Usma is the main watercourse in Øksendalen. The river originates from a small pond located between Søndre Steinbruhø and Kleivhø inland towards the Aursjø area. The river flows past the Moldbakken farm and the farms in Jønstad before continuing further down the valley towards the Brandstad farms. The river takes up some inflow from tributaries on the way down the valley.
Usma power plant utilises the waterfall from Grindbakken, which is halfway between Brandstad and Jønstad, and further down towards the Brandstad farms.
The river has long been used for mill operations for the farms. Remains of the mill walls can be seen today on the other side of the river where the station now stands. The river has a high water level with variable water flow. The catchment area for the Usma power plant is about 40 km2.
The idea of a power plant project emerged in 1999. The two landowners wanted to strengthen the income of the farms and agreed early on to divide the waterfall rights in two, with 50% for each.It quickly became clear that a development would entail relatively extensive investments. They therefore agreed to seek an external partner instead of taking the risk of building themselves. Following negotiations with several different partners, they signed a contract with Småkraft in December 2004. The landowners expect the facility to make a valuable financial contribution to the farms for many years to come. One positive aspect of the development is that the people of Øksendal can now benefit from new buried power cables, as well as high-speed broadband and cable TV via fibre cable.
The Usma power plant has two vertical Francis turbines and generators. Maximum flow rate is 4.5 m3/s with an installed capacity of 4.6 MW. All power is converted to 22KV and delivered to the grid. The waterway consists of a 1450 metres of buried GRP pipe with about 260 metres of unlined tunnel towards the intake. The power station building was built in accordance with Småkraft’s aesthetic guidelines, which includes a glass façade.