In 1917 the government in response to the league's request dispatched engineer Lawrence Birk (1874–1924) from the Public Work Department on the first of two visits (20 to 28 September and 1 to 8 December) to investigate the demand for electricity and potential for hydro-electric generation in Southland.

This allowed them to directly engage Gisborne consulting engineer F. C. Hay to investigate in more detail the best source of generation, the expected cost and how to reticulate the resulting electricity throughout Southland.

[8] At the same time the League believing that for Southland to progress, electricity needed to be made available throughout the province and not just to the major population centres.

Until the loan was obtained SEPB would temporarily fund its activities using a bank overdraft with the collateral being the ability to rate people in the district.

[11] After unsuccessfully trying to employ either Lawrence Birk or Evan Parry as their engineer SEPB engaged the newly established Wellington firm of Hay and Vickerman (which consisted of F.C.

Investigations were undertaken into how best to do this, with consideration given to trucks, horse-pulled carts, traction engine as well as transporting it up the Waiau River which would require some blasting to remove hazards.

The decision was made to employ a traction engine and two trucks which required SEPB to upgrade the existing roads and also extend them to the construction site.

[14] By the end of 1920 a total of 80 men and 40 horses were working in the project, building the road and preparing the sites for the construction camp and powerhouse.

By early 1921 not only was the access road to Lake Monowai completed but also the construction camp as well as a new suspension bridge across the Waiau River at Sunnyside.

In 1921 there was a world-wide economic slump made worse by the termination of the commandeer system (which resulted in a dramatic fall in the export prices of meat, wool and dairy products), caused the New Zealand government to look at means of reducing public and private expenditure.

Among the reasons were the absence of both Hay and Vickerman during the early stage of the work, their estimates were proving to be too low, progress was slow on upgrading the roads to allow their use in winter, materials were being purchased before they were required and at high prices.

As the dam was formed the lake level rose and found a new outlet through the control gates, through which the water flowed before rejoining the original river bed.

[24] The roiled plates were then dripped in a boiling pitch and tar to protect them then riveted in 6 ft (1.8 m) long sections before being transported to required location for mounting on a cradle.

Progress had reached the point by this time that SEPS placed orders for the turbines, valves, generators, exciters and switchgear.

As a result, it was decided to redesign the foundations so that it was of the "tank" top with allowed the river could rise 5 ft (1.5 m) above the floor level without interfering with the power station's operation.

[28] With construction work completed Alfred Walker was appointed Station Superintendent with a total of 13 permanent staff serving at Monowai.

[29] By 1934 the SEPB was running short of electricity with an increasing number of dairy farms beginning to use vacuum pumps which placed considerable pressure on the network at peak times.

[32] During the Second World War the Monowai power scheme was regarded as being of strategic value, which meant that a blackout was applied to the powerhouse and village, with sentries at the bridge and nighttime patrols of the pipeline and canal.

In the mid-1990s with much of the original equipment reaching the end of its physical and economic life the consulting firm of Royds Garden was engaged to investigate the various options available to upgrade and develop Monowai.

SEPS decided to proceed with a scheme that involved diverting water from the river upstream of the existing headpond through a short canal and longer pipeline to the powerhouse.

[36] In 1993 upon the passing of the Southland Electricity Act Monowai together with all other assets of SEPS was vested in The Power Company Limited (TPCL).

The passing into law in August 1998 of the Electricity Industry Reform Act, which required the separation of ownership of generation and retailing from lines businesses.

[39] At the time they purchased the power station Pioneer knew that while it had been well maintained the equipment was old and becoming unreliable, with a considerable number of unplanned outages.

With no remote control facility operating staff had to attend the power station seven days a week, which by this time was only during daylight hours.

if the problem was more serious than an operator could resolve then Pioneer was reliant on maintenance contractors who were generally based in Invercargill, who took a minimum of two hours to reach the site.

This idea, however, failed, as well as later plans to use a single generator with one turbine at either end, partly because of the difficult access to the station, leading over a single-lane suspension bridge which imposed weight and size restrictions.

The work was undertaken by Invercargill firm Alltec Engineering Limited and the station now operates with three Swedish TURAB 2,566 kW vertical Francis turbines coupled to Spanish Alconza 3,183 kVA synchronous generators.

As a result, in 2012 in order to reinforce the dam and improve general security, a downstream shoulder was added, the freeboard increased and the upstream face covered in rip rap to manage the impact of waves.

From the forebay a 53 ch (1,100 m) long 8.74 ft (2.66 m) diameter steel pipeline (raised above ground level on concrete cradles) leads to a surge tank.

Three penstocks 200 ft (61 m) long take the water from the surge chamber down a one in 10 gradient to directly connect to Francis turbines coupled to synchronous generators in the powerhouse, which is located on the west bank of the Waiau River.