < EL m) 120 mins 180 mins Sluice gates (Lake Level > EL m) 60 mins 60 mins Crest gates No minimum No minimum Sluice Gate Operation Sequences The order of operation for opening the sluice gates under each strategy is: L M K N J O I P Sluice gates are to be closed in reverse order of opening. Any inoperable sluice gates are to be dropped from the opening or closing sequences. Regulator Valve Considerations During the initial opening or final closure sequences of sluice gate operations it is permissible to replace the discharge through a sluice gate by the opening of one or more regulator valves. This allows for greater control of low flows and enables a smooth transition on opening and closing sequences. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 42

44 SOMERSET DAM FLOOD OPERATIONS Regulator valves are to be kept fully closed when the tail water level below Somerset Dam is above the invert of the valves (EL m). Operating the valves under these circumstances can damage the valves. This requirement may be ignored if the structural safety of Somerset Dam is at risk. Equipment Failure or Malfunction Procedure If one or more of the regulator valves, sluice gates or crest gates are inoperable during the course of the Flood Event, the openings of the working valves and gates are to be adjusted to provide the required discharge from Somerset Dam. Closing the Crest Gates There are no detailed operational records of instances during which the Somerset Dam crest gates have been used to regulate flow. Accordingly, making a decision to close the crest gates when the Somerset Dam Lake Level is greater than EL m carries with it the risk that the crest gates jam in the closed position. This risk and its consequences must be carefully considered in the formulation of a Release Plan that involves closing the crest gates. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 43

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46 EMERGENCY FLOOD OPERATIONS 7. Emergency Flood Operations 7.1 Introduction While every care has been exercised in the design and construction of the Dams, there still remains a low risk that the Dams may develop an emergency condition as a result of Flood Events or other causes. Vigilance is required to recognise emergency flood conditions such as: occurrence of a flood that may cause overtopping of the Dams; failure of the operation of one or more radial gate, regulator valve, sluice gate or crest gate during a flood; development of a piping failure through the embankment of Wivenhoe Dam; damage to the Dams by earthquake; or damage to the Dams as a result of an act of terrorism. Responses to these conditions are contained in the primary guidance document for emergency conditions at the Dams, the Emergency Action Plans. The sections following provide some additional guidance for particular circumstances, as follows: Section 7.2 provides guidance for possible Dam operations if it is predicted that one or both of the Dams will exceed their maximum safe levels. Section 7.3 provides guidance for possible Dam operations for conditions potentially leading to structural failure below the maximum safe levels. Section 7.4 provides Dam operation procedures for Dam Operators if communications are lost with the Flood Engineers during an event. Section 7.5 provides guidance on potential actions in the event of equipment failure at the Dams. Section 7.6 provides guidance on potential actions in the event of failure of components of the FFS. 7.2 Overtopping of Dams As described in Section 3.2, the structural safety of the Dams is the primary consideration in the operation of the Dams during Flood Events. In the extreme circumstance that it is predicted that one or both of Wivenhoe and Somerset Dams will exceed their maximum safe levels, EL 80.0m at Wivenhoe Dam, and EL m at Somerset Dam (all crest gates open), a Release Plan may be developed using professional judgement in an attempt to minimise the likelihood of dam failure and/or to maximise the chance that one of the Dams may survive. In this circumstance, reasonable attempts should be made to inform the CEO and the Chief Executive and consult and collaborate on the available options, the proposed Release Plan, and the Release Plan to be adopted. Whatever the circumstances, every endeavour must be made to prevent the Lake Levels reaching these critical levels. Should it be judged very likely that Wivenhoe Dam will fail, consideration should be given to minimising the chance of Somerset Dam also failing. Should it be judged very likely that Somerset Dam will fail, consideration should be given to the ability of Wivenhoe Dam to absorb the flood wave from Somerset Dam. Should it be judged very likely that both Dams will exceed their maximum safe levels, a Release Plan that matches the predicted maximum increase of each lake level above their maximum safe levels may be considered. The behaviour of the Dams at such extreme levels is highly unpredictable. The concrete Somerset Dam may be better able to withstand a greater depth of overtopping than the earthfill Wivenhoe Dam, but the extent of erosion downstream of Somerset Dam in such a large event is unpredictable, and failure of Somerset Dam may lead to a cascade failure of Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 45

47 EMERGENCY FLOOD OPERATIONS Wivenhoe Dam. It is acknowledged that a Release Plan developed to minimise the likelihood of dam failure and/or to maximise the chance that one of the Dams may survive may not achieve its objectives. 7.3 Structural Failure of the Dams During Flood Events The Dams may fail at levels below the maximum safe levels nominated in this Manual in Flood Events owing to failure modes such as described in Section 7.1. In this circumstance, an Alternative Procedure may be developed using professional judgement in an attempt to minimise the likelihood of Dam failure and/or to maximise the chance that one of the Dams may survive. In this circumstance the Alternative Procedures provisions in Section 4.5 applies. The behaviour of the Dams under these conditions is highly unpredictable. It is acknowledged that a Release Plan developed to minimise the likelihood of Dam failure and/or to maximise the chance that one of the Dams may survive may not achieve its objectives. 7.4 Dam Operator Actions in the Event of Communications Failure During a Flood Event, it is possible that communications could be lost between a Dam and the Flood Operations Centre. If difficulties are experienced in communications with the Flood Operations Centre, the Dam Supervisor should attempt to contact the Flood Operations Centre using each of the following means: landline telephone; mobile telephone; satellite telephone; Seqwater radio network; facsimile; ; via other Seqwater personnel using the contact details contained in the Emergency Action Plans for the Dams; via the Dam Supervisor at the other Dam or via the Dam Supervisor at North Pine Dam; and via Police and Emergency Services personnel. If attempts at direct communications fail, but one or more of these communication sources remains operable, the Dam Supervisor should attempt to contact the Seqwater personnel listed in both the Wivenhoe Dam and Somerset Dam Emergency Action Plans to determine if a line of communication can be established with the Flood Operations Centre indirectly. If communications still cannot be established with the Flood Operations Centre, the Dam Supervisor is to follow the procedures set out below. Wivenhoe Dam Loss of Communications Procedure In the event of communications loss between the Flood Operations Centre and Wivenhoe Dam, the Dam Supervisor at Wivenhoe Dam is to assume responsibility for flood releases from the Dam. Once it has been established that communications have been lost, the Dam Supervisor at Wivenhoe Dam is to: take all practicable measures to restore communications and periodically check the lines of communication for any change; log all actions in the event log; remain in the general vicinity of Wivenhoe Dam while on duty; follow the procedures set out below to determine the appropriate radial gate openings; and ensure Wivenhoe Dam is near FSL at the end of a Flood Event. If communications with the Flood Operations Centre are lost, appropriate radial gate openings at Wivenhoe Dam are determined by following the radial gate operating sequence as set out in the following table. Where one or more fuse Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 46

48 EMERGENCY FLOOD OPERATIONS plugs in the auxiliary spillway have been eroded, the relevant table contained in Appendix F is to be substituted for the table below. Table Lake Level Gate 1 Opening Gate 2 Opening Gate 3 Opening Gate 4 Opening Gate 5 Opening Total Opening Discharge Gate Operated EL (m) (m) (m) (m) (m) (m) (m) (m 3 /s) , , , , , , , , , , , ,680 5 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 47

49 EMERGENCY FLOOD OPERATIONS Lake Level Gate 1 Opening Gate 2 Opening Gate 3 Opening Gate 4 Opening Gate 5 Opening Total Opening Discharge Gate Operated EL (m) (m) (m) (m) (m) (m) (m) (m 3 /s) , , , , , , , , , , , , , , , , , , , , , , ,2,4, ,2,3,4, ,2,3,4, ,2,3,4, ,2,3,4,5 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 48

50 EMERGENCY FLOOD OPERATIONS Lake Level Gate 1 Opening Gate 2 Opening Gate 3 Opening Gate 4 Opening Gate 5 Opening Total Opening Discharge Gate Operated EL (m) (m) (m) (m) (m) (m) (m) (m 3 /s) ,2,3,4, ,2,3,4, ,2,3,4, ,2,3,4, ,2,3,4, ,2,3,4, ,2,3,4, Fully Open ,2,3,4, Fully Open Fully Open The table above shows individual sequence steps against a target Lake Level. The minimum time intervals between each step in the radial gate opening sequence are shown in the table below. Falling behind or being in front of the target gate openings is permissible when the Lake Level is less than EL 74.0 m, but not allowed when the Lake Level is greater than EL 74.0 m. When the Lake Level is below EL 74.0 m, the operating intervals shown in the table below must be followed and can only be reduced to protect the structural safety of Wivenhoe Dam. Table Minimum Intervals Between Operating Sequence Steps Item Minimum Opening Interval Minimum Closing Interval Radial gates (Lake Level < EL 74.0 m) 10 minutes 20 minutes Radial gates (Lake Level EL 74.0 m) No minimum No minimum When operating under this scenario, care must also be taken to ensure the radial gates are not overtopped. Overtopping of the radial gates may result in damage that causes the gates to become inoperable. Accordingly, the minimum radial gate openings shown in the following table apply to ensure the radial gates are not overtopped. Table Minimum Radial Gate Openings to Prevent Overtopping Lake Level (m AHD) Minimum Radial Gate Opening (required for all gates) (metres) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 49

51 EMERGENCY FLOOD OPERATIONS In the event of one or more radial gates becoming jammed, the remaining gates are to be operated to provide the same total gate opening (in metres) for a particular Lake Level, as shown in the table above. In the event of one or more radial gates becoming jammed, while one or more fuse plugs in the auxiliary spillway have been eroded, the relevant table contained in Appendix F shows the total gate opening (in metres) for a particular Lake Level that is to be matched. In these circumstances, gates are preferably operated in the order of 3, 2, 4, 1, and 5 moving through the sequence shown in the table. Under these circumstances, the bulkhead gate is only to be used to prevent a situation occurring which could endanger the safety of Wivenhoe Dam. When extreme rises in Lake Level are being experienced, Dam Operators may have difficulty in continually matching minimum gate openings to Lake Level. In these circumstances it is permissible to estimate target Lake Levels one hour in advance, based on Lake Level rises in the previous hour and undertake gate operations on this basis. Somerset Dam Loss of Communications Procedure In the event of communications loss between the Flood Operations Centre and Somerset Dam, the Dam Supervisor at Somerset Dam is to assume responsibility for flood releases from the Dam. Once it has been established that communications have been lost, the Dam Supervisor at Somerset Dam is to: take all practicable measures to restore communications and periodically check the lines of communication for any change; follow the procedures set out below to determine the appropriate regulator valve, sluice gate and crest gate settings; log all actions in the event log; remain in the general vicinity of Somerset Dam while on duty; and ensure Somerset Dam is near FSL at the end of a Flood Event. The following actions apply at Somerset Dam if communications with the Flood Operations Centre are lost: Unless communications with Wivenhoe Dam are available, the Wivenhoe Dam Lake Level is to be assumed as the level shown on gauge boards located downstream of Somerset Dam. The crest gates are normally to be kept fully raised to allow uncontrolled discharge. However, if some crest gates are closed when communications are lost, these gates may be kept closed if the dam level is under EL106.5 m. Follow the instructions included on Figure regarding opening crest gates. In all circumstances, all crest gates must be opened before the dam level reaches m. The regulator valves are to be closed and in nearly all circumstances kept closed if the tail water level exceeds EL m. The only exception to this is that the regulator valves may be used to protect the safety of Somerset Dam if Wivenhoe Dam is not in danger of overtopping and the Somerset Dam Lake Level exceeds EL m. The sluice gates are operated as either fully opened or fully closed. The order of operation for opening the sluice gates is LMKNJOIP. Sluices are to be closed in reverse order of opening. Any inoperable sluices are to be dropped from the opening or closing sequences. Plot the current Lake Level in Wivenhoe and Somerset Dams on Figure and take the action indicated. Table Somerset Dam Lake Level (m AHD) Maximum Allowable Number of Open Sluice Gates Less than or equal to EL Between EL and EL Between EL and EL Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 50

52 EMERGENCY FLOOD OPERATIONS Somerset Dam Lake Level (m AHD) Maximum Allowable Number of Open Sluice Gates Between EL and EL Between EL and EL Between EL and EL Between EL and EL Between EL and EL Greater than EL Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 51

53 EMERGENCY FLOOD OPERATIONS Figure Somerset Dam Loss of Communications Procedure Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 52

54 EMERGENCY FLOOD OPERATIONS 7.5 Equipment Failure In the event of equipment failure the action to be taken is indicated in Appendix G for Wivenhoe Dam and Appendix C for Somerset Dam. 7.6 Failure of the FFS The FFS is a robust system with a number of levels of redundancy in the Monitoring Network, Data Collection Component, Modelling Platform and Dam Operations Module, and the logistical systems (power, computer network, communications, office space/equipment, etc) supporting these components. Failure of one or more components of the FFS can reduce the accuracy and reliability of the FFS and result in the development of sub-optimal Release Plans. Should one or more components of the FFS and/or logistical systems fail or partially fail, the Duty Engineer may apply appropriate alternative methods to develop Release Plans based on professional judgement. In the event of critical failure of the FFS and/or logistical systems, the Duty Engineer may use the Loss of Communications Procedures (described in Section 7.4) to guide the operation of the Dams. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 53

55 DECLARATIONS OF TEMPORARY FULL SUPPLY LEVELS FOR FLOOD MITIGATION 8. Declarations of Temporary Full Supply Levels for Flood Mitigation 8.1 Glossary In this Section 8: Declaration means a declaration by the Minister under section 395 of the Act pursuant to which a temporary full supply level for Somerset Dam and / or Wivenhoe Dam is set to mitigate the impacts of a potential flood; Minister means the Minister (or the Minister's delegate) administering the Act; and temporary full supply level means the Lake Level for a Dam specified in a Declaration. 8.2 Purpose Section 8.3 to 8.5 sets out the operational procedures that apply to releases of water which are to be made to lower the Actual Lake Level of a Dam to a temporary full supply level, which has been declared by the Minister to mitigate the impacts of a potential flood. Section 8.6 provides guidance on the changes to be made to the operational procedures in Sections 5, 6 and 7 when a temporary FSL applies. 8.3 Application a. The operational procedures in this Section 8 only apply where: i ii. a Declaration is made and, at the time the Declaration is made (whether or not the temporary full supply level has commenced), the Actual Lake Level in a Dam exceeds the temporary full supply level; or following a Declaration and a release of water under this Section 8, but before the commencement date of the temporary full supply level set in the Declaration, the Actual Lake Level rises above the temporary full supply level. b. For the avoidance of doubt: i. the operational procedures in this Section 8 do not apply during Flood Events; and ii. other than as expressly indicated below, Section 1.1 and Section 2 to 7 of this Manual do not apply to the release of water under this Section 8 (but nothing in this provision derogates from Seqwater's ongoing obligations, including under Section 2.2). 8.4 Procedures for Release of Water Stored Above the Temporary Full Supply Level at Wivenhoe Dam Seqwater shall release water stored above the temporary full supply level of Wivenhoe Dam in accordance with the procedures set out below. a. Release Strategy The Duty Senior Flood Operations Engineer will determine the release strategy and direct the operation of Wivenhoe Dam in accordance with that strategy, with the primary objective of releasing water stored above the temporary full supply level as soon as practicable. Within this requirement, the Duty Senior Flood Operations Engineer shall give consideration to the following matters: i. the BoM forecasts over the period of the release; ii. the volume of water to be released; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 54

56 DECLARATIONS OF TEMPORARY FULL SUPPLY LEVELS FOR FLOOD MITIGATION iii. any program developed through discussion with relevant Agencies for the timing of the inundation of bridges downstream of Wivenhoe Dam (as listed in Appendix J) to limit disruption to impacted communities; iv. the release rate from Wivenhoe Dam is to aim for a maximum target flow of 400 m 3 /s at Burton's Bridge, unless an increase in the release rate is judged likely to reduce the potential for the flow at Moggill to exceed 4,000 m 3 /s from an impending rainfall event; and v. minimising environmental impacts on bank stability and riparian flora and fauna where practicable. b. Bridge Closure Advice Prior to the inundation of bridges downstream of Wivenhoe Dam (as listed in Appendix J) in accordance with the release strategy, the Duty Senior Flood Operations Engineer should aim to ensure that the agency responsible for the closure of the bridge is notified. This notification should, where practicable, allow sufficient time for the agency responsible to close the bridge in an orderly manner prior to its inundation. c. Flood Event Commencement If, during the release of water under these procedures, run-off generated by rainfall causes: i. the release strategy to be materially altered; or ii. the Wivenhoe Dam or Somerset Dam Actual Lake Level to rise; or iii. any other event the Duty Senior Flood Operations Engineer determines, the Duty Senior Flood Operations Engineer shall declare a Flood Event. In this circumstance, the operational procedures in this Section 8 shall no longer apply and the operational procedures in Sections 4, 5 and 6 of the Manual shall apply with the following variations: A. for the purposes of the Flood Event, the FSL shall be the temporary full supply level B. the Duty Senior Flood Operations Engineer will plan a transition to the operational procedures in Sections 4,5 and 6 using professional judgement. 8.5 Procedures for Release of Water Stored Above the Temporary Full Supply Level at Somerset Dam Seqwater shall release water stored above the temporary full supply level of Somerset Dam in accordance with the procedures set out below. a. Release Strategy The Duty Senior Flood Operations Engineer will determine the release strategy and direct the operation of Somerset Dam in accordance with that strategy, with the primary objective of releasing water stored above the temporary full supply level as soon as practicable. Within this requirement, the Duty Senior Flood Operations Engineer shall give consideration to the following matters: i. the release rate from Somerset Dam should not exceed 400 m 3 /s, unless an increase in the release rate is judged likely to reduce the potential for the flow at Moggill to exceed 4,000 m 3 /s from an impending rainfall event; and ii. the impacts to riparian flora and fauna are to be minimised where practicable. b. Flood Event Commencement Follow the guidelines under Section 8.4c if run-off generated by rainfall occurs during the release of water stored above the temporary full supply level at Somerset Dam. 8.6 Modifications to Strategies and Procedures When A Temporary FSL is in Force The strategies and procedures provided in Sections 5, 6 and 7 continue to be applied when a temporary FSL level is in force, with the following minor modifications: References to FSL are to refer to the temporary FSL currently in force; Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 55

57 DECLARATIONS OF TEMPORARY FULL SUPPLY LEVELS FOR FLOOD MITIGATION The Wivenhoe Dam Guide Curve (Figure 5.3.1) is to be modified as described below; The Somerset Dam Guide Curve (Figure 6.2.1) is to be modified as described below. Wivenhoe Dam Guide Curve When a temporary FSL applies, the Wivenhoe Dam Guide Curve provided in the Flood Mitigation Strategy (Section 5.3) is to be modified using the coordinates provided on the following figure. Figure Adjustments to Wivenhoe Dam Guide Curve for Temporary FSLs (Note the y axis on the above figure is an example assuming a temporary FSL of EL 65m is in force.) Somerset Dam Guide Curve When a temporary FSL applies, the Somerset Dam Guide Curve provided in the Somerset Dam Strategy (Section 6.2) is to be modified as follows: A straight line extension is to be added to the left bottom corner of the guide curve, connecting the declared temporary FSLs to the 67m, 99m point on Figure Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 56

58 REFERENCES 9. References Bergin M and Baddiley P (24 July 2006) Rainfall Forecasting for the Wivenhoe Catchment. (see Witness Statement to the Qld Flood Commission of Inquiry, P Baddiley, Annexure PB-7.) DEWS (2014) Wivenhoe and Somerset Dams Optimisation Study Report, Department of Energy and Water Supply, Final Report. DSITIA (2013) An analysis of the time between closely spaced flood events in South-East Queensland, Department of Science, Information Technology, Innovation and the Arts. Rous B and Seed A (Sept 2011) Assessment of the accuracy of NWP forecasts for significant rainfall events at the scales needed for hydrological prediction, The Water Information Research and Development Alliance (WIRADA) Technical Report. Seqwater (Dec 2013) Brisbane River Flood Hydrology Models Seqwater (July 2014) Wivenhoe and Somerset Dam Optimisation Study Simulation of Alternative Flood Operation Options URS (Mar 2014) Somerset Dam Safety Review Water Resources Commission (June 1989) Interim Report on Operation of Wivenhoe Dam During floods (April May 1989) Webb R (30 August 2013) Letter from the Regional Director, Qld, BoM to the Director General, Department of Energy and Water Supply. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 57

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61 APPENDIX A Appendix A Control of the Manual The controlled copy of this Manual is maintained on the web at this location: The current approved version of the Manual is also managed in Seqwater s document management system, and hard copies of the Manual are maintained in the Flood Operations Centre for use in Flood Events. All printed copies of this Manual are uncontrolled. Relevant agencies are advised of revisions of the Manual through the Communications Protocol for Releases from Seqwater s Gated Dams. All relevant agencies are responsible for ensuring they reference the current version of the Manual in any event. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 60

62 APPENDIX B Appendix B Somerset Dam Technical Data Significant Levels Key Level (mahd) ~ 54.7 Dam foundation 57.8 Foundation tunnels Stilling basin dissipator slab floor ~ 61 Stanley River channel invert ~ 66.0 Lower gallery Sluice outlets (downstream centreline) Cone valve Regulators (centreline) Description Sluice gate intakes (upstream centreline); crest of dissipator retaining walls 88.8 Upper gallery 99.0 Full supply Ogee Spillway crest; change of slope for non-overflow monoliths Flood of Record January Adopted maximum safe level with crest gates closed Dam crest ( breezeway section) Original design maximum flood level for the dam < Approximate limit level for minor potential erosion due to overtopping flow Approximate level for moderate to severe erosion potential due to overtopping flow Adopted maximum safe level with crest gates open 1 Limit for Monolith N (central spillway), Monolith R (abutment non-overflow breezeway ) and Monolith S (abutment breezeway ) to satisfy all required factor of safety 1 Abutment erosion potential to be severe (potential head cutting beneath abutment >109.8 Monoliths and likely failure) Top of bridge piers 1 Limit for Monolith N and Monolith S at upper gallery level to satisfy required factor of safety Limit for Monolith S at change of slope level to satisfy required factor of safety Limit for Monolith M to satisfy required factor of safety ~ Potential transition of overtopping flow (through breezeway ) from weir flow to orifice flow Bridge deck 1 - Sourced from Somerset Dam Safety Review (URS 2014) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 61

63 APPENDIX B Discharge Relationships Lake Level (EL m) Reservoir Capacity (x10 3 ML) Temporary Flood Storage (x10 3 ML) Discharge per Regulator (m 3 /s) Discharge per Sluice (m 3 /s) Discharge per Spillway Bay (m 3 /s) Maximum Available Discharge (m 3 /s) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,675 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 62

64 APPENDIX B Lake Level (EL m) Reservoir Capacity (x10 3 ML) Temporary Flood Storage (x10 3 ML) Discharge per Regulator (m 3 /s) Discharge per Sluice (m 3 /s) Discharge per Spillway Bay (m 3 /s) Maximum Available Discharge (m 3 /s) , , , , ,334 The outlet works for Somerset Dam consist of: four (4) regulator valves; eight (8) sluice gates; and eight (8) crest gates. The regulator valves are drowned out when the Wivenhoe Dam tail water level reaches EL 68.6 m and the valves should, in most circumstances, not be used under these conditions. Discharge for each regulator valve may be calculated using the following equation: Q Regulator = *(Lake Level ) 0.5 Discharge for each sluice gate may be calculated using the following equation: Q Sluice = *(Lake Level ) The crest gates are normally kept open and come into operation whenever the Lake Level exceeds EL m. Discharge for each crest gate may be calculated using the following equation: Q Crest = *(Lake Level ) At EL m, floodwaters commence to flow over the dam crest. To account for this discharge, the dam crest is assumed to operate as a broad crested weir with a spillway width of metres and a weir coefficient of 1.7. Discharge in these circumstances may be calculated using the following equation: Q Overflow = 1.7*135.33*(Lake Level ) 1.5 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 63

65 APPENDIX C Appendix C Somerset Dam Auxiliary Equipment Discharge Regulation The normal operating procedure for Somerset Dam in the event of a flood requires the spillway gates to be raised to provide an uncontrolled spillway followed by opening of the low level outlets some time later. Plans of the Dam and spillway are contained in Appendix D. Emergency Power Supply In the event of a power failure at Somerset Dam, both a fixed and a mobile diesel generator are available to operate the regulators, sluice gates and radial gates. The fixed generator can also power the crane. A mobile auxiliary generator is also available for emergency operation of the regulators and gates. Failure of Spillway Gates Machinery If a spillway gate cannot be raised due to failure of the lifting machinery, the gantry crane may be attached to the gate and the gate can be raised using the gantry crane. Failure of Sluice Gate Machinery In the event of a sluice gate being jammed in the open position or the lifting machinery failing, the coaster gate at the Dam can be lowered over the inlet to the sluice to preserve the water supply storage. Revision No: 12 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 64

66 APPENDIX D Appendix D Somerset Dam Plans, Maps and Photographs Figure 1: Somerset Dam Plan View Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 65

67 APPENDIX D Figure 2: Somerset Dam with Regulator Releases Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 66

68 APPENDIX D Figure 3: Somerset Dam Looking Upstream Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 67

69 APPENDIX D Figure 4: Somerset Dam central plan and elevation of Dam Revision No: 12 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 68

70 APPENDIX E Appendix E Wivenhoe Dam Technical Data Significant Levels Key Level (mahd) 45.0 Toe of Flip Bucket 57.0 Spillway Crest 67.0 Full Supply Level 73.0 Top of Closed Radial Gate Flood of Record January 2011 Description Fuse Plug Embankment Crest Levels (see Appendix E for details) 80.0 Saddle Dam Crest 80.0 Estimated maximum safe level 80.1 Dam Crest Level (Top of Wave Wall) 1 - From Brisbane River Flood Hydrology Models report (Seqwater Dec 2013) Discharge Relationships See notes following table. Lake Level (EL m) Reservoir Capacity (x10 3 ML) Temporary Flood Storage Capacity 3 (x10 3 ML) Discharge per Regulator 2 (m 3 /s) Discharge per Spillway Bay 2, 5 (m 3 /s) Maximum Available Discharge (m 3 /s) , , , , , , , , , ,995 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 69

71 APPENDIX E Lake Level (EL m) Reservoir Capacity (x10 3 ML) Temporary Flood Storage Capacity 3 (x10 3 ML) Discharge per Regulator 2 (m 3 /s) Discharge per Spillway Bay 2, 5 (m 3 /s) Maximum Available Discharge (m 3 /s) , , , , , , , , , , , , , ,028 5, , ,098 5, , ,170 5, , ,244 6, , ,319 6, , ,396 7, , ,474 7, , ,554 7, , ,636 8, , ,719 8, , ,804 9, , ,890 9, ,232 1, ,978 9, ,313 1, ,067 10, ,395 1, ,158 10, ,480 1, ,250 11, ,566 1, ,343 11, ,655 1, ,438 12, ,746 1, ,535 12, ,839 1, ,632 13, ,934 1, ,700 13, ,032 1, ,700 13, ,132 1, ,700 13, The information in this table is based on a FSL of EL 67.0 m. 2. This is the maximum discharge of an individual spillway bay or regulator. Total discharge is calculated by adding the contributions of each gate or regulator. 3. The temporary storage is assumed to be the storage above normal FSL of EL 67.0 m. If another FSL is in use, the temporary storage values should be adjusted accordingly. 4. The table does not include Fuse Plug discharges. The first fuse plug is designed to trigger at EL 75.7 m. Once fuse plugs are triggered, the release through the emergency spillway should be added to the values in the Maximum Available Discharge column. 5. 'Discharge per Spillway Bay' refers to discharge without the gate interfering with the flow; that is, as an uncontrolled flow. 6. If the mini-hydro is in operation during a Flood Event, the discharge should be assumed as 13m 3 /s, unless advised differently by the Dam Supervisor on duty. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 70

72 APPENDIX E Individual Gate Rating Table Outflow in m 3 /s Lake Level (m AHD) Gate Opening (m of Tangential Travel) EL m Revision No: 12 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 71

73 APPENDIX E Individual Gate Rating Table Outflow in m 3 /s Lake Level (m AHD) Gate Opening (m of Tangential Travel) EL m * * * * * * Flow impacted by bridge deck Gate overtopped Uncontrolled outflow Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 72

74 APPENDIX E WIVENHOE DAM RADIAL GATES TOP AND BOTTOM GATE LEVELS FOR VARIOUS GATE OPENINGS GATE OPENING (m tangential opening) BOTTOM OF GATE 1 (EL m) TOP OF GATE (EL m) GATE OPENING (m) BOTTOM OF GATE 1 (EL m) TOP OF GATE (EL m) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 73

75 APPENDIX E WIVENHOE DAM RADIAL GATES TOP AND BOTTOM GATE LEVELS FOR VARIOUS GATE OPENINGS GATE OPENING (m tangential opening) BOTTOM OF GATE 1 (EL m) TOP OF GATE (EL m) GATE OPENING (m) BOTTOM OF GATE 1 (EL m) TOP OF GATE (EL m) Owing to the curvature of the water surface over the ogee crest this level does not directly equate to dam level. See previous table for an indication of when the bottom edge may emerge from the water, in reference to issues associated with shallow submergence described in Section 5.7. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 74

76 APPENDIX E Fuse Plug Plan Fuse Plug Details Fuse Plug Type Width (L) (m) Ogee Crest Level (EL m) Fuse Plug Pilot Channel Invert Level (EL m) Storage Level Corresponding to Fuse Plug Pilot Channel Invert Level 1 (EL m) Bay 1 Ogee Bay 2 Ogee Bay 3 Ogee Lake Level is as per that measured at the staff gauge. Fuse plug initiation is expected to occur when the Lake Level exceeds the Lake Level at fuse plug pilot Channel by metres. 2. Includes 0.03 metres of drawdown from the fuse plug pilot channel invert to the Lake Level. 3. Includes 0.08 metres of drawdown from the fuse plug pilot channel invert to the Lake Level. Discharge for each fuse plug may be approximated using the following equation: Q Fuse Plug = C*L*(Lake Level ) 1.5 Where L = Width of fuse plug bay in metres C = Coefficient of discharge as per the table below Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 75

77 APPENDIX E Fuse Plug Ratings Lake Level (EL m) Coefficient of Discharge Bay 1 (m 3 /s) Fuse Plug Discharge Bay 2 Bay 3 (m 3 /s) (m 3 /s) Total (m 3 /s) Figure 5: Fuse Plug Ratings Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 76

78 APPENDIX F Appendix F Wivenhoe Dam Breached Fuse Plug Scenarios This Appendix applies in the circumstances set out in Section 7.4 (and may provide guidance under the Dam Safety Strategy). WIVENHOE DAM RADIAL GATE SETTINGS LOSS OF COMMUNICATIONS CENTRE FUSE PLUG ERODED Lake Level (EL m) Radial Gate 1 Opening (m) Radial Gate 2 Opening (m) Radial Gate 3 Opening (m) Radial Gate 4 Opening (m) Radial Gate 5 Opening (m) Total Opening (m) Actual Total Outflow (m 3 /s) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 77

79 APPENDIX F WIVENHOE DAM RADIAL GATE SETTINGS LOSS OF COMMUNICATIONS CENTRE FUSE PLUG ERODED Lake Level (EL m) Radial Gate 1 Opening (m) Radial Gate 2 Opening (m) Radial Gate 3 Opening (m) Radial Gate 4 Opening (m) Radial Gate 5 Opening (m) Total Opening (m) Actual Total Outflow (m 3 /s) Fully Open Fully Open Fully Open Fully Open Fully Open Fully Open >75.80 Fully Open Fully Open Fully Open Fully Open Fully Open Fully Open Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 78

80 APPENDIX F WIVENHOE DAM RADIAL GATE SETTINGS LOSS OF COMMUNICATIONS TWO FUSE PLUGS ERODED Lake Level (EL m) Actual Total Outflow Fuse Plug Breach and Gates (m 3 /s) Radial Gate Opening (required for all gates) (m) Total Required Radial Gate Opening (m) # * * * * * * * * * * Fully Open Fully Open * Radial gates must be opened to prevent overtopping. The total discharge from the Dam will exceed the target discharge in these circumstances, due to uncontrolled outflows from the auxiliary spillway. # This is the discharge for EL 72.5m (not for all lower Lake Levels). Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 79

81 APPENDIX F WIVENHOE DAM RADIAL GATE SETTINGS LOSS OF COMMUNICATIONS THREE FUSE PLUGS ERODED Lake Level (EL) Actual Total Outflow Fuse Plug Breach and Gates (m 3 /s) Radial Gate Opening (required for all gates) (m) Total Required Radial Gate Opening (m) # * * * * * * * * * * * * * * * * * * * * Fully Open Fully Open * Radial gates must be opened to prevent overtopping. The total discharge from the Dam will exceed the target discharge in these circumstances, due to uncontrolled outflows from the auxiliary spillway. # This is the discharge for EL72.5m (not for all lower Lake Levels). Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 80

82 APPENDIX G Appendix G Wivenhoe Dam Radial Gate Operating Considerations Spillway Operating Principles The radial gates are sequentially numbered from 1 to 5 from left to right looking in the downstream direction. Plans of the Dam and spillway are contained in Appendix H. The flip bucket spillway is designed to control the discharge from the reservoir and to dissipate the energy of the discharge. The flip throws the discharge clear of the concrete structures into a plunge pool where the energy is dissipated by turbulence. Under non-symmetric flow conditions, or when gates 1 and 5 are not operating, the discharge jet may impinge on the walls of the plunge pool, which has been excavated into erodible sandstone rock, and cause nonpredictable erosion. Upstream migration of this erosion is to be avoided. The wing walls adjacent to the flip bucket deflect the discharge away from the walls of the plunge pool when gates 1 and 5 are operated. Therefore in operating the spillway, the principles to be observed are, in descending order of priority: 1. The discharge jet into the plunge pool is not to impinge on the right or left walls of the plunge pool; and 2. The flow in the spillway is to be generally symmetrical. The main purpose of gating the spillway is to exercise maximum possible control over the flow in the Brisbane River in so far as river flows in excess of 4,000 m 3 /s at Moggill cause significant damage to property downstream, although lower flows will still cause damage. The radial gates also allow the routing of much larger floods with substantial flood mitigation being achieved. Radial Gate Operating Principles Each radial gate consists of a cylindrical upstream skin-plate segment that is attached to the radial arms. The cylindrical axis is horizontal. Each gate rotates about two spherical trunnion bearings that are on this axis. The position of a radial gate is controlled by two hydraulically driven winches that are located on the piers either side of each radial gate. Wire ropes attach the downstream face of the radial gate skin plate to each winch through a pulley system. The hydraulic motors work off a common pressure manifold and apply an equal lifting force to each side of the radial gate. This system does not sense rope travel and will take up slack rope. The system corrects skewing of the skin plate segment between the piers. If skewing occurs, skids will come into contact with the side seal plates to limit movement. The design of the system is such that it is not possible to operate a single winch independently of the second winch attached to a radial gate. When the hydraulic winch motors are not energised, the radial gates are held in position by spring loaded friction brakes on the winches. There are two brake bands per winch and each band is capable of supporting half the weight of the radial gate. One winch can support the total weight of a radial gate on both its brake bands, but not on one. Each radial gate can be fully opened in 35 minutes or at a rate of one metre every two minutes. Up to two radial gates can be operated simultaneously. Maximum mechanical capability is not a constraint when undertaking radial gate operations during flood events unless a mechanical failure is experienced. While the radial gates have been designed to withstand some overtopping, it should be avoided if possible. The Lake Levels and the structural state of the radial gates when in the closed position are as follows: Lake Level (EL m) Radial Gate Stress Condition with Gate Closed 73 Within design limits of radial gate 77 Limit of structural security (33% overstressed) 79 Critical structural failure likely Once overtopped, the radial gates become inoperable if the lifting tackle is fouled by debris from the overflow. However, the radial gates will remain structurally secure until the Lake Level exceeds EL 77.0 m. Above this level, structural damage that causes the radial gates to become inoperable is possible. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 81

83 APPENDIX G Free Fall of the Radial Gates Under no circumstances are the radial gates allowed to free fall. The lower skin plate sections are overstressed if a freefall of 60 millimetres is arrested by the seal plate on the spillway. If a radial gate becomes stuck in an open position, attempts are to be made to free the radial gate by applying positive lifting forces. Under no circumstances are the winches to be unloaded and the direct weight of the radial gates used to yield the obstruction. Operation in High Wind Other than during Flood Events, the radial gates are not to be raised or lowered when clear of water, during periods of high winds. The radial gates can however, be held on their brakes in any position in the presence of high wind. The term "high wind" means any wind that causes twisting or movement of the radial gate. A precise figure cannot be placed on these velocities, as it is also a function of wind direction. This limitation is required to prevent the radial gate from twisting from skew on one side to skew on the other side. While the radial gate is being raised or lowered, skewing cannot be prevented by the hydraulic lifting system and any impact forces encountered may damage the radial gate. Maintenance Considerations No more than one radial gate is to be inoperable at any one time for maintenance. Radial gate maintenance is to be scheduled so that the spillway bay can be cleared of obstructions in a reasonable time to allow its use in the event of major flooding. Bulkhead Gate Operating Limitations The bulkhead gate can be used to control discharge in an emergency situation where a radial gate is inoperable. It is transported to, and lowered upstream of the inoperable radial gate by means of the gantry crane. The following considerations apply in these circumstances: the bulkhead gate can always be lowered with any type of underflow; and it is not possible to raise the bulkhead gate once it has been lowered past certain levels depending on upstream conditions without there being a pool of water between it and the radial gate. It is thus possible to preserve storage by effectively closing the spillway even with one radial gate inoperable. However, it will not be possible to raise the bulkhead gate until the inoperable radial gate has been lowered and is again storing water. The bulkhead gate is not to be used for flood regulation until the Lake Level is falling and not likely to rise within the period needed to repair the inoperable radial gate. The spillway gantry crane is to be used to raise and lower the bulkhead gate. The crane operates at two speeds, 1.5 metres/minute and 3.0 metres/minute. When within the bulkhead gate guides, the bulkhead gate is to be moved only at 1.5 metres/minute. Bulkhead Gate Overtopping In the event that the bulkhead gate is overtopped (Lake Level exceeds EL 69.0 m when bulkhead gate is closed), it cannot be removed unless a pool of water fills the space between it and the upstream side of the radial gate. The closed bulkhead becomes critically stressed when the Lake Level overtops it to EL 71.4 m. It is not possible to engage the lifting tackle while overtopping is occurring. While there is any risk that the bulkhead gate may be overtopped, the lifting gear is to be left engaged so that the bulkhead gate can be raised once the downstream radial gate becomes operable. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 82

84 APPENDIX G Bulkhead Gate Discharge Regulation This procedure should only be used if the safety of Wivenhoe Dam is at direct risk or to preserve the water supply stored in Wivenhoe Dam. In the event that a radial gate is inoperable in a partially open position, the bulkhead gate can be used for flow regulation provided that the lower lip of the radial gate is clear of the underflow jet. Where a pool exists between the bulkhead gate and a radial gate under flow conditions, the bulkhead gate will be subjected to additional pull-down and possibly subjected to vortex-induced vibrations. When this condition occurs, the bulkhead gate is to be lowered to dewater the pool. The bulkhead gate can then be adjusted to regulate the flow provided the underflow jet remains below the lower lip of the radial gate. Inoperable Radial Gates In the event of a major flood, where the full discharge capacity of the four operable radial gates is required, these gates are to be used to their full capacity to protect the embankment from overtopping. Under certain abnormal conditions, it may not be possible to operate one gate. The following guidelines are to be adopted where practicable: Gate 3 Inoperable Gates 2 and 4 are to be used to regulate flood discharges, until the discharge impinges on the walls of the plunge pool. Gates 1 and 5 are then to be opened sufficiently to deflect the discharge into the plunge pool. The bottoms of gates 1 and 5 are to be maintained at or below those of gates 2 and 4 respectively. Either Gate 2 or 4 Inoperable Normal gate operating procedures are to be adopted, except that only the operable gate 2 or 4 is available for flood regulation beyond 500 m 3 /s and not both. Either Gate 1 or 5 Inoperable Normal gate operating procedures are to be adopted until the discharge impinges on the walls of the plunge pool. Thereafter the operable gate 1 or 5 is to be used in lieu of using the radial gate adjacent to the inoperable gate. The other radial gates are to be used in the normal way to control discharge. Equipment Malfunction Normal gate operation is by means of two electric hydraulic pumps supplied by external mains supply electric power, with Pump Number 1 connected to radial gates 1 and 2 and the penstock gate, and Pump Number 2 is connected to radial gates 3, 4 and 5. Normal radial gate operation may not be possible in the event of equipment malfunctions during the passing of a flood. The procedures to be followed under the various scenarios are outlined on the following page. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 83

85 APPENDIX G Failure of External Electric Power The fixed diesel electric generator at the Dam is used to provide a power supply. The generator supplies sufficient power to operate the radial gates normally. Failure of One Electric Hydraulic Pump If one electric hydraulic pump fails, the connecting valves between pumps are to be switched such that both sets of hydraulic lines are connected to the operable pump, thus permitting operation of all 5 gates from the operating pump. Failure of Two Electric Hydraulic Pumps In the event that both electric hydraulic pumps fail, either the mobile or the fixed emergency diesel hydraulic pump is to be used to operate the radial gates, one gate at a time. Rupture of Hydraulic Lines Depending on location and severity, a hydraulic line rupture may cause a radial gate to become inoperable. Accordingly any ruptures to the hydraulic lines are to be repaired as soon as practicable. Depending on the location of the rupture, it may be possible to use the mobile emergency diesel hydraulic pump to operate the impacted radial gate. Contamination of Winch Brakes Oil contamination of the winch brakes will reduce their holding capacity and possibly allow the radial gate to fall. The brake bands are to be inspected regularly and cleaned immediately if any contamination is observed. Fouling of Radial Gate Lifting Tackle The lifting tackle consists of blocks, wire ropes and winch drums. If the radial gate is overtopped, debris may be collected on the wire ropes that may in turn foul the blocks or the winch drums. This may result in jamming of the wire rope or in uneven lifting, both of which may cause the radial gate to jam. Fouling of Side Skids The side skids have been designed to limit the side-sway and skew of the radial gates during operation. Under ideal conditions, the skids should not be in contact with the side seal plates. If the winches are lifting the radial gates unevenly or in a skewed position, the lifting gear should be adjusted. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 84

86 APPENDIX H Appendix H Wivenhoe Dam Plans, Maps and Photographs Figure 6: Wivenhoe Dam Aerial View Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 85

87 APPENDIX H Figure 7: Wivenhoe Dam with Centre Gate Open Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 86

88 APPENDIX H Figure 8: Wivenhoe Fuse Plugs Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 87

89 APPENDIX H Figure 9: Wivenhoe Dam General Arrangement Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 88

90 APPENDIX I Appendix I Key Reference Gauges Location Gauge Zero (EL m) 1974 (m) Peak Gauge Height 2011 (m) Gauge Height (m) Minor Flood Level Approx Flow 3 (m 3 /s) Gauge Height (m) Moderate Flood Level Approx Flow 3 (m 3 /s) Gauge Height (m) Major Flood Level Approx Flow 3 (m 3 /s) Brisbane River at Lowood Brisbane River at Lowood Pump Station Brisbane River at Savages Crossing Brisbane River at Mount Crosby , , Bremer River at 1, Ipswich Brisbane River at Moggill Brisbane River at Jindalee Bridge 4,000 6,000 Brisbane River at Brisbane Port Office ,300 7, Flows are approximate only and heights are tide dependent in the lower reaches. 2. Impacted by backwater from Brisbane River. 3. Flows are based on ratings in the Brisbane River Flood Hydrology Models report (Seqwater, Dec 2013) Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 89

91 APPENDIX J Appendix J Bridges and Dam Recreation Areas Impacted By Floods Bridges Impacted by Elevated Lake Levels in Somerset Dam WATERCOURSE ROAD DECK ELEVATION (EL m) LOCAL AUTHORITY AREA Mary Smokes Creek D Aguilar Highway Somerset Regional Council Kilcoy Creek D Aguilar Highway Somerset Regional Council Beam Creek Esk Kilcoy Road Somerset Regional Council Scrubby Creek D Aguilar Highway Somerset Regional Council Oakey Creek Esk Kilcoy Road Somerset Regional Council Recreation Areas Affected by Elevated Lake Levels in Somerset Dam SOMERSET DAM LAKE LEVEL (mahd) DESCRIPTION OF IMPACTS 99.5 Close Somerset Dam Recreation Area Remove Recreation Area Infrastructure Recreation Area Office Flooded (Electrical disconnection required) Inundation of Sewage Holding Tank Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 90

92 APPENDIX J Figure 10: Bridges and Recreation Areas Impacted by Elevated Lake Levels in Somerset Dam Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 91

93 APPENDIX J Bridges Impacted by Elevated Lake Levels in Wivenhoe Dam BRIDGE/ WATERCOURSE A&PM Conroy Bridge at Sandy Creek ROAD DECK ELEVATION (EL m) LOCAL AUTHORITY AREA Wivenhoe Somerset Road Somerset Regional Council Deep Creek Wivenhoe Somerset Road Somerset Regional Council Kipper Creek Wivenhoe Somerset Road Somerset Regional Council Meirs Gully Esk Kilcoy Road Somerset Regional Council Tea Tree Creek Brisbane Valley Highway Somerset Regional Council Logan Creek Brisbane Valley Highway Somerset Regional Council Five Mile Creek Brisbane Valley Highway Somerset Regional Council Reedy Creek Wivenhoe Somerset Road Somerset Regional Council Haslingdens Bridge at Stanley River Esk Kilcoy Road Somerset Regional Council Coal Creek Brisbane Valley Highway Somerset Regional Council O Sheas Bridge at Brisbane River Esk Kilcoy Road Somerset Regional Council Tea Tree Gully Brisbane Valley Highway Somerset Regional Council Middle Creek Wivenhoe Somerset Road Somerset Regional Council Recreation Areas Affected by Elevated Lake Levels in Wivenhoe Dam WIVENHOE DAM LAKE LEVEL (mahd) DESCRIPTION OF IMPACTS 67.5 Commence closure of Wivenhoe Dam Camping Grounds. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 92

94 APPENDIX J Figure 11: Bridges Impacted By Elevated Lake Levels in Wivenhoe Dam Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 93

95 APPENDIX J Bridges Impacted by Releases from Wivenhoe Dam BRIDGE NAME ROAD CAPACITY 1 (m 3 /s) DECK ELEVATION (EL m) Twin Bridges Wivenhoe Pocket Road Fernvale Bridge Brisbane Valley Highway Savages Crossing Banks Creek Road Burtons Bridge E Summerville Road Kholo Bridge Kholo Road Mount Crosby Weir Allawah Road Colleges Crossing Mount Crosby Road It is noted that the flow carrying capacity of the bridges downstream of Wivenhoe Dam are estimates as the actual capacity will vary from year to year depending on the time since the last Flood Event, the amount of erosion/deposition at the location and the amount of vegetation in the channel. 2. Affected by tidal flows. 3. Contact details for the officers at the agencies responsible for closure of the bridges are contained in Communications Protocol for Releases from Seqwater s Gated Dams. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 94

96 APPENDIX J Figure 12: Bridges Impacted By Releases From Wivenhoe Dam Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 95

97 APPENDIX K Appendix K Historical Floods Estimated Peak Inflows and Outflows to Somerset and Wivenhoe Dams in Historical Events The tables below show recorded peak water level and estimated peak inflow and outflow flow rates and volumes for selected historical events, drawn from Table 5-3 and 5-4 of the Brisbane River Flood Hydrology Models report (Seqwater Dec 2013). All flows are estimates only, and were developed based on assumptions described in that report. Somerset Dam Flood Data Event (yyyymmdd) Start level (m AHD) Peak water level (m AHD) Inflow (m 3 /s) Peak Outflow (m 3 /s) Inflow (ML) Flood volume Outflow (ML) , , , , , , ,200 6, , , , ,400 1, , , ,200 1, , , , , , ,600 2, , , ,600 2, , , , , , , , , ,100 31, , , , , ,100 1, , , ,200 83, , , , , ,900 1, , , , , , , ,800 89, ,200 1, , ,000 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 96

98 APPENDIX K Wivenhoe Dam Flood Data Event (yyyymmdd) Start level (m AHD) Peak water level (m AHD) Inflow (m 3 /s) Peak Outflow (m 3 /s) Inflow (ML) Flood volume Outflow (ML) ,200 1, , , ,200 1, , , , , ,300 1,800 1,190, , ,000 80, , , , , , , ,400 1, , , , , ,600 1, , , ,600 1, , , ,300 7,500 2,750,000 2,710, , , , , , , ,400 1, , ,000 1 Temporary FSL of 65.6m declared for Wivenhoe Dam during event. Estimated Historical Flows Downstream of Wivenhoe Dam The following table shows estimated flood peak flows for a range of flood events under the basin configuration applicable at the time of the event, drawn from Table 8-4 in the Brisbane River Flood Hydrology Models report (Seqwater Dec 2013). All flows are estimates only, and were developed based on assumptions described in that report. Event (yyyymmdd) Basin Configuration Brisbane R at Wivenhoe (m 3 /s) Brisbane R at Mount Crosby (m 3 /s) Bremer R at Ipswich (m 3 /s) Brisbane R at Moggill (m 3 /s) ,100 6,460 3,950 8, ,910 8,900 1,730 9, ,370 15,980 1,100 16, ,410 14,260 2,010 15,500 No Dams ,320 8,590 1,180 8, ,300 9, , ,210 6, , ,370 6,500 1,110 6, ,920 7, , ,220 2,280 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 97

99 APPENDIX K Event (yyyymmdd) Basin Configuration With Somerset Dam Brisbane R at Wivenhoe (m 3 /s) Brisbane R at Mount Crosby (m 3 /s) Bremer R at Ipswich (m 3 /s) Brisbane R at Moggill (m 3 /s) 6,790 5,800 1,200 5, ,860 1, , ,610 1,260 3, ,310 3,470 1,020 3, ,250 2, , ,060 1, , ,810 3, , ,210 4, , ,290 1, , ,790 3, , ,860 10,460 3,770 11, ,380 2, , ,160 1,580 1, With Somerset & Wivenhoe Dams 1,100 2, , ,200 1,350 1, ,620 1, , ,490 1, , ,440 1, , ,810 1,470 3, ,800 2, , ,100 1, , ,500 1, , ,460 1, , ,590 1,580 1,010 1, ,470 9,130 2,770 10, ,820 2,380 1,920 3, ,840 1, ,140 Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 98

100 APPENDIX K Estimated Basin Average Rainfall and Flood Volumes for Historical Events The following table shows estimated basin average rainfall and flood volumes for selected historical events drawn from Table 2-1 in the Wivenhoe and Somerset Dam Optimisation Study Simulation of alternative flood operations options report (Seqwater July 2014). All flows are estimates only, and were developed based on assumptions described in that report. Flood Event (year.mth) Basin Average Rainfall (mm) Stanley River (ML) Upper Brisbane River (ML) Lockyer Creek (ML) Bremer River (ML) Lower Brisbane to Moggill (ML) Total Volume (Moggill) (ML) , , , , ,000 1,933, ,000 1,585, , , ,000 3,539, ,436,000 2,186, , , ,000 4,639, ,000 1,621, , , ,000 3,764, , , , , ,000 1,788, ,000 1,296, , , ,000 2,799, , , , , ,000 2,023, , , , , ,000 1,756, , , , , ,000 2,013, , , , ,000 59,000 1,548, , , , ,000 71,000 1,145, , ,000 98, ,000 44,000 1,068, , ,000 41,000 12,000 62, , ,000 1,394, , , ,000 3,595, , , , ,000 53,000 1,297, , ,000 77,000 63,000 45, , , , , , ,000 1,711, , ,000 85,000 99,000 89,000 1,606, ,000 1,910, , , ,000 3,987, , , , ,000 96,000 1,601,000 Note: The volumes presented in this table are for a total duration of 430 hours and have been estimated using the assumptions presented in the Wivenhoe and Somerset Dam Optimisation Study Simulation of alternative flood operations options report (Seqwater July 2014), and hence may differ slightly from event volumes reported in other sources. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 99

101 APPENDIX K Historical Flood Recessions at Savages Crossing The graph below provides the flow rates during flood recessions in a range of historical events. This graph may be used to provide guidance in the selection of recession rates during dam operations. In interpreting this graph, it should be noted that: Events post 1984 are affected by the historical operation of Wivenhoe Dam and Somerset Dam, the events are affected by the historical operation of Somerset Dam. Savages Crossing is downstream of the Lockyer Creek inflow. Some of the plotted events did not peak much higher than the portion of the hydrograph shown, while others were much larger events. Every event has a different spatial and temporal pattern of rainfall, and the causes of bank slumping are complex. It is understood that significant bank slumping occurred in the early April 1989 event (as reported in the Interim Report on Operations of Wivenhoe Dam During Floods (April-May 1989) (Water Resources Commission June 1989)), and hence the recession rate for that event is considered too steep. This graph is useful for evaluating the desired recession during the portion of drain down when releases are being reduced from targeting Mount Crosby Weir Bridge (1800 m 3 /s) to Burtons Bridge (430 m 3 /s). Based on this graph, it is suggested that this reduction in downstream flows should be undertaken over 18 hours or longer. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 100

102 APPENDIX L Appendix L Flood Forecasting System (FFS) The FFS is not a single component or model, but a suite of tools used to support flood operations decision making. The term FFS is used to broadly describe four (4) individual components that are described as follows: Monitoring Network this component consists of Gauging Stations located throughout the Dams' catchments and areas downstream. The Gauging Stations consist of rainfall and water level sensors that use the Event Reporting Radio Telemetry System (ERRTS) to transmit data to the Flood Operations Centre. Data Collection this component captures rainfall and stream height (including Lake Level) data in real time and processes the data for input into the Modelling Platform component. The Data Collection Component runs continuously collecting data every time an event (tip of a bucket or change in water level) occurs at a station and sends output data to the Modelling Platform at any regular intervals. In addition to recordings from rainfall gauges, gridded forecast rainfall from BoM is also collected at regular intervals through the day. Modelling Platform this component processes point recorded and gridded forecast rainfall data to estimate stream flow hydrographs at selected points throughout the basin using a suite of calibrated hydrologic models. It contains validated catchment models that provide coverage over the Dams' catchments and areas downstream. These models run at discrete times selected by the Duty Engineer(s), based on the spatial and temporal patterns of rainfall in the Brisbane River basin. There is capacity to include rainfall predictions within the modelling. The output from the Modelling Platform is used as input to the Dam Operations Model component. Dam Operations Model this component is used to evaluate Dam outflow strategies and to calibrate the flow hydrographs from the Modelling Platform component. Broadly, it determines Dam Lake Levels based on inflows determined from the Modelling Platform component and allows the Duty Engineer(s) to investigate a range of gate operating strategies to determine the most appropriate strategy to use at any point in time. To support this process, it provides a broad range of outputs that are used to evaluate potential gate operations strategies. These outputs include: o o o o o o o a graphical output showing Dam inflows and the flows generated from the Lockyer and Bremer catchments; a graphical output showing inflows and outflows to and from Wivenhoe Dam; a graphical output showing inflows and outflows to and from Somerset Dam; a graphical output showing actual and modelled Lake Levels in Somerset Dam; a graphical output showing actual and modelled Lake Levels in Wivenhoe Dam; a graphical output showing actual and modelled Brisbane River flows at Lowood and Moggill; and a graphical output comparing actual and modelled Lake Levels in Somerset Dam to actual and modelled Lake Levels in Wivenhoe Dam (interaction examination). Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 101

103 APPENDIX M Appendix M Brisbane River Schematic Diagram Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 102

104 APPENDIX N Appendix N Alternative Procedures Communications Protocol Between the Regulator and Seqwater Communications Protocol for seeking authorisation of Alternative Operating Procedures Scope Division 8 of Chapter 4 of the Act applies when the Dam owner is seeking authorisation to observe a different operational procedure (an alternative procedure) to that specified in an approved Flood Mitigation Manual. This protocol provides clarity and guidance for communication between the Chief Executive and the Duty Senior Flood Operations Engineer when seeking authorisation of alternative operational procedures. Contact positions The following delegates of the Chief Executive are to be used as contacts for communications by the Dam owner subject to the guidance set out below: Director, Dam Safety, Queensland Water Supply Regulator, Department of Energy and Water Supply; General Manager, Queensland Water Supply Regulator, Department of Energy and Water Supply; Director-General of Department of Energy and Water Supply. Means of Communication The following means of communication are to be used for communication by the Dam owner subject to the guidance set out below: Landline telephone; Mobile telephone; Satellite telephone; Two-way Radio; /Internet; Face to Face / Courier; Facsimile; Letter. Guidance Relevant contact details will be established on approval of this flood mitigation manual and maintained as required (but at least annually) by exchange of letters. While there is no strict hierarchy to the contacts or means of communication, the means of communication adopted will be dependent on the: available means of communication; proximity of the parties; time available to make the decision; extent of prior knowledge the decision maker has of the circumstances leading up to the request; the complexity and quantity of data/information required to support/justify the decision; consequences of the decision. Matters to be considered include: means of communication should be chosen that are two-way in nature as first preference; initial communication should preferably be by the most direct means; multiple means of communication may be appropriate as part of a coordinated approach; for operational communications the order of contacts would normally be those listed; for operational purposes, contact need only be established with one responsible delegate; communications must be continually reviewed against timeframes and consequences. What needs to be provided: Authorisation Request Information in accordance with section 379 of the Act; time available to make the decision; any other factors the Dam owner considers critical to effective alternate operations. Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam 103

105