Low River Contingency for Hamilton's Water Treatment Plant - Keeping the Flow When the River Goes Low

Hamilton City is dependent on the Waikato River as its sole raw water source. The water treatment plant receives water through a fixed river intake structure, which places the city’s water supply at extreme risk if river levels drop below it.

In three of the last four summers river levels have fallen to critical levels due to drought in the Lake Taupo catchment which supplies the river. Climate change forecasts suggest seasonal river levels are likely to further reduce, meaning abstraction may become impossible with current infrastructure. An emergency plan to pump water into the Treatment Plant intake structure from a deeper part of the river has been deployed in the past, but never implemented, and was only ever a ‘band-aid’ solution which would still impose severe water restrictions on residents and businesses.

Amending the intake structures was budgeted at $26M, and would expose the city to further risk as operation of the intake structure would be compromised, if not halted, during a three-year construction phase

This paper outlines the investigation into the cause and effect of lower Waikato River levels, with a focus on resilience for the water treatment plant and the decision to construct and deploy a floating pumping platform capable of maintaining water supply to the city during periods of low river levels. This interim solution had to be able to supply 70 million litres of water daily for the city, and be scalable to allow for increased water demand (up to 90 million litres daily) over the next 15 years. Following funding approval in February 2015, it had to be designed and built to provide security of supply in the 2015/16 summer.

This paper also describes the Treasury Better Business Case model applied in the project approval process, design and construction hurdles which had to be overcome, the integration of the project with existing infrastructure and design amendments required to meet changing river levels during commissioning.

The completed project enables the deferment of $26M in capital works for 15 years, provides an alternative pumping solution during construction of the long term solution, and with a 12-month construction time was available to deploy if needed in the 2015/16 summer. During March