Maylands Lakes

The City of Bayswater will be undertaking works to remove vegetation on the islands in Lake Brearley (indicated in red, on the attached map). Clearing will only occur where evidence of nesting has occurred the other islands will be monitored for activity. Contractors have been arranged to carry out the removal of the following species which have been identified as invasive by the Department of Biodiversity Conservation and Attractions (DBCA):

• Casuarina cunninghamiana

• Schinus terebinthifolia

The islands are populated in the winter months by cormorants, which are contributing to water quality challenges within Lake Brearley. The birds are not utilising the site at present, thus allowing works to be undertaken. Following the removal of invasive vegetation, the islands will be revegetated with endemic species to promote biodiversity. This action is part of the City of Bayswater’s continuing efforts to mitigate water quality issues within the Lakes. The change in vegetation will result in the cormorant population moving to more appropriate areas away from the lake, and will ease the nutrient loading that they had previously added to the lake. Bird droppings will be removed from the islands before any vegetation is planted, which will also assist in reducing additional nutrients entering the lake. The works will be undertaken in February and should last approximately a week. Works will include the use of chainsaws and machinery, and will be undertaken during business hours.

The City engaged GHD to provide a technical assessment of the dredging undertaken at Lake Brearley. GHD have provided their report to the City, and concluded the overall objectives of the program appear to have been substantially achieved, as follows:

• Completion of dredging in the identified priority area;

• More than half the available nutrients in the target area have been removed (an estimated 59% of total organic compounds, totalling approximately 17 tonnes); and

• Dredging was significantly more successful than the Lake Bungana dredging works, recovering approximately 187m3 vs 56m3 of dewatered silt.

It is anticipated the removal of nutrients via dredging will work in concert with the other long-term water quality initiatives (mechanical mixers and solar powered ultrasonic units) to progressively reduce eutrophication, algal blooms and midge populations over time. A copy of the full GHD report is available in the documents section.

The limestone from the dredging laydown pad is being reused to create paths in natural areas in the City. The first path has been completed at Maylands Samphire's recently and the remaining limestone will be removed in coming weeks to create a path in Lightning Swamp Bushland.

The City of Bayswater is working with the Friends of Maylands Lakes to restore and enhance the vegetated area around Lake Bungana as part of water quality improvement works.

The project aims to:

• Improve water quality
• Provide habitat for native animals
• Improve the visual amenity of the Lake.

The area in question is classified as completely degraded and dominated by Melaleuca quinquenervia and Casuarina cunninghamiana. These species have been identified as requiring management by the Department of Biodiversity Conservations and attractions (DBCA). As part of the Maylands Lakes Restoration Plan the City is seeking to increase riparian vegetation along the lake shore to assist with nutrient stripping and create a more diverse habitat reflective of a naturally occurring environment to provide habitat for fauna. The invasive species have formed a root shelf preventing the establishment of riparian vegetation and turtle nesting at the site. Works are being undertaken in collaboration with the friends of Maylands Lakes who successfully obtained grant funding to support the restoration.

A Community planting day will be held on June 25 and will begin the process of creating a biodiverse natural area. To get involved check the City's website https://www.bayswater.wa.gov.au/communityplantingdays

The eight-week dredging program has now been completed, and the contractor has demobilised from site. It is estimated that the contractor was able to dredge >90% of the target area. Given the operational uncertainties associated with the project, such as dredge access, anchor point locations and pumping distances, achieving that level of coverage is considered a good result. Based on the experience from dredging Lake Bungana, it could take approximately 18 months for the dredging in Lake Brearley to improve water quality and clarity.

Power has been reconnected to the mechanical mixer and the solar powered ultrasonics returned to optimal locations last week. Post-dredging sediment sampling will be undertaken to verify the effectiveness of the dredging program at removing the nutrient rich sediment. Fencing will be realigned this week to enable residents to access the path adjacent to Lake Brearley but keeping the sediment bags secure while they dry which is anticipated to take 4 - 6 weeks. Once the sediment is sufficiently dry the bags and limestone pad will be removed and the grass and reticulation reinstated. While the lake has been fenced off City officers have taken the opportunity to plant approximately 400 sedges along the limestone walls, adjacent to Tourer Court and at Hinkler Loop. This planting will contribute to improving biodiversity in the lake and nutrient removal. City officers will continue monitoring of the water quality and midge levels to assist in understanding the effectiveness of actions taken to date.

Following positive results on the amount of sediment being removed as well as the progress of dredging in Lake Brearley, the dredging contractor, Apex Envirocare has been instructed to complete the full 8 week dredging program. To date approximately 68% of the area targeted for dredging has been completed and the dredge will move to complete the north western section of the target area. The sediment is consolidating well in the two geopro bags so a second laydown pad will not be required. The dredging is due to be completed the week of 28th March 2022 and it is anticipated the sediment bags and laydown pad will be removed by early May 2022.

In accordance with the Maylands Lakes water quality improvement plan, dredging of Lake Brearley commenced this week. The dredging is targeting the removal of nutrient rich sediment that has built up in the lake. The dredging program is scheduled to run for eight weeks.

A community information session will be held to brief residents on the upcoming partial dredging of Lake Brearley. The session will be held at Maylands Sports and Recreation Club on Monday 31st January at 6:30pm and will be presented by City officers and representatives from Apex Envirocare who are undertaking the dredging. Completion of the dredging is part of the Maylands Lakes restoration plan approved by Council in 2020 to improve water quality and reduce nuisance midge levels. The dredging will require the construction of two temporary laydown sites indicated in the image below by the red quadrants. Construction of the laydown site nearest Tranby Rd is scheduled to commence on 31 January 2022. The dredging will also require the temporary closure of the Lake Brearley footpath between Tranby Road and Tourer Court (highlighted in red in image below) to enable the installation and operation of dredge cable anchor points. Apologies in advance for any inconvenience caused. A copy of the presentation provided is available in the documents section.

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.