Skaha Lake crossing, innovations in pipeline installation

This paper describes the construction of a 10.8 km long NPS16 (406 mm, 16 inch diameter) pipeline, across Skaha Lake, in the south Okanagan valley, British Columbia, Canada. The water crossing is part of the 32 km South Okanagan Natural Gas Pipeline Project (SONG) operated by BC Gas. The pipeline is located in a region dependent on year-round tourism. Therefore, the design and construction was influenced by sensitive environmental and land use concerns. From earlier studies, BC Gas identified surface tow or lay as preferred installation methods. The contractor, Fraser River Pile and Dredge departed from a conventional laybarge methodology after evaluating environmental data and assessing locally available equipment. The contractor proposed a surface tow with multiple surface tie-ins. This approach modification to the ``Surface Tow and Buoy Release Method`` (STBRM) used previously with success on relatively short underwater pipelines. A total of 10 pipe strings, up to 1 km long, were towed into position on the lake and tied-in using a floating platform. The joined pipeline was lowered to the lakebed by divers releasing buoys while tension was maintained from a winch barge at the free end of the pipeline. From analysis and field verified measurement the installation stressesmore » were well below the allowable limits during all phases of construction. The entire construction, including mobilization and demobilization, lasted less than three months, and actual pipelaying less than three weeks. Installation was completed within budget and on schedule, without any environmental or safety related incidents. The SONG pipeline became operational in December 1994.« less