Assessment of Environmental Impacts Due to the Southern Expressway Construction Using Remote Sensing and GIS Techniques

The Southern Expressway of Sri Lanka has significantly contributed to the development of the country, while its construction and operation have caused different changes to its surrounding environment. This study was focused on analyzing the ecological impacts and Land Use and Land Cover (LULC) changes caused by the construction of the Southern Expressway of Sri Lanka by using Remote Sensing (RS) and Geographic Information Systems (GIS) techniques. Here, the study is based on a Before–During–After Control Impact – Remote Sensing (BDACI-RS) approach to perform a systematic analysis of environmental changes during its three major construction phases across three different buffer zones: 0–250 m, 250–500 m and 500–1000 m. Here, its ecological changes were analyzed through Normalized Difference Vegetation Index (NDVI), Normalized Difference Moisture Index (NDMI) and Land Surface Temperature (LST) as the major ecological indicators, LULC changes were analyzed by classifying the area into four major land cover categories, namely,  built-up areas, vegetation areas, bare lands and water areas, through a supervised classification, and predictive modelling for future LULC patterns was performed with the aid of the Modules for Land Use Change Evaluation (MOLUSCE) plugin of QGIS software. In ecological analysis, both the NDVI and NDMI indicated continuous decrements and LST indicated continuous increments mainly during the construction period. In LULC analysis after its construction, it showed a sharp increment of 54.71% in the extent of built-up areas and decrements in the extent of bare lands, vegetation areas and water areas by 60.95%, 12.18% and 1.03%, respectively. The findings of the study highlighted that the closest buffer zone to the expressway experiences the highest environmental impacts due to its construction.