history of the Creek 3 ecosystem and the origin of its partial destruction
on New Years Eve 2001
The unique ecosystem surrounding
Creek 3 has been largely destroyed by uncontrolled salt water flooding.
This damage may be remediated by the provision of levies, the replacement
of the original pipe at the entrance of Creek 3, desalinisation of affected
wetlands, and provision of frog habitat lost by tree death.
60 years ago a unique ecosystem initiated around Creek 3 at the western
end of Kooragang Island, NSW, Australia. Early last century as part of a
program to convert a morass of saltpans, swales and industrial fill to productive
freshwater habitat a series of culverts were built on tidal creeks in the
area. Higher ground became grazing land and Casuarina forest offered foraging
habitat for a range of waterbirds, especially when flooded after heavy rain.
As the salt leached from saltpans they became grazed flats and after heavy
rain shallow ponds supporting a myriad of wetland wildlife including large
numbers of frogs. The swales became more permanent freshwater ponds surrounded
by sedges and patchy forest. One large area of more permanent saline mudflat
habitat was an important “refueling” site for small migratory
waders (many threatened species) from the frozen tundra on the other side
of the world.
In the early 1990s
a population of endangered Green and Golden Bell frogs was located in
this area. Further investigation showed this population was one of the
largest surviving in NSW. This area was also shown to support the threatened
Australasian Bittern another species depending on freshwater habitat.
The number of other rare species dependent on the freshwater habitat is
not known as extensive fauna surveys were not conducted before a program
of uncontrolled salt water flooding by the opening and widening of the
old estuarine flow lines was initiated in the early 1990s.
|One area, the
freshwater wetlands surrounding Creek 3, has received particular attention
by conservationists. A pipe was placed at the mouth of the creek in
about 1934 to restrict tidal flow. With the culvert in place mangroves
had maintained vigorous growth until at least 1974. However, by 1993
considerable die off
of mangroves at the upstream end of this creek was apparent. A report by
the University of Newcastle recommended clearing of the pipe to restore
tidal flow would restore mangrove growth. Subsequently the pipe was cleared
of rock fill and although subsequently driftwood often blocked the pipe
vigorous mangrove growth was re-established.Even
mangroves which were apparently dead sprouted new growth even at the part
of Creek 3 furthest from the creek entrance.
There was clearly no need to further increase flow into the Creek 3 beyond
the proper maintenance of the pipe and preventing frequent blockage by driftwood.</span>
an intention to open
the mouth of the creek to 30 meters was eventually reduced to a development
application to open it to 2 meters.An
hydrological report suggested that increased tidal flow could damage Green
and Golden Bell Frog habitat and the development application was granted
under the condition that no increase of the tidal footprint into freshwater
wetland was tolerated. Therefore, a suitable structure had to be provided
to satisfy this condition.
the old pipe (90cm diameter/ 6361cm2 area) was replaced by an insubstantial
log barrier which not only had an area of flow almost twice that of
the old pipe but allowed increasing flow with time, as tidal scouring
rapidly enlarged the open area at its base ( 200 cm width x 40 cm
depth/ 8000cm2). By new years eve 2001 a combination of high tides,
the large gap under
the new culvert, and
erosion of the insubstantial foundation (allowing flow around the structure)
resulted in massive flows of salt water into Green and Golden Bell Frog
habitat north of Creek 3 at the end of December 2001
water flooding has altered or is altering most freshwater habitats
in the area to dense mangroves. These mangrove areas offer little
diversity of wildlife .In fact even the authorities promoting the
salt water flooding have themselves pulled up mangroves in their management
area to preserve bird habitat. Recently an international authority
has described mangrove infestation of mud flats in the area as a major
problem to the survival of threatened bird species.
At the western
end of Kooragang Island salt water inundation has resulted in a devastation
of freshwater habitat and destruction of frog populations. The new culvert
is just one of a series of activities resulting in the destruction of Green
and Golden Bell Frog habitat at the western end of Kooragang Island.
this section by Rodney Wright