Scrivener Dam: sluice gate replacement

The National Capital Authority is currently replacing sluice gate 2 at Scrivener Dam. A sluice gate is a valve that controls the flow of water out of a body of water. Some of their main purposes include:

• controlled water releases to maintain desired water levels or assist in reducing water levels as needed (like what is happening at the moment for the Scrivener Dam Dissipator Strengthening Project); and
• flood management: during heavy rain events sluice gates can be opened to release excess water, each sluice gate can release up to 18,600 litres of water per second;

How are they different from flood gates? Sluice gates are designed for controlled, routine water regulation consisting of smaller and more precise flows, flood gates are designed primarily for large, rapid water releases commonly associated with floods.

Whilst sluice gates are designed to last for decades and undergo regular maintenance, they operate in harsh conditions including constant water pressure and exposure to debris. Over time, these conditions can cause deterioration. Routine inspections identified it was time to replace sluice gate 2 to ensure ongoing safe and efficient operation of Scrivener Dam. The NCA will continue to monitor the condition of sluice gates 1 and 3, with similar upgrades likely to be required over the coming years. 

Construction is underway at sluice gate 2. There are a number of steps to this process:

1. Undertake detailed design of the new gate, including 3D scanning of the existing sluice to ensure an accurate fit;
2. Fabrication of the new sluice gate parts;
3. Heat treatment to relieve stress in the steel after the welding process;
4. Galvanising and paint coating to protect the new sluice against corrosion;
5. Installation of a temporary ‘bulkhead’ cover at the lake inlet to allow for safe removal without draining all the water out;
6. Crane lifting of the new sluice through the bridge deck to the internal gallery of the dam; and
7. Transport the new sluice through the gallery and install it within the existing valve body.

3D survey work and fabrication are complete and the new sluice gate is now off for heat treatment and corrosion protection. Installation of the sluice gate is currently scheduled for September 2026. It will take approximately one week to complete works onsite and there will be occasional partial and full closures of the Lady Denman Drive bridge over Scrivener Dam. 

Why do we need road closures?

To enable the replacement of the sluice gate, a bulkhead needs to first be installed. A bulkhead is a heavy-duty barrier which is used to seal off a section/s of a waterway to create a dry area for works to be undertaken. A single lane closure will be required to both install and then remove the bulkhead.

The new sluice gate will be craned in from the bridge deck above Scrivener Dam requiring a full road closure for up to 6 hours. Due to the nature of these works, they are unable to be completed at night with any road closure intended to occur in off-peak hours.

Further information on timing and traffic arrangements will be available ahead of works beginning.