Treating Urban Runoff in Australia Using Floating Wetlands Christopher WALKER 1,2 , Darren DRAPPER 3 , Peter NICHOLS 2 , Kristin REEVES 2 , and Terry LUCKE 2 1 Covey Associates Pty Ltd, 124 Duporth Avenue, Maroochydore, Queensland, 4558 Australia 2 University of the Sunshine Coast, School of Science and Engineering, 90 Sippy Downs Drive, Sippy Downs, Queensland 4556 Australia 3 SPEL Environmental, 96 Cobalt St, Carole Park, Queensland 4300 *Corresponding author’s e-mail: [email protected]ABSTRACT Overview It is widely accepted that Australia's increasing levels of urbanisation will result in increased stormwater runoff and higher levels of pollution. Water sensitive urban design (WSUD) has risen in prominence as a consequence of the need to address stormwater issues in relation to urban development. Integrating urban planning and management practices to protect and conserve the urban water cycle and ensuring that urban developments are sensitive to natural hydrological and ecological processes are key principles of WSUD. Constructed wetlands and bioretention systems have been used previously to replicate and enhance the environmental benefits and ecosystem services provided by natural buffer systems (e.g. natural wetlands). This paper describes the performance evaluation of an innovative solution to treating stormwater in the form of an artificial floating wetland. Floating Wetlands Treatment (FWT) systems have the potential to provide greater stormwater pollution removal rates per unit area compared to constructed wetlands and other treatment systems. A research study is underway at Bribie Island in Southeast Queensland (SEQ) to assess the ability of FWT to treat stormwater. The experimental design of the study incorporates an array of impermeable baffles which directs all of the catchment stormwater runoff through the FWT system, eliminating short circuiting and allowing the efficacy of the system to be assessed in variable flow conditions. This approach has successfully eliminated the short circuiting issues experienced in previous studies. This approach makes the FWT an on-line treatment system and enables real- time water sampling to be undertaken to accurately evaluate the FWT pollution removal performance. 1
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Treating Urban Runoff in Australia Using Floating Wetlands
Christopher WALKER1,2, Darren DRAPPER3, Peter NICHOLS2, Kristin REEVES2, and Terry LUCKE2
1Covey Associates Pty Ltd, 124 Duporth Avenue, Maroochydore, Queensland, 4558 Australia2University of the Sunshine Coast, School of Science and Engineering, 90 Sippy Downs
MUSIC urban residential range (mg/L) 61.7 - 372 1.07 – 3.09 0.162 – 0.708
Based upon the results outlined in Table 3, the FWT demonstrated pollutant concentration
reductions from the inlet to the outlet of 56.1% for TSS, 27.1% for TN and 83.33% for TP.
Results – 3 July 2015 (Pump Test)The pump test was conducted to assess three separate, but linked, issues. First, to test the flow
meter in controlled conditions,; second, to utilise a rhodamine dye to determine the hydraulic
residence time through the FWT in a simulated Q3-MONTH event (200L/s flow rate); and third, to
utilise the dye to determine if there were any breaches in the impermeable baffles that may be
affecting flow readings at the Sontek IQ Plus. While the above issues were being tested,
samples were collected by all three autosamplers at 10 minute intervals, with 6 samples
collected at a flow rate of 100L/s and 17 samples collected at a flow rate of 200L/s. The
average pollutant concentrations for the 100L/s and 200L/s flow rates are summarised in Table
4.
Table 4 - Sample results from 3/7/14 (Pump test)Flow Rate (L/s) Sampler Average Concentrations
TSS (mg/L) TN (mg/L) TP (mg/L)100
(n-6)S1 302.67 1.68 0.11
(n-6) S2 137.83 1.16 0.06S3 9.33 0.93 0.01
200(n=17)
S1 79.35 1.09 0.04(n=17) S2 86.53 1.07 0.04
S3 23.47 0.94 0.01MUSIC urban residential
range (mg/L) 61.7 - 372 1.07 – 3.09 0.162 – 0.708
Based upon the results in Table 4, the average pollutant concentration reductions from the inlet
to the outlet of the system in a 100L/s flow rate were 96% for TSS, 41% for TN and 91% for
TP. In a 200L/s flow rate, the average pollutant concentration reductions from the FWT inlet
to outlet were 68% for TSS, 13% for TN and 63% for TP.
The rhodamine dye test was conducted in a simulated flow rate of 200L/s, which equates to a
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Q3MONTH event. The dye was observed exiting the FWT system after approximately 8 minutes,
giving an estimated HRT of 8 minutes, for the test configuration, in the frequent flow event.
During the dye test, it was observed that there were some minor repairs required to the
impermeable baffle, as trace amounts of dye were noticed escaping at the top edge of the FWT
system. Whilst this will not adversely affect the function of the FWT, it may influence the
accuracy of the flow measurement.
DISCUSSION OF PRELIMINARY RESULTSThe preliminary results suggest that the FWT system has the potential to effectively remove
pollutant loads from stormwater runoff. The results also show that the efficacy of the FWT
appears to be inversely proportional to flowrate similar to existing stormwater treatment
measures (i.e. the greater the flowrate, the less effective the treatment). However, the results
outlined in this paper are preliminary only and should be considered in this context. Two
sample sets cannot be considered to be representative of stormwater treatment efficacy,
particularly as these two sample sets were collected on time-based intervals, rather than flow,
and one of the sample sets was a simulated event.
Although simulated, the pump test provided a valuable insight into the effectiveness of the
FWT in treating stormwater over time and under variable flow conditions. Figure 3 highlights
the differences in water clarity observed between some of the water samples taken during the
pump test. The left hand bottles in Figure 3 contain the FTW inlet water samples collected
from Sampler 1. The water in the middle bottles were collected from Sampler 2. The water in
the right hand bottles shown in Figure 3 were from Sampler 3 located at the outlet of the FTW
(Figure 2). It is clear from Figure 3 that the clarity of the water samples improved as it
travelled further along the floating wetland.
The study is ongoing and we are continuing to optimise the testing methodology and fine-tune
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the equipment operational issues. The initial results are very encouraging and we will update
our research findings as the research progresses. However, based upon the results of similar
studies by Borne et al. (2013) and Winston et al. (2013), it is anticipated that the study results
will continue to show an improvement in the quality of the urban stormwater runoff achieved
by the FWT.
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Figure 3 – Samples taken during pump test on 3/7/14. Left hand bottles were from Sampler 1 (FTW Inlet), Middle Bottles were from Sampler 2, Right hand bottles were from Sampler 3 (FTW Outlet)
LESSONS LEARNED This research study was originally planned to commence in November 2013. However, there
were a number of unforeseen events which delayed the start of the project. The study was
established within an active construction site with its own deadlines and constraints, many of
which impacted the installation timeframes for the FWT. Bulk earthworks construction was
ongoing during the trial installation and the batters of the study lake needed to be re-profiled for
future landscaping. These works would prevent the installation of the FWT and were in turn
delayed by sporadic rainfall. It was difficult to anticipate these constraints. Therefore with any
research study in a similar setting, it is critical to be flexible with start times and research
budget. Timing of outputs, and similar, should not be reliant on a firm commencement date. As
a conservative estimate, it should be assumed that any studies timeframe can be at least
doubled. These delays can be due to sporadic weather events, on-site construction activities, or
availability of relevant personnel.
Equipment faults are often common in storm event sampling and this study has been no
exception. The research team is currently investigating alternate means to record flow data and
have this approach be a trigger point for sampling to commence. The current approach in
which a Sontek IQ Plus triggers the sampling once a 0.03m/s velocity is recorded, in tandem
with a minimum of 2mm of rainfall in 30 minutes, with a 19,500L flow-weighting, is not
working as the flow meter is failing to record any flow velocity. This has led to at least three
rainfall events being missed and having to rely on time-based sampling rather than flow-based
intervals. An alternate approach is required where flow velocities through the FWT can still be
profiled, so this can be correlated to pollutant reduction performance.
Effective communication and collaboration between industry and research partners is also
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critical. While there were delays to commencing the research study, all parties involved were in
regular communication so all stakeholders were quickly aware of said delays and able to adapt
as required. This also proved to be extremely valuable in refining the research method, as all
parties were able to effectively build an approach that would yield meaningful and valuable
outcomes to all stakeholders. In addition to effective communication, it is also advisable to ask
for as much help in the design from recognised experts as possible. While refining this research
study, we found a number of internationally recognised experts were generally quite willing to
share their experiences and offer valuable advice. Input and constructive criticism from outside
parties should be welcomed to realise a useful and robust outcome. This can help the study to
adapt to unforeseen circumstances or approaches/methods that may have been overlooked.
It was critical to design this research study to be as flexible as possible. Presently, there is no
standard approach or method for trialling proprietary stormwater treatment products within
Australia. The lack of a standardised method can create difficulties, as it is not possible to
cater for every eventuality. Therefore, it is critical that the approach taken be adaptable. As
there is little data on the efficacy of floating wetlands in treating urban stormwater, this study
design has made allowance for additional floating wetland modules to be installed in the system
at a later date if required. This will allow the results to provide a better understanding of
floating wetland area requirements in a variety of catchments.
CONCLUSIONThe paper presents initial findings of an investigation into using floating wetlands to treat
urban stormwater runoff in Australia. Preliminary test results of a real rainfall event showed
that the FWT system reduced average pollutant concentrations from the inlet to the outlet of
56.1% for TSS, 27.1% for TN and 83.33% for TP. Simulated pump testing results
demonstrated average pollutant concentration reductions from the inlet to the outlet of 96% for
TSS, 41% for TN and 91% for TP at a flow rate of 100L/s. During a test using a flow rate of
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200L/s, the average pollutant concentration reductions from the FWT inlet to outlet were found
to be 68% for TSS, 13% for TN and 63% for TP. The study results suggest that floating
wetlands may offer an innovative and cost-effective approach to stormwater treatment.
The study is ongoing and we are continuing to optimise the testing methodology and fine-tune
the equipment operational issues. The initial results are very encouraging and we will update
our research findings as the research progresses. However, based upon the results of similar
studies it is anticipated that the study results will continue to show an improvement in the
quality of the urban stormwater runoff achieved by the FWT. Once the initial teething issues
are taken care of, the results of this research study will be of significant interest for developers
and local government authorities both in Australia and internationally.
ACKNOWLEDGEMENTSThe authors of this paper would like to acknowledge the developer for the site, Mr Ty Wardner
of Wardner Developments, for his encouragement, support and use of the development land for
this research project. We would also like to acknowledge Moreton Bay Regional Council for
their interest and support of this project. Last but not least, we would especially like to thanks
Mr Darryl Sullivan and Mr Michael Nielsen from USC Analytical Services for all their help
and support.
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Presenter’s BIO
Chris Walker moved to Australia in 2002 from New York to study at the University of the
Sunshine Coast, completing a Bachelors of Environmental Science (Marine Specialty) and
followed with an Honours Degree at Queensland University of Technology. The Honours
degree was the start of his research into stormwater and water sensitive urban design. This
research continued in a PhD study at the University of the Sunshine Coast. Chris has been
employed at Covey Associates since 2007 as the Senior Environmental Scientist and is also the
Environmental Manager for the company. Chris’s role sees him involved in a wide range of
development projects, both in Australia and abroad.
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