Maylands Lakes

The mechanical mixer in Lake Bungana was commissioned last week. Over the coming weeks and months the mixer will work to mix deeper and shallow water throughout the lake. As part of the commissioning it was necessary to integrate the power source for the mechanical mixer in Lake Bungana with that of the fountain. As a result, the fountain has been temporarily disconnected pending the receipt of required electrical components. The fountain is expected to be operating again in the next few weeks.

The early monitoring data from Lake Brearley is indicating the mixing device is performing as per design. This has resulted in a rapid equalisation of temperature in the shallow and deep water, as well as a spike in dissolved oxygen at depth (which for both Lake Brearley and Bungana has historically been almost completely deoxygenated). The monitoring unit is not immediately next to the mixer and is in fact approximately 60m from the mixing device. There has also been a distinct ‘lake wide’ change in colour of Lake Brearley (from yellowish to green) post commissioning of the mixing device indicating a progressive lake wide impact.

Despite the best efforts of all parties, the contractors have been unable to finalise the commissioning of the mechanical mixing device in Lake Bungana prior to Christmas. This is due to parts and labour being unavailable – a problem which is becoming common to many projects across the State and Australia-wide. This has now been scheduled to be completed by mid-January 2022.

Following the emergence of visible algal slicks and a deterioration in water quality in Lake Bungana in October/November 2021, City officers have undertaken a trial application of a bio remedial product called Aquaritin. This trial will determine its potential effectiveness in assisting to maintain water quality in the Maylands Lakes. Aquaritin is a concentrated liquid that contains micronutrients, including silica, which promote diatom growth. The premise of the product is the increase in density and richness of diatoms reduces nutrient availability (particularly nitrate) for nuisance algal growth. The product is not harmful to any other aquatic life. Initial field observations have highlighted a marked improvement in water clarity and a significant reduction in floating algal slicks in Lake Bungana post application of the product. Water quality sampling has been conducted throughout the trial by independent consulting firm Urbaqua to enable a comprehensive assessment of its effect.

City officers and contractors have finalised commissioning of the mechanical mixing device in Lake Brearley.

As the mixing device funnels water from the surface to the bottom of the lake there is the potential for temporary discolouration of the lake as sediment beneath the mixer is disturbed. Such discolouration will have no impact on lake fauna or ongoing water quality.

Over the coming months the mixer will progressively mix shallow and deeper water, creating a more consistent temperature throughout the water column and increase oxygen in deeper water creating conditions that reduce the potential for nutrients to be released from the sediment.

City officers are continuing to work with contractors to commission the mechanical mixing device in Lake Bungana. It is expected that this will be finalised and operational prior to Christmas.

Late rains have resulted in an increase in nutrients in the lakes, and this has contributed to midge and mosquitoes breeding. We understand the impact this has had on residents surrounding the lakes, and we are taking action.

the GHD report identified dredging will remove nutrients and the feedback from residents and the results of midge larvae sampling indicated the dredging of Lake Bungana resulted in lower levels of midge, so the City will dredge Lake Brearley in early February 2022. This is later than we had planned, however a specialist contractor is required and they are not available until this date.

Large mechanical mixers in Lake Brearley and Lake Bungana are in the process of being commissioned and are expected to be fully operational prior to Christmas. The mixers will increase oxygen in deeper water and create less favourable conditions for nutrients to be released from the sediment. This is a sustainable, cost and energy effective approach using an established technology.

In September, the City installed two solar powered ultrasonic devices in Lake Brearley as part of a twelve month trial. Early field observations indicate they are making a positive impact, with a reduction in floating algae slicks and the reduced build up of algae around the edges of the lake.

The City is also continuing to use larvicide treatments to reduce midge numbers; and is monitoring water quality so we can measure the effectiveness of these actions.

Unfortunately, there isn’t just one solution to the issues being experienced, but we are committed to following the advice of GHD and working with the community to achieve the best possible outcome.

Following Queensland COVID risk status being reduced to very low risk on 27^th October 2021, the WEARS contractors who are supplying and installing the mechanical mixers have now been able to gain access to Western Australia. Final preparations are now being undertaken and a mixer will be installed in Lake Brearley and Lake Bungana this week.

The installation of the mixers is an important milestone in the delivery of the water quality improvement plan as they are designed to address the stratification (lack of mixing of cooler and warmer water) of the water within the lakes. The GHD monitoring report identified stratification as a key contributor to excess nutrient levels in the lakes. It is anticipated the mixers should reduce the stratification within approximately two months, which as part of the range of approved actions, should progressively improve the water quality in the lakes.

The City has signed a contract with Apex Envirocare to undertake dredging of Lake Brearley. Dredging is scheduled to commence on 29th November 2021. The dredge being used is significantly more powerful than the dredge used on Lake Bungana. City officers will work with Apex Envirocare to monitor the volume of sediment removed and the area of lake floor dredged.

City officers are continually monitoring emerging technology and innovative options to improve water quality and reduce midge at Maylands Lakes. Recently this has resulted in the City commencing a 12 month trial installation of ultrasonic units in Lake Brearley. The devices are solar powered and emit ultrasonic waves that cause gas pockets in algae cells to collapse resulting in the algae sinking and dying. There have been no reports of harm to humans, fish, birds and other fauna due to ultrasonics. The installation of the units is an additional action being taken by the City to complement the other initiatives that are already planned and being actioned.

The raingarden at Tourer Court is now complete and will reduce some of the nutrients flowing into Lake Brearley.

A focused regime of midge and mosquito treatment was undertaken this past summer and feedback and monitoring indicated midge levels were lower. The same treatment approach has commenced early this year in response to midge levels.

Clean fill has been placed into the corner of Lake Brearley adjacent to Sopwith Elbow and Tourer Court which suffers from reduced circulation and tends to collect the floating algae. Final levels of this fill will be achieved once the water level reduces – we are targeting fill level to be approximately at the low water mark. This area will be planted with sedges once the final fill levels are achieved.

The floating wetlands have been removed from Lake Brearley as they were not thriving and they have been relocated to Lake Bungana, Brickworks Lake and the pond at Bardon Park.

Approximately 40 sedges have been installed along the hard wall in the south eastern corner of Lake Brearley. Installation of plants in these locations is challenging as there is limited fill and primarily limestone rock. City officers are trialing a new installation technique to determine its effectiveness. If it is found to be effective, there are a further 300 sedges to be planted once the water levels reduce.

In addition to the above actions, the City continues to monitor the latest advances in technology and water management approaches to ensure the most appropriate and impactful actions are taken at Maylands Lakes.

Three successful planting days have been held this planting season:

• 30 May 2021 at Lake Brearley in partnership with Friends of Maylands Lakes
• 7th August 2021 at Brickworks Stream in conjunction with Friends of Maylands Lakes
• 15^th August 2021 at Brickworks Reserve in conjunction with Friends of Maylands Brickworks.

It was great to see so many community members participate in the planting days with a total of approximately 5000 plants planted.