Floating gardens protect water quality

It is a  keen concern of AUSMEPA members for clean water to enter the ocean from the land. For that to happen we need to make sure our watercourses and ground water are healthy and clean before reaching the sea.

We had the privilege of interviewing Dr. Chris Walker, Environmental Manager of the engineering consultancy firm, Covey and Associates in relation to his work on the design and implementation of floating gardens for water treatment. It has been Dr Walker's long time passion and career path to integrate two seemingly disparate disciplines, engineering and environmental science. 

A Sunshine Coast Daily article by Janine Hill, 25 Nov 2015, Headed New water treatment system floated at Bli Bli subdivision said,

"A NEW floating wetland water treatment system at a Bli Bli subdivision will be the subject of a four year research project.The floating water treatment system at Parklakes II is the first time such a system has been used on a greenfield development of such size. The system will involve the installation of 230 "living" pontoons to filter man-made lakes which will tackle the stormwater from 436 residential lots, a school, and a 226 unit retirement village in the subdivision."

It was noted in the article that Dr Walker had been working with the University of the Sunshine Coast since 2010 to optimise the system. Research and monitoring of the system is on-going as the wetland system has great potential in environmental management. Here is what he told us about the Bli Bli project:

Q: Engineering and Environment are seemingly at odds with each other in many instances, what lead you to this niche space?

A: This is a really great question! Engineering and the environment are often seen to be at odds, but so much of what we know about engineering stems from nature. There is a significant shift towards adopting more nature based solutions in engineering and I think that it is fantastic and something I’ve pursued as part of my research. My research actually led to my career at Covey Associates and led me to this niche space. As an environmental scientist in the engineering field, my role is to work out science-based solutions to difficult engineering questions. I work really closely with some amazing civil engineers and researchers to address some complex questions and it’s a great role and experience.

Q: What compels Covey to choose best practice environmental stormwater solutions?

A:  We have to comply with relevant local government policy and state government policy, as well as obligations under federal legislation. But if you integrate stormwater treatment correctly, it can certainly be a value adding outcome, socially, environmentally and from an economic point of view. We aim to add value to the developments we work in and we think stormwater treatment can be an opportunity to provide this.

Q: What prompted the trial of the Floating Water Treatment System  (FWTS ) in the greenfield development site at Parklakes II?A: We wanted to try something different. I had been involved with floating wetland design and research at sites in Gladstone and Bribie Island and the data suggested it would work on a larger scale. In close collaboration with the developer of Parklakes 2 and Council, we developed an approach that we believed would suit. We have also incorporated a detailed research program as part of implementing the floating wetlands, which is ongoing and will hopefully fill some key knowledge gaps

Q: The Maroochy River has had some water quality issues over the years. Are the three lakes at Parklakes II part of the Maroochy River system or are they man-made?

A: The three lakes are man-made and serve as a tiered detention system, as well as playing home to a number of fish species (e.g. Australian Bass and Silver Perch). We also have a recirculation system that draws water up from the bottom lake and discharges to the top lake to keep the lakes oxygenated and healthy.

Q: How does the water from the detention basin (lake) system actually enter the waterways to the ocean?
A: The lakes drain down into the cane drains to the north of the development, ultimately enter the Maroochy River and then make their way to the ocean.

Q: What performance indicators are you looking for, and how is the site holding up against the benchmarks?

A: The key performance indicator is how the floating wetland plant roots remove pollutants from stormwater runoff. The roots are the most critical component of event-based treatment, as they disperse flow velocity and promote settlement and ‘trapping’ of stormwater pollutant (i.e. suspended solids). The biggest issue we’ve had on site is that during the events, the pollutant concentrations coming into the system are so low, it’s difficult to assess the performance. If you’ve got clean water coming in and clean water going out, it’s not easy to say it’s removing much.

Q: How do you choose plants for the floating garden?
A: How do you choose plants for the floating garden? We chose Carex appressa on the basis of previous research, however, we are looking at several different plants in different projects. It's a constantly evolving process.

Q: What contingents impact on the successful mitigation of runoff pollution from greenfield sites like these?

A: There are several things that could impact successful treatment of runoff. First, poor design of a treatment system. If it is not sized appropriately, it won’t function effectively. Second, not taking into account the type of development. Certain treatment approaches are suitable for certain development types and not suitable for others. There needs to be careful consideration as to how the community will ultimately view the treatment asset. I also feel that trying to establish custodianship within the community is a great way to get people to think about their impacts and adapt behaviours to reduce pollution. There are a range of other things that could impact the successful implementation of a water treatment system in a greenfield development, but those two issues, in my opinion, are some of the most critical.

Q: Are FWT Systems adaptable to changing weather patterns expected with a warming planet?

A: They certainly are. The biggest impact that climate change might have on floating wetland systems is prolonged drought. As these systems need water to function, it’s critical that they are implemented in appropriate places. It’s unlikely to be successful in arid regions of the outback, that is for sure. But on the other end of the spectrum, they do quite well in severe storm situations, as they fluctuate upwards with the water level. The most critical thing there is the anchor design and we’ve learned a lot from some trials and tribulations in the earlier days of the floating wetland installation at Parklakes 2.

Q: There are no fences around the lakes. It begs the question whether water treatment lake areas like this are suitable for swimming?

A: The lakes are designed for passive, not active recreations. We didn’t want to put fences up as it creates a very sterile and unwelcoming outcome. We do have some fences around the floating wetlands, but this was largely due to the fact Council was not entirely sure as to how the community would react to a large scale system. In lieu of fences, we’ve created passive barriers to the lakes through dense, lake-edge vegetation. Not only does this create an aesthetic outcome, it also creates critical riparian habitat, which is really important from an ecological perspective.

Q: Within your context, has thought been given to seasonal migration and wildlife corridors through the redefined land spaces since the lakes are cut off from the forest? Have residents been encouraged to make their yards havens for these migrations?

A:This is an interesting question! I think it needs to be considered in the context of the pre-development scenario. Prior to Parklakes 2, the site was a cane field, which is obviously serving an agricultural purpose and not one that generally promotes biodiversity or wildlife movement. With the creation of the lakes, this presents a unique habitat for birds that was not present previously. So in the case of Parklakes 2, there was no real protected corridors on the site. Generally speaking, however, I firmly believe that if there are existing wildlife corridors that may be impacted by a development, all due care and consideration should go into the design to mitigate these impacts and recreate, or better, enhance the corridors.

Q: In regard to the "proof of the pudding," how does biodiversity in the lakes compare to other water collection basins near developments that do not have floating treatments.

A: We’re not actually sure, but again, a great question. It’s presumed that the floating wetlands will provide enhanced habitat, as it will allow juvenile fish to have a ‘safe space’ to grow to maturity, lessening the likelihood of predation by waterfowl species and similar. It’s not a key component of the research project, as the critical driver was water quality improvement. It would be great to get some additional research into this space, however.

Many thanks to Dr Walker for this interview. We hope will serve as inspiration to others involved in land change and communities who care for the environment and desire to contribute to healthy oceans. 

More free information and school materials on marine topics are available at our website 
www.ausmepa.org.au