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There's tonnes of silt smothering the East Coast right now in badly hit flood areas.
But what is it? Where did it come from? Is it bad for us? What to do with it?
This area has long been one of the worlds leading hot spots in sediment uplift and erosion.
Professor Troy Baisden principal investigator at Te Pūnaha Matatini Centre of Research Excellence on Complex Systems talks to Jesse.
Rail tracks covered in silt in the Esk Valley by flooding during Cyclone Gabrielle, 20 February. Photo: RNZ / Jimmy Ellingham