Wetland monitoring in the Australian tropics: saltwater intrusion processes – towards a calibrated hydrodynamic model

The Northern Territory faces land loss and saltwater intrusion due to sea level rise at a rate of up to 8mm p.a., some three times the global average. The effect that this increased rate of SLR has had on the local wetland ecosystem is significant. The Mary River coastal wetland lies below the mean spring high tide and has undergone 250 km2 of saltwater intrusion since the 1940s. This has resulted in, among other phenomena, dieback of 40 km2 of melaleuca (Melaleuca viridiflora, M. cajuputi, M.leucadendra, and M. citrolens), and an exponential increase in network magnitude. A numerical model of the Mary River has been developed using MIKE 21 to simulate the hydrodynamics of the channelfloodplainsystem; the model includes bathymetry, vegetation, dynamic inputs, temperature, andsalinity. Calibration of the model, with 3-d velocimetry, discharge, and conductivity-temperature-depth measurements at eight sites, is being undertaken. Sea level rise scenarios were simulated and likely future adaptation methods designed for these wetlands. In light of these simulations of predicted conditions over the next century, a new scoring/ranking system for both traditional and eco-engineering options was proposed. In the case of the Mary River wetlands, traditional engineering was neither required, nor beneficial; ecological engineering associated with conservation and rehabilitation was deemed a more effective management response.