Should nature shape the coast rather than seawalls as seas rise?

Could working with nature rather than fighting it may be the best response to sea level rise for areas near Thames and for other communities? The foreshore between Kopu and Rhodes Park, Thames appears to be an ideal place to gradually allow the sea to encroach naturally, create a wetland and possibly a waterfront park for Thames?  The foreshore of the Hauraki Plains is another area where nature may be left to take its course?

The knee-jerk reaction to sea level rise has traditionally been to maintain the shoreline’s position at all cost, by building new flood defence structures or upgrading old ones. More than US$10 billion per year is already spent worldwide on “grey” infrastructure such as concrete walls and levies to protect against coastal flooding. Equally large are the costs incurred when coastal defences fail.

The alternatives are “nature-based solutions” to coastal flooding and erosion, which work with natural processes to reduce flood risk and incorporate ecosystems into flood defence.

Rather than seeing the coast as a static line, these alternatives rethink the coastlines as zones with valuable habitats such as beaches, dunes and wetlands that act as carbon stores, places for recreation and natural buffers against the waves.

While such interventions do not enable full control over water levels and waves, they are designed to keep them at a safe distance from humans.

The area between Kopu and Thames has a wide strip of land between the coast and the vital State Highway.  If a nature-based solution to sea level rise was devised for this area, obviously some careful long term planning would be required about relocating existing infrastructure such as the wastewater plant and the airfield which is close to the existing coastline.  The State Highway access to Thames and the western side of the Coromandel Peninsula would have to be protected at all costs and could provide a new landward line of defence?  

Similar considerations come into play on the Hauraki Plains where the State Highway is an absolutely vital transport link.  Fortunately, it too is located some distance inland providing a nature-based buffer area to the north where the sea could be allowed to advance as seas rise? 

Apart from Holland, the UK has been actively implementing natural processes as a sea level rise response.

U.S. city leaders are reconsidering their flood defences. Instead of sea walls, they’re increasingly opting for waterfront parks that welcome the tides in and pose less of a threat to local marine life.  Planners like the idea because it gives them a better opportunity to divert the flooding wherever they want it to go, all while avoiding some of the issues that are typically attached to sea walls: Coastal erosion, soaring costs,

Boston is one of the larger cities ditching sea walls for parks. The New England metropolis originally planned to construct a massive four-mile barrier around the Boston Harbour. But as the projected price climbed to $11.8 billion and experts warned it was a short-term solution at best, city officials changed their strategy.

Last month, Mayor Martin Walsh announced a new plan to build a network of waterfront parks. These parks would ultimately add 67 acres of green space to the coast — and restore 122 tidal acres.

 

These ideas are also gaining traction in New Zealand. 

In a recent review of climate change hazards, a regional councillor is quoted  –  in an obvious reference to Thames or the Hauraki Plains –

“We’ve got areas that are sinking and we believe by the end of the century they may have dropped a metre … we can’t continue to keep on building up the levels of the stopbanks. Ratepayers have got a finite rating base and can’t continue to be paying to support that high level of service. So, we’ve been looking at how else could we manage these schemes: What are our options?”

And this reference clearly referring to the Hauraki Plains –

“We’ve traditionally provided a 100-year protection level for flooding. But what we’re seeing is that scale of an event happening every 20 years. And not so long ago we had three within two years. And we can’t continue to keep on building up the levels of the stop bank. Ratepayers have got a finite rating base and we can’t continue to be paying to support that high level of service. So, we’ve been looking at how else could we manage these schemes: We have done economic analyses on the value of the land that the scheme is protecting and thinking, this land; actually, it’s not worth paying $2m to have a high stop bank in this area. Maybe we should let this area flood and then compensate the landowner when it happens as opposed to continually doing these hard engineering sorts of solutions.”

As future plans are considered these natural processes must be on the table.