Geomorphological changes caused by Tsunami 2004 in the coastal environment of Weligama Bay in Southern Sri Lanka

The coastal area of Weligama bay was severely affected by the tsunami disaster on 26th of December 2004. It caused 396 deaths locally in addition to the destruction of valuable properties. Also most of the geomorphological features have been altered severely. The objective of this study was to examine how the tsunami waves have impacted on geomorphological features in Weligama Bay. Changes in geomorphological features were identified through the analysis of satellite images before 2004 and after 2005. ArcView GIS software was used for hazardous mapping and damage analysis of the area. The pre and post-tsunami map overlay technique of ArcView software was used to determine the changes of geomorphological features in the area concerned. The tsunami waves altered the coastal features by shrinking and spreading estuaries, eroding the coast and blocking the estuary. Such changes can be observed in the estuaries of Polwatta Ganga, Pemuyana and Rassamuna headlands, and Weligama bay beach. North of the Polwatta Ganga estuary was broadened by about 5 m and the breath of sand spit of the estuary was increased in about 2 m. The tsunami waves attacked the Pemuyana headland in the south of the bay causing serious damages to Weligama town area and the base of the headland was eroded by about 1 m. The Kapparatota natural harbor which was located in the northern part of the bay of Weligama was altered as a bay beach by sand deposition.