Recent, Rapid Evolution of the Lower Mary River Estuary and Flood Plains

The Lower Mary River is located 90 km to the east of Darwin, the capital city of the Northern Territory of Australia. The wetlands of the Lower Mary are a valuable ecological and economic resource supporting tourism and primary industry. The wetlands have had minimal disruption by human interaction and form a large component of the Northern Territory’s coastal wetland systems. The top end of the Northern Territory is in the wet-dry tropics where the annual rainfall of 1,700 mm falls mainly between December and April. The region also experiences regular cyclonic activity during these periods. The wetlands and floodplains formed up to 5,000–8,000 years ago when sea levels stabilised. The coastal plains prograded rapidly and extensive mangrove forests and freshwater habitats formed. It has been evident that during the last 50 years the coast has receded, the estuarine channels have expanded and become deeper and wider and tributary channels have grown across the flood plains invading previous freshwater environments. The cut and no recover model of coastal retreat is proposed as the dominant process of coastal erosion allowing the tidal creeks to expand onto the floodplains and change the environment from dominantly freshwater to saltwater. It is forecast that over the next 40 years the Lower Mary River estuary may continue to grow and become similar to neighbouring estuaries and those of the north-facing coast of the Northern Territory.