Management of flooding downstream of dams

Transcription

1 Management of flooding downstream of dams Attachment to Victoria State Flood Emergency Plan

2 Version 1.0 (6 February 2013) This plan is produced by the Victoria State Emergency Service and Department of Environment and Primary Industries as an attachment of the State Flood Emergency Plan. The Plan is to be reviewed and updated (as necessary) every 3 years with the first revision in February Ensuring the information it contains is accurate and current, would not be possible without the contributions and assistance of many people from the various organisations identified within its pages. Endorsed by the State Emergency Response Planning Committee on 19 March For matters regarding this plan: Chief Officer Operations Victoria State Emergency Service 168 Sturt Street, Southbank, Victoria, 3006 Phone: (03) Fax: (03) [email protected] Website:

3 Contents 1. Purpose Effects of Dams on Flooding Flood Mitigation Types of Flooding Downstream of Dams Natural floods Man-made floods Dam failure floods Roles and Responsibilities Victoria State Emergency Service (VICSES) Department of Environment and Primary Industries (DEPI) Bureau of Meteorology (BoM) Dam Owners and Operators Water Corporations Private and farm dam owners Parks Victoria and local government operated dams Significant Events Requiring a Multi-agency Response Command and Control arrangements For natural floods For dam safety incidents unlikely to cause flooding downstream For dam failure likely to cause downstream impacts Flood warning Flood warning communities immediately downstream of a dam Informing communities of natural flooding Informing communities of man-made flooding Informing communities of the dam failure flood risk Dam Failure Emergency Planning for Downstream Consequences Dam hazard classifications Dam failure emergency planning for downstream consequences Arrangements to Contact Response Agencies VICSES DEPI BoM Activation Levels and Escalation Figure A: Typical inflow/outflow hydrograph for a gated dam Figure B: Activation Levels Appendix 1: Abbreviations

4 1. Purpose The purpose of this document is to clarify the arrangements relating to the management of flooding consequences downstream of dams. The aim of this document is to provide guidance for the command and control arrangements for a flood response downstream of dams and collaboration between dam operators, Victoria State Emergency Service (VICSES), Department of Environment and Primary Industries (DEPI) and other agencies that have responsibilities in flood management. The types of incidents considered include controlled releases from dams and uncontrolled releases due to a dam safety emergency. The document applies to all types and sizes of dams including flood retarding basins. 2. Effects of Dams on Flooding Dams on waterways impose a range of permanent effects on natural stream flows and typically modify the peak flow, timing and duration of floods such that downstream flooding effects are reduced. Depending on their operating rules, dams with control devices such as gates, valves or fuse plugs may have the ability to further modify flood flows. When control devices are used to release water during flood events, downstream flooding consequences can occur rapidly, which can create unexpected adverse impacts on downstream communities. Only a small number of dams in Victoria have spillway gates, providing the capability to make flow releases during or prior to a flooding event. Such dams are owned by water corporations. Each catchment responds differently to rainfall events. Therefore it is important that all dam operators, and emergency response and support agencies understand the unique behaviour of the catchment and operating requirements for each dam within their region. Particular notice should be given to response capability and flood preparedness for flooding from dams within the Macalister catchment (Lake Glenmaggie), Buffalo catchment (Lake Buffalo) and Loddon catchment (Cairn Curran, Tullaroop and Laanecoorie Reservoirs). The dams in these catchments are relatively small in volume compared with the size of the catchment. These catchments have a history of responding rapidly to heavy rainfall and can produce significant floods with little warning. 3. Flood Mitigation Generally, large dams in Victoria are not designed or operated specifically for flood mitigation, although some flood mitigation is provided as a result of the flow being attenuated by the dam. The degree of flood mitigation a dam can provide depends on a number of factors including: The operating rules of the storage; Size of the flood event; Catchment size; Level of water in the dam at the beginning of the event; Capacity of the reservoir to store floodwaters above its full supply level; and The discharge capacity of the spillway. Dams can provide mitigation for small floods and reduce downstream flooding by lowering the peak flow and delaying the outflow as illustrated in Figure A. The amount of mitigation generally reduces as the size of the flood increases, with little mitigation benefit for larger floods. 1

5 Figure A: Typical inflow/outflow hydrograph for a gated dam 4. Types of Flooding Downstream of Dams Flooding events downstream of dams can be the result of any one of the following three scenarios: 4.1. Natural floods Natural floods occur when there is significant rainfall in the catchment causing large inflows to the dam. Depending on the water level in the dam prior to the rain event, the dam may provide some flood mitigation to the downstream floodplain. All flood operating procedures require the flood to be safely routed through the dam. Although this type of flooding may result in an emergency response downstream of the dam, the structure will be operated in accordance with normal operating procedures with minimal risk to the dam structure. The primary objective of the operating procedures is to ensure the safety of the dam during flood operations. The majority of floods passed through dams are natural floods caused by rainfall in the catchment which do not threaten the safety of the dam Man-made floods Flooding may occur if the water level in the dam needs to be lowered rapidly to create additional airspace to absorb a forecast flood or for dam safety reasons. Significant environmental flow releases can also create over bank flood flows into natural wetlands and floodplains. In each of these instances, the release of water would be controlled by the dam owner and time would be available to inform downstream communities. 2

6 4.3. Dam failure floods The failure of a dam can result in the uncontrollable release of water flooding downstream areas. Dams can fail due to one or more of the following scenarios. Extreme upstream floods, which can overtop a dam wall causing erosion or the movement of the dam; Seepage and possible piping of water through the dam wall or its foundations; Earthquakes, which can cause damage to a dam wall or outlet infrastructure; Human factors relating to the operation of a dam or wilful damage. Flooding caused by a dam failure can occur in a relatively short period. Downstream communities located close to the dam typically have short warning times. Sunny day failures are events other than flood induced failures. In some instances, the time available to warn downstream communities can be very short. 5. Roles and Responsibilities 5.1. Victoria State Emergency Service (VICSES) VICSES is responsible for the emergency response management of flood consequences downstream of dams regardless of the cause of the flood. VICSES response activities include warnings and information to the community and recommending evacuation as provided for in the Emergency Management Manual Victoria (EMMV). Warning and informing the community regarding flood risks downstream of a dam will be based upon the best information made available by dam operators and DSE Department of Environment and Primary Industries (DEPI) DEPI has a regulatory role in the safety of dams in Victoria. This includes dams categorised as farm dams, private dams and dams operated by water corporations, Parks Victoria and local government. DEPI is the nominated Control Agency for dam safety incidents as described in the EMMV. This means DEPI has the ultimate control of the response to dam safety incidents at a dam site in relation to the integrity of a dam. This role will be coordinated with the dam owner and with VICSES as the Control Agency for floods to manage the response activities. For command and control arrangements during a dam safety incident, refer section Bureau of Meteorology (BoM) BoM has the responsibility to issue warnings on gales, storms, rainfall and other weather conditions likely to endanger life or property, or give rise to floods. It also has responsibility to provide weather forecasts and meteorological and hydrological information. BoM will include information on flood releases provided by dam operators in its forecasting methodology to ensure flood predictions for downstream gauges account for releases. BoM will issue relevant flood warnings for agreed flood warning locations as per flood warning arrangements. BoM does not have a role in issuing warnings for dam failure. 3

7 5.4. Dam Owners and Operators Water Corporations Most of Victoria s large dams are owned and operated by water corporations. The primary role of these dams is for water supply and irrigation purposes and any flood mitigation is considered incidental or opportunistic. During the passage of natural floods through dams, water corporations support VICSES and BoM by following standard operating procedures and distributing inflow and release information and situation reports as appropriate. This role changes little during man-made floods, as water corporations are expected to provide sufficient release data to help VICSES (and BoM) inform and protect downstream communities. During the initial response phase of a dam safety incident at a water corporation dam, water corporations are required to take on the role of the Incident Controller and directly manage the local emergency response relating to the integrity of the dam. This means that a water corporation will activate its Dam Safety Emergency Plan (DSEP) and establish an appropriate incident management structure. The water corporation will liaise directly with VICSES to ensure adequate information is available to undertake their control functions. Unless a replacement appointment is made, a water corporation must remain in control of the situation at the dam site. An important role for water corporations is to maintain operational procedures which ensure operational data and forward planning is provided to VICSES and where required coordinated with VICSES to achieve safe dam operation and minimise risk to the downstream community Private and farm dam owners Emergency management requirements for licensed private/farm dam owners are given in the booklet: Your dam, Your Responsibility - A Guide to Managing the Safety of Farm Dams which is available from DEPI. It requires private dam owners to: Use the services of a suitably qualified engineer to design and construct the dam; Make periodic visual inspections of the dam; Monitor conditions that may affect the safety of the dam; Perform regular maintenance; Maintain an up-to-date Dam Safety Emergency Plan (DSEP); Carry out repairs where and when required to meet current design and construction standards; and Have an experienced dam engineer investigate any unusual conditions which could result in partial or total failure. The safety of private/farm dams are regulated through a licensing process. Administration of these licenses is delegated to five water corporations: Goulburn-Murray Water, Grampians Wimmera Mallee Water, Lower Murray Water, Southern Rural Water and Melbourne Water. As part of their licence conditions, licensed dam owners are expected to maintain an up-todate Dam Safety Emergency Plan with appropriate notification and response arrangements. Apart from farm dams, private dam owners include energy and mining companies. While DEPI remains the Control Agency for the integrity of such dams, the operators of these dams are required to provide the initial response in line with their Dam Safety Emergency Plan. The command and control arrangements will be as described in section

8 Parks Victoria and local government operated dams Other dam operators include Parks Victoria and local government who manage mostly recreational dams. These dam operators need to ensure that they maintain Dam Safety Emergency Plans for each dam and that notification protocols and response arrangements are consistent with the principles outlined in this document. While DEPI remains the Control Agency for the integrity of such dams, the operators of these dams are required to provide the initial response in line with their Dam Safety Emergency Plan. During a dam safety incident the command and control arrangements will be as described in section Significant Events Requiring a Multi-agency Response An effective response to a flood emergency requires a multi-agency approach involving VICSES, DEPI, BoM, Victoria Police (VICPOL) and dam operators. The EMMV designates DEPI as Control Agency for dam safety and VICSES for flooding, so it is important to note the following agreed arrangements are in place to ensure that the allocation of Control Agency accountability is clear for the scenarios as described below Command and Control arrangements For flood-related incident response, there can only be one Control Agency, regardless of the number of agencies that may have control responsibilities for aspects of the response For natural floods VICSES will be the Control Agency, appointing the Incident Controller for situations where high inflows following rainfall in the catchment of a dam can cause an emergency response downstream. In this circumstance, the dam operator or DEPI will be a support agency responsible for dealing with the passage of water through the dam while VICSES will be responsible for managing the response to flood consequences For dam safety incidents unlikely to cause flooding downstream DEPI will be the Control Agency in cases where a dam has a safety incident but is unlikely to fail and cause flooding downstream. During the initial response phase DEPI requires water corporations to take on the role of the Incident Controller if the dam is operated or licensed by a water corporation. In other cases, DEPI will appoint a suitable Incident Controller For dam failure likely to cause downstream impacts VICSES will be the Control Agency, appointing the Incident Controller for a dam safety incident in situations where: The dam safety incident is likely to result in a flood with community consequences; or A major flood event is occurring with VICSES already established as the Control Agency and a dam safety incident is likely. 5

9 Where VICSES is the Control Agency, DEPI or a water corporation (if the dam is operated or licensed by a water corporation) will be a Support Agency responsible for dealing with the structural integrity of the dam. VICSES will be responsible for the wider community consequences including the management of public warning and information relating to any potential downstream flooding. When forming an Incident Management Team (IMT) in response to the management of flooding downstream of a dam, it is important that DEPI and VICSES along with the dam operator all have representation and/or expertise to an appropriate level present within the IMT. Regular updates and situation reports provided by the Dam owners / operators to the IMT will ensure a common operating picture for all agencies. The IMT may be located at the incident site or at an Incident Control Centre (ICC) Flood warning Flood consequences can be from either natural flooding or due to a dam failure. VICSES is responsible for the emergency response management of flood consequences downstream of dams. This includes warnings and information to the community and recommending evacuation for floods Flood warning communities immediately downstream of a dam There are instances where houses are located immediately below the dam. Warning time and flood travel time to these households can be short. In such situations, communication with these residents may be better managed by the dam operator given the short timeframe available. This should only be done where there is written agreement between VICSES and the dam operator. In the absence of any locally agreed arrangements, VICSES will remain responsible for flood warning and informing downstream communities. DEPI and the dam operator (in the case of a water corporation) will continue to provide technical expertise and advice to VICSES in order to prepare updates and warnings to the downstream communities. It is important to note that the context at each dam site will vary and the notification arrangements will need to be developed by agreement with relevant stakeholders on a case by case basis Informing communities of natural flooding Arrangements for flood warning resulting from natural flooding are contained within the State Flood Emergency Plan. The exception being where there is an agreement in place for the dam owner to undertake warning and information to a community immediately downstream of the dam. See section 6.3. In the event of a dam owner realising that a significant volume of water needs to be released from the dam which has the potential to cause flooding downstream, the dam operator needs to provide information to VICSES and, where there are downstream flood warning gauges, to BoM. Information provided should include storage levels, actual and prospective water releases and their likely impacts on downstream flooding. 6

10 6.5. Informing communities of man-made flooding Dam operators need to notify all relevant agencies (including VICSES and BoM) and downstream communities (unless other agreements are in place, such as with Catchment Managment Authorities) when controlled operational releases outside of flood events are likely to result in large flows or flooding. A communication plan should be developed in consultation with VICSES, BoM, Catchment Management Authority (CMA) and other relevant agencies, which includes storage levels, actual and prospective water releases and their likely impacts on downstream flooding. These events are infrequent and are generally planned in advance (although emergency releases may be planned on a very short timeframe) hence time is available to warn downstream communities Informing communities of the dam failure flood risk Effective communication between the dam operator, DEPI and VICSES is essential to ensure the management of a dam safety incident and of any downstream consequences. VICSES is responsible for the emergency response management of flood consequences downstream of dams. This includes warnings and information to the community and recommending evacuation for floods, including those resulting from the failure or potential failure of a dam based upon the best information made available by dam operators and DEPI. 7. Dam Failure Emergency Planning for Downstream Consequences 7.1. Dam hazard classifications Dams are classified based on the downstream consequences of their failure. The Australian National Committee on Large Dams (ANCOLD) provides guidance on such classifications. The consequence categories provide a useful basis for identifying dam safety management requirements, including planning for emergencies. Each dam can have a consequence category based on two scenarios. These are for sunny day failure condition with the reservoir full or a flood failure condition which occurs during a flood event. ANCOLD provides seven consequence categories: Very Low This category would apply to those dams where the consequences of a failure would be negligible (for example, small farm dams in remote regions). Low, Significant, High A, High B and High C Provide a graded range between the Very Low Category and Extreme Category. Extreme This category includes those dams where the effects of a failure would have immense consequences in terms of damage to property and infrastructure and could put many lives at risk with the potential for large loss of life if the dam fails (eg. large dams with major population centres downstream). 7

11 7.2. Dam failure emergency planning for downstream consequences Operators of large and hazardous dams are required to have appropriate operating and emergency management plans in place. The scope of emergency management plans will depend on the size and failure consequences associated with the dam. Where dams are identified with high potential downstream consequences of failure, particularly those with ANCOLD classifications of High A, High B, High C or Extreme, VICSES in partnership with the dam operator and in consultation with VICPOL, Local Government and the Municipal Emergency Management Planning Committees should ensure that arrangements are developed to manage the downstream consequences of any dam failure. Such planning should focus on arrangements for the warning and evacuation of the downstream community. The dam operator and DEPI will assist VICSES emergency planning for response to downstream flooding consequences. To confirm planning assumptions, dam operators will supply VICSES, where available, the following information: The ANCOLD consequence category of the dam The period over which a potential dam failure may occur Inundation maps Peak water levels Travel time for the flood wave to reach critical downstream locations (including both the front of the wave and its crest where possible) Likely flood inundation durations Flow velocities and depths Emergency contact information Dam operators need to align the response actions and communication procedures of their Dam Safety Emergency Plans with those of the VICSES. Section 9 provides a suggested alert level escalation process for dam safety events. VICPOL will need to contribute to planning for evacuation. It would be prudent to consult all relevant stakeholders when dam operators exercise their emergency plans. 8. Arrangements to Contact Response Agencies 8.1. VICSES The dam operator is responsible for contacting VICSES through its primary call taking and dispatch arrangements. The dam operator should be prepared to provide the following details: Location of the dam including nearest cross street if possible The name of the dam Contact details for the dam operator who is managing the incident at the dam Nature of the situation at the dam Prognosis of the situation at the dam Contact numbers can be obtained through VICSES Regional Offices The dam operator should at least annually confirm contact arrangements with VICSES. 8

12 Private dam owners without dam safety emergency plans will need to contact VICSES through its emergency assistance number. During heavy rainfall or earthquake events, if the failure of a dam is likely to result in a threat to lives, then the dam operator should contact Triple Zero (000) and ask for Police, stating the above details, which will also result in the activation of VICSES. VICSES is responsible for contacting other emergency services including Victoria Police, Country Fire Authority (CFA) (where they have a local response capacity) and will confirm notification with the relevant DEPI Duty Officer DEPI The dam operator is responsible for notifying DEPI Agency Commander of an imminent or actual dam safety event on the 24/7 emergency contact: DEPI will confirm notification of the dam safety incident by contacting VICSES through the call taking and dispatch priority line. In circumstances where VICSES or other agency is first to observe a dam safety incident, DEPI and the dam operator must be notified immediately BoM Dam operators should periodically contact the BoM Victorian Regional Office, Flood Warning Section to obtain current BoM contact arrangements. 9. Activation Levels and Escalation Flood Operations Plans or Dam Safety Emergency Plans developed by dam operators include warning arrangements to provide timely notice to the DEPI, VICSES and other stakeholders of a potential situation concerning flooding arising from controlled releases from a dam, escalating up to uncontrolled releases and from a possible flood arising from the failure of a dam. Various alert levels are set for dam operators to notify DEPI and VICSES of the dam conditions that may have the potential to escalate to a dam failure. These conditions include factors associated with extreme rainfall as well as sunny day events which may arise without pre-existing conditions. The adoption of the following activation levels (Figure B) within the dam owner s Dam Safety Emergency Plans is recommended. These activation levels should be agreed in consultation with the VICSES and aim to provide adequate time for people to evacuate before dam failure flooding occurs. Alert levels can best be considered after estimating the length of time needed to evacuate a community. 9

13 Figure B: Activation Levels Activation Level Defining Condition Dam Operator Action DSE Action VICSES Action No Alert Business as usual Normal dam operation No action required No action required No action required Tier 1 Potential dam safety incident Potential dam safety Incident (eg. observation of changed conditions at dam embankment or associated works ) Preliminary notification of DEPI Increase monitoring Check operational readiness Consider preliminary notification of VICSES Ensure dam owner has appropriate control of site issues Ensure dam owner seeks expert dam engineering advice Confirm with DEPI Notification of support agencies Monitoring of areas at risk downstream Check operational readiness Tier 2 Actual dam safety emergency Dam Safety Incident has occurred, Potential Emergency Observations of embankment slides/ slumps, prominent new cracking in embankments or concrete structures, reservoir vorticies, confirmed anomalous instrumentation readings, deformations, pressures, new/increased seepage, prediction of historic high storage levels, confirmed intentional threat, significant earthquake Failure possible if storage level continues to rise or structural anomaly not fixed Immediately contact DEPI and VICSES Activate DSEP Implement any agreed information notifications to downstream communities at risk Focus on the dam integrity Make dam expertise available on site to provide advice on action to minimise risk of dam failure Confirm / Notify VICSES and agreed command and control arrangements Ensure appropriate notifications and escalation processes are occurring Confirm Incident control priorities Ensure availability of dam safety expertise Confirm / Notify DEPI Notification of support agencies Establish appropriate command and control arrangements Confirm incident control priorities Warn downstream population at risk to prepare to evacuate Recommend to VICPOL to evacuate communities that may be affected by additional controlled releases Tier 3 Dam failure Failure imminent or occurring Immediately contact DEPI and VICSES Focus on the dam integrity Make dam expertise available on site to provide advice on action to minimise risk of dam failure Confirm / Notify VICSES Confirm Incident control priorities Ensure dam safety issues are being managed by owner Ensure availability of dam safety expertise Confirm / Notify DEPI Notification of support agencies Establish appropriate command and control arrangements Confirm Incident Control priorities Implement any agreed information notifications to downstream communities at risk Appropriate command and control in place Recommend to VICPOL to evacuate downstream populations For Water Corporation dams, Water Corporation will also be a Support Agency at the dam site 10

14 Appendix 1: Abbreviations ANCOLD BoM CFA CMA DEPI DSEP EMMV VICPOL VICSES Australian National Committee on Large Dams Bureau of Meteorology Country Fire Authority Catchment Management Authority Department of Environment and Primary Industries Dam Safety Emergency Plan Emergency Management Manual Victoria Victoria Police Victoria State Emergency Services 11