“Growing resilience with natural defences” AHEIT Seminar 31st May 2014

Sand dunes and wetlands: ‘living shorelines’ as natural buffer zones in the face of sea level rise

Rodney Chambers B.P&R Mgmt Coastal Area Head Ranger, Christchurch City Council

Coastal sand dunes and wetlands - the frontline for climate change and sea-level rise

…The greatest impact of sea level rise in the city will be the raised risk of storm inundation and “the greater frequency of extreme tidal levels” …The other major impact will be the “progressive shoreline retreat of low-lying areas,” the report warned.

Coastal sand dunes and wetlands - the frontline for climate change and sea-level rise

• What’s our future going to be? • Stay and spend (a lot?) on hard armouring? • Adapt to living with flooding and spend (a lot) to build?

• Retreat and spend (a bit?) to recreate natural buffer processes?

Coastal sand dunes and wetlands - the frontline for climate change and sea-level rise Christchurch Coastline To Change Dramatically The Press -Tonkin and Taylor …At best, protection measures could minimise the impact rising sea levels could have but the report warned a “retreat” from coastal areas maybe needed over time.

“Sand dunes remain Christchurches cheapest insurance policy, but like all insurance they’re never free, and we never quite know the payout until the policy is tested!”

Sand Dunes – a valuable but endangered habitat • Sand dune ecosystems occupy about 1100 km of the New Zealand coastline of 15-18,000km. They are a limited resource. • 95% of New Zealanders living within 50 km of the coast, 65% within 5km so beaches play important roles in our lives.

• The way we have chosen to live, work and play on the coast has often bought us into conflict with natural coastal processes and as a result our sand dunes are one of our most highly modified and degraded ecosystems. • Today, dune ecosystems remain under pressure from development, weeds and animal pests, and usage such as vehicles and people destroying sand binding plants. • To ensure we can enjoy our sand dune ecosystems in the future and all the practical, functional and aesthetic benefits they provide - we need to understand them and look after them. Dunes Restoration Trust of New Zealand

Coastal protection – soft vs hard armouring

• Hard armouring

– prevents the natural landward migration of beaches and deflecting wave energy, – contributes to beach and wetland erosion which negatively impacts both ecosystem functions and the public’s ability to access the coast. – causes dune, beach, and wetland ecosystems to disappear. – interferes with the ability of coastal ecosystems to filter water, support fisheries, and provide other valuable ecosystem services that would be costly for coastal communities to replace. – negative impacts of a concrete coast are stark and may be offensive to local residents and beachgoers. – Ad hoc private armouring of the coast may lower property values.

• Soft armouring

– techniques that use natural infrastructure, such as sand, gravel, dune grass, or wetlands, to strengthen coastlines. – not only is more aesthetically pleasing than hard-engineered structures but also it can enhance coastal ecosystem services and protect recreational resources. – can be seen as expensive but they do produce a “living shoreline” .

Sand Dunes – how public perceptions change

“Parade residents want dunes topped” (1990’s) by Peter Mathias "North New Brighton residents say they are fed up with

the Christchurch City Council failing to lower sand dunes along Marine Parade" according to North New Brighton Residents' Association president Terry Holling. “Residents along Marine Parade have had enough", he said. “They cannot even see the sea from their upstairs windows now but they could 30 years ago when they built their houses". The dunes were out of control and the association wanted them lowered to five metres above low tide mark. “I’m worried about the low gaps in the dunes!” (2010’s) A phone call to Christchurch City Council after the Japanese earthquakes

Christchurches coastal changes ‘over time’ 9000 yrs ago

1000 yrs ago

6500 yrs ago

Sand Dunes – natural storm buffers Storm Erosion in Pegasus Bay by Dr Bob Kirk

“…We can never have too much sand for protection" he concluded.”

The Press -Tonkin and Taylor …Coastal dunes and other natural elevated margins are very important in providing a barrier protecting lower lying inland areas from flooding.

Sand Dunes – natural storm buffers GIS System Assessment of Tsunami vulnerability on a dune coast by Deirdre E. Hart and Gemma A. Knight (Canterbury University)

“We conclude that the preservation and development of ‘natural’ dune barriers provides a greater level of protection along the Christchurch city coast than the construction of sea walls and buildings”.

Christchurch sand dunes naturally dynamic

A Living Shoreline • Projects that incorporate natural habitat restoration or conservation, such as restoring a sand dune or a band of marsh habitat, into shoreline stabilization.

• Projects incorporating living shoreline principles may be a superior

alternative to hard armouring in some circumstances, particularly in estuarine environments that are not subject to high-energy wave action.

• Some people have suggested that because these wetlands will

eventually be inundated, the prospect of sea level rise is a justification for relaxing wetland protection requirements. However, even from the narrow perspective of a particular parcel of land, this justification ignores the biological productivity that these wetlands can provide until they are inundated, as well as the value of submerged aquatic vegetation that could develop after they are inundated.

• Moreover, from the broader perspective, even if particular parcels are flooded, society has options for ensuring the continued survival of wetland communities as sea level rises, such as allowing them to migrate inland or promoting their vertical accretion

Wetlands: a natural buffer

Sand dunes: a natural buffer Christchurch Coastline To Change Dramatically The Press -Tonkin and Taylor …The protection and, where practical and appropriate, enhancement of natural buffer zones is fundamental to any effective management of coastal flooding hazard