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GC/NE/7421 

10.1 South Creek Floodplain Risk Management Plan 

Purpose 

REPORT 

To seek Council adoption of the final version of the South Creek Floodplain Risk Management Plan 

(R2411v3) dated 14 March 2008. 

Report 

The South Creek Flood Study, Floodplain Risk Management Study and Floodplain Risk 

Management Plan were adopted by Council on 22 April 2008 (report to Council attached). They 

form part of the formal process for defining flood affected land and flood management measures as 

detailed in the NSW Flood Policy. They include a detailed technical investigation of flood 

behaviour; provide information for Council and residents about the extent of flooding; and outline 

specific management actions for managing flood risk. The reports were undertaken in partnership 

with NSW Department of Environment and Climate Change (DECC). 

Due to an electronic administrative error, Report R2411v2 dated 10 February 2008 was adopted at 

the 22 April 2008 Council meeting instead of the correct final version, Report R2411v3 dated 

14 March 2008 (provided as an attachment booklet with the business papers). The differences 

between the two versions were minor. The correct final version included small text changes 

requested by DECC in order to clarify some points and improve readability. There were no 

changes to flood maps or management options in the correct final version and therefore there is no 

change to the flood impact on residents from the adoption of this version of the report. Accordingly, 

there is no requirement to modify the notations that have already been placed on s.149 certificates, 

following the resolution of Council at the meeting of 

22 April 2008. 

The other two reports, South Creek Flood Study and South Creek Floodplain Risk Management 

Study adopted at the 22 April 2008 Council meeting are the correct final versions and do not 

require any further consideration by Council. 

Financial Impact 

Nil 

Policy Impact 

Nil 

Manager Natural Environment 

RECOMMENDATION OF DIRECTOR COMMUNITY AND ENVIRONMENTAL SERVICES 

That Council note the report and adopt the final version of the South Creek Floodplain Risk 

Management Plan (R2411v3) dated 14 March 2008. 

ITEM 10.1 Page 53 

Report of Warringah Council Meeting on 22 July 2008

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Report of Warringah Council Meeting on 22 April 2008 Item 10.1 

ATTACHMENT 1 

10.1 Adoption of South Creek Flood Investigation Reports 

Purpose 

EXECUTIVE SUMMARY 

To seek Council adoption of the South Creek Flood Study, Floodplain Risk Management Study, 

and Floodplain Risk Management Plan. 

Summary 

The South Creek Flood Study, Floodplain Risk Management Study and Floodplain Risk 

Management Plan form part of the formal process for defining flood affected land and flood 

management measures as detailed in the NSW Flood Policy. They include a detailed technical 

investigation of flood behaviour; providing information for Council and residents about the extent of 

flooding and specific management actions. 

These reports have been undertaken in partnership with NSW Department of Environment and 

Climate Change and are now complete. 

The South Creek Flood Study has been previously adopted by Council in December 2004. As 

Council progressed with the next stage, it was identified that a sub-catchment had been 

overlooked in the Flood Study model. The consultant amended the model and report and it is now 

being presented to Council for adoption with the other flood reports as a revised South Creek 

Flood Study. This contributed to delays in the process which are explained further in Section 1 of 

the report and resulted in an additional 21 properties being identified on 149 certificates as flood 

affected. 

All updates made in the amended South Creek Flood Study were incorporated in the next two 

stages; South Creek Floodplain Risk Management Study and Floodplain Risk Management Plan. 


The actions identified in the Floodplain Risk management Plan amount to approximately 

$4.7 million. Any actions arising from the Management Plan are eligible for funding under the State 

Government’s Flood Risk Management Program on a 2:1 basis, and Council’s Environment and 

Stormwater Special Rate program. Any future actions will be budgeted in accordance with 

Council’s budgetary and project prioritisation processes 

Policy Impact 

The adoption of these reports will allow better consistency in the application of development and 

assessment policies and will also provide for an holistic approach to the management of both 

floodplain and catchment management in Warringah. 

RECOMMENDATION OF DIRECTOR COMMUNITY AND ENVIRONMENTAL SERVICES 

A. That Council adopt the South Creek Flood Study, Floodplain Risk Management Study, and 

Floodplain Risk Management Plan. 

B. That the flood affected properties as shown in the South Creek Floodplain Risk Management 

Plan be appropriately reflected on Section 149 Planning Certificates. 



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ATTACHMENT 1 

REPORT 

Background 

The South Creek Flood Study, Floodplain Risk Management Study, and Floodplain Risk 

Management Plan were initiated as part of the NSW Government Flood Policy. 

The reports were prepared by consultants Webb McKeown and Associates, and Cardno Lawson 

and Treloar for Warringah Council. Funding for the reports was provided from the NSW 

Government’s Flood Risk Management Program and Warringah Council’s Environment and 

Stormwater Special Rate on a 2:1 basis. 

1 NSW State Government’s Flood Policy 

Under the NSW State Government’s Flood 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 NSW Government’s Flood Policy provides for: 

• a framework to ensure the sustainable use of floodplain environments, 

• solutions to flooding problems; and 

• a means of ensuring new development is compatible with the flood hazard. 

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

stages: 

NSW Government Flood Policy Recommended 

steps 

Council has complied with the Policy as follows: 

• Formation of a committee This committee already exists as the Narrabeen 

Lagoon Joint Estuary/Floodplain Management 

Committee. The committee was consulted 

throughout the development of the floodplain 

documents. 

• Flood Study: determines the nature and 

extent of the flood problem. 

• Floodplain Risk Management Study: 

evaluates management options for the 

floodplain in respect of both existing and 

proposed development. 

• Floodplain Risk Management Plan: 

involves formal adoption by Council of a 

plan of management for the floodplain. 

• Implementation of the Plan: construction 

of flood mitigation works to protect existing 

development, and the use of Local 

Environmental Plans to ensure that new 

The revised South Creek Flood Study was 

provided to Council by consultants Webb, 

McKeown and Associates Pty Limited in May 

2006. 

The South Creek Floodplain Risk management 

Study was provided to Council by consultants 

Cardno Lawson Treloar on 4 February 2008. 

The South Creek Floodplain Risk Management 

Study was provided to Council by consultants 

Cardno Lawson Treloar on 14 March 2008. 

This report to Council provides the opportunity 

for Council to adopt the Flood Study, Floodplain 

Risk Management Study and the Floodplain 

Risk Management Plan. The actions 



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ATTACHMENT 1 

development is compatible with the flood 

hazard. 

recommended from the Floodplain Risk 

Management Plan can then be prioritized for 

implementation and funding when considered 

against Council’s other priorities for holistic 

catchment management. 

There have been a number of delays in reaching the current stage. Following is a brief explanation 

for Council’s information: 

2005 South Creek Flood Study completed and adopted by Council (Webb McKeown and 

Associates) 

South Creek Floodplain Risk Management Study and Plan commissioned (Cardno 

Lawson and Treloar) 

2006 On reviewing the South Creek Flood Study, Cardno Lawson and Treloar identified that 

a subcatchment had accidentally been overlooked in the flood model. Webb McKeown 

and Associates were asked to revise the model and mapping of the South Creek Flood 

Study while the South Creek Floodplain Risk Management Study and Plan was put on 

hold. 

Revised Flood Study completed by Webb McKeown and Associates 

Cardno Lawson and Treloar continued with the South Creek Floodplain Risk 

Management Study and Plan. Additional ground surveys were done and basic 

upgrades to the model were undertaken in order to be able to better assess flood 

modification options. 

These updates to the model resulted in an additional 21 properties being inside the 

100yr flood extent. 

Additionally during 2006, operational resourcing decisions focussed priorities 

elsewhere which resulted in further delay. 

2007 June - Community consultation of flood modification options were undertaken by letter 

box drop with questionnaire and flood map sent to all people in the 100yr ARI and PMF 

with an additional buffer (including all additional 21 properties). All comments provided 

were considered in completing the preliminary draft reports. 

August - Preliminary draft reports were distributed to the committee for comment. All 

comments provided were considered in completing the exhibition draft reports. 

November - Public Exhibition of draft reports. A personally addressed letter and flood 

map was posted to all residents and owners in the 100yr ARI, PMF and an additional 

buffer. All comments provided were considered in completing the final reports. 

There have been no unnecessary delays in 2008 and Council is now in a position to consider the 

documentation, report and recommendations. 

2 South Creek Catchment description 

The South Creek catchment includes the Wheeler Creek subcatchment and drains to Narrabeen 

Lagoon through Beacon Hill, Narraweena and Cromer. The catchment is bounded by Narrabeen 

Lagoon to the north, Cromer industrial area to the east, Warringah Road to the South and Oxford 

Falls to the west. The catchment covers a total area of 7.3km² and is shown in Figure 1. 

In the past, flooding within the South Creek catchment has caused property damage and posed a 

hazard to the residents living near the watercourses. Over past decades, South Creek has 



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ATTACHMENT 1 

experienced significant flood events including those in March 2003, April 1998 and November 

1984. 

Figure 1 South Creek Catchment 

3 Flood affected properties 

The flood levels and extents from the reports indicate that a number of properties within the 

floodplain are susceptible to above-floor flooding, even in events such as the 5 year ARI (annual 

recurrence interval) flood. Details can be seen in Table 1. 

Flood Event 

Number of Flood 

Affected Properties 

Number of buildings with 

over-floor flooding 

5 year Annual Recurrence 

Interval (ARI) 

65 14 

10 year ARI 80 18 

50 year ARI 111 32 

100 year ARI 128 42 



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ATTACHMENT 1 

Probable Maximum Flood 275 185 

Table 1 Properties currently affected by flooding 

As a result of South Creek flood investigations, 128 properties have been identified in the 100 year 

ARI flood. These properties have had flood notations placed on their Sections 149 Planning 

Certificates. These properties will be subject to flood planning controls as per the Warringah LEP 

should they wish to redevelop in the future. 

4 South Creek Flood Study 

The South Creek Flood Study has been previously adopted by Council in December 2004. As 

Council progressed with the next stage, it was identified that a sub-catchment had been 

overlooked in the Flood Study model. The consultant amended the model and report and it is now 

being presented to Council for adoption with the other flood reports as a revised South Creek 

Flood Study. 

All updates made in the amended South Creek Flood Study were incorporated in the next two 

stages; South Creek Floodplain Risk Management Study and Floodplain Risk Management Plan. 

5 South Creek Bank Management Plan 

In addition to flooding, South Creek also suffers from problems such as weed infestation, erosion 

and sedimentation. As part of the South Creek Floodplain Risk Management Study, a Bank 

Management Plan has been included as an Appendix to assist staff in identifying problem areas 

and appropriate remediation measures. 

Consultation 

The Flood Study was originally adopted by Council in December 2004. Community consultation 

was undertaken through the Narrabeen Lagoon Joint Estuary/Floodplain Management Committee 

together with a variety of methods such as flyers, questionnaires, advertisements, one month 

library and civic centre exhibitions and a website exhibition. 

When the Flood Study was updated, the entire document was not re-exhibited. The updated maps 

however were exhibited as part of the community consultation process for the Floodplain Risk 

Management Study and Plan, although no comments were received by Council. 

Throughout the development of Floodplain Risk Management Study and Plan, the Narrabeen 

Lagoon Joint Estuary/Floodplain Management Committee has continued to assist Council by 

providing valuable input, bringing together views from key Council staff, NSW government 

agencies and the views of the community. 

Other consultation included for these reports included: 

• Questionnaires distributed throughout the floodplain to gather information on past flood 

events and preferred management actions (followed up by phone calls where appropriate), 

• One month public exhibition period and community workshop, 

• Letters being sent to 850 home occupiers and residents within (and adjacent to) the Probable 

Maximum Flood Extent (PMF) inviting them to comment on the reports, 

• Posting of the draft reports on Council’s web site, 

• Displays in the Customer Service foyer of the Civic Centre, and all Council libraries; 

• An advertisement in the Council Notices section of “The Manly Daily”; and 



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ATTACHMENT 1 

• Internal consultation with Manager Strategic Planning and Team Leader Development 

Engineering based in Planning and Development Services. 

Approximately 35 submissions were received during the public exhibition. Comments from the 

committee, public exhibition and feedback forms highlighted the following focus areas. This 

feedback resulted in appropriate changes being made to the reports and additional actions being 

included in the final Plan: 

• Culvert maintenance – Option FM12 was expanded to include a Culvert Maintenance 

Strategy as well as increased recommended culvert maintenance budget. 

• Flooding in Ara Cres area – Option FM13 was included in the final list of preferred options; 

Willandra Road (Lower) Culvert enhancement 

• Weeds choking the creek and build-up of sediment– Option BM2 was included; Weed and 

Sediment Management in Wheeler and South Creeks 

• Childcare Centre at Toronto Ave – Option EM4 included; Targeted Flood Education 

Programs 

• Debris control structures to protect culverts from blockage – Option included: FM20 Detailed 

Assessment for Potential Debris Control Structures and FM21 Debris Control Structure on 

Wheeler Creek. 

Unfortunately some suggestions were not able to be incorporated into the final documents due to 

reasons such as flood benefit, cost benefit, conflicting community support, appropriate location and 

scope of the study. These include: 

• Additional levee banks, 

• Creation of a lake in the lower reaches of Cromer, 

• Raising of bridges; and 

• Construction of pedestrian overpass at proposed wetland. 

Timing 

It is proposed once the South Creek Flood Study, Floodplain Risk Management Study, and 

Floodplain Risk Management Plan are adopted by Council, the recommended actions in the Plan 

will be implemented. 

Policy Impact 

The adoption of these reports will allow better consistency in the application of development and 

assessment policies and will also provide for an holistic approach to the management of both 

floodplain and catchment management in Warringah. 


The actions identified in the Floodplain Risk management Plan amount to approximately $4.7 

million. Any actions arising from the Management Plan are eligible for funding under the State 

Government’s Flood Risk Management Program on a 2:1 basis, and Council’s Environment and 

Stormwater Special Rate program. Any future actions will be budgeted in accordance with 

Council’s budgetary and project prioritisation processes. 

Manager Natural Environment

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