Coastal seawalls take on new urgency as properties crumble
Cyclone damage shines a spotlight on applications by Aucklanders to shore up their homes from damaging erosion, writes Jonathan Killick.
Consent applications for seawalls are taking on new urgency as coastal residents scramble to stop homes collapsing into the water.
Their mission has been thrown into sharp relief in the wake of Cyclone Gabrielle, which saw hillsides and cliff-faces crumble across the city – forcefully bringing home the imminent risk faced by some multimillion-dollar properties.
Some wealthy owners are fighting back and want to protect their properties with fortress-like rock seawalls that will hold back the forces of nature.
In Sunkist Bay in Beachlands, three households have applied to armour the shores with rock and mortar fortifications, in addition to the five already there.
Conal Dempsey applied for a consent for his investment rental property on Hawke Crescent in August last year and has been waiting for a decision from independent commissioners.
While consultants and council planners argue the virtue of managed retreat, the $1.75m property continues to crumble away as a result of extreme weather events like Cyclone Gabrielle.
The tenant told Sunday News that since last November the property had lost around half a metre of land, and the cliff was now less than two metres from the fence line.
‘‘I woke up one morning and the sprinkler hoses were exposed out of the cliff. My big fear is that it’s getting undercut by the sea at the beach, and it could all collapse.’’
Cliff failures in Auckland frequently make headlines. Most recently, a bach in Manukau Heads was taken out in a landslide, seriously injuring three holidaymakers inside it during the fall.
The problem is that waves and weather lash the brittle sandstone. The solution is described as ‘‘toe armouring’’. Seawalls are certainly not a new thing. Tamaki Dr has been bolstered by boulder walls for a century. Auckland Council figures show that around 100 new seawalls have been consented over the past 10 years. But perhaps what is new is the scale of these fortifications.
Dempsey’s plan is to build a 24m, two-tiered rock wall with 11m2 of planting. The bulwark will reach 5m above the shore at its peak.
His own home a few doors down already has a winding path carved down the cliff leading to an extensive rock masonry rampart.
That’s not surprising. He owns half of Dempsey Wood, a major civil construction firm that claims to move 3 million cubic metres of earth each season, and pulls in contracts worth hundreds of millions of dollars.
But the age of climate-proof castles might be over before it really began.
Council consultants seem positive about Dempsey’s proposal but have warned it should be the last one.
‘‘I strongly suggest that this site should remain as the last property to include such coastal protection intervention before retaining a more naturalised coastal edge,’’ landscape architect Peter Kensington wrote. ‘‘I would not wish to see the entire coast of this localised bay having hard protection structures in place.’’
A resident in Belmont on Auckland’s North Shore came up against similar scrutiny.
When Allen Peters applied for consent to build a 51m wall beneath his two properties on Seacliffe Ave in 2020, he was told that the crumbling cliff was an ‘‘outstanding natural feature’’, and erosion was part of that.
Independent resource consent commissioners granted the consent but it took two years and several consultants. ‘‘It was extremely long and at times frustrating. The consultants certainly weren’t cheap but, ultimately, we believe we are doing the right thing.’’
Peters has built himself a slice of paradise in a garden he’s been working on for 15 years with bromeliads, palms and po¯ hutukawa in every direction. Naturally he’s keen to protect it.
Over more than a decade
Peters has watched erosion at work and has decided that building a seawall is better than watching your property slip away. ‘‘There are dozens and dozens of properties affected by recent weather events, and it’s my belief that, with a seawall at the bottom, a number of them would have been protected.’’
He pointed to where a group of
four neighbours in 2003 put a retaining wall on the top of the cliff with 18m-deep piles, and those properties had been fine, he said.
However, Peters admits the cliff is unstable. He’s actually benefitted from it. Some time in the 1960s a landslide provided the property with sloping beach access.
Another slip in 1972 took out a retaining wall that dumped steel and concrete on the beach where it still lies today. But those seawalls weren’t built to today’s engineering standards and strict rules, he said.
Peters believes homeowners have a right to protect private property and views the endeavour as a way of saving iconic
overhanging po¯ hutukawa. ‘‘I sometimes question why the hell we’re doing it when we already have access to the beach. Why spend the money? But we want to tidy the beach and protect the land.’’
Richard Reinen-Hamill is the technical director of coastal engineering at Tonkin + Taylor, a major consulting firm in Auckland, and believes it’s a matter of time before homeowners will flee the coast.
‘‘Historically seawalls have been the solution of choice but no structure is permanent. It can only buy you more time. Meanwhile property owners
spend money developing the land behind the seawall and the value goes up, so the risk profile increases because the asset gains in value.’’
He said seawalls should be viewed only as a means to temporarily protect an asset as the city transitions away from risky coastal development, and threatened areas should not be further developed or invested in.
The Government has said it intends to introduce legislation on managed retreat before the end of 2023, and Reinen-Hamill expects this may include some people having to give up their land. ‘‘We fundamentally cannot seawall the
whole of Auckland’s coast. Every structure requires maintenance and it could be a big liability for the council or future landowners who would get stuck with that.’’
Stonemason Len Lavas’ family has been building seawalls in Auckland since 1927 and he doesn’t think ‘‘managed retreat’’ holds much water.
‘‘Every wall we’ve built has completely stopped erosion. It’s no problem to do it, I’ve built kilometres of them. Don’t worry about rising sea levels and all that shit, we build two metres above high tide and put another wall above that along with a platform with planting.’’
Lavas said a typical seawall might cost between $100,000 and $200,000. His company has five consented seawalls ready to go this year and a further eight awaiting resource consent. He’s investigating a 90m seawall in Stanley Point where a large slip in November last year put three houses, collectively worth nearly $10m, in jeopardy.
He said the problem was the wait time and the number of consultants involved.
‘‘You have to take photos to show a before and after, make impressions, submit a planting plan which is all fine, but then if one of the experts doesn’t like it you have to go to the
Environment Court. We’ve got every consent we’ve helped apply for but instead of it taking three to four months like it used to, it takes around two years.’’