Flood Risk Management ~ a potential policy for the future

Issue: The draft does not distinguish between riverine floodplains and coastal floodplain systems (coastal wetlands, estuarine backswamps, groundwater‑affected lowlands). Coastal wetlands function as critical flood storage and water‑quality infrastructure, and development impacts are typically irreversible.

Change requested: Insert an explicit policy distinction recognising coastal floodplain wetlands, estuarine backswamps and coastal lowlands as critical natural infrastructure that must be managed primarily for avoidance, protection and resilience, rather than as developable “resource” land.

Suggested insertion (Section 1 – Purpose):

“Council recognises that coastal floodplains, estuarine backswamps and coastal wetlands function differently to riverine floodplains. These lands provide critical flood storage, water quality, ecological and climate‑adaptation functions and are to be managed primarily for risk avoidance, protection and resilience, rather than development potential.”

Issue: Clause 1.1(b) states flood‑prone land is a “valuable resource” that should not be “sterilised.” This legacy statement is not appropriate for coastal floodplains and wetlands, where filling/drainage causes permanent loss of flood storage, acid sulfate soil risk, degraded coastal water quality, and long‑term public costs.

Change requested: Replace 1.1(b) with a risk‑aligned objective that excludes coastal wetlands/high‑hazard areas from intensification.

Suggested replacement (1.1(b)):

“Recognise that while some flood‑prone land may support compatible uses, land that performs critical flood storage, coastal hazard mitigation or ecological functions—particularly coastal floodplains and wetlands—must be protected from intensification and managed to reduce long‑term risk to the community.”

Issue: The draft relies on “merit‑based” assessment and classification, but does not require proponents to demonstrate avoidance first, to show no reasonable alternative location, or to address cumulative impacts.

Change requested: Introduce a clear avoidance hierarchy and refusal triggers.

Suggested insertion (Section 5 – Statement):

“Council will apply a risk hierarchy of avoidance, minimisation, then mitigation. Development that increases exposure to flood risk, displaces flood storage, or relies on long‑term structural mitigation will not be supported where avoidance is reasonably achievable, particularly within coastal floodplains, flood storage areas and high‑hazard land.”

Issue: While the draft mentions climate and sea level in general terms, it does not require modelling of catchment–estuary interactions, tidal locking, groundwater emergence, or entrance conditions, nor does it link decisions to the relevant Coastal Management Program(s).

Change requested: Strengthen the coastal provisions and reference CMPs.

Suggested amendments:

• Expand 5.1(j) to require explicit consideration of estuarine water levels, tidal influence, groundwater response, entrance conditions and sea‑level rise pathways, consistent with best‑practice coastal flood modelling.
• Add the Coastal Management Act 2016 and relevant Coastal Management Program(s) to Section 7 (Related Documents).

Issue: Clause 5.1(g) mentions cumulative impacts without method, scope or decision consequence.

Change requested: Make cumulative assessments mandatory and decisive.

Suggested insertion:

“Where development is proposed within flood storage areas, coastal floodplains or locations subject to compound flooding, Council will require a cumulative impact assessment identifying approved and likely future development and demonstrating no worsening of flood behaviour, flood duration or emergency response capability.”

Issue: The draft does not make it clear that reliance on evacuation or shelter‑in‑place is not mitigation for new or intensified development.

Change requested: Add a risk‑to‑life safeguard and access test.

Suggested insertion (Section 5):

“Council will not support development that increases reliance on emergency response, evacuation or shelter‑in‑place during flood events, particularly where access routes are constrained or subject to concurrent coastal and riverine flooding.”

Issue: Clause 1.2 measures success as “implementation” of an approach—this is not an outcome.

Change requested: Replace with measurable risk outcomes.

Suggested replacement (1.2):

“Success will be measured by demonstrable reductions in risk to life, avoidance of new exposure to flood hazard, protection of flood storage and coastal systems, and improved community resilience over time.”

To assist, I propose the following concise policy inclusions that align with current NSW best practice and can be cross‑referenced in the LEP/DCP:

1. No net loss of flood storage and zero net fill within mapped coastal wetlands/backswanps and a minimum 50 m vegetated buffer (larger where hydrology or habitat values warrant).
2. Mandatory catchment–estuary coupled modelling (ARR2019; coastal boundary conditions) for proposals affecting coastal floodplains.
3. Mandatory acid sulfate soil investigation and management for any excavation or drainage changes in coastal floodplains.
4. Mandated cumulative impact assessment demonstrating no worsening of flood behaviour or emergency response outcomes.
5. Preferred land uses in coastal wetlands: environmental protection/restoration, passive recreation and education infrastructure designed for no‑fill and reversible installation.

Coastal swamps, backswamps and estuarine wetlands:

• Store floodwaters for long durations, not just peak flows
• Slow drainage, reducing flood peaks downstream
• Moderate storm surge and tidal back‑up
• Buffer rainfall flooding and ocean‑driven flooding simultaneously

This dual function does not occur in riverine floodplains, where floodwaters are typically conveyed and recede rapidly. [soe.epa.nsw.gov.au], [unsw.edu.au]

When coastal wetlands are filled or drained:

• Flood storage is permanently lost
• Flood peaks increase elsewhere
• Recovery time after floods lengthens
• Flood risk is exported to neighbouring communities rather than reduced. [dpi.nsw.gov.au], [unsw.edu.au]

Most NSW coastal floodplain wetlands contain Class 3–4 acid sulfate soils.
Disturbance through filling, drainage or excavation causes:

• Acid discharge (pH as low as 2–3)
• Fish kills, oyster industry damage, and estuary collapse
• Long‑term contamination requiring expensive remediation

These impacts are documented across the Tweed, Clarence, Macleay, Hastings, Manning and Shoalhaven floodplains. [unsw.edu.au], [dpi.nsw.gov.au]

Riverine floodplains rarely carry this level of latent chemical risk.

NSW has already lost over 50% of coastal wetlands since colonisation, with some catchments exceeding 80% loss.[nature.org.au], [thepoint.net.au]

Coastal swamp forests, saltmarsh and freshwater wetlands on coastal floodplains:

• Are listed Endangered Ecological Communities
• Support threatened species and migratory birds
• Provide blue‑carbon storage and climate mitigation

Once filled, these systems cannot be recreated elsewhere—unlike some riverine floodplain uses (e.g. agriculture) which can coexist with periodic flooding. [environment.gov.au], [soe.epa.nsw.gov.au]

While development may deliver short‑term private gain, the public bears the long‑term costs, including:

• Flood mitigation retrofits
• Drainage upgrades
• Water quality remediation
• Loss of fisheries, tourism and cultural values

The NSW Marine Estate and UNSW WRL studies show that wetland degradation increases downstream economic losses, particularly to fishing, aquaculture and tourism industries. [dpi.nsw.gov.au], [unsw.edu.au]

Coastal floodplains sit:

• At or below 1–1.5 m AHD
• Within the zone of projected sea‑level rise (up to 1 m this century)

Development requires permanent pumping, floodgates and levees, creating long‑term liabilities that councils ultimately inherit when systems fail. [unsw.edu.au], [unsw.edu.au]

The SCCG’s Protecting Sydney’s Wetlands Model DCP:

• Explicitly prioritises avoidance of development in wetlands
• Treats wetlands as critical infrastructure, not surplus land
• Requires expanded buffers and hydrologic protection zones. [sydneycoas…ils.com.au], [sydneycoas…ils.com.au]

NSW’s own coastal framework requires development to:

• Not increase coastal hazard risk
• Protect coastal water quality and ecosystems
• Consider long‑term coastal processes, not just present‑day flood levels

These requirements directly contradict policies encouraging “appropriate development” of coastal swamp land. [planning.nsw.gov.au], [classic.au…lii.edu.au]

Councils including Tweed, Northern Beaches, Central Coast and Lake Macquarie increasingly:

• Zone coastal wetlands for conservation or open space
• Prohibit fill and intensification
• Use wetlands as part of their flood mitigation strategy, not development land. [sydneycoas…ils.com.au], [lgnsw.org.au]

The statement that flood‑prone land should not be “sterilised” assumes:

• Flood risk is temporary
• Land can recover after development
• Impacts are localised

None of these assumptions hold true for coastal swamp and wetland floodplains.

In reality:

• Damage is permanent
• Impacts propagate across catchments and estuaries
• Public risk and cost increase over time

Recommended Policy Replacement

Port Stephens Council recognises that coastal floodplain wetlands, backswamps and estuarine lowlands perform essential flood mitigation, water quality, ecological and climate adaptation functions that are fundamentally different to riverine floodplains.

Development that involves filling, draining or intensifying land within coastal wetlands or coastal floodplains shall be avoided. These lands are to be prioritised for protection, restoration, buffering and flood risk reduction functions.

Where land is identified as coastal floodplain or wetland, the precautionary principle applies. Land use planning must demonstrate avoidance of flood risk and environmental harm before consideration of mitigation, and must account for cumulative impacts, climate change and sea‑level rise.

Coastal floodplain wetlands are recognised as critical natural infrastructure and shall not be treated as surplus or under‑utilised land for development.

This alternative approach:

• Aligns with the Flood Risk Management Manual (2023)
• Supports the Coastal Management Act 2016
• Reduces long‑term public liability
• Protects tourism, fisheries and community resilience
• Reflects best‑practice NSW coastal governance.