Air cushion surge chambers for underground power plants

Nine air cushion surge chambers in essentially unlined rock have been commissioned in Norway since the concept was introduced in the early 1970s. They have been used for headrace tunnel lengths of up to 13 km. Six of the nine installations have functioned satisfactorily as constructed. At two sites, remedial work has been necessary to reduce air loss. This article covers the geometry, dynamic behavior, operation and performance of these surge facilities. Air loss from the rock caverns is discussed, and remedial work at two sites is outlined. Recommendations for the design for air cushion surge chambers are put forward.