Developing options for enhancing hydropower capacity in a legacy facility

Lake Coleridge Power Station

The Lake Coleridge hydropower facility on the Rakaia River is one of the oldest major infrastructure projects in New Zealand. As demand for power has grown, Lake Coleridge has upgraded capacity in response. The scheme now comprises the Wilberforce and Harper River diversions, storage of 150 million cubic metres of water, and a powerhouse with 39 megawatts installed capacity. Currently operating at 85 percent maximum generating capacity, the facility plays a critical role providing consistent power supplies alongside wind and solar.

With an eye to creating greater and more consistent output, the facility’s operator, Manawa Energy, engaged us to lead a collaborative pre-feasibility study with Manawa, Riley Consultants, and Peter Lilley. Our job? To consider enhancement opportunities around the existing Coleridge hydro-electric scheme. Key to developing options was the utilization of an additional 25 cubic metres per second peak discharge, bringing the potential maximum power station discharge up to 65 cubic metres per second.

Our recommended options included constructing a new waterway conveyance for power generation, increasing waterway discharge by constructing a new surge chamber, a “pumped-over” new waterway option to take advantage of time-of-day price differentials, and a fourth option—a new intake, surge chamber, penstock, and powerhouse, as well as underpinning, lowering, and uprating intake tunnel one. 

As New Zealand moves to ever more power from renewables, the Lake Coleridge hydropower scheme shows how a legacy facility can still play an important role more than 100 years on from its commissioning.