Securing the Future of our Coastline Information Session Theme 2 - - PowerPoint PPT Presentation

Securing the Future of

• ur Coastline

Information Session Theme 2 Tuesday 25th June 2020

Welcome and Introduction

• Acknowledgement of Country
• Meeting protocols:
• Recording of meeting.
• Use of chat function to register questions.
• Please don’t use chat function to make comments.
• Will try to respond to questions after each presentation, or otherwise

via Q&A’s on website.

• Impact assessment – Reference Group involvement

Agenda

1. Welcome and introduction (Steve Dangerfield) 2. Context and purpose (Steve Dangerfield) 3. Presentations (James Guy, Murray Townsend, Andrew Short)

• Semaphore
• West Beach
• Securing the future of our coastline
• Interim management
• Climate change
• Impact assessment
• Examples from elsewhere

4. Next steps (Steve Dangerfield) 5. Wrap up and close (Cate Hart and Steve Dangerfield)

• 2. Context and Purpose

Reference Group Context and Purpose

Information Workshops

Workshop (3 sessions) Community issues, concerns, topics of interest Information Sessions Department Presentations Independent Expert

Securing the future

• f our Coastline

Reference Group

Terms of reference Pipeline design / external source Engagement/ Communications input

Individual Group Meetings Resident meetings One on one discussions

March – June 2020

Supported by Communication materials

Semaphore Working Group External sand working group?

• 3. Presentations

Theme 2

Presenters

Dr Murray Townsend Manager Coast and Marine, DEW. James Guy Project Manager Securing the Future of Our Coastline, DEW Professor Andrew Short, OAM School of Geosciences, University of Sydney

Introduction

• A quick recap of last week’s topics.
• This week:
• Murray
• Semaphore Park, Semaphore breakwater, Semaphore South
• James
• West Beach, DHI Study, Securing the future of our coastline, interim management,

climate change, impact assessment.

• Andy
• Examples from elsewhere and other observations.

• Geographical setting and

physical processes.

• Development and early

coastal management.

• Major studies from the Culver

Report in 1970 to Adelaide’s Living Beaches Technical Report in 2005.

• 9 May 2016 storm.

Last Session

Semaphore

• Dr Murray Townsend, Manager Coast and Marine Branch, DEW

• Erosion hotspot.
• 1982 onwards, dune buffer

maintained by sand carting from Semaphore.

• By late 1990s, extraction rate

exceeded accretion rate at source beach.

• 1997 review recommended

construction of a groyne at Bower Road.

• Subsequent work recommended

an offshore breakwater

Semaphore Park

The Trial Breakwater

• Designed by WRL (University
• f NSW) based on coastal

processes modelling.

• 200m long, 200m offshore
• 1st tube laid in early 2004
• last tube placed Feb 2005
• salient pre-filled with

120,000m3 sand

Location was selected to balance:

• change point

from erosion to accretion

• protection of

Semaphore Park

• distances for

moving sand (to Sem. Park and from Semaphore)

ORIGINAL SHOREWARD EDGE

• Design life of temporary

structure = 5 to 8 years.

• Failure of tubes and resulting

sand volume losses.

• After 18 months, most top

tubes had rolled off.

• Original crest = +1.0m AHD
• Crest Nov ’06 = - 0.9m AHD

The Trial Breakwater

Predicted (Modelled) versus Actual

Parameter Design Prediction (GENESIS) Actual Survey Data (2008) Salient accretion rate 40,000m3 per year (for crest level = 1.0m AHD) 45,000m3 per year (when crest was 1.0m AHD) Salient width 100m (assumed no prefilling of salient) 130 – 142m (salient was prefilled) Extent of updrift effects 475 – 525m 500m Extent of downdrift effects 675 – 800m 1,000m Maximum downdrift recession 40 – 80m 60m

The Permanent Breakwater

Design by Aurecon Pty Ltd

Permanent breakwater

The accumulation

• f sand in the

updrift area has re- established dune buffers and protected Semaphore Park.

Permanent breakwater

Significant downdrift erosion during May 2016 storm.

Semaphore South dune restoration

• 30,000m3 of

sand from north

• f Largs Bay

Jetty

• Restoring

historic profile.

• Planting to start

soon.

Designed to recreate natural dune system at the same location.

• Detailed flora

survey March 2020.

• Also informed

planting design.

• Detailed survey monitoring.
• Before and after DEMs.
• Dunes, beach, offshore areas.

West Beach

• James Guy, Project Manager Securing the Future of Our

Coastline, DEW

River Torrens outlet WBSLSC Seawall West Beach Parks West Beach harbour

West Beach

West Beach

• A quick photographic tour from south to north.

1950

1956

1960

1975

1975

1978

1981

1985

1988

1990

1967

1972

1991

1992

2002

2009

9 May 2016

10 May 2016

Late 1930s?

1968

1975

2009

2014

2014

2020

West Beach

• Coastal Processes and Management

Sediment transport rates along the Adelaide coast (WRL 2003). Uncertainty around modelling results at West Beach.

ALB Strategy (2005) divided metro coast into Management Cells based on interruptions to littoral transport. Cell 3 = West Beach (from West Beach Harbour to Torrens Outlet

• First four years:
• Backpass 25,000m3/year from Torrens outlet to Brighton
• Forward pass 25,000m3/year from Torrens outlet to Henley Beach South
• Backpass 40,000m3/year from Torrens outlet to West Beach Parks.
• Then (each year thereafter):
• Use new northern pipeline to backpass 50,000m3 from Semaphore

breakwater to Henley Beach South

• Use new West Beach pipeline to backpass 40,000m3 from Torrens outlet to

West Beach Parks

• Consider offshore breakwater north of WBSLSC if necessary to manage

erosion.

• Consider offshore breakwater south of WBSLSC if necessary to further

stabilise West Beach Parks dunes.

ALB Strategy (2005) - West Beach

ALB - the first four years at West Beach

Year Backpass Torrens to Brighton (m3) Backpass Torrens to West Beach Parks (m3) Forward pass Torrens to Henley Beach South (m3) 2005-06 25,000 23,000 40,000 20,000 25,000 25,000 2006-07 25,000 40,000 30,000 25,000 25,000 2007-08 25,000 40,000 25,000 40,000 2008-09 25,000 40,000 127,000 25,000 41,000 Totals 100,000 23,000 160,000 177,000 100,000 131,000

No northern pipeline. West Beach (Cell 3):

• Forward pass 25,000m3/year from Torrens outlet to

Henley Beach South

• Backpass 75,000m3/year from Torrens outlet to West

Beach Parks.

• Consider offshore breakwaters if necessary to control

erosion north and south of WBSLC seawall

Revised ALB adopted 2009

The “Yellow Line”

Figure 6.3 from the ALB Technical Report (2005). Intention was to re-introduce sand that was impounded at the Torrens outlet into the active beach system. Yellow line “indicates the extent

• f the dunes that may be

progressively eroded by subsequent storms”. 200019 200071

Yellow line marker post at beach access path, Henley Sailing Club (June 2020)

Erosion at the northern end of West Beach SLSC seawall (Rockingham Dunes)

By 2017:

• Failed seawall in front of WBSLSC.
• Ongoing retreat Adelaide Shores dunes.
• Erosion immediately north of WBSLSC.
• Shoreline realignment? (Torrens to WBSLSC).
• Harbour management (seagrass wrack).
• Uncertainty around littoral drift rates.
• Was the West Beach Parks sand being lost offshore?

Which led to the West Beach Coastal Processes Modelling Study. Commissioned in May 2017 Final Report August 2018.

Questions (John Dundon, Save West Beach Sand)

• You did not state the dune halved by the yellow line at West

Beach was an ALB sand source. Why?

• If ALB needed the supporting sand-piping system installed

along the entire coast why did Govt continue to mine cell 3 regardless of the visually clear loss of our beach and dunes.

• Why was science in the form of the survey data volumes

unexamined/not interrogated to aid West Beach?

• How was West Beach allowed to get so degraded and out of

equilibrium by the CPB in stark contrast to every other metro beach flourishing during ALB?

• If the 3rd sand pipeline (the unspoken but installed pipeline)

from Glenelg to Glenelg North was a failure, why was sand not carted from Glenelg to Glenelg North to nourish Glenelg North/West Beach?

• Then if West Beach was totally cut-off from nourishment why

did we continue with the sandmining unabated when the dune and beach loss was so evident?

• Why did cell3 nourish every other northern cell from say, 2000

to 2016 without any nourishment/replenishment into West Beach?

John Dundon Statement:

• Praising ALB and by default CPB/governance is clearly wrong

when referring directly to the decimation of West Beach and the quantifiable loss of 750,000m3 of sand (beach and dunes) from

• ur community.

One last question:

• Are we now spending $48.4 mill to fix ALB cell 3 discrimination?

West Beach Coastal Processes Modelling (The DHI Study)

• James Guy, Project Manager Securing the Future of Our

Coastline, DEW

West Beach Study (2017 – 2018)

Funded by:

• DEW
• Coast Protection Board
• City of Charles Sturt
• Adelaide Shores

Study Objectives

• Establish and validate a coastal sediment transport model of

West Beach.

• Using the model, evaluate alternative coastal management

scenarios.

• Assess possible design modifications to the Adelaide Shores

boat harbor breakwater to minimise sand and seagrass wrack ingress and wave penetration

DHI (Danish Hydraulics Institute)

• Independent, private and not-for-profit organisation.
• 80% of 1,200 employees hold an MSc or a PhD degree.
• Knowledge represents 50 years of dedicated research.
• 21% of resources are allocated to R&D to enhance knowledge

and innovation.

DHI Study – Sediment Transport

Used sophisticated computer modelling to calculate sediment transport rates. Also used DEW survey data to calculate sediment transport rates. Conclusion:

• The littoral transport rate at West Beach is between 50,000

and 150,000m3 per year, with an average rate of around 100,000m3 per year.

DHI Study – Sediment Volumes

DHI analysed historic survey data to determine total sand volumes within the West Beach cell. Conclusions:

• The West Beach sediment cell has lost in the order of

500,000m3 of sand since the late 1990s and the rate of decline has accelerated since approximately 2011.

• No significant volumes of sand are being lost from West

Beach to off-shore areas. Significant volumes are being transported and accumulating in the northern sediment cells.

What Options were Considered?

Hard Engineering Structures?

• Offshore breakwaters and “headland control” structures were

considered, together with “hybrid” combinations of hard engineering structures and replenishment.

• Not supported due to:
• Significant cost
• Do not resolve underlying sediment deficit problem
• Require initial and ongoing sand nourishment
• Complexity of assessing impacts, potential for downdrift erosion.
• Public safety and amenity issues.

Geotextile groynes or submerged

• ffshore

breakwaters?

One of the existing Somerton groynes

Geotextile groynes or submerged breakwaters

• Provide limited protection unless of sufficiently large size to

break waves or interrupt sand movement during storm events (i.e. at very high water levels).

• Unless the structure causes waves to break during storm events,

it can cause increased erosion due to wave refraction and focussing of energy.

• Can create rip currents during stormy conditions, which increase

rate of sediment transport.

• Durability issues.
• Not used successfully anywhere else.

Modelled Management Options

“The most feasible, sustainable and cost effective management

• ption identified for West Beach was one that incorporated some

variation on a large scale nourishment option, to restore the littoral volume in the West Beach cell and provide a large source

• f sediment to meet the downdrift transport capacity of the

Henley Beach cell into the future.”

Pg 22 West Beach Coastal Processes Modelling (DHI, 2018)

Advantages of Large Scale Nourishment

• Cost efficiencies in sourcing large nourishment volumes.
• Ongoing supply to downdrift beaches
• Shoreline response can be more reliably predicted.
• Nourishment can be constantly adjusted based on shoreline

response.

• Public safety and amenity risks are reduced.

Modelled Management Options

Scenarios: 1 – Do nothing. 2 – Mass renourishment (“sand engine”) 3 – Interim management. 4 – Backpassing from northern beaches.

Modelled Management Options

2 – Mass renourishment approx. every 10 years (1.8 million m3)

• 500,000m3 added to full length of West Beach cell
• plus 1,000,000m3 added to West Beach (south of Torrens outlet)
• 300,000m3 added to Henley Beach south
• Backpassing using pipeline from Torrens outlet to West Beach

Parks after 5+ years.

Modelled Management Options

3 – Interim management.

• Small scale initial nourishment around Torrens outlet (100,000m3).
• New seawall from WBSLSC to West Beach Harbour (along West

Beach Parks dunes).

• Backpassing 30,000m3 prior to each summer to create a beach in

front of seawall.

Modelled Management Options

4 – Backpassing from northern beaches:

• First 4 years 150,000m3/year to West Beach; 20,000m3/year to

Henley Beach South

• Then 100,000m3/year to West Beach and nothing to Henley Beach

South

1 – do nothing 2 – mass renourishment, 1.8 million m3 3 – Interim management, seawall and minor replenishment 4 – ongoing backpassing from northern areas

Modelling results

Adopted Strategy

Hybrid of mass nourishment and backpassing options:

• Mass nourishment of West Beach with 500,000m3 of sand from
• utside the metropolitan beach system.
• Backpass sand from northern beaches to West Beach to match

alongshore sand transport rate using sand pumping system (approx. 115,000m3/year).

• Stabilise and revegetate dunes.
• Interim replenishment of West Beach with 115,000m3/year for

two years during planning and delivery.

Rationale for Adopted Strategy

• Availability of (and to maximise efficiency of using) external sand:

500,000m3 vs 1.8 million m3.

• Minimises impacts on northern beaches through use of external sand

(compared with mass replenishment from northern beaches)

• Successful operation of the pumping system from Glenelg to

Kingston Park.

• Flexibility: to deal with seasonal and long term variability of coastal

processes.

• Adaptability: to deal with rising sea levels and a changing climate.

Impact Assessment

Interim replenishment (2019-20 and 2020-21) from northern beaches.

• DEW assessed likely impacts associated with moving sand from

the northern beaches to include maximum dune recession of approximately 4.0m to 6.0m.

• Dune vegetation assessment by DEW found no high value

native vegetation at risk (since confirmed by March 2020 independent assessment).

Impact Assessment

Longer term impacts following completion of the pipeline.

• Movement of sand back to West Beach from areas of

accumulation will be based on monitoring.

• Amount of sand to be moved back to West Beach = Amount of

sand leaving West Beach.

• No net impact on volumes of sand in the northern beaches.

Cell 3 (West Beach) Cell 6 (Semaphore, Largs, Taperoo).

Volume changes 1994 to 2016

Independent Expert Comments

Professor Andrew Short OAM School of Geosciences, University of Sydney

Why manage?

• Adelaide sand movement is part of a natural system extending

from Seacliff to North Haven & operating for the past 7,000 years

• It is a natural system that is slowly running out of sand
• Since 1800s it has also been hindered in part by human

impacts

• Unless it is managed the southern beaches & dunes will erode
• Property and infrastructure will be at risk
• Public beach amenity will deteriorate

Some other similar issues and solutions

• Mackay Harbour, Qld:

northward transport of sand is stopped by the harbor walls. Sand is pumped from south side to northside of harbor

Presented by independent coastal expert, Professor Andrew Short, 25 June 2020

Some other similar issues and solutions

• Collaroy Beach, Sydney: sand

is dredged and trucked from the northern tidal inlet. Pumping has been proposed as a better solution but not initiated as yet.

Some other similar issues and solutions

• Port Geographe, WA:

northward transport of sand & seagrass stopped by entrance wall. Sand is pumped from south side to northern side. Seagrass debris removed by equipment.

Some other similar issues and solutions

• Port Bouvard, WA: When

entrance walls were built a hook groyne and pumping system was incorporated and now regularly pumps sand under the entrance from south to north

Some other similar issues and solutions

• Gold Coast: most heavily

managed and best managed beaches in the world. Includes: major sand pumping

• perations under Tweed River

since 2000 and Seaway since 1986 (~500,000 m3/yr)

Some other similar issues and solutions

• An offshore reef was

constructed at Surfers Paradise in 1999 to trap sand but has been ineffective

• Surfers Paradise Beach:

Sand backpassing (recycling) is proposed from Seaway back to Surfers Paradise beach, to begin in 2020. Permanent buried pipeline with several

• utlets onto beach

Some other similar issues and solutions

• Surfers Paradise Beach:

Sand backpassing pipeline

• 8 km long
• Buried
• Permanent
• several outlets onto beach

Use of Structures

• Global trend is to use nourishment and replenishment instead of

hard engineering structures like seawalls, groynes, breakwaters. e.g. USA, Holland.

• Replenishment is a more flexible and adaptive solution &

maintains the natural beach-dune environment.

• Any structures must be combined with replenishment to prefill

and manage downdrift impacts.

• Submerged geotextile offshore structures:
• Risk increasing erosion (refraction, rip currents, public hazard)
• Don’t know of successful examples
• e.g. Narrowneck on Gold Coast

Adelaide Beaches

• Not enough sand to maintain beaches between West Beach &

Semaphore

• Excess sand continues to accumulate at Semaphore breakwater

and Largs Bay

• Sand recycling is required to maintain both northern beaches

and southern in their natural state, affording amenity, dunes and protection

• If not managed Semaphore-North Haven beaches & dunes will

continue to widen, while beaches to south erode back to seawalls

• In both cases public amenity is impacted, too little or too much

sand

Questions (for Andy Short):

John Dundon: What is your expert opinion upon the volume loss of 750,000m3 of dune and sand from 1997 to 2016 which effectively continued unabated? Warwick Norman: What are some policies which would minimise the damage to source beaches caused by the extraction of sand?

Questions (Murray and James)

Craig Wilkins: Has there been any modelling/is there any sense of what the potential impact will be of the proposed new artificial reef off Glenelg? Nick Crouch: Has any work been done to calculate the sand erosion benefit of restoring the seagrass beds? First session: How has climate change been considered?

Questions (Murray and James)

Warwick Norman:

• What is DEW’s assessment of the impacts of the “Securing the Future
• f our Coastline” strategy on beaches at Semaphore Park, Semaphore

South, Semaphore, Largs Bay, Largs North, Taperoo and Osborne?

• What is the suitability for dune replenishment of sand from land in

the area west of Tapleys Hill Road West Beach, which is administered by the West Beach Trust and Adelaide Airport?

• What impact will the development of a parallel runway at Adelaide

Airport have on the amenity of West Beach Parks and the associated beach area? (https://www.adelaideairport.com.au/corporate/community/adelaide- airport-master-plan )

Questions (Murray and James)

Warwick Norman (cont.)

• Is it still the view of DEW that "the value of recently created

dunes (e.g. at the Torrens Outlet and Semaphore) is primarily for protection, beach amenity and a reservoir of sand rather than to provide a habitat for flora and fauna" and that the "the majority

• f dune colonising vegetation on Adelaide's coast is non-

indigenous or cosmopolitan of low ecological significance, and

• ften weed-infested"?

Questions (Murray and James)

Jill Kennare:

• James highlighted the use of “Cells” in the strategies used by DEW. Cells

are defined by interruptions to the littoral drift. The graphic below was presented showing Cells 1-4. The northern beaches do have cells as there are interruptions at North Haven and outer Harbour, but they are not included in the Adelaide beach management system.

• What is evident here is that DEW and the CPB do not consider the

northern beaches as anything other than a sand source. This has been raised with DEW previously and the graphic was withdrawn from the

• website. However, it reappeared at the meeting and was praised by

Professor Andrew Short as he said the 4 Cells were being managed very

• well. It is highly offensive and angers our community to be only considered

in this way as we are being treated as second class.

Questions (Murray and James)

Jill Kennare (cont.): Keeping in mind that Semaphore/Largs Bay is the nearest beach for about a third of Adelaide’s population, how does DEW see this area in relation to its management of Adelaide beaches plan?

• Is it simply a sand source as has been evidenced in previous department

documentation?

• Or is it more highly valued?? Surveys we took last year indicated that the

majority of people using the beach and foreshore are not local. Barossa, Salisbury, Modbury, Mawson Lakes, etc. Virtually anyone north of Bower and Grand Junction Rds uses this area. Secondly, how is DEW going to achieve meaningful consultation of the community? Will community meetings be held prior to the pipeline being built?

Questions

Have also received:

• Tony Bazeley (PAREPG): 5 pages of questions
• Catherine Fitzgerald (via Jill Kennare): 11 questions

• 4. Next Steps

Impact Assessment

DEW acknowledges the strong theme emerging from the April 2020 information sessions that an independent assessment of impacts on the northern beaches is desired.

• DEW propose to commission an independent review of the

impacts.

• Propose to involve nominated members of CRG in the process

through a smaller working group.

• Will include shorter term impacts (interim sand movement) and

longer term impacts (post pipeline implementation).

Next Steps

• Independent impact assessment, nomination of smaller working

group.

• Formation of the Community Reference Group (July 2020)
• Focus of the CRG will be on delivery of the Securing the Future of

Our Coasts project.

• 5. Wrap up and Close

Conclusion

Cate Hart Executive Director Environment Heritage and Sustainability, DEW Chair of the Project Steering Group.

Close

• Steve Dangerfield