Bankstown Business Estate

Transcription

1 Bankstown Business Estate Flood Emergency Management Plan Prepared for Represented by Leda Holdings Pty Ltd Gemma Wawn, Development Manager Document owner Click here to enter text. Approval date Revision 0.1 Classification Restricted

2 CONTENTS 1 Introduction Background information Types of flooding at the Business Estate Indicative flood levels Flood warning times Important flood management infrastructure Flood evacuation Georges River flooding Milperra Drain catchment flooding Flood event hazards Flood management roles and contacts References FIGURES Figure 1 Bankstown Business Estate site Figure 2 Bankstown Business Estate proposed development Figure 3 Bankstown Business Estate Flood Infrastructure Figure 4 Evacuation path Georges River Flood Figure 5 Evacuation path Milperra Drain catchment flood bankstown business estate flood emergency management plan v1.docx / crm / i

3 1 Introduction This document is the flood emergency management plan for the Bankstown Business Estate. It provides a description of the hazards caused by flooding of the Business Estate, a flood evacuation plan, emergency response actions that should be carried out prior to or during a flood, and identifies the roles individuals and organisations will be responsible for during an event. More detailed information about how flooding occurs at the site can be found in the flood study report Bankstown Airport Flood Modelling Bankstown Business Estate Development, Final Report (DHI, 2015). 2 Background information 2.1 Types of flooding at the Business Estate The Bankstown Business Estate is located at the southwest corner of Bankstown Airport on Milperra Road, on the eastern side of the Georges River. The Business Estate area and surrounding roads are shown in Figure 1. Floodwaters arrive at the Business Estate from two directions: From the Georges River, when heavy rainfall in the headwaters of the Georges River catchment to the southeast of Campbelltown causes the river to rise, spilling over its banks across Henry Lawson Drive and Tower Road and into land around the Business Estate From the Milperra Drain catchment, when heavy rainfall over Condell Park and Bankstown Airport produces large volumes of stormwater, which runs overland through the airport towards the Business Estate, and also along Milperra Drain towards the southern side of the Business Estate Not all floods will produce flooding around or within the Business Estate. Only larger and rarer events will overtop the river banks, or produce large amounts of stormwater running across the airport towards the site. Large Georges River floods present the most risk to the Business Estate. Georges River floods that overflow the river banks may start to fill up airport land surrounding the Business Estate. These large river floods are produced by long storms generally lasting more than 12 hours. Milperra Drain catchment storms are less likely to flood the Business Estate than river floods. The worst Milperra Drain catchment flooding is produced by short intense storms lasting 30 minutes to several hours. These produce much faster flooding than river flood events, however they are less likely to produce high water levels that will flood the Business Estate. bankstown business estate flood emergency management plan v1.docx / crm /

4 Figure 1 Bankstown Business Estate site bankstown business estate flood emergency management plan v1.docx / crm /

5 Figure 2 Bankstown Business Estate proposed development bankstown business estate flood emergency management plan v1.docx / crm /

6 2.2 Indicative flood levels Georges River events Georges River flood levels have been estimated based on design floods. These are hypothetical floods that are expected to occur on average once in a given number of years. For example, the 1% Annual Exceedence Probability (AEP) event is expected to occur on average once every 100 years (i.e. in 1% of years). AEP is the probability of a design flow being equalled or exceeded. The 1% AEP flood (on average once in 100 years) is expected to have a level of approximately 5.8 metres AHD on the northwest side (Tower Road side) of the Estate; this water level will overflow into the Estate carparks and roads, and run southwards towards Milperra Road The 5% AEP flood (on average once every 20 years) is expected to have a level of 4.9 metres AHD on the northwest side (Tower Road side) of the Estate; this would not overflow into the Business Estate Milperra Drain catchment events Milperra Drain catchment flood design events produce lower peak flood levels than Georges River flood design events: The 1% AEP (on average once in 100 years) is expected to have a level of approximately 5.3 metres AHD on the northwest side (Tower Road side) of the Estate; this level is below (but approaching) the level at which overflow starts to run into the Estate carparks and roads. The above levels are from the Bankstown Airport Flood Modelling Bankstown Business Estate Development, Final Report (DHI, 2015), and from the Georges River Flood Study (NSW Public Works, 1991). 2.3 Flood warning times The warning time depends on whether the flood is caused by Georges River flooding or Milperra Drain catchment stormwater runoff. Georges River flooding Georges River floods will generally have long warning times. The Georges River Flood Study (NSW Public Works, 1991) reviews the recorded hydrographs of historical floods in 1978, 1983 and 1986 and 1988 on the Georges River at Liverpool, upstream of the Business Estate. In each case, there is at least 12 hours between river levels starting to rise and the peak flood level occurring. However each flood will differ and the SES should be taken as the best source of information in every flood as it arises. In a Georges River flood event the Bureau of Meteorology will issue warnings based on forecast and observed rainfalls on the upstream Georges River catchment. Based on these rainfalls and monitoring of water levels at Liverpool and Milperra, the Bureau will forecast likely flood arrival times and peak levels at river gauges along the Georges River. Milperra Drain catchment flooding Milperra Drain floods will have short warning times. The Milperra Catchment Flood Study Update (BMT WBM 2013) identifies the Milperra Catchment as having a critical storm duration of 2 hours. However shorter or longer storms may also cause extensive flooding at the Estate site. bankstown business estate flood emergency management plan v1.docx / crm /

7 There are unlikely to be detailed warnings provided by the Bureau of Meteorology or the SES of major stormwater runoff from the Milperra Drain catchment. Water levels in drains surrounding the Estate may start to rise as quickly as minutes after the start of a major rainfall. They may then continue to progressively rise as more water runs through the airport drainage system, and overland across the airfield. This potentially short warning time means responsible staff (see Section 5) within the site will need to monitor airport drain flows during and after very heavy rainfall events. 2.4 Important flood management infrastructure To prevent floodwater in the airport from getting too high and flooding buildings and other infrastructure, the Business Estate includes several important infrastructure features (the locations of these features is shown in Figure 3): Non-return outlet valves underneath Tower Road: Large culverts drain the airport and run underneath the Tower Road roundabout at the Tower Road entrance to the Business Estate. Non-return flaps on the outlet of these culverts prevent Georges River floodwater from flowing back up the culverts and into the airfield. These valves operate as soon as Georges River flood levels are above the culvert outlet level. Flood relief culverts under the Business Estate: Large culverts run underneath the Business Estate, allowing floodwater to run from airport land near Tower Road underneath the Estate, and exiting near Milperra Road. Overland flow through the Business Estate: A floodway allows water to run directly through the Business Estate from airport land towards Milperra Road. This overland flow path only operates in the largest events, when the capacity of the flood relief culverts under the Estate is exceeded. Note that there are two specific areas within the flowpath that are kept clear of development the Northwestern Floodway and the Southern Floodway. The correct operation of this infrastructure is important as it minimises flood risk to the Business Estate as well as to adjacent sites. It is recommended that staff responsible for flood management familiarise themselves (see Section 5) with this infrastructure. bankstown business estate flood emergency management plan v1.docx / crm /

8 Figure 3 Bankstown Business Estate Flood Infrastructure Non-return valves under Tower Road Flood relief culverts under Estate Northwest Floodway Flood storage Southern Floodway bankstown business estate flood emergency management plan v1.docx / crm /

9 3 Flood evacuation Flood evacuation procedures from the Business Estate depend on the source of the flooding. Georges River flooding and Milperra Drain catchment flooding require different evacuation approaches. 3.1 Georges River flooding Monitoring and warning procedure A major flood in the Georges River will be forecast and broadcast by the Bureau of Meteorology and the SES. If heavy rainfall in the Georges River catchment is forecast by the Bureau of Meteorology: Responsible site personnel (see Section 5) will monitor warning broadcasts, distribute current warning information to all properties within the Estate, and advise them to start evacuation preparations; and Upon a major flood warning being issued they will advise all properties within the Estate to begin evacuation. Evacuation procedure If a major flood warning for the Georges River is issued then the Business Estate should be evacuated, and people should be advised not to enter the site. Evacuation should proceed as follows (also see Figure 4): Evacuation should be carried out as soon as possible after the flood warning is given Do not wait until the Georges River breaks its banks at Milperra: o The preferred evacuation route from the Business Estate is northwards along Tower Road by either vehicle or on foot o Evacuation along Milperra Road should only be attempted if there has not been heavy rainfall over the Business Park and Condell Park area, and if the road is completely free of flooding In the case that the Georges River at Milperra has broken its banks before evacuation has been possible: o If there is any flooding on Tower Road, evacuation must be by foot within the airport o Move to the northeast boundary of the Business Estate, next to the Airport southern taxiway o Paying close attention to any plane movements within the airport, leave the Business Estate and pass through the security gate into the airport (see Figure 5) o Walk to the southeast along the edge of the southern taxiway (towards Bunnings and Nancy Ellis Leebold Drive), as indicated in Figure 5 Airport Evacuation Plan) o At the end of the taxiway walk around the eastern edge of the airfield along Nancy Ellis Leebold Drive, heading to the north towards Condell Park High School. Evacuation timing Evacuation without any notice of Georges River flooding is very unlikely. However, the vehicular evacuation routes of Tower Road and Milperra Road are both susceptible to flooding in a major Georges River flood: By the time the Georges River at Milperra has broken its banks, Milperra Road may have become unpassable. bankstown business estate flood emergency management plan v1.docx / crm /

10 As river levels at Milperra rise further, Tower Road will then become flooded before the Business Estate becomes flooded. This means it may be too late to evacuate by vehicle if evacuation is deferred until the Estate starts to flood. In summary, in order to avoid people being isolated within the site during a Georges River flood event, evacuation should be carried out as early as possible following a major flood warning. 3.2 Milperra Drain catchment flooding Monitoring and warning procedure As discussed in Section 2.3, there are unlikely to be any formal warnings for flooding originating from the Milperra Drain catchment. It will be up to personnel within the Business Estate site to monitor the surrounding area to initiate evacuation. The monitoring and warning process is as follows: If heavy rainfall occurs over the Milperra Drain catchment, responsible site personnel (see Section 5) will monitor the water level in the Tower Road Drain (at the Tower Road roundabout entrance to the Estate) If water enters the major flood relief culverts that run underneath the Estate towards Milperra Road: o responsible site personnel will issue a warning to all property owners to prepare for evacuation within the site o As a precautionary measure all vehicles should be removed from the carpark within the floodway and placed on higher ground in the northern part of the Estate If water levels within the major flood relief culverts continue to rise and reach halfway up the pipe cross-section, evacuation within the site should start Evacuation procedure If water levels have risen in the flood relief culverts to over halfway of the cross-section, evacuation inside the site should proceed as follows (also see Figure 6): All people in the south west part of the site (in Lot 2, Lot 3, Lot 4 and Lot 5 in Figure 2) should immediately move to the northern area of the Estate, which has higher ground levels They should remain in the northern part of the Estate for the duration of the event, which will remain flood free in all events up to and including the Probable Maximum Flood (BMT WBM, 2015) bankstown business estate flood emergency management plan v1.docx / crm /

11 Figure 4 Evacuation path Georges River Flood Preferred vehicle evacuation route (Tower Road) Indicative security gate location Alternative foot evacuation route (to Nancy Ellis Leebold Dr) bankstown business estate flood emergency management plan v1.docx / crm /

12 Figure 5 Airport Evacuation Routes (provided by Bankstown Airport Limited) bankstown business estate flood emergency management plan v1.docx / crm /

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14 Figure 6 Evacuation path Milperra Drain catchment flood Evacuation from Lots 2, 3, 4 and 5 into Lot 6 bankstown business estate flood emergency management plan v1.docx / crm /

15 4 Flood event hazards There are a number of hazards within and around the site to be considered. It is recommended that Estate personnel responsible for flood management review these hazards periodically to minimise their impact should an event arise: Vehicle stability site access: Travelling to and from the Estate by vehicle is not advised if roads become flooded. Light vehicles in general lose traction and will start to move in flows approaching metres deep. Driving through any depth of water should be avoided given the difficulty in estimating flood depths, and variations in stability between vehicles. Vehicle stability carparks: Parked vehicles will become mobile as floodwaters rise, and will start to move and become potentially hazardous as they collide with other vehicles, buildings or people during the flood. They may also block critical flood and drainage channels and culverts. Furthermore, they may leak oil and fuel and contaminate floodwater. For these reasons, it is required carparks in the southern part of the site (in particular between the floodways) are emptied prior to the onset of flooding. Pedestrian stability: People wading through floodwater will become unstable depending on the speed of the flood and the depth of floodwater. All wading should be avoided unless absolutely necessary. Wading in the northwest floodway adjacent to Tower Road and southern floodway near Milperra Road is to be avoided in particular. Floodwater contamination: Buoyant, dissolvable or dispersible materials will potentially contaminate floodwaters. It is recommended responsible personnel identify potential sources of contamination prior to any events, and plans are prepared for their removal, protection or sealing should a flood occur. Structure collapse: Floodwaters place large static and dynamic loads on structures. Finished floor levels of buildings within the Estate are well above the 1% AEP flood level. However it should be noted that any minor structures such as kiosks may collapse under a significant depth or fast-moving flow. Debris: Flood debris from outside the Estate, or which has become mobilised within the Estate, poses a significant hazard to wading pedestrians and property, and to critical flood and stormwater infrastructure. bankstown business estate flood emergency management plan v1.docx / crm /

16 5 Flood management roles and contacts Role Business Estate Flood Hazard Manager Flood Event Manager SES Local Controller Person or Estate management role responsible [Name] Phone: Mobile: [Name] Phone: Mobile: [Name] Phone: Mobile: Description - Review overall flood preparedness of Estate - Identify and mitigate contamination, structure collapse and debris hazards - Liaise with SES and Bankstown Council on emergency preparedness - Liaise with property owners within the Estate and Bankstown Airport to keep them informed of procedures - Brief Flood Event Manager on role - Maintain this document - Monitor and alert the Estate to potential flood situations - Manage evacuation - Coordination of flood activities within the Local Government Area - Working to raise flood awareness bankstown business estate flood emergency management plan v1.docx / crm /

17 6 References BMT WBM, Milperra Catchment Draft Flood Study Update, BMT WBM, October 2013 BMT WBM, Bankstown Business Estate Development at Bankstown Airport Flood Impact Assessment (DRAFT), BMT WBM, May 2015 DHI, Bankstown Airport Flood Modelling Bankstown Business Estate Development, DHI Water and Environment Pty Ltd, July 2014 NSW Public Works, Georges River Flood Study, PWD Report No , December bankstown business estate flood emergency management plan v1.docx / crm /

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