Power |
Telecom |
Transport |
Others
A Remote Sensing and GIS based least cost routing of pipelines
Background
In response to industry demand, SAC has developed a methodology for pipeline alignment using remote sensing and GIS techniques. A small study on pipeline routing using remote sensing derived land use formed the basis for this development. This study, completed in 1999 for a survey company under training project, saved 1 km pipeline length over existing 35-km alignment. Realizing the potential, SAC initiated in-depth evaluation of potential of RS/GIS techniques for pipeline alignment in 2000.
Development of pipeline alignment technique
A methodology for semi-automated pipeline alignment was developed using sample data of 15x12 km area. Objective of the study was to develop a comprehensive package for semi-automated pipeline alignment on an image processing and GIS software backbone.
The available algorithms of GIS software like path analysis and drainage analysis on accumulated cost surface, conducted by NASA under Commercial Remote Sensing Program in 1997, have limitations of local optimization, boundary constraints and high computational load, and lack flexibility in assigning start, intermediate and end points for route optimization.
The cornerstones of the SAC methodology are the cost surface and the route analysis on this surface. The cost surface is generated by combining all the thematic costs of laying the pipeline on a given terrain by a system of ranks and weights. This is consistent with the basic problem as the pipeline routing is a compromise between the minimum (straight line) distance from source to destination and the physical conditions existing above and below ground. The themes relevant for cost surface represent the physical conditions of terrain and their choice may vary by locale and project requirements. In development phase a fairly general set of themes like slope, soil, land use, geology, road/rail networks and streams are considered for generating cost surface. The cost ranking for features within the themes and weights for each theme are assigned by general recommendations, subject knowledge and expert opinion.
The route of least cost between source and destination points is searched iteratively over corridors of narrowing width using network analysis approach. The cost is computed as weighted sum of material cost of pipeline, the construction cost of laying the pipeline and the access cost of approaching the route. Thus the first rough route is obtained over entire rectangular area encompassing start and end points. The subsequent route search is limited to a broad buffer zone around the previous route. Generally third iteration with narrow corridor of buffer zone ends this global search option. Path analysis is then used to locally optimize the route, which yields final alignment.
Dry run showed clearly that routing between start and end points passed through minimum cost areas. The final route was 51 % longer than the straight-line path and has cost implications of just a fraction of percent of the straight-line cost, because the straight line passed over a hilly terrain.
1.Validation of pipeline alignment technique
A 42-km water pipeline in south of Udaipur (India) was manually aligned by a private company ( M/s MultiMantech, Ahmedabad) for carrying water from a reservoir at 800 MSL to Hindustan Zinc Ltd plant at 500 MSL under gravity flow ( i.e. without pumping). The terrain is hilly and the manual alignment mostly followed highways and roads. This problem was repeated using SAC technique as validation exercise, which was completed in two-month time.
Twelve cost layers (topography, slope, geology, soil, land use, road, distance from road, rail, forest, water bodies and streams) are selected and created using satellite data and other maps and ranked for cost contributions by features distribution. Variable weights are assigned to each of layers to reflect the project requirements and general routing criteria. The Combined Weighted Cost Surface (CWCS) is generated and semi-automated route search with three narrowing corridors is executed with cost ratio of 60:40 for material and construction costs (access cost were not considered).