Sarneraatal Valley Flood Protection, River Sarneraa and Flood Relief Tunnel (East)

The project encompasses flood protection measures and ecological upgrades on the River Sarneraa as well as a flood relief tunnel from Sarnersee lake to below Wichelsee lake. It will optimise fulfilment of protection goals around Sarnersee lake aand along River Sarneraa between Sarnersee and Wichelsee lakes, while simultaneously taking environmental aspects into consideration. During flooding the flood relief tunnel (east) will significantly increase the currently restricted discharge capacity from the Sarnersee lake thereby providing safe and controlled relief for the Sarnertaal Valley.

Main Data

  • Flood relief tunnel (east) as a pressure tunnel  (length: 6.6 km, inner diameter: 6.4 m, discharge capacity: 130 m3/s)
  • Inlet structure permanently located approx. 9 m below water as lake water intake with adjacent operating rooms and inspection and emergency gate
  • Outlet structure with redundant gates, stilling basin and flow into the River Sarneraa
  • Flood protection and ecological upgrade measures on the River Sarneraa (length: 3.7 km)
  • Inflatable Sarneraa weir to regulate Sarnersee lake in the event of flooding and ecological cultivation of adjacent biosphere areas (width: 14 m, height: 1.6 m)
  • Moving Etschischwelle barrier upstream to Wichelsee weir and the associated lowering of the river bed as well as widening and ecological upgrade of the River Sarneraa


Obwalden Canton, Office of Forest and Countryside


IUB Engineering Ltd. in consortium

Construction period

Project design Phase: 2010 to date

Construction costs

Cost estimate: CHF 115 million

Scope of services

  • Preliminary study, construction project and detailed planning for construction
  • Total contractor tender for components of the flood relief tunnel (east)
  • Feasibility study for hydropower use
  • In the future: engineering services up to commissioning