Latitude -31.00, Longitude 152.95
Located in the Mid North Coast Region of NSW, nearest large town Kempsey
Source: Macleay River Estuary Processes Study
The region from Kempsey to the coast was once covered by the ocean. A sea level high occurred during the Pleistocene period around 120,000 years ago (the Last Interglacial period, 117,000 to 133,000 years before present). At this time, sea levels were around 5 metres above their present levels (Troedson et al., 2004). The last glacial period between 25,000 and 15,000 years ago saw sea levels around 110-130m below their present level. After this, sea levels rose rapidly and reached the present level around 6,500 years ago, in the Holocene period. Sea levels have remained within 1 to 2m of their present levels since that time (Troedson et al., 2004).
Elevated sea levels inundated the pre-Holocene Macleay Valley and resulted in the deposition of a transgressive (mobile) sand dune between the headlands (former islands) of Crescent Head, Hat Head and South West Rocks. This would have been the first boundary blocking the ocean and at the same time forming a lagoon to the west of the sand where estuarine mud and marine sediments accumulated.
The Macleay River is estimated to have a catchment of some 11,500 sq km. There is a considerable drop in elevation from the upper reaches of its catchment in the New England Tableland (elevation 1200-1600m) to the coast and the river has carved out deep gorges and valleys utilising the power of gravity. On its journey, the river acquired sediment from the erosion of the tableland and carried it until it was deposited as the flow of the river slowed in the lowlands close to the coast.
The lagoon mentioned above was the penultimate destination of the Macleay River before it exited to the Tasman Sea at Grassy Head. The shallow waters of the lagoon slowed the speed of the river allowing alluvial deposits to drop to the floor of the lagoon and eventually produced the present deltic plain. The present day Belmore and Clybucca swamps represent the last areas of the central mud basin which are continuing to slowly infill with sediment transported by Kinchela Creek and Belmore River.
The deposition of unconsolidated estuarine and floodplain sediments in the coastal region of the Macleay Valley has provided a resource of reasonable quality groundwater which Kempsey Shire Council and local residents have been able to tap.
The forces of geology can be seen at work in the migration of the Macleay River entrance from Grassy Head in the 1800s to just north of South West Rocks in 1893 when a major flood breached the sand barrier which was formed in the pre-Holocene period.
The Macleay Valley is located in the Mid North Coast Region of New South Wales and its main town is Kempsey. You can see the Belmore Swamp via Belmore Road between Gladstone and Crescent Head. Clybucca Swamp lies between South West Rocks and Clybucca. Large sand dunes are located in the southern section of Hat Head National Park.