Cosseys Creek Dam

Engineering Work (eg road, bridge, sawmill, dam)


Cosseys Creek Dam, completed in 1955, was the first of a series of rolled earth water supply dams in Auckland's Hunua Ranges. Rolled earth dam design in New Zealand was signficantly advanced by these dams constructed between 1950 and 1977.

The context for this system's construction is detailed in the Hunua Ranges Water Supply Rolled Earth Dams entry.

Cossey's Creek is a tributary of the Wairoa River and the dam's site is situated in a young gorge valley. The dam was built using rolled fill consisting entirely of residual clays and rubbles from greywacke – argillite rock. All materials were existing within a haul distance of five kilometres. The clays and clay-rubble for the core and rock rubbles at the faces were easily selectable at the borrow area, and the core construction readily controlled by the use of standard moisture content and compaction density checks. Use of the newly introduced Euclid T24 earthmovers, and tractor-drawn sheep’s-foot rollers made for speedy completion – 411,000 cubic metres of material in 190 placing days over three seasons.

Diversion of the stream took place during construction through a 4.3 metre (m) tunnel, 235 m long, which was subsequently sealed with the valve tower and its five intakes. The spillway is of the bellmouth type, feeding to a spillway tunnel discharging to a lined channel below the downstream toe of the dam. The spillway capacity is 15,000 cusecs (441 cumecs).

Filling of the reservoir commenced on 13 May 1955, and was completed by 12 July 1956 following much heavier than normal rainfall.

Dam details
Crest length: 168 m
Height above foundation: 41.2 m
Catchment area: 2,200 ha
Safe yield: 40,800 cu.m./day
Reservoir area when full: 119 ha
Storage volume: 14.460,000 cu.m.


No Attachments


Hunua Ranges Regional Park, Auckland


Access Info
The dam and reservoir can be seen from the Cosseys-Massey Loop walk. Access information is available on the Auckland Council website.

Nature of Engineering
Infrastructure (incl. Road, water, ports)


Cossey's Dam on the headwater of the Wairoa River, Hunua Ranges, Auckland Region, 12 February 1965. Whites Aviation Ltd: Photographs. Ref: WA-63447-F. Alexander Turnbull Library, Wellington, New Zealand.

(Click image to enlarge )

Cossey's Dam, March 1956. Sir George Grey Special Collections, Auckland Libraries, 1207-930.

(Click image to enlarge )

Lat: -37.061196 Long: 175.106556