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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Australian Catchment, River and Estuary Assessment 2002
National Land and Water Resources Audit, 2002
ISBN 0 642 37125 3
Assessment findings
Table 23. Condition of Australia's estuaries by process type.
| Class | Subclass | Near-pristine | Largely unmodified | Modified | Extensively modified | Total |
|---|---|---|---|---|---|---|
| Wave | estuary | 28 | 41 | 62 | 25 | 156 |
| strandplain | 36 | 13 | 10 | 1 | 60 | |
| other | 40 | 30 | 22 | 17 | 109 | |
| Tide | estuary | 57 | 25 | 9 | 4 | 95 |
| tidal flat/creek | 210 | 43 | 16 | 15 | 284 | |
| other | 40 | 17 | 23 | 9 | 89 | |
| River | wave–dominated delta | 28 | 24 | 30 | 12 | 94 |
| tide–dominated delta | 36 | 16 | 11 | 9 | 72 | |
| Not classified | 9 | 1 | 3 | 0 | 13 | |
| Total | 484 | 210 | 186 | 92 | 972 | |
Tidal flats and creeks
Most of Australia's estuaries are tide-dominated systems with tidal flats and creeks particularly dominant (29%). Tidal flats are low gradient accumulations of fine sediment or mud, often dissected by numerous tidal channels. Tidal flats occur in regions that have a high tidal influence and are most extensive in macrotidal regions (e.g. Northern Territory, north-west Western Australia) and along muddy low-gradient coastlines (e.g. Gulf of Carpentaria).
Tidal flats drain out at low tide and have mangrove-lined channels with expanses of saltmarsh located further landward, between intertidal and supratidal levels.
Tidal creeks are small tidal channels cut into coastal flats. They are often associated with tidal flats, draining and filling the flats during each tidal cycle. The banks of tidal creeks are generally above the high tide limit. An example of a typical tidal flat system is Moonlight Creek located on the south coast of the Gulf of Carpentaria.
Tidal flats and creeks are well mixed and often naturally turbid. Tidal flows usually have enough velocity to re-suspend fine sediments (mud). Seventy-four percent of Australia's tidal flats and creeks are in near-pristine condition. Most of the tidal flats and creeks have small coastal catchment areas, often in undisturbed condition.
Note:
Near-pristine
Largely unmodified
Modified
Extensively modified
True estuaries
From a geomorphic perspective an 'estuary' is a discrete type of coastal waterway. They are defined as the 'seaward limit of a drowned valley, which receives sediment from both river and marine sources and is influenced by wave, tide and river processes'. Of the coastal waterways assessed, 26% were classified as 'true' estuaries in a geomorphic sense (16% are wave-dominated estuaries and 10% are tide-dominated estuaries).
Wave-dominated estuaries are characterised by a sandy barrier parallel to the shoreline at the mouth with a low energy central basin landward. Built by wave action, the bar often constricts the entrance of wave-dominated estuaries. Wave dominated estuaries have a high tendency to trap sediment and are generally partially mixed. This type of system tends to be seasonally stratified with naturally low turbidity (except during high winds or flood events). Nutrients recycled from the sediments in the central basin may make systems susceptible to algal blooms. An example of a typical wave-dominated estuary is Lake Illawarra in New South Wales. Wave-dominated estuaries are also known as barrier estuaries, coastal lakes or lagoons.
Geomorphic formations such as the barrier, and flood and ebb tide delta, coupled with the longshore drift and accumulation of marine sediment, reduce the opportunity for ocean exchange and flushing of wave-dominated estuaries. In Australia, wave-dominated estuaries are popular for recreational and residential development. Sediments and nutrients from the catchment generally accumulate in the estuary, making wave-dominated estuaries susceptible to problems associated with poor flushing and increased nutrient levels.
The natural susceptibility of wave-dominated estuaries to development pressures is reflected in the high proportion of modified wave-dominated estuaries. A common management response to water quality problems and navigation difficulties is to artificially open the entrance. Artificial opening is achieved either permanently with training walls (e.g. Wallis Lake New South Wales, Lakes Entrance Victoria) or by bulldozing the beach berm (e.g. many of the smaller New South Wales and Victorian wave-dominated estuaries). This can have serious ecological consequences (e.g. immature black swans can become stranded in wetlands and unable to travel to open water, such as at Smith's Lake and Lake Cathie - Lake Innes, New South Wales). Artificial opening strategies are the subject of many community debates. Certainly strategies need to recognise a range of management objectives and values including waterbird breeding, fisheries, navigation needs, water quality, flooding risk and likelihood of rapid re-closure from seasonal wave conditions.
Note:
Near-pristine
Largely unmodified
Modified
Extensively modified
Tide-dominated estuaries are typically funnel-shaped, and contain elongated sand bodies known as tidal sand banks in the main tidal channel(s). These elongated sand banks are generally orientated parallel to the direction of tidal flows. Tide-dominated estuaries trap coarse sediment as part of the development of the tidal sand banks and fine sediment on the margins in the form of intertidal flats, mangroves and salt marshes. Driven by higher velocity tidal flows than their wave-dominated counterparts, tide-dominated estuaries generally have naturally high turbidity and are well mixed throughout the year. An example of a typical tide-dominated estuary is Adelaide River in the Northern Territory.
Tide-dominated estuaries are generally highly turbid due to strong tidal currents. The relatively unconstricted entrance and strong tidal currents enhance flushing, relieving them from some of the impacts of nutrients and sediments. These systems act as a conduit for sediments and nutrients from the catchment to the near-shore marine zone. This underlies the importance of improved catchment management to reduce sediment and nutrient loads in the river basins with these types of estuaries (e.g. Fitzroy River adjoining the Great Barrier Reef).
Deltas
Seventeen percent of Australia's estuaries are deltas (10% wave-dominated, 7% tide-dominated). Deltas are broadly defined as coastal accumulations of river-derived sediment that generally protrudes into the near-shore environment. Deltas are generally net exporters of sediment due to the high river influence.
Wave-dominated deltas have bow-shaped shorelines, poor flushing generally low turbidity and experience partial mixing and salt wedges. Tide-dominated deltas are generally turbid and well mixed.
Sediment delivered to the coast in regions of high wave energy (e.g. New South Wales ) may be transported along the shoreline and the wave-dominated delta may not protrude (e.g. Brunswick River, New South Wales). An example of a typical wave-dominated delta is Nassau River (Queensland); an example of a typical tide-dominated delta is McArthur River (Northern Territory).
Both tide and wave-dominated deltas contribute substantial amounts of sediments and nutrients to the near-shore environment. Along the New South Wales coast, sediments and nutrients escaping deltas are transported along the coast by wave and ocean currents. Along the Queensland coast progradation of deltas into the near-shore environment may be extensive (e.g. Burdekin River).
Note:
Near-pristine
Largely unmodified
Modified
Extensively modified
Jerusalem Creek: a wave-dominated strandplain in near-pristine condition.
Photo: Department of Land and Water Conservation, New South Wales.
Strandplains, coastal lakes and lagoons
Six percent of Australia's estuaries are drainage points for strandplains. Strandplains are sand bodies that run parallel to the shore and contain beaches, swales and dunes. They are found along prograded linear coasts. Strandplains are not associated with embayments, but are dune systems inter-filling between headlands.
Strandplains are usually associated with small to negligible river input and drain the immediate area of dunes and swales. Wetland and coastal heath systems are often extensive, with creeks usually only intermittently open to the ocean. An example of a strandplain is Jerusalem Creek, New South Wales.
Note:
Near-pristine
Largely unmodified
Modified
Extensively modified
Estuaries of Australia's capital cities
The diversity of estuary types distributed around Australia is indicated by the estuaries associated with Australia's capital cities
| Port | Estuary class/subclass | Condition | |
|---|---|---|---|
| Darwin | Darwin Harbour | tide/other | largely unmodified |
| Brisbane | Brisbane River | river/tide-dominated delta | extensively modified |
| Sydney | Port Jackson | tide/other | extensively modified |
| Melbourne | Yarra River | river/tide-dominated delta | extensively modified |
| Hobart | Derwent River | tide/other | extensively modified |
| Adelaide | Port River Barker Inlet | tide/tidal flat/creek | extensively modified |
| Perth | Swan River | wave/estuary | extensively modified |
Application of the results
Excess nutrients in estuaries cause algal blooms.
Photo: Rochelle Lawson.
A more detailed study of Australia's modified estuaries enhances our understanding of their condition and the pressures they face. The assessment provides an on-line framework to encourage others to contribute information and knowledge, on what is and is not known, for the estuaries where they live and work. This information will enhance our collective understanding of estuarine management issues and the appropriateness of different management strategies for preventing further degradation and improving estuarine condition.
Limitations of the assessment
The assessment provides an excellent overview of the condition of Australian estuaries with some limitations:
- although based on existing data where available, the assessment is highly subjective and grounded in expert opinion;
- insufficient data was available to support a quantitative assessment of the condition of many Australian estuaries;
- due to the lack of data on both modified and near-pristine estuaries, the assessment was unable to define precise benchmarks to establish the extent of change for Australia's modified estuaries; and
- assessments were conducted as snapshots in time and do not provide trend information.
Key pressures on estuaries: common challenges facing Australia's modified estuaries
- Excess nutrients - nitrogen and phosphorus, are necessary for plant and animal growth. High levels of nutrients can cause algal blooms or epiphytic growth that block sunlight and lower oxygen levels in the water. This can result in the loss of underwater vegetation and fish kills. Nutrients are sourced from decaying plant and animal material, eroded soil, sewage, industrial discharges, stormwater run-off, fertilisers, garden waste and agricultural run-off.
- Sedimentation - infilling as a result of the contribution of fine
grained sediments from the catchment and near-shore marine sands is
particularly significant for wave-dominated systems.
Excess sediment can cause problems as many nutrients, toxicants and pathogens are transported with the sediment. Vegetation clearing and land use in the catchment can cause an increase in catchment erosion and sediment inputs to the estuary. For tide-dominated systems particularly, where sediments are transported through the estuary, plumes of sediment extend offshore, particularly after floods and heavy rains. - Habitat loss - estuarine habitats provide food, cover, migratory corridors and breeding/nursery areas. These habitats perform other important functions (e.g. improving water quality and reducing flooding). Important habitats (e.g. shallow sandy flats, seagrass beds, saltmarshes, mangroves and floodplain wetlands) have been affected by drainage, clearing for commercial and recreational developments and dredging.
- Changes to natural flows and tidal flushing - freshwater is an increasingly valuable resource in a continent as dry as Australia. The construction of dams and weirs and the extraction of freshwater has altered the amount and flow regime of freshwater entering estuaries. Natural drought cycles increase the adverse effects of these changes, including increased sedimentation and impacts on fish reproduction and shellfish survival. Many structures restrict freshwater and tidal flows (e.g. bridges, causeways, floodgates and levees).
- Pathogens and toxicants - pathogens are disease-causing organisms such as viruses, bacteria and parasites. Toxicants such as heavy metals, pesticides and polychlorinated biphenyls accumulate in the tissues of plants and animals. Pathogens and toxicants can lead to closures of shellfish areas, fisheries, and swimming and surfing beaches. Sources of pathogens include human and animal waste from boats and marinas, sewage, and stormwater. Toxicants enter estuaries via industrial discharges, stormwater, agricultural run-off and shipping.
- Introduced pests - intentional or accidental introductions of biota from other environments can result in unexpected ecological and economic impacts to estuaries. Introduced organisms can destroy native populations, introduce pathogens, degrade habitats and interfere with fishing, boating and swimming. Examples include rice grass and the black striped mussel. Sources of introduced pests include ship ballast waters, aquaculture and the aquarium trade.
- Modifications to ocean entrances. Training walls and artificial entrance opening regimes can have significant impacts on estuarine ecology such as larval recruitment to the estuary.
Photo: Department of Natural Resources and Environment, Victoria.
Case study: Gippsland Lakes
Illustrating the complex nature of estuary management
Introduction
In 1995 the funding and responsibility for 12 local ports in Victoria was transferred from the Port of Melbourne Authority to the Department of Natural Resources Environment. In 1996 the Department of Natural Resources and Environment outsourced the management of these ports and appointed local port managers. In the case of the five Gippsland Regional Ports the manager is the Gippsland Ports Committee of Management.
The Port of Gippsland Lakes encompasses one of Australia's largest estuaries stretching from Sale in the west to Lakes Entrance in the east. The port is the largest of the Gippsland Ports and covers the lower reaches of the Latrobe, Nicholson, Mitchell and Tambo rivers as well as Lakes Wellington, Victoria and King.
Photo: Department of Natural Resources and Environment, Victoria.
The Gippsland Lakes are home to one of Victoria's largest fishing fleets (in terms of vessel numbers [about 65] and landed catch value) and an increasingly popular tourist and recreational boating destination due to its sheltered waters.
Access to the ocean is via Lakes Entrance. This man-made entrance was opened in 1899 and has provided an important contribution to the region's history and economy since that time.
Two of the major issues for the Gippsland Lakes are the silting of the channels and entrance (which requires ongoing dredging to maintain ocean access and navigable internal channels) and the increased demand for land based recreation and tourism facilities (which are sometimes incompatible with, and are placing pressure on the port areas).
Estuary use and value
The Port of Gippsland Lakes is used by both commercial fishermen, who use the entrance to access the ocean, and recreational boaters, who take advantage of the sheltered waters within the lake system for fishing and cruising.
Photo: Department of Natural Resources and Environment, Victoria.
The main commercial fishing port is located at Lakes Entrance and provides catch discharge and processing facilities as well as maintenance facilities (e.g. slipways) and moorings. There are also boating facilities located at Paynesville, including marinas, a boat yard and associated services.
To meet the needs of the port users the estuary primarily has to provide a safe, navigable entrance to the open sea and navigable internal channels.
Benefits and estimates of monetary value
The commercial fishing industry is the major user of the Lakes Entrance channel with approximately 13 000 crossings annually.
The Lakes Entrance Fisherman's Co-operative supplies 35-40% of Melbourne's fish product and is a key employer in the region.
Overall Lakes Entrance channel users, including commercial fishermen and recreational boaters account for:
Photo: Department of Natural Resources and Environment, Victoria.
- 32% of regional employment (67% contributed by the commercial fishing sector alone);
- 29% of household income;
- 35% of total regional economic activity (with commercial fishing accounting for 70%); and
- 0.5% of Victoria's entire employment, income and output.
Management issues
The major management issue at Lakes Entrance is the siltation of the entrance and immediate internal channels. The action of normal coastal processes is to form a sand bar across the entrance to the lakes. The water flows within the estuary caused by having an opening to the sea leads to siltation of the internal channels. To maintain safe navigability ongoing dredging of both the entrance and internal channels is required. To alleviate the problem and maximise the efficiency of dredging the internal channels a new sand transfer system has been installed at a cost of approximately $1.5 m. This system pumps the dredge spoil through a series of pumps and pipes back to the open ocean environment. The system has resulted in a reduction of the net inflow of sand into the estuary.
Photo: Department of Natural Resources and Environment, Victoria.
Other management issues include dealing with the sewage discharged from boats (both commercial and recreational) and containing the contaminants (both airborne and water-borne) that are generated during boat servicing/repair.
One final issue facing the Port Manager is that of balancing the requirements of an industrial port with those of a burgeoning tourist industry. The increasing demand for shore based tourism and recreational facilities places pressure on the areas in which port activities have traditionally taken place.
Conclusion
The issues in the Gippsland Lakes are similar though on a different scale to those experienced in all estuaries that contain port facilities. They highlight the need for a balanced approach between natural resource management and development.
Case Study: South-east Queensland regional water quality management strategy
Illustrating the complex nature of estuary management
South-east Queensland's coastal regions and waterways, including Moreton Bay, are complex ecosystems that support healthy populations of dugongs and turtles, migratory wading birds and major recreational and commercial fisheries. Population increases in south-east Queensland have the potential to seriously impact on the ecological and economic health of its waterways and catchments. Nutrients (particularly nitrogen), fine sediments and, to a lesser extent, pesticides and heavy metals have already been identified as causes of significant environmental problems within these systems.
In response to these threats, government, industry and community stakeholders are working to implement a regional water quality management strategy.
The strategy forms part of the South East Queensland Regional Framework for Growth Management 1998 and is a joint Commonwealth, State and local Government initiative covering the south-east Queensland region, including coastal waters, estuaries and freshwater streams from Noosa to the Gold Coast and west to the Great Dividing Range. It covers 15 major catchments with a combined catchment area of approximately 22 352 km2 and includes 19 local government areas.
- Stage 1 (1993-1995) reviewed available information and delivered a model for strategy development.
- Stage 2 (1996-1998) focused on urban areas in the lower catchment, marine and estuarine areas of the Moreton Region and was developed by six local councils, the Environmental Protection Authority and other State agencies, industry and community.
- Stage 3 (1999-2001) of the strategy is focusing on the freshwater catchment areas of the Moreton region and incorporates the north (Noosa, Maroochy and Mooloolah) and south (Logan, Albert and Gold Coast) regions.
This collaborative approach has been a key characteristic of the strategy. Based on strong local political leadership and advocacy, it has allowed the development of an effective, 'whole of community' organisational approach to action plans that protect and enhance water quality and ecological/economic sustainability.
The vision
South-east Queensland's catchments and waterways will, by 2020, be healthy living ecosystems supporting the livelihoods and lifestyles of people in south-east Queensland and will be managed through collaboration between community, government and industry.
Strengths of the strategy
The major strengths of the strategy are:
- effective collaboration between government, industry and community in decision making;
- a collaborative and coordinated approach to the scoping, gathering and communication of scientific information;
- providing stakeholders with information as it comes to hand;
- consideration of social, cultural and economic impacts of environmental choices;
- unified Healthy Waterways campaign;
- integration with regional planning and statutory processes; and
- whole-of-community monitoring and feedback.
Major achievements to date
Important achievements of the strategy to date include:
- a much better understanding of ecosystem processes and effects of pollutants;
- agreed ecological health indicators, such as seagrass depth range, sediment nutrient fluxes, denitrification efficiency, and phytoplankton productivity and abundance;
- environmental values, goals and water quality objectives defined for marine and estuarine waterways;
- sustainable point source nitrogen loads determined for different waterways;
- technology to track sewage;
- a framework for sewage management for the next 20 years; and
- continuing determination of sustainable stormwater loads and a framework for stormwater management.
Key lessons
- Large scale planning process can often take time, including an initial gestation period, during which few tangible results appear. This period often involves getting the scope of the project right and building the community involvement processes necessary for later success (which often then come with a rush). Patience during these early stages is important, as is rapidly exploiting consequent opportunities for delivery.
- It is necessary to develop an effective process for inter-agency interaction. It is important to never give up on this issue.
- Local political leadership can play a key role in obtaining and maintaining support and funding and in dealing with the bureaucratic issues.
- The Commonwealth Government can play a key role in providing seed funding and political/social imprimatur to get parties together.
- It is crucial to get scientists, industry and community representatives on decision-making committees where they can interact directly with politicians and State government officers.
- The project must be grounded within the established regional planning framework, ideally through a catchment-based approach.
- A common vision must be developed early in the process to maintain focus and momentum.
- There is no substitute for the delivery of good information by scientists speaking effectively with one voice and the community confidence that results from getting this process and the information right.
Conclusion
The strategy is an example of a successful regional planning process. Its success is due to:
- effective collaboration between government, industry and community;
- providing consistent information directly to all participants, including scientific findings, computer modelling predictions, impacts and costs of various management actions and impacts and costs of doing nothing;
- developing healthy waterways as a unified identity and vision that can be used by all participants; and
- all participants agreeing to own and implement on-ground management actions to achieve the vision.
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