An Overland-Hydrographical Spill Model and Its Application to Pipeline Consequence Modeling
Authors: Zuczek Patricia , Deng Chuntao , Mihell Jim , Adams Keith 
Published: July 2009

Hazardous liquid transmission via large diameter pipelines relies on the integrity of the pipeline system. An accidental loss of containment at any point along the pipeline can result in widely ranging environmental impacts depending on local geography, as well as design and operational parameters. Instead of “Rule of Thumb”, a state-of-the-art consequence assessment may require a robust and comprehensive computer tool to effectively prioritize areas for maintenance and mitigation, as well as to develop an appropriate spill response plan. An approach for quantifying the consequences associated with a liquid spill has been developed and described. The results are used in a consequence analysis by computing the estimated costs for response and environmental damage based on the outflow volumes and environmental factors. This is further incorporated into a risk analysis to provide an illustration of the probability and severity of a failure along the pipeline. The final results may be used as an aid in response training, contingency planning, and prevention and mitigation strategies. The basis of the consequence analysis is a transient three-dimensional (3-D) overland-hydrographical spill simulation package, which has been developed to model the trajectory of a liquid spill. The spill simulation package is an in-house VBA extension of ArcGIS™ that uses a digital elevation model to determine the flow path of a spill. The spill model includes three modules: the oil trajectory simulation module, which predicts pooling and the primary direction of oil spreading; the physical module, which determines the transient rate of spreading and pooling, the depth of infiltration into soil, the width of the lateral spread and other parameters that are concerned; and a module that detects the boundaries of land/water transitions. A description is provided of the procedures that were established to programmatically plot the extent of the impact in ArcGIS™. In addition, a hydrographical flow model is described which determines the amount of contaminant entering any stationary or non-stationary water bodies that may intersect with the spill and which displays the potential impact area over the water within the emergency response time. The paper outlines how the spill simulation package is integrated with a cost analysis module, which is applied to determine the estimated clean-up costs for the contaminated area on land and water. An illustration is provided as to how an iterative calculation procedure can be set up to model spill consequences at each potential failure site along the pipe centerline. Using this procedure, high consequence pipe segments are identified and highlighted and are overlaid on the GIS map to identify those areas where a spill will have the greatest impact. This enables the development of a quantitative consequence profile which may then be used as part of a quantitative risk assessment and/or to aid in proactive engineering design, maintenance, mitigation and response optimization.