Shoreline Change Detection and Future Prediction for Southwestern Coastline, Sri Lanka

Coastal zones, important for human settlements and economies globally and particularly in Sri Lanka, are experiencing significant changes driven by natural and human-induced activities. This study investigated the shoreline changes over the southwestern coastal zone between for three periods as; 1988 to 2023, 1988 to 2001 and 2001 to 2023 by calculating the change rates, preparing erosion/accretion maps and predicting future positions for years 2034 and 2044.Landsat images and Normalized Difference Water Index (NDWI) were used for shoreline extraction and Digital Shoreline Analysis System (DSAS) tools was used to calculate change rates and predict future positions.. Findings reveal significant changes over the three study periods. During the 1988-2001 period, the mean Endpoint Rate (EPR) averaged 2.31 m/year, while the mean Linear Regression Rate (LRR) averaged 2.34 m/year. The majority of the study area faced land accretion, with only 200 out of 3,475 transects experiencing erosion. However, during the 2001-2023 period, erosion became predominant at an alarming rate of 62.72%, with 2,192 out of 3,495 transects facing erosion. During this period, the mean EPR and mean LRR shiftedto -0.46 m/year and -0.25 m/year, respectively. During the overall period of 1988-2023, only 404 transects out of 3,422 transects were eroded, with a decreased percentage of 11.81%. The mean EPR was 0.61 m/year, while the mean LRR was 0.52 m/year. Kalutara, Beruwala, Hikkaduwa, Kahawa, and Galle experienced significant erosion, aligning with previous vulnerability assessments. Predictions for 2034 and 2044 suggest a trend towards land accretion, potentially influenced by recent beach nourishment efforts. Even though the erosion rate decreased for the overall period 1988-2023, mitigation measures should be taken, especially for Kalutara, Beruwala, Hikkaduwa, Kahawa, and Galle areas.