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 the removal of sediment.
Nutrient-rich sediments have built up on the bed of the Lower Vasse River over many decades and are an important factor in 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.
Stage 1 sediment removal is complete
Stage 1 of sediment removal was completed in May 2022 with 630 tonnes of sediment (dry solids) 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 slurry of sediments 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 sediment were transported off site and treated for acid sulfate soil. Due to the composition of the dewatered sediments, they could only be reused as daily landfill cover at the Dunsborough Landfill site.
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 of sediment removal will start in April 2023 in a section of the river upstream from the Causeway Road Bridge. Similar dredging and dewatering techniques used for Stage 1 will be used for Stage 2. The dredging works will last up to 8 weeks and the sediments will be left to dewater in geotextile bags for up to 6 months. The same laydown area in Rotary Park will be used for dewatering the sediments. The Playground in Rotary Parks will be closed for the duration of the dredging operations for safety reasons.
Stage 3 sediment removal
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 further 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 removing as much nutrient-rich sediments as possible to improve water quality in the Lower Vasse River. As opportunities arise, more funding applications will be made to support continued sediment removal in the River.
Image: Laydown area for geotextile bags – 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
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 Sulfate Soils, prior to reuse
Stage 2
April-June 2023 - Stage 2 Dredging works (upstream of the Causeway Road Bridge)
June-October 2023 - Sediment slurry dewatering
November 2023-February 2024 - Dewatered sediments transported off site and treated for Acid Sulfate Soils
Stage 3
Autumn 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