Lower Vasse River Management - Improving Water Quality

Removal of Sediment

This project is part of a multi-staged approach to reducing nutrients and improving health of the Lower Vasse River. The City aims to improve water quality of the River by progressing with staged removal of sediment.

Nutrient-rich sediments have accumulated on the bed of the Lower Vasse River over many decades and are an important factor fuelling the cycle of summertime algal blooms. 

While sediment removal alone is not expected to prevent algal blooms occurring in the River, it is an important step if we are to achieve the aim of significantly reducing the extent, severity and duration of blooms in the future.

Sediment removal in the Lower Vasse River is being implemented in a staged approach, targeting a priority stretch of the river at each stage. Where each stage takes approximately 12 months to complete.

Stage 1 sediment removal is complete

Stage 1 dredging was completed in May 2022 with approximately 630 tonnes of sediment (dry weight) removed over the course of seven weeks.

The area dredged, spanned from the Causeway Road Bridge to upstream from the pedestrian bridge on Peel Terrace.

The sediment slurry was pumped into porous geotextile bags, which retained the fine sediments while water was expelled and returned to the River.

The sediments continued to dewater for an additional 6 months. The dewatered sediments were transported off site and treated for acid sulphate soil. Sediment composition limits options for reuse, currently sediments are able to be reused as daily landfill cover, however additional options are being investigated for future stages.

Water quality in the River was closely monitored for the duration of the works to ensure no detrimental impacts from the dredging operation and the dewatering of the sediments.

Stage 2 sediment removal

Stage 2 is well underway, sediments were dredged from May to June 2023 from the section of river, Causeway Road to Old Boat Ramp.

This stage used the same techniques and dewatering area (Rotary Park) as Stage 1, enabling both, refinements in methodology, and cost savings by eliminating the need to establish a new laydown and dewatering area.

It is estimated that 670 tonnes (dry weight) of sediments were removed during Stage 2. These sediments are dewatering in Rotary Park, and will be removed ahead of the War Memorial works due to start in December 2023. Sediments will be transported off-site, treated with lime for ASS (Acid Sulphate Soils) and utilised as daily landfill cover at the Dunsborough Waste Facility.

The Playground in Rotary Park will be closed for the duration of the dredging and dewatering operations for safety reasons.

As in Stage 1, water quality in the River was closely monitored for the duration of the works to ensure no detrimental impacts from the dredging operation and the dewatering of the sediments.

Stage 3 sediment removal

Stage 3 is tentatively scheduled for 2024. The City has been successful in securing $407,964 in funding from the State Natural Resource Management's Community Stewardship Grant Program. Funds will assist with Stage 3 sediment removal works in the Lower Vasse River in a section upstream of the Strelly Street Bridge (Stage 3).

Future Stages

The City is committed to the Sediment Removal Program as a means to improve water quality in the Lower Vasse River. Where practical, and as opportunities arise, more funding applications will be made to support continued sediment removal in the River.

Image: Laydown area showing dewatering geotextile bags (Stage 2) – Rotary Park

Project Timeline

February 2021 - Lower Vasse River Management Advisory Group selects sediment removal as the highest priority recommendation for implementation

September 2021 - City was awarded $350,000 under the Healthy Estuaries WA program

February 2022 - Environmental and Heritage approvals granted

Stage 1

April to June 2022 - Stage 1 Dredging works (downstream from Causeway Road bridge)

June-October 2022 - Sediment slurry dewatering in Rotary Park

November 2022 - City was awarded $407,964 under the State NRM Community Stewardship Program for Stage 3 of sediment removal

November 2022-February 2023 - Dewatered sediments transported off site and treated for Acid Sulphate Soils, prior to reuse

Stage 2

May-June 2023 - Stage 2 Dredging works (upstream of the Causeway Road Bridge)

June-October 2023 - Sediment slurry dewatering in Rotary Park

November 2023-February 2024 - Dewatered sediments transported off site, treated for Acid Sulphate Soils, and repurposed as landfill daily cover

Stage 3

Spring 2023 - Carter’s Freshwater Mussel survey and relocation

Autumn/winter 2024 - Stage 3 of sediment removal (upstream of the Strelly Street Bridge) to commence

 

Mayor's Message - Lower Vasse River Sediment Removal Project

FAQs

Lower Vasse River Sediment Removal FAQs

Related Information

Sediment Removal EPBC Compliance Report

Sediment Disposal and Reuse Options Assessment

Environmental Management Plan for Carter's Freshwater Mussel Westralunio Carteri

Survey of Carter's Freshwater Mussel in the Lower Vasse River

Lower Vasse River - Dredge and Disposal Management Plan

Lower Vasse River - Acid Sulfate Soil and Dewatering Management Plan

Acid Sulfate Soil and Dewatering Management Plan

 

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