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Treating runoff in the construction and operational
phases of a greenfield development using floating
wetland treatment systems
Traiter les eaux de ruissellement dans les phases de
construction et d'exploitation d'un aménagement à l'aide de
Dr Christopher Walker
, Dr Terry Lucke
, Dr Floris
Boogaard*** and Mr Peter Schwammberger
* Covey Associates Pty Ltd, Sunshine Coast, Australia
** Stormwater Research Group, University of the Sunshine Coast, Australia
*** Water Management, Delft University of Technology
Les systèmes flottants de traitement des zones humides (FWTS) sont une technologie innovante pour
le traitement des eaux pluviales, qui est actuellement à l'essai en Australie. Les FWTS apportent un
soutien aux espèces de plantes sélectionnées pour éliminer les polluants provenant des eaux
pluviales déversées dans un plan d'eau. Les racines des plantes fournissent de grandes surfaces pour
la croissance du biofilm, qui sert à piéger les particules en suspension et à permettre l'absorption des
nutriments biologiques. Les FWTS peuvent être installés au début de la phase de construction et
peuvent donc commencer à traiter les eaux de ruissellement de construction presque immédiatement.
Les FWTS ont le potentiel de fournir une gamme complète de traitements des eaux pluviales (par
exemple, les sédiments et l'élimination des nutriments) à partir de la phase de construction. Un
système FWTS de 2 100m2 a été installé dans un nouveau site de développement sur la Sunshine
Coast, dans la région du Queensland. Une étude de quatre ans est en cours pour cibler les trois
objectifs suivants : (1) caractériser la qualité des eaux de ruissellement à partir d'un développement
Greenfield dans la phase de construction et la phase opérationnelle; (2) vérifier les performances
d’élimination de la pollution des eaux pluviales d'un système FWTS pendant la phase de construction
et d'exploitation d'un développement Greenfield; et (3) caractériser la capacité du FWTS à gérer la
santé du plan d’eau urbain. Ce document présente la méthodologie appliquée à la recherche.
Floating wetland treatment systems (FWTS) are an innovative stormwater treatment technology
currently being trialled on a larger scale in Australia. FWTS provide support for selected plant species
to remove pollutants from stormwater discharged into a water body. The plant roots provide large
surface areas for biofilm growth, which serves to trap suspended particles and enable the biological
uptake of nutrients by the plants. As FWTS can be installed at the start of the construction phase, they
can start treating construction runoff almost immediately. FWTS therefore have the potential to provide
the full range of stormwater treatment (e.g. sediment and nutrient removal) from the construction
phase onwards. A 2,100m
FWTS has been installed within a greenfield development site on the
Sunshine Coast, Queensland. A four-year research study is currently underway which will target the
following three objectives; (1) characterise the water quality of runoff from a greenfield development in
the construction and operational phases; (2) verify the stormwater pollution removal performance of a
FWTS during the construction and operational phases of a greenfield development; and (3)
characterise the ability of FWTS to manage urban lake health. This extended abstract presents the
proposed research methodology and anticipated outcomes of the study.
Construction runoff, floating wetlands, greenfield development, stormwater treatment, urban runoff
Floating Wetland Treatment Systems (FWTS) have been used in aquatic enhancement projects for
over 20 years internationally to treat effluent and to provide and/or improve water habitats (Burgess
and Hirons, 1992; Kerr-Upal et al., 2000; Headley and Tanner, 2008; Sukias et al., 2011). The
purpose of several early FWTS projects was to provide habitat for aquatic waterfowl (Kerr-Upal et al.,
2000), while other projects focused on the removal of total suspended solids (TSS) pollutants from
mine tailings (Burgess and Hirons, 1992; Smith and Kalin, 2000; Walker et al., 2015a). These are
designed to simulate naturally occuring floating wetlands with the aim of maximising root exposure to
the water column, therefore providing a significant surface area for biofilm growth.
Manufactured FWTS are supported by a floating medium, typically comprised of woven plastic,
matting, or fibreglass, where plant roots grow directly into the water column, similar to a hydroponic
system. As the plant roots grow through the floating medium and into the water below, they provide an
extensive surface area for biofilm to grow on the root hairs (Figure 1). Biofilm coverage is an essential
requirement for the sequestration of nutrients from stormwater (Borne et al., 2013; Winston et al.,
2013), as it helps remove nutrients (particularly nitrogen) from the water through
nitrification/denitrification processes, and is ultimately taken up by the macrophytes. Phosphorus can
be retained through binding processes that occur within the biofilm (e.g. adsorption) and uptake of
orthophosphates is achieved by vascular macrophyte species.
Figure 1 - Floating Wetland Schematic
Research in the United States (Stewart et al., 2008) and New Zealand (Sukias et al., 2011) has found
that FWTS can provide an effective, low cost and low maintenance means of treating domestic and
agricultural wastewater. Sukias et al. (2011) found that FWTS were capable of reducing TSS by up to
81%, total nitrogen (TN) by up to 34%, and total phosphorus (TP) by up to 19%. However, the number
of studies on the performance of FWTS in treating urban stormwater runoff is limited.
To quantify the ability of FWTS to remove sediment and nutrients from runoff, a total 2100m
being installed within a new greenfield development, Parklakes 2, on the Sunshine Coast, in
Southeast Queensland, Australia. This will be the largest installation of FWTS into a greenfield
development in the world and is subject to a four-year research project. This research project will
address the following objectives:
(1) characterise the water quality of runoff from a greenfield development in the
construction and operational phases;
(2) verify the stormwater pollution removal performance of a FWTS during the
construction and operational phases of a greenfield development; and
(3) characterise the ability of FWTS to manage urban lake health. This paper
will present the research methodology.
In order to achieve the above objectives, field and laboratory monitoring will take place. The field
monitoring will be event-based, with samples collected at the inlets and outlets of two floating wetland
areas (Figure 2). Lab verification testing will take place to verify the results of the field study in
controlled circumstances, using real and artificial stormwater. Pollutant removal performance will be
investigated in both the construction and operational (e.g. build form) phases of the development.
Low-intensity storm events will be replicated using a recirculation pump that has been installed in the
development. As part of the event replication, analysis will be conducted on the ability of the FWTS to
remove algal cells and reduce cholophyll-a concentrations. The purpose of this assessment is to
determine if FWTS are an adequate management strategy for algal growth in constructed water
Figure 2 - Parklakes 2 FWTS
4 ANTICIPATED OUTCOMES
Many WSUD stormwater treatment systems, such as bioretention basins and constructed wetlands,
function best when ‘offline’, with extended detention depths minimised and events greater than four
Exceedances per Year (EY) bypassing such systems (Water by Design, 2012a, 2012b). This often
requires detention/retention basins to be separate from treatment systems. In contrast, FWTS have
the potential to substantially reduce the footprint required for stormwater treatment compared with
other systems for two main reasons. Firstly, the hydroponic nature of root development allows for a
great surface area for biofilm growth and inherently more contact between biofilm coated roots and
polluted stormwater. It is anticipated that the results of this study will clearly show that FWTS have the
potential to provide significantly greater rates of stormwater pollution removal per unit area compared
with constructed wetlands, as biofilm growth is limited to plant stalks in constructed wetlands (Walker
et al., 2014a; Walker et al., 2014b).
Secondly, FWTS are not affected by variations in extended detention depths, as the floating matrix
rises with the water level during storm events. In contrast, prolonged extended detention in
constructed wetlands and bioretention basins can lead to plant mortality. These factors allow detention
and treatment systems to be combined on a large scale with minimal impact to treatment efficacy.
Subject to appropriate system design, there is virtually no impact on flood storage capacity. It is also
theerfore anticipated that the results of this study will demonstarte how FWTS can substantially reduce
the stormwater treatment footprint on residential development, thereby providing greater areas of
passive / active open space or increasing lot yields per hectare.
In addition to the above, given that the FWTS are not impacted by extended detention and can be
incorporated into detention systems, these systems are able to be installed during the construction
phase of a development, rather than at its completion. In Australia, WSUD systems are not typically
established (e.g. planted) until 80% of the dwellings within the contributing catchment are completed,
as the impacts from sediment laden runoff can significantly reduce the lifespan of traditional systems
(e.g. constructed wetlands and bioretention basins). In contrast, FWTS are not impacted by
construction runoff and may in fact benefit from it, as fine particles within construction runoff are often
bound by nutrients, due to the greater surface area and greater binding capacity provided by fine
sediment particles. The results of this study are expected to demonstrate the benefits of implementing
FWTS at the start of the construction phase.
LIST OF REFERENCES
Borne, K.E., Fassman, E.A., and Tanner, C.C. (2013), Floating treatment wetland retrofit to improve
stormwater pond performance for suspended solids, copper and zinc, J. Ecological Engineering
Burgess, N.D. and Hirons, G.J.M. (1992), Creation and management of artificial nesting sites for
wetland birds, Journal of Environmental Management, 34(4), 285-295.
Headley, T.R. and Tanner, C.C. (2008), Floating Treatment Wetlands: An Innovative Option for
Stormwater Quality Applications, 11th Int. Conf. on Wetland Systems for Water Pollution Control,
Nov. 1-7, Indore, India.
Kerr-Upal, M., Seasons, M., and Mulamoottil, G. (2000), Retrofitting a stormwater management facility
with a wetland component, Journal of Environment Science and Health, 35(8), 1289 – 1307.
Smith, M.P. and Kalin, M. (2000), Floating wetland vegetation covers for suspended solids removal,
Treatment Wetlands for Water Quality Improvement Conference, Quebec, Canada.
Stewart, F.M., Mulholland, T., Cunningham, A.B., Kania, B.G., and Osterlund, M.T. (2008). Floating
islands as an alternative to constructed wetlands for treatment of excess nutrients from
agricultural and municipal wastes – results of laboratory-scale tests, Land Contamination &
Reclamation, 16(1), 25-33.
Sukias, J., Yates, C., and Tanner, C.C. (2011), Floating islands for upgrading sewage treatment
ponds. National Institute of Water & Atmospheric Research Ltd, Hamilton, New Zealand.
Walker, C., Nichols, P., Reeves, K., Lucke, T., Nielsen, M., Sullivan, D. (2014a) Use of Floating
Wetlands to Treat Stormwater Runoff from Urban Catchments in Australia, 13
Conference on Urban Drainage, 7-12 September, 2014, Sarawak, Malaysia.
Walker, C., Drapper, D., Nichols, P., Reeves, K., Lucke, T. (2014b). Treating Urban Runoff in Australia
using Floating Wetlands, Stormwater Australia National Conference, 13 – 17 October, 2014,
Water by Design (2012a), Bioretention Technical Design Guidelines (Version 1), Healthy Waterways
Water by Design (2012b), Maintaining Vegetated Stormwater Assets (Version 1), Healthy Waterways
Winston, R.J., Hunt, W.F., Kennedy, S.G., Merriman, L.S., Chandler, J., and Brown, D. (2013),
Evaluation of floating treatment wetlands as retrofits to existing stormwater retention ponds,
Ecological Engineering, 54, 254-265.