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Environmental consideration in railway route selection with GIS - Case study: Rasht-Anzali railway in Iran
2.2. Environmental parameters and data acquisition
To achieve research goal, effective parameters in railway route selection must be identified. Following parameters indicate those items are considered in current study.
Land cover: land cover maps provide information on general cover that may be used in railway route selection. To produce this map a subset of Landsat–7 ETM data dated on May 2000 was analyzed. Rectification of satellite data was implemented using ground control points method. To achieve a better resolution the multiespectral bands were fused with ETM-Pan. Suitable spectral transformations and color composites were performed on the satellite data. Image classification was performed using a new approach (digital and visual). The land use map checked for accuracy by field study.
River: For minimization environmental impact, routes should be far from rivers. Railway construction costs will be increased to fill in or build bridges over rivers, ponds or sections of lakes too. The map of the rivers was extracted from digital topographic map at the scale of 1:25000.
Road: Reduction of intersection of railway with existing road, decrease construction cost and increase safety of transportation. For this aim map, of roads was produced base of the existing digital map.
Cultural heritage: Cultural heritage forms identity of each society and nation. So people should try to preserve and enhance their place and conditions in the environment. To create a map about the heritage, documents and existing maps were studied.
Geology: Geological studies were done for recognition of resistance of rocks underlying superficial layers. For this aim, maps of geology related to the study area digitized.
Soil: Susceptible soils to erosion and unconsolidated material need much cost for rail construction than consolidated types. For this aim, a reliable soil map of the area digitized and used for producing desired classified soil map.
2.3. Evaluation of effective parameters in railway route selection
In order to minimize environmental impacts and to achieve sustainable development in route construction projects, it is essential to determine the relative importance of the considered parameters. There are some methods for this aim. Selection of a method depends on the trade-offs between ease of use, accuracy, the degree of understanding on the part the decision maker, and the theoretical foundation underlying a given method, the availability of computer software, and the way the method can be incorporated into GIS-based multicriteria decision analysis. Empirical applications suggest that the pairwise comparison method is one of the most effective techniques for spatial decision-making including GIS-based approaches (Malczewski 1999). This method was developed by Saaty (1980) in the context of the Analytical Hierarchy Process (AHP). This method involves pairwise comparisons to create a ratio matrix. As input, it takes the pairwise comparisons of the parameters and produces their relative weights as output.
It is recommended to consider environmental and civil expert’s views regarding to relative priority of the parameters. In this study, it was collected from a questionnaire that has been designed for this aim. Weights of parameters calculated according to these views and prioritized in this order: cultural heritage, land covers and land use, slope, soil type, geology, rivers and roads.
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