New Zealand's Environment Reporting Series: The Ministry for the Environment and Statistics New Zealand
The data identifies five classes of land in New Zealand at risk of erosion:
1. high landslide risk – delivery to stream 2. high landslide risk – non-delivery to steam 3. moderate earthflow risk 4. severe earthflow risk 5. gully risk
Landslide erosion is the shallow (approximately 1m) and sudden failure of soil slopes during storm rainfall. Earthflow erosion is the slow downward movement (approximately 1m/year) of wet soil slopes towards waterways. Gully erosion is massive soil erosion that begins at gully heads and expands up hillsides over decadal time scales.
Erosion can have negative consequences on land productivity, water quality (via increased sedimentation and turbidity), the natural form of the land, and infrastructure.
New Zealand experiences high rates of soil erosion. In the North Island, this is mostly due to the historical clearance of forest for agriculture (see also Estimated long-term soil erosion). In contrast, erosion in the South Island is mostly due to natural processes, primarily high rainfall and steep mountain slopes.
It is important to identify areas of land at risk of severe erosion to inform land-use decisions and help prioritise regional soil conservation work.