Lower Hawkesbury Estuary
The Lower Hawkesbury River Estuary is a drowned river valley, which was incised into Hawkesbury sandstone bedrock during the historical ice ages, when ocean levels were much lower then present 1. The estuarine areas of Hornsby Shire extend from the ocean entrance at Broken Bay upstream to Wisemans Ferry. There are a number of major tributaries to the Lower Hawkesbury Estuary including Mangrove, Berowra, Mooney Mooney, Mullet, and Cowan Creeks.
Estuaries are influenced by both fresh and salt water inputs, making them unique natural areas. They provide a variety of habitats that support plants and animals in a rich, diverse and highly interrelated web of aquatic and terrestrial ecosystems 2. The ecology of the Lower Hawkesbury is diverse, containing mangroves, seagrasses, saltmarshes, soft sediments and rocky foreshores 1.
The catchment is unique in that the foreshore areas contain significant forested areas with relatively little foreshore development. The majority of the foreshore and adjacent land is national park 3. The drowned river valley morphology, with steep sandstone slopes and incised gorges has meant foreshore areas are largely only accessible by boat. Those foreshores that are relatively flat are mostly occupied by private development or natural mangrove barriers. The large extents of national park and the rivers steep topography have limited access and development of foreshores, preserving the natural character and beauty of the estuary 4.
With its tall, highly weathered vertical sandstone cliffs and gorges, open waterways, secluded bays and expanse of natural vegetation the Lower Hawkesbury is one of the most visually spectacular waterways in NSW. The area is rich in both Aboriginal and European heritage and its accessibility to the population of Sydney and the Central Coast make it a very popular destination for a large number of recreational visitors 1. In addition, the Lower Hawkesbury provides a valuable conservation and educational resource with studies being conducted by students and professional researchers.
The most pressing issues facing the estuary as identified by the Berowra Creek and Brooklyn Estuary Management Plans are:
- Catchment runoff
- Discharge from boats
- Sewage disposal
- Boating and tourism pursuits
- Aquaculture and fishing
- Marine and catchment ecology and diversity
- Heritage and cultural values
1 WBM Oceanics Australia, 2006. Brooklyn Estuary Management Plan. WBM Oceanics Australia.
2 NSW Government, 1992. Estuary Management Manual. Crown Copyright, Sydney.
3 Kimmerikong, 2005. Scoping Study: Hawkesbury-Nepean River Estuary management Final Report. Kimmerikong Pty Ltd.
4 BMT WBM, 2008. Draft Lower Hawkesbury Estuary Management Plan. BMT WBM Australia.
