Protecting Natural Gas Pipelines from Geo-Hazards Exacerbated by a Change in Climate

H. Jack Meyer and Bruce L. Paskett
NW Natural, Portland, OR

NW Natural operates over 600 miles (1000 km) of high pressure natural gas transmission pipelines in western Oregon. 235 miles (392 km) of these pipelines traverse the Oregon Coast Range mountains. The combination of high winter rainfall, deep weathering, ancient landslides, and disturbed drainage systems can produce geo-hazards such as erosion and landsliding which may affect the safe operation of a pipeline. In the Pacific Northwest rainfall appears to occur in “wet” or “dry” cycles of 20 to 25 years duration. The majority of NW Natural’s Coast Range transmission pipelines were constructed in the late 1960’s near the end of a “wet” cycle. During the subsequent “dry” cycle of 20 plus years, pipeline Rights of Way (ROW) were stable. In the mid-1990’s, the climate switched to a “wet” cycle. As a consequence, ROW’s, particularly when impacted by intense Pacific storms, became much more susceptible to geo-hazards. NW Natural’s response to this “climate change” was to create a risk-based “Geo-Hazard Program” for their transmission pipeline system. The program entails identification, assessment, remediation and ongoing monitoring of geo-hazards. Key to this program was the formation of a team, which consisted of pipeline engineers, geotechnical professionals and pipeline field personal that had the responsibility of addressing geo-hazard issues. Another important element involved training ROW maintenance personnel to recognize geo-hazards, report/repair them and collect monitoring data. Rainfall “triggers” were established to initiate immediate inspection of pipeline ROW’s. The Geo-Hazard Program exceeds the minimum requirements of Federal pipeline safety regulations, 49 CFR, Part 192. The program was voluntarily initiated by NW Natural in a partnership with the Oregon Public Utility Commission.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas