Bank Erosion and Encroachment Model Development to Enhance Pipeline Integrity Management

Abstract Bank erosion can expose pipelines at watercourse crossings or in floodplains at encroachment sites. Once a pipeline is exposed, failure can occur due to water loading, debris loading, excessive strain, or vortex-induced vibration (VIV). Empirical engineering formulae have been developed to predict scour depths in rivers and can be used at pipeline watercourse crossings to estimate the annual probability of pipeline exposure from scour. Vulnerability algorithms can then be used to estimate the annual probability of pipeline failure at watercourse crossings, which most commonly results from VIV. However, bank erosion has generally proven to be complex and time-consuming to assess, and it is therefore often considered at the site scale rather than at a screening level in system-wide assessments of hydrotechnical hazards. This paper describes a novel bank erosion model developed and validated using morphological characteristics and historical aerial imagery from over 240 detailed assessments of pipeline watercourse crossings and encroachment sites across North America. The model predicts the rate of bank erosion based on channel and floodplain morphology, as well as other site characteristics such as debris presence where data exists. Based on these characteristics, as well as the actual rate of observed erosion where possible, a time to pipeline exposure is estimated at watercourse crossings and encroachment sites. The estimated time to pipeline exposure and bank protection type is then used to assign an annual probability of pipeline exposure. This paper also addresses a gap in the current practice by providing a framework for assessing vulnerability at encroachment sites where flow is parallel or sub-parallel to the pipeline and VIV is unlikely to occur. The probability of pipeline failure at both watercourse crossings and encroachment sites can then be assessed by considering site-specific characteristics, such as the potential free span length, pipe properties, and pipeline operating conditions. As the models use morphological characteristics observable on the ground or in a desktop review and known pipeline data, the results can be used to prioritize actions (e.g., ground inspections or mitigation) at watercourse crossings and encroachment sites and to guide geohazard management strategies to enhance pipeline integrity management.