Much of the environmental damage in the Hunter River estuary
has been due to past practices which have altered water flows across
the floodplain. Managing water on the floodplain and protecting threatened species
are central to improving the environment at Kooragang Wetlands.
While we create freshwater ponds and block flows into or out of some areas that are
particularly important for the conservation of threatened species,
most of our water and water flow management involves:
removing culverts
In a number of tidal creeks on Ash Island, we replaced
constricting culverts (pipes) with bridges. This restored tidal
flows in the creeks and increased the extent and vigour of mangroves
along them. The effect on saltmarsh depended largely on the lie of
the land. Where surrounding land was gently sloped away from the
creek, saltmarsh increased in area as well. Where the creeks banks
were steep, increased flows were not able to reach beyond the
creek-line and saltmarsh areas were unable to expand and were
sometimes even replaced by mangroves. Fish, benthic (mud dwelling)
invertebrates, shorebirds and a number of other species were
monitored for two years before and after the culvert removal.
Numbers and variety of fish and crustaceans increased following
culvert removal, while results for birds were too variable to draw
any definite conclusions.
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Before: Tidal flows greatly
reduced by
this culvert. Photo:1993 |
Before culvert removal:
insufficient tidal flows result in very poor saltmarsh.
Photo:1993 |
After: much
greater tidal flows possible after culvert replaced . Photo:1995 |
After culvert removal:
increased tidal flows (and cattle
removal) result in mangroves & healthy
saltmarsh. Photo:2001 |
opening floodgates
Floodgates built in the Hunter River estuary have effectively
stopped tidal exchange and decreased mangrove and saltmarsh vigour
and extent. On our Tomago site, this loss of tidal exchange has
destroyed an important high tide roost site for migratory shorebirds
Our attempts to restore our Tomago site have focussed on both
restoring the migratory shorebird high-tide roost site and enhancing
fisheries nursery habitat while maintaining rainwater drainage
run-off from neighbouring properties and ensuring that tidal
influence is contained within the project boundary.
We are working with the NSW Department of Environmental
Conservation in this area. Hydrological modelling and studies have
been done; a Review of Environmental Factors completed; neighbouring
landholders consulted and written agreements are being sought for
floodgate opening to proceed. We hope to complete the opening by
June 2006.
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Before: Floodgates
stop
tidal flows into our Tomago site. |
Before: Reduced
fish and prawn habitat and loss of saltmarsh high tide roost
areas for migratory & local shorebirds. |
Before: The area of our Tomago site
where we wish to reinstate a high tide roost site for
shorebirds. Photo:2005 |
View of the future?: Spread
of tidal waters after a floodgate flap was found open in 2003. |
excavating
marginal pasture to create intertidal saltmarsh
Coastal saltmarsh is now listed as an endangered ecological community
in NSW, and in the Hunter River estuary more than 1400 hectares
has been lost in the past 50 years. As saltmarsh is valuable
shorebird and fisheries habitat, we are trying to compensate for
this loss by creating additional saltmarsh in previously unsuitable
areas.
In 2001 we excavated 3 hectares of marginal pasture to the level
of a nearby area of saltmarsh. We carefully monitored the depth
to ensure the area would only be inundated by 25 percent of the
tides – perfect conditions for growing coastal saltmarsh.
In two years the excavated area was almost completely covered with
saltmarsh species, including seablite (Suaeda australis)
and samphire (Sarcocornia quinqueflora). Most importantly
shorebirds including sandpipers and black-necked storks were sighted
using this new habitat.
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Before: Marginal pasture
Photo: 2001 |
Survey stakes were used
to mark depth of excavation. |
After: Three months after excavation. Photo:
2002 |
After: Saltmarsh
covers more than 80% of this same area three years
after excavation. Photo: 2004 |
In late 2003 we excavated a further 7 hectares in the same area.
Three viewing mounds and a pathway around the northern edge of the
saltmarsh were incorporated into the overall excavation. Monitoring
by students from the University of Newcastle has shown that this
excavation is also being colonized by saltmarsh species. The Hunter
Bird Observers Club recently recorded 24 red-capped plovers and
27 red-necked stints running along the surface, a sure indication
of the success of this saltmarsh creation.
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Before: Slashed
area of marginal pasture prior to excavation. Photo: 2003 |
Excavation to a level
that only allows 1.7metre tides or greater - perfect for
satmarsh. |
Several ponds like this one on the right
were created alongside the main excavation. These only fill
with rain and are for frogs. |
Red-capped plover have
given their seal of approval to the new saltmarsh area. |
creating inter-tidal lagoons
The Hunter estuary is the most important site for migratory
shorebirds in NSW, attracting 8-16,000 annually in the early 1970's.
Loss of high tide roosting sites in the estuary is thought to have
contributed to their declining numbers in the decades since then.
Sand dredged during the construction of Stockton Bridge in 1971
was called Stockton
Sandspit. This later became a popular high tide
roosting site for migratory shorebirds. However, by the late 1980s,
the sandspit had become overgrown with woody weeds and no longer
functioned as a high tide roost site.
In 1995 we removed the woody weeds and reconfigured the sandspit
to make a lagoon. A weir was put in place to allow only tides
greater than 1.7metres into the lagoon. Under these conditions
saltmarsh flourished and many shorebirds including eastern curlew,
bar-tailed godwits and red-necked avocets flocked in great numbers
to the sandspit at high tide.
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Before: Stockton Sandspit
overgrown with woody weeds and not functioning as a high tide
roosting site in 1985. |
Weeds were removed and a
lagoon excavated at the sandspit in 1995. |
After: Stockton Sandspit attracts thousands of
shorebirds at high tide during summer. |
Red-necked avocets,
bar-tailed godwits and sandpipers at Stockton Sandspit.
Photo: C. Herbert |
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