FAQs

Living streams are a way to manage stormwater by mimicking a natural stream to improve water quality or ecological values. Living Streams are one of the concepts the City of Busselton are considering for the Lower Vasse River. Aspects of Living Streams such as altering the morphology (shape of river channel), hydrology, shading, sediment removal, and planting vegetation are being considered for the Lower Vasse River.

The Living Stream approach for the Lower Vasse River was first investigated during the preparation of the Lower Vasse River Waterway Management Plan, in close consultation with the community and stakeholders. It has since been further developed with assistance from a company called Alluvium.

While it remains essential to reduce nutrient output in the catchment, it is becoming apparent that catchment management alone will not be sufficient to see the level of change the community is asking for. Which prompted the City, as the Lower Vasse River asset manager, to start looking at in-situ treatments, such as the Living Stream approach.  

This project focuses on a section of the river from the Butter Factory weir to the old boat ramp, upstream form the City of Busselton Administration Office. Refer to map below.

This area was selected as it has the worse water quality and blue-green algal blooms, combined with higher public use

Preliminary costings are in the order of $6.5 million to implement the full proposal.

While the City has allocated some funding in its Long Term Financial Plan towards the project, it will need to secure significant State and/or Federal funding before being able to proceed with the project.

One of the key objectives of the project is to protect and enhance habitat for wildlife. This will be achieved through enhancing the existing aquatic habitat by improving water quality and removing soft organic sediments, which provide a poor substrate for beneficial aquatic plants like macrophytes and poor habitat for benthic invertebrates like Carter’s Freshwater mussels. The proposed constructed wetland will also create additional habitat for fauna like Western Ringtail Possums, frogs, fish and birds.

Processes will be put in place to mitigate any potential impacts during works such as the temporary relocation of the threatened Carter’s Freshwater mussels during sediment removal. These will be guided by relevant environmental approvals from State and Federal government.

The Reconnecting River Study undertaken by the Department of Water and Environmental Regulation (2018) concluded that the Lower Vasse River could be partially filled without increasing flood risks.

As part of the Living Stream detailed design phase, Alluvium will undertake a detailed hydraulic assessment to ensure the success of any works and safety of the public.

This will depend on how quickly the City can secure funding and State and Federal government approvals. It is anticipated the project would start with removing sediment from a priority section of the river.

The project is still at the scoping and design phase and no decision has been made with regards to implementation. Further community consultation will be undertaken before.

Yes, the City will need to secure relevant State and Federal government approvals before the project can proceed to ensure potential environmental impacts are managed.

Constructed wetlands are used all around the world to treat and remove pollutants from wastewater and stormwater through the biofiltration process of plants. Some WA examples include the Wharf Street wetland in the City of Canning and the Eric Singleton Bird Sanctuary in the City of Bayswater. The proposed constructed wetland for the Lower Vasse River is different because it also relies on shading and reducing residence time through water re-circulation to reduce blue-green algal blooms.

Removal of sediments is frequently undertaken in artificial water bodies such as man-made lakes, marinas and wastewater treatment ponds. It is less commonly done in natural waterways.

Altering river morphology (or shape of river channel) has been done all over the world to reduce flooding, erosion and increase biodiversity values.

Aeration and oxygenation have been proven to work in waterbodies, however with slightly different conditions to the Lower Vasse River, when there is low oxygen levels and stratification of water column (i.e. little mixing). The Lower Vasse River has high oxygen levels throughout the water column when the algal bloom is established and is not stratified as it is shallow enough to be mixed by the wind. 

A number of commercial products exist that claim to improve water quality through the introduction or enhancement of micro-organisms such as bacteria and enzymes. However most of the evidence is anecdotal only and usually applicable to small scale situations like dams and ponds. 

However the Living Stream approach does not preclude any intervention and may create conditions where the use of smaller scale in-situ treatments are applicable. It preferably builds on natural processes as they provide additional benefits such as habitat for native fauna, increased social amenity and usually have lower ongoing operating costs but other interventions are not mutually exclusive.

Areas of open water are included in the wetland design to create habitat for predators that will eat mosquito larvae. Predators include macroinvertebrates such as dragonflies, and native and exotic fish. The design of the LIA wetland outlet should consider allowing fish to access the wetland and fulfill this predatory role. Creating flowing conditions in the river and wetlands should also help to control mosquito larvae by flushing them from emergent vegetation into open water, where they are vulnerable to predation.

The Lower Vasse is green over summer months due to algal blooms. The blooms are made up of millions of phytoplankton (tiny photosynthetic organisms) which discolour the water. Phytoplankton are an important part of all aquatic ecosystems, however in the Lower Vasse River blue-green algae (cyanobacteria) are often the dominant type of phytoplankton over summer months. Blue-green algae are particularly concerning because they can produce harmful toxins. Algal blooms in the Lower Vasse River have been common over many decades and recorded as early as 1931.

Algal blooms occur when there are a combination of suitable environmental conditions including warm weather, light, high nutrients and calm water. Nutrients are very high in the Lower Vasse River all year round, but algal blooms only occur in warmer months when temperatures are higher, there is little shading and river flows are low. Naturally the Lower Vasse River would not have flowed in summer and would have dried out like other rivers in the catchment. Installation of weir boards (now removed) near the Old Butter Factory in the 1930s and gradual landfill behind the boards has changed the river into a still pool over summer months, providing ideal conditions for algal blooms. Sediment that has built up in the river over many decades has also contributed to water quality problems.

Only removing sediments will not stop algal blooms because nutrients can still enter the river from other sources such as catchment and stormwater run-off and groundwater seepage. Removing sediments needs to be part of a broader intervention program such as the proposed Living Stream approach.

Unfortunately flushing out the Lower Vasse River to improve water quality is not feasible. There are a number of reasons why we can’t flush algal blooms and sediments out of the river:

• Algal blooms happen in the Lower Vasse River over summer months when there is inadequate flows to flush the river.
• There are limited feasible alternative sources of water over summer to flush the river (e.g. purpose-built dam or groundwater)
• The landscape is so flat that even under high winter flows the velocity of water is usually insufficient to remove sediment
• If sediments were removed through flushing they would end up in the Vasse estuary which is part of the internationally protected Vasse Wonnerup wetlands

Options to increase flows were evaluated in the Reconnecting Rivers project. For more information visit this link (RGW-RR-web-A4.pdf (dwer.wa.gov.au).

Mexican waterlily is an invasive aquatic weed that covers large areas of the Lower Vasse River, impacting on the ecological and amenity values of the river. They have however been found to improve water quality and reduce the severity of algal blooms in the river. The City of Busselton is currently managing further spread of Mexican waterlily through strategic herbicide control to gradually reclaim areas of open water, targeting important waterbird habitat, while minimising adverse impacts and preventing a return to algal blooms in these areas. This work is due to continue.