Provider
Kraftwerk Sousbach AG, a partner company of BKW and EWL Genossenschaft Lauterbrunnen, began building the Sousbach hydropower plant in summer 2020. The plant has been in operation since August 2025 and makes optimal use of the hydropower potential of the Sousbach river. The plant is equipped with a multi-nozzle Pelton turbine with an output of 11.3 megawatts. It produces 30.6 gigawatt hours of renewable electricity annually – enough to supply around 6,700 four-person households. The power plant thereby makes an important contribution to the canton of Bern’s hydropower expansion target and to supplying the region with sustainable energy.
The power plant in figures
| Installed capacity: | 11,3 MW |
| Expected annual production: | 30,6 GWh |
| Cost of construction: | CHF 69 million |
| Water flow quantity: | 1.4 m³ per second |
| Minimum residual flow: | 50 l per second |
| Usable gross head: | 917 m |
| Headrace length in tunnel and shaft system: | 2,980 m |
The project
The start of construction in August 2020 was preceded by a 12-year planning phase to harness the hydropower potential of the Sousbach between “Schluuchi”, below Sousläger, and the hamlet of Sandweidli for the production of renewable energy. After the canton of Bern granted the water usage concession in November 2018, the building application (including a project amendment) was approved in July 2020. The permits were granted following a two-stage environmental impact assessment. As part of this process, Kraftwerk Sousbach AG developed a hydroelectric power project that was eligible for approval and meets all requirements under environmental law.
Water catchment
The water catchment is located in a hidden rocky hollow below Sousläger. The intake installation consists of a weir embedded in the rock, which impounds the water and directs it into the inlet structure. This channels the water through a gravel trap and fine rakes into the adjoining desanding tunnels, which are approximately 50 metres long. Here, a flushing pipe transports the deposited material back to the tailwater.
The inlet structure also houses a compensation water sluice, through which the residual water is discharged. This area also serves as a downstream passage for fish. Lowering the sluice allows the debris collected by the fine screen to be discharged into the tailwater.
Headrace
The tunnel and shaft system, with a length of just under three kilometres, forms the main part of the headrace. This consists of two tunnels that are 1,032 and 1,568 metres long (excavated using conventional drill-and-blast methods) and a 380-metre solder shaft constructed using the raise-and-boring method. The two tunnel sections have a gradient of 20 percent. The lower tunnel is accessed via the “Sandweidli” portal. The “Hacketewald” portal structure provides access to the shaft head cavern and the upper pressure tunnel via a 30-metre-long access tunnel.
Powerhouse
The powerhouse building is located in the hamlet of Sandweidli on the Sousbach. An assembly opening in the roof allows bulky machine components such as the turbine and generator to be installed using a mobile crane. The turbine hall houses the safety shut-off valve (spherical valve), the Pelton turbine and the synchronous generator. As there is a risk of debris flow from the Sousbach in the area around the powerhouse, the existing protective dam will be extended towards the powerhouse building.
Protected flora and fauna, residual water volume and replacement measures
The permits were granted following an extensive environmental impact assessment. Key environmental compliance measures include a monitoring programme and compensation measures agreed with the cantonal environmental offices.
A 280-metre-long section of the Weisse Lütschine in Lauterbrunnen will be upgraded to compensate for the loss of brown trout habitat in the Sousbach. By installing groynes and boulder clusters, the flow diversity in the section will be increased, creating well-sorted gravel banks between the groynes. These serve as potential spawning grounds for trout. This measure is being implemented with Schwellenkorporation Lauterbrunnen as part of the Mösli rehabilitation project.