Rototuna Reservoir Construction – Securing Water for the Future

Hamilton City’s water distribution system consists of a single water treatment plant and distribution via a ring main system to eight reservoirs throughout the City.

In order to cater for current and future city growth, Hamilton City have invested $21m in a new 24Ml reservoir in Rototuna, which is anticipated to be completed by September 2017. In addition to facilitating city growth the new reservoir will provide significant benefits to network operation and resilience.

Geographically 95% of the current water storage is located on the western side of the city, with only one operational reservoir located on the eastern side. The city is therefore critically reliant on strategic river crossings to provide water to the east in emergency situations. The Rototuna Reservoir will provide some balance to the east/west storage.

A major strategic shift in the operation of the City water network is from the water treatment plant managing the demand of the city, to the treatment plant supplying reservoirs which will manage the demand by zones (Demand Management Areas). This change in operational philosophy will maximize reservoir utilization by allowing buffering of demand fluctuations and thereby alleviating the stress placed on the water treatment plant output rates.

This strategic shift changed the intended purpose of the reservoir pumphouse from simply supplying water at a steady head to the ring main, to supplying a primarily residential zone with a dynamic flow range of between 35l/s to 650l/s. This paper will focus on how the ranges of flow demands of a primarily residential zone were met, and the impacts of a strategic shift in how the network was operated after the design was completed.

This project faced challenges in the design phase including seismic requirements and geotechnical challenges, and the paper will also touch on Contractor led value engineering proposals, safety in design, and the twin bulk main design for reservoir filling and operational supply, including how to get water to the reservoir at the opposite end of the city from the Treatment Plant and at a high RL.