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Abstracts

Brown R. R. and Farrelly M. A. (2009). Delivering Sustainable Urban Water Management: a review of the hurdles we face. Water Science and Technology. 59(5): 839-846.

Sustainable urban water management (SUWM) requires an integrated, adaptive, coordinated and participatory approach. Current urban water policies are beginning to reflect this understanding yet the rhetoric is often not translated to implementation. Despite the 'new' philosophy, urban water management remains a complex and fragmented area relying on traditional, technical, linear management approaches. Despite widespread acknowledgement of the barriers to change, there has been little systematic review of what constitutes the scope of such barriers and how these should be addressed to advance SUWM. To better understand why implementation fails to occur beyond ad hoc project interventions, an extensive literature review of observed and studied barriers was conducted. Drawing on local, national and international literature from the field of integrated urban water management and other similar fields, 53 studies were assessed, resulting in a typology of 12 barrier types. The analysis revealed the barriers are largely socio-institutional rather than technical, reflecting issues related to community, resources, responsibility, knowledge, vision, commitment and coordination. Furthermore, the meta-analysis demonstrated a paucity of targeted strategies for overcoming the stated institutional barriers. Evaluation of the typology in relation to capacity building suggests that these systemic issues require a sophisticated programme of change that focuses on fostering social capital, inter-sectoral professional development, and inter-organisational coordination.

Brown, R. R. and Farrelly, M. A. (2009). Challenges ahead - social and institutional factors influencing sustainable urban stormwater management in Australia. Water Science and Technology. 59(4): 653-660.

In a time of climate uncertainty and drought in Australia, improved urban stormwater quality management practices are required not only for protecting waterway health, but also as a fit-for-purpose supply source. To conceive of urban stormwater as an environmental threat as well as a water supply source requires a substantial shift in our traditional linear supply and wastewater structures towards more hybrid and complex infrastructure systems. To understand what drives and limits treatment technology adoption for stormwater management, over 800 urban water professionals in three Australian capital cities completed an online questionnaire survey in November 2006. Using the conceptual framework of receptivity assessment, the results revealed the professional community to be highly associated with the importance of improving stormwater quality for receiving waterway health, yet they do not consider that politicians share this perspective by placing a substantially lower level of importance on stormwater quality management. Significant acquisition barriers within each city, including institutional arrangements, costs, responsibilities, and regulations and approvals processes were all identified as constraining more sustainable practices. Capacity building programs, fostering greater socio-political capital and developing key demonstration projects with training events are recommended as useful policy interventions for addressing current institutional impediments.

Brown, R. R., Farrelly, M. A. and Keath, N. (2009). Practitioner Perceptions of Social and Institutional Barriers to Advancing a Diverse Water Source Approach in Australia. International Journal of Water Resources Development. 25(1): 15-28.

Traditional urban water management systems are ill-equipped to address future challenges. Despite policy rhetoric supporting Total Water Cycle Management and the diverse water supply approach, there are many social and institutional barriers to effective implementation. A quantitative online survey with over 1000 practitioners in three Australian capital cities identified practitioners' level of receptivity to the diverse water source approach, and their experience of the scope and priority of such barriers to their implementation. The analysis revealed a high level of practitioner support, yet a critical lack of institutional tools and incentives for supporting implementation. The paper provides a series of recommendations for addressing this issue.

Brown, R., Keath, N. and Wong, T. (2009). Urban Water Management in Cities: Historical, Current and Future Regimes. Water Science and Technology. 59(5): 847-855.

Drawing from three phases of a social research programme between 2002 and 2008, this paper proposes a framework for underpinning the development of urban water transitions policy and city-scale benchmarking at the macro scale. Through detailed historical, contemporary and futures research involving Australian cities, a transitions framework is proposed, presenting a typology of six city states, namely the 'Water Supply City', the 'Sewered City', the 'Drained City', the 'Waterways City', the 'Water Cycle City', and the 'Water Sensitive City'. This framework recognises the temporal, ideological and technological contexts that cities transition through when moving towards sustainable urban water conditions. The aim of this research is to assist urban water managers with understanding the scope of the hydro-social contracts currently operating across cities in order to determine the capacity development and cultural reform initiatives needed to effectively expedite the transition to more sustainable water management and ultimately to Water Sensitive Cities. One of the values of this framework is that it can be used by strategists and policy makers as a heuristic device and/or the basis for a future city state benchmarking tool. From a research perspective it can be an underpinning framework for future work on transitions policy research.

Keath, N. and Brown, R. (2009). Extreme Events: Being Prepared for the Pitfalls with Progressing Sustainable Urban Water Management. Water Science and Technology. 59(7):1271-1280.

It is widely accepted that new, more sustainable approaches to urban water management are required if cities and ecosystems are to become resilient to the effects of growing urban populations and global warming. Climate change predictions show that it is likely that cities around the world will be subject to an increasing number of extreme and less predictable events including flooding and drought. Historical transition studies have shown that major events such as extremes can expedite the adoption of new practices by destabilising existing management regimes and opening up new windows of opportunity for change. Yet, they can also act to reinforce and further entrench old practices. This case study of two Australian cities responding to extreme water scarcity reveals that being unprepared for extremes can undermine progress towards sustainable outcomes. The results showed that despite evidence of significant progress towards sustainable urban water management in Brisbane and Melbourne, the extreme water scarcity acted to reinforce traditional practices at the expense of emerging sustainability niches. Drawing upon empirical research and transitions literature, recommendations are provided for developing institutional mechanisms that are able to respond proactively to extreme events and be a catalyst for SUWM when such opportunities for change arise.

Roy A.E., Wenger S.J., Fletcher T.D., Walsh C.J., Ladson A.R., Shuster W.D., Thurston H. W. and Brown R.R. (2008). Impediments and solutions to sustainable, watershed-scale urban stormwater management: lessons from Australia and the United States. Environmental Management. 42(2): 344-359.

In urban and suburban areas, stormwater runoff is a primary stressor on surface waters. Conventional urban stormwater drainage systems often route runoff directly to streams and rivers, thus exacerbating pollutant inputs and hydrologic disturbance, and resulting in the degradation of ecosystem structure and function. Decentralized stormwater management tools, such as low impact development (LID) or water sensitive urban design (WSUD), may offer a more sustainable solution to stormwater management if implemented at a watershed scale. These tools are designed to pond, infiltrate, and harvest water at the source, encouraging evaporation, evapotranspiration, groundwater recharge, and re-use of stormwater. While there are numerous demonstrations of WSUD practices, there are few examples of widespread implementation at a watershed scale with the explicit objective of protecting or restoring a receiving stream. This article identifies seven major impediments to sustainable urban stormwater management: (1) uncertainties in performance and cost, (2) insufficient engineering standards and guidelines, (3) fragmented responsibilities, (4) lack of institutional capacity, (5) lack of legislative mandate, (6) lack of funding and effective market incentives, and (7) resistance to change. By comparing experiences from Australia and the United States, two developed countries with existing conventional stormwater infrastructure and escalating stream ecosystem degradation, we highlight challenges facing sustainable urban stormwater management and offer several examples of successful, regional WSUD implementation. We conclude by identifying solutions to each of the seven impediments that, when employed separately or in combination, should encourage widespread implementation of WSUD with watershed-based goals to protect human health and safety, and stream ecosystems.

Wong, T., and Brown, R. (2009). The Water Sensitive City: Principles for Practice. Water Science and Technology. 60(3):673-682.

With the widespread realisation of the significance of climate change, urban communities are increasingly seeking to ensure resilience to future uncertainties in urban water supplies, yet change seems slow with many cities facing ongoing investment in the conventional approach. This is because transforming cities to more sustainable urban water cities, or to Water Sensitive Cities, requires a major overhaul of the hydro-social contract that underpins conventional approaches. This paper provides an overview of the emerging research and practice focused on system resilience and principles of sustainable urban water management Three key pillars that need to underpin the development and practice of a Water Sensitive City are proposed: (i) access to a diversity of water sources underpinned by a diversity of centralised and decentralised infrastructure; (ii) provision of ecosystem services for the built and natural environment; and (iii) socio-political capital for sustainability and water sensitive behaviours. While there is not one example in the world of a Water Sensitive City, there are cities that lead on distinct and varying attributes of the water sensitive approach and examples from Australia and Singapore are presented.

Blecken, G.-T., Y. Zinger, A. Deletic, T. D. Fletcher, A. Hedstrom and M. Viklander (in press). Laboratory study on stormwater biofiltration; nutrient and sediment removal in cold temperatures. Journal of Hydrology.

Stormwater biofilters have the ability to remove nutrients from stormwater. Reliable pollutant removal during the cold season is particularly important due to the comparably high contamination levels. However, the removal performance might be negatively affected by low temperatures. A biofilter column study was conducted in thermostat-controlled climate rooms (at 2, 7 and 20 °C) to investigate the effect of low temperatures on nutrient removal. Phosphorus and suspended solids removal were significantly correlated and consistently very high (typically in excess of 90 and 95%, respectively, at all temperatures). This is important for the successful implementation of biofilters in cold climates since phosphorus is commonly of principal concern, often being the limiting factor for eutrophication in freshwater ecosystems. Unfortunately, nitrogen removal was poor and leaching was shown, which increased with temperature. The increasing nitrate-nitrogen production rates with temperature were well described by the Arrhenius relationship with temperature coefficients Q10 in the range which is typically used to describe temperature effects on nitrification. Thus, temperature effects have to be considered when nitrogen removal is targeted and the biofilter might be exposed to cold temperatures.

Blecken, G.-T., Y. Zinger, A. Deletic, T. D. Fletcher and M. Viklander (2009). Impact of a submerged anoxic zone and a cellulose based carbon source on heavy metal removal in stormwater biofiltration systems. Ecological Engineering, 35(5): 769-778.

Given the substantial pollutant loads in urban stormwater, biofilters are a potentially effective treatment option, particularly for heavy metals. However, to increase their nitrogen treatment efficacy, the introduction of a submerged (anoxic) zone (SZ) and a cellulose based carbon source (C) has been recommended because it has been shown to enhance denitrification, thus increasing overall nitrogen removal. To examine the impact of this design modification on the removal of heavy metals, a laboratory study using biofilter mesocosms with different levels of SZ with and without added C was conducted. The results show that SZ and C have a significant impact on metal treatment. In particular, the removal of Cu was improved significantly. The presence of SZ and C allows outflow Cu concentrations to meet Swedish and Australian water quality target values, which are not met with a biofilter without SZ or C. Even the already high Zn and Pb removal was enhanced slightly by the presence of a SZ. However, since removal of these metals is already very high (>95%), this improvement is of less practical importance. The best metal treatment was achieved with 450 mm and 600 mm SZ. Based on these results, the incorporation of SZ with C in stormwater biofilters is recommended.

Blecken, G.-T., Y. Zinger, A. Deletic, T. D. Fletcher and M. Viklander (2008). Heavy metal removal by stormwater biofilters: can it withstand alternative wetting and drying conditions? 11th International Conference on Urban Drainage (ICUD). Edinburgh, Scotland. August 31-September 5, 2008.

Urban stormwater contains substantial loads of Cu, Pb and Zn, which are considered as key stormwater contaminants. Stormwater biofiltration is a promising option to treat these contaminants. Biofilters are exposed to an alternate cycle of drying and wetting, and the influence of this on pollutant removal performance is as-yet unknown. To investigate the effect of drying and subsequent rewetting on the retention of heavy metals by stormwater biofilters, a laboratory study has been conducted using three groups of biofilter columns, which were dosed with semi-synthetic stormwater according to three different drying and wetting regimes. Some biofilters were fitted with a submerged zone combined with a carbon source, at the bottom of the filter. Overall, the biofilters were very effective in heavy metal removal, provided that they received regular stormwater input. However, after drying extending to three or four weeks, removal of heavy metals decreased significantly. A statistically significant correlation between antecedent dry days and metal removal was shown. Furthermore, a clear effect of the submerged zone was found: after extended dry periods, biofilters with this feature performed significantly better than those without it. In particular, the removal of Cu was clearly increased both during wet and dry periods; for Pb the negative effect of drying was completely eliminated by introducing a submerged zone.

Blecken, G.-T., Y. Zinger, T. D. Fletcher, A. Deletic and M. Viklander (2010). Laboratory studies on metal treatment efficiency of stormwater biofilters. Paper presented at 5th International Short Course: Advances in Knowledge of Urban Drainage from the Catchment to the Receiving Water. University of Calabria, Rende, Italy. June 15, 2010.

Stormwater biofilters are a reliable technology to remove metals from stormwater. A solid carbon source in the filter (combined with a submerged zone) enhances especially Cu removal further; the already high Pb and Zn removal is slightly enhanced. However, the submerged zone helps to minimize (Cu, Zn) or eliminate (Pb) the negative effects which prolonged drying has on the removal rates. Thus, the introduction of a submerged zone is only recommended if nitrogen treatment is targeted (Zinger et al. 2007) or if drying is expected.
Temperature differences might have a little influence on especially Cu treatment. However, this influence is not of practical importance indicating that biofilters can successfully be implemented throughout the whole seasonal cycle.
A high proportion of metals are retained at the top of the filter which is important for biofilter design and maintenance planning. A filter less than the currently recommended 800 to 900 mm might be sufficient for reliable metal treatment. Furthermore, scraping of the top layer could delay replacing of the whole filter media.

Blecken, G.-T., Y. Zinger, T. D. Fletcher, A. Deletic and M. Viklander (2009). Influence of intermittent wetting and drying conditions on heavy metal removal by stormwater biofilters. Water Research, 43(18), 4590-4598.

Biofiltration is a technology to treat urban stormwater runoff, which conveys pollutants, including heavy metals. However, the variability of metals removal performance in biofiltration systems is as yet unknown. A laboratory study has been conducted with vegetated biofilter mesocosms, partly fitted with a submerged zone at the bottom of the filter combined with a carbon source. The biofilters were dosed with stormwater according to three different dry/wet schemes, to investigate the effect of intermittent wetting and drying conditions on metal removal. Provided that the biofilters received regular stormwater input, metal removal exceeded 95%. The highest metal accumulation occurs in the top layer of the filter media. However, after antecedent drying before a storm event exceeding 3-4 weeks the filters performed significantly worse, although metal removal still remained relatively high. Introducing a submerged zone into the filter improved the performance significantly after extended dry periods. In particular, copper removal in filters equipped with a submerged zone was increased by around 12% (alpha=0.05) both during wet and dry periods and for lead the negative effect of drying could completely be eliminated, with consistently low outflow concentrations even after long drying periods.

Blecken, G.-T., Y. Zinger, T. M. Muthanna, A. Deletic, T. D. Fletcher and M. Viklander (2007). The influence of temperature on nutrient treatment efficiency in stormwater biofilter systems. Water Science and Technology, 56(10): 83-91.

Nutrients can cause eutrophication of natural water bodies. Thus, urban stormwater which is an important nutrient source in urbanised areas has to be treated in order to reduce its nutrient loads. Biofilters which use soil filter media, biofilms and plants, are a good treatment option for nutrients. This paper presents the results of a biofilter column study in cold temperatures (+2°C, +8°C, control at +20°C) which may cause special problems regarding biofilter performance. It was shown that particle-bound pollutants as TSS and a high fraction of phosphorus were reduced well without being negatively influenced by cold temperatures. Nitrogen, however, was not reduced; especially NOx was produced in the columns. This behaviour can be explained with both insufficient denitrification and high leaching from the columns.

Blecken, G. T., M. Viklander, T. Muthanna, Y. Zinger, A. Deletic, and T.D. Fletcher (2007). Biofilter treatment of stormwater; temperature influence on the removal of nutrients. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France. June 24-28, 2007.

Nutrients can cause eutrophication of natural water bodies. Thus, urban stormwater which is an important nutrient source has to be treated in order to reduce its nutrient loads. Biofilters which use media, biofilms and plants, are a good treatment option regarding nutrients. This paper presents the results of a biofilter column study in cold temperatures (+2°C, +8°C, control at +20°C) which may cause special problems regarding the biofilter performance. It was shown that particle bound pollutants as TSS and a high fraction of phosphorus were reduced well without being negatively influenced by cold temperatures. Nitrogen, however, was not reduced; especially NOx was produced in the columns which can be explained with both insufficient denitrification and high leaching from the columns.

Bratieres, K., T. D. Fletcher and A. Deletic (2009). The advantages and disadvantages of a sand-based biofilter medium: results of a new laboratory trial. 6th International Water Sensitive Urban Design Conference and Hydropolis#3. Perth, Australia. 5-8 May 2009.

Biofilters (biofiltration or bioretention systems) have been proven to be an effective option for the treatment of pollutants in urban stormwater. In general, a loamy sand base is recommended for biofilters, based on detailed filter media specifications provided by the Facility for Advancing Water Biofiltration. The aim of this study was to test a potentially easier method for producing the required filter media specifications to achieve effective pollutant removal in biofilters. This paper presents a one year column trial of 20 sand based biofilters, using experimental protocols consistent with previous research which looked at loamy sand biofiltration systems, to allow the results from the two trials to be directly compared. Whilst the pollutant outflow concentrations were relatively high in the first six months (probably necessitating further treatment), the results showed that after almost a year, the treatment performance of the sand based filters had increased significantly. For vegetated configurations in particular, the pollutant outflow concentrations were not significantly different between the two filter media types, demonstrating that sand based biofilters could be used for the treatment of stormwater as an alternative to the generally recommended loamy sand based biofiltration systems. The advantages of this alternative specification are its reproducibility and reduced variability.

Bratieres, K., T.D. Fletcher, A. Deletic, L. Alcazar, S. Le Coustumer, D. McCarthy and Y. Zinger (2008). Removal of nutrients, heavy metals and pathogens by stormwater biofilters. 11th International Conference on Urban Drainage (ICUD). Edinburgh, Scotland. August 31-September 5, 2008.

Biofilters (bioretention systems) are a potentially effective treatment option for the treatment of pollutants in urban stormwater, such as nutrients (nitrogen and phosphorus in particular), heavy metals, and even pathogens. A large-scale column study was conducted in Melbourne, Australia, to quantify the treatment performance of biofilters for the above mentioned pollutants, and to assess the effect of a range of different factors on the removal efficiency: presence and type of vegetation, depth and type of filter media, the magnitude of storms and their pollutant inflow concentrations, the presence of an anoxic zone in the bottom of the biofilter and the presence of drought periods. The results demonstrated that vegetation selection is critical for nitrogen removal (e.g. columns planted with Carex showed 70% removal after 8 months of exposure to stormwater). Phosphorus was efficiently removed (>80%) by most biofilter designs, providing that no organic matter was added to the filter media. All biofilter configurations performed well for heavy metals (80% for lead and >98% for copper and zinc), if their depth was >300mm. Although antecedent dry weather periods had a negative influence on pathogen treatment, mean removal was found to be >80% for indicators of viruses, bacteria and protozoa. Questions remain as to whether this is adequate to allow safe non-potable use of water discharged from stormwater biofilters.

Bratieres, K., T. D. Fletcher, A. Deletic, N. Somes and T. Woodcock (2010). Hydraulic and pollutant treatment performance of sand based biofilters. Novatech 2010. 7th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France. June 27-July 1, 2010.

Biofilters (also called biofiltration or bioretention systems) have been proven to be an effective option for the treatment of pollutants in urban stormwater. The aim of this study was to independently test an alternative sand based filter media, which could be reliably and easily specified and constructed from inert material, and which would (i) sustain adequate plant growth, (ii) maintain hydraulic conductivity, and (iii) achieve effective pollutant removal.
Twenty biofilter columns were constructed for this experiment, using two fine sands of different initial drainage rates, tested in vegetated and non-vegetated configurations. The results showed that, independently of the type of sand used, plant growth was sustained in all biofilters, and that after one year (i.e. at the time of the last sampling event), the pollutant treatment performance of vegetated columns was comparable to loamy sand based biofilters, which are typically used in current practice. However, the results also showed that after one year of exposure to stormwater, the hydraulic conductivity of the filters had greatly deteriorated, in particular for the vegetated configurations.
The results of this study demonstrated that sand based biofilters, built according to these simple filter media specifications, could be used as a viable option for stormwater treatment. The main advantages of this alternative specification are its reproducibility and reduced variability.

Bratieres, K., T. D. Fletcher, A. Deletic and Y. Zinger (2008). Optimisation of the treatment efficiency of biofilters; results of a large-scale laboratory study. Water Research, 42(14): 3930-3940.

A large-scale column study was conducted in Melbourne, Australia, to test the performance of stormwater biofilters for the removal of sediment, nitrogen and phosphorus. The aim of the study was to provide guidance on the optimal design for reliable treatment performance. A variety of factors were tested, using 125 large columns: plant species, filter media, filter depth, filter area and pollutant inflow concentration. The results demonstrate that vegetation selection is critical to performance for nitrogen removal (e.g. Carex appressa and Melaleuca ericifolia performed significantly better than other tested species). Whilst phosphorus removal was consistently very high (typically around 85%), biofilter soil media with added organic matter reduced the phosphorus treatment effectiveness. Biofilters built according to observed ‘optimal specifications’ can reliably remove both nutrients (up to 70% for nitrogen and 85% for phosphorus) and suspended solids (consistently over 95%). The optimally designed biofilter is at least 2% of its catchment area and possesses a sandy loam filter media, planted with C. appressa or M. ericifolia. Further trials will be required to test a wider range of vegetation, and to examine performance over the longer term. Future work will also examine biofilter effectiveness for treatment of heavy metals and pathogens.

Bratieres, K., D.T. McCarthy, T.D. Fletcher and A. Deletic (2009). Stormwater monitoring manual: principles and implementation. 6th International Water Sensitive Urban Design Conference and Hydropolis#3. Perth, Australia. May 5-8, 2009.

State agencies, local councils and research groups are often required to monitor stormwater systems. Field monitoring can be an expensive exercise, yet it is sometimes undertaken without adequate attention given to the appropriate monitoring level or the relative cost of collecting and analysing data compared with the usefulness of the data obtained. Currently, no existing document in Australia provides complete guidance and assistance in collecting and reporting data from a stormwater based monitoring programme. A stormwater monitoring manual is therefore being created to provide guidance on the strategies, approaches and techniques that are appropriate and useful for the development of a stormwater monitoring programme. It is not intended for this manual to provide a set of “standards”, but instead it provides guidance and recommendations. This paper summarises the contents of the stormwater monitoring manual, and aims to ensure that, in future, stormwater monitoring programmes around Australia are well defined and meet their objectives.

Daly, E., Y. Zinger, A. Deletic, and T.D. Fletcher (2009). A possible mechanism for soil moisture biomodality in humid-land environments. Geophysical Research Letters, 36.

The origin and causes for the existence of two distinct steady-state modes of soil moisture probability distribution (pdf) have been attributed to several processes, such as land-atmosphere feedbacks or shifts in climatic conditions within seasons. Here we argue that the interaction between saturated and unsaturated zones in soils with shallow water tables might represent a possible mechanism leading to such bimodality. This conclusion is achieved by analyzing soil water content measurements in vegetated soil columns artificially constructed in a laboratory. We used these observations to develop a stochastic model for the daily soil water balance, which shows how the interplay between the water table and the unsaturated zone is able to induce soil moisture bimodality.

Fletcher, T. D., Y. Zinger, A. Deletic and K. Bratieres (2007). Treatment efficiency of biofilters: results of a large scale biofilter column study. 13th International Rainwater Catchment Systems Conference and 5th International Water Sensitive Urban Design Conference, Sydney, Australia. August 21-23, 2007.

In order to evaluate the optimal design of biofilters for treatment of sediment, nitrogen and phosphorus, 140 biofilter columns were constructed, using different plant species, different depths and types of filter media, along with different storm volumes and input concentrations. All biofilters tested were found to be highly effective for removal of TSS, reducing inflow concentrations by an average of 98%. Total phosphorus was reduced by an average of 80%, whilst nitrogen removal was much more variable, including some configurations which yielded a net increase in nitrogen concentration. However, careful selection of plants and media type was able to achieve a simultaneous reduction of 50-70% of nitrogen and 90% of phosphorus. Carex appressa and to a lesser extent Melaleuca ericifolia performed very well in nutrient removal, whilst Dianella revoluta, Leucophyta brownii and Microlaena stipoides did not, within the nine months of testing, effective in facilitating nitrogen removal. Appropriate sizing of biofilters relative to their catchment area, as well as careful selection of plants for climate condition may be critical for biofilter performance. Further research will be undertaken to determine whether relatively poorly performing biofilter designs can be improved by retrofitting a saturated anaerobic zone, to promote denitrification and enhance drought tolerance.

Hatt, B. E., A. Deletic, and T. D. Fletcher (2009). Pollutant removal performance of field scale stormwater biofiltration systems. Water Science and Technology, 59(8): 1567-1676.

The pollutant removal performance of three separate stormwater biofiltration systems in two different climates was assessed. At one of the sites, rain events were simulated, while actual runoff events were monitored at the other two sites. In all cases, concentrations of total suspended solids (TSS), copper, lead and zinc were effectively and reliably reduced, despite variations in inflow concentrations. Two biofiltration systems also effectively reduced phosphorus concentrations, however the third system discharged elevated phosphorus concentrations relative to inflow; this is attributed to poor specification of filter media properties. Effluent nitrogen concentrations were more variable at all sites and ranged from being substantially lower to considerably higher than inflow concentrations. Flow was also measured at two sites, where it was determined that volumetric reductions in runoff further improved pollutant removal. TSS and heavy metals will be reliably removed by a wide range of soil-based filter media, as will phopshorus, as long as the phosphorus content of the filter media is low. However, nitrogen removal remains a challenge because it is easily transformed to soluble forms and is influenced by wetting and drying. These results are essentially consistent with related laboratory studies.

Hatt, B. E., A. Deletic, and T. D. Fletcher (2006). Stormwater reuse: designing biofiltration systems for reliable treatment. Joint Urban Drainage Management and Water Sensitive Urban Design Conference. Melbourne, Australia. April 3-7, 2006.

Stormwater reuse is increasing in popularity as a technique for overcoming water shortages in urban Australia. However, technology for the reliable treatment of stormwater for reuse is still not fully developed. This paper presents the first steps in refining biofilters (also know as bioretention systems) for stormwater reuse. Six different filter media were selected, to target specific stormwater pollutants, such as heavy metals and nutrients, as well as support plant growth. They were tested in the laboratory, where the filters were dosed three times per week with semi-synthetic stormwater (that contained both particulate and dissolved pollutants typical for Australian conditions) for five weeks. Pollutant removal performance was monitored, and revealed that all soil-based filters performed similarly (while sand filters behaved somewhat differently). All filters removed more than 80% of solids and greater than 90% of total heavy metals (lead, copper, and zinc ). Three filter types were able to remove some phosphorus (particularly in the top 30 cm of the media). Apart from sand, all filter media were net producers of nitrogen, leading to an important conclusion that non-vegetated, soil-based filters are not suitable for targeting nutrients. However, since heavy metals are the primary pollutant of concern with respect to stormwater reuse for irrigation (the most popular end use), it was concluded that biofilters may be promising technologies for treatment of stormwater for reuse. Further testing is required to test the temporal treatment performance of these filters, and this is currently being undertaken.

Hatt, B. E., T. D. Fletcher and A. Deletic (2008). Hydraulic and pollutant removal performance of fine media stormwater filtration systems. Environmental Science & Technology, 42(7): 2535-2541.

Stormwater runoff from urban areas has multiple negative hydrologic and ecological impacts for receiving waters. Fine media stormwater filtration systems have the potential to mitigate these effects, through flow attenuation and pollutant removal. This work provides an overall assessment of the hydraulic andpollutantremovalbehavior ofsand-andsoil-basedstormwater filters at the laboratory scale. The influence of time, cumulative inflow sediment, cumulative water volume, wetting and drying, and compaction on hydraulic capacity was investigated. The results suggested that the primary cause of hydraulic failure was formation of a clogging layer at the filter surface. Loads of sediment and heavy metals were effectively retained; however, the soil-based filters leached nitrogenandphosphorus for the duration of the experimental period. Media pollutant profiles revealed significant accumulation of all pollutants in the top 20% of the filter profile, suggesting that elevated discharges of nutrients was due to leaching of native material, rather than failure to remove incoming pollutants. It is recommended that the top 2-5 cm of the filter surface be scraped off every two years to prevent hydraulic failure; this will also avoid excessive accumulation of heavy metals, which may otherwise have been of concern.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). Treatment performance of gravel filter media: implications for design and application of stormwater infiltration systems. Water Research, 41(12): 2513-2524.

Stormwater infiltration systems are widely used to address the flow and water quality impacts of urbanization. However, their pollutant removal performance is uncertain, with respect to varying filter depth, and over time. Seven simulation experiments were conducted on a laboratory-scale gravel infiltration system to test the pollutant removal under a range of water level regimes, including both constant and variable water levels. Gravel filters were found to be very effective for removal of sediment and heavy metals under all water level regimes, even as the system clogged over time. Despite the sediment particle size distribution being much smaller than the filter media pore size, sediment and its associated pollutants were effectively trapped in the top of the gravel filter, even when the water level was allowed to vary. A media depth of 0.5 m was found to achieve adequate pollutant removal. Breakthrough of pollutants may not be of concern, since physical clogging occurred first (thus determining the lifespan of the filter media). However, gravel filters were less effective at nutrient removal, particularly for dissolved nutrients.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). Stormwater reuse: designing biofiltration systems for reliable treatment. Water Science and Technology, 55(4): 201-209.

Stormwater reuse is increasing in popularity as a technique for overcoming water shortages in urban Australia. However, technology for the reliable treatment of stormwater for reuse is still not fully developed. This paper presents the first steps in refining biofilters for stormwater reuse. Six different filter media were selected, to target specific stormwater pollutants, as well as support plant growth. They were tested in the laboratory, where the filters were dosed three times per week with semi-synthetic stormwater for five weeks. Pollutant removal performance was monitored, and revealed that all soil-based filters performed similarly (while sand filters behaved somewhat differently). All filters removed more than 80% of solids and greater than 90% of lead, copper, and zinc. Three filter types were able to remove some phosphorus (particularly in the top 30 cm of the media). Apart from sand, all filter media were net producers of nitrogen, leading to an important conclusion that non-vegetated, soil-based filters are not suitable for targeting nutrients. However, since heavy metals are the primary pollutant of concern with respect to stormwater reuse for irrigation (the most popular end-use), it was concluded that biofilters may be promising technologies for treatment of stormwater for reuse.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). Hydraulic and pollutant removal performance of stormwater filters under variable wetting and drying regimes. Water Science & Technology, 56(12): 11-19.

Biofiltration systems are an effective stormwater treatment technology. However, their robustness is yet to be tested, particularly their performance following extended dry periods. The hydraulic and treatment performance of five different non-vegetated, soil-based filters under varying periods of inundation and drying was assessed. The infiltration capacity of the filters decreased during wet periods and increased following dry periods, most probably due to swelling and shrinkage of the filter media. Treatment of sediment, heavy metals and phosphorus was not influenced by the wetting and drying regime. However, outflow concentrations of nitrogen were significantly higher upon re-wetting following extended dry periods compared with wet periods. This result has implications for current design practices, as these nitrogen pulses could negatively impact the ecological health of downstream receiving waters.

Hatt, B. E., T. D. Fletcher and A. Deletic (2007). The effects of drying and wetting on pollutant removal by stormwater filters. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France. June 24-28, 2007.

Biofiltration systems experience high levels of variability in the frequency and period of inundation and intervening dry period. The effect of alternate wetting and drying on the treatment performance of five different non-vegetated, soil-based filters was tested in the laboratory, where they were exposed to varying periods of inundation and drying. The wetting and drying regime did not influence the treatment of sediment, heavy metals and phosphorus. However, it did have a marked influence on nitrogen, with significantly higher outflow concentrations observed upon re-wetting following extended dry periods compared with wet periods. This result has implications for current design practices, since these nitrogen pulses could have detrimental ecological consequences for downstream receiving waters.

Hatt, B. E., N. Siriwardene, A. Deletic, and T. D. Fletcher (2006). Filter media for stormwater treatment and recycling: the influence of hydraulic properties of flow on pollutant removal. Water Science and Technology, 54(6-7), 263-271.

Improved urban water management in Australia is of national importance. Water resources are stretched and urban runoff is a recognized leading cause of degradation of urban waterways. Stormwater recycling is an option that can contribute to easing these problems. Biofilters are effective structural stormwater pollution control measures with the potential for integration into stormwater treatment and recycling systems. However, premature clogging of biofilters is a major problem, with resulting decreased infiltration capacity (and hence the volume of stormwater the system can detain) and increased detention time. This paper presents preliminary findings with respect to the effect of clogging on pollutant removal efficiency in conventional stormwater filter media. A one-dimensional laboratory rig was used to investigate the impact of clogging on pollutant removal efficiency in a conventional biofiltration filter media (gravel over sand). Both the individual gravel layer and the overall multi-filter were highly efficient at removing suspended solids and particulate-associated pollutants. This removal efficiency was consistent, even as the filters became clogged. Removal of dissolved nutrients was more variable, with little reduction in concentrations overall. Although preliminary, these results challenge the concept that increased detention time improves the treatment performance of stormwater filtration systems.

Hatt, B. E., N. Siriwardene, A. Deletic, and T. D. Fletcher (2005). Novel bioretention systems for stormwater treatment and reuse - laboratory scale performance testing. 10th International Conference on Urban Drainage. Copenhagen, Denmark. August 21-26, 2005.

Le Coustumer, S. and S. Barraud (2007). Long-term hydraulic and pollution retention performance of infiltration systems. Water Science and Technology, 55(4): 235-243.

Infiltration techniques are now widely used to manage stormwater in urban areas. These techniques are used and recognized around the world for their many advantages, such as decreasing stormwater flow in sewer systems and recharging groundwater. But numerous cases of infiltration devices that failed after a few years of operation are still being reported. This study, which is based on sitemonitoring of operational infiltration systems, is part of the Field Observatory for Urban Water Management (OTHU). The main goals of this study are to improve knowledge of long-term hydraulic behaviour, especially as concerns the clogging speed and the quality of the runoff. This article will present the site, the monitoring process and the model that will be used to assess the hydraulic behaviour. First results of the calibration of the model show that the model is able to assess the hydraulic behaviour of the basin when it is clogged (average value of hydraulic resistance 17.1 h) and when it has been scraped (hydraulic resistance less than 3.8 h). However, further data are needed in order to validate the model. We also show that the experimental setup is well designed to assess the water volume and the sediment brought to the basin with low uncertainties.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2008). Influence of time and design on the hydraulic performance of biofiltration systems for stormwater management. 11th International Conference on Urban Drainage (ICUD). Edinburgh, Scotland. August 31-Sept 5, 2008.

Hydraulic conductivity of soil used in biofiltration systems is one of the key parameters to assess when designing and building such systems. However, changes in hydraulic conductivity over time may be a real issue and may lead to a loss of treatment capacity, more frequent overflow and problems with stagnant water. This article aims to study clogging phenomena using a laboratory approach, in order to assess the influence of design parameters (vegetation, size, soil type and inflow concentration) on hydraulic conductivity and its evolution. Hydraulic conductivity was measured on 125 biofiltration columns over a 72 week period. Initial values were within Australian guidelines (50 – 200 mm/h), with a median value of 186 mm/h. After almost 1.5 year of operation, hydraulic conductivity dropped to 27% of the initial value (median of 51 mm/h). Vegetation did not have an influence on clogging, except when a species with course roots, such as Melaleuca, is used. In this case, hydraulic conductivity increases over time. The size of the system relative to its catchment is of prime importance. Small systems (in our case, systems designed at 0.7% of their catchment) are more prone to rapid clogging than are larger systems (designed at 2% or 4% of their catchment). Clogging rate is also influenced by the inflow concentration, increasing with higher concentrations of sediment. These results will inform improved design guidelines for biofilters.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2007). Hydraulic performance of biofilters for stormwater management: first lessons from both laboratory and field studies. Water Science and Technology, 56(10): 93-100.

In order to improve knowledge on stormwater biofiltration systems, the Facility for Advancing Water Biofiltration (FAWB) was created at Monash University in Melbourne, Australia. One of the aims of FAWB is to improve hydraulic performance of biofilters, given that there are numerous cases of infiltration devices failing after a few years of operation. Experiments were conducted in the field to evaluate the performance of existing systems, and in the lab to understand the factors that influence hydraulic behavior over time. The field experiments show that 43% of tested systems are below nominal Australian guidelines for hydraulic conductivity. The preliminary lab results show a decrease in hydraulic conductivity during the first weeks of operation (µ= 66% reduction), although most remain within acceptable limits. Influences of the size of the biofilter relative to its catchment and the importance of the type of media, on the evolution of hydraulic conductivity, are examined.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2007). Hydraulic performance of biofilters: first lessons from both laboratory and field studies. Novatech 2007. 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France. June 24-28, 2007.

In order to improve knowledge on stormwater biofiltration systems, the Facility for Advancing Water Biofiltration (FAWB) was created at Monash University in Melbourne, Australia. One of the aims of FAWB is to improve hydraulic performance of biofilters, given that there are numerous cases of infiltration devices failing after a few years of operation. Experiments were conducted in the field to evaluate the performance of existing systems, and in the lab to understand the factors the influence hydraulic behaviour over time. The field experiments show that 43% of tested systems are below nominal Australian guidelines for hydraulic conductivity. The preliminary lab results show a decrease in hydraulic conductivity during the first weeks of operation (µ=66% reduction), although most remain within acceptable limits. Influences of the size of the biofilter relative to its catchment and the importance of the type of media, on the evolution of hydraulic conductivity, are examined.

Read, J., T. D. Fletcher, T. Wevill, and A. Deletic (2010). Plant traits that enhance pollutant removal from stormwater in biofiltration systems. International Journal of Phytoremediation, 12(1), 34-53.

Plants species have been shown to improve the performance of stormwater biofiltration systems, particularly in removal of N and P. Recent research has shown that plants vary in their contribution to pollutant removal, but little is known about the type of plant that is best suited to use in biofilters in terms of survival, growth rate, and performance. In this study, growth responses of 20 species to applications of semi-synthetic stormwater were measured, and the roles of key plant traits in removal of N, P, and several metals were investigated. There was no evidence of negative effects of stormwater application on plant growth, and plant traits, particularly root traits, were strongly correlated negatively with N and P concentrations of effluent stormwater. The most common and strong contributors to N and P removal appeared to be the length of the longest root, rooting depth, total root length, and root mass. The plants that made the strongest contribution to pollutant removal, e.g., Carex appressa, combined these traits with high growth rates. Investigation of other plant traits (e.g., physiology), causal mechanisms, and effects of more complex planting environments (e.g., species mixtures) should further guide the selection of plants to enhance performance of biofiltration systems.

Read, J., T. Wevill, T. D. Fletcher and A. Deletic (2008). Variation among plant species in pollutant removal from stormwater in biofiltration systems. Water Research, 42(4-5): 893-902.

Biofiltration systems use vegetation to improve efficiency of pollutant removal from stormwater, but little is known of how plants vary in their capacity to improve biofilter effectiveness.We used a pot trial of 20 Australian species to investigate how species vary in the removal of pollutants from semisynthetic stormwater passing through a soil filter medium. Effluent levels of total suspended solids (TSS), Al, Cr, Cu, Pb and Zn were similarly low for vegetated and non-vegetated soils, with reduction to <1-12% of levels in the stormwater input. N and P effluent concentrations were generally lower from vegetated than non-vegetated soils, but total N increased on average in effluent of both vegetated and non-vegetated soils relative to stormwater input. Effluent concentrations varied 2-4-fold among species for TSS, total N and P, total dissolved N (TDN), organic nitrogen and Cu, to more than 20-fold for NOx, NH4+, Mn, Pb and Fe. Species also varied markedly in pollutant removal per root mass (a means of standardising for plant size), with 18-50-fold variation among species in effluent concentrations of total P and N, TDN and organic N, to >150-fold variation in NOx and NH4+. Hence, choice of plant species may have marked effects on biofilter effectiveness.

Zinger, Y., A. Deletic and T. D. Fletcher (2007). The effect of various intermittent wet-dry cycles on nitrogen removal capacity in biofilters systems. Conference on Rainwater and Urban Design. Sydney, Australia. August 21-23, 2007.

Stormwater biofilter systems have the potential to remove nutrients from urban runoff. These systems operate in unique intermittent dry-wet cycles that may affect their performance. Current consensus suggests that sediment drying promotes the release of potentially significant amounts of bio-available nitrogen and phosphorus upon re-wetting. We sought to investigate the impact of drying/wetting cycles on biofilter performance. Eighteen columns were planted with Carex appressa which reached maturity after eight months. The recovery of biofilter systems was tested in a range of drying periods from one to eight weeks with and without a Submerged Anoxic Zone (SAZ) and carbon supplement in the filter media. In all experiments, moisture content, adjacent soil and ambient temperature were logged in parallel to record the drawdown profile behaviour. A freely drained biofilter configuration was used as a control. The results indicated that having a submerged anoxic zone is critical for nitrogen removal at dry periods greater than two weeks. In addition, the anoxic zone was able to enhance biofilter nitrogen removal recovery and make it less dependent on drying/wetting.

Zinger, Y., T. D. Fletcher, A. Deletic, G. T. Blecken and M. Viklander (2007). Optimisation of the nitrogen retention capacity of stormwater biofiltration systems. Novatech 2007, 6th International Conference on Sustainable Techniques and Strategies in Urban Water Management, Lyon, France. June 24-28, 2007.

Excess nitrogen in stormwater is a principal cause for eutrophication of many water bodies in the world. Biofilters, which used a vegetated soil media, have been shown to reduce nitrogen concentrations in stormwater, although there is substantial scope to improve their current nitrogen removal performance. This paper explores the nitrogen transformations in biofilters and optimised theirs design to maximise removal. To achieve this, 20 columns were constructed to test a range of submerged anoxic zone (SAZ) depths, to maximise denitrification. The effect of adding a carbon source to act as an electron donor supplement in the filter media was also tested. Nitrate removal of up to 99% was achieved, with removal by columns with added carbon significantly greater, with a mean removal of greater than 90%, whilst the non-carbon columns showed an average 50% nitrate removal. Depth profiles revealed that mineralization is the limiting step of nitrogen removal in the biofilter columns. The results will contribute to guidelines for optimal biofilter design.

Hatt, B. E., T. D. Fletcher and A. Deletic (2009). Hydrologic and pollutant removal performance of biofiltration systems at the field scale. Journal of Hydrology, 365(3-4): 310-321.

Biofiltration systems are a recommended and increasingly popular technology for stormwater management; however there is a general lack of performance data for these systems, particularly at the field scale. The objective of this study was to investigate the hydrologic and pollutant removal performance of three field-scale biofiltration systems in two different climates. Biofilters were shown to effectively attenuate peak runoff flow rates by at least 80%. Performance assessment of a lined biofilter demonstrated that retention of inflow volumes by the filter media, for subsequent loss via evapotranspiration, reduced runoff volumes by 33% on average. Retention of water was found to be most influenced by inflow volumes, although only small to medium storms could be assessed. Vegetation was shown to be important for maintaining hydraulic capacity, because root growth and senescence countered compaction and clogging. Suspended solids and heavy metals were effectively removed, irrespective of the design configuration, with load reductions generally in excess of 90%. In contrast, nutrient retention was variable, and ranged from consistent leaching to effective and reliable removal, depending on the design. To ensure effective removal of phosphorus, a filter medium with a low phosphorus content should be selected. Nitrogen is more difficult to remove because it is highly soluble and strongly influenced by the variable wetting and drying regime that is inherent in biofilter operation. The results of this research suggest that reconfiguration of biofilter design to manage the deleterious effects of drying on biological activity is necessary to ensure long term nitrogen removal.

Hatt, B. E., T. D. Fletcher and A. Deletic (2008). Improving stormwater quality through biofiltration: lessons from field studies. 11th International Conference on Urban Drainage (ICUD). Edinburgh, Scotland. August 31-Sept 5, 2008.

Biofiltration systems are an increasingly popular low-energy treatment technology for improved stormwater management. However, while extensive laboratory testing has demonstrated their capacity for effective removal of a wide range of stormwater pollutants, field-scale performance data is limited. Three stormwater biofiltration systems of varying size, age and catchment characteristics, and in two different climates, were monitored to evaluate their pollutant removal performance. Concentrations of suspended solids and heavy metals were effectively and reliably reduced at all three sites. Effluent nutrient concentrations, on the other hand, were more variable and ranged from being substantially lower, through to considerably higher, than influent stormwater concentrations. These results are essentially consistent with related laboratory studies. Suspended solids and heavy metals will be reliably removed by a wide range of soil-based filter media and phosphorus also, provided the filter media has a low phosphorus content. Retention of nitrogen remains a challenge because it is easily transformed to soluble forms and is influenced by the variable wetting and drying that is inherent in biofilter function. However, a related laboratory study of biofiltration systems that incorporates a permanent pool of water at the bottom of the systems has demonstrated the potential for buffering against desiccation.

Hatt, B. E., J. Lewis, A. Deletic and T. D. Fletcher (2007). Insights from the design, construction and operation of an experimental stormwater biofiltration system. Conference on Rainwater and Urban Design. Sydney, Australia. August 21-23, 2007.

Biofiltration systems are being installed on an ever-increasing scale, both for stormwater quality improvement and as a component of stormwater reuse systems. However, there is currently a general lack of knowledge regarding their design, implementation and performance. This paper reports on the issues encountered and lessons learnt during the installation and operation of an experimental biofiltration system. While the water industry familiarizes itself with biofiltration technologies, effective communication and clear guidance is required to ensure successful construction and operation of biofilters. The studied biofiltration system consisted of three separate cells, each containing a different, soil-based media type. Compaction of filter media, organic matter and moss growth significantly reduce hydraulic conductivity, however root penetration and the addition of vermiculite and perlite appear to assist in maintaining porosity. Preliminary treatment performance results indicate that all three cells effectively remove sediment and heavy metals (lead, copper and zinc), however they are all net producers of nitrogen and phosphorus. However, biofiltration systems appear to be promising technologies for treatment of stormwater, both for reuse and aquatic ecosystem protection.

Le Coustumer, S., T. D. Fletcher, A. Deletic and S. Barraud (2007). Hydraulic performance of biofilters: first lessons from both laboratory and field studies. Water Science and Technology, 56(10), 93–100.

In order to improve knowledge on stormwater biofiltration systems, the Facility for Advancing Water Biofiltration (FAWB) was created at Monash University in Melbourne, Australia. One of the aims of FAWB is to improve hydraulic performance of biofilters, given that there are numerous cases of infiltration devices failing after a few years of operation. Experiments were conducted in the field to evaluate the performance of existing systems, and in the lab to understand the factors the influence hydraulic behaviour over time. The field experiments show that 43% of tested systems are below nominal Australian guidelines for hydraulic conductivity. The preliminary lab results show a decrease in hydraulic conductivity during the first weeks of operation (µ=66% reduction), although most remain within acceptable limits. Influences of the size of the biofilter relative to its catchment and the importance of the type of media, on the evolution of hydraulic conductivity, are examined.

Le Coustumer, S., T. D. Fletcher, A. Deletic, S. Barraud and J. F. Lewis (2009). Hydraulic performance of biofilter systems for stormwater management: influences of design and operation. Journal of Hydrology, 376(1-2), 16-23.

In order to evaluate the long-term performance of stormwater biofilters, a study was undertaken to assess their hydraulic conductivity. Despite variability in conductivity (40% being below the recommended range of 50–200 mm/h, 43% within it, and 17% above), treatment performance is unlikely to be affected, as most systems are over-sized such that their detention storage volume compensates for reduced media conductivity. The study broadly reveals two types of systems: some with a high initial conductivity (>200 mm/h) and some with a low initial value (<20 mm/h). Significant reduction in conductivity is evident for biofilters in the former group, although most are shown to maintain an acceptably high conductivity. Those with initially low conductivity do not change greatly over time. Site characteristics such as filter area (relative to catchment area), age and inflow volume were not useful predictors of conductivity, with initial conductivity of the original media being the most powerful explanatory variable. It is clear therefore, that strict attention must be paid to the specification of original filter media, to ensure that it satisfies design requirements.

Lewis, J. F., B. E. Hatt, S. Le Coustumer, A. Deletic and T. D. Fletcher (2008). The impact of vegetation on the hydraulic conductivity of stormwater biofiltration systems. 11th International Conference on Urban Drainage. Edinburgh, UK. August 31-Sept 5, 2008.

Stormwater biofiltration systems are an increasingly popular treatment technology and are being installed in all major cities in Australia. Their concept is very simple and easily implemented in all urban forms. Unfortunately, we know very little about the performance of biofiltration systems, particularly with respect to their long-term hydraulic performance. There is some concern regarding the ability of biofiltration systems to treat the design volume of stormwater for the duration of their intended lifespan, or whether factors such as compaction of the filter media and surface clogging will impede their infiltration performance. To address this knowledge gap, the Facility for Advancing Water Biofiltration has been monitoring the hydraulic capacity of field-scale biofiltration systems. Vegetation was shown to be critical in maintaining the infiltration capacity of biofiltration systems, helping them to recover from the inevitable reduction in hydraulic conductivity due to initial compaction of the filter media under hydraulic loading. The creation of macropores due to root growth and senescence is thought to contribute to this behaviour. Biofiltration systems were shown to attenuate mean peak flows by 80% (range 45 - 96%). A performance analysis of a lined biofiltration system demonstrated that, on average, 42% of an event volume (range: 15 - 83%) was retained by the filter media and subsequently lost via evapotranspiration. This high level of losses is mainly due to the fact that the monitored events were largely small to medium in their size (monitoring of large events was not conducted).

Smith, N., R. Allen, A. McKenzie-McHarg, A. Deletic, T. D. Fletcher and B. Hatt (2007). Retrofitting functioning stormwater gardens into existing urban landscapes. Cairns International Public Works Conference, Cairns. August 26-30, 2007.

Urban stormwater runoff has a major impact on waterway health in South East Queensland. Over the next 20 years an additional one million people are expected to move to the region, further increasing pressure on waterways. In line with growth in South East Queensland, Brisbane's population is expected to expand by 15%, most of which will be accommodated through infill and redevelopment of existing urban land. Stormwater gardens (street-scale biofiltration systems) are one of a number of devices currently being investigated by Brisbane City Council to improve urban stormwater quality. These systems provide an opportunity for Water Sensitive Urban Design (WSUD) to be retrofitted in existing urban areas as well as implemented as part of infill and redevelopment of appropriate sites. The constraints that existing urban infrastructure places on the design and construction of WSUD measures presents a considerable challenge to the retrofit potential of these systems in Brisbane. This paper documents the design, construction and maintenance of a retrofit stormwater garden in the northern suburbs of Brisbane. Ongoing simulated and actual storm-event monitoring of these stormwater gardens presents a unique opportunity to gain a greater understanding of the treatment processes and performance of these systems under Brisbane's climatic conditions.