Persistent Waterhole 200m-Segment data for NAWRA

Persistent waterholes provide important refuge habitats. Waterhole persistence data shows the percentage of years where surface water has been identified along the stream channels during the driest period of the dry seasons from 1988 to 2015 and is derived from Landsat imagery. This dataset was created for the CSIRO Northern Australia Water Resource Assessment (NAWRA) project. This dataset uses another dataset (also available on the Data Access Portal titled ‘Persistent waterholes derived from Landsat archive for NAWRA’), where waterholes were mapped at the end of each dry season (based on available cloud-free Landsat scenes) using a Normalised Difference Water Index derived from Landsat imagery. This method is described in Sims et al. (2016) and only looks at the persistence of water within each pixel through time.\nThis dataset allows for the fact that a waterhole can vary in shape and local location through time, by providing the percentage of years that at least one water pixel is identified within along-stream segments at the end of each dry season. \nFurther information is provided as a supported attachment.\n\nLineage: The end-of-dry-season waterhole images from 1988 to 2015 were used along with an in-channel mask containing a 500m buffer from the watercourse which was divided into 200m segments along each streamline. This was done in ArcGIS where point locations at 200m intervals were extracted from the river lines (XTools Pro-> Feature Conversions->Convert Features to Points, fixed interval = 200m). These points were used to create Theissen polygons (ArcTools->Analysis Tools->Proximity-> Create Theissen Polygons) which in turn were clipped to a 500m buffer either side of the river line. \nThe percentage of end-of-dry-seasons containing at least one pixel (30m x 30m) of water within each 200m segment was calculated. Permanent dams were masked out of the images. \n