Several hydrological methods are available to determine flood discharge and scour of streams at pipeline crossings. These methods are appropriate for streams dominated by purely hydrological processes, but fail where other, more hazardous processes occur within the design recurrence interval. Several investigations have shown that scour, impact and aggradation associated with debris flows, outburst floods or related phenomena may fundamentally change the parameters needed for proper pipeline crossing design. Depending on the process type, the peak discharge of the hazardous process can exceed that of the design flood (typically 50 to 200 year return period) by a factor of 2 to 50. Similarly, scour or aggradation by a non-fluvial process can exceed the hydrologically-derived estimates by several factors. It is therefore recommended that a geomorphic approach be taken in recognizing and quantifying the potential for non-fluvial processes and that the findings be integrated in the design of pipeline crossings.
Pembina Pipeline Corporation (Pembina) owns and operates close to 10,000 km of crude, natural gas liquids (NGL), and natural gas pipelines across North America, with the majority of assets in western Alberta and eastern British Columbia. The Pembina pipeline network includes over 1,600 river and stream crossings, most of which are subject to varying degrees of vertical and/or lateral erosion. 1,260 crossings were in Alberta at the onset of the study. Identifying potential lateral erosion hazards is a critical component of geohazard management program for pipeline integrity. In 2012, Pembina initiated a three-phase program to proactively address lateral-stability issues at river and stream crossings in Alberta: phase one identified and short-listed crossings that have potential lateral channel-shifting problems; phase two assessed which short-listed crossings have insufficient cover depth to accommodate the potential channel-shifting activities and ranked these crossings as high risk of exposure; and phase three will develop plans for repair and/or replacement of the high-risk crossings. Through this program, Pembina explores the significance of lateral erosion and encroachment at pipeline water crossings of various vintages, with regards to pipeline integrity. This paper provides discussion as to how crossing geohazard risks are identified, with particular emphasis on stream bank erosion, and how this fits into Pembina’s overall risk management program. As well, selected case studies are provided.
No abstract
Pipeline systems must contend with many hazards, of which ground movements such as landslides and washouts represent one type. Under the broader umbrella term, natural hazards, individual ground movement threats can be subdivided into geotechnical and hydrotechnical hazards. A four-phase natural hazard and risk management system (NHRM) is being developed. Although research and development are ongoing, implementation over the past seven years spans approximately 25,000 km of main-line pipeline in North and South America. It complies with CSA requirements for ‘hazard identification’ as well as current standard-of-care guidelines related to case-law in Canada. It is designed as a simple yet reproducible methodology that can be operated by pipeline companies, particularly their field staff. The first two phases of hazard identification/assessment are described here with reference to a recent study of hydrotechnical hazards along the Trans Mountain Pipe Line Co. Ltd. main line from Hinton, Alberta to Kamloops, British Columbia in the mountains of western Canada. The relative hazard ratings generated by the Phase I and II methodology can be integrated into existing risk management methodologies used in the industry. Alternatively, the risk assessment and risk management methodology of the NHRM system can be used as outlined in this paper.
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