Terrain analyses and geologic hazards assessments are recognized as important components for pipeline planning, permitting, and asset management. Although the two types of assessments have inherently different objectives and outputs, there is some overlap in the results between the two and they tend to complement each other; thus, there are benefits to conducting the two assessments in parallel, and integrating the results. Likewise, situations may arise where information from both assessments may simultaneously prove useful in driving decision-making.
Terrain analyses seek to identify homogenous terrain units based on material types, surface expression, depth to bedrock, slope, drainage, and geomorphological processes. Information compiled during a terrain analysis helps to develop a detailed understanding of the local terrain, which can be used to estimate geotechnical soil properties, provide cost savings, and formulate sound decision-making throughout the life of a pipeline.
Geologic hazards assessments generally seek to individually identify, map, characterize, and ultimately allow for mitigation/monitoring of potential geologic hazards, through increasingly detailed geomorphic/geologic assessments. Some typical geologic hazards that are evaluated include landslide, seismic, subsidence, and hydrotechnical hazards. Once identified, a qualitative hazard classification (e.g., low, moderate, high) is generally assigned to each possible hazard, based on several criteria such as the activity level of the geologic process, rate and magnitude of movement of the hazard, the areal extent and proximity of the hazard, the estimated likelihood that the hazard would affect or engage a pipeline during its service life. The hazard classifications are often then tied to recommendations for additional assessment and/or response and mitigation.
The identification of a landslide will be used as an example to highlight how the two assessments can overlap and complement one another, but still provide unique information, and how the two assessments can be used in conjunction to inform better decision-making. Both assessments may identify the location of the same landslide or potentially unstable slope. The geologic hazards assessment would further characterize the landslide’s spatial relationship to the pipe both laterally and vertically, its activity level, etc., in order to evaluate the potential hazard the landslide poses to the pipeline. If mitigation was deemed necessary, information from both the terrain mapping and geologic hazards assessment could be used to evaluate the specific characteristics of the landslide, as well as the surrounding terrain, in order to select the most suitable form of mitigation.