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APPENDIX J

Floodplain Risk Management Guideline

NSW Government

DEPARTMENT OF ENVIRONMENT & CLIMATE CHANGE

FRM Guidelines are prepared to assist Councils in the preparation and implementation of their FRM plans Queries can be directed to your local DECC floodplain risk management contact or [email protected]

Version No: 1.01 Status: Final Issue date 25/10/2007 Authorisation: Director Coast & Floodplain ManagementNote: This information does not constitute legal advice

© State of New South Wales through the Department of Environment & Climate ChangeThe User is responsible for ensuring that the most recent version of this guideline is used

SummaryThis floodplain risk management (FRM) guideline outlines the outputs from the FRM process required to assist the State Emergency Service (SES) in effective emergency response planning (ERP). The outputs and the associated work required depend upon the type and scale of emergency response problems for the location as discussed in the FRM Guideline – Flood Emergency Response Classification for Communities.

Introduction

The Floodplain Development Manual, 2005 requires studies and plans to incorporate extra information to enable the SES to undertake effective ERP. This requires an understanding of both the emergency response problem and associated emergency response logistics.

Effective ERP requires consideration of events other than peak flood events where areas may need evacuation as it is essential to consider the differences in logistics between:

Historic events (testing for real events).

A range of design events (5, 20, and 100 year average recurrence interval (ARI) flood events and the probable maximum flood, PMF).

Shorter duration events (100 year ARI flood event and the PMF). Testing events that may be critical for evacuation logistics even though they may produce slightly lower peak flood levels. For example, where a key emergency response route may be cut leaving an area isolated in a smaller ARI event or much sooner than in the peak level design flood.

In addition, some information provided in studies now needs to also be presented in a different format to enable it to be more readily used by the SES.

Recommendations

It is recommended that the SES be provided with information relevant to the specific location as outlined in the following sections of the guideline and in the specific formats indicated:

Section 1 Inclusions in a Flood Study

Section 2 Inclusions in a Floodplain Risk Management Study

Section 3 Extra information required for areas protected by existing or proposed levees

Section 4 Format of Data

Section 5 Simplistic Example to Illustrate Use of the Guideline

This information is to be provided electronically at the draft study stage and in the final format on the final project CD with a summary of the inclusions provided in an appendix to the study.

References

Department of Infrastructure Planning and Natural Resources. “Floodplain Development Manual: the management of flood liable land”, gazetted May 2005.

McLuckie D.B. Opper S. Co-operative Management of Flood Risk, 2003. Australian National Disaster Conference. Canberra September 2003.

McLuckie D.B. How the Floodplain Risk Management Process can assist Emergency Response Planning. Gunnedah February 2007. FRM Workshop with FMA Conference.

SES Requirements from the FRM Process

APPENDIX J

SES Information Requirements from the FRM ProcessFloodplain Risk Management Guideline

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Section 1 Inclusions in a Flood Study

An integral part of effectively managing the full range of flood risk requires investigations under the flood study is to provide additional flood intelligence to the SES and provide more specific information on flood behaviour and the associated risks. This includes:

Summary of historic information and other intelligence collected as part of data collection.

Plans indicating cross section location or chainages as per the river long section, for ease of data interpretation.

Plans showing the base digital terrain/elevation model to AHD where appropriate and available.

Plans showing river long sections with flood level variations for historical and design events related directly to the key warning gauge heights. Separate plans should be provided for historical and design floods. Confidence banding should be added to the planning flood long sections based upon calibration and sensitivity analyses.

Provision of a description of physical flood behaviour in plain English terms for a layman audience. This is to include a description of the development and pattern of flood behaviour.

Describe specific risk areas in the context of the potential consequences of flooding from more frequent, major and extreme events. The descriptive criteria in FRM Guideline Flood Emergency Response Classification of Communities should be used to delineate areas of the floodplain for different scale events.

Where the flood study includes an assessment of flood damages, a spreadsheet of ground and floor levels for houses and flood levels for design and historic events, relative to the key flood warning gauge height is to be provided. This can be based upon the information developed for the damage assessment. The source of the base information should be included.

Plans indicating a minimum of flood extents, floodways, flood storage areas and flood fringe areas. Definition of flood hazards should be included (where assessed) based upon the categorisation in the Floodplain Development Manual or similar approach as agreed with DECC.

Where levees exist, the information requirements for levees outlined in Section 3, are to be met.

Modelling of flood behaviour that defines the variation over time of flood levels, extents and velocities for each of the critical design events. This may require modelling of shorter duration 100 year ARI and PMF or equivalent extreme events to provide advice in relation to the potential differences in time available for response.

Specific input is to be prepared for the SES to consider when next updating the local flood plan. Annex A of the Local Flood Plan: describes physical flood behaviour. This section needs to be reviewed and an update drafted. The update can be based around the description in the management study but needs to be in plain English terms for a layman audience.

Section 2 Inclusions in a Floodplain Risk Management Study

An integral part of effectively managing the full range of flood risk requires investigations under the FRM study to:

Review the local flood plan, identify deficiencies in information and provide selected draft input, whether the existing plan specifically addresses the study area or not.

Provide additional flood intelligence to the SES as indicated in below.

Provide additional information for existing and proposed levees as per Section 3.

The SES will consider this information in any future review of the local flood plan.

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Annex B of the Local Flood Plan: describes specific risk areas in the context of flood consequences. This section needs to be reviewed and an update drafted in light of the understanding of flood behaviour and the associated consequences from the study.

The study may identify different risk factors, a larger range of flood risk, more specific information on risk and new areas of risk. The description needs to relate to specific information as outlined below and to the impacts and consequences of an extreme flood event:

Describe the flood warning system and key warning reference gauge(s) for the area and the basis of the available warning.

Indicate the average times between flood producing rain and exceedance of critical flood levels (typically overtopping of key evacuation routes or to exceed levee design height as discussed with SES) at key warning reference gauges based upon the hydrological modelling of rainfall. Table 1 indicates the range of floods to be considered and associated information necessary.

Compare these times against warning lead times specified in the SES NSW State Flood Plan. If required warning times exceed the physical time between rainfall and critical flood levels, then a higher risk to quantitative flood forecasting, involving quantitative precipitation forecasts

from numerical weather predictions may be necessary. This involves a higher risk approach to flood forecasting than simple using recorded rainfall in hydrological modelling and should be discussed with the Bureau of Meteorology.

Identify the flood classification of particular Identify the flood classification of particular areas in accordance with FRM Guideline – Flood Emergency Response Classification of Communities. A plan is to be produced that shows these areas and their classification.

For each classification in FRM Guideline – Flood Emergency Response Classification of Communities provide the information outlined for the classification in Table 2.

This information should also be provided in a tabular form similar to Tables 3 and 4. This should be supported by specific information on impacts and consequences.

Identify issues limiting the potential of evacuation centres in the flood plan. This may relate to evacuation routes or flooding of centres. Alternate centres may be indicated for consideration.

Impacts of recommended management options. This should describe the changes in impacts resulting due to the implementation of each action in the recommended management plan. This should include any resultant changes to Table 3.

Table 1 Indicative Timing to Reach Critical Consequence Height

Critical Consequence Heights

Levee Design Height

Key Evac Routes

Cut

Private Property Floods

Homes Start to Flood

Whole Area

FloodedPeak Flood Height

m

Time to

Peak hrs

Isolation Time hours

Warning Lead Time

hours (from State Flood Plan)

Level m Gauge Height

Flood Event Time - Flood Producing Rain to Critical Height Exceedance hrs

Key Historical

20 yr ARI Peak Height

100 yr ARI Peak Height

100 yr ARI Short

Peak Height PMF

Short Duration* PMF

* A short duration event with significant impacts at critical consequence heights is to be tested to provide an indication of the sensitivity of available lead times to storm patterns

Section 2.1 - Specific Draft Input into the Local Flood Plan for SES Consideration

APPENDIX J


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Table 2 Key Considerations for Areas with Different Flood Emergency Response Classifications

Key Considerations

High Flood

Islands HFI

Low Flood

Islands LFI

High Trapped

Perimeter(HTP) Area

Low Trapped

Perimeter (LTP) Area

Area with Overland Escape Route (OER)

Area with Rising Road

Accessible (RRA)

Indirectly Affected

Areas(IAA)

External Access Cut, area becomes isolated * * * * *Key Internal Roads Cut * * * *

Overground Flooding of Private Ground Starts * *Over Floor Flooding of Houses/Businesses Starts * *Over Floor Flooding of Speacial Evacuation Needs

(Child/Aged Care & Schools) Starts * *Transport Infrastructure Shutdown (Railways/

Airports) * * * * * * *Flooding of Key Response Infrastrcture Starts

(Hospitals/Evacuation Centres) * * * *Risk of flooding of Key Public Utilities (water/

sewage/gas/power) starts * * * * * * *Whole Area Flooded or Max Flood Extents Occur * * * * * * *

* Key considerations for Particular Flood Emergency Response Classifications

Table 3 Impacts/Consequences at Specific Locations Relative to Gauge Height

Notes:a. A Plan is to be produced that shows these areas and their flood emergency response classification (refer FRM Guideline – Flood Emergency

Response Classification of Communities and Table 2).b. These figures are to be indicative only

Location/Classification/Description

egs - Evac - how & where to (self evac, SE)

road cut - where, how, (by local LF or river flooding RF)

Gauge Height

(m Gauge)

Properties AffectedProperties Affected Above Floor Level

Indicative Time

Above this Level

Hrs

Issue or Event Location/Classification Residential Others Residential Others

Effective Warning Time Description

Evacuation Starts

Access Cut

Private Property FloodsKey Infrastructure Flooding

Starts


Businesses start to FloodAll Houses Flooded

Whole Area Flooded

APPENDIX J


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This involves the following (where not provided in or updated since the flood study):

Summary of historic information and other intelligence collected as part of data collection.

Plans indicating cross section location or chainages as per the river long section, for ease of data interpretation.

Plans showing the base digital terrain/elevation model to AHD where appropriate and available.

Plans showing river long sections with flood level variations for historical and design events related directly to the key warning gauge heights. Separate plans should be provided for historical and design floods. Confidence banding should be added to the planning flood long sections based upon calibration and sensitivity analyses.

Provision of a description of physical flood behaviour in plain English terms for a layman audience. This is to include a description of the development and pattern of flood behaviour.

Describe specific risk areas in the context of the potential consequences of flooding from more frequent, major and extreme events. The descriptive criteria in the FRM Guideline on Flood Emergency Response Classification of

Communities should be used to delineate areas of the floodplain for different scale events.

A spreadsheet of ground and floor levels for houses and flood levels for design and historic events, relative to the key flood warning gauge height is to be provided. This can be based upon the information developed for the damage assessment. The source of the base information should be included.

Plans indicating a minimum of flood extents, floodways, flood storage areas and flood fringe areas. Definition of flood hazards should be included (where assessed) based upon the categorisation in the Floodplain Development Manual or similar approach as agreed with DECC.

Where levees exist or are proposed, the information requirements for levees outlined in Section 3 are to be met.

Modelling of flood behaviour that defines the variation over time of flood levels, extents and velocities for each of the critical design events. This may require modelling of shorter duration 100 year ARI and PMF or equivalent extreme events to provide advice in relation to the potential differences in time available for response.

Table 4 Consequences Relative to Gauge Height

Notes:a. Information in Table 4 comes directly out of Table 3 but is in gauge height order.b. Consequences should be indicated in height increments of 0.1 to 0.5m, depending upon the overall variation in flood level.c. No people affected is indicative only and can be based upon no buildings affected and assumptions to be stated.

Gauge Height Range (including

sensitivity)m Gauge

Location (Area)

DescriptionExamples

evacuation - where to & how (Self evac (SE)road cut - where, how (by local LF or

Riverine RF flooding)

Consequences

No Building AffectedIndicative No People

Affected

Residential Others Residential Others

Height 1

Height 2

Height 3

Section 2.2 - Update of Flood Intelligence

APPENDIX J


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The following additional information (where available) is to be provided to the SES in relation to existing and proposed levees in addition to the information outlined in Sections 1 and 2.

It is likely that in many cases output relating to overtopping and backwater flooding will vary between different floods. In these cases a description of each flood scenario; and details of associated required outputs and an indication of confidence will be required.

Description of the levee, detailing, location, construction type and the areas protected.

The name, id number and gauge zero (in metres AHD) for the relevant flood warning gauge.

The following heights relative to the relevant flood warning gauge and their respective AEP:

Levee Design Height and Imminent Failure flood (where calculated)

Overtopping Heights of Levee Low Points

Levee Spillway Heights

Likely locations of levee overtopping and the sequence of overtopping and flooding (these outputs should be presented in a spatial format, accompanied by a description).

Size of the population, the number of residential and commercial properties, and critical infrastructure affected by levee over-topping or failure. This output should be expressed in relation to a variety of flood magnitudes, including a worst case scenario.

Scope for additional development in areas protected by levees, considering current zoning of land.

The height relative to the relevant flood warning gauge that any backwater flooding commences impacting upon urban areas behind each levee and the pattern of inundation.

Once over-topped the length of time taken to fill the basin area behind each levee and the development and pattern of flood behaviour.

Details of ground profile (topography) inside each levee and the height of potential high points of land relative the relevant flood warning gauge.

Location of any parts of each levee which need to be closed other than drains (example: gates for roadways and railways) and the height relative to the relevant flood warning gauge that action must be completed by.

Knowledge of any critical issues including structural integrity affecting each levee.

Section 3 - Additional Information for Existing and Proposed Levees

Data is to be provided electronically at the draft study stage and in the final format on the final project CD with a summary of the inclusions provided in an appendix to the study. It is to be provided in the following formats unless otherwise agreed to in writing by SES HQ.

Text is to be provided in Microsoft Word format.

Spreadsheets in Microsoft Excel format.

Plans are to be readable, have legible text at A3 scale and able to be produced at that size. Electronic copies of plans produced for the studies are to be in a format compatible with Autocad, ARCGIS9 or MapInfo.

Flood GIS outputs should be provided with polygons as a minimum with preference for the provision of grid (rastor) information if available and coordinated to an appropriate grid.

Section 4 - Format of Data

Section 5 - Simplistic Example To Illustrate Use of the Guideline

Following is a simple example of developing Tables 1 to 4 in the document. The associated information in the tables can then be used to assist in ERP.

Sites 1 and 4 shown in Figure 1 are the focus of this example. Figure 1 shows the extent of the 100 year ARI flood in the area showing that sites 1 and 4 are

isolated. Figure 2 shows the extent of the PMF in the area and highlights that site 4 is completely inundated whilst site 1 has a reasonable sized area above the PMF. They are therefore classified as low and high flood islands respectively. The key considerations for these are outlined in Example Table 2.

APPENDIX J


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Flood Levels versus Time

Access Cut

Area Flooding

Houses Flooding

Whole Area Flooded

100 yr peak

PMF peakPMF short

2

4

6

8

10

12

14

0 12 24 36 48

Time hours

Floo

d Le

vel (

m G

auge

Hei

ght)

Figures 1 and 2 Showing potential development sites with 100 year ARI (left) and PMF (right) flood extents. Note Classification of Areas. Interest is in Areas 1 and 4 only.

High Flood Island

Low Flood Island

Figure 3 Flood Hydrographs for the Location

Figure 3 gives flood hydrographs for the location highlighting the importance of considering timing and different duration and scales of flooding for ERP. The hydrograph is translated into key levels versus timings in the Example Table 1.

Figure 4 highlights the hydraulic categories to indicate the hydraulic function of different areas of the floodplain. Figure 5 indicates the degree and type of hazard and highlights that ERP is a key issue for both Sites 1 and 4, as these are flood islands.

Example Table 3 summarises the key emergency response impacts and consequences for Area 4 for different gauge heights. Example Table 4 combines the consequences of different areas so that actions can be summarised for the broader area relative to the gauge height they need to be completed by or occur at.

All the information developed in this simplistic example is useful for ERP.

APPENDIX J


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Figures 4 and 5 Hydraulic Categories and Flood Hazard Degrees and Types

Hydraulic Categories

Floodway

Flood Fringe

Flood Storage

LLLLLL

Velocity

Emergency Response

Depth

High Hazard

Low Hazard

Type & Degree of Hazard

Low Flood Island

High Flood Island

APPENDIX J


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Example Table 1 Indicative Timing to Reach Critical Consequence Height

Critical Consequence Heights

Bridge Cut

Private Property Floods


Whole Area

FloodedPeak Flood Height

m

Time to

Peak hrs

Isolation Time hoursCritical Gauge Height m 7 9 9.5 10.75

Flood Event Time - Flood Producing Rain to Critical Height Exceedance hrs

100 yr ARI Peak Height 13 15 16 - 10.5 19 15

Peak Height PMF 11 13 13.5 15 13.85 20 21

Short Duration* PMF 9 11 12 12.75 13.15 16 17

Key ConsiderationsHigh Flood Islands HFI

Low Flood Islands LFI

External Access Cut, area becomes isolated * *Key Internal Roads Cut *

Overground Flooding of Private Ground Starts *Over Floor Flooding of Houses/Businesses Starts *

Over Floor Flooding of Speacial Evacuation Needs (Child/Aged Care & Schools) Starts *Transport Infrastructure Shutdown (Railways/Airports) * *

Flooding of Key Response Infrastrcture Starts (Hospitals/Evacuation Centres) *Risk of flooding of Key Public Utilities (water/sewage/gas/power) starts * *

Whole Area Flooded or Max Flood Extents Occur * *

Example Table 2 Key Considerations for Areas with Different Flood Emergency Response

* Key considerations for Particular Flood Emergency Response Classifications

APPENDIX J


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Example Table 3 Impacts/Consequences at Specific Locations Relative to Gauge Height

Location/Classification/DescriptionExamples

Evac - how & where to (self evac, SE)

road cut - where, how, (by local LF or river flooding RF)

Gauge Height

(m Gauge)

Properties AffectedProperties

Affected Above Floor Level

Issue or Event Area 4 - Low Flood Island Houses Others Houses Others

Effective Warning Time Min 9 hours

Evacuation Starts If Flood Predicted > 6.25m 5

650

31 total10 Commercial

1 School*3 Public*

15 Industrial1 Club

1 Nursing Home*

Access CutBridge Overtopped/Access Cut - Evac needs to be completed or assistance

required7

Private Property Floods 9

Key Infrastructure Flooding Starts 9.25

Homes Start to Flood 9.5 5

Businesses start to Flood 9.75 150 1All Houses Flooded 10.25 650 20

Whole Area Flooded 10.75 650 31

Example Table 4 Consequences Relative to Gauge Height

Gauge Height Range

m Gauge

Location (Area)

DescriptionExamples

evacuation-whereto&how(Selfevac(SE)road cut - where, how (by local LF or Riverine RF flooding)

Consequences

No Building Affected

Houses Others

4.0m Rural Areas Flooding Starts in Rural Areas

5.0m Southern Rural Areas Areas to Town Cut - Evacuate to Next Town

Area 4 Start Evac if Peak predicted >6.25m

6.0m Southern Rural Areas Farm Buildings Flood 2

6.5m Southern Rural Areas Cut off - Evacuation needs to be completed 5

6.75m Area 4 Evacuation needs to be completed 107.0m Area 4 Isolated-AccesstoTown&nextTownCut 5 12

Southern Rural Areas Rural Homes Start to Flood 5 12

9.0m Area 4 Private Homes Start to Flood 5 15

9.5m Area 4 Houses Start to Flood 15 20

10.25m Area 4 All Houses Flooded 665 35

10.75m Area 4 Whole Area Flooded 665 51

* Developments which are particularly vulnerable in emergency response

APPENDIX J


Queries can be directed to your regional DECC floodplain risk management contact or [email protected]

Version No: 1.0 Status: Final Issue date 15/08/2007 Authorisation: Director Coast & Floodplain ManagementNote: This information does not constitute legal advice© State of New South Wales through the Department of Environment & Climate ChangeThe User is responsible for ensuring that the most recent version of this guideline is used

NSW Government

DEPARTMENT OF ENVIRONMENT & CLIMATE CHANGE

SummaryThis guideline was developed in conjunction with the State Emergency Service (SES) to provide a basis for the flood emergency response categorisation of floodplain communities (both existing and future). Classification provides an indication of the relative vulnerability of the community in flood emergency response and when used with FRM Guideline SES Information Requirements from the Floodplain Risk Management (FRM) Process it identifies the type and scale of information needed by the SES to assist with emergency response planning (ERP).

Introduction

The Floodplain Development Manual, 2005 requires flood studies and FRM studies and plans to address the management of continuing flood risk to both existing and future development areas. As continuing flood risk varies across the floodplain so does the type and scale of emergency response problem and therefore the information necessary for effective ERP.

This guideline provides a basis for the categorisation of floodplain communities into various flood ERP classifications. Table 1 provides an indication of the response required for areas with different classifications. However, these may vary depending on local flood characteristics and resultant flood behaviour i.e. in flash flooding or overland flooding areas.

These classifications are defined in Section 1 and are determined by using the flowchart provided, Figure 1.

Recommendations

It is recommended that the ERP classification of the floodplain be undertaken for the 20 and 100 year average recurrence interval (ARI) and Probable Maximum Flood (PMF) events.

References

Department of Infrastructure Planning and Natural Resources. “Floodplain Development Manual: the management of flood liable land”, gazetted May 2005.

Flood Emergency Response Planning Classification Of Communities

ClassificationResponse Required

Resupply Rescue/Medivac Evacuation

High Flood Island Yes Possibly Possibly

Low Flood Island No Yes Yes

Area with Rising Road Access No Possibly Yes

Areas with Overland Escape Routes No Possibly Yes

Low Trapped Perimeter No Yes Yes

High Trapped Perimeter Yes Possibly Possibly

Indirectly Affected Areas Possibly Possibly Possibly

Table 1 Response Required for Different Flood ERP Classifications

APPENDIX J


Version No: 1.0 Status: Draft Issue date 30/05/2007 Authorisation: Director Coast & Floodplain ManagementNote: This information does not constitute legal advice© State of New South Wales through the Department of Environment & Climate ChangeThe User is responsible for ensuring that the most recent version of this guideline is used

Flood Emergency Response Planning Classification of Communities


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Section 1 Flood ERP Classification of Communities

To assist in the planning and implementation of response strategies the SES classifies communities according to the impact that flooding has on them. Flood affected communities are those in which the normal functioning of services is altered either directly or indirectly because a flood results in the need for external assistance. This impact relates directly to the operational issues of evacuation, resupply and rescue. The classifications used are described below.

NOTE: These definitions are described in terms of the impact of a PMF or equivalent extreme event. Because of the difference in flood effects at lower levels, the operational classification of an area during an actual flood of lower severity could be different to the PMF planning classification. The classification of the area should also be undertaken for the 100 year ARI flood event (or dominant planning flood) and stated on any classification.

Section 1.1 Flood Islands

These are inhabited or potentially habitable areas of high ground within a floodplain linked to the flood-free valley sides by a road along a low ridge. The road can be cut by floodwater, closing the only evacuation route and creating an island. After closure of the road the only access to the area is by boat or by aircraft.

Flood islands are classified according to what can happen after the evacuation route is cut as follows:

High Flood Island (HFI). The flood island includes enough land higher than the limit of flooding (i.e. above the PMF) to cope with the number of people in the area. During a flood event the area is surrounded by floodwater and property may be inundated. However, there is an opportunity for people to retreat to higher ground above the PMF within the island and therefore the direct risk to life is limited. The area will require resupply by boat or air if not evacuated before the road is cut. If it will not be possible to provide adequate support during the period of isolation, evacuation

will have to take place before isolation occurs.

Low Flood Island (LFI). The flood island is lower than the limit of flooding (ie below the PMF) or does not have enough land to cope with the number of people in the area. During a flood event the area is isolated by floodwater and property will be inundated. If floodwater continues to rise after it is isolated, the island will eventually be completely covered. People left stranded on the island may drown and property will be inundated.

Section 1.2 Trapped Perimeter Areas

These would generally be inhabited or potentially habitable areas at the fringe of the floodplain where the only practical road or overland access is through flood prone land and unavailable during a flood event. The ability to retreat to higher ground does not exist due to topography or impassable structures. Trapped perimeter areas are classified according to what can happen after the evacuation route is cut as follows.

High Trapped Perimeter (HTP) Area. The inhabited or potentially inhabited area includes enough land to cope with the number of people in the area that is higher than the limit of flooding (ie above the PMF). During a flood event the area is isolated by floodwater and property and may be inundated. However, there is an opportunity for people to retreat to higher ground above the PMF within the area and therefore the direct risk to life is limited. The area will require resupply by boat or air if not evacuated before the road is cut. If it will not be possible to provide adequate support during the period of isolation, evacuation will have to take place before isolation occurs.

Low Trapped Perimeter (LTP) Area: The inhabited or potentially inhabited area is lower than the limit of flooding (ie below the PMF) or does not have enough land to cope with the number of people in the area. During a flood event the area is isolated by floodwater and property may be inundated. If floodwater continues to rise after it is isolated, the area will eventually be completely covered. People trapped on the island may drown.

APPENDIX J





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Section 1.3 Areas Able to be Evacuated

These are inhabited areas on flood prone ridges jutting into the floodplain or on the valley side. However, their categorisation depends upon the type of evacuation access available, as follows.

Areas with Overland Escape Route (OER) are those areas where access roads to flood free land cross lower lying flood prone land. Evacuation can take place by road only until access roads are closed by floodwater. Escape from rising floodwater is possible but by walking overland to higher ground. Anyone not able to walk out must be reached by using boats and aircraft. If people cannot get out before inundation, rescue will most likely be from rooftops.

Rising Road Access (RRA) Areas are those areas where access roads rising steadily uphill and away from the rising floodwaters. The community cannot be completely isolated before inundation reaches its maximum extent, even in the PMF. Evacuation can take place by vehicle or on foot along the road as floodwater advances. People should not be trapped unless they delay their evacuation from their homes. For example people living in two storey homes may initially decide to stay but reconsider after water surrounds them.

These communities contain low-lying areas from which persons will be progressively evacuated to higher ground as the level of inundation increases. This inundation could be caused either by direct flooding from the river system or by localised flooding from creeks.

Section 1.4 Indirectly Affected Areas (IAA)

These are areas which are outside the limit of flooding and therefore will not be inundated nor will they lose road access.

However, they may be indirectly affected as a result of flood damaged infrastructure or due to the loss of transport links, electricity supply, water supply, sewage or telecommunications services and they may therefore require resupply or in the worst case, evacuation.

Section 1.5 Overland Refuge Areas

These are areas that other areas of the floodplain may be evacuated to, at least temporarily, but which are isolated from the edge of the floodplain by floodwaters and are therefore effectively flood islands or trapped perimeter areas. They should be categorised accordingly and these categories used to determine their vulnerability.

APPENDIX J





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Figure 1 – Preliminary Flow Chart for Flood Emergency Response Classification

Homes Below PMF orAccess Rds in Floodplain?N

Vehicle Evac Route cut beforeResidential Area Flooded?

Roads Rise Continuously to PMF

Vehicle Evac Route cut beforeResidential Area Flooded?

START HEREIndirectly Affected AreaMay requires resupply or evac before

or after loss of services

Y

Not Flood Affected

N

N

Rising Road Access AreaContinuous Vehicle Evac possible

as water advances onresidential properties

Y

NY

People Can Walk Overlandto Nearby Road or Community

Above PMF

Area with OverlandEscape Route

Vehicle evacuation completed before roadcloses. Once road closed residents canreach safety unassisted but may need

transport to evacuation centres

Y

N

Low Trapped Perimeter AreaVehicle evacuation must be completed before

routes close. After Closure Must RescuePeople by Air/Boat BEFORE Inundation

Road Closure point higher thanbut beyond residential area

YAre There Habitable

Areas above PMF Largeenough for Refuge ?

Are Homes First Surrounded by Water Then Flooded

Are Residential Landssurrounded by Water at

the PMF?

NN

Low Flood IslandVehicle evac must be completed

before routes close. A fter ClosureMust Rescue People by

Air/Boat BEFORE Inundation

Y

YHigh Flood Island

Vehicle evac must be completed beforeroutes clo se. After closure resupply

insitu or transport by Air/Boat

High Trapped Perimeter AreaVehicle evac must be completed before routes

close. After closure resupply insitu or transported by Air/Boat

NY

Classification of Floodplain Communitiesfor Emergency Management

Notes: Designed for Use on a Broad or Precinct Basis Overland Refuge Area is an area that may be passed through on the way to an areas beyond the Floodplain Other Definitions in Guideline

Overland Refuge Area OnHigh Flood Islan d or HighTrapped Perimeter Area

If necessary rescue required byAir/Boat

People can Walk tonearby Refuge Above PMF but Isolated by Floodwater

N

Overland Refuge AreaOn Low Flood Island or

Low Trapped Perimeter AreaVehicle evacuation must be completed before

routes close. After Closure Must RescuePeople by Air/Boat BEFORE Inundation

Y

Can People WalkOverland to Nearby Road

or Community beyond PMF

N

Area with OverlandEscape Route

Vehicle Evacuation completed beforeroad closes. Once road closed residents

can reach safety unassisted

Y

N

People can Walk tonearby Refuge Above PMF but Isolated by Floodwater

Overland Refuge Area OnHigh Flood Islan d or HighTrapped Perimeter AreaIf necessary rescue required by

Air/Boat

Y

APPENDIX J

1

KEY FLOODPLAIN RISK MANAGEMENT ISSUES FOR THE SES

(IN ACCORDANCE WITH THE NSW FLOODPLAIN DEVELOPMENT MANUAL)

The State Emergency Service (SES) is the agency responsible for dealing with floods, storms and tsunami in NSW. This role includes, planning for, responding to and coordinating the initial recovery from floods. As such, the SES has an interest in the public safety aspects of the development of flood prone land, in particular, the potential for changes to land use to either exacerbate existing flood risk or create new flood risk for communities in NSW.

The SES recommends that consideration of flooding issues is undertaken in accordance with the requirements of NSW Government’s Flood Prone Land Policy as set out in the Floodplain Development Manual, 2005 (FDM) and relevant planning directions under the EP&A Act.

In brief, the SES considers the principles on following page to be of particular importance, although this list should not be considered to be exhaustive.

The consent authority (usually the Local Council) will need to be satisfied that these considerations are adequately addressed as part of the assessment process. Due entirely to the need to meet priorities dictated by legislated responsibilities, the SES is not in a position to assess any detailed development proposal or to work with developer’s consultants in preparing any such proposal.

State Headquarters

Level 3, 6-8 Regent Street

Wollongong NSW 2500

PO Box 6126

Wollongong NSW 2500

Phone 02 4251 6111

APPENDIX J

2

KEY FLOODPLAIN RISK MANAGEMENT ISSUES FOR THE SES

Risk assessment should consider the full range of flooding, including events up to the Probable Maximum Flood (PMF) and not focus only on the 1% AEP flood.

Risk assessment should consider not only risk to the occupants, structures and contents of the development but any change in flood risk for the whole community in the floodplain due to the development.

Development should not result in an intolerable increase in risk to life, health or property of people living on the floodplain.

Risk assessment should have particular regard to flood warning and evacuation demand on existing and future access/egress routes. Consideration should also be given to the impacts of localised flooding on evacuation routes.

Self evacuation of the community should be achievable and in a manner which is consistent with the SES’s principles for evacuation.

Development must not conflict with the SES’s flood response and evacuation strategy for the existing community.

Evacuation must not require people to drive through flood water.

Development strategies relying on deliberate isolation or sheltering in buildings surrounded by flood water are not equivalent, in risk management terms, to evacuation.

Development strategies relying on an assumption that mass rescue may be possible where evacuation either fails or is not implemented are not acceptable to the SES.

As articulated in the FDM, the SES is opposed to the imposition of development consent conditions requiring private flood evacuation plans rather than the application of sound landuse planning and flood risk management.

APPENDIX J

appendix j - kempsey.nsw.gov.au · behaviour and the associated risks. this includes: summary of...

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