Resumo

DAZA-LEGUIZAMON, Omar; VERA LOPEZ, Enrique  e  CHIAS, Luis. Cartographic assessment of vulnerability to pipeline oil spills. Environmental and social consequences. Invest. Geog [online]. 2020, n.101, e59851.  Epub 02-Out-2020. ISSN 2448-7279.  https://doi.org/10.14350/rig.59851.

Modeling and spatial analysis led to improved management of the integrity of pipelines of hazardous liquids because it facilitates the identification and classification of sections of oil pipelines according to the extent of environmental affectation that may result from a potential spillage. Although analytical tools based on Geographic Information Systems are available for the identification of sections of pipelines, these fail to prioritize properly the management activities related to pipeline integrity, as the results thereof do not include an integrated analysis of the territory. This article outlines a methodology that combines spatial data on population, environmentally sensitive areas, infrastructure, streams, route of pipelines transporting hydrocarbons, to identify the indirect consequences of leakage of transported liquids. Our findings provide information related to the impact of spills, which are easily integrated to methodologies for integrity management based on risk analysis.

The methodology is based on the use of the Hierarchical Analysis Process (PAJ, in Spanish) and the calculation of the Minimum Cumulative Cost (CMA) to group together points along pipelines with simultaneous impacts involving several heavily affected areas. PAJ defines each at-risk element in the territory and determines the relative vulnerability by calculating weighting factors. The CMA is calculated from the element of interest to each point in the pipe; this process leads to identifying the proximity between them based on a surface spill. The transportation cost is used mainly to modify the vulnerability as a function of distance, so that vulnerability decreases with increasing distance and the cost of transportation from the pipeline. Implementation requires the design of cartographic models to describe data processing and analysis and spatial information. The cartographic models designed include spatial analysis processes for calculating cost maps, CMA, algebraic overlay, and estimates of impact levels for specific pipeline points.

PAJ contemplates the fulfilment of four phases: the first defined as an issue the need to classify pipelines according to the extent of environmental and social consequences. The second identified vulnerable elements in the territory and proposed a hierarchical three-level structure. The third set paired-comparison matrices, and calculated the weighting factors for each element at each level of the hierarchical structure with the Delphi method and a panel of experts. The fourth calculated the weighting factors for the last level using comparison values for intermediate pairs (Saaty, 2008).

The spatial representation of the CMA of the spill requires a map of surface transport cost considering transport at ground level and through rivers. For ground transport, we used Manning’s equation assuming very wide rectangular cross sections (flat and convex plots) and parabolic sections (concave plots). For river transport, we included a constant k, which is higher than 1 for costs associated with water flows; this allows simulating the increased spill rate when transported by rivers. CMA represents the shortest time needed for a spill to travel the distance between the pipeline and any of the elements analyzed in the territory. The data required for calculation with the ArcGIS software are the map of costs, the digital elevation model, and vertical and horizontal cost factors. The layers of standardized minimum cost are overlaid algebraically using the weighting factors calculated previously. Finally, values are assigned to each point on the route of the pipeline.

The proposed methodology offers significant advantages compared to traditional methods regarding the identification of sections that impact heavily affected areas. The implementation of cartographic models yielded a classification of pipeline points, considering an analysis that integrates environmental and social aspects of the territory. On the other hand, the impact index, expressed in a range of 0 to 1, can be easily integrated to risk assessment matrices in pipeline integrity management programs. Finally, the methodology is flexible and can be reproduced in other geographic areas with differing social and environmental characteristics.

Palavras-chave : management of integrity; vulnerability; risk analysis; cartographic model; multicriteria analysis.