History
Due to Tauranga's increasing demand for electricity a scheme was developed to create a waterfall on the Wairoa River. It was thought that 3,000 to 3,500 horsepower could be obtained. The falls were later renamed McLaren Falls after the couple that operated the cook house, who had lost a son in the First World War.
A concrete arch dam was built in a narrow gorge where the water was normally 6.7 metres deep. A 487 metre long 2 metre square diversion tunnel was driven from just above the water below the present bridge to the river above the dam site. A branch to this tunnel was then driven under the deep pool at the dam site to drain it while the dam excavations and filling were carried out.
The powerhouse and arch dam were constructed using the local rhyolite rock for fine and coarse aggregate. All structures were designed so as to impose low stresses on the concrete. The quarry for the power house rock was situated downstream on the same side, the rock being transported by manually-pushed trolleys on rails.
The static head was 26 metres, the arch dam being 24.5 metres high. After two and a half years of design and construction the first of two 1,400kW vertical shaft turbine-generator sets was started up on 25th June, 1925, the second starting a few months later. A third tunnel was built to divert the Mangakarengorengo Stream into the twenty hectare Lake McLaren. The total cost of the scheme was $165,764.
In 1982/1983 the level of Lake McLaren was raised by 1.2 metres to increase the storage capacity for hydro-electric generation. Over fifty years of silting had reduced the capacity. The existing dam was strengthened, and the spillway raised to the same level, so now both act as a spillway.
The original McLaren Falls Power Sation was essentially decomissioned in 1981 with the commissioning of the Ruahihi Power Station.
Easy parking off the road, and then a 100m easy walk to the cache. A 570ml xeonic plastic.
FIRST TO FIND HONOURS WENT TO: MAC ROSS