When the new sea wall was built in front of the old one at St Clair in 2004, a lot of people said something also had to be built to protect it.

After years of increasing beach scouring, the eventual exposure of its toe and inevitable sink-holes in the footpath above in the late 1990s, there were many warnings from experts.

The warnings were that wave pressure and sand erosion at St Clair Beach needed somehow to be mitigated or the wall, and the beach, would take a beating.

They were accompanied by high level of concern from the community.

Every person agreed that when waves reflected off the wall they scoured the beach.

As the beach became lower the waves could reach the wall more easily, smacking into it harder and scouring more and more sand from its front.

Canterbury University engineering dean Prof Alex Sutherland warned that without mitigation, the vertical sea wall would continue to lower the beach level.

The Dunedin City Council's consultant engineers said a breakwater was needed to break waves offshore and create a reservoir of sand at the beach.

A Otago Regional Council hearings panel - despite turning down consent to build a breakwater - suggested the city council investigate options to mitigate waves hitting the wall and beach scouring.

''... and a longer-term management strategy to address these effects as far as is reasonably practicable.''

Members of the public welcomed a new wall, but said it should be only the first step in protecting the area.

It was the appearance of sinkholes in the Esplanade - not unlike those that have appeared there now - and the exposure of the original wall's foundations in the late 1990s that prompted the council to start seeking advice.

Councillors were soon advised the wall was unstable, and could collapse in the next big storm.

A new wall was built in front of it in 2004.

At the time council staff were clear further protection also had to accompany the wall.

They suggested that long-term, the installation of a $2.5 million artificial offshore reef, made of sand-filled sausages, to reduce the power of the waves could solve the sand erosion problems.

But they also said it would be several years before the council would be able to consider such a project.

A great citywide debate about what to do about the wall followed.

Engineer Maurice Davis, then of Duffill Watts and Davis, who prepared the initial beach report for the council, told a public meeting at the time a wall was not ideal at all. But because one had been built there at a time when no-one knew what effect it would have, and houses had long since been built behind it, the city was stuck with it.

A new wall would have to be built in the same place, as close to the old wall as possible.

Its negative effects could be alleviated by encouraging the deposit of sand on the beach and limiting the sand's longshore drift, he said.

As well as the artificial reef idea, people at the meeting also discussed other long-term options, including building a permeable or solid breakwater out from the headland and building sand-trap fences along the beach.

Duffill Watts and Davis eventually recommended the council build a 20m breakwater out from the St Clair salt water pool.

It is understood its plans were reviewed by other experts, who recommended the breakwater extend further than that, but when the council eventually applied for consent to build the sea wall, a 20m breakwater was included.

It was not a popular idea.

There was a strongly negative reaction from surfers, and a regional council panel declined to give resource consent for it based on the health and safety risks it posed to surfers.

The panel was also concerned the breakwater would project into a known channel used by surfers and affect wave breaks and currents in an area that was so important to surfing.

''We consider that the value that a readily accessible good surfing beach offers Dunedin must be preserved. The rock groyne would be inconsistent with the classification of St Clair beach as a coastal recreation area,'' its decision said.

In 2005, a report for council prepared by Duffill Watts and King on damage to a sea ramp on the new wall raised the issue of the breakwater again.

It said the wave conditions of the previous six months and the ''dramatic degrading'' of the beach provided a sound argument for the council to reconsider the project.

The beach profile was ''seriously sucked down'' and there was little sand protecting the base of the wall and ramp, director Barry Chamberlain told councillors.

It was left to staff and a council consultant to consider the groyne suggestion.

It seemed to fizzle out.

In 2007, the council commenced a substantive investigation into stabilising the city's beaches, following storm damage to dunes at Middle Beach.

Submissions reflected concern from the community about the sea wall's effect on erosion at St Clair Beach, and support for an artificial reef to solve the problem again came through strongly.

At some point, the council suggested taking sand from Tomahawk to replenish St Clair and Middle Beaches, a plan abandoned after Tomahawk locals did not take kindly to it.

From the investigations came the long-term Ocean Beach Domain Management Plan.

Adopted last year, it says the area in front of the sea wall is managed by a separate city council process and proposes no action for the area other than maintaining the sea wall.

The nature of that ''separate process'' is unclear, although parks and recreation manager Mick Reece said it was related to the consent, which says the wall shall be maintained in good repair throughout the 35-year term of the consent.

Chairman of the hearings committee Cr Colin Weatherall said St Clair Beach was out of the project's scope.

''It was always going to be the difficult quantum, but we never envisaged what's happened there now.''

Last week, he asked council staff for a report as soon as possible.

If everyone said the sand migration issues needed to be addressed, why has it not been done?It seems the reasons are complex.

The answer would require a close reading of dozens of reports, studies and assessments on the matter done by council staff and experts over the past 15 years.

There have been changes in councils and council staff.

The man responsible for the sea wall now is transportation operations manager Graeme Hamilton, who says he inherited the sea wall from the council's parks and recreation department 18 months ago.

Parks and recreation inherited it from the city architect/city planning department, which dealt with it when the wall was replaced.

Mr Hamilton's focus is on fixing the immediate problem: stopping the Esplanade from slumping any more.

He has not thought too much about sand yet.

''If the wall was built on rock, there wouldn't be an issue with sand.''

The long-term options for sand retention would be determined and reported back to the council for a decision, he said.

At this stage, it seems councillors will not receive that report until September, as it will not be ready for the next committee round in July.

Cr Paul Hudson, who was on the hearings committee which dealt with submissions on the 2008 sand investigations, said the whole area was part of those discussions and councillors were well briefed on issues along the coast, including St Clair, as part of that.

It is not that nothing has happened to try to divert the sea's energy at St Clair; work such as dumping stones at the foot of the wall had taken place from time to time, he said.

It seems likely the council may now have to seriously consider doing something about the sand situation.

And that will come back to money, of course, of which there is not much to splash around.

The 2004 sea wall and Esplanade was originally to cost $3 million and ended up costing about $7 million.

The cost of another major project is unlikely to be something any council, especially one in a tight spot, will welcome.

Any options involving more rocks or structures on the beach or in the water are also unlikely to be popular.

But perhaps people will have to accept it could well be a choice between some effects on the amenity - visual or otherwise - and no beach at all.

- debbie.porteous@odt.co.nz

Steve Moynihan, of Moynihan Coastal Consulting Ltd, provides some food for thought about the St Clair sea wall.

Quite a lot has been said about the St Clair sea wall.

I have joined the party late, mainly because I have had to carry out some calculations and prepare a drawing.

I am a coastal engineer working from home in Omakau (not because of expected sea-level rise), and I have been involved in new beach design.

Research on many beaches has shown soft (sand/shingle) beaches will adopt an equilibrium shape in plan when adjacent to a headland such as the seawater pool area at St Clair.

Equilibrium is a state where there is no more erosion because the shoreline is everywhere in line with the incoming waves. A beach that has not reached an equilibrium shape will continue to erode until it does so. This is the case at the St Clair corner, which explains why there have been problems there since first occupation in the late 1800s.

The picture published here titled ''Erosion'' has a red line showing where the back of the beach wants to be. In trying to reach this line, the beach may encounter hard rock or a seawall which constrains the back of the beach to the line of the wall.

However, a sea wall does not stop erosion and the seabed in front of the wall will have been continuing to lower until it reaches a depth at the location of the wall, as if the back of the beach did in fact lie along the red line.

The wall would have no problems if it had a strong base that went below the eroded depth, but this would not leave much of a beach in front. Of course the whole situation is very dynamic and sand will come and go, but the overall effect would be that of a poor beach.

A change could be made by pushing out the headland into the sea by way of a breakwater.

The picture labelled ''Beach'' has a yellow line showing where the edge of the beach would lie with a 150m breakwater in place. The result would be a beach of up to 50m width, with the sea wall sheltered by permanent sand.

My inexpert drawing ''Breakwater-Beach'' shows what this would look like. There would be room for activity like beach volleyball. Studies would be required to show no harm to the surf break. More beach could be obtained with a longer breakwater.

The downside is cost. A strong breakwater would be required - costing $8 million to $10 million, depending on whether sand would have to be imported, on final design, studies, and consent costs.

Food for thought anyway.

It says preliminary tests indicate there is no immediate concern about the safety of the rest of the sea wall.

At least one business owner in the area yesterday expressed concern about a lack of information being provided by the council on the status of the wall.

Starfish Cafe co-owner Cushla Dodds said because the holes appeared to be growing and the council had told her nothing, she had checked her insurance policy, just in case. She said she knew other businesses had too.

Business was being affected because people thought they could no longer walk around the Esplanade or bring their dogs there, she said.

People also wanted to know the long-term plans for the seafront. She had not contacted the council, but felt she should not have to.

Next door, florist Carley Jones told Radio New Zealand that each day the drama went on, the more scary it became.

Council roading network engineer Peter Standring said the situation yesterday was that the council expected sinkholes in front of the South Coast Board Riders' Association at the north end of the sea wall would continue to grow in a northerly direction over the next week, as contractors worked in two-hour bursts around tides, to plug gaps underneath the sea wall at that end.

The amount of walkway fill being sucked out through those gaps had already been reduced by remedial action taken since the first hole appeared on Sunday, but material could still disappear until sheet piling along the base of the northern end of the wall was completed, he said.

The sheet piles were being sunk 3m deeper than the foot of the sea wall along the 50m section of wall.

The work was being done in sections and had started around the St Clair Surf Life Saving Club's ramp, where the biggest gaps were. It was expected to take at least another week, because access was limited by the tides.

He said it was anticipated the pits in the walkway would eventually extend along more or less that whole section of the walkway, to the northern end.

However, engineers had indicated the damage would be contained to that area.

A preliminary check by engineers and a ground-penetrating radar had not revealed any voids under the remainder of the wall or walkway along to the salt water pool.

Mr Standring said the priority was to plug the gaps where the beach level had gone below the bottom of the wall.

A more extensive assessment of the rest of the wall would then be made and a long-term response considered once that work was completed.

A portion of the Esplanade walkway along its length and about 3m back from the wall would remain cordoned off until at least then. The cordon still allowed room for foot traffic.

Council operations manager Tony Avery said the council had not approached businesses or residents in the area because there was no concern about the remainder of the wall, although it certainly would if there were any concerns.

He said anyone wanting information could contact the council on 477-4000.

debbie.porteous@odt.co.nz

Advice will also be taken on providing a long-term solution to problems such as the one which caused a section of the Esplanade to be undermined.

While the integrity of the wall was believed to be still intact, the Dunedin City Council would have the entire seawall assessed as a precautionary measure, council roading maintenance engineer Peter Standring said yesterday.

The assessment would be carried out by contract engineers.

The first of several large holes appeared on Sunday behind the seawall in front of the St Clair Surf Life Saving Club and the South Coast Boardriders' Association, after heavy seas and high tides depleted the beach of sand, exposing the toe of the wall.

That allowed waves to flush behind the wall, washing out the backfill, causing the paving above to collapse.

The area from Forbury Rd to the north end of the wall is cordoned off and most access from the Esplanade to St Clair Beach is closed until further notice.

Tracked excavators have been on site since Monday, shifting rocks to protect the bottom of the seawall.

Vertical sheet steel piling is being installed in front of the seawall, on either side of the lifesaving club's ramp, along with cross-bracing under the ramp itself.

Mr Standring said contractors would backfill the area between the seawall piles and the sheet piles with concrete today and tomorrow.

He said much of the beach was at the lowest level staff had seen.

Because tides were so high, the waves had been hitting the sea wall without breaking, putting significant pressure on it. The situation was expected to improve after Tuesday's king tide.

However, it had highlighted the need for a long-term solution which worked with the natural environment, he said.

''This is a natural occurrence and we will be getting expert advice on how to best deal with these challenges in the future.''

He said some St Clair businesses and residents had reported heightened building vibrations this week.

That was ''more than likely'' happening because of the lack of backfill behind the wall at the northern end, which would normally dampen pounding waves.

He emphasised it was important for people to avoid the cordoned-off area while work continued.

There was public access to St Clair Beach via Middle Beach.

Updates on the project are available on the council's website.

-debbie.porteous@odt.co.nz

A further hole has opened up in the Esplanade at St Clair and two holes which appeared yesterday have merged into one larger opening.

The holes in the paved area in front of St Clair Lifesaving Club first appeared yesterday as big swells pounded the coast.

The new hole is on the Lawyers Head side of the surf-lifesaving ramp.

Dunedin city council staff are assessing the situation amid a steady stream of onlookers. 

About 2.30pm yesterday, police and contractors began to cordon off the seaward side of the Esplanade, from the St Clair Lifesaving Club to the car park, as a precaution.

The Esplanade was full of people watching the waves crashing against the sea wall.

One of the holes in the paved area in front of the life-saving club grew from about 1m long to about 4m long and others had also grown in size after the high tide at 4.30pm.

Swells of 2.3m are predicted and tides of similar heights are forecast for next few days.

Life-saving club president Antony Mason said he called the Dunedin City Council and Fire Service after finding the tiled area to be a ''bit spongy underfoot''.

''It got bad real quick. Within an hour there were two holes.''

The news grew worse when he realised the club's ramp to the beach had moved about 20mm and water was going under the ramp's tunnel, he said.

''We've got no access to the beach and the polar plunge is in three weeks.''

He had seen bigger seas and the beach in worse conditions than yesterday.

Dunedin City Council roading engineer Peter Standring inspected the site yesterday afternoon and found a significant ''drop out'' below the tiles.

''If you looked back underneath, the tiles were suspended.''

It was for that reason the Esplanade was cordoned off, he said. While the tiles looked fine on the surface along the rest of the Esplanade, there could be a void opening up underneath.

He believed yesterday's high tides and swells shook the tiles loose but the undermining of the ground had probably occurred over time, as the sea sucked material out from behind the sea wall.

''It's been an ongoing process. It highlights the need to look at everything.''

From his assessment of the site, he did not believe the integrity of the sea wall had been compromised.

Engineers would visit the site today to get a better idea of what was happening, he said.

The holes are the latest problem to beset the Esplanade.

The stairs and ramps to the beach have failed several times, due to what the council believed was a combination of construction and design faults. The high tides also brought surface flooding to Portobello Rd and the streets off Portsmouth Dr late yesterday afternoon.

-rebecca.fox@odt.co.nz

A detailed design for a buried backstop wall to halt erosion at St Clair and St Kilda beaches in Dunedin, including costings and drawings, will be completed in the next financial year.

The update was contained in a report for councillors considering the draft annual plan for 2013-14.

In it, council parks manager Lisa Wheeler noted there was no funding in 2013-14 for the backstop wall, which councillors approved last July as part of long-term measures to mitigate coastal erosion in the Ocean Beach Domain between St Clair and Lawyers' Head.

However, about $250,000 from this year's budget, which remained unspent, would be carried through to the 2013-14 budget and used to prepare an application to extend the current resource consent for emergency works in the area, which expires in 2014.

It would also be used to develop detailed costed design drawings for a buried backstop wall from behind the eastern edge of the St Clair seawall to the cultural centre.

It would be the first section of a buried wall that would eventually stretch to the St Kilda Surf Club.

Once the design work and costing had been done, staff would refer it to councillors for consideration against other projects.

In the long-term ''adaptive management approach'' for battling erosion along the Ocean Beach Domain, adopted by councillors last year, it was intended to install the wall in 10 to 15 years' time, but earlier if required.

Ms Wheeler said since July the council had spent $44,000 mitigating the effects of a storm on June 28, when 40-knot to 50-knot winds combined with 2.5m waves hit the coast and the Ocean Beach dunes, eroding sand at the end of the St Clair wall and the car park above Marlow Park.

A sand survey was under way at present, but the last one, in March 2012, showed there did not appear to be any abnormal sand movement from the beach, and no long-term trends apart from in front of the seawall, where fluctuations of sand levels were the greatest.

There was enough sand stockpiled at Tahuna Park ready for any emergency works after one more storm event.

The stockpile would be reassessed at the end of the financial year, when more would be brought in to retain the levels needed.

Historically the dunes were most vulnerable to damaging winds in May and June, Ms Wheeler said.

- debbie.porteous@odt.co.nz

Any resolution is also expected to include a decision on new access to the beach.

Early this year, a report to the council said the sea wall had failed to gain a code of compliance certificate when it was completed in 2004, mainly because of concerns over the durability of a ramp and stairs leading from the Esplanade to the beach.

Since then, the ramp and stairs have been damaged in heavy seas six times, most recently in September last year when they were closed after concrete cracked, exposing steel reinforcing rods.

A council report after incidents in 2004 and 2005 found failures then were caused by a combination of construction and design faults.

Design consultant Duffill Watts and King and construction company Naylor Love agreed to strengthen and repair the ramp and staircase at no cost to the council, and the facilities were replaced in 2007.

The most recent damage appears to be in the same area, materials used to reinforce the ramp having failed.

Duffill Watts and King has merged with the firm CPG, which has not accepted liability for the failings.

The council is seeking resolution through a settlement, rather than court action, while also working with the company on redesigning the sea wall's steps and ramps.

Council transportation operations manager Graeme Hamilton said councillors were updated on progress last week, in a non-public part of the infrastructure services committee meeting.

He could not discuss details, saying he did not want to prejudice the outcome of the meeting, but said council staff would discuss "everything" with CPG at a meeting in mid-August.

The council has previously said the existing ramp and some of the existing stairs would be removed and a new set of stairs built at the St Clair Salt Water Pool end of the sea wall, but Mr Hamilton would not confirm that yesterday, other than to say design, location and a timeframe would be discussed at the meeting.

The council has tagged $250,000 for the beach access project this financial year.

He was "always optimistic" a resolution could be reached with CPG, he said.

"It's [the meeting's] a positive move forward, to resolve what has been a difficult issue."