The Bayswater Brook in Western Australia is one of the top contributors of nitrogen and phosphorous into the Swan River. Adjacent to the brook is the man-made wetland, Eric Singleton Bird Sanctuary, which was in poor ecological condition and in environmental decline. The sanctuary covers approximately four hectares and was a seasonally wet depression. It was drained in the 1950’s and became a permanent wetland when the surrounding area was used for landfill between 1972 and 1981.
In the early development of the City of Bayswater, deep drainage channels were dug to lower groundwater levels. This poor and outdated approach to drainage flushes pollutants from storm water and groundwater directly into the river; and was steadily worsening due to increasing population density.
The sanctuary was an environmental problem for the City. Despite the fact it was a highly degraded man-made wetland; the area held an iconic status in the community's collective mind and was in dire need of rehabilitation in order to preserve it.
The main issue was the environmental decline of the site, which had rendered it an ineffective and water consuming wetland that was contributing to the poor health of the Swan River.
We needed to protect the waterway and its wildlife for future generations. A big part of the problem was the amount of nutrients and other pollutants in the stormwater that runs off and flows into the river from urban catchments.
The goal was to turn ESBS into a productive, nutrient stripping wetland and an outstanding environmental and community asset.
ESBS needed to be rehabilitated to provide:
- Sustainable improvement of water quality within the wetland and the Bayswater Brook catchment; and significantly reduce pollutants flowing into the Swan River
- Eliminate unsustainable groundwater extraction into the wetland
- Significant improvement to the ecological value of the wetland as habitat for birds, fauna and native plants
- An enhancement of the social amenity of the area.
The City of Bayswater was the first local council to challenge traditional policy and take the unique step of bringing the various water management organisations together to form the Bayswater Brook Working Group. The result of this collaboration was the creation of the Bayswater Brook Action Plan, which identified the Eric Singleton Bird Sanctuary as a priority project.
One of the largest projects of its kind, the rehabilitation of the Eric Singleton Bird Sanctuary was completed in partnership with the Department of Biodiversity, Conservation and Attractions.
Design and an extensive community consultation and engagement process began in 2012, with detailed designs created throughout 2013 by GHD Pty Ltd in consultation with the City, Parks and Wildlife, Water Corporation, and Department of Environmental Regulation. The project began construction works in late December 2014 and was completed in October 2015.
The final design provided the following benefits:
- Onsite stabilisation and capping of contaminated and potentially acid forming sediments
- Diversion of flow from the Bayswater Brook into a gross pollutant trap before entering the wetland through a sedimentation pond
- A wetland treatment train of over 25,000 square metres and 170,000 plants
- Construction of a series of internal control weirs and overflow structures to ensure suitable ability to both control treatment flow and protect the wetland from flooding
- Introduction of increased public access to the wetland through significant reshaping.
Construction was almost entirely accomplished using local materials and labour. The most significant material supply was limestone and sand topsoil as a growing medium, as well as locally sourced concrete products. The topsoil used was of very poor quality and essentially waste overburden from a local quarry. It would have been of limited use in dryland rehabilitation or as sand fill; however it was a perfect planting medium for wetland plants which take their nutrients from the diverted water.
An accessible space was created for people to be part of the wetland. This was a primary concern as Bayswater is an inner-city, densely populated suburb in Western Australia and environmental, eco-recreational opportunities are critical.
The benefits for the community include:
- Access through the middle of the wetland - the horseshoe shape landform was not only hydraulically efficient, but allowed the opportunity to create access to the wetland while still protecting the flora and fauna
- Eco-windows - a footpath circles the wetland and is a popular walk
- Interaction - a Visitor Management Plan has been developed and includes signage, seating, QR codes and online information to help people interact with the wetland
- Schools use ESBS on a weekly basis as part of the "Nearer to Nature" workshops run by the State government.
The outcomes of the project have far exceeded the expectations of the City of Bayswater, project stakeholders and the local community. Since opening, the wetland has attracted a diverse array of birds to the site and provides a serene, eco-recreational space for the local community.
Water from the Bayswater Brook is diverted into the sanctuary and flows through a gross pollutant trap to remove pollutants, sand, rubbish and any other large materials before entering the wetland.
The water then moves through alternating deep and shallow vegetated marshes to aid nutrient removal.
- The design diverts water from the Bayswater Brook through a pipe towards the gross pollutant trap (GPT)
- Water moves through the GPT. This GPT includes a dual outlet configuration which splits the treated flow to both the wetland and back to the brook and is designed to remove 27.5 tonnes of pollutants annually
- Water enters the wetland via a sedimentation basin designed to capture further suspended solids and finer gross pollutants that pass through the GPT. It captures 2.5 tonnes of pollutants annually
- Storm water is transferred from the sedimentation basin to the main wetland via a control weir and submerged pipe. The water then flows through alternating deep and shallow vegetated marshes which aids in the removal of nutrients
- Treated water exits the wetland through a partially submerged, adjustable control outlet that allows water depth and flows to be manipulated to maximise treatment benefits and wetland health. The outlet also contains a one way flap that stops water from the brook flowing back into the wetland
- The weir board controlled structure and one way flow pipes have been installed to allow further manipulation of the wetland flow and depth. The weir also allows the wetland to be drained quickly if estuarine waters enter the wetland
- This weir has been designed to perform a dual purpose:
- Being upstream, it lets water into the wetland during Bayswater Brook flooding events, protecting the embankment from flood damage
- Assists in rapidly restoring wetland water levels after flooding.
Prior to the rehabilitation project, the ESBS wetland had limited ecological value, with high levels of nutrients and heavy metals, and dissolved oxygen levels regularly outside healthy ranges. There was also evidence of mono-sulphide material. The result was an underperforming ecosystem with poor water quality and limited environmental value. The wetland was the City's single largest consumer of groundwater, as bore water was used to top up the wetland in summer.
After the rehabilitation project, the ultimate objective of creating a healthier wetland and delivering cleaner water into the Swan River was achieved. The wetland had successfully been redesigned to use ecosystem processes to passively improve water quality before the treated water flowed back into the Bayswater Brook and the Swan River.
The habitat needs of native fauna, specifically birds, were successfully addressed by gradually changing the depth of the water for denitrification, which also matched a range of habitat needs of specific species of birds.
The deep, anaerobic zones of the wetland create water bodies for birds such as cormorants, egrets and grey teales, while the vegetated intermediate zones create habitats for species like the purple swamp hen. The shallow areas are perfectly suited for wading birds.
To specifically encourage black swans, a landing stretch of 50 meters was created, as well a deep water area in the wetland. A native plant species, shoenoplectus validus, was used as it is known to be a favourite for nesting swans, as well as an excellent wetland nutrient stripper.
The project has substantial on-going benefits for the local economy, including significantly improving the public amenity of the area which will attract visitors from across Perth; and providing an outstanding local asset that has strong community ownership, provides education on environmental matters, encourages physical activity and engagement with our local, natural environment.
Water quality monitoring undertaken by the City of Bayswater shows notable improvement outcomes for the Brook and adjacent Swan River and the project is expected to prevent 1.35 tonnes of nitrogen, 200kg of phosphorous, and around 40 tonnes of sediment and other rubbish from entering the Swan River each year. This is approximately half of the catchment’s target nutrient reduction.
There has also ceased to be spending on unproductive and unsustainable bore-water wetland top ups.
The sanctuary has brought nature closer to the people and is a weekly venue of the "Nearer to Nature" program in schools, run by the State Government.
The sanctuary is an outstanding local asset with strong community ownership and provides education on environmental matters, encourages physical activity and engagement with our local natural environment.
The Eric Singleton Bird Sanctuary rehabilitation categorically delivered the goals of the project and provides a number of benefits for the community and the environment.
The latest assessment of the Stormwater Treatment Performance can be read here.