IN THIS SECTION
The
Mitchell River Catchment
History
Activities
Climate
Fauna & Flora
Bio-physical
aspects
Management
issues
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The Mitchell River
Catchment
The Mitchell River
catchment in Tropical North Queensland, Australia,
spans 72,000 square kilometres (the size of Tasmania)
across the base of Cape York Peninsula. It incorporates
five major river systems: the Mitchell, Alice,
Palmer, Walsh and Lynd, and involves four local
government areas; namely Tableland, Cook, Carpentaria
and Kowanyama Communities Local Government Area.
History
The main reason Europeans moved
into the Mitchell River Catchment area in the
late 1800s was mining, in particular gold. There
were numerous battles between the Aboriginal
peoples and the Europeans and this is reflected
in the names of many localities, such as Battlecamp
Road. Once the miners moved into an area there
was an associated increase in demand for support
services such as food provision. This
therefore meant that graziers would follow the
miners into a new area to provide this service,
resulting in the use of the land for agriculture.
Activities
Grazing remains the most extensive
land use in the catchment area whilst mining
activities are making a resurgence due to high
base metal prices. The Mareeba Dimbulah Irrigation
Scheme established in the 1950's has also made
the upper catchment of the Mitchell and Walsh
Rivers viable for agriculture, horticulture and
small scale cattle fattening projects. Furthermore,
tourism and fishing have risen in prominence
in recent years.
The Mitchell River Catchment area consists of
mainly large grazing leases, although the exceptions
to this are the Kowanyama Aboriginal Community
DOGIT (Deed Of Grant In Trust) and the freehold
areas of Southedge Station, part of Wrotham Park
Station and many smaller blocks in the East of
the catchment. Indigenous people own several
holdings in the catchment, including Kondaparinga,
Bulimba, Bonny Glen, Oriners, Powis and Sefton.
The Catchment area also contains the following
National Parks:
- Hann Tableland National Park Mitchell
- Alice Rivers National Park
- Chillagoe-Mungana Caves National Park
- Part of Bulleringa National Park to the South
- Most of the 40 Mile Scrub National Park
Climate
The climate is tropical and monsoonal
with ninety-five percent of the mean annual rainfall
of between 800 mm and 2000 mm occurring from
November to April. The Mitchell Catchment is
the largest watershed in Queensland in terms
of average annual run-off, with a mean discharge
of nearly 12,000,000 megalitres.
Fauna & Flora
The vegetation in the Mitchell
River Catchment area ranges from the World Heritage
Wet Tropic rainforest on the eastern highlands
to the open savannah on the western and lower
Mitchell plains. The extensive mangroves and
lagoon systems at the delta of the Mitchell River
are recognised worldwide. The
permanent waters in the upper catchment are associated
with springs and water holes and much of the
catchment overlays the Great Artesian Groundwater
Province.
Few comprehensive biological and ecological studies
have been undertaken in the catchment area to
date. However, it is known that eighteen species
of animal classified as rare, vulnerable, or
endangered, including the Golden Shouldered Parrot,
the Gouldian Finch and the Northern Bettong are
known to occur in the catchment. The inshore
islands of the Gulf of Carpentaria also harbour
a rich variety of marine life, including turtles
and dugong. The Mitchell River, though poorly
studied, may possibly contain the most ecologically
diverse aquatic system in the country, reflecting
the rich variety of habitats in a large river
system with wet tropics, dry tropics and monsoonal
influences.
Bio-physical aspects
The Mitchell River catchment
occupies an area across both the Einasleigh Uplands
and Gulf Plains bioregions and abuts the Cape York
Peninsula bioregion on its northern boundary.
The river and its tributaries have long been
carving through the rough and weathered highlands
in the east of the catchment, depositing sediments
on the broad flood plains and wetlands of the
Gulf Savannah. The annual monsoonal wet season
provides a pulse of water that transports sediments,
organic matter, and, unfortunately, chemical
residues from agriculture and mining in the catchment
and, for a time, links the terrestrial and marine
environments. It is this seasonal pulse of water
that provides the major connection between different
resource uses, as well as connecting the various
communities within the Mitchell River Catchment
area. It also allows for the migration of many
plants and animals, both native and feral, whether
a beneficial or a nuisance species, as well as
shaping the land.
The Mitchell River Catchment are also contains
tropical rainforest, wet sclerophyll forest,
a variety of woodland types, savannah, tidal
plains, as well as extensive wetlands, estuaries,
and mangroves.
Eastern Highlands
The landforms in the Eastern Highlands
are dominated by hills and mountains of sedimentary
and metamorphic rock with numerous creeks and
seasonal drainage systems making very rugged
country.
Central Uplands
This region is mostly undulating
country, underlain by metamorphic and granitic
rocks. Rock outcrops of a similar but older type
also occur in a belt throughout the centre of
the area.
Western Plains
These plains form the bridge between
the high country to the east and the floodplains
to the west with a thick bed of sediments laid
down in the Tertiary period dominating the area.
Lower Mitchell Plains
This is a huge floodplain
which includes virtually the whole area where the
main tributaries join the Mitchell River. It consists
of alluvial sands, silts and clays which have
collected near sea level.
Coastal Plains
These occupy a small area along
the coast of the Gulf of Carpentaria and consist
of recently deposited marine and land sourced
clays and sands.
Management issues
Water quality
The Mitchell River
Catchment is a very large area affected by the
monsoonal wet and dry seasons. In the dry season
many rivers cease to flow, which highlights the
value of, and the need for management of, perennial
creeks and waterholes in the catchment. Part
of the Mareeba-Dimbulah Irrigation Area is within
the Mitchell River Catchment and receives water
from both Lake Tinaroo and the Walsh River. Of
increasing concern is that the pest fish Tilapia
could escape from Lake Tinaroo and make its way
into the Mitchell River Catchment. This pest
could severely impact on the environment as well
as recreational and commercial fishing industries
in the Gulf of Carpentaria. Tilapia exclusion
screens have been installed in the irrigation
channels to minimise the risk of this happening.
The intensification of agricultural crops in
the irrigation area coupled with inappropriate
irrigation practices could also impact on water
issues in the catchment.
Land degradation
There are many forms of land degradation, but
the most common in the Mitchell River Catchment
is accelerated erosion as much of the area has
very fragile soils with low fertility and minimal
groundcover. These areas erode readily if the
surface vegetation is disturbed by either natural
events, such as flooding and associated streambank
erosion, or problems caused by grazing pressure
and the associated spread of weeds.
Weeds
A wide range of weeds, with both economic and
environmental implications, have gained a foothold
in the Mitchell River Catchment. Rubbervine was
considered to be the greatest threat to large
areas of the catchment, but is being displaced
by bellyache bush (Jatropha gossypiifolia) in
two known areas. Bellyache bush is a weed species
from tropical America that blankets out native
species and has poisonous berries that have killed
cattle eating it in the absence of other feed.
Prickly acacia, chinee apple, parkinsonia, Giant
Rats Tail Grass and many other pest plants are
also commonly found in the catchment. Aquatic
weeds such as salvinia, hyacinth and cumbungi
are also threats to the Mitchell's waterways
and aquatic ecosystems. There is a need for improved
coordination and cooperation amongst the community
to control and manage these weeds.
Nature Conservation
The Mitchell River Watershed is home to a large
diversity of flora including rainforest, eucalypt
forest and woodland, savannah, wetlands, dunes
and mangroves. Only some areas of the catchment
have been intensively studied, and there is little
recorded information on much of it to use in
catchment planning. There is a sizeable reserve
of protected areas in the catchment and the Wet
Tropics World Heritage Area fringes the catchment
in the Eastern highlands. The Mitchell-Alice,
Chillagoe/Mungana Caves and the Hann Tableland
are all notable National Parks in the Mitchell
River Catchment.
Conservation areas cannot be declared everywhere,
nor should conservation interests be restricted
to parks only. All land management decisions
should include consideration of nature conservation
aims, incorporating set standards to protect
and enhance the existing environmental values
and ecosystem services of the land.
Fire Management
Fire in the Mitchell River catchment is an integral
part of the ecosystem with most vegetation communities
adapted to, and modified by, the frequency of
fire. Fire will occur whether lit naturally,
accidentally, negligently or deliberately. The
vegetation communities of woodland and eucalypt
forest are both susceptible and adapted to fire,
whilst the climatic conditions of Australia are
conducive to the propagation and spread of fire.
Firebreaks are a necessity where fire could spread
to areas where burning is not wanted. Removal
of dead plant material that could fuel a fire
and the promotion of green vegetation or the
use of fire resistant trees are effective firebreak
methods in small acreage areas, especially on
sloping land.
Fire frequency is often a question of social
response versus safety needs and fire management
is for life, property and environment - but which
takes precedence is often debated. Recent studies
have suggested that poorly timed back burning
may have a detrimental effect on certain types
of vegetation, even creating conditions that
may encourage the spread of weed species, and
has a negative impact on the animals that rely
on the suppressed native vegetation as feed or
habitat.
For more information on fire management go to the
Fire North website. Check out the web site
link that gives you access to current fire
hotspot information and lots more.
Intensive Agriculture
Although intensive agriculture is a commercially
significant land use in the Mitchell River catchment,
it represents less than two percent of the total
catchment area. It is mainly limited to the Upper
Walsh portion of the Mareeba-Dimbulah Irrigation
Areas (MDIA) and the Upper Mitchell Catchment
north of Mareeba at Biboohra, Julatten and Maryfarms.
Intensive agriculture can impact on its surrounding
environment and downstream waterways in several
ways.
Land clearing, for example, can sometimes increase
erosion and reduce wildlife habitat and cause
changes to catchment hydrology through water
extraction, changes in vegetation cover, and
the addition of irrigation water. Potential also
exists for serious environmental damage to water
quality and aquatic ecosystems through poor management
of farm chemicals and fertilisers. Many of these
potential impacts can be reduced through sound
planning and developing the capability to recognise
and address a variety of management needs to
protect and enhance the existing environmental
values and ecosystem services of the catchment.
Grazing Management
Grazing is the most extensive land use in the
catchment and properties tend to be large, with
low intensity management. Much of the
grazing lands in the Mitchell are nutrient poor
and soil fertility is greatest on river frontages
and floodplains, making these areas of high value,
both to graziers and for their biodiversity and
ecosystem services. A key element of sustainable
land use could be to consider grazing on river
banks and flats as a last resort in hard times,
as their continual use can too readily degrade
these key areas of the aquatic ecosystem. The
environmental impacts of grazing in the Mitchell
cannot be attributed to any single factor and
cattle are attracted to virtually all permanent
waters in the Mitchell.
Pasture, ground cover and fuel loading can decline
over large areas due to grazing pressure and
in turn these can be contributing factors to
weed and land degradation problems. Road and
track networks to service the industry can often
lead to erosion problems. Many of these issues
can only be addressed in the context of property
management planning that considers not only stock
management needs but also sustainable land use
and maintenance of the existing environmental
values and ecosystem services of the land.
Fisheries Management
The Mitchell River is a rich fisheries resource
and valued species for commercial and recreational
fishing found in this catchment include barramundi,
salmon, grunter and crab. The Coleman River and
North Mitchell River are also nursery grounds
for commercially fished prawn species, particularly
the banana prawn.
The Mitchell River provides an important and
varied food resource for indigenous people as
well as making a significant contribution to
the development of the commercial fishing industry
in Karumba. A growing number of recreational
fishermen are also now sharing in the fishery
resources of the Mitchell River Catchment area.
These fishery resources could be under threat
from the pest fish Tilapia if it establishes
itself in the Mitchell River Catchment. There
has also been little information gathered for
sound management of the Mitchell's fisheries.
Necessary fisheries management information should
include reports on sustainable fisheries harvest,
requirements that would require studies of the
various fish populations and their respective
abilities to sustain specific harvest levels.
Feral animals
Several feral animal species now make their home
in the Mitchell River Catchment area and includes
pigs, cane toads, horses, cats, dogs & some
species of fish. Landholders have a responsibility
to control their numbers as some of these feral
animals are declared under the Rural Lands Protection
Act 1985.
The impacts of feral animals vary between species
and the local environment. In selected areas
some feral animals have become valued resources,
but in most areas feral animals are at best a
nuisance and at worst a serious economic and
environmental threat. Strategies for feral animal
management must consider many factors if they
are to be cost effective and worthwhile but without
baseline information, feral animal control strategies
are difficult to formulate. Current information
on feral animal distribution is sketchy and very
poorly documented. Collecting information on
most feral animal species is difficult because
the Mitchell River Catchment is large and sparsely
populated by humans, therefore, there is little
information available to base any scientific
research on.
Tourism and recreation
Many areas of the Mitchell River Watershed are
used for Tourism and Recreation. From the mouth
in the Gulf of Carpentaria to the mountain ranges
of the Wet Tropics, the catchment is under increasing
pressure from recreational activities. Many of
these activities occur on land that is not designated
or supported for tourism and recreational use.
The access provided by four-wheel drives, trail
bikes and quad bikes to previously inaccessible
areas of the catchment has created an increasingly
popular recreational use that is particularly
difficult to manage. Four-wheel drives offer
self-contained travel, often producing little
economic benefit to areas being visited. Road
improvements on the Cape and Burke Developmental
Roads are now allowing greater numbers of people
in standard vehicles to access the catchment.
Management problems including fires, rubbish,
access disputes, weed dispersion, water pollution
and site impacts from camping and rest areas
(commonly in riparian zones), and public safety
issues and will ultimately increase as visitor
numbers rise. Access to the recreational resources
of the Mitchell is important to a large, but
hard to identify, segment of catchment stakeholders
and land use and management planning must recognise
and account for this.
Mining
Mining is a significant industry in the Mitchell
River catchment. It is the oldest non-aboriginal
land use in the catchment, being a significant
activity in the region for more than 120 years.
However, with the benefits have come some costs.
The social cost of early mining operations is
highlighted by boom-and-bust towns, such as Maytown,
Irvinebank and Chillagoe, the battles between
the aboriginal peoples and the miners on many
goldfields, and the mine explosion disaster at
Mt Mulligan Mine.
Despite early setbacks, not the least of these
being the remoteness of much of the region, mining
has flourished and remains a significant industry
in some areas of the catchment. Small scale alluvial
and hardrock gold and tin operations have dominated
mining activities in recent times. However, increases
in some metal prices have led to an increased
interest in other mineral deposits and large-scale
mining may commence, or recommence, in some parts
of the catchment.
Historic mining and mineral processing sites
may have many special land management issues
due to the presence of site contamination from
mining residues and other pollutants. The condition
of these sites is the result of an era in which
winning minerals was paramount and environmental
damage was not a consideration. Whilst such environmental
damage would never be acceptable today, historic
mining works are an important element of the
cultural history of many communities.
Cultural Heritage
Cultural heritage (both European and Aboriginal)
can be a deeply emotive issue that provides knowledge
of our ancestry and a sense of belonging for
many people. Cultures have clashed violently
in the Mitchell River Catchment area in the past,
but planning for a sustainable future for the
catchment can only be based on mutual recognition
of, and respect for, the values, especially environmental
and cultural, of all the communities living in
the area. There are many documented heritage
sites within the catchment and the non-indigenous
sites are mostly found within and around old
mining centres, such as Chillagoe, Irvinebank,
Mt Carbine and Maytown.
Most of the formally recorded Aboriginal sites
also occur near these mining centres and include
shelters, rock art and utilitarian evidence of
indigenous inhabitants. One cave on Ngarrabullgan
(Mt Mulligan) contains evidence of over 37,000
years of Aboriginal occupation. The distribution
of recorded Aboriginal sites near mining centres
perhaps reflects the fact that discovery of sites
by Europeans is more likely to have occurred
around areas of intensive European activity.
No doubt many more sites exist unrecorded, and
maybe even unknown, in areas cleared of their
aboriginal peoples by miners and graziers. Cooperative
management provides the best avenue to ensure
that all cultural heritage is retained. Information
about local cultural heritage is being collected
and children are being involved in school programs
to ensure the passing on of this information. |
