Flood Management Advisory Committee Meeting

28 March 2019

 

 

Minutes of Meeting

Thursday 28th March 2019

Ashfield Administration Centre Meeting Room 1

Level 6, 260 Liverpool Rd Ashfield 

 

Meeting commenced at 3.05pm

 

 

ACKNOWLEDGEMENT OF COUNTRY BY CHAIRPERSON

 

Acknowledgement of Country by Clr Marghanita Da Cruz

 

I would like to acknowledge the Gadigal and Wangal peoples of the Eora nation who are the traditional custodians of this land. I would also like to pay respect to Aboriginal Elders, past and present, and acknowledge their young people who will be our future leaders.

 

COMMITTEE REPRESENTATIVES PRESENT

 

Voting Members

 

Inner West Council

Clr Marghanita Da Cruz   (Chair)

State Emergency Service

Alexander Bailey

State Emergency Service

Robert Baker

Community Representative

Lois Gray

Community Representative

Shad Wall

 

 

Non-voting Technical Advisory Members

Inner West Council

Wal Petschler

Inner West Council

Tony Giunta

Inner West Council

James Ogg

Inner West Council

David Birds

Inner West Council

Jai Read

NSW Office of Environment & Heritage

Sadeq Zaman

NSW State Emergency Service

Klaus Neuscheler

NSW State Emergency Service

Pilar Lorenzo

Sydney Water

David Grasby

NSW Roads and Maritime Services

Ashraf Awadalla

Burwood Council

Pablo Barreto

 

APOLOGIES

 

Inner West Council

Clr Lucille Mckenna OAM

Inner West Council

Clr Colin Hesse

Community Representative

Tim Harnett

Community Representative

Lindy Junkari

Inner West Council

Elizabeth Richardson

Inner West Council      

Joe Di Cesare

Inner West Council

Cathy Edward-Davis

Inner West Council

Jan Orton

Inner West Council

Harjeet Atwal

Inner West Council

Jean Brennan

NSW Office of Environment & Heritage

Greg Davis

NSW Department of Primary Industries

Carla Ganassin

NSW State Emergency Service

George Jeoffreys

NSW State Emergency Service

Daniel Walker

NSW Roads and Maritime Services

Mark Millington

NSW Roads and Maritime Services

Susannah Webb

City of Sydney

Peter Garland

City of Sydney

Shah Alam

TERMS OF REFERENCE

 

The Committee is advisory in nature and any recommendations are not binding on Council. The Committee currently has nine voting members of which five voting members were present, satisfying a quorum of 50% for the meeting.

 

DISCLOSURES OF INTERESTS:

 

Nil declared

 

CONFIRMATION OF MINUTES 

 

Minutes of the previous meeting held 14 December 2017 were accepted as correct.

 

Committee Recommendation:

 

THAT the minutes of the previous Flood Management Advisory Committee meeting be noted and accepted.

 

For Motion: Unanimous.

 

 

MATTERS ARISING

 

·           Committee was advised that Council had been unsuccessful in obtaining interagency cooperation from WestConnex and Metro projects to consider a gravity line drainage solution, proposed by Council, as part of their works to connect intersection of May/ Campbell streets St Peters directly to the Eastern Channel.

 

 

STAFF REPORTS

 

FMACC0319(1) Item 1          Presentation of the Draft Dobroyd Canal and Hawthorne Canal Flood Risk Management Study and Plan

RECOMMENDATION

 

THAT the Draft Hawthorne Canal and Dobroyd Canal Flood Risk Management Study and Plan dated March 2019 be endorsed for community engagement.

 

 

 The Committee was presented with an overview of the background and context behind the Dobroyd Canal and Hawthorne Canal Floodplain Risk Management Study and Plan. The Plan recommends projects within three broad areas - property modification, response modification and flood modification.

 

A total of fifty-six potential options were reduced to six  after a high level assessment that removed options that had no flood change, negative cost-benefit, or significant technical constraints. Options to proceed to Community Engagement include:

 

 i.       Underground detention basins at Pratten Park and Arthur Street Tennis Courts

 

The installation of detention basins would reduce depths by up to 0.15m between Pratten Park and the railway and remove property inundation above the floor level for 42 properties in the event of a 1% AEP event. Some challenges for this option include property ownership and short-term disruption to the playing field.

 

ii.       Grosvenor Crescent and Smith Street flowpath pipe upgrade and detention basin

 

Involves an upgrade to the existing pipeline beneath the rail embankment draining Grosvenor Crescent, and the installation of a dam wall within Darrell Jackson Gardens to create a detention basin within the park. This would result in a reduction of property inundation for four properties, as well as a reduction in some road inundation. Substantial reduction in ponding depths also achieved in Grosvenor Crescent in smaller scale storms.

 

iii.       Nowranie Street to Hawthorne Canal Pipe Upgrade

 

This option proposes a 1.2m diameter pipeline from Morris Street and extending to Smith Street, before discharging to Hawthorne Canal. This option has a relatively high benefit-cost ratio, and reduces flood depths for the extent of the upgrade by up to 0.5m, however only reduces dwelling inundation for three properties in the 2% AEP event.

 

iv.       Petersham Park Above Ground Detention Basin

 

This option can achieve reductions in flood depths between Petersham Park, Parramatta Road and Hawthorne Canal by up to 0.5m. The study identified that only three properties within the study area would however accounting for the properties within Leichhardt, the Benefit-Cost Ratio is likely to be significantly higher.

 

The Flood Risk Management Study will be amended prior to being put on public exhibition to include the benefit to properties north of Parramatta Road.

 

Existing Heritage concerns and protected Bandicoot species within this park was noted. This will be accommodated within the multi-criteria assessment and continued review of the mitigation program as it is rolled out.

 

v.       Sloane Street Pipe Upgrade

 

This option would reduce depths by approximately 0.3m and provide a reduction in property inundation for five properties.

 

vi.       Waratah Street to City West Link Hawthorne Canal Levee

 

This option was included within the draft report as it had high community interest, due to recurrent flooding from rising tides. This option however showed little impact on tidal heights and actually expanded the flood affected area and increased levels behind the levee by up to half a metre.

 

It is recommended that this option be removed from the plan given the high detrimental impacts, and included within the Appendix with the other discounted options.

 

The committee concurred with this assessment, however recommended that this option be discussed within a separate section of the report.

 

Questions & Discussions Regarding Report:

 

Issues raised by Committee Members included:

 

·         Potential to include potential WSUD options (eg – water harvesting or wetlands instead of detention basins, raingardens instead of pipe extensions).

 

It was noted that WSUD acts in a complimentary manner with Flood Mitigation. Effective WSUD infrastructure is best utilised in the smaller more frequent rain events. It is noted that the proposed options do not preclude the construction of future WSUD components, and there would likely be capacity to incorporate construction of select WSUD elements as part of the infrastructure upgrade.

 

·         Impact on the Flour Mill site.

 

The Flour Mills site had not commenced construction at the time that the model was reviewed. Therefore the model does not show impacts caused by this development. The approved development was required to comply with Council’s Flood Risk Development Controls including management and mitigation of flooding within the site. Existing flood behaviour around the site is generally maintained as modelled.

 

·         Potential for alternative options to account for the potential challenges/ constraints in design and construction.  

 

The exact alignment and construction techniques for each option would be confirmed as they progress to detailed design. The current options have been chosen to minimise the potential for conflict with site constraints.

 

·         Management of tidal flooding at Hawthorne Parade, in the vicinity of 254 and 292 Hawthorne Parade.

 

Flow valves were installed 18 months ago to prevent backflow from the canal; however the valve has not been performing to specification and Council is currently pursuing rectification.

 

·         Opportunities for funding contributions for shared or common assets.

 

Council would liaise with the relevant agencies (such as RMS, Sydney Water, OEH or adjacent Councils) to negotiate/ apply for potential funding contribution.

 

·         Defence Force land located off Hawthorne Canal and requirements for flood mitigation as part of its development approval and potential for use as a retention basin.

 

The site has been previously identified as a flood affected property. There is an existing consent to divide and develop the land with new dwellings within this flood affected area. The development consent required stormwater works were undertaken as part of the initial development, with further works still to be undertaken in O’Conner Street. In addition, the new properties would still be subject to some degree of flooding in the design event, and would be required to meet current development controls with regard to safe floor levels and provision of flow paths through the property.

 

·         Impact on flooding to Blackmore Oval or Canal Road.

 

This site is contained within the Leichhardt Flood Risk Management Study and Plan, previously adopted by Council in 2018. It was noted that Canal Road was a trapped low point created in the construction of City West Link in order to maintain sufficient headroom clearance beneath the rail embankment for truck entry and exit from Canal Road. This pipe frequently blocks and Council is reviewing the source of this blockage and any potential improvements.

 

·         Consideration given to congestion caused by cars as they leave a flooded area for higher ground.

 

Traffic congestion is generally considered a factor that must be considered in emergency management planning led by SES.

 

·         impact to apartments/basements below the flood level or other structures.

 

New developments have specific controls that require all accesses to basements to be raised above the design flood level before descending below ground. This typically ensures that the basement is isolated from the surface flood waters. Supplemented with site flood management plan.

 

COMMITTEE RECOMMENDATION:

 

THAT: The report be endorsed and Council progress to community engagement subject to the following:

-       The Cost-Benefit assessment of Petersham Park (Option 4) be amended to include reductions in flood damage north of Parramatta Road

-       That the proposed levee along Hawthorne Canal (Option 6) not be supported and discussed in an addendum to the report only.

-        

For Motion: Unanimous.

 

 

GENERAL BUSINESS

 

1.    Progress on investigations into upgrade / naturalisation of Whites Creek.

 

The committee has previously been advised on potential works within Whites Creeks to renew existing canal walls and the covered culvert. Whites Creek can be considered in terms of two separate sections

-       A covered channel between Parramatta Road and Booth Street

-       An open channel between Booth Street and Rozelle Bay

 

Sydney Water’s renewal schedules, based on condition assessment, do not necessarily require upgrade for flood conveyance. However it has been noted in the Leichhardt Flood Risk Management Plan that the surrounding stormwater network will continue to have poor flood performance if maintained at the existing capacity.

 

The most recent advice to Council from Sydney Water was that any works within Whites Creek were not scheduled for the near future. Council will continue discussions about potential upgrade designs which can support additional upgrade funding when it does come time to renew the relevant sections of the canal.

 

2.    State Emergency Services Changes

 

       SES advised that the existing Sydney West Region SES has been incorporated into metropolitan region. For flood responses in some instances the distance to travel has become further now, given the greater response area, so early warning time assists greatly in proper allocation of resources.

 

Increasing community awareness plays a significant part in flood response. Marrickville SES had practiced street meets at known flooding hotspots, discussing expectations with new volunteers, and further raising community awareness.

 

3.    Progress of remaining Flood Studies across Inner West Council.

 

Council had applied for and was successful in receiving grants from the Office of Environment and Heritage for the following projects;

-        Whites Creek and Johnsons Creek Flood Risk Management Study and Plan

-        Alexandra Canal Flood Risk Management Study and Plan

-        Marrickville South Flood Study

 

Council intends to commence these studies in the second half of 2019.

 

 

 

Meeting closed at 4:55pm.