Our Paradise lost

By Patrick O'Sullivan patrick osullivan@hbtoday co nz

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COASTAL INTEGRITY: Hawke's Bay Regional Council Asset Group manager Mike Adye says this year people will have their say regarding long-term coastal solutions affecting Westshore Beach. PHOTO/WARREN BUCKLAND
COASTAL INTEGRITY: Hawke's Bay Regional Council Asset Group manager Mike Adye says this year people will have their say regarding long-term coastal solutions affecting Westshore Beach. PHOTO/WARREN BUCKLAND

SIX YEARS AGO, when Deborah Ennis turned 106, she was asked by Hawke's Bay Today to name the greatest change she had witnessed in Hawke's Bay.

"Westshore," she said. "The beach - it's gone."

Westshore Beach was a popular sandy beach, as two remaining surf lifesaving clubs attest to.

Today it struggles to hold onto land, sand and people.

Hawke's Bay Regional Council Asset Management Group manager Mike Adye regularly walks the beach, which he says is at equilibrium thanks to trucked-in gravel and sand.

The "lovely beach" people remember was a temporary phenomenon.

Until the 1931 earthquake, when the seabed and land were lifted nearly 2m, Westshore was a thin gravel spit.

He said for about 30 years after the earthquake the sea slowly working its magic, whittled the seabed to its long-term depth which was helped by the occasional healthy storm.

"It moved sand and a lot of that came ashore and built up the beach," he said.

"I think that was until the late 1950s and then it found its equilibrium and as a result it started eroding back again.

"That process of erosion is carrying on today and a lot of people can remember back to the 1950s and 1960s when it was a nice sandy beach, from all the sand that had come in from the raised seabed.

"Over time the sea has worked against that and returned it to what it is today, and probably was before the earthquake when it was just a gravel spit."

Fingers were pointed at Napier Port's breakwater preventing sand and gravel northerly drift from reaching Westshore, but a 2007 report by coastal oceanographer Dr Paul Komar said the port was more likely preventing Westshore erosion by protecting it from waves.

With the port's breakwater exonerated fingers shifted to the Port's dredging programme which keeps shipping channels open.

Port chief executive Garth Cowie said the amount of dredged sand was very small compared with the majority silt and mudstone recovered.

"It is a muddy mix that is dredged out," he said.

"That material goes out to a dumping ground and when we find good sand we put it as close to the beach area as we can."

Dredged sand was nowhere near enough the amount needed replace northerly drift from Westshore.

The port is planning significantly more dredging as it prepares for bigger shipping volumes and bigger ships. Mr Cowie said reports commissioned for the consenting process would be made available to residents.

Mr Komar's report said the 20th Century diversion of the Tutaekuri River away from Awatoto, joining a rerouted Nagaruroro River near Clive, were contributing factors to erosion.

"At present they do not even supply the beaches with gravel, and it will be more than a century before they do so," it said.

"Of the rivers, only the Tukituki now supplies significant volumes of gravel and coarse sand to the beaches, estimated to average about 28,000cu m per year, but with large variations from year to year depending on the occurrences of floods."

Mr Adye said from 1993 to 2014 gravel was moved from the north side of the port and delivered to Westshore Beach to mitigate erosion, with costs evenly shared between Napier City and the Regional Council.

"The latest reports say taking from there is not sustainable so we stopped that last year."

Gravel was now sourced from rivers to be dumped on the beach.

While there is a shortage of gravel and sand on the beaches there is a surplus inland. Mr Adye said parts of the upper Tukituki River had built up gravel to the point where the riverbed was above the Ruataniwha Plains.

There was not enough commercial demand for the high quality resource and the cost of transporting it to the beach, killing two birds with one stone, was "huge".

When the 1931 quake hit it tilted the Hawke's Bay coast. North of Awatoto went up and south went down.

It was from Awatoto that 1.5 million cu m of beach sediment was extracted for 30 years from 1973.

"The significance of this commercial extraction at Awatoto is that it has exceeded the quantities of gravel reaching this stretch of shore, from the Tukituki River and from sea-cliff erosion along Cape Kidnappers," Mr Komar's report said.

"As a result, the total quantity of gravel and sand contained within the beach between the Cape in the south and Bluff Hill and the Port's breakwater in Napier has significantly decreased over the years, making this stretch of shore more susceptible to property erosion and flooding."

Of particular concern is a devastating 100-year storm which the report said could bring 10m waves "with the largest waves in the order of 18m."

Napier's low-lying CBD would be flooded and coastal housing damaged.

This year the Regional Council will consult with the public on what to do about coastal hazards, following a new report.

"Identifying the hazards is technical work and reasonably factual," Mr Adye said.

"The next phase will be what are the best options. You might have the best option but what is the best option at a reasonable price that the community can afford?"

Solutions needed to extend the length of the coast, including Haumoana south of Awatoto, where homeowners are retreating thanks to regular wave incursions.

"I think we need to work through and find a level of comfort about what is the best long-term solution or options for each of these areas - that includes Haumoana as well as Westshore.

"Should we defend, should we retreat, is there something in between, what happens if we do one or the other, what is the cost and is it sustainable in the long term etc.

"We have to come out with a pragmatic sort of solution, thinking about the whole of Hawke's Bay."

- Hawkes Bay Today

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