LOWER BELLINGER AND KALANG RIVER FLOOD STUDY DRAFT … · Lower Bellinger and Kalang River Flood...

LOWER BELLINGER AND KALANG RIVER FLOOD STUDY

DRAFT REPORT

September 2015

Level 2, 160 Clarence Street Sydney, NSW, 2000 Tel: 9299 2855 Fax: 9262 6208 Email: [email protected] Web: www.wmawater.com.au


DRAFT REPORT

SEPTEMBER 2015

Project Lower Bellinger and Kalang River Flood Study

Project Number 111036-04

Client Bellingen Shire Council

Client’s Representative Azim Zahurul

Authors Isabelle Testoni Monique Retallick Mark Babister

Prepared by

Date 30 September 2015

Verified by

Revision Description

Distribution Date

4 3 2 DRAFT REPORT BSC, OEH SEPT 2015 1 INITIAL DRAFT REPORT FOR DISCUSSION

ONLY BSC, OEH 4 May 2015


TABLE OF CONTENTS

PAGE

FOREWORD .............................................................................................................................. 1

EXECUTIVE SUMMARY ............................................................................................................ 2

1. INTRODUCTION ........................................................................................................ 3

1.1. Report Outline ............................................................................................ 3

2. BACKGROUND ......................................................................................................... 5

2.1. Study Area .................................................................................................. 5

2.2. Previous Studies ......................................................................................... 5

3. AVAILABLE DATA .................................................................................................. 10

3.1. Rainfall Information ................................................................................... 10

3.1.1. Historic Rainfall Data ................................................................................ 10

3.1.2. Design Rainfall Data ................................................................................. 10

3.2. Water Level Data ...................................................................................... 10

3.2.1. Time Series Water Level Data .................................................................. 10

3.2.2. Peak Flood Heights .................................................................................. 11

3.3. Topographic Information ........................................................................... 12

3.4. Culvert and Structure Data ....................................................................... 13

4. ADOPTED MODELLING APPROACH ..................................................................... 14

5. HYDROLOGIC MODELLING ................................................................................... 15

5.1. Overview .................................................................................................. 15

5.2. Review of Bellinger, Kalang and Nambucca River Catchments Hydrology 15

5.3. 0.05% AEP Event ..................................................................................... 16

6. HYDRAULIC MODELLING ...................................................................................... 17

6.1. Model Configuration .................................................................................. 17

6.2. Boundary Conditions ................................................................................ 17

6.3. Model Calibration ...................................................................................... 18

6.4. Calibration Results and Discussion ........................................................... 18

6.5. Model Verification ..................................................................................... 20

6.6. Verification Results and Discussion .......................................................... 20

7. DESIGN FLOOD BEHAVIOUR ................................................................................ 23

7.1. Boundary Conditions ................................................................................ 23

7.1.1. Design Inflows .......................................................................................... 23

7.1.2. Tailwater Conditions ................................................................................. 23

7.1.3. Entrance Conditions ................................................................................. 24

7.2. Design Event Results ............................................................................... 25

7.3. Sensitivity Analysis ................................................................................... 26

7.3.1. Rainfall Sensitivity..................................................................................... 26

7.3.2. Parameter Sensitivity ................................................................................ 29

7.4. Climate Change ........................................................................................ 30

7.5. Hydraulic and Hazard Categories ............................................................. 31

7.6. Flood Planning Area ................................................................................. 33

7.7. Impacts of Sea Level Rise on Flood Planning Area .................................. 33

8. FLOOD DAMAGES .................................................................................................. 34

8.1.1. Background .............................................................................................. 34

8.1.2. Assessment of Tangible Flood Damages .................................................. 34

8.1.3. Tangible Damages – Residential Properties ............................................. 35

8.1.4. Results ..................................................................................................... 36

9. EMERGENCY RESPONSE ...................................................................................... 38

9.1. Preliminary Flood Emergency Response Planning Classification of

Communities ............................................................................................. 38

9.2. Evacuation Routes and Length of Inundation ............................................ 39

9.3. Correlation between Newry Island U/S Gauge and Newry Island Bridge .. 42

10. TIDAL CALIBRATION .............................................................................................. 43

10.1. Verification to a Tide ................................................................................. 43

10.2. High High Water Solstice Spring ............................................................... 43

11. CONCLUSIONS ....................................................................................................... 44

12. REFERENCES ......................................................................................................... 45

LIST OF APPENDICES

Appendix A: Glossary

LIST OF TABLES

Table 1: Significant Peak Flood Levels at Bellinger Bridge ........................................................ 11

Table 2: Calibration and Verification Events .............................................................................. 14

Table 3: Adopted Manning’s “n” Values..................................................................................... 18

Table 4: Calibration Events - Modelled vs Observed Flood Levels -1974 ................................. 19

Table 5: Calibration Events - Modelled vs Observed Flood Levels - 1977 ................................ 20

Table 6: Verification Events - Modelled vs Observed Water Levels - 2001 ................................ 21

Table 7: Verification Events - Modelled vs Observed Water Levels - 2009 ................................ 21

Table 8: Ocean Boundary Peaks (mAHD) ................................................................................. 24

Table 9: Entrance Erosion ......................................................................................................... 25

Table 10: Design Flood Levels at Key Locations ....................................................................... 25

Table 11: Comparison of 1% AEP Flood Level with Previous Studies ....................................... 25

Table 12: Catchment Average Rainfall Comparison (mm) ......................................................... 27

Table 13: FFA Flow Comparison (m3/s) .................................................................................... 27

Table 14: Changes in Design Flood Level – Bellingen (mAHD) ................................................. 28

Table 15: Sensitivity Analyses ................................................................................................... 30

Table 16: Climate Change Results ............................................................................................ 31

Table 17: Affected Properties .................................................................................................... 36

Table 18: Estimated Flood Damages ........................................................................................ 37

Table 19: Response Required for Different Flood ERP Classifications ...................................... 38

Table 20: Design flood levels at low points in roads. ................................................................. 39

Table 21: Inundation times of road low points ........................................................................... 40

Table 22: Event when access and evacuation is cut ................................................................. 40

LIST OF FIGURES

Figure 1: Study Area

Figure 2: Available Survey Data

Figure 3: Hydrologic Model Layout

Figure 4: Hydraulic (TUFLOW) Model Layout

Figure 5: Manning’s n Values

Figure 6: Model Calibration –Modelled vs Observed – 1974 Event

Figure 7: Model Calibration - Modelled vs Observed – 1977 Event

Figure 8: Model Validation – Modelled vs Observed – 2001 Event – Bellingen Bridge

Figure 9: Model Validation – Modelled vs Observed – 2001 Event – Repton

Figure 10: Model Validation - Modelled vs Observed – 2001 Event – Urunga

Figure 11: Model Validation - Modelled vs Observed – 2001 Event – Newry Island

Figure 12: Model Validation – Modelled vs Observed – 2009 Event – Bellingen Bridge

Figure 13: Model Validation – Modelled vs Observed – 2009 Event – Repton

Figure 14: Model Validation – Modelled vs Observed – 2009 Event – Urunga

Figure 15: Model Validation - Modelled vs Observed – 2009 Event – Newry Island

Figure 16: Model Calibration –Peak Flood Level - 1974 Event

Figure 17: Model Calibration – Peak Flood Level - 1977 Event

Figure 18: Model Validation – Peak Flood Level - 2001 Event

Figure 19: Model Validation – Peak Flood Level - 2009 Event

Figure 20: Design Event Flood Level Profiles – Bellinger River

Figure 21: Design Event Flood Level Profiles – Kalang River

Figure 22: Design Event – Peak Flood Depths and Level Contours – 5 Year ARI Event

Figure 23: Design Event – Peak Flood Depths and Level Contours – 10 % AEP Event



Figure 26: Design Event – Peak Flood Depths and Level Contours – 0.5 % AEP Event



Figure 29: Design Event - Peak Flood Depths and Level Contours – PMF Event

Figure 30: Design Event – Peak Flood Velocities – 5 Year ARI Event

Figure 31: Design Event – Peak Flood Velocities – 10 % AEP Event



Figure 34: Design Event – Peak Flood Velocities – 0.5 % AEP Event

Figure 35: Design Event - Peak Flood Velocities – 0.2 % AEP Event

Figure 36: Design Event – Peak Flood Velocities – 0.05 % AEP Event

Figure 37: Design Event – Peak Flood Velocities – PMF Event

Figure 38: Design Event – Peak Flood Depths and Level Contours – 1 % AEP Event with a

10% Rainfall Increase

Figure 39: Design Event - Peak Flood Depths and Level Contours – 1 % AEP Event with a


Figure 40: Design Event – Peak Flood Depths and Level Contours – 1 % AEP Event with a


Figure 41: Design Event – Peak Flood Depths and Level Contours – 1 % AEP Event 2050 Sea

Level Rise

Figure 42: Design Event – Peak Flood Depths and Level Contours – 1 % AEP Event 2100 Sea

Level Rise

Figure 43: Ocean Boundary Conditions

Figure 44: Impact of 1% AEP boundary conditions

Figure 45: Hydraulic Categorisation – 1 % AEP Event

Figure 46: Hydraulic Categorisation – PMF Event

Figure 47: Hydraulic Hazard – 1 % AEP Event

Figure 48: Hydraulic Hazard – PMF Event

Figure 49: Flood Planning Area – 1% AEP Event

Figure 50: Flood Planning Area – 1% AEP Event 2050 Sea Level Rise

Figure 51: Flood Planning Area – 1% AEP Event 2100 Sea Level Rise

Figure 52: Flood Planning Area Difference – 1% AEP with Sea Level Rise

Figure 53: Preliminary Flood Emergency Response Planning Classification of Communities

Figure 54: Catchment Time of Inundation in 1% AEP Event

Figure 55: Time of Inundation in 1% AEP Event

Figure 56: Time of Inundation in 1% AEP Event – Newry Island and Urunga

Figure 57: Time of Inundation in 1% AEP Event – Waterfall Way

Figure 58: Time of Inundation in 1% AEP Event – Newry Island Drive

Figure 59: Time of Inundation in 1% AEP Event – Bellingen Bridge

Figure 60: Time of Inundation in 1% AEP Event – Yellow Rock Road

Figure 61: Ground First Inundated

Figure 62: Ground First Inundated - Bellingen

Figure 63: Ground First Inundated - Raleigh

Figure 64: Ground First Inundated - Mylestom

Figure 65: Ground First Inundated – Newry Island

Figure 66: Floor First Inundated

Figure 67: Floor First Inundated - Bellingen

Figure 68: Floor First Inundated - Raleigh

Figure 69: Floor First Inundated - Mylestom

Figure 70: Floor First Inundated - Newry Island

Figure 71: Model Calibration – Modelled vs Observed –Tide – Urunga

Figure 72: Model Calibration – Modelled vs Observed –Tide – Repton

Figure 73: Model Calibration – Modelled vs Observed –Tide – Newry Island

Figure 74: Model Calibration – Peak Tide Depth – Tide

Figure 75: High High Mean Tidal Area

Lower Bellinger and Kalang River Flood Study

WMAwater 111036-04:Lower_Bellinger_Kalang_FS:30 September 2015

1

FOREWORD

The NSW State Government’s Flood Policy provides a framework to ensure the sustainable use

of floodplain environments. The Policy is specifically structured to provide solutions to existing

flooding problems in rural and urban areas. In addition, the Policy provides a means of ensuring

that any new development is compatible with the flood hazard and does not create additional

flooding problems in other areas.

Under the Policy, the management of flood liable land remains the responsibility of local

government. The State Government subsidises flood mitigation works to alleviate existing

problems and provides specialist technical advice to assist Councils in the discharge of their

floodplain management responsibilities.

The Policy provides for technical and financial support by the Government through four

sequential stages:

1. Flood Study

• Determine the nature and extent of the flood problem.

2. Floodplain Risk Management

• Evaluates management options for the floodplain in respect of both existing and

proposed development.

3. Floodplain Risk Management Plan

• Involves formal adoption by Council of a plan of management for the floodplain.

4. Implementation of the Plan

• Construction of flood mitigation works to protect existing development, use of

Local Environmental Plans to ensure new development is compatible with the

flood hazard.

This report is an extension of the RMS Hydraulic Modelling Report – Bellinger and Kalang

Rivers which defined flood behaviour under existing and a changed climate. This report

incorporates the findings of the RMS Bellinger and Kalang Rivers Hydraulic Modelling Report

with additional components addressed which are required to complete the flood study stage.

Bellingen Shire Council has prepared this document with financial assistance from the NSW

Government through its Floodplain Management Program. This document does not necessarily

represent the opinions of the NSW Government or the Office of Environment and Heritage.



2

EXECUTIVE SUMMARY

The study area includes Lower Bellinger and Kalang river catchments located in Bellingen Shire.

The Kalang River joins with the Bellinger River and discharges to the ocean at Urunga. The

catchment area of the combined Bellinger and Kalang Rivers and their tributaries is 1110 km2.

The Bellinger and Kalang Rivers study area is defined as:

• Upstream to Bellingen Bridge (Lavenders Bridge) on the Bellinger River,

• To 2.5km past the Brierfield Bridge on the Kalang River, and

• Downstream to the Pacific Ocean.

This study builds upon earlier hydrology and hydraulic modelling studies (Reference XX) to

produce a flood study for Council. The hydraulic model has been used to reproduce the

historical flood behaviour from events in 1974, 1977, 2001 and 2009. The TUFLOW model has

been used to define flood behaviour for a range of design events (5 Year ARI, 10, 2, 1, 0.5, 0.2

and 0.05 % AEP and Probable Maximum Flood).

The study contains further investigations relating to:

• hydraulic and hazard analysis,

• emergency response classification

• evacuation routes and length of inundation and

• a flood damages assessment.

The study also includes community consultation.

The Lower Bellinger and Kalang Rivers Hydraulic Modelling Report has been further assessed

and is considered suitable for future use by Council in the floodplain risk management planning

process.



3

1. INTRODUCTION

In 2012, Roads and Maritime Services produced a hydraulic model of the Lower Bellinger and

Kalang Rivers as part of the Warrell Creek to Urunga Pacific Highway Upgrade. This model is

described in the document “Lower Bellinger and Kalang Rivers Hydraulic Modelling Report”

(Reference 27). In order to assess the suitability of this model for use in floodplain management

planning, further analysis has been under taken.

The Bellinger and Kalang Rivers study area is defined as:




This report details the investigations, results and findings of the flood study for the Bellinger and

Kalang Rivers. This includes some work conducted as part of previous studies and additional

investigations completed as part of this study. Flood study elements undertaken as part of

previous studies include:

• a summary of available data,

• hydraulic model development,

• calibration of the hydraulic model, and

• definition of the design flood behaviour through the analysis and interpretation of model

results.

Additional flood study elements undertaken as part of this study:

• Provisional hydraulic hazard,

• Emergency response classifications,

• evacuation routes and length of inundation and

• a flood damages assessment.

A glossary of flood related terms is provided in Appendix A.

1.1. Report Outline

This report provides background information on the catchment and previous studies in Sections

2. The available data used is described in Section 3. Section 4 describes the adopted modelling

approach.

Details of the hydrologic modelling that was undertaken to determine inflows to the hydraulic

model are contained in the earlier Review of Bellinger, Kalang and Nambucca Rivers Catchment

Hydrology (Reference 3) which investigates known hydrologic issues in the Bellinger, Kalang

and Nambucca River catchments. A summary of this report is included in Section 5. Also

included in Section 5 is the development of the 0.05% AEP flows.

Hydraulic modelling of the Bellinger and Kalang Rivers are detailed in Section 6. This includes



4

model calibration, verification and sensitivity analysis. Design flood behaviour is discussed in

Section 7. Section 8 discussed the emergency response classification. Flood damages

calculations are described in Section 9. Tidal calibration and tidal planes are discussed in

Section 10.



5

2. BACKGROUND

2.1. Study Area

The study area (refer to Figure 1) includes the Bellinger River and Kalang River catchments.

The Bellinger and Kalang Rivers are located within Bellingen Shire Council. The Bellinger and

Kalang Rivers join and discharge into the Pacific Ocean near Urunga. The total catchment area

of both rivers is 1110 km2. The catchment area of the Kalang River upstream of its junction with

the Bellinger River is approximately 340 km2.

The headwaters of the catchments are located in the Great Dividing Range and are

characterised by steep topography. The lower reaches are characterised by broad floodplains

and farmland. Residential development within the catchments generally consists of small

settlements. Major centres exist at Bellingen and Urunga.

The Study area is defined as (Figure 1):




2.2. Previous Studies

A number of flood studies and assessments have previously been undertaken within the

Bellinger and Kalang River catchments. These studies range from lot sized flood assessments

to large scale studies encompassing both the Bellinger and Kalang Rivers. A brief overview of

the more significant studies is provided below. A review of the “Lower Bellinger and Kalang

Rivers Hydraulic Modelling Report” (Reference 27) is not contained here as the contents of that

report largely form this report. Council has also recently completed an Estuary Inundation

Mapping report (BMT, 2015) which uses the model and boundary conditions from the current

study.

New South Wales Coastal Rivers Floodplain Management Studies Bellinger Valley

(Cameron McNamara, December 1980)

Part of a series of reports on NSW coastal rivers this report (Reference 6) details floodplain

management measures within the Bellinger valley and makes recommendations on policy. The

report contains recorded water levels and selected aerial photographs of historical floods.

Proposed Industrial Area, Urunga NSW (Outline Planning Consultants, May 1984)

The report (Reference 7) covers a proposed industrial area situated adjacent to the Pacific

Highway and the North Coast Railway line, on the northern fringe of Urunga. The site

characteristics and its suitability for the proposed development were assessed. Flooding on the



6

site was assessed based on available flood maps. The Pacific Highway is noted to act as a

levee and protect some low lying areas in the middle of the site. The majority of the site was

found to be flood free based on the available data. The northern end of the site was found to be

flood affected from backwater flooding by an intermittent creek.

Bellinger River May 1980 Flood Report (PWD, 1981)

This report (Reference 8) details data collected for the May 1980 flood in the Bellinger Valley

and presents rainfall, flood heights and stage hydrographs for the event. Insufficient information

was available to include this event in the model calibration.

Bellinger River Flood History 1843-1979 (PWD, 1980)

This study (Reference 9) was undertaken to document flood data in the tidal section of the

Bellinger River (up to Bellingen) to be used in preparing flood maps for Bellingen. A flood

frequency analysis was conducted using recorded data for the Bellingen Bridge. Floods with

peak heights greater than 8.3m were included. Due to a lack of data downstream of Bellingen

flood heights determined for the 1%, 2% and 5% AEP events at Bellingen were combined with

estimated flood gradients to determine flood levels and flood maps for downstream towns. The

report details personal recollections of residents about significant historical events. Flood

reference points for significant flood events including the 1962, 1974 and 1977 events are

reported which were used for model calibration.

Lower Bellinger River Flood Study (PWD, 1991)

The Lower Bellinger River Flood Study (1991, Reference 10) investigated flooding in the

Bellinger River below Bellingen and the Kalang River downstream of Picket Hill Creek. A

CELLS hydraulic model was developed to determine flood levels for the 1%, 2%, and 5%

Annual Exceedance Probability (AEP) and extreme design flood events. The 1962, 1974 and

1977 historical events were used for model calibration and verification. The effects of ocean

levels and bed scour were incorporated into the model. A RORB hydrological model was

developed of the Bellinger and Kalang River catchments to convert rainfall to flow hydrographs.

Model data and results from the hydraulic model developed for this study were used to provide

boundary conditions and topographic information for the Newry Island Flood Study. This report

was used as a comparison with new model results. The hydrologic model subcatchment layout

formed a basis for the hydrologic model layout for the current study.

Lower Bellinger River Flood Study, Location of Flood Marks Engineering Survey Brief

(Cameron McNamara, 1991)

As part of the 1991 Lower Bellinger River Flood Study, a survey of local residents was

conducted of the area downstream of Bellingen (on the Bellinger River) and Picket Hill Creek

(on the Kalang River). The survey identified 46 flood reference points and information on the

flood behaviour. The report (Reference 11) shows the location and photos of the survey

reference points.



7

Lower Bellinger River Flood Study Compendium of Data (PWD, 1991)

This report (Reference 12) provides a review of available data for the Lower Bellingen River

Flood Study. Total rainfall isohyets were drawn for selected events. A summary of results from

the resident survey for the 1950, 1962 and 1974 flood events is presented.

Bellinger and Kalang River’s Floods of February and March 2001 (Bruce Fidge and

Associates, 2003)

Rainfall and flood level information for the February and March 2001 floods is summarized in

this report. Survey of peak flood debris levels was undertaken by Council following the March

2001 event. Based on the design flood behaviour defined in the 1991 Flood Study and Flood

History Report (Reference 13) the recurrence interval for the events at various locations within

the catchments were estimated. The February 2001 event was estimated to have a 5 year

Average Recurrence Interval (ARI) for Repton, 6 year ARI for Newry Island and 10 year ARI for

Urunga. The March 2001 event was estimated to have a 12 year ARI for Repton, 6 year ARI for

Newry Island and 10 year ARI for Urunga. Compared to the February flood, the March 2001

event was bigger on the Bellinger River. However, the February and March events were of

similar magnitude on the Kalang River and in the vicinity of Newry Island. The 2001 event was

used in the current study for model verification.

Floodplain Risk Management Study Stage 2- An Assessment of Floodplain Management

Options and Strategies (Bellingen Shire Council, April 2002)

The report (Reference 14) was commissioned by Bellingen Shire Council to investigate

management strategies for flood prone land in the Bellinger and Kalang River catchments.

Floodplain risk management options are considered and prioritised. The report recommended

additional rainfall and water level gauges be installed on the Kalang River and Lower Bellinger

River, to improve flood prediction and supplement the existing system. Flood management

recommendations for Newry Island included increasing the level of Newry Island Drive so that

rural residents have access during a 5 and 10% AEP floods and the expansion of Newry Island

bridge to improve evacuation.

Upper Kalang River Flood Assessment, (Bellingen Shire Council, December 2006)

This report (Reference 15) modelled 26.5 km of the Upper Kalang River to Pickett Creek using a

one dimensional MIKE 11 model. Boundary conditions were drawn from the Lower Bellingen

River Flood Study. The Lower Bellinger Flood Study RORB model was adopted for the Upper

Kalang River. An areal reduction factor of 0.6 was adopted to be consistent with the Lower

Bellinger Flood Study and the Upper Bellinger River Flood Assessment. Filtering of the temporal

patterns was undertaken. A critical storm duration of 12 hours was adopted in comparison to 36



8

hours which was adopted by the 1991 Flood Study. Flood frequency analysis undertaken for this

study used heights which is not ideal as it is unable to take into account the variance in the

cross section. A combined record of the 3 Kooroowi –Scotchman gauges was derived. Peak

height correlations between the stations was enabled by the establishment of a MIKE 11 model.

The intent of the study is to provide indicative flood levels and therefore the model is not

calibrated. The flood levels should be used for general purposes only and do not have the same

reliability as a flood study. Cross section survey undertaken for this study was used in the

current study.

South Arm Road Flood Study (Final) (DeGroot and Benson Pty Ltd, June 2000)

The report (Reference 16) details the hydrologic and hydraulic modelling of the existing

conditions in the vicinity of South Arm Road and the unnamed creek that drains into Boggy

Creek. South Arm Road is subject to flooding from the Kalang River (via backwater flooding

from Boggy Creek), local runoff and a combination of both. The road is subject to frequent

inundation between Short Cut Road and the Riverside Drive subdivision, cutting off the main

access to the area. The hydraulic modelling for this study was undertaken using a water

balance model originally developed for the Central Urunga Flood Study. The report investigates

the effect of raising the road to 2.5, 3.0, 3.5 and 4.0 mAHD. Raising the road was found to have

minimal effect on the flood level at Urunga (<15mm), due to the conveyance capacity of the

wetland area at that level. Details of the culverts under South Arm Road are described in this

report. The report recommends raising South Arm Road to no greater than 3.30 mAHD if the

existing culvert arrangement was to remain.

Upper Bellinger River Flood Assessment (Bellingen Shire Council, 2006)

The Lower Bellinger Flood Study (Reference 10) RORB model was adopted for the Upper

Bellinger River Flood Assessment (Reference 17). An areal reduction factor of 0.6 above Thora

and 1.0 for all other catchments was required in order to fit the flood frequency analysis.

Filtering of the temporal patterns resulted in the 12 hour event being critical rather than the 36hr

which was found to be critical in the Lower Bellinger Flood Study. The RORB model was refined

in the Never Never River catchment to provide inflows to the hydraulic model. On the Never

Never River a larger than standard practice continuing loss (7.5mm/hr) was adopted, with an

initial loss of 0mm. A rating curve extrapolation was undertaken for 900m downstream of

Bellingen using the CELLS model developed as part of the Lower Bellinger Flood Study. This

flood assessment provided flood levels for design events in the Upper Bellinger. A detailed

calibration of the hydraulic model was not undertaken as part of the study. Cross section survey

undertaken for this study was used in the current study.

Newry Island Flood Study Draft (WMAwater, 2008)

The Newry Island Flood Study (Reference 18) developed a TUFLOW model of the Lower

Bellinger and Kalang Rivers. Inflows for the TUFLOW model were derived from the Lower

Bellinger Flood Study RORB and CELLS models. Model calibration and validation was



9

conducted using the 1974, 1977 and 2001 events. Information on the 2001 event derived as part

of the Newry Island study was used to inform the current study.

Warrell Creek to Urunga Upgrade Environmental Assessment (RTA, 2010)

The Warrell Creek to Urunga Upgrade Environmental Assessment (2010) (Reference 5)

assessed the impact of the proposed pacific highway upgrade crossing on the Kalang River on

flood levels. A RORB model was developed of the catchment. In order to fit the flood frequency

analysis results the study adopted the Australian Rainfall and Runoff (ARR) temporal patterns

for zone 3 rather than zone 1.

Review of Bellinger, Kalang and Nambucca Rivers Catchment Hydrology (WMAwater,

2011)

The Review of Bellinger, Kalang and Nambucca Rivers Catchment Hydrology (Reference 3)

investigates known hydrologic issues in the Bellinger, Kalang and Nambucca River catchments.

This area of the NSW north coast has presented a range of challenges for a number of studies

where problems have been encountered matching rainfall runoff modelling with flood frequency

results. As part of the study WBNM models were developed for each catchment and calibrated

to historical events. The hydrology developed as part of the study has been used for the current

study.

Kalang River – 2009 Flood Event (WMAwater, 2011)

This study (Reference 19) modelled the March/April 2009 flood event using the hydraulic model

established as part of the Newry Island Flood Study (Reference 18) using inflows developed by

Reference 3. Overall a good calibration to the observed flood levels during 2009 event was

achieved. This study verifies the calibration of the Newry Island Flood Study TUFLOW model.

Bellinger and Kalang Rivers Flood Event of 31 March 2009 Collection and Collation of

Flood Data (Enginuity Design, 2010)

This report (Reference 20) contains the results of an extensive data collection exercise

undertaken following the 2009 event. The report contains rainfall data and observed flood level

marks for the March 2009 event. This data has been used in the current study to inform the

calibration of the hydraulic model.

Warrell Creek to Urunga: Pacific Highway Upgrade Modelling (WMAwater, 2012)

This report (Reference 24) contains a detailed assessment of the impacts of the Pacific Highway

Upgrade on flood levels in the Bellinger / Kalang River system. The study used the hydraulic

model used for the current study.



10

3. AVAILABLE DATA

3.1. Rainfall Information

3.1.1. Historic Rainfall Data

Historical rainfall data was obtained at a number of locations within the study area and

surrounds. Daily rainfall and pluviograph data was obtained for a number of gauges within the

region from a number of sources including the Bureau of Meteorology (BoM) and Manly

Hydraulics Laboratory (MHL).

Historic rainfall data available for the 1974, 1977, 2001 and 2009 events on the Bellinger and

Kalang Rivers is documented in Reference 3 and Reference 19. For the 1974 and 1977 events

no pluviograph information was available within the catchment though several pluviometers

were located in adjacent catchments. A limited set of pluviometer records was available for the

historical events examined in the 1991 Flood Study (Reference 10). The largest set of

pluviometer data used in the 1991 Flood Study was for the 1977 event (though none were

located within the catchment). More pluviometer records were available for the more recent

events. Resident rainfall totals collected as part of the post flood data collection for the 2009

event (Reference 20) were included in the vicinity of Urunga where the official gauges were

considered to have under recorded.

3.1.2. Design Rainfall Data

Design rainfall data available for the Bellinger and Kalang River is documented in Reference 3.

All of the BoM long term daily and pluviograph gauges within and near the catchment were

analysed on a 24hr 9am restricted basis to produce new IFD estimates. This was supplemented

by at site analysis of other gauges which was incorporated into the surface mapping.

3.2. Water Level Data

3.2.1. Time Series Water Level Data

Manly Hydraulics Laboratory (MHL) operates a number of water level recorders in the Bellinger,

Kalang Rivers catchments. These being:

• Newry Island,

• Urunga,

• Repton, and

• Bellinger Bridge.

Stage hydrograph data was obtained from the MHL operated water level stations. The recorded

time-series of water levels was used for model calibration purposes. It should be noted that

these water level recorders are located within the tidal limit. The opportunity for the water level

record to be translated into a corresponding flow hydrograph is therefore limited except for



11

Bellingen which is at the very upper limit of the tidal limit and for which rating curves exist.

However, the recorders do provide a valuable record of flood level behaviour during an actual

flood.

A number of temporary gauges operated by OEH and MHL were located on the Bellinger and

Kalang rivers during 2009 as part of a water quality study (Reference 26). Many of the gauges

were damaged during the event or did not record the peak. Where possible these gauges were

used as a comparison to model results eg. for timing of the rising limb.

3.2.2. Peak Flood Heights

The Bellinger and Kalang River Valley’s have a long history of flooding. Flood records for

Bellingen date back to the 1840’s (Reference 9). In comparison to the Bellinger River, there is

less observed peak flood height data available for historical events on the Kalang River.

However, most large floods on the Bellinger occur at the same time as a large event on the

Kalang. A summary of significant events which have occurred in the area is presented in Table

1. The more recent events for which significant data is available for calibration and validation

purposes occurred in 1974, 1977, 2001 and 2009.

The 1962 event though used in previous studies for calibration was not included in this study for

the following reasons:

• No pluviographs within the catchment at the time of the event,

• Limited observed data available including water level recorders,

• The more recent 2009 event was larger and had significantly more data available.

Table 1: Significant Peak Flood Levels at Bellinger Bridge

Year

Gauge Height

(mAHD) Comment

1870 11.5 Bellingen Flood History 1843 to 1979









1890 9 Bellingen Flood History 1843 to 1979



2009 8.8 MHL readings

2001 8.77 MHL readings




12

1989 8.6 SES readings











A review of previous studies and available data found some observed peak flood heights at a

number of locations within or near the study area. The most significant flood events within the

catchment for which suitable calibration data is available occurred in 1974, 1977, 2001 and

April/March 2009. Data for the 1974 and 1977 events are presented in Reference 10.

Reference 13 and 20 contain data for the 2001 and 2009 event respectively. Several data

collection exercises have been undertaken to collect peak flood levels and anecdotal evidence

of significant floods in the area (Refer Section 2.2).

3.3. Topographic Information

There is a considerable amount of topographic data available for the study area. However, the

accuracy and suitability of these existing datasets for use in the present study varies. This

includes contours, hydrosurvey, cross sections and Airbourne Laser Scanning.

Council provided topographic contours of the study area in GIS format (at 10 m intervals over

the majority of the catchment and at 2 m intervals over a limited area including Newry Island).

Hydrosurvey of the estuary was available from OEH (Refer Figure 2). The hydrosurvey was

collected between Sept to Nov 2008. It provides waterway cross sections for the estuarine

reaches of the Bellinger River, Kalang River and Pickets Creek. The hydrosurvey shows a

significant amount of sediment at the entrance which OEH staff advised was eroded during the

2009 event. A significant amount of erosion also occurred on the Kalang River.

Aerial photography collected by the Lands and Property Management Authority was also

available within the catchment boundary. This was utilised in the assigning of Manning’s n

values and identifying catchment changes.

Cross sections from the MIKE 11 models used as part of the Upper Bellinger and Upper Kalang

Flood Assessments (Reference 17 and 15) were also available in the areas where hydrosurvey

was not available.

Airbourne Laser Scanning (ALS) ground levels were provided for the study area. The ALS

collection was part of the Coastal capture program by the Lands and Property Management



13

Authority. It captures from the coast to the 10m contour interval. Spatial accuracy of the ALS in

the horizontal and vertical directions was reported as 0.8m and 0.3m respectively.

Due to issues with the data processing used to produce the original grids provided, the raw ALS

files were obtained. The non ground strikes were filtered from this data set. Within a 60m buffer

of the waterway the ground strikes and hydrosurvey were tinned and a DEM produced. This

DEM and the ALS grid (outside of the 60m buffer) were combined to create a DEM for use in the

2D model.

A DEM (Digital Elevation Model) at a 1m grid resolution was used in order to:

• confirm sub-catchment and catchment watershed boundaries; and

• inform the 2D model used in the study.

3.4. Culvert and Structure Data

Details of culverts and structures along the existing highway and Waterfall Way were obtained

from Roads and Maritime Services works as executed plans and culvert database. For local

roads details of culverts and bridge structures were collected on a site visit and based on council

records. Where culvert details were not available a reasonable estimate was made based on

upstream culverts. Some details on culverts and structures under the North Coast Railway were

available from the Newry Island Flood Study (Reference 18).

The Nambucca Heads to Urunga Pacific Highway upgrade currently under construction was

included based on the final construction design plans (option PHU 049 as at 8/10/2014).

3.5. Community Consultation

To Be Completed



14

4. ADOPTED MODELLING APPROACH

The primary objective of this study is to define the flood behaviour under historical and existing

floodplain conditions in the Study Area while addressing possible future variations in flood

behaviour due to climate change and provide information for its management.

The approach adopted for this study has been influenced by the study objectives, accepted

practice and the quality and quantity of available data. There are two basic approaches to

determining design flood levels namely:

• a flood frequency approach based upon a statistical analysis of the flood record, and

• using a rainfall/runoff routing approach (hydrologic modelling) to obtain flows, and then

inputting these flows into a hydraulic model of the floodplain.

The flood frequency approach was undertaken as part of an earlier study for the Bellinger,

Kalang, and Nambucca River catchments. The results of Reference 3 were used to inform the

current study. Flood frequency analysis was undertaken at Thora, Bellingen, and Kooroowi.

A hydrologic (WBNM, Watershed Bounded Network Model, Reference 4) model was established

for each catchment to determine inflows into the hydrodynamic model. A combined one and two

dimensional hydrodynamic (TUFLOW) model was used to define the flood behaviour using ALS

and hydrosurvey.

The TUFLOW models were calibrated and verified to a range of historical events (Table 2).

Table 2: Calibration and Verification Events

Catchment Calibration and Verification Events

Bellinger and Kalang Rivers 1974, 1977, 2001, 2009

The calibrated hydraulic models were then used to assess the flood levels and hydraulic flood

hazard for the 5 Year ARI, 10%, 2%, 1%, 0.5%, 0.2%, 0.05% AEP and Probable Maximum

Flood (PMF) design events.



15

5. HYDROLOGIC MODELLING

5.1. Overview

Hydrologic models of the Bellinger, Kalang and Nambucca and Warrell Creek catchments were

established as part of Review of Bellinger, Kalang and Nambucca River Catchments Hydrology

Report (Reference 3). All models were developed using the Watershed Bounded Network Model

(WBNM).

WBNM (Reference 4) is widely used throughout Australia and particularly NSW. WBNM

simulates a catchment and its tributaries as a series of sub-catchment areas linked together to

replicate the rainfall and runoff process through the natural stream network. Input data includes

the definition of physical catchment characteristics including surface area of sub-catchments,

proportion of impervious surfaces, stream length adjustments, initial and continuing losses,

temporal and spatial patterns over the catchment.

Key parameters for WBNM represent the physical characteristics of the catchment. Typical

model parameters include;

• Rainfall Losses: two values, initial and continuing loss, modify the amount of rainfall

excess to be routed through the model sub-catchments;

• Lag Parameter: this affects the timing of the runoff response to the rainfall and is subject

to catchment size, shape and slope; and

• Non Linearity Exponent: adjustment of the non-linearity of catchment response.

The parameters adopted for this study were based on those recommended in ARR 1987

(Reference 1), previous experience and calibration. Some of the information is summarised

briefly below and further details on the parameters used for each of the catchments can be

found in Reference 3). A good fit to observed data was achieved with default lag and no linearity

parameters.

5.2. Review of Bellinger, Kalang and Nambucca River Catchments

Hydrology

Full details of the development of the WBNM model can be found in Reference 3. Figure 3

shows the hydrological model layout for the Bellinger and Kalang River catchments. As part of

the Review of Bellinger, Kalang and Nambucca River Catchments Hydrology Report (Reference

3) historical rainfall data was obtained at a number of locations within and surrounding the study

area. Historic stream flow data was also obtained for a number of gauges within the catchments.

A number of stream flow gauges within the catchment were investigated to provide an indication

of the reliability of the rating curves used. Due to the unreliability of the extrapolation techniques

used in extending rating curves for many of the stream flow gauges new rating curves were

estimated in locations where cross sections at the gauge location were available.

Historical event inflows for 1974, 1977, 2001, 2009 were estimated using the hydrologic model.



16

As with the previous models, temporal and spatial patterns were established from recorded

rainfall data in the region. The WBNM model was calibrated to known historic flood levels and

flows as part of Reference 3.

Due to concerns over the ARR 1987 design rainfall estimates (and prior to the release of the

BoM 2013 IFDs), revised estimates were produced for a range of design events in an approach

consistent with that being proposed for the new version of ARR. Design rainfalls for events up to

the 0.2% AEP event were established from the revised IFDs whilst the PMP estimates were

made using the Generalised Tropical Storm Method as Revised (GTSMR).

Temporal patterns were also applied to the design rainfall as described in Reference 3. Initial

and continuing losses were varied with event size. Losses for the 0.5% and 0.2% AEP were

calculated in accordance with ARR Book IV (Reference 25) by interpolating between the 1%

AEP and PMF losses. More detail on the hydrologic model development can be found in

Reference 3. For design events, the 48 hour storm was found to be the critical duration for the 5

year, 10%, and 2% AEP events. For the 1%, 0.5% and 0.2% AEP events the 36 hours storm

was found to be critical and the 24 hour storm critical for the PMF.

5.3. 0.05% AEP Event

The 0.05% AEP Event rainfall depths were calculated using the guidance in Australian Rainfall

and Runoff Book VI (ARR, Reference 25) by interpolating between the 2% AEP, 1% AEP and

PMP depths. ARR Book VI recommends that the GTSMR spatial patterns are applied for an

extreme event such as the 0.05% AEP. The GTSMR patterns were found to produce

inconsistent peak flows for the 0.05% AEP when compared to the 0.2% AEP and PMF events

and therefore the ARR patterns as used in the smaller design events were applied to the 0.05%

AEP also.



17

6. HYDRAULIC MODELLING

A model of the study area was developed in the hydrodynamic modelling package (TUFLOW).

TUFLOW (Reference 2) is widely used in Australia and internationally for assessing flood

behaviour and hydraulic hazard. TUFLOW is a finite difference numerical model which is

capable of solving the depth averaged shallow water equations in both the one and two

dimensional domains.

The model extent for each catchment was determined in conjunction with the Roads and

Maritime Services (RMS), Bellingen Shire Council and Office of Environment and Heritage

(OEH). The purpose of the model was to both meet the needs of Council and OEH in terms of

the NSW Flood Study Program and the RMS to assess the impacts of proposed waterway

crossings.

A combined one and two dimensional hydrodynamic model (TUFLOW) model of the Bellinger

and Kalang Rivers was established.

6.1. Model Configuration

The model consists of a 2D 15m grid defining the overbank and the channel for the Bellinger

River, lower Kalang River and its tributaries. The upper reaches of the Kalang River are defined

by a combined one and two dimensional model, with the one dimensional network defining the

main channel. The extent of the TUFLOW model is shown in Figure 4.

The model extends a sufficient distance upstream and downstream of the study area such that

the imposed boundary conditions do not influence the model results in the region of interest.

The TUFLOW model limits were:

• Upstream limit on Bellinger River - 3km upstream of the Bellinger River Bridge at

Bellingen,

• Upstream limit on Kalang River – 2.5km past the Brierfield Bridge, and

• Downstream limit – Pacific Ocean.

A 15 metre digital terrain model (DTM) was created using the topographic data outlined in

Section 3. Within the one dimensional component of the model cross sections were derived

from the hydrosurvey and cross sections from the Upper Bellinger and Upper Kalang Flood

Assessments (Reference 15 and 17). Culverts under a number of roads and the North Coast

Railway Line were incorporated in the model including culverts under both the old and new

Pacific Highway’s.

6.2. Boundary Conditions

Inflows and boundary conditions for the TUFLOW model consist of a number of time varying

flow hydrographs developed using the WBNM model. At the downstream boundary of the

model, a tailwater level defining the river entrance was used. The tailwater conditions were



18

based on recorded tide levels at Coffs Harbour, experience on nearby catchments and OEH

guidelines (Reference 22). Figure 4 shows the inflow locations and boundary condition types.

6.3. Model Calibration

Model calibration was undertaken using historical data for the 1974 and 1977 flood events.

These events were adopted as a reasonable amount of observed data exists within the

catchment. Time varying water level data is also available in the lower estuary for these events.

Previous studies on the Bellinger/Kalang system have used these events for calibration and

been able to reproduce observed flood behaviour.

Inflows to the hydraulic model for these events were developed as part of Reference 3.

The hydraulic efficiency of the creeks is represented (in part) within the TUFLOW model by the

roughness or friction factor, Manning’s “n” value. Manning’s “n” is used to describe the influence

of the following factors on flow behaviour:

• channel roughness,

• channel sinuosity,

• vegetation and other debris/obstructions in the channel, and

• bed forms and shapes.

As part of the calibration process the Manning’s “n” roughness value was adjusted within

reasonable limits to best match the recorded flood heights along the creek system. Adopted

values were selected based on an assessment of the ground cover types and vegetation density

within the floodplain. The adopted values (Refer to Table 3 and Figure 5) were then used for the

hydraulic modelling of the design events and assessment of the proposed highway (refer to

Reference 24).

Table 3: Adopted Manning’s “n” Values

Description Manning’s “n” Value

Low Density Residential, Farms 0.04

Medium Density Residential / Overbank 0.06

Dense/Thick vegetation 0.08 - 0.1

Grass/open space 0.04

Main channel 0.025

Vegetated Creeks 0.045

Roads/railway line/culverts 0.02

Other Channel 0.025

6.4. Calibration Results and Discussion

The 1974 and 1977 events were used for calibration of the hydraulic model. These events were

adopted for calibration as they had been used by previous studies which achieved a good

calibration to observed values. Time varying water level data was only available for Bellingen



19

Bridge for these events. Observed water levels were based on SES data and only available near

the peak of the event. The model calibrated reasonably well to observed flood levels (Table 4

and Table 5). Peak flood levels and depths for the 1974 and 1977 events are shown in Figure

16 to Figure 17. Comparison of modelled and observed time varying water levels at Bellingen

Bridge in shown on Figure 6 and Figure 7.

The modelled levels for the 1974 event were generally within 0.4 m of the observed values. The

model showed a bias towards being slightly high. A fair calibration was achieved to the observed

points in Bellingen. Some of the observed peak flood levels in Bellingen appear to contradict

each other. The model however provides a good fit to the time varying water levels at Bellingen

(Figure 6). A poor calibration was achieved to an observed level in the Upper Kalang River

(Observed 9.7mAHD, Modelled 7.55mAHD). There could be many reasons for such a mismatch

between levels including accuracy of the observed level, datum error or sparsity of pluviograph

information. The accuracy of this observed level is thought to be suspect due to a datum error.

The sparsity of pluviograph rainfall information makes calibration to early events difficult as it is

difficult to know what the temporal pattern of rainfall was. Modelled flood levels in the lower

Bellinger and Kalang were strongly influenced by the entrance conditions used.

The modelled levels for the 1977 event were generally within 0.1m of the observed levels except

for:

• Downstream of the entrance where the adopted entrance erosion conditions strongly

influence the modelled levels,

• At Bellingen where modelled water level is 8.74mAHD and the observed peak is

8.2mAHD. However the time varying water level recorded by the SES peaks at

8.52mAHD.

Table 4: Calibration Events - Modelled vs Observed Flood Levels -1974

River Location

Observed

Level

(mAHD)

Modelled

Level

(mAHD)

Difference

(m)

Bellinger

Bellingen Bridge 9.5 9.46 -0.04

Dowle St, North Bellingen backwater 9.8 9.59 -0.21

Cnr. Hammond and Black Sts., North Bellingen backwater 9.3 9.82 0.52

0.4km DS Bellingen Bridge 9.2 8.89 -0.31

Black St., North Bellingen backwater 9.2 8.86 -0.34

Old Butter Factory, East Bellingen 8.7 8.45 -0.25

Fernmount E. Cox 5.7 5.58 -0.12

Raleigh Road Bridge 4.2 4.33 0.13

Raleigh McBaron 4.1 4.27 0.17

Raleigh house 0.4km west of MaBaron 4.1 4.31 0.21

Raleigh CDA Factory 3.9 4.22 0.32

0.1 km US Man Arm Creek Jn. 3.6 4.02 0.42

Summer Breeze Cabins Raleigh 2.6 2.95 0.35

Kalang

Jn, Kalang River & Spicketts Creek 9.7 7.55 -2.15

Northern trip Newry Island 2.7 2.93 0.23

Newry Island opposite Golden Fleece 2.6 2.89 0.29



20

Table 5: Calibration Events - Modelled vs Observed Flood Levels - 1977

River Location

Observed

Level

(mAHD)

Modelled

Level

(mAHD)

Difference (m)

Bellinger

Bellingen Bridge 8.52 8.74 0.22

Raleigh McBaron 3.4 3.41 0.01

Raleigh house 0.4km west of McBaron 3.4 3.46 0.06

Kalang

Newry Island opposite Golden Fleece 2.3 2.37 0.07

Yellow Rock Road Paxton 2.2 2.11 -0.09

0.7km DS Urunga Road Bridge Privett 2.2 1.71 -0.49

Urunga Pinfolds boatshed 2.1 1.39 -0.71

6.5. Model Verification

Model verification was conducted, using the calibrated model and parameters (as discussed in

Section 6.3). The 2001 and March/April 2009 events were used for model calibration. A

significant amount of observed levels and rainfall data was available for these events. Time

varying water level data was also available for the lower estuary for both these events at

Bellingen, Repton, Urunga and Newry Island. The March/April 2009 event is the largest event

for which calibration data is available on the lower Bellinger and Kalang Rivers.

Both events were modelled previously using the Newry Island Flood Study TUFLOW model

(Reference 18 and 19). A reasonable calibration was achieved by the previous studies.

Reference 18 postulated that the Newry Island U/S gauge was suspect during the 2001 event

but no solid proof of this could be found. Reference 19 on face value confirmed this to be the

case.

6.6. Verification Results and Discussion

Peak flood levels for the 2001 and March/April 2009 events are shown in Figure 18 and Figure

19. Comparisons of modelled and observed time varying water levels for Bellingen, Repton,

Urunga and Newry Island gauges are shown in Figure 8 to Figure 15.

For the 2001 event the model calibrated well to observed flood levels. The modelled levels were

generally within 0.2 m of the observed values except for Bellingen Bridge where the model was

0.4m high. A comparison of observed and model levels are shown in Table 6.

For the March/April 2009 event a poor calibration was achieved to observed levels in the Upper

Kalang River (refer to Figure 19). Sensitivity testing indicated that a 1.5 increase in local flows

would not result in a good calibration. A similar difference between modelled and observed was

noted for the 1974 event in this area. Further investigation into local effects not modelled is

warranted. It is possible these level discrepancies are caused by a bias in the local datum

control or very localized rainfall, as it is not possible match these observed levels with any

reasonable modification of parameters. A comparison of observed and model levels are shown

in Table 7.



21

Near Bellingen the March/April 2009 event was approximately a 10% AEP event. In the lower

reaches of the Bellinger River the event is between a 10% and 2% AEP event. On the Kalang

River the event was significantly larger. Upstream of Newry Island the event has a return period

in the order of 0.5% AEP. At Newry Island the event is between a 1% and 0.5% AEP event and

at Urunga in the order of a 2% AEP event.

Table 6: Verification Events - Modelled vs Observed Water Levels - 2001

River Location Observed Level

(mAHD)

Modelled Level

(mAHD)

Difference

(m)

Bellinger

Bellingen brigde 8.77 9.19 0.42

Norco Depot 8 7.81 -0.19

Marx Hill Bridge 6.6 6.38 -0.22

Burdett Park Creek 5.9 5.99 0.09

Connells Bridge 4.8 4.67 -0.13

Camerons Corner 4.4 4.34 -0.06

Repton 3.24 3.23 -0.01

Kalang

Newry Island 2.38 2.57 0.19

Caravan Park, Urunga 2.13 2.09 -0.04

Urunga 1.84 1.73 -0.11

Table 7: Verification Events - Modelled vs Observed Water Levels - 2009

River Location Observed Level

(mAHD)

Modelled

Level

(mAHD)

Difference

(m)

Bellinger

110 Gleniffer Road 10.1 10.05 -0.05

110 Gleniffer Road 9.94 10.05 0.11

1301 Waterfall Way 9.56 9.27 -0.29

1301 Waterfall Way 9.49 9.27 -0.22

Lavenders Bridge 8.81 8.94 0.13

Waterfall Way 7.01 7.74 0.73

Waterfall Way 7 6.98 -0.02

794 Waterfall Way 6.38 6.08 -0.30

895 North Bank Road 5.1 4.58 -0.52

Valery Road 4.24 3.99 -0.25

North Street 3.9 3.78 -0.12

Repton Gauge 3.56 3.44 -0.12

474 Yellow Rock Road 3.09 2.82 -0.27

476 Yellow Rock Road 3.07 2.82 -0.25

Reserve 3.03 2.90 -0.13

427 Yellow Rock Road 2.95 2.77 -0.18

427 Yellow Rock Road 2.94 2.77 -0.17

427 Yellow Rock Road 2.93 2.78 -0.15

Kalang

2 Hains Lane 10.69 9.12 -1.57

32 Hains Lane 10.17 9.02 -1.15

88 Hains Lane 9.79 8.77 -1.02

88 Hains Lane 9.24 8.53 -0.71

1046 South Arm Road 7.2 6.63 -0.57

915 South Bank Road 6.69 6.44 -0.25

869 South Arm Road 6.35 6.39 0.04



22

?? Martells Road 4.33 4.32 -0.01

504 South Arm Road 4.26 4.39 0.13

Newry Island Gauge 4.19 4.35 0.16

1053 Martells Road 4.24 4.40 0.16

5 Burrawing Parade 3.65 3.75 0.10

110 Newry Island Drive 3.58 3.55 -0.03

Pacific Hwy 3.56 3.37 -0.19

114 Newry Island Drive 3.54 3.55 0.01


21 Newry Island Drive 3.53 3.50 -0.03

2 Marshall Place 3.53 3.46 -0.07


Cnr Short Cut Road 3.36 3.46 0.10

Urunga Gauge 2.82 2.87 0.05

MHL Temporary Gauge Site 10 1.7 1.54 -0.16



23

7. DESIGN FLOOD BEHAVIOUR

7.1. Boundary Conditions

7.1.1. Design Inflows

As with the historical events the TUFLOW inflows for the 5 Year ARI, 10, 2, 1, 0.5, 0.2 and

0.05% AEP and Probable Maximum Flood (PMF) design events were obtained from a number

of time varying flow hydrographs taken from the WBNM model (refer to Section 5 and Reference

3). These inflow hydrographs were then applied to the calibrated TUFLOW hydraulic model to

produce design flood levels.

7.1.2. Tailwater Conditions

In addition to runoff from the catchment, the lower reaches of the estuary can also be influenced

by backwater effects resulting from elevated ocean levels. Hence, the height of the tide at the

time of the arrival of the peak runoff from the catchment can also have an influence on flood

levels in the lower reaches. However, these two distinct flooding mechanisms may or may not

result from the same storm. Consideration must therefore be given to accounting for the joint

probability of coincident flooding from both catchment runoff and backwater effects due to

elevated ocean levels.

A full joint probability analysis is beyond the scope of the present study. Traditionally, it is

common practice to estimate design flood levels in these situations using a ‘peak envelope’

approach that adopts the highest of the predicted levels from the two mechanisms.

The 1991 Lower Bellinger Flood Study and the 2008 Newry Island Flood Study (draft) adopted a

1% AEP (100 year ARI) ocean tide boundary condition of 2.6mAHD.

Design tidal hydrographs in this study were based on the experience in nearby catchments,

previous studies in the area, and OEH guidelines. Reference 22 recommends the use of a 2.6

mAHD 1% AEP tide (including wave run up, wave setup etc) for a small untrained narrow and

shallow entrance. (ie. small creek or river with no seawalls). The Bellinger River Entrance in

contrast is large and a large amount of seawalls keeping the entrance open. For large entrances

(such as the Bellinger entrance) it suggests a site specific assessment be undertaken. The

recommended 2.6mAHD includes ocean components that would not be present for the Bellinger

entrance such as wave set up and runup. These effects are of a short term nature and due to

the large storage volume in the estuary and the long period of flooding. Wave setup would not

persist for long enough to effect flood level on the Bellinger and Kalang Rivers.

Based on the characteristics of the entrance of the Bellinger River discussed above WMAwater

recommend the use of 2.1mAHD for the 1% AEP ocean boundary. In order to support this

recommendation a sensitivity analysis was undertaken to determine the area which would be

impacted by a change in the 1% AEP ocean boundary (Error! Reference source not found.).



24

Therefore the model was run with a small river event (10% AEP) and either a 2.1mAHD or

2.6mAHD ocean boundary. The influence of these varying boundary conditions were mainly

confined to the lower reaches (e.g. downstream of Urunga). Therefore a shift from the currently

adopted ocean boundary condition (2.6mAHD and associated flood planning level) to 2.1mAHD

would not affect any major areas of development other than the Council Caravan Park.

While either 1% AEP boundary condition (2.1 or 2.6) could be adopted for current conditions this

will have longer term planning issues for Council with incorporation of sea level rise in the future.

A 1% AEP ocean level of 2.6mAHD plus 0.9m sea level rise will not be very defensible and

would classify large areas as undevelopable. It is therefore suggested that Council adopt a

2.1mAHD 1% AEP ocean level. Council could opt to adopt the 2.1mAHD ocean level plus 0.4m

Sea level rise which would result in a similar planning level to the current one.

Table 8: Ocean Boundary Peaks (mAHD)

Event Peak Ocean Level (mAHD)

5 Year ARI 1.45

10% AEP 1.64

2% AEP 2

1% AEP 2.1

In addition to the above it is not unreasonable to expect that the effects of a severe storm in

terms of ocean levels and runoff could be coincident for a catchment of this size. Hence to

establish the design flood levels in the present study, the relative phasing of the ocean levels

was adjusted such that the peak of the tidal hydrograph would approximately coincide with the

peak of the catchment runoff. For example a 1% AEP catchment event was run with a 0.9

variable tide. A 1% AEP ocean event was run with a 10% AEP catchment event. These 2

scenarios were enveloped to form the 1% AEP event.

For the 0.5%, 0.2% AEP, and 0.05% AEP and PMF events, the 1% AEP design tidal hydrograph

was adopted. All other events were enveloped with the corresponding AEP tide case.

Table 8 and Figure 43 Present the adopted ocean boundary conditions.

7.1.3. Entrance Conditions

The hydrosurvey represented a fairly accreted condition for Bellinger and Kalang Rivers

entrance. Advice from OEH officers is that the river was eroded significant in 2009 after the

hydrosurvey collection. Due to the extremely trained nature of the entrance, it is likely that this

accreted material would erode during a large flood event. As a result the amount of erosion was

varied with the size of the event. Table 9 summarise the amount of erosion applied to the

different size design events in the hydraulic model. The amount of erosion was determined

based on the calibration events.



25

Table 9: Entrance Erosion

Event Average Erosion Depth Compared to Hydrosurvey (m)

5 Year ARI, 10% AEP 0

2% AEP -2.6

1% AEP and rarer events -4.1

7.2. Design Event Results

Peak flood level profiles for the 5 Year ARI, 10, 2, 1, 0.5, 0.2 and 0.05 % AEP and Probable

Maximum Flood (PMF) design events are presented in Figure 22 to Figure 29. Peak velocities

within the study area for the design events are presented in Figure 30 to Figure 37. Table 10

documents design flood levels at key locations.

Table 10: Design Flood Levels at Key Locations

ID Location

Flood Level (mAHD)

5YR

ARI

10%

AEP

2%

AEP

1%

AEP

0.5%

AEP

0.2%

AEP

0.05%

AEP PMF

1 Fernmount 4.65 5.49 7.18 7.83 8.32 8.97 9.90 12.78

2 U/S PacificHighway Bellinger

River 2.88 3.46 5.09 5.61 6.03 6.60 7.39 10.07

3 Mylestom 2.13 2.48 3.35 3.82 4.32 5.13 6.30 8.66

4 Confluence Bellinger and

Kalang River 1.81 2.00 2.05 2.17 2.94 4.05 5.44 7.50

5 D/s NewryIsland 1.99 2.32 3.01 3.45 4.01 4.87 6.12 8.49

6 U/S NewryIsland 2.15 2.56 3.50 3.90 4.34 5.08 6.26 8.75

7 U/S Brierfield Bridge 5.68 6.65 8.66 9.38 9.82 10.44 11.96 16.77

8 Confluence Picket Hill Ck 2.29 2.80 4.06 4.56 5.03 5.68 6.83 9.88

9 OppNorco 2.59 3.17 4.62 5.01 5.36 5.88 6.77 9.22

10 MHL Newry Island U/S

Gauge 2.18 2.62 3.58 3.99 4.41 5.14 6.31 8.89

11 MHL Urunga Gauge 1.98 2.30 2.89 3.29 3.87 4.77 6.03 8.36

12 MHL Repton Gauge 2.40 2.91 4.15 4.57 4.97 5.62 6.62 9.10

13 Bellingen Bridge 7.65 8.78 10.78 11.42 11.87 12.51 13.39 16.54

Table 11 compares estimates of the 1% AEP flood level at Kalang River, Bellingen Bridge and

Urunga from the current and previous studies. Differences between the 1991 Flood Study and

the current study are a result:

• The use of a two dimensional model (current study) compared to a one dimensional

model (1991 study),

• Improved IFD estimates in the current study, and

• Change in hydrologic model to one with more realistic parameters.

Table 11: Comparison of 1% AEP Flood Level with Previous Studies



26

Study Kalang River (Just upstream of

Newry Island) (mAHD) Bellingen Bridge

(mAHD) Urunga

1991 Lower Bellinger Flood Study (PWD)

3.9 10.9 3.2

Upper Bellinger Flood Assessment (2006)

- 11.1 -

Newry Island Flood Study (2008)

3.6 - 3.2

RTA – 2010 4.11 - -

Current Study 3.99 11.42 3.29

7.3. Sensitivity Analysis

The model established for this study relies on a number of assumed parameters, the values of

which are considered to be the most appropriate for the study area. A range of sensitivity

analysis was undertaken on different key parameters in order to quantify potential variations

corresponding to different modelling assumptions.

7.3.1. Rainfall Sensitivity

The Review of Bellinger, Kalang and Nambucca Rivers Catchment Hydrology (Reference 3,

referred to herein as the Regional Study) investigates known hydrologic issues in the Bellinger,

Kalang and Nambucca River catchments. This area of the NSW north coast has presented a

range of challenges for a number of studies where problems have been encountered matching

rainfall runoff modelling with flood frequency results.

7.3.1.1. Approach

For the mid north coast region an assessment of the effect of the new BoM 2013 IFD’s on

design flood quantile estimates was undertaken for OEH (Reference 30). A summary of the

analysis for the Bellinger and Kalang Rivers is reproduced here. Comparisons were undertaken

for the following:

• Catchment average rainfall to a key location,

Design flow estimates compared to FFA, and

• Change in flood level.

7.3.1.2. Catchment Average Rainfall Comparisons

Catchment average rainfalls to a key point in each catchment (corresponding to the flow

comparison locations undertaken in Section 7.3.1.3) were extracted from the 1987 and 2013 IFD

grids (Table 12). The change in catchment average rainfall as a percentage was found to be

less than the resultant change in flow. All Catchment Average rainfalls are for the 48 hour

duration.

For the catchments covered by the Regional Hydrology study the IFDs developed as part of the

Regional Hydrology study are also included in Table 12. These estimates are similar to the 2013

IFD.



27

Table 12: Catchment Average Rainfall Comparison (mm)

EVENT

Thora Bellingen Kooroowi

1987 IFD

Regional Study

2013 IFD

1987 IFD

Regional Study

2013 IFD

1987 IFD

Regional Study

2013 IFD

20% AEP/ 5Y

ARI 387 324 300 372 341 313 381 317 325

10% AEP 459 397 371 440 416 385 453 385 396

5% AEP 551 - 442 529 - 457 546 - 466

2% AEP 680 571 540 652 596 556 674 549 560

1% AEP 784 651 619 752 678 634 778 624 632

Note:

• The 5 Y ARI and 20% AEP are not equal but presented together here for simplicity. The 1987 IFD and

Regional study values are 5 Y ARI values while the 2013 IFD is a 20% AEP estimate.

• A 20 Y ARI/ 5 % AEP estimate was not developed as part of the Regional Study

7.3.1.3. Design Flow Estimates Comparison

Design flood estimates were extracted from the previous hydrologic modelling (Reference 3)

For the Bellinger and Kalang Rivers design flow estimates were available using an IFD method

similar to the 2013 IFDs and the 1987 IFDs using the same parameters. Estimates were

compared at the key gauging sites of:

• Bellinger River @ Bellingen,

• Bellinger River @ Thora, and

• Kalang River @ Kooroowi.

The design parameters used for the previous modelling were applied to the 2013 IFD’s with no

changes to understand the change in flow estimate. Table 13 summaries the flow estimates.

At Thora, Bellingen and Kooroowi design flow estimates reduce by 20-35% for the 2013 IFDs

compared to the 1987 IFDs across the full range design events. In the Bellinger and Kalang

catchments this produces an estimate closer to the FFA estimates at the gauge locations. It is

possible in the Bellinger and Kalang valleys that small changes to the adopted model

parameters would result in similarly good fits to the FFA as those achieved in Reference 3.

Table 13: FFA Flow Comparison (m3/s)



28

EVENT

Thora Bellingen Kooroowi

1987 IFD

Regional Study

2013 IFD

FFA 1987 IFD

Regional Study

2013 IFD

FFA 1987 IFD

Regional Study

2013 IFD

FFA

20%

AEP/

5Y ARI

1010 690 580 530 1340 1070 900 1170 470 320 340 270

10Y

ARI

10%

AEP

1380 1040 910 810 1850 1600 1390 1620 630 480 500 480

20Y

ARI 5%

AEP

1950 - 1390 - 2660 - 2100 2220 860 - 690 680

50Y

ARI

2%

AEP

2900 2290 2130 2170 4000 3520 3220 3370 1250 960 990 920

100Y

ARI

1%

AEP

4090 2960 2840 3020 5680 4570 4270 4590 1700 1200 1260 1060

Note:

• The 5 Y ARI and 20% AEP are not equal but presented together here for simplicity. The 1987 IFD and

Regional study values are 5 Y ARI values while the 2013 IFD is a 20% AEP estimate.

• A 20 Y ARI/ 5 % AEP estimate was not developed as part of the Regional Study

7.3.1.4. Conversion of Flows to Height - Bellingen

In order to assess the sensitivity of design flood levels to these potential changes in flow, flow

estimates at Bellingen were converted to levels using the stage-flow rating curve (Reference 3).

Note that the losses were the same for all cases. Both the Regional Study and the 2013 IFDs

produce lower flood levels than the 1987 IFD. Flood levels are up to 0.4m lower than those

currently adopted by Council (Table 5) although the change in flow from that adopted is

generally less than 10%. The 1% AEP level developed for the Regional Study is 0.2m higher

than that derived for the 2013 IFDs.

Note that the model parameters were not changed from those adopted in the Regional Study for

the 2013 IFD estimate and the Regional Study calibrated well to flood frequency. It is likely that

minor changes to parameters to fit the FFA would result in similar estimates for the Regional

Study and the 2013 IFDs. While there are significant changes in flood level between the cases

presented because the flood heights are anchored on flood frequency analysis the design flood

levels would only change marginally.

Table 14: Changes in Design Flood Level – Bellingen (mAHD)

EVENT 1987 IFD Regional Study

(Adopted) 2013 IFD

20% AEP/ 5Y ARI 8.1 7.6 7.0



29

10Y ARI

10% AEP 8.9 8.6 8.2

20Y ARI

5% AEP 9.7 9.3 9.2

50Y ARI

2% AEP 10.7 10.4 10.1

100Y ARI

1% AEP 11.9 11.1 10.9

Note:

• The 5 Y ARI and 20% AEP are not equal but presented together here for simplicity. The 1987 IFD and Regional study

values are 5 Y ARI values while the 2013 IFD is a 20% AEP estimate.

7.3.1.5. Advice on Rainfall

For the Bellinger, Kalang and Nambucca catchments the 2013 IFDs are a significant change

from the 1987 IFDs. It is likely that flood frequency analysis can be matched without the use of

unorthodox parameters. Given the Regional Hydrology study used IFDs similar to the 2013 IFDs

there is no need to revise the flood studies to the 2013 IFDs.

7.3.2. Parameter Sensitivity

The following scenarios were considered to represent the envelope of likely parameter values:

• ± 0.5mm/hr change in loss rates in the WBNM hydrologic model,

• ± 20% change in the C storage routing parameter in the WBNM hydrologic

model,

• ± 20% change in Manning’s “n” value, and

• Ocean Boundary Conditions (2.1mAHD and 2.6mAHD for the 1% AEP).

For the scenarios listed above the hydrologic/hydraulic models were run for the 1% AEP design

storm and the results are provided in Table 15.

Changes in the continuing losses resulted in a change in flood levels of ±0.1m. A ±20% change

in the storage routing parameter resulted in up to a 0.4m change in flood levels.

A 20% increase and decrease in Mannning’s n value resulted in up to 0.4m change in flood

levels.

All bridges with spans less than 6m and all culverts were blocked by 50% to determine

sensitivity to blockage. The impacts of blockage are localised to the structures and minimal. The

model is relatively insensitive to changes in parameter values.



30

Table 15: Sensitivity Analyses

Location

1% AEP

Flood

Level

(mAHD)

Flood Level (mAHD)

+ Loss -Loss +20%

C

-20%

C

+20%

Mannings

-20%

Mannings

50%

Blockage

Fernmount 7.83 -0.07 0.06 -0.32 0.34 0.31 -0.31 0.00

U/S Pacific Highway

Bellinger River 5.61 -0.06 0.06 -0.23 0.26 0.21 -0.21 0.00

Mylestom 3.82 -0.07 0.07 -0.21 0.23 0.21 -0.22 0.00

Confluence Bellinger

and Kalang River 2.16 -0.10 0.11 -0.22 0.25 0.02 0.20 0.00

D/s Newry Island 3.45 -0.09 0.08 -0.21 0.24 0.16 -0.15 0.00

U/S Newry Island 3.90 -0.06 0.06 -0.16 0.17 0.16 -0.17 0.00

U/S Brierfield Bridge 9.38 -0.09 0.04 -0.35 0.31 0.42 -0.48 0.00

Confluence Picket Hill

Ck 4.57 -0.07 0.07 -0.20 0.20 0.27 -0.32 0.01

Opposite Norco 5.01 -0.04 0.05 -0.17 0.20 0.16 -0.15 0.00

MHL Newry Island U/S

Gauge 3.99 -0.07 0.06 -0.16 0.17 0.18 -0.20 -0.01

MHL Urunga Gauge 3.30 -0.10 0.08 -0.22 0.25 0.16 -0.17 0.00

MHL Repton Gauge 4.58 -0.07 0.06 -0.20 0.21 0.19 -0.21 0.00

Bellingen Bridge 11.39 -0.03 0.06 -0.32 0.33 0.30 -0.22 0.00

7.4. Climate Change

The 2005 Floodplain Development Manual (Reference 211) requires that Flood Studies and

Floodplain Risk Management Studies consider the impacts of climate change (sea level rise and

rainfall increase) on flood behaviour. The following climate change scenarios (rainfall by the

year 2070) are considered in this climate change assessment:

• Increase in peak rainfall and storm volume:

- low level rainfall increase = 10%,

- medium level rainfall increase = 20%,

- high level rainfall increase = 30%.

• Sea level rise:

- a 0.4m increase in level by year 2050

- a 0.9m increase in level by year 2100

A high level rainfall increase of up to 30% is recommended for consideration due to the

uncertainties associated with this aspect of climate change. It is understood that work currently

being undertaken by Engineers Australia, CSIRO and the Bureau of Meteorology as part of the

revision of Australian Rainfall and Runoff which will provide better direction on the possible

impacts of climate change on rainfall.

A 10% increase in rainfall results in up to a 0.55m increase in flood levels with an increase of

approximately 0.3m at most locations. A 30% increase in rainfall increases flood levels for a 1%

AEP event by almost a metre. A 0.4m and 0.9m sea level rise result in an increase in flood

levels in the lower to mid reaches of the Bellinger and Kalang rivers. A 0.4m and 0.9m increase



31

in sea levels would result in a 0.36m and 0.85m increase in 1% AEP flood levels at the

confluence of the Bellinger and Kalang Rivers. Table 16 summarises the impact of climate

change on the 1% AEP flood levels. Error! Reference source not found.Table 16 and Figure

38 Error! Reference source not found.to Figure 42 present the climate change peak flood

levels and depths.

Table 16: Climate Change Results

Location 1% AEP Flood

Level (mAHD)

Change in Flood Level (m)

10% Rainfall

Increase

20% Rainfall

Increase

30% Rainfall

Increase

0.4m Sea

Level

Rise

0.9m Sea

Level

Rise

Fernmount 7.83 0.35 0.67 0.99 0.00 0.00

U/S PacificHighway

Bellinger River 5.61 0.30 0.58 0.87 0.00 0.01

Mylestom 3.82 0.35 0.71 1.11 0.01 0.04

Confluence Bellinger

and Kalang River 2.16 0.55 1.06 1.63 0.36 0.86

D/s NewryIsland 3.45 0.38 0.78 1.21 0.02 0.09

U/S NewryIsland 3.90 0.30 0.62 0.99 0.01 0.04

U/S Brierfield Bridge 9.38 0.34 0.65 0.96 0.00 0.00

Confluence Picket Hill

Ck 4.57 0.29 0.61 0.94 0.01 0.04

OppNorco 5.01 0.24 0.48 0.74 0.00 0.01

MHL Newry Island U/S

Gauge 3.99 0.29 0.60 0.96 0.01 0.04

MHL Urunga Gauge 3.30 0.38 0.80 1.25 0.03 0.10

MHL Repton Gauge 4.58 0.27 0.55 0.88 0.00 0.01

Bellingen Bridge 11.39 0.35 0.66 0.97 0.00 0.00

7.5. Hydraulic and Hazard Categories

For the purposes of floodplain risk management in NSW floodplains are divided into one of three

Hydraulic categories (floodway, flood storage and flood fringe) and two Hazard categories (low

or high). These terms are defined in Reference 21. Further details of this process are provided

in the NSW Governments Floodplain Development Manual (2005, Appendix L) (Reference 21).

The provisional hazard categorisation was determined quantitatively based on available

hydraulic and survey information. High Hazard was assumed where either the peak flood depth

is 1 m or greater, or the velocity depth product (peak velocity x the peak depth) is 1 or greater.

Low hazard is where, should it be necessary, a truck could evacuate people and their

possessions; able-bodied adults would have little difficulty in wading to safety. Error! Reference

source not found. and Error! Reference source not found. present hydraulic hazard for the

1% AEP and PMF events.

It is considered that the hydraulic hazard does not need to be refined to reflect other factors that

influence hazard (such as warning time, flood readiness, rate of rise, duration of flooding,

evacuation problems, effective flood access and the type of development).



32

Hydraulic categories describe the flood behaviour by categorising areas depending on their

function during the flood event, specifically, whether they transmit large quantities of water

(floodway), store a significant volume of water (flood storage) or do not play a significant role in

either storing or conveying water (flood fringe). As with categories of hazard, hydraulic

categories play an important role in informing floodplain risk management in an area. Although

the three categories of hydraulic function are described in the Floodplain Development Manual

(Reference 21), their definitions are largely qualitative and the manual does not prescribe a

method to determine each area. The Manual gives one indication of how to quantitatively

differentiate floodway and flood storage, when it states that flood storage areas, when

completely filled with solid material, will not raise peak flood levels by “more than 0.1 m and/or

would cause the peak discharge anywhere downstream to increase by more than 10%”.

The use of velocity and depth to delineate areas of different hydraulic category follows the

approach proposed by Howells et al. in their 2004 paper (Reference 28). At each grid cell, the

peak velocity (v), peak depth (d) and their product (v*d) is considered, and the cell is

categorised based on the following criteria.

1. If both v*d > 0.25 and v > 0.25, then ‘floodway’

2. If both v > 1 and d > 0.15, then ‘floodway’

3. If neither of the above apply and d > 0.7, then ‘flood storage’

4. Otherwise, ‘flood fringe’.

The areas were expanded by first changing any ‘islands’ of non-floodway to floodway, that is,

areas that are surrounded by floodway. Then flood runners were manually added to the

floodway area, and their width was increased until they were sufficiently wide.

Lowering the thresholds of v, d and v*d may also be used to select more area; however, this

was not possible for the study area, as a number of features on the floodplain, including roads

and irrigation canals, obstructed small flood runners, and so considering v, d or v*d does not

produce any unbroken flood runner or flow path outside the high flow zone.

Hydraulic categorisation is presented in Figure 45 and Figure 46 for the 1% AEP and PMF

events. The majority of the Bellinger River floodplain and Newry Island is considered floodway.

Managing the floodplain: a guide to best practice in flood risk management in Australia

(Reference 29) provides revised hazard classifications which add clarity to the hazard

categories and what they mean in practice. The classification is divided into 6 categories which

indicate the restrictions on people, buildings and vehicles:

• H1 - No constraints,

• H2 – Unsafe for small vehicles,

• H3 - Unsafe for all vehicles, children and the elderly,

• H4 - Unsafe for all people and all vehicles,

• H5 - Unsafe for all people and all vehicles. Buildings require special engineering design

and construction, and

• H6 - Unsafe for people or vehicles. All buildings types considered vulnerable to failure.



33

Figure 47 and Figure 48 present the alternate hazard classifications. Under this classification for

a 1% AEP event much of the floodplain between Bellingen and Urunga is considered unsafe for

all people and all vehicles with buildings require special engineering design and construction.

With large areas upstream of the Pacific Highway crossing of the Bellinger River considered

unconditionally dangerous. In a PMF only small fringe areas of both the Bellinger and Kalang

Rivers are not classified as unconditionally dangerous.

7.6. Flood Planning Area

The flood planning level (FPL) is used to define land subject to flood related development

controls and is generally adopted as the minimum level to which floor levels in the flood affected

areas must be built. The FPL includes a freeboard above the design flood level. It is common

practice to set minimum floor levels for residential buildings, garages, driveways and even

commercial floors as this reduces the frequency and extent of flood damages. Freeboards

provide reasonable certainty that the reduced level of risk exposure selected (by deciding upon

a particular event to provide flood protection for) is actually provided.

The Flood Planning Area is defined as the 1% AEP event plus a freeboard. In the Bellinger and

Kalang Rivers the use of a 0.5m freeboard is considered appropriate. Figure 49 shows the

proposed Flood Planning Area.

7.7. Impacts of Sea Level Rise on Flood Planning Area

The impacts of a 0.4m increase in level by year 2050 and a 0.9m increase in level by year 2100

on the 1% AEP planning level was determined. This includes a 0.5m freeboard. Figure 50

shows the proposed Flood Planning Area with 2050 Sea Level Rise. Figure 51 shows the

proposed Flood Planning Area with 2100 Sea Level Rise. Sea level rise is unlikely to result in

any significant change in flood planning area as the floodplain is already inundated to the steep

foothills. The majority of the change in flood planning area occurs in the Urunga Lagoon area

and is due to roads being overtopped where minor culverts are not included in the model (Figure

52). There is no infrastructure, public land and property affected by the increase in planning

area.



34

8. FLOOD DAMAGES

8.1.1. Background

A flood damages assessment was also undertaken as part of this Flood Study. The cost of flood

damages and the extent of the disruption to the community depends upon many factors

including:

• the magnitude (depth, velocity and duration) of the flood,

• land usage and susceptibility to damage,

• awareness of the community to flooding,

• effective warning time,

• the availability of an evacuation plan or damage minimisation program,

• physical factors such as erosion of the river bank, flood borne debris, sedimentation.

Flood damages can be defined as being “tangible” or “intangible”. Tangible damages are those

for which a monetary value can be assigned, in contrast to intangible damages, which cannot

easily be attributed a monetary value (stress, injury, loss to life, etc.).

Some historic floor level survey was available from the Floodplain Risk Management Study

(Reference 15). Floor level survey was conducted for the remaining properties within the PMF

extent. Each of the 984 properties was “assigned” a GIS tag which was then used to obtain a

flood level for the full range of design flood events. This level was then used with the

appropriate formulae and damages curve to determine the tangible property damages for each

event.

There are a number of issues with “assigning” a single flood level to a property to estimate flood

damages. These include:

• no account is taken of the actual openings where floodwaters could enter a building

relative to the applicable flood gradient. Thus a rear door may allow the water to enter

rather than the front door,

• the level “assigned” is usually taken as the flood level midway across the property. For

areas with low flood gradients this is appropriate, however in “long” properties and

factories or areas with strong flood gradients this may not necessarily be appropriate.

• the “assigned” flood level is only relevant for estimating flood damages and should not

be used for development control purposes. These latter levels must be obtained from

interpolation of the flood contour maps.

8.1.2. Assessment of Tangible Flood Damages

Quantification of tangible flood damages is generally based upon data derived from post-flood

damage surveys obtained following historical flood events and is industry practice in NSW.

Floods by their nature are unpredictable and conditions variable. It is therefore unlikely that a

self-assessment survey would have predicted the scale or extent of the damages which

occurred in Nyngan in 1990 or North Wollongong in August 1998. For this reason it was

decided to use the post-flood damage approach in assessing flood damages for the study area.



35

The most comprehensive damage surveys include those carried out for Sydney (Georges River

-1986), Nyngan (1990), Inverell (1991) and Katherine (1998). Some of the problems in applying

data from these studies to other areas can be summarised as follows:

• varying building construction methods, e.g. slab on ground, pier, brick, timber,

• different average age of the buildings in the area,

• the quality of buildings may differ greatly,

• inflation must be taken into account,

• different fixtures within buildings, e.g. air-conditioning units, machinery, etc.,

• change in internal fit out of buildings over the years or in different areas, e.g.

more carpets and less linoleum or change in kitchen/bathroom cupboard

material,

• external (yard) damages can vary greatly. For example in some areas

vehicles can be readily moved whilst in other areas it is not possible,

• different approaches in assessing flood damages. Are the damages assessed

on a “replacement” or a “repair and reinstate where possible” basis? Some

surveys include structural damage within internal damage whilst others do

not,

• varying warning times between communities means that the potential versus

actual damage ratio may change significantly,

• variations in flood awareness of the community.

8.1.3. Tangible Damages – Residential Properties

Tangible direct damages are generally calculated under the following components:

• Internal,

• Structural,

• External.

Tangible indirect damages can be subdivided into the following groups:

• accommodation and living expenses,

• loss of income,

• clean up activities.

Damages may be calculated as either estimated actual damages or estimated potential

damages. If potential damages are calculated an Actual/Potential (A/P) ratio is assigned based

upon (as well as other factors) the likely flood awareness of the community and the available

warning time.

The flood awareness of the majority of the Bellinger and Kalang Rivers community is likely to be

high and the available flood warning time in the order of 12hrs. Based upon the limited data

available it is considered that the A/P ratio for the communities within the Bellinger and Kalang

Rivers would most likely be similar to that applicable at Nyngan and Inverell.



36

The approach adopted for estimating flood damages was therefore based on that derived from

the Nyngan and Inverell flood damages surveys with updating for inflation and the different type

of buildings in the catchment.

8.1.3.1. Direct Internal Damages

Internal damages are based upon the following formulae recommended by OEH (Reference 21).

Allowing for inflation and differences in the types of buildings and their contents, a contents

value of $60,000 was adopted for this study for houses. Structural damages were not included in

the above figures.

8.1.3.2. Direct Structural Damages

Structural damages were assumed follow the relationship adopted in Reference 21 for houses.

In floods larger than the 1% AEP event there is the possibility that some buildings may collapse

or have to be destroyed. The cost of these damages have not been included in the analysis.

8.1.3.3. Direct External Damages

External damages (laundry/garage/yard/vehicle) were assumed to $6700 for houses as

recommended by Reference 21. This assumes that the majority of vehicles are moved by

residents.

8.1.3.4. Indirect Damages

Indirect damages were assumed to be a linear relationship from $0 at 0 m above floor level to a

maximum of $4,000 at 0.5 m.

8.1.4. Results

The number of buildings inundated above floor level along with the estimated flood damages are

summarised for the range of design flood events in Table 18. Table 17 indicates the number of

yards inundated. Due to the frequent flooding of low lying areas houses at low levels would have

been raised. The majority of properties are located above the 100yr ARI level. A significant

increase in the number of flooded properties occurs between the 100 year ARI and 200 year

ARI.

Table 17: Affected Properties

Event

RESIDENTIAL COMMERCIAL TOTAL

No.

Properties

Affected

Flooded

Above

Floor Level

No.

Properties

Affected

Flooded

Above

Floor Level

No.

Properties

Affected

Flooded

Above

Floor Level

20% 31 8 1 0 32 8

10% 61 16 4 2 65 18

2% 234 95 15 13 249 108



37

1% 357 183 18 16 375 199

0.5% 469 365 19 19 488 384

0.2% 592 530 21 21 613 551

0.05% 811 770 32 30 843 800

PMF 920 909 64 57 984 966

Table 18: Estimated Flood Damages

Event No.

Properties Affected

No. Flooded Above Floor

Level Total Damages for Event

Ave. Damage Per Flood Affected Property

20% 32 8 $ 402,300 $ 12,600

10% 65 18 $ 999,700 $ 15,400

2% 249 108 $ 7,329,800 $ 29,400

1% 375 199 $ 13,839,100 $ 36,900

0.5% 488 384 $ 25,484,100 $ 52,200

0.2% 613 551 $ 48,219,300 $ 78,700

0.05% 843 800 $ 86,639,400 $ 102,800

PMF 984 966 $ 138,038,200 $ 140,300

Average Annual Damages (AAD) $ 1,035,100 $ 1,100

Note: * Excludes all damages to public assets. Includes external damages that may or may not occur with building floor

inundation.

The standard way of expressing flood damages is in terms of Average Annual Damages (AAD).

AAD represents the equivalent average damages that would be experienced by the community

on an annual basis, by taking into account the probability of a flood occurrence. By this means

the smaller floods, which occur more frequently, are given a greater weighting than the rare

catastrophic floods. The Average Annual Damages (AAD) based on the above values is

estimated to be $1,035,100. Most dwellings are located above the 1% AEP flood level.

Figure 61 to Figure 65 show the event at which the ground is first inundated, while Figure 66 to

Figure 70 show the event at which the floor level of a property is first inundated. Flood levels first

enter the grounds of properties in Bellingen in a 10% AEP event, Newry Island, Mylestom,

Urunga, Raleigh in a 5 yr ARI event. Above floor flooding in Bellingen occurs at the golf course

and Show grounds in a 5 yr ARI event. Flooding in a 2% AEP event flooding of residential

buildings in Bellingen above floor level occurs. Flooding above flood level occurs in Mylestom,

Urunga, Raleigh in a 5 yr ARI event. Houses are flooded in a 5 Year ARI event include a group

of holiday rentals and houses on Yellow Rock Road downstream of Tuckers Island. These

properties are located in a low flood island.



38

9. EMERGENCY RESPONSE

9.1. Preliminary Flood Emergency Response Planning Classification of

Communities

The Floodplain Development Manual (NSW State Government, 2005) requires flood studies 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 Emergency Response

Planning (ERP). Classification provides an indication of the vulnerability of the community in

flood emergency response and identifies the type and scale of information needed by the State

Emergency Services (SES) to assist in emergency response planning (ERP).

Criteria for determining flood ERP classifications and an indication of the emergency response

required for these classifications are provided in the Floodplain Risk Management Guideline,

2007 (Flood Emergency Response Planning: Classification of Communities). Table 19

summarises the response required for areas of different classification. However, these may

vary depending on local flood characteristics and resultant flood behaviour, i.e. in flash flooding

or overland flood areas.

Table 19: Response Required for Different Flood ERP Classifications

Classification Response 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

Area 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

In undertaking this assessment for the Bellinger and Kalang Rivers, all roads have been

considered trafficable in a flood event, both paved and unsealed. The suitability for use of

particularly unsealed roads should be reviewed with the SES. Figure 53 presents the ERP

classifications.

Most of the main population centres of Bellingen and Urunga are classified as Rising Road

Access as the properties are inundated but flood free access roads provide a retreat to flood

free land. Small parts of North Bellingen, Newry Island and Urunga are classified as High Flood

Islands. Newry Island is classified as a Low Flood Island as practical access is cut and they are

inundated during an event.



39

9.2. Evacuation Routes and Length of Inundation

Time of inundation in a 1% AEP event shown on Figure 54 for all grid cells within the model. The

majority of areas are inundated for between 10 and 40 hrs. Some low lying areas are inundated

for almost 3 days. Some extremely low lying areas may experience inundation for longer.

Table 20 provides the levels of low points in key evacuation routes within the catchment and the

flood levels at these locations for a range of events. These low points were surveyed as part of

the study or levels were derived from the ALS. This gives an indication of during what size

event these roads are likely to be first cut. Figure 55 and Figure 56 depict graphically when the

roads are first cut. Figure 57 to Figure 60 are event hydrographs at selected low points.

The length of time in a 1% AEP event till a low point in the road is cut and how long it can be

expected to be cut is presented in Table 21. Table 22 shows road low points by SES Flood

Management Zone and what event access via that road is cut, event in which evacuation to that

area is cut and the Emergency Response classification for that area.

Table 20: Design flood levels at low points in roads.

ID Road Name

Level of

low

point in

road

(mAHD)

Design Flood Levels at Low Point (mAHD)

5YR

ARI

10%

AEP

2%

AEP

1%

AEP

0.5%

AEP

0.2%

AEP

0.05

%

AEP

PMF

1 Island Pl Newry 2.185 3.99 3.50 4.15 4.86 6.15 8.45

2 The Grove Newry 4.125 4.88 6.11 8.47

3 Marshall Place Newry 3.003 3.53 4.21 4.86 6.16 8.45

4 Newry Island Dr 1.568 2.36 2.39 3.24 3.70 4.19 4.99 6.19 8.63

5 Hollis Cl Newry 6.579 8.47

6 Marina Cres 1.699 2.36 3.59 3.48 4.97 4.86 6.14 8.44

7 Yellow Rock Rd 2.884 3.34 3.93 4.84 6.96 8.39

8 Old Punt Rd 4.566 4.85 6.12 8.47

9 Bellingen St 1.867 1.98 2.30 2.86 3.26 3.84 4.74 6.76 8.31

10 Allison St 2.7 3.00 3.44 4.30 4.87 6.11 8.49

11 Panorama Parade 2.801 3.00 3.44 4.30 4.87 6.11 8.49

12 Melaleuca Pl 2.95 3.61 4.12 4.94 6.13 8.52

13 Rosedale Dr 2.799 3.66 4.16 4.96 6.17 8.55

14 Tambar Pl 3.408 4.16 4.96 6.17 8.55

15 Myall Ct 2.881 3.65 4.15 4.95 6.17 8.56

16 Pacific Highway 2.876 3.53 4.15 4.86 6.14 8.44

17 South Arm Rd 9.849

18 Riverside Drive 6.307 8.46

19 Crescent Cl 1.82 1.98 2.36 2.94 3.38 3.95 4.83 6.79 8.43

20 Ranger St 12.41

21 Gossip Rd 3.611 3.63 4.43 4.51 5.27 6.44 9.70

22 Kalang Br US 2.704 3.67 4.23 4.44 5.17 6.34 9.15

23 Kalang Br DS 2.028 2.62 3.57 3.98 4.40 5.12 6.29 8.86

24 Waterfall way 16.3343

25 Waterfall way Lowpt 2.949 3.26 5.51 6.93 6.56 7.15 7.95 1.48

26 Mylestom Dr 2.147 2.19 2.59 3.58 3.96 4.45 5.24 6.37 8.76



40

27 Bellingen br 4 7.56 8.65 1.52 11.14 11.57 12.19 13.28 16.77

28 Waterfall way US 4.9 5.52 7.36 8.21 8.54 9.24 1.28 13.35

29 South Arm us 1.929 2.36 2.96 4.58 5.12 5.63 6.26 7.38 1.30

Table 21: Inundation times of road low points

ID Road Name Level of low point in road

(mAHD)

Hours before

inundated in 1%

AEP Event

Total time of

inundation (hrs)*

1 Island Pl Newry 2.185 24.75 45.5

2 The Grove Newry 4.125 0

3 Marshall Place Newry 3.003 26 7

4 Newry Island Dr 1.568 20 24.25

5 Hollis Cl Newry 6.579 0

6 Marina Cres 1.699 22.5 17.75

7 Yellow Rock Rd 2.884 27.75 4.25

8 Old Punt Rd 4.566 0

9 Bellingen St 1.867 23.5 16

10 Allison St 2.7 25.5 8.75

11 Panorama Parade 2.801 25.75 8

12 Melaleuca Pl 2.95 28.25 1.5

13 Rosedale Dr 2.799 26 44

14 Tambar Pl 3.408 0

15 Myall Ct 2.881 26.25 43.75

16 Pacific Highway 2.876 26.25 43.75

17 South Arm Rd 9.849 0

18 Riverside Drive 6.307 0

19 Crescent Cl 1.82 22.75 17.5

20 Ranger St 12.41 0

21 Gossip Rd 3.611 23.5 9

22 Kalang Br US 2.704 20.75 19

23 Kalang Br DS 2.028 18.5 26

24 Waterfall way 16.3343 0

25 Waterfall way Lowpt 2.949 19.5 50.75

26 Mylestom Dr 2.147 19.75 24

27 Bellingen br 4 10.75 38.5

28 Waterfall way US 4.9 17.5 22.5

29 South Arm us 1.929 17 29.25

*Inundation is defined as a depth of greater than 0.1m

Table 22: Event when access and evacuation is cut

ID

SES Flood

Management

Zone

When Access Road is Cut When Evacuation is cut ERP

1 Newry Island

(Residential) 2% AEP 2% AEP Low Flood Island

2 Newry Island

(Residential) 0.2% AEP 2% AEP Low Flood Island

3 Newry Island

(Residential) 1% AEP 2% AEP Low Flood Island



41

4 Newry Island

(Rural) 5YR ARI 5YR ARI Low Flood Island

5 Newry Island

(Residential) PMF 2% AEP Low Flood Island

6 Yellow Rock 10% AEP 10% AEP Low Flood Island

7 Yellow Rock 1% AEP 1% AEP Rising Road

Access

8 Yellow Rock 0.2% AEP 0.2% AEP

Overland Refuge

Area on High

Flood Island

9 Urunga 5YR ARI 5YR ARI Rising Road

Access

10 Urunga 2% AEP 2% AEP Rising Road

Access


Access


Access


Access

14 Urunga 0.5% AEP 0.5% AEP Rising Road

Access


Access

16 Kalang Rural 1% AEP 1% AEP Low Flood Island

17 Kalang Rural Not cut 2% AEP Not cut

18 Kalang Rural PMF 2% AEP

Overland Refuge

Area on High

Flood Island

19 Urunga 5YR ARI 5YR ARI Rising Road

Access

20 Urunga Not cut 0.05% AEP Not cut

21 Kalang Rural 2% AEP 2% AEP

Overland Refuge

Area on High

Flood Island


Overland Refuge

Area on High

Flood Island


Overland Refuge

Area on High

Flood Island

24 Bellingen Rural Not cut 10% AEP Not cut

25 Bellingen Rural 10% AEP 10% AEP Not Classified

26 Mylestom 5YR ARI 5YR ARI Low Trapped

Perimeter

27 Bellingen 5YR ARI 5YR ARI Rising Road

Access

28 Bellingen Rural 10% AEP 10% AEP Not Classified

29 Kalang Rural 5YR ARI 2% AEP Not Classified



42

9.3. Correlation between Newry Island U/S Gauge and Newry Island

Bridge

Diagram 1 depicts the correlation between the Newry Island U/S gauge and Newry Island bridge

based on the hydraulic model. The hydraulic model results for the historical events are also

plotted. No historical observed levels exist at the site of the Newry Island Bridge. As a priority

flood levels in future event should be collected at the bridge.

Diagram 1: Correlation between Flood levels at Newry Island Bridge and Newry Island U/S gauge



43

10. TIDAL CALIBRATION

10.1. Verification to a Tide

In order to assess if the model was suitable for assessing tidal planes extent the model was

verified against a period of tidal record with no rainfall or flood events. The period chosen was

March 2008. A reasonably good fit to the tidal record was found (Figure 71 to Figure 73). The

timing of the peaks is slightly early with the second peak within 0.1m. Figure 74 depicts the

extent of the peak water level during this event.

10.2. High High Water Solstice Spring

Manly Hydraulics Laboratory prepared the NSW Tidal Planes Analysis: 1990-2010 Harmonic

Analysis report on behalf of the NSW Office of Environment and Heritage. It was released in

October 2012 and was based on data from 188 tidal monitoring stations from the 1st July 1990

to the 30th June 2010. The closest long term ocean site is Coffs Harbour. The High High Water

Solstice Spring (HHWSS) (1.077mAHD) was used to determine the tidal inundation for a regular

tidal event. The HHWSS was also modelled in the hydraulic model assuming a 0.4 and 0.9m

sea level rise. Figure 75 depicts the tidal extent for current and future climates.

Under current climate conditions the tidal extent is limited to within the river banks with some

overbank flooding between Back Creek and the Bellinger river, backwater areas upstream of the

Pacific Highway near Short Cut road and a small area near the new Pacific Highway bridge over

the Kalang River. With climate change regular tidal inundation will extend and public

infrastructure is likely to be affected. Inundation will occur around the low lying areas near

Urunga, Back Creek and Boggy Creek and Raleigh. Infrastructure likely to be affected includes

Urunga Golf Course, Crescent Close and Atherton Drive Urunga, Yellow Rock Road, Hebbard

Drive, Marina Crescent, Newry Island Drive and Island Place, Newry Island.



44

11. CONCLUSIONS

A detailed hydraulic model (TUFLOW) has been developed to quantify the flood behaviour of the

Lower Bellinger and Kalang Rivers, making best use of the data currently available.

This model has been used to reproduce the historical flood behaviour from events in 1974,

1977, 2001 and 2009. The TUFLOW model has been used to define flood behaviour for a range

of design events (5 Year ARI, 10, 2, 1, 0.5, 0.2 and 0.05 % AEP and Probable Maximum Flood).

Community consultation and hazard classification were undertaken. The model developed for

the current study is suitable for further floodplain planning and use in setting planning levels

within the study area.

It is recommended that data collection in future events target the Kalang River above Newry

Island.



45

12. REFERENCES

1. Pilgrim DH (Editor in Chief)

Australian Rainfall and Runoff – A Guide to Flood Estimation

Institution of Engineers, Australia, 1987.

2. WBM BMT

Tuflow User Manual – GIS Based 2D/1D Hydrodynamic Modelling

2010

3. WMAwater

Review of the Bellinger, Kalang and Nambucca River Catchments Hydrology

July 2011

4. Boyd M, Rigby T, VanDrie R, and Schymitzek I

WBNM User Guide

2007

5. RTA

Warrell Creek to Urunga Upgrading the Pacific Highway Environmental

Assessment - Volume 1 Environmental Assessment

January 2010

6. Cameron McNamara

New South Wales Coastal Rivers Floodplain Management Studies Bellinger

Valley

December 1980

7. Outline Planning Consultants

Proposed Industrial Area, Urunga NSW

May 1984

8. PWD

Bellinger River May 1980 Flood Report

1981

9. PWD

Bellinger River Flood History 1843-1979

1980



46

10. PWD

Lower Bellinger River Flood Study

1991

11. Cameron McNamara

Lower Bellinger River Flood Study, Location of Flood Marks Engineering

Survey Brief

1991

12. PWD

Lower Bellinger River Flood Study Compendium of Data

1991

13. Bruce Fidge and Associates

Bellinger and Kalang River’s Floods of February and March 2001

2003

14. Bellingen Shire Council

Floodplain Risk Management Study Stage 2- An Assessment of Floodplain

Management Options and Strategies

April 2002


Upper Kalang River Flood Assessment,

December 2006

16. DeGroot and Benson Pty Ltd

South Arm Road Flood Study (Final)

June 2000


Upper Bellinger River Flood Assessment

2006

18. WMAwater

Newry Island Flood Study Draft

2008

19. WMAwater

Kalang River 2009 Flood Event

2011



47

20. Enginuity Design

Bellinger and Kalang Rivers Flood Event of 31 March 2009 Collection and

Collation of Flood Data

2010

21. NSW Government

Floodplain Development Manual: The management of flood liable land

April 2005

22. Department of Infrastructure, Planning and Natural Resources

Floodplain Management Guideline No 5 – Ocean Boundary Conditions

23. NSW Government

Draft Sea Level Rise Policy Statement

2009

24. WMAwater

Warrell Creek to Urunga – Pacific Highway Upgrade Modelling

2012

25. Nathan, RJ and Weinmann, E,

Estimation of Large to Extreme Floods, Book VI in Australian Rainfall and

Runoff - A Guide to Flood Estimation,

The Institution of Engineers, Australia, Barton, ACT, 1999.

26. MHL

Bellinger and Kalang Rivers Data Collection – July 2008 to September 2009 (MHL Report Number 1951) NSW Public Works, 2010

27. WMAwater

Hydraulic Modelling Report - Bellinger and Kalang Rivers

2012

28. Howells L, McLuckie D., Collings G., Lawson N.

Defining the Floodway – Can One Size Fit All?

2004

29. Australian Government

Managing the floodplain: a guide to best practice in flood risk management in

Australia



48

2013

30. WMAwater

Advice on the use of the 2013 Design Rainfall for NSW

2014


WMAwater 111036-04 :Lower_Bellinger_Kalang_FS:30 September 2015 A1

APPENDIX A: GLOSSARY

Taken from the Floodplain Development Manual (April 2005 edition)

acid sulfate soils

Are sediments which contain sulfidic mineral pyrite which may become extremely

acid following disturbance or drainage as sulfur compounds react when exposed

to oxygen to form sulfuric acid. More detailed explanation and definition can be

found in the NSW Government Acid Sulfate Soil Manual published by Acid Sulfate

Soil Management Advisory Committee.

Annual Exceedance

Probability (AEP)

The chance of a flood of a given or larger size occurring in any one year, usually

expressed as a percentage. For example, if a peak flood discharge of 500 m3/s

has an AEP of 5%, it means that there is a 5% chance (that is one-in-20 chance)

of a 500 m3/s or larger event occurring in any one year (see ARI).

Australian Height Datum

(AHD)

A common national surface level datum approximately corresponding to mean

sea level.

Average Annual Damage

(AAD)

Depending on its size (or severity), each flood will cause a different amount of

flood damage to a flood prone area. AAD is the average damage per year that

would occur in a nominated development situation from flooding over a very long

period of time.

Average Recurrence

Interval (ARI)

The long term average number of years between the occurrence of a flood as big

as, or larger than, the selected event. For example, floods with a discharge as

great as, or greater than, the 20 year ARI flood event will occur on average once

every 20 years. ARI is another way of expressing the likelihood of occurrence of

a flood event.

caravan and moveable

home parks

Caravans and moveable dwellings are being increasingly used for long-term and

permanent accommodation purposes. Standards relating to their siting, design,

construction and management can be found in the Regulations under the LG Act.

catchment

The land area draining through the main stream, as well as tributary streams, to a

particular site. It always relates to an area above a specific location.

consent authority

The Council, government agency or person having the function to determine a

development application for land use under the EP&A Act. The consent authority

is most often the Council, however legislation or an EPI may specify a Minister or

public authority (other than a Council), or the Director General of DIPNR, as

having the function to determine an application.

development

Is defined in Part 4 of the Environmental Planning and Assessment Act (EP&A

Act).

infill development: refers to the development of vacant blocks of land that are

generally surrounded by developed properties and is permissible under the

current zoning of the land. Conditions such as minimum floor levels may be

imposed on infill development.

new development: refers to development of a completely different nature to that

associated with the former land use. For example, the urban subdivision of an

area previously used for rural purposes. New developments involve rezoning and

typically require major extensions of existing urban services, such as roads, water

supply, sewerage and electric power.



redevelopment: refers to rebuilding in an area. For example, as urban areas

age, it may become necessary to demolish and reconstruct buildings on a

relatively large scale. Redevelopment generally does not require either rezoning

or major extensions to urban services.

disaster plan (DISPLAN)

A step by step sequence of previously agreed roles, responsibilities, functions,

actions and management arrangements for the conduct of a single or series of

connected emergency operations, with the object of ensuring the coordinated

response by all agencies having responsibilities and functions in emergencies.

discharge

The rate of flow of water measured in terms of volume per unit time, for example,

cubic metres per second (m3/s). Discharge is different from the speed or velocity

of flow, which is a measure of how fast the water is moving for example, metres

per second (m/s).

ecologically sustainable

development (ESD)

Using, conserving and enhancing natural resources so that ecological processes,

on which life depends, are maintained, and the total quality of life, now and in the

future, can be maintained or increased. A more detailed definition is included in

the Local Government Act 1993. The use of sustainability and sustainable in this

manual relate to ESD.

effective warning time

The time available after receiving advice of an impending flood and before the

floodwaters prevent appropriate flood response actions being undertaken. The

effective warning time is typically used to move farm equipment, move stock,

raise furniture, evacuate people and transport their possessions.

emergency management

A range of measures to manage risks to communities and the environment. In

the flood context it may include measures to prevent, prepare for, respond to and

recover from flooding.

flash flooding

Flooding which is sudden and unexpected. It is often caused by sudden local or

nearby heavy rainfall. Often defined as flooding which peaks within six hours of

the causative rain.

flood

Relatively high stream flow which overtops the natural or artificial banks in any

part of a stream, river, estuary, lake or dam, and/or local overland flooding

associated with major drainage before entering a watercourse, and/or coastal

inundation resulting from super-elevated sea levels and/or waves overtopping

coastline defences excluding tsunami.

flood awareness

Flood awareness is an appreciation of the likely effects of flooding and a

knowledge of the relevant flood warning, response and evacuation procedures.

flood education

Flood education seeks to provide information to raise awareness of the flood

problem so as to enable individuals to understand how to manage themselves an

their property in response to flood warnings and in a flood event. It invokes a

state of flood readiness.

flood fringe areas

The remaining area of flood prone land after floodway and flood storage areas

have been defined.

flood liable land

Is synonymous with flood prone land (i.e. land susceptible to flooding by the

probable maximum flood (PMF) event). Note that the term flood liable land

covers the whole of the floodplain, not just that part below the flood planning level

(see flood planning area).



flood mitigation standard

The average recurrence interval of the flood, selected as part of the floodplain risk

management process that forms the basis for physical works to modify the

impacts of flooding.

floodplain

Area of land which is subject to inundation by floods up to and including the

probable maximum flood event, that is, flood prone land.

floodplain risk

management options

The measures that might be feasible for the management of a particular area of

the floodplain. Preparation of a floodplain risk management plan requires a

detailed evaluation of floodplain risk management options.

floodplain risk

management plan

A management plan developed in accordance with the principles and guidelines

in this manual. Usually includes both written and diagrammetic information

describing how particular areas of flood prone land are to be used and managed

to achieve defined objectives.

flood plan (local)

A sub-plan of a disaster plan that deals specifically with flooding. They can exist

at State, Division and local levels. Local flood plans are prepared under the

leadership of the State Emergency Service.

flood planning area

The area of land below the flood planning level and thus subject to flood related

development controls. The concept of flood planning area generally supersedes

the Aflood liable land@ concept in the 1986 Manual.

Flood Planning Levels

(FPLs)

FPL=s are the combinations of flood levels (derived from significant historical

flood events or floods of specific AEPs) and freeboards selected for floodplain risk

management purposes, as determined in management studies and incorporated

in management plans. FPLs supersede the Astandard flood event@ in the 1986

manual.

flood proofing

A combination of measures incorporated in the design, construction and alteration

of individual buildings or structures subject to flooding, to reduce or eliminate flood

damages.

flood prone land

Is land susceptible to flooding by the Probable Maximum Flood (PMF) event.

Flood prone land is synonymous with flood liable land.

flood readiness

Flood readiness is an ability to react within the effective warning time.

flood risk

Potential danger to personal safety and potential damage to property resulting

from flooding. The degree of risk varies with circumstances across the full range

of floods. Flood risk in this manual is divided into 3 types, existing, future and

continuing risks. They are described below.

existing flood risk: the risk a community is exposed to as a result of its location

on the floodplain.

future flood risk: the risk a community may be exposed to as a result of new

development on the floodplain.

continuing flood risk: the risk a community is exposed to after floodplain risk

management measures have been implemented. For a town protected by levees,

the continuing flood risk is the consequences of the levees being overtopped. For

an area without any floodplain risk management measures, the continuing flood

risk is simply the existence of its flood exposure.

Those parts of the floodplain that are important for the temporary storage of



flood storage areas floodwaters during the passage of a flood. The extent and behaviour of flood

storage areas may change with flood severity, and loss of flood storage can

increase the severity of flood impacts by reducing natural flood attenuation.

Hence, it is necessary to investigate a range of flood sizes before defining flood

storage areas.

floodway areas

Those areas of the floodplain where a significant discharge of water occurs during

floods. They are often aligned with naturally defined channels. Floodways are

areas that, even if only partially blocked, would cause a significant redistribution of

flood flows, or a significant increase in flood levels.

freeboard

Freeboard provides reasonable certainty that the risk exposure selected in

deciding on a particular flood chosen as the basis for the FPL is actually provided.

It is a factor of safety typically used in relation to the setting of floor levels, levee

crest levels, etc. Freeboard is included in the flood planning level.

habitable room

in a residential situation: a living or working area, such as a lounge room, dining

room, rumpus room, kitchen, bedroom or workroom.

in an industrial or commercial situation: an area used for offices or to store

valuable possessions susceptible to flood damage in the event of a flood.

hazard

A source of potential harm or a situation with a potential to cause loss. In relation

to this manual the hazard is flooding which has the potential to cause damage to

the community. Definitions of high and low hazard categories are provided in the

Manual.

hydraulics

Term given to the study of water flow in waterways; in particular, the evaluation of

flow parameters such as water level and velocity.

hydrograph

A graph which shows how the discharge or stage/flood level at any particular

location varies with time during a flood.

hydrology

Term given to the study of the rainfall and runoff process; in particular, the

evaluation of peak flows, flow volumes and the derivation of hydrographs for a

range of floods.

local overland flooding

Inundation by local runoff rather than overbank discharge from a stream, river,

estuary, lake or dam.

local drainage

Are smaller scale problems in urban areas. They are outside the definition of

major drainage in this glossary.

mainstream flooding

Inundation of normally dry land occurring when water overflows the natural or

artificial banks of a stream, river, estuary, lake or dam.

major drainage

Councils have discretion in determining whether urban drainage problems are

associated with major or local drainage. For the purpose of this manual major

drainage involves:

• the floodplains of original watercourses (which may now be piped, channelised

or diverted), or sloping areas where overland flows develop along alternative

paths once system capacity is exceeded; and/or

• water depths generally in excess of 0.3 m (in the major system design storm

as defined in the current version of Australian Rainfall and Runoff). These



conditions may result in danger to personal safety and property damage to

both premises and vehicles; and/or

• major overland flow paths through developed areas outside of defined

drainage reserves; and/or

• the potential to affect a number of buildings along the major flow path.

mathematical/computer

models

The mathematical representation of the physical processes involved in runoff

generation and stream flow. These models are often run on computers due to the

complexity of the mathematical relationships between runoff, stream flow and the

distribution of flows across the floodplain.

merit approach

The merit approach weighs social, economic, ecological and cultural impacts of

land use options for different flood prone areas together with flood damage,

hazard and behaviour implications, and environmental protection and well being

of the State=s rivers and floodplains.

The merit approach operates at two levels. At the strategic level it allows for the

consideration of social, economic, ecological, cultural and flooding issues to

determine strategies for the management of future flood risk which are formulated

into Council plans, policy and EPIs. At a site specific level, it involves

consideration of the best way of conditioning development allowable under the

floodplain risk management plan, local floodplain risk management policy and

EPIs.

minor, moderate and major

flooding

Both the State Emergency Service and the Bureau of Meteorology use the

following definitions in flood warnings to give a general indication of the types of

problems expected with a flood:

minor flooding: causes inconvenience such as closing of minor roads and the

submergence of low level bridges. The lower limit of this class of flooding on the

reference gauge is the initial flood level at which landholders and townspeople

begin to be flooded.

moderate flooding: low-lying areas are inundated requiring removal of stock

and/or evacuation of some houses. Main traffic routes may be covered.

major flooding: appreciable urban areas are flooded and/or extensive rural areas

are flooded. Properties, villages and towns can be isolated.

modification measures

Measures that modify either the flood, the property or the response to flooding.

Examples are indicated in Table 2.1 with further discussion in the Manual.

peak discharge

The maximum discharge occurring during a flood event.

Probable Maximum Flood

(PMF)

The PMF is the largest flood that could conceivably occur at a particular location,

usually estimated from probable maximum precipitation, and where applicable,

snow melt, coupled with the worst flood producing catchment conditions.

Generally, it is not physically or economically possible to provide complete

protection against this event. The PMF defines the extent of flood prone land,

that is, the floodplain. The extent, nature and potential consequences of flooding

associated with a range of events rarer than the flood used for designing

mitigation works and controlling development, up to and including the PMF event

should be addressed in a floodplain risk management study.



Probable Maximum

Precipitation (PMP)

The PMP is the greatest depth of precipitation for a given duration

meteorologically possible over a given size storm area at a particular location at a

particular time of the year, with no allowance made for long-term climatic trends

(World Meteorological Organisation, 1986). It is the primary input to PMF

estimation.

probability

A statistical measure of the expected chance of flooding (see AEP).

risk

Chance of something happening that will have an impact. It is measured in terms

of consequences and likelihood. In the context of the manual it is the likelihood of

consequences arising from the interaction of floods, communities and the

environment.

runoff

The amount of rainfall which actually ends up as streamflow, also known as

rainfall excess.

stage

Equivalent to Awater level@. Both are measured with reference to a specified

datum.

stage hydrograph

A graph that shows how the water level at a particular location changes with time

during a flood. It must be referenced to a particular datum.

survey plan

A plan prepared by a registered surveyor.

water surface profile

A graph showing the flood stage at any given location along a watercourse at a

particular time.

wind fetch

The horizontal distance in the direction of wind over which wind waves are

generated.

LOWER BELLINGER AND KALANG RIVER FLOOD STUDY DRAFT … · Lower Bellinger and Kalang River Flood...

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