The Maitai Dam was commissioned in 1987 and provides a reservoir capacity of 4 million cubic meters of water.

This reservoir is a very important water source for the city sitting on the North branch of the Maitai River and supplemented by the original water take from the South branch

Improving environmental health

The reservoir has consents that include reviews for operational improvement where possible with consideration for the environment.

A recent review has varied the consent amending parameters for oxygen saturation in the reservoir to improve water quality, especially during summer.

Temperature stratification during the summer period (November to April) affects dissolved oxygen levels within the reservoir and as a result, in the Maitai River south branch. This leads to elevated concentrations of naturally occurring contaminants.

These conditions can create additional complexity for the water treatment plant if water is needing to be sourced from the depths of the reservoir.

What is this project?

This project has investigated means of improving the oxygen levels within the reservoir with the development of a 3D model that has been validated by engineering specialists in ecosystem and water management.

A suitable engineering solution has been recommended and is essentially a large Goldfish Bowl bubbler system introducing compressed air into the water column.

What work will be done?

Council will now install 75kW oil-free air-cooled compressors in a new control building and these will deliver up to 240 litres per second (free air delivery) of air through a submerged distribution pipe (or sparge) in the bottom of the reservoir.

The 90mm diameter sparge is located in the valley of the reservoir along the original North branch river course and has a number of discharge nozzles allowing the distribution of bubble plumes to encourage natural mixing, which will increase oxygen saturation within the reservoir.

To assist with location and maintenance of the pipe delivery system, mooring buoys will be installed also serving to anchor the a second pipe which contains a heavy chain that either holds the sparge close to the reservoir floor, or allows it to be lifted to the surface for maintenance.

A power supply upgrade is required and will extend a new cable to a new transformer provided by Network Tasman.

The Council’s maintenance contractor Fulton Hogan will be installing the new aeration system with expected commissioning in January 2025.

How will the effects on the environment be monitored?

Cawthron Institute will be assisting with ongoing monitoring of the reservoir to review the performance of the aeration system in addition to consent work we already undertake for monitoring the physical, chemical, and ecological conditions of the Maitai River.