The Swan Canning river system

The Swan Canning river system drains a catchment of 2 090 km2, stretching from near Gingin in the north to Armadale in the south (see Figure 1). It includes the Swan and Canning ‘estuaries’, which are influenced by both marine tides and river flows, and the Swan and Canning ‘rivers’ and their tributaries. The Swan River flows from Walyunga National Park where it meets the Avon River (with a catchment of 126 000 km2), down to its mouth at Fremantle Harbour. The Canning River originates in the Darling Ranges, and joins the Swan River in Applecross, downstream from the Kent Street Weir. 

The Trust is directly responsible for the Development Control Area (DCA) and Riverpark. The DCA includes the waters of the Swan and Canning rivers and a thin strip of land fringing the rivers including adjoining parks and recreation reservations. The Riverpark is 72 km2 of waterways, public land and adjoining river reserves of the Swan, Canning, Helena and Southern rivers.

The Swan Canning river system has 31 sub-catchments. These have a variety of urban, industrial and agricultural land uses. Urban development surrounds the lower estuary and middle reaches of the Swan and Canning rivers. Land uses in the upper estuary and river zones of the Swan River include cattle grazing, horticulture, light industry and urban settlements.

Historic land uses along the edge of the rivers have left a legacy of contaminated sites. These include rubbish tips and heavy industry, from wool scouring plants in Fremantle to a fertiliser factory and foundries in Bayswater and Bassendean.

A changing environment

Humans have permanently changed the Swan and Canning rivers and their catchments. The Swan River was mostly brackish before the rocky Fremantle bar was removed by early settlers in the 1890s and the area dredged to build the Fremantle Harbour. The lower reaches of the river system became a permanently open estuary that changed from fresh/brackish in winter and spring, to saline during summer and autumn. Our drying climate has caused the bottom waters of the middle and lower reaches of the river system to be saline for most of the year.

It is not possible to return the river system to its original condition. Instead, the Trust attempts to keep the rivers healthy and resilient in the face of growing pressures and demands of urban development, climate change, agriculture, industry and recreational and commercial use.

Threats to river health

There are many threats to the environmental health of the Swan Canning river system. In 1999 the Trust identified excessive nutrients (nitrogen, phosphorus and organic matter) as the primary cause of algal blooms in the rivers. Nutrients flow into the rivers from urban and rural catchments, and old landfill sites.

Excess nutrients fuel algal blooms, which die and fall to the river bed (see Figure 2). The algae are broken down by bacteria. This process removes oxygen from the water, which kills fish and can also result in the release of nutrients from the sediment. These extra nutrients and organic matter can in turn, help to fuel further algal blooms.

The low oxygen conditions commonly occur in the middle and upper Swan and Canning rivers, particularly in autumn when water flow increases and in the spring when river flow decreases. These conditions have become worse in recent years due to our declining rainfall.

Reducing the nutrients that enter the rivers will reduce algal blooms and improve oxygen conditions. The result will be a healthier and more resilient river (see Figure 3).

 

The Trust and DoW have identified a number of other threats that affect the health of the Swan Canning river system. They include:

• erosion and sedimentation
• climate change
• changes in the quantity of water flowing through rivers and drains
• loss or degradation of salt marsh and shoreline vegetation
• non-nutrient contamination
• acidification
• a ‘salt wedge’ of water pushing upstream that does not mix with fresh surface water heading downstream.

Managing the Swan and Canning rivers and their catchments

The Swan River Trust Act 1988 established the Trust in 1989 to simplify river management, which had become the responsibility of around 30 agencies and Local Government Authorities (LGA). The Trust was seen as a solution to an overlap of responsibilities and poor coordination, especially in relation to planning and development applications.

The Swan and Canning Rivers Management Act 2006 came into effect in 2007. The Act outlined the Trust’s responsibilities to provide a more coordinated and collaborative approach to managing the river system. These included to:

• establish the Swan Canning Riverpark and DCA
• protect and enhance the ecological and community benefit and amenity of the Riverpark and DCA
• prepare and implement a River Protection Strategy (RPS), which describes the responsibilities that agencies and LGAs have to protect and enhance the Riverpark
• advise the Minister for the Environment on development proposals in the DCA
• provide advice to LGAs and the Western Australian Planning Commission (WAPC) on town planning issues affecting the rivers
• promote community awareness of issues that affect the health of the river system and increase community involvement in river protection and restoration.

In fulfilling their role the Trust delivers programs in six areas:

• strategic programs to achieve collaborative and coordinated Riverpark management
• statutory planning to ensure land use planning protects the Riverpark
• Riverpark management to enhance community benefit and amenity
• environmental management to improve river system health and resilience
• community engagement
• business management.

DoW is responsible for managing and protecting rivers and estuaries in Western Australia(WA) under the Water Agencies (Powers) Act 1984. DoW has collaborated with the Trust to monitor water quality in the Swan Canning river system since 1995. DoW has also provided scientific and technical advice.

There are 15 agencies and 21 LGAs with a statutory requirement to manage specific aspects of the Riverpark (Appendix 1). In September 2013, the Minister for Environment announced the amalgamation of the Trust with the Department of Parks and Wildlife which is responsible for  monitoring  and  maintaining  the  State’s  biodiversity.  The  Swan  and Canning Rivers Management Amendment Bill 2014 was introduced into Parliament in May 2014.