Nutrient Stripping Wetland
Working to protect our environment
The City of Bayswater and the Department of Parks and Wildlife have restored the Eric Singleton Bird Sanctuary. This exciting project is already providing many ecological benefits, such as increased biodiversity, creation of a sustainable bird habitat and improved water quality to benefit the health of the Eric Singleton Bird Sanctuary and Swan River.
You can watch the development of the project in short YouTube clips.
Clip 1: https://www.youtube.com/watch?v=RUW1OujzTrI
Clip 2: https://www.youtube.com/watch?v=CEkpPMkCT64
Clip 3: https://www.youtube.com/watch?v=vIlK-a3ufgo
Clip 4: https://www.youtube.com/watch?v=1SmgNwa5h0c
Recent media articles about the health of the Swan River suggest more effort should be put in to prevent nutrients flowing into the Swan River catchment.
We need to protect the waterway and its wildlife for future generations. A big part of the problem is the amount of nutrients and other pollutants in the stormwater that runs off and flows into the river from urban catchments.
The Bayswater Brook catchment is one of the biggest in metropolitan Perth and the City has been working in partnership with other organisations, such as Water Corporation, CSIRO and the Department of Water, on programs to remove unwanted nitrogen and phosphorus from the water flowing into the river.
The City has a number of strategies in place to achieve this, including the Bayswater Brook Action Plan and Bayswater Drainage Implementation Strategy.
A $3 million partnership with Parks and Wildlife to revitalise the Eric Singleton Bird Sanctuary is one of the most important projects undertaken to achieve the required catchment nutrient reduction.
The construction works are now finished and the wetland is open to the public, already attracting a diverse array of birds to the site, and providing a serene eco-recreational opportunity for the local community. Early water quality data collected by the City of Bayswater indicates the wetland is performing as designed.
Design and an extensive community consultation and engagement process began in 2012 with detailed design undertaken 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 project will deliver a healthy wetland for flora and fauna, and is also expected to prevent around 1.35 tonnes of nitrogen, 200kg of phosphorus, and 40 tonnes of sediment and other rubbish from entering the Swan River each year.
Why revitalise the Eric Singleton Bird Sanctuary
Prior to restoration, the Eric Singleton Bird Sanctuary wetland relied on bore water for its viability and over time this led to a number of unwanted effects, including the build-up of heavy metals and formation of mono-sulphide materials, (which can release acids when exposed to the air). The result was that the water quality was very poor and the wildlife diversity had decreased over time. Now the sanctuary has many environmental benefits, including:
• Restoring the health of the bird sanctuary;
• Encouraging increased bio-diversity; and
• Decreasing the amount of unwanted nutrients flowing into the Swan River from the Bayswater Brook.
These nutrients can contribute to the formation of algal blooms that adversely impact on the wellbeing of the Swan Canning River system.
The project is in line with what Mr Eric Singleton envisioned and will help reach his goals for a sustainable natural wetland that forms a safe haven for birds and other wildlife.
How the wetland works
As part of the project, water from the Bayswater Brook is diverted to run through the bird sanctuary (as per the stages below). The wetland was designed to treat only a portion of the total drain flow to ensure that this treatment is effective. Water is diverted to a trap that removes pollutants, sand, rubbish and any other large materials before entering the wetland. The water then flows through alternating deep and shallow vegetated marshes to aid in nutrient removal.
Stage 1: Drain diversion - The design diverts water (up to 200 L/s) from the Bayswater Brook through a pipe towards the gross pollutant trap (GPT).
Stage 2: GPT - Water moves through the GPT. This GPT includes a dual outlet configuration which splits the treated flow to both the wetland (50 L/s) and back to the brook (the remaining 150 L/s). The GPT is designed to remove 27.5 tonnes of gross pollutants annually, in an easily maintained structure which can be cleared monthly.
Stage 3: Sediment basin - Water enters the wetland via a sedimentation basin designed to capture further suspended solids and finer gross pollutants that pass through the GPT. The sedimentation basin captures an additional 2.5 tonnes of pollutants annually, and will require cleaning approximately each 5-10 years.
Stage 4: Wetland treatment train - Stormwater is transferred from the sedimentation basin to the main wetland via a control weir and submerged pipe. The diverted water then flows through alternating deep (anaerobic) and shallow (aerobic) vegetated marshes which aids in the removal of nutrients. The central “groyne” provides access to the wetland for the community and maintenance, maximising integration but minimising potential disturbance to the native fauna.
Stage 5: Wetland water outlet – Treated water exits the wetland through a partially submerged, adjustable control outlet that allows the wetland 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.
Stage 6: Primary overflow weir – This weir board controlled structure and one way flow pipes have been installed to allow further manipulation of the wetland flow and depth. This weir also allows the wetland to be drained down quickly in the instance of estuarine waters pushing up the brook and entering the wetland, ensuring impact on the wetland from such an event is limited.
Stage 7: Protection overflow weir - This weir has been designed to perform a dual purpose: a) being upstream, it lets water into the wetland during Bayswater Brook flooding events, protecting the earthen bund from flood damage until water levels equalise; and b) assists in rapidly restoring normal wetland water levels after flooding.
Construction commenced in December 2014 with the installation of a limestone bund along the southern side of the wetland which protected the works from tidal and flood inflow. This allowed the slow process of dewatering via evaporation to commence, with the remainder of the water managed through containment cells.
Through February to April 2015 over 25,000 tonnes of limestone was imported and spread across the entire wetland surface. This limestone provided several functions: a) it helped dewater and consolidate in-situ sediments, b) treated potential acid sulphate soils, c) encapsulated contamination and provided a stable wetland base able to be sculpted to the precise levels required for the hydraulic design to be successful.
From March to July 2015 the hydraulic control structures were built beginning with the installation of the gross pollutant trap, followed by the diversion weir and internal control weirs and finally the outlet control structures.
The site was topsoiled with a nutrient poor topsoil (so as not to add extra nutrients back to the wetland) in June 2015, followed by mulching and planting of 170,000 plants over August to September 2015. The project was completed in early October 2015.
Awards and Recognition
A year after completion, the Eric Singleton Bird Sanctuary was recognised at two separate award ceremonies for the great success the project has had to help improve the health of the Swan River. The project has also received a letter of recognition from the Pro-Vice Chancellor of Research at UWA.
Premier's Excellence in Public Sector Management Award 2016
Joint Winner for the Managing the Environment Category
Australian Engineering Excellence Awards 2016
Winner for the WA environmental category