An Analysis of the Impact of Urbanization on Natural Character of Coastline Along Southern Suburbs of Colombo, Sri Lanka

Abstract

Coastal ecosystems, including mangroves, swamps, sand bars, and coastal vegetation, play a vital role in maintaining environmental sustainability. However, rapid urban expansion and shoreline development have disrupted these natural systems, resulting in ecosystem degradation. Achieving sustainable development in coastal zones therefore requires the careful management of natural resources alongside the conservation of ecological functions. This study investigates the impacts of shoreline constructions and urban growth along a 30 km coastal stretch from Moratuwa to Kalutara, extending 1 km inland. Temporal changes in the coastline between 2004 and 2021 were assessed using high-resolution satellite imagery from Google Earth. Shorelines were digitized and analyzed in ArcGIS to evaluate spatial variations and to determine the influence of revetments, groynes, and breakwaters on coastal stability. Built-up expansion was quantified using supervised classification with the maximum likelihood technique on geo-referenced imagery from 2004 and 2021. The results indicate notable increases in both shoreline engineering and urban development during the study period. Shoreline structures contributed to coastal stabilization and, in several areas, facilitated seaward extension of the coast. Conversely, analysis of built-up area growth revealed that relatively low-urbanized areas preserved more natural coastlines, while densely developed regions exhibited extensive shoreline modifications. Field investigations supported these findings, highlighting the progressive transformation of natural coastlines into engineered environments. The study concludes that although shoreline constructions enhance coastal stability, the accelerated expansion of the built environment threatens the persistence of natural coastal ecosystems. These findings underscore the need for balanced development strategies that integrate coastal protection with ecosystem conservation to safeguard long-term sustainability.