Maitai Dam

Pre-dam schemes

The Maitai River was first considered for water supply in the 1930s. At this time the Brook Scheme (commissioned in 1867) was unable to meet demand.

Rather than proceed with the Maitai, the Government backed a weir on the Roding River, as this was seen to benefit not only the city (a much smaller place than today!) but also the Tahunanui Town Board, Stoke (then Waimea County) and Richmond Borough. The Roding succeeded for a time but by the 1950s more water was needed. A dam on the Maitai was proposed. The pipeline part of the scheme was completed in 1963 but the dam was postponed in favour of a temporary, intake grating on the South Branch.

A dam at last

By the 1970s Nelson's water supply was suffering not only volume problems but also quality  problems. A Maitai dam was once again proposed, in 1973, but was heavily debated. The earth dam received scores of reports, financial and environmental assessments, public relations campaigns, letters to the editor, water right applications and appeals which dominated media and local politics for more than a decade.

Design for the new Maitai Water Supply Scheme was finalised during 1984, construction started later that year and the work was completed in 1987.

The Dam

• Height: 36 metres
• Length of crest: 140 metres
• Width of base: 185 metres
• Volume of Fill (Dam core) 272,000 cubic metres
• Additional Fill (platform) 100,000 cubic metres

The Reservoir

• Area 32 hectares
• Volume 4 million cubic metres
• Greatest depth 32.75 metres

Diversion Culvert

This culvert served as a diversion channel during construction (to enable the earth fill to be placed in dry conditions) and now holds the supply and scour pipes of the dam.

Intake Tower

Sits atop the valve chamber. The three pipes are each capable of taking 600 litres per second from the reservoir.

The Earthfill Dam

Piezometers were placed at 27 sites throughout the dam to measure seepage; flows from the various filter drains are also measured.

Concrete Spillway

Flow capacity of 125 cumecs (cubic metres per second) which corresponds to a 100 year flood event. Events larger than this will overflow to an unlined auxiliary spillway.

Cost in 1987 Dollars

• Design and supervision - $1.8 million
• Preliminary Works - $150, 000
• Dam Works - $6.7 million
• South Branch Works - $650, 000
• Control & Instrumentation - $400,000
• Total - $9.7 million

Nelson City Council received a subsidy from the Health Department of $1 million. The remainder of the cost was funded from loans which by 2005 were paid off.

Resource Consents

Among the Resource Consent conditions are requirements that minimum flows in the Mahitahi/ Maitai River are 300 litres per second from April to October and 175 litres per second from November to March. In addition, any water drawn from the South Branch intake must be replaced with stored water from the reservoir.

Supply

Designed for peak demand of 40,000 cubic metres per day. The Roding scheme contributes 13,000 cubic metres per day.

Nelson Water Treatment Plant

Opened in 2004 - supplies international standard water. Enables an additional 1 million cubic metres of previously unusable water from the Maitai Reservoir to be treated for supply. In 2005 it supplied an average peak demand of around 42,000 cubic metres per day and has the potential to treat 52,000 cubic metres per day.

This material is taken from the Nelson Heritage Trust Plaque at the Maitai Dam, 2000. Updated 2022

Story by: Janet Bathgate