Remedial protection of a pipeline crossing of the River Wye, UK

This project is of interest to those involved in construction, siting, and repair of pipeline crossings of rivers, streams, and estuaries. In early 1999, Mainline Pipelines Ltd discovered that its pipeline crossing of the River Wye in the UK had been exposed by river scour. Originally laid in 1972, the line provides petroleum products' main supply from the port at Milford Haven to the Midlands, UK, and operates at a high pressure. A break in, or temporary shutdown of, the pipeline would have had serious implications. Remedial protection options were needed rapidly to ensure the integrity of the pipeline. A review of historical air photographs and maps, dating back to 1888, showed that the meandering channel of the River Wye has shifted to the north at an average rate of 0.65m per year, Thus, the remedial works would have to account for continuing vertical and lateral scour. It was recognized that river-training works would be required at the site to ensure continued protection of the pipeline in the long term. The recommended design and remedial construction techniques allowed for safety issues, the potential impact on the river ecology, recreational river users, the river hydrology, and restricted access to the steep northern river bank. The design comprised filling of the eroded river bed and bank with rock aggregate and placing a protective layer of graded rock riprap. Grout-filled fabric formwork bags were placed beneath the pipeline to minimize deflection and the development of unacceptable stresses in the exposed length during rock placement. Rock-filled wire mattresses were placed immediately on top of the pipeline to protect it from point loading of the angular riprap. A satellite-guided positioning system was used to control material placement, and environmental monitoring of river water quality was carried out continuously during construction.