A house in Esk Valley following the cyclone. Photo: RNZ / Tess Brunton
Esk Valley residents are concerned about the effect of silt dust on their health and quality of life, as sun and high winds cause dust storms along the valley.
Steve Wheeler's lifestyle block was buried under two metres of silt during the cyclone in February.
His family had recently bought a new home, and he said he didn't know how those who were staying could do it.
He told Nine to Noon he had observed how the silt sparkled in the sun, "like millions and millions and millions of stars", and said it was likely silica catching the light.
Cleaning one of the rooms of his house, on a morning when the sun was coming in at just the right angle, he observed fine particulate matter hanging in the air.
"That means that that's extremely fine particulate, because it is airborne."
Listen to the full interview on Nine to Noon
There had been frequent mini dust storms in the valley as the weather improved, and on occasion, major dust storms.
The silt was being piled into rows in order to clear it from properties, which had "kind of made the problem even worse", Wheeler said.
"We now have up to five-metre tall wind rows, about 10 metres apart, right down the valley floor. And of course when the wind gets up and they get dry... boom, it just becomes airborne - and it tastes bad."
He said he was worried about the effect of the dust on his family's health, including their animals.
"We're very, very concerned for the respiratory systems of our cows and our sheep and our horses, to say nothing of the dog and the cats."
Esk Valley on 20 February following Cyclone Gabrielle. Photo: RNZ/ Nick Monro
Scientists are working on understanding the phenomenom.
NIWA air quality scientist Dr Elizabeth Somervell told Nine to Noon they had placed monitoring devices up and down the Esk Valley, as well as theTūtaekurī Valley further south, focused around areas where people lived and the silt depositories.
She said the goal was to determine the extent of the impact.
"What we're looking for is how much of the silt is being picked up [and] how much we can track silt plumes up and down the valley with the winds."
The problem was self-perpetuating - as the silt dried in the sun, it was easily picked up by the wind, which then exposed the next layer down.
But Somervell said removing it was the only practical solution to get people home and make the land usable again.
"Eventually nature would do its thing," Somervell said. "[The silt] would crust over... and you would get colonising plants coming in, but it's a slow process.
"And in the meantime, of course, people need to return, as much as possible, the land back to being productive. So we're kind of out of step with nature's timeline and forcing the process through so that we can go on with our lives."
The recently declared El Niño was contributing to dryer and hotter than average weather, which would increasingly exacerbate the problem.
She said Niwa had been working alongside local medical officers of health and health agency Te Whatu Ora to develop advice for people.
"One of the key reasons we're doing this in the long term is to provide a record of the concentrations, so that if there are health-risk assessments that are done later on, they have the information there at-hand to do that."
Silt recovery taskforce lead Darren de Klerk told Nine to Noon silt workers wore PPE, including dust masks and respirators.
"The last few days have been pretty terrible for dust," he said.
Funding for its removal had been patchy, with the taskforce running out several times, before being topped up by central government, and then running out again.
Another funding injection of $10 million was announced last week, but de Klerk said it wouldn't be enough to finish the job - "that will allow us to do a small sum of what's required. After that, things will come to a halt again."