Temporary Closures: Current advice
Scrivener Dam Dissipator Project
Image
Project Type
Asset Renewal
Design and Construction
Construction
Maintenance
Construction Start Date
2024
Completion Date
2025
Temporary Road or Lake Closures
No
Project Overview
The NCA is undertaking a major strengthening project at Scrivener Dam. The project will involve strengthening work on the downstream structure of the dam – the Dissipator.
History of the Dam
On 20 September 1963, fifty years after the founding of the National Capital, Minister for the Interior Gordon Freeth, closed the valves on the newly completed Scrivener Dam (the Dam) thus allowing the waters of the Molonglo River to form Lake Burley Griffin (the Lake) - one of Canberra’s main recreational and tourist attractions.
Image: Completion of Scrivener Dam in 1963. (Credit: nla.obj-143774761)
The Dam is named after Charles Robert Scrivener (1855-1923) who recommended the site for the national capital in 1909.
Learn more about the Dam on the Scrivener Dam Attractions page.
Why are we doing the project?
Scrivener Dam is a concrete gravity dam. The design and mass of the dam retains the water which forms Lake Burley Griffin. The Dam is equipped with five flood gates and three sluice gates, all of which are used to control the water level in Lake Burley Griffin.
The spillway located immediately downstream of the dam includes a dissipator structure. The dissipator is a concrete structure comprising of a horizontal concrete slab, concrete chute blocks and vertical concrete baffle blocks. The dissipator absorbs the energy of the water flowing over the flood gates and prevents potentially damaging erosion in the river channel downstream of the dam.
The dam plays a critical role in controlling the flow of water and managing the risk of floods by controlling water levels at a consistent level, that in turn protects the residents of Canberra from flooding and downstream areas from sudden fluctuations in water flows. These work s will be the most significant strengthening works completed on the dam since it was first built in 1963.
Recent studies commissioned by NCA have identified the need to strengthen the Scrivener Dam Dissipator. NCA worked with the University of New South Wales Water Research Laboratory (UNSW WRL), and the Dam Safety Engineers (SMEC) to design, construct and test a scale model of Scrivener Dam. The model and other investigative methods were used to ascertain how the dam and its environs function under a range of operational scenarios.
The modelling and subsequent assessments identified structural risk with the dissipator under flood conditions. There is the potential for the dissipator to be significantly damaged during a major flood event, which in turn, could lead to the failure and subsequent collapse of Scrivener Dam. The project will involve:
- Strengthening the existing horizontal concrete slab of the dissipater by installing approximately 700 new anchor points into the foundation rock of the dam (10 to 20 meters deep).
- Increasing the thickness of the horizontal concrete slab of the dissipator by half a meter.
- Reconstructing new baffle blocks to match the increased thickness of the concrete slab.
- Reinforcing the adjacent riverbanks downstream of the dam to minimise erosion that could lead to failure of the dissipater structure.
The strengthening work will ensure the ongoing safety of the dam during flood events.
Project Timeline
Latest News
Public Notification:
The National Capital Authority (NCA) released a public notification and an approach to market through Austender, calling for Expressions of Interest (EOI) for construction work to enhance the structural integrity of Scrivener Dam.
Click here to view the relevant Public Notification and visit Austender to view the approach to market.
Detailed Design:
NCA are working with a detailed design consultant to complete the detailed design for the project. The detailed design is expected to be complete by October 2023
Other studies:
During the detailed design, the NCA has undertaken several supporting investigations and studies. These include:
- Acoustic and vibration studies to understand the likely noise that will be generated by the project
- Environmental impact Assessment to understand the if the project will have any significant environmental impact
- Heritage Impact Assessment to understand if the project will have a significant impact on the heritage values of the Dam.
- Hydrology studies to inform construction staging and temporary works
Public Works Committee approval and other approvals
NCA has recent provided a submission for the project to the Joint Standing Committee on Public Works. It is anticipated that the NCA will attend a hearing for the project in October 2023.
Pending PWC approval, the NCA will also seek the relevant Works Approvals and Environmental Approvals for the project prior to construction activities.
Public Interest Certificate
A Public Interest Certificate has been issued. Click here to view the Public Interest Certificate.
The construction of Scrivener Dam was completed in 1963 - which is now 60 years ago. Since the dam was first constructed, the standards of construction and the body of knowledge regarding dam safety have improved. Based on several investigations and studies undertaken in recent years, the NCA has identified several structural risks with the dissipator of the dam. During flood conditions, there is a risk that the dissipator structure could fail, which in turn could cause the dam to fail. Hence, the NCA must undertake the Dissipator Strengthening project to ensure the ongoing safety of the dam.
NCA are aiming to commence works on site in early 2024 and it will likely take between 12 and 18 months.
There are two likely community impacts, as follows:
Lowering Lake Burley Griffin – in order to effectively manage the risk for construction while working in the spillway of the dam, NCA will be lowering the level of the lake. it is planned to lower the lake by a maximum of 500mm during construction. This will be reduced as far as possible to minimise the impact to lake users.
NCA urges all lake users to consider the impacts and potential new hazards prior to setting out onto the water.
Increased traffic on Lady Denman Drive – during construction there will be an increase in construction traffic on Lady Denman Drive. Construction traffic will enter the site on the western access road to Scrivener Dam and will cross the existing bike path adjacent to Lady Denman Drive. Traffic will be controlled during construction, however NCA urges all users to take care when navigating the area.
The NCA will continue to work with the community to understand and mitigate impacts wherever practical.
There will be no extended closures of the bike path or the bridge over the dam during construction. From time to time, we anticipate that there could be short closures to allow movement of construction vehicles, however, disruption will be kept to a minimum.
The project will involve drilling for roughly 700 new ground anchors between 10 to 20 meters deep. The process used to drill these holes will be noisy. However, NCA has undertaken a noisy and vibration impact assessment as part of the design for the project. The study has identified that all noise generated during the project will be below ACT guidelines for the areas surrounding the dam. The NCA will monitor noise during the project and will work with stakeholders to mitigate impact during the project.
We are keen to keep the community involved and aware as to what’s happening at Scrivener Dam. Keep checking back on this website and register for project updates.