Tasman: Landslide study offers new model

Wednesday 16 Dec 2020

Ex-Tropical Cyclone Gita left behind more than 4500 landslides when it slammed into the Nelson-Tasman region in February 2018.

The authors of a new research article, published in the New Zealand Journal of Forestry Science, used gridded rainfall, topography, lithology and land cover surfaces to develop a high-resolution model of the landslides that occurred in a 196 square kilometre area of Tasman District during the time Gita brought heavy rain to the region.

“Our results ... reinforce the relevance of land cover, rainfall and topography as predictors of landslides but, most importantly, imply that effective land use management could substantially reduce landslide occurrence in Tasman,” the article says.

“In particular, our model suggests that increasing the extent of permanent forest cover and limiting clear- fell harvest of plantation forests on landslide-prone slopes could substantially reduce landslide occurrence during high-intensity rainfall events.”

ames Griffiths, Claire Lukens and Roger May, who is a forestry consultant based in Tasman District, were behind the article.

May said his work identified 4719 landslides in the study area, most of which occurred during Gita or were extended during Gita. Of the total, 10 to 20 only had “close to the same shape” pre- and post-Gita, he said.

Those 4719 landslides covered about 179ha in total, ranging in size from 0.001ha to 1.2ha.

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