An Approach for Prioritizing Pipeline Water Crossings (WC) for Effective Mitigation and Monitoring

This paper provides an approach for assessing and classifying riverine pipeline crossings to prioritize effective mitigation and monitoring. These processes require understanding of and accounting for channel processes, river dynamics, geomorphic principals and soil mechanics to estimate bed scour and bank erosion degradation mechanisms at water crossings and their potential effects on the pipeline. The intent of this paper is to share generic experiences in ranking water crossings based on their susceptibility to and identification of integrity threats under multiple existing and future hydrologic scenarios causing potential for pipeline exposure, spanning or damage. The intent is not to present or provide an analysis or review of the various methods for estimating channel bed or bank erosion. The details of such calculations are highly site specific and a variety of both qualitative and quantitative methods can be applied depending upon available site data, and as such, are outside the scope of the work presented here. Pipelines are static features within a dynamic environment with rivers and floodplains representing some of the most active areas within a landscape. Rivers can change course, migrate, deepen, and widen slowly over time or suddenly during large flood events. These hydrologic effects can impact existing pipelines thereby putting pipelines at risk for damage or failure. Understanding how rivers alter the landscape and transport water and sediment from the mountains to the sea provides a framework for realizing the potential toll that riverine changes can have on pipeline infrastructure. Further, integrating analysis of how rivers at specific pipeline crossing locations are likely to change can increase the effectiveness in protecting the environment during the design, construction, operation and integrity management of pipelines at river crossings. The paper provides an approach comprised of five (5) stages: 1. WC Inventory and Desktop Data Gathering 2. Screening Process: Preliminary WC Classification 3. Detailed Assessment 4. Final WC Classification, Prioritization, and Risk Assessment 5. Development of Mitigation and Monitoring Strategies This paper also presents two (2) case studies illustrating how assessing the geomorphic condition and processes of the river system being crossed by pipelines provides for a better understanding of susceptibility to existing hydro-geotechnical threats to the pipeline as well as the susceptibility for flood-related forces in the future. The first case study illustrates how changes to a river’s cross section as a result of construction activities upstream of a pipeline water crossing can cause significant and potentially damaging impacts, downstream. The second case study reinforces the importance of understanding the history of watershed and channel changes over time, both at the specific water crossing location, but also both upstream and downstream from the crossing itself to be able to identify and understand all potential threats to pipelines located within rivers and floodplains. A method for assessing and classifying the magnitude and probability of flood related risk at each case study is discussed. These cases are presented as generic examples for educational purposes only as every pipeline has its own specific characteristics conditions with jurisdiction-specific regulatory requirements requiring process customization and enhancements.