The variation of coastal geomorphology at Unawatuna bay beach area during last five decades

Unawatuna bay beach area belongs to a dynamic coastal region in Sri Lanka giving stunning aesthetic and socio-economic advantages for a long period. This area was selected to study the annual and long-term variation of the coastal geomorphology, to verify the reasons for such changes and to examine how geomorphological changes have influenced the natural environment and socio-economic status of the area. Firstly, the digital thematic maps of the study area were prepared for the period of 1974 to 2016 using sequential aerial photographs and satellite images. Coastline changes were identified using these maps. Then the relationship between identified changes and variables which are effect on coastal geomorphology were examined using tidal, wind and data relevant to coast oriented activities of the area. After the analysis of thematic layers, it was found that the coastline changes from 1974 up to sand nourishment which was established in 2015 shows a continuous pattern of degradation and also wide sandy beach has been washed away. The trend in degradation of the coastline in Unawatuna central GN division is more than that of Welle devalaya site during 1974 to 1994. It is due to concentration of more tourism related activities within that coast. Analysis of thematic layers show a significant change in coastline at Welle devalaya site from 1994 to 2002. A catastrophic coral depletion occur after the El-nino event in 1998 can be surmised as the main reason for such observation. Breakwater and sand nourishment which were established in the area also have been caused to change the nature of bay and beach. Annual variation of the bay beach are occur due to wind and wave actions which accelerates during Southwest monsoonal period while the rest of the period have been influenced by spring tides. It can conclude that, distinctive geomorphological changes occur due to human interventions while annual variation pattern has been controlled by the monsoonal activities and spring tides.