Broughton Creek Floodplain Risk Management Study and Plan

Committee Meeting – 12 April 2012

• Study Objectives • Study Area • Study Approach • Existing Flood Behaviour • Summary of Community Feedback • Flood Management Options • Forthcoming Activities

Overview

Study Objectives

Form a Floodplain Risk Management Committee

Data Collection

Flood Study

Floodplain Risk Management Study

Floodplain Risk Management Plan

Adoption and Implementation of the Plan

Monitor and R

eview

NSW Floodplain Management

Process

• Review the flood study.

• Update flood modelling to improve understanding of

flood behaviour.

• Consider the available flood management options.

• Compare the management options and identify preferred

options.

Study Objectives

Study Area

Berry

Broughton Village

Back Forest

Far Meadow Meroo

Meadow

Jaspers Brush

Bundewallah Broughton Vale

Bundewallah

Broughton Vale

Jaspers Brush

David Berry

Hospital

• Update flood modelling • Stakeholder consultation

– Council, SES, RMS (RTA), Utilities.

• Community consultation – Survey, information day, public exhibition

• Develop & assess management options • Identify preferred management options • Develop Floodplain Risk Management Plan

Study Approach

Existing Flood Behavior

Figure: 1% AEP Flood Event Extent

Major Flowpaths

• Major Waterways

– Broughton Mill Creek – Bundewallah Creek

• Flowpaths

– Town Creek – North St Overland Flowpath – Hitchcocks Lane Creek

Broughton Creek

• Passes through south east corner of model area • Primarily affects rural land • Affects access to David Berry Hospital

Major Flowpaths

• Major Waterways – Broughton Creek

– Bundewallah Creek

• Flowpaths

– Town Creek – North St Overland Flowpath – Hitchcocks Lane Creek

Broughton Mill Creek

• Runs past east side of Berry • Overbank flooding affects eastern Berry • A high hazard floodway • Affects access along Woodhill Mountain Rd and

the Princes Highway

Major Flowpaths

• Major Waterways – Broughton Creek – Broughton Mill Creek

• Flowpaths

– Town Creek – North St Overland Flowpath – Hitchcocks Lane Creek

Bundewallah Creek

• Runs north of Berry • Affects rural land and some properties near the

confluence with Broughton Mill Creek • Affects access along Woodhill Mountain Rd

Major Flowpaths

• Major Waterways – Broughton Creek – Broughton Mill Creek – Bundewallah Creek

• Flowpaths

– North St Overland Flowpath – Hitchcocks Lane Creek

Town Creek

• Flows through Berry • Responsible for the majority of flood damages in

the study area • Channel flows are high hazard, overbank flows

generally low hazard

Major Flowpaths

• Major Waterways – Broughton Creek – Broughton Mill Creek – Bundewallah Creek

• Flowpaths

– Town Creek

– Hitchcocks Lane Creek

North St Overland Flowpath • Affects properties along North St, Alexander St

and Albert St • Conveys relatively little water • A low hazard flowpath

Major Flowpaths

• Major Waterways – Broughton Creek – Broughton Mill Creek – Bundewallah Creek

• Flowpaths

– Town Creek – North Street Overland Flowpath

Hitchcocks Lane Creek • Affects access along the Princes Highway • A high hazard region, low velocity but depths up

to 1.6m through the floodway

• Options Development: – Results of flood modelling, – Community consultation outcomes, – Engineering judgement.

• Options Assessment: – Economic

• Cost of implementation vs. likely reduction in flood damages – Environmental

• Potential positive or negative impacts on the environment – Social

• Likely positive or negative social impacts.

Triple Bottom Line

Flood Management Options

• Three option categories – Structural options – Property Modification Options – Response Modification Options

• Different options will suit different regions of the study area

• Broadly speaking, the study area can be divided up into three broad regions – Berry Township – affected by Town Creek flooding – Berry Township – affected by Broughton Mill Creek flooding – Rural properties – affected by Shoalhaven River flooding

Flood Management Options

Structural Management Options

• Physical changes to alter the flood behaviour • Drainage upgrades • Channel improvements • Levees • Detention Basins

• Aimed at removing or reducing the flood risks / damages

• These options would be best suited to managing Town Creek flooding, where the

volume of flood waters is small enough to be effectively managed

Modelled Structural Options

Property Modification Options

• Changes to structures to make them more flood compatible • Planning controls • Flood proofing • House raising • Voluntary purchase • Stock mounds

• Aimed at making structures better able to cope with flooding, and thus reducing the

flood damage

Emergency Response Modification Options

• Changes to how emergency services, Council and residents respond to flood events • Preparation of a local flood plan • Flood warning systems • Public awareness campaigns • Flood warning signs

• Aimed at improving the response to flood events to reduce the risk to life and

property

• They would be suitable to be applied across the study area

The Princes Highway Upgrade • The RTA is proposing to upgrade the Princess Highway which incorporates a

by-pass around Berry

• At present, two options are being investigated – a northern option and a southern option

• The northern option has the opportunity to help alleviate flooding – Inclusion of storage north of the highway to reduce downstream flooding – The diversion of Town Creek – The use of excess cut to create stock mounds to provide flood safe regions for animals

• The southern options does not offer any flood alleviation opportunities

• As such, two Plans have been prepared, taking into account each scenario

Proposed FRM Plan – Summary

• Existing Conditions / Southern By-Pass • Implementation $2,729,000 • Recurrent $17,200

• Northern By-Pass • Implementation $482,200 • Recurrent $12,200

• Key differences in the Plans is that the northern by-pass allows

for the removal of the Town Creek detention and diversion options from the Plan.

• An effort has been made to have the first stages the same for both options, to allow time for the Princes Highway diversion option to be determined

Existing / Southern By-Pass Plan ID Description Priority

EM1 Information transfer to the

SES High

EM4 Public awareness and

education High

DC1 Data collection following

a flood event High

P2 Building and

Development Controls High

P1 LEP Update High

P8 Flood Proofing Guidelines High

FM

1.2

Town Creek Vegetation

Clearing High

ID Description Priority

EM2 Preparation of Local Flood

Plans and update of DISPLAN Medium

EM5 Flood warning signs Medium

FM

1.7 Town Creek Diversion Medium

FM

4.1 Stock Mounds Medium

EM3 Flood warning system Low

FM

1.6 North St Diversion Swale Low

Next Steps • Council Review of the draft FRM Study & Plan

• Public exhibition of the draft FRM Study & Plan, and gathering of community

comments

• Update of the FRM Study & Plan based on Council and community feedback

• Finalisation of the FRM Study & Plan

Questions?