Identifying and defining an erosion gully as distinct from a watercourse (or ‘stream’) may not appear to be important, or of great consequence. We contend that the distinction matters. The ramifications of confusing the two landforms, or assuming them to be similar, are enormous: for
- methods involved in achieving the Great Barrier Reef water quality targets,
- modelling of catchment dynamics and sediment yields,
- prescription of rehabilitation methods, and
- compliance with waterway management policies.
We have developed ways to distinguish and define ‘gullies’ from ‘streams’ through
- pioneering techniques for accurate, high-resolution, broad-scale mapping of gullies in the GBR catchments, and
- developing classification methods for gullies.
To undertake a classification for erosion gullies and to map them digitally from lidar imagery in the Lower Burdekin-Bowen-Bogie Rivers and Normanby-Laura Rivers catchments, we
- categorically defined what is, and what is not a gully;
- stated the criteria that are the distinguishing factors;
- defined a stream channel as not-a-gully;
- evaluated the distinction through the weight of evidence.
Applying these definitions and criteria in our gully research has
- greatly aided the technique for broad-scale mapping of gullies at high resolution,
- in the process, highlighted discrepancies with prior presence/absence mapping of gully features,
- allowed much more accurate estimation of eroded sediment volumes and erosion rates, more accurate sediment yield estimations, and
- allowed more confident estimations of rehabilitation and management costs and requirements.
Separating gullies from streams has importance for current gully management guidelines and is also being recognised in the nascent Queensland river and stream bank management guidelines.