Parting the Avon River for a safe tide gate replacement

Innovation by Citycare Water to deliver a stormwater pump station renewal project for Christchurch City Council held back the waters of the Avon River Ōtākaro so the team could work safely. 

A hinged tide gate was built on the Locksley Stormwater Pump Station in Burwood in 1986 as an emergency bypass on the river. It opens in times of flooding when excess stormwater upstream can be channelled into the river. The old flooding mitigation gate, made of wood and steel, had deteriorated through constant submersion. 

To undertake the renewal of the tide gate, a cost-effective and environmentally friendly hydro barrier was used for the first time by the Citycare Water Pumps Maintenance Team. 

To address the main challenge of holding back the river to prevent inundation while the team were at work, Project Manager Kevin Walker researched alternative ways to safely divert water from the gate construction area rather than using traditional steel sheet piles. 

Kevin had success with Kaiapoi company Hydro Response, which has a barrier product able to hold back and contain water up to 2.4 metres in depth. The Geodesign Barriers rely on the weight of the water to anchor the system securely to the ground. 

Christchurch City Council approved the use of the barrier in the Avon River Ōtākaro for this project. 

A new gate was manufactured from Accoya timber and stainless steel. The timber product is made from New Zealand-grown radiata pine, which is processed in a facility in The Netherlands to alter the physical properties of the wood so it’s more durable, stable and has a lifespan similar to hardwoods. It will withstand submersion without rotting. 

The Pumps Team timed the gate replacement work for when everything was ready to go, so the river diversion was in place for just a week. 

There are three phases in the Locksley Stormwater Pump Station renewal. The first was to replace electrical cables and the control panel. The new tide gate is phase two, while two new pumps will be installed soon as phase three.