National Wetlands Update September 2012
Issue No. 21, September 2012
Restoring tidal inundation to improve estuarine wetland habitat in Hexham Swamp
Dean Chapman, Amanda Hyde, Hunter-Central Rivers Catchment Management Authority
Hexham Swamp, a mosaic of habitats. (Hunter
Central Rivers Catchment Management Authority)
The Hexham Swamp Rehabilitation Project involves the progressive opening of floodgates on Ironbark Creek to restore 650 hectares of estuarine wetland in the internationally recognised Hexham Swamp, part of the Hunter Estuary Ramsar Site near Newcastle, NSW.
The project aims to reinstate tidal inundation to promote the transition of dominant freshwater vegetation to estuarine wetlands. The expected outcomes include the restoration of nursery habitat for fish and prawns and an increase in visitation of waterbirds including migratory waders, protected under international agreements.
The floodgates were originally installed in the early 1970s, as part of the Lower Hunter Flood Mitigation Scheme to prevent floodwater from the Hunter River entering the swamp. However, the closed floodgates eliminated tidal inundation with negative environmental impacts evident almost immediately.
By 2002, the area of mangroves had reduced from 180 to 22 hectares, saltmarsh had reduced from 900 to six hectares and common reed (Phragmites australis) had expanded its range from 170 to 1005 hectares.
The rehabilitation project was approved by the New South Wales Department of Planning in November 2006 and the first of eight floodgates was opened in December 2008, achieving a major milestone for the project after 12 years of planning, research and stakeholder consultation.
The total cost of the project was $7 million for land acquisition, bund construction and ecological surveys. The complex process required innovative methods including the development of easements for inundation.
Ironbark Creek floodgates - 6 open, 2 to go.
(Hunter Central Rivers Catchment Management
The project is currently in stage three with six of the eight floodgates open allowing for tidal inundation of about 380 hectares.
Stage three has seen a notable transition from phragmites-dominant freshwater wetland to a mosaic of habitats including mangroves, saltmarsh and open water.
Rigorous monitoring of vegetation, birds, mosquitoes, fish and invertebrates, benthic macroinvertebrates, water levels and water quality continues. Significant bird sightings from summer 2012 include the migratory Latham's snipe and black-necked stork.
Parts of the swamp remain freshwater and continue to provide habitat for species such as the Australasian bittern, known to inhabit Hexham Swamp.
The remaining two floodgates are due to be opened later in 2012. The challenge is to continue to balance the transition without causing any deleterious impacts to water quality and wildlife while also meeting community expectations.
Implementation of earth works continues throughout stage three to improve drainage of properties on the project boundary while monitoring of mosquito populations continues.
For further information contact Hunter-Central Rivers Catchment Management Authority on (02) 4930 10130.