Channel extension and the geomorphology of tidal creeks in Kakadu National Park, Northern Territory

Environment Australia, 1998

Internal Report 280
Cobb SM
Supervising Scientist Division

About the report

The aim of this thesis is to determine the rate, spatial extent and geomorphological character of saltwater intrusion in Kakadu National Park, northern Australia. Intrusion of saltwater into freshwater wetlands through the process of tidal-creek extension has been identified as the major coastal management problem in the Alligator Rivers Region and adjacent areas. This research acts as a facet of the Coastal Monitoring Program already existing at the Environmental Research Institute of the Supervising Scientist. Research methods were employed to document the coastal changes associated with saltwater intrusion of the Alligator Rivers Region. The progress of tidal creek extension and mangrove encroachment of the Wildman, West, South and East Alligator Rivers of the eastern Alligator Rivers Region was reconstructed from aerial photographs for the years 1950, 1975, 1984 and 1991 at a scale of 1:100,000. Specific sites were chosen from the different stream sections identified by Chappell (1988) for more detailed examination of evidence of saltwater intrusion. Detailed maps were constructed of the specified sites from aerial photographs at 1:25,000 and field surveys were mapped using a Global Positioning System.

Changes in the spatial characteristics and distribution of the tidal creeks and mangroves in the eastern Alligator Rivers Region indicate that the saltwater reach has expanded along extending creek lines since 1950. Tidal creek growth has occurred through a combination of head ward extension and tributary development. The most vigorous rates of extension were along the low-lying palaeochannel swamps of the South and East Alligator Rivers. Mangrove growth has increased at an exponential rate for the four river systems. Collation of field data suggested that different processes of saltwater intrusion are dominating the different field sites. This research has completed the current understanding of the extent of saltwater intrusion of the wider Alligator Rivers Region in Van Diemen Gulf.