Whakawhirinaki: Wellington’s Silverstream Pipe Bridge and Shared Path Project

Whakawhirinaki: The Silverstream Pipe Bridge is a major infrastructure upgrade in Wellington’s Bulk Water Supply Network, designed to provide increased resilience of critical Water Supply to Porirua City and through to Karori in Wellington City, the project includes the construction of a purpose-built bridge to carry the Te Mārua–Karori bulk water main across Te Awa Kairangi / Hutt River. The bridge also doubles as a shared path for pedestrians and cyclists improving connections on the Hutt River Trail.

The key project objective was to replace the aging and seismically vulnerable section of pipeline currently running across the Silverstream road bridge off State Highway 2. The new pipe bridge crossing secures a critical bulk water supply route that carries as much as 40% of Wellington’s bulk water transmission.

The existing pipeline, beginning at Te Marua and carrying over 60 million litres of water a day to the regions many water storage reservoirs was a vital but vulnerable water supply link to much of Wellington. Suspended alongside the Fergusson Drive/State Highway 2 road bridge which was first opened in 1939, the critical pipeline was at high risk of disruption as the existing bridge is vulnerable to both flood and earthquake damage. This project to increase resilience across Wellington’s Drinking Water network is just one of many undertaken across region in recent years, including the Kaitoke Flume Bridge, Omaroro Water Storage Reservoir, Te Marua Treatment Upgrades and many Community based emergency water supply points.

Deeco was engaged by consulting engineers GHD to consider the demanding project objectives, then design automatic, stand-alone hydraulic protection to this critical pipeline bridge crossing in the case of a major earthquake or flooding events while maintaining the pipelines continued operation. To withstand major seismic activity the pipe joints are made with specialised flexible couplings allowing for significant movement and potential offset from one side of the river to the other,  while this flexibility and anticipated movement provides resilience to the pipeline integrity – it also presents scenarios of very high-pressure surge, requiring reliable and automatic mitigation measures to ensure the pipelines protection.

Taking a multi layered approach to Hydraulic Protection of the pipeline, Deeco’s control valve experts supported GHD in design of primary pressure protection with redundancy backup by utilising Bermad’s high performance 700 SIGMA series control valves for pressure surge anticipation and high pressure relief.  Included in the scope of supply are multiple DN250 PN25 rated, pressure control valves, DN150 PN25 rated direct acting pressure relief valves, and PN25 rated air release/vacuum break valves of the following models.          

• Bermad Model 730 Pressure Relief Valves (250mm): Fast-acting valves that instantly relieve pressure spikes to prevent overloading the pipe.
• Bermad Model 735M Surge Anticipating Control Valve (250mm): Pre-emptively opens on sharp pressure drop in anticipation of high pressure surge, therefore protecting the system from pressure rebound.
• Vent-O-Mat RBX Air Release Valve (150mm): Automatically manages trapped air and vacuum conditions, reducing pressure shocks and supporting smooth flow.

These products were selected for their proven reliability and performance in high-capacity, high-risk environments, and for their ability to provide passive protection in the event of emergencies.

Deeco’s involvement didn’t end at supply as our factory trained technicians will be on hand to support start-up commissioning and fine tuning to ensure exacting protection performance of these critical assets, Deeco will also provide operator familiarisation and products training as needed. With over 80 years of experience in NZ infrastructure projects, we were proud to contribute our expertise to this landmark investment in Wellington’s future water resilience.

The project is now in the final stages and soon to be brought online, Once operational, the system will offer significantly improved resilience to seismic events, with surge and pressure events automatically mitigated by the installed BERMAD valves.

The project forms a key link in a modernised network designed to keep water flowing to hundreds of thousands of residents—even under extreme conditions.

Learn more about the project on Wellington Water website here

Bermad Model 730 – Pressure Relief Valve
Instantly opens to release overpressure and snaps shut drip-tight when normal flow returns. Ideal for fast-acting safety in high-capacity systems.

Bermad Model 735M – Surge Anticipating Control Valve
The Model 735-M Surge Anticipating Valve is an off-line, hydraulically operated, diaphragm-actuated valve. Sensing line pressure, the valve opens in response to the pressure drop associated with abrupt pump stoppage. The pre-opened valve dissipates the returning high-pressure wave, eliminating the surge.