Draft Proposals Paper - Full - Victorian Environmental Assessment ...

Environmental water
The River Red Gum Forests Investigation Discussion
Paper highlighted the long term environmental impact
of insufficient flooding on the survival of wetlands and
riverine forests in the Investigation area. There are already
large areas of native vegetation in very poor condition due
to insufficient flooding. If insufficient flooding continues,
these areas would eventually turn into degraded versions
of the adjoining dryland vegetation that survive on
local rainfall—such as mallee, saltbush and clay pan
communities. Under current flood regimes, the health
and expanse of wetland and riverine communities will
continue to decline, providing little resilience to the
impacts of climate change in the future.
Deterioration of the remaining wetlands and forests will
have devastating consequences for the plant and animal
communities dependent upon these habitats. The River
Murray and its associated tributaries form a vast
interconnected dispersal corridor across the eastern half
of the Australian continent. This corridor crosses climatic,
biogeographic and bioregional boundaries, maintaining
essential genetic dispersal for a wide range of aquatic and
terrestrial species. Many of our rarest and most vulnerable
species will only survive future climate change if they are
able to move significant distances along contiguous
longitundinal corridors. With its wide geographic spread
and comparatively contiguous vegetation corridors, the
Murray and its tributaries constitute the single most
significant north–south trans-continental corridor in the
country. The wetlands and riverine forests of the
Investigation area constitute a vital link in this
environmental chain.
The riverine forests of the Investigation area are loved and
visited by tens of thousands of people every year. They are
a treasured natural resource for all Victorians and their
deterioration would constitute an irreplaceable loss for
many, not least for the Aboriginal people of the area
whose cultural and spiritual connections to their Country
are profound. The tourism and timber industries of the
region would also be devastated. Already around 75
percent of riverine trees in much of the Investigation area
are dangerously stressed. If only a third of wetlands and
riverine forests were lost through insufficient flooding (a
scenario that is probable rather than merely possible)
approximately 80,000 hectares of highly significant native
vegetation would be lost in Victoria alone. Losses in both
South Australia and New South Wales are likely to be of
a similar magnitude. No other factor poses a comparable
imminent and potentially disastrous threat to the
environment of the Investigation area.
Changes to public land-use categories alone will do
virtually nothing to avert this problem. Increased reserve
system protection must be underpinned by more water
reaching wetlands and floodplain forests. There are
significant initiatives currently under way to do just that.
The Living Murray First Step plans to provide an extra 500
gigalitres per year for the six ‘icon sites’ along the River
Murray. However, it must be remembered that the
completed flooding of Barmah–Millewa forest in 2005
using around 500 gigalitres (see page 270 and Map D in
the Discussion Paper for details) only reached about half of
the Barmah–Millewa floodplain. Many stands of stressed
River Red Gums remain—including some within two
kilometres of the River Murray. Besides the
Barmah–Millewa forest example, other managed floods
have been limited to discrete sites such as the lower
Gunbower forest, Hattah Lakes, Lindsay–Wallpolla, Burra
Creek and Lake Murphy, for ‘emergency’ watering and
small ongoing allocations of water to wetlands, mostly
from Victoria’s existing environmental water entitlements.
Although insufficient, this flooding is nevertheless
extremely important to sustain these areas in the interim
until more substantial inundation occurs. However, this
flooding covers a comparatively small total area—certainly
not approaching the many tens of thousands of hectares
under threat. In particular, it does little to assist many
areas, especially outside the ‘icon sites’—such as most of
the long stretch of narrow floodplain between
Gunbower–Perricoota and Hattah–Kulkyne. In addition,
this flooding often involves small discrete flows along
channels, distributary creeks (‘runners’) and through
pumps. Except in areas near the Barmah choke there are
very limited overbank flows, so the critical ecological
connectivity between the rivers and their floodplains, and
along the length of rivers is lost. To maintain these
connections and the health of large areas of wetlands and
riverine forests will require much larger flood events,
mimicking natural floods, where water flows across much
of the floodplain as the flood pulse moves downstream.
Such a single large inundation also maximises water
efficiency—river channel heights only need to be raised
once, rather than repeatedly raised which would be the
case if different sites were flooded in separate events.
Whilst survival of the wetland and riverine forests is
dependent on mimicking some aspects of natural flood
events, it is clearly not feasible or necessarily useful to
recreate the natural flood regime of the Murray system in
total. The level of diversions required to support irrigated
agriculture preclude this option. There would also be little
value in flooding areas which no longer support significant
areas of potentially healthy native vegetation. Broadly,
the outcome sought is to maintain or restore the health
of native vegetation that is currently healthy or would be
if flooded in the near future. The question then becomes:
what regime is required to achieve this objective?
Proposed flood regimes
Clearly different ecosystems require different flooding
regimes. A major flood would be required relatively
infrequently (say once every ten years) to maintain
vegetation dominated by Black Box in a healthy state,
whereas some wetlands require almost annual inundation.
Most ecosystems dominated by River Red Gums probably
require flooding in the order of every two to five years.
The optimal regime may involve occasional major floods,
frequent small floods (perhaps not greatly different from
the current environmental watering regime) and floods of
intermediate size and frequency. To minimise the amount
of water required and maximise the similarity to natural
seasonality, deliberate floods would be timed to coincide
with natural flood events in the spring of naturally wet
years when inflows to the system are higher than usual
and floodplain soil moisture is high as a result of rain.
10 River Red Gum Forests Investigation July 2007