What is the proposed project?
The proposed works would see the reinforcement of the dam wall at The Gong, Buninyong Botanic Gardens, which runs underneath a section of Cornish Street at the lake’s western edge.
The proposed work consists of construction of a filter layer, raising the dam wall approximately by 500 mm, construction of rock embankment (riprap) upstream of dam wall and upgrading the outlet of the dam.
Why does the wall need to be replaced?
The City of Ballarat has monitored seepage at the base of the dam wall within the Buninyong Botanic Gardens for several years. Earlier this year we engaged engineering consultants to assess the condition of the wall.The assessment found that the dam wall was not constructed to modern engineering standards. It also identified that the dam wall needed to be raised to prevent over-topping of the wall in large storms.
What happens if you don’t do the works?
If the wall is not reinforced, there is a long-term risk that the wall could fail. This has the potential to affect properties downstream of the dam.
When will the works be undertaken?
The project will start with a phase of community consultation, providing the community with the opportunity to hear about the seepage issue, the engineer’s assessment of the site and the proposed solution.
This phase will give the community the opportunity to view the plans and provide feedback.
Following consultation, we hope to begin construction in 2020.
How long will works take to complete?
We expect the project may take up to six months to complete.
Will you need to drain the Gong to enable the works to take place?
Some dewatering of the dam will be needed during the works. A ‘coffer dam’ (a watertight enclosure pumped dry to allow construction work below the waterline)may be used to protect the work site. The successful contractor will assess the situation onsite and a decision on how best to construct the dam.
Will Cornish street be closed off for the duration of the works?
Yes. Because the works will involve significant reinforcement of the wall, we will need to close the section of Cornish Street between Scott Street and Simpson Street while the works are completed. We will notify affected users before any works start.
Why hasn’t the City of Ballarat taken action to fix this sooner?
We have already taken some actions to improve the outflow from the dam to reduce the seepage.We have also engaged consultants to carry out risk assessments, soil testing and concept designs.
What steps will you take to ensure the worst doesn’t happen?
The City of Ballarat has worked with a leading consultant in dam engineering to upgrade the dam wall. The proposed work consists of construction of a filter layer, raising the dam wall by 300 to 450 mm, construction of riprap (rock reinforcement) on the upstream slope of the dam wall and upgrading the outlet of the dam. Further landscaping will be carried according to the developed landscape plan.
How many trees will need to be removed as part of these works?
All trees on the dam wall embankments will be removed as part of the works. This includes the strawberry trees and the crack willow trees as they have a negative impact on the dam wall mainly due to their roots.
Will these trees be replaced?
Trees cannot be planted on the dam wall because national standards for dam construction do not allow it. We have developed a landscape plan and trees removed would be replaced with small shrubs as per the landscape plan.
Have heritage impacts been considered?
Yes, we have identified the heritage significance of the area and we have worked with Heritage Victoria on this project. We have engaged a heritage consultant to undertake the heritage permit required for the works.
How can I be involved in this process?
You can view the plans online and have your say on the project page at the City of Ballarat mySay website. The plans will also be on display at Buninyong Foodworks until Friday 20 December.