Studying the shoreline variations based on the monsoon seasonality in Mirissa

Abstract

Sri Lanka is an island consisting of a 1600 km long shoreline. The shoreline is the boundary between the ocean and the land. The coastal area of Sri Lanka provides a different range of natural resources and the most effective conditions for economic and social development. Coastal areas are threatened by natural and human activities and regular erosion. Some reasons such as unauthorized constructions, unplanned manmade barriers, changes in the rainfall, sea level rise, mean tidal range, mean wave height, coastal slope, and land use pattern shoreline were changed (Pusella, 2015). The major cause of changes in shoreline position in coastal zones is the accretion or erosion of sand. Coastal management needs to recognize how sand accretion and erosion are affected by monsoon seasonality and human impacts to implement the most effective coastal protection techniques. Shoreline change is named coastal erosion and it became a major problem in many regions of the world and is particularly important for countries in low-lying coastal areas such as the south coasts of Sri Lanka. As an example, in Weligama Bay in the south, about 175000 to 285000 m2 of the coastal land area is lost due to erosion in the year (Lowry and Wickremeratne, 2012). Mirissa is a small town on the south coast of Sri Lanka, located in the Matara District of the Southern Province. It is approximately 150 kilometres south of Colombo and is situated at an elevation of 4 meters above sea level. This area is in Sri Lanka with the Global Position System (GPS) coordinates of 5 ̊56ʼ53.7432ˮ N and 80 ̊28ʼ17.7168ˮE. Mirissa Beach makes a popular tourist destination. Further, Mirissa coastal area consists of a fishery harbour and one of the island's main whale and dolphin viewing sites (Brinkhoff & Thomas, 2012). Mirissa area immensely helps to develop the economy of our country. However, improvement of this economic destination is not considered by the relevant authorities. This study mainly focuses on the detection of shoreline changes and geomorphological changes in Mirissa, on Sri Lanka's southern coast. The shoreline time series were obtained using the "CoastSat" software. The toolkit uses Google Earth Engine's capabilities to quickly retrieve Landsat and Sentinel-2 photos cropped to any user-defined area of interest. With a precision of 10 m, separation was used to map the location of the shoreline (Vos, Splinter, Harley, Simmons, & Turner, 2019)). By using CoastSat a precise output can be gained for the small beach area. But using Sentinel -2 images, an accurate comparison can be obtained to the Landsat images. Determining the shoreline variation according to the monsoon seasonality and identifying the geomorphological changes in Mirissa coastal area are specific objectives of this study.