Internationally recognised experts in urban stormwater management and biofiltration design, Professor Tim Fletcher from the University of Melbourne and Doctor Belinda Hatt and PhD student Emily Payne from Monash University, presented research findings at the Advancing biofilters in Western Australia seminar held on 31 July 2012 at the State Library in Perth. The research was a culmination of a 3 year ARC Linkage project that investigated the performance of 22 south-west WA and Victorian plant species in terms of nutrient removal, resilience to drought conditions and maintenance of media permeability. Winthrop Professor Zed Rengel from the University of Western Australia also presented findings from a 20 month research project investigating the contaminant removal performance of local soil media and four south-west WA plant species.
Approximately 100 people attended the seminar which aimed to addres knowledge gaps currently limiting the adoption of biofilters in WA. The seminar provided a much greater understanding of “how to get it right” with regards to biofilter design, noting that it was necessary to design for site context and objectives including scale, function and performance characteristics, as well as to try to achieve multiple benefits (not just improved water quality). Some of the key learnings were:
- Correct specification of filter media is critical and needs to be low in nitrogen and phosphorous and contain a carbon source. Getting the media right provides greater flexibility in plant selection.
- The importance of the saturated zone to maintain plant health, survival and system recovery was emphasised, particularly in WA south west conditions, as well as to improve overall performance.
- Vegetation is a key component of biofilters and plant uptake is an important nutrient removal pathway. Plant characteristics are important. Favourable characteristics for nutrient removal are high root biomass, fine roots and high growth rate. Plants with thicker roots are also required to maintain the long-term infiltration capacity of the biofilter. Plants deeper roots and plants which are capable of regenerating are recommended to enable the system to survive or recover from prolonged dry periods. The option to use a variety of plants to address different types of pollutants was recommended, as well as to achieve greater resilience, amenity and community acceptance of biofilters.
- All plant species were effective for total nitrogen and total phosphorous removal during the wet period (where biofilter columns were dosed with stormwater twice per week).
- Plant species achieved total nitrogen reductions of 50 – 95%, significantly more effective than the un-vegetated biofilter columns.
- Extended drying significantly reduces the performance of biofilters. Leaching of nitrate and dissolved organic nitrogen is the greatest concern.
- Incorporating a saturated zone in the biofilter design is particularly important for sustaining performance during dry conditions.
- The release of a pulse of nitrogen following re-wetting of dried soil is a common phenomenon.
- Biofilters achieve very high removal of metals.
- Other benefits of biofilters include reducing the volume and frequency of stormwater runoff, enhancing urban amenity, contributing to biodiversity and mitigating urban heat.
An overview of the Little Stringybark Creek project in Victoria was presented; a world-first demonstration of whole-of-catchment retrofitting to restore the ecological health of an urban creek. The project is developing simple, cheap and safe approaches to stormwater retention and use. Alternative economic instruments for funding stormwater management and innovative approaches to community engagement were trialled, including a ‘stormwater auction’. The main learnings were:
- Enhancing stream health requires restoration of key characteristics of the natural flow regime, as well as improvement of water quality.
- Aim to achieve near-zero directly connected imperviousness (i.e. no impervious surfaces directly connected via pipes and drains to waterways).
- Successful community engagement strategies include:
Having an identity independent of government
Providing a single point of contact
Offering a financial incentive
Keeping information simple and concise
Undertaking one-on-one engagement and assistance
Using existing stakeholder networks
Allowing time for people to become involved in the project
- In addition to addressing the impacts of existing urban development, policy and planning approaches to manage future development are essential for long-term waterway protection.
In closing the Seminar, participants were asked how they would like to receive the final biofilter research results. Almost all participants preferred a combination of a training workshop to produce a design, and an onsite practical session where a biofilter was being constructed. This strong response demonstrates the ongoing need for professional development regarding WSUD practices.
The seminar was supported by New WAter Ways, with support and sponsoring by the Department of Water.
Links and further information:
Advancing biofilters in Western Australia – Seminar overview, program and speakers biographies
Seminar presentations 31 July 2012:
Introduction to Biofiltration: Benefits, principles and design elements – B. Hatt
Summary of previous research findings and rationale for the ARC linkage project – T. Fletcher
Understanding the role of vegetation in nitrogen removal by biofiltration – E. Payne
Investigation into biofiltration systems under Western Australian climate conditions – Z. Rengel
A preliminary investigation of readily available local soils that are suitable filter media for biofiltration systems in WA – A. Torre
Implications for design – B. Hatt & T. Fletcher
Stream rehabilitation through stormwater management: The Little Stringybark Creek case study – T. Fletcher & B. Hatt
Barlee Street rain garden in Busselton – Design and monitoring summary (draft paper)
A Dual-mode Biofilter System: Case study in Kfar Sava, Israel. Y. Zinger, A. Deletic, T. D. Fletcher, P. Breen, T. Wong. 12ICUD, Sept 2011 – This biofilter is an example of a dual-use system that combines stormwater harvesting and treatment during the wet season, while being used to treat polluted aquifer groundwater during the dry season.
FAWB (2009). Adoption Guidelines for Stormwater Biofiltration Systems, Facility for Advancing Water Biofiltration, Monash University, June 2009.
Little Stringybark Creek project