Australian Natural Resources Atlas

Natural Resource Topics

Estuary Assessment 2000: Western Australia

Western Australia

Location map of Estuary basins in Western Australia. Broke Inlet, Western Australia. Source: Ernest Hodgkin

Key findings

Process-based classification and condition assessment for Western Australia

Key messages

Key needs

Management arrangements

Responsibility for the management of estuaries currently lies with the Department of Environment under the Waterways Conservation Act 1976 (WA) and the Environmental Protection Act 1986 (WA). Estuarine and catchment water quality data is maintained in the Department of Environment and fisheries data resides with the Department of Fisheries. The Department of Environment collects, manages and uses data from estuaries and rivers. The department has developed rigorous quality assurance and data management procedures specifically for estuarine and water quality data. Much of the department's work is related to eutrophication, algal blooms and local estuarine management issues.

Until very recently key estuaries under risk were managed through community-based waterways management authorities. These were the Albany Harbours, Wilson Inlet, Leschenault Inlet and the Peel-Harvey Inlet. The Swan Canning estuary is managed separately under the Swan River Trust a statutory authority operating under the Swan River Trust Act 1972 (WA). The Swan River Trust is unique in that it has planning and development powers within the trust area.

Building on the experience gained from the management authorities, estuarine management is now considered an integral component of catchment management which in the Western Australian model is regional and community based. Community-based advisory committees will provide a focus for local initiatives in partnership with State agencies and local government under the umbrella of regional catchment management strategies. For example on the south coast the umbrella regional grouping is the South Coast Regional Initiative Planning Team or SCRIPT covers the region from Broke Inlet to the areas east of Esperance under which the Albany Hinterland Catchment Group works on natural resource management initiatives in the Albany, Wilson Inlet and Torbay Inlet catchments. Local estuary-specific issues are addressed by the Wilson Inlet Management Group under this regional strategy.

Community initiatives

Western Australian communities generally are highly aware of the values and management needs of estuaries. Waterwatch and Ribbons of Blue link in with agency activities in improving awareness of natural resources issues. As noted above, estuaries are managed with community-based regional strategies. Geocatch, for example, is a community-based agency partnership sponsored by the Water and Rivers Commission that is implementing extensive restoration activities on the Vasse River and Vasse Wonnerup Estuary centred on the town of Bussleton.

Around the State

From Albany east to Esperance rainfall drops off markedly and becomes much less predictable. All the estuaries along this coast are classified as wave-dominated and have seasonal bar openings. These estuaries typically open infrequently and for a short period in response to specific rainfall events that may be in summer as often as winter. Rising water tables in the over-cleared catchments have resulted in more rapid run-off. This is starting to change the frequency of bar openings (e.g. Culham Inlet which reputedly opened once in the last century has opened three times in the last ten years; the changed hydrology is having a great effect on the estuary).

Most of the catchments are heavily cleared (85%) and salt-affected and the associated estuaries are showing signs of stress, especially the Beaufort, Gordon and Wellstead estuaries. Sedimentation is a major issue in all of the estuaries along this coast. In the central part of this coastline the Fitzgerald National Park and World Biosphere Reserve has outstanding natural values and includes Fitzgerald and St Mary's inlet entirely within the park. Oldfield estuary is still largely pristine and despite a heavily cleared catchment much of the riparian vegetation remains. Oldfield is the darkest of these tannin-coloured estuaries.

In general the estuaries along this coast are poorly studied and understood. They have high tourism and recreational potential and associated development pressure. A new pressure in the form of large-scale mining for nickel, tantalite, and silver/lead/zinc in the floristically rich Ravensthorpe Range has also emerged. The South Coast Regional Initiative Project Team groups catchment communities and agencies mainly concerned with agricultural catchments and their associated estuaries. Not all catchments have active community groups and interest in estuarine and coastal issues varies along the coast.

South coast (west of Albany)

The area west of Albany to the south-west corner of Western Australia encompasses a high rainfall (falling mostly in the winter) and highly forested band of catchments. Some catchments are semi-protected state forest and others are being actively logged. The upper catchments are geologically distinct and in general are heavily cleared for agriculture. Salinity is a major problem on the wheatbelt portion of these catchments.

The estuaries along this coast facing the Southern Ocean are wave-dominated and tidal ranges are very low. In the western portion as far as Walpole/Nornalup the estuaries are only slightly modified. Broke Inlet is near-pristine with an almost completely forested catchment; half of the Walpole/Nornalup catchment is forested and good riparian vegetation remains on the lower stretches of the rivers. Many have seasonally open bars although Walpole/Nornalup is permanently open to the sea.

The catchments of the smaller estuaries between Walpole and Albany range from natural to cleared but in general are still in good condition. Even Wilson Inlet, which has been the subject of considerable attention due to the increase in macrophyte and phytoplankton growth, is still in good condition. Here the bar is artificially opened and then closes naturally on an annual basis. The eastern portion of Wilson Inlet and the neighbouring Torbay catchment are extensively drained to prevent waterlogging. Sandy soils and high nutrient loading in the shallow water in these systems has produced cyanobacteria blooms during the summer months. Torbay Inlet, which is artificially opened for brief periods in the summer, is now subject to Nodularia blooms. There is limited commercial fishing along this coast with Wilson Inlet recording the highest catches.

The Albany Harbours, Princess Royal and Oyster Harbour, permanently open to the sea, have had increased management activity since the loss of seagrasses from both harbours. Extensive macroalgae growths were harvested over a number of years without mitigating the problems of enrichment. Reduction of point sources in Princess Royal has greatly reduced the nutrient loading but little progress has been made in reducing nutrient loading from the extensively cleared Oyster Harbour catchment. Gillnet fishing for mullet, King George whiting, flathead, herring, cobbler and garfish is common in these estuaries. These estuaries are highly productive (due to anthropogenic nutrient loading and increased marine exchange).

The coastline around Albany is highly scenic with high aesthetic, tourism and biodiversity values. Community awareness and concern about estuarine issues varies along the coast. In some cases communities in the upper catchments have little connection with the coast partly because dryland salinity is the major natural resource concern.

Broke Inlet at the mouth of the Shannon River is the only estuary in near-pristine condition in this region. It is a large lagoon and is connected to the sea by a long, narrow channel through coastal dunes. The estuary is located entirely within the D'Entrecasteax National Park, which extends along the coast. Broke Inlet has many conservation values and is also important for recreational and commercial fishing. The inlet is geologically similar to many estuaries on the south coast, making it useful as a benchmark to compare with problems of nutrient enrichment and sedimentation within other inlets and estuaries.

South west

The south-west coast of Western Australia has tidal ranges of 0.5-1.0 m and estuaries in the region are wave-dominated. Many of the estuaries are now permanently open using training walls although a few are still seasonally closed. The Mediterranean climate and rainfall pattern in this region results in a floristically rich vegetation pattern, coastal heath and extensive forests in the wetter areas of the south-west corner. This region of the coast is intensively used by dairy, beef and piggery operations, and horticulture, all of which contribute nutrients to the estuaries. Bauxite and coal mining in the hinterland and sand mining along the coastal plain are the major extractive industries. Acid waters from mine dewatering is an issue in the catchment of the Leschenault estuary.

Further to the south on the Scott coastal plain that runs into Hardy estuary, intensive horticulture (e.g. potato growing) contributes high nutrient loads to the estuary. The Swan coastal plain from the Peel-Harvey catchment through to the Vasse-Wonnerup catchment near Busselton is extensively drained to prevent waterlogging on the over-cleared catchments. This has resulted in highly modified flows to estuaries and in combination with high nutrient loading land practices and low nutrient retention on the predominantly sandy soils has led to blue-green algae blooms, fish kills, and modified flows to the estuaries. Many of the estuaries in this area are extensively modified.

The Peel-Harvey is well known for the Dawesville Cut, an opening to the ocean to relieve the estuary from extensive Nodularia spumigena and macroalgae blooms. Although this has been effective, cyanobacteria blooms still occur in the tidal regions of the incoming streams. Since nutrient losses from the catchment are unabated, there is concern that the Peel-Harvey will again experience macroalgal growth. The potentially toxic Lyngbya masucla has been detected in the region. The Leschenault estuary now has a permanent opening and the southern portion has been developed for the Port of Bunbury. The estuary faces increasing development pressure. The Vasse River has been diverted to the ocean bypassing the Vasse Wonnerup estuary and at the mouth of the estuary a barrage restricts tidal inflow into this Ramsar wetland. Algal blooms and fish deaths are common in the estuary during summer and intensive agriculture and canal developments are threats to the estuarine ecology. The very small Margaret River estuary has suffered reduced flows from water abstraction, mainly for viticulture.

The south west is the fastest growing residential area in Western Australia (e.g. towns of Dunsborough and Bussleton). There is some community awareness of the issues in their estuaries and a number of catchment groups are active. Many developments are not compatible with the maintenance of estuarine values and many residents adjacent to the estuaries do not appreciate these values (e.g. complaints are often received about natural levels of plant growth and the associated smell).

Swan-Canning estuary

This estuary contains Perth and is extensively modified. The bar at Fremantle was removed in the 1890s and the Port of Fremantle has been dredged and expanded a number of times. As a result 85% of the tidal prism at Fremantle makes its way to the upper Swan resulting in a salt wedge estuary that is highly stratified in summer. Agricultural and urban catchments contribute a range of contaminants including nutrients, which lead to macroalgal blooms. Reduction of point source pollution and sewage from the estuary has led to an improvement although algal blooms during the summer period remain a problem. Urban drainage and groundwater are major contributors of nutrients to the estuary during the summer. The Swan-Canning Cleanup Program has been instituted to improve estuarine condition and to minimise likelihood of algal blooms. The Avon catchment is very extensive (the size of Tasmania) and contributes the bulk of the water flow to the Swan-Canning estuary. Flood events in this catchment can move large quantities of nutrient in to the estuary with potentially dramatic effect as evidenced by the Microcystis bloom of February 2000.

Mid-coast

This area is the stretch of coastline from Perth to Shark Bay. Shark Bay (13 000 km2) is a declared World Heritage Area and marine park due to its world-renowned stromatolite deposits. A salt lease covers part of the area and the park is extensively fished both recreationally and commercially. Dugongs graze on the extensive seagrass beds and dolphins are a tourist attraction. The Murchison River drains an extensive agricultural and pastoral catchment entering the sea at the popular tourist town of Kalbarri. Mining in the catchment has led to lead contamination of the estuarine sediments from old mine tailings. The mid-west coast is arid with sandy soils and is characterised by small riverine estuaries that are heavily impacted by agriculture south of Geraldton. Sedimentation and algal blooms are issues of concern.

Relatively little is known about these estuaries and community catchment activity is not well developed except for the Moore River where community activity is strong. The bar separating the Moore river from the ocean is opened for short periods during the winter. The catchment is extensively cleared, highly saline and affected by floods. Riparian vegetation around the estuarine portion is in reasonable condition. Estuarine water levels in the summer are sustained by groundwater inflow (high in nutrient in the lower reaches and lower in nutrients in the upper reaches).

In this region, marine and terrestrial species with tropical affinities mix with species of temperate affinities. Further research is needed to fully understand the ecological communities that are under threat in these estuaries. The estuaries in this area are important for recreational fishing. Commercial fishing is not viable due to eutrophication and habitat loss.

Pilbara

The Pilbara is a region of arid coastline with rivers that only run to the sea during the irregular wet seasons. At this time the rivers empty directly to the coast. In drier periods, the rivers peter out before they enter the ocean creating inland deltas and may seek alternative paths to the ocean in the next substantial wet. Estuaries along this coast are classified as tide-dominated with tide ranges up to 4 m. Catchments are extensively grazed and mining is a significant industry. Port Hedland and Dampier/Cape Lambert have been developed as export ports for the mining and oil industries and salt works. Karratha is a base for the offshore oil industry.

Kimberley

Estuaries from the Dampier Archipelago to the Northern Territory border in Northern Western Australia are characterised by rocky catchments with very high tides of more than 10 m. Estuaries in this region are tide-dominated and include many tidal creeks and strand plains.

Monsoonal rainfall also has a seasonally important influence on the ways these estuaries function. Many are dominated by fluvial inputs for a month or two. Extreme heat and evaporation cause stunted growth in estuary-associated vegetation such as mangroves, but little more is known about the natural processes driving these estuaries. Land tenures for this region are Indigenous and non-Indigenous leasehold, defence, mining tenement and conservation reserve. Potential impacts to estuaries include fishing activity, both commercial and recreational.

In a few areas (e.g. the Ord) aquaculture projects have been proposed or are being developed. Mining on the plateau is a significant industry and an ore loading facility is planned for Londonderry Creek. Fishing charter activity is having some minor impact. Cotton growing impacts are being assessed. Near-pristine estuaries in this area are important for cultural values, pearl aquaculture, commercial and recreational fishing, and eco-tourism.

Major areas of irrigated agriculture have been established in the Ord and will increase with the second stage of the Ord release. There is some concern that the Keep estuary will be affected by agricultural expansion into the catchment. There is evidence that abstraction has led to increased sedimentation of the lower Ord.

The level of estuary management is this region could be described as benign neglect. Management plans have already been formed for safari eco-tourism. Integrated planning agreements are needed to identify potential threats and to make specific recommendations on how to maintain and manage these estuaries in near-pristine condition.

King Edward River Drysdale River Pentecost River Keep River Ord River Prince Regent River Isdell River Lennard River Cape Leveque Coast Fitzroy River Sandy Desert Port Hedland Coast De Grey River Fortescue River Onslow Coast Ashburton River Lindon-Minilya Rivers Gascoyne River Wooramel River Murchison River Greenough River Esperance Coast Moore-Hill Rivers Swan Coast Murray River Busselton Coast Blackwood River Warren River Albany Coast Navigable state map of AWRC river basins with estuaries

Further information

For further information about the Australia-wide assessment, please contact: National Land and Water Resources Audit Phone: 02 6263 6035 Email: info@nlwra.gov.au

CRC Coastal Zone, Estuary and Waterway Management

Link to the Map Maker to make a map using this information.

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