Name: LANDCARE Highly Erodible Land

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Description: Highly erodible land is defined as land at risk to severe mass-movement erosion (land slide earth flow and gully) if it does not have protective woody vegetation. To be at risk to land slide erosion a slope threshold must be exceeded. If the land has protective woody vegetation (i.e. indigenous forest exotic forest or scrub) then it is considered not at risk to severe land slide erosion nor to earthflow or gully erosion. The algorithm used to define classes of highly erodible land is as follows: 1. A slope threshold was defined for each erosion terrain (Table 3). These thresholds were obtained from published field measurements where available. 2. All pixels in a 15-m pixel DEM above the threshold defined by the pixel's erosion terrain were assigned to "high land slide risk”. 3. The pixel-based map was converted to a hillslope basis by using an aspect-based filterwitha25% risk rule(2-ha minimum mapping unit). 4. All "high landslide risk”pixels were examined to see if they could deliver sediment to a water course or not. Land was considered capable of delivering sediment if it was possible to traverse down DEM streamlines until a watercourse was reached without encountering two consecutive pixels of low slope(i.e. 5degrees). If "high land slide risk”can deliver sediment to a water course then it is labelled as "high landslide risk delivery to stream”. Otherwise it is labelled as "high landslide risk -non-delivery to stream”. 5. All pixels in moderate earth flow land were assigned to "moderate earth flow risk”. 6. All pixels in severe earth flow land were assigned to "severe earth flow risk”. 7. All pixels in gully land were assigned to "gully risk”. 8. All highly erodible land was examined to see if it had protective woody vegetation on it according to the EcoSat woody layer ( 2001). If it did then land was labelled as "woody vegetation”. In other words land is not highly erodible when there is protective woody vegetation. This algorithm produces 5 classes of highly erodible land: 1. High land slide risk –delivery to stream 2. High land slide risk - non-delivery to stream 3. Moderate earth flow risk 4. Severe earth flow risk 5. Gully risk

Service Item Id: a084942f87f647a8bbff3a5aef5b8a86

Copyright Text: Landcare Research Contract report: LC0708/094, 2008

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