Pumped hydro is a means of storing surplus electricity generation capacity. During times of low demand, water is pumped uphill and run back down through the turbines to provide power when demand increases.

The installation most would be familiar with would be the Tumut 3 plant which has been operating since 1972.

Tumut 3 is primarily a power generator, and the pumped system was installed to use excess power generated by coal.

Coal fired power stations were the only other means of generating electricity at the time and they lack the ability to quickly respond to demand fluctuations. In fact, they work best when run at a constant speed, which leads to over supply of power when demand is low and possible undersupply at times of high demand.

Things are a lot different fifty years later. Much power is now generated by renewable resources, with the inherent unpredictably of sunshine and wind speed.

The problem now is managing this variability, and with the phasing out of coal generation over the next few years, it will become more important. There is also a wholesale energy market now with prices to retailers varying widely (and wildly) as supply and demand change

One solution to the problem of matching supply to demand is the use of batteries like the large one in South Australia and the one proposed for the power station site at Wallerawang.

The Yetholme pumped hydro project is not primarily a generator (capacity is 325MW, Tumut 3 is 1,800) - it is a form of battery which can store electricity at times of low demand or low wholesale prices and release it quickly when things change.

The Yetholme project proposes the construction of two dams connected by a large pipe, one at the top of Mount Tennyson and the other lower in a nearby valley, with the generators and pumps submerged in the lower dam.

Water for the project will be drawn from the Fish River a few kilometres before O'Connell. Connection to the grid will be by an underground cable to an existing 330kV transmission line.

Construction is scheduled to start in 2023 with completion and commissioning in 2026.

The company proposing the development is ATCO, a subsidiary of a Canadian company. As well as operating the largest reticulated gas network in WA, the company operates two power stations (Karratha in WA, Osborne SA) and builds and rents onsite accommodation for construction sites and mining projects.

Opposition to the proposal comes from four directions - environmental damage, possible health impact, heritage issues and water extraction.

"If this goes ahead, it will be a disaster for the Fish River and Bathurst," O'Connell resident, Sandy Bathgate said.

"Not a single irrigator will sell their water rights to ATCO."

The environmental impact will come from the construction of the two dams, which will require clearing of many hectares of forest which is currently home to several critically endangered species and also communities of koalas, Gang Gang cockatoos and the Purple Copper butterfly (found in only three places).

There is also the suggestion that the project will block animal migration between the neighbouring Wambool and Eusdale nature reserves, although the company disputes this.

Health issues arise from the effect of blasting (the top of Mount Tennyson will be removed for the upper dam). This will release dust into the air which could contain toxic chemicals such as arsenic and molybdenite and the dust could have a wide distribution.

This is a problem which occurs whenever the surface of the Earth is disturbed, such as near mines, and is certainly a matter for concern,

The area proposed for the project has significant Indigenous heritage value and was a meeting place for travellers from several directions, who used Mt Tennyson as a guide post.

The area is rich in Indigenous artifacts indicating very long use and occupancy.

While there is a greater sensitivity today to the signs of Australia's past and the beliefs and traditions of the Indigenous population, there is a history of such concerns being ignored.

Filling the dams will require 3.3 gigalitres of water (about equal to a year's supply for Bathurst) and the annual requirement to account for evaporation and seepage is 400 megalitres - 160 Olympic swimming pools, to use a standard unit of volume.

While the loss of this much water from the river would be almost disastrous, the company states in several places that they will be legally restricted to only taking water when the flow exceeds any requirements for irrigators or river quality.

This allocation for the dams is based on 100 years of records of the river's behaviour and takes both droughts and flood into account.

Information about the objections to the project came from several concerned community groups.

The company was not available for comment, with their presented point of views drawn from information on the ATCO website or their regular newsletters.

There will be public information sessions in Bathurst (September 23), Yetholme (September 24) and O'Connell (September 25) following the release of the Environmental Impact Statement in mid-September.

The Oberon Review will be following this project as it progresses.

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