COASTLINE CHANGE ANALYSIS BASED ON SATELLITE IMAGERY BY REMOTE SENSING METHODS AT SABA BEACH, GIANYAR REGENCY, BALI

• Main Author: Ari Riska Dayanti, Made
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/63916
• Institution: Institut Teknologi Bandung

Waves, ocean currents, tides, winds, sediment supply or the effects of sea level rise trigger changes in shoreline positions. Accretion and abrasion are indicators of changes in the position of the shoreline which help in determining the boundaries of management of coastal and marine areas. Coastline changes have a high potential to occur in all beaches on the Southeast coast of Bali, especially in Gianyar Regency. Saba Beach in Gianyar Regency with a length of 1.3 km is one of the beaches experiencing abrasion due to sea waves. Two rivers flank Saba Beach, the Petanu River in the southwest and the Kutul River in the northeast. The problem of abrasion on Saba Beach threatens the existence of a place of worship for Hindus called Pura Alas Rengked. The lack of beach protection triggers an increase in the rate of abrasion on Saba Beach. Remote sensing technology plays an important role in identifying shoreline changes. Sentinel-1 satellite imagery with a resolution of 10 meters was implemented to monitor shoreline changes on Saba Beach in 2017-2021. In this study, the results of the Sentinel-1 image extraction using the thresholding method were corrected against tidal data based on the Mike- 21 Tide Prediction to obtain an accurate shoreline position. The shoreline change analysis utilizes the Digital Shoreline Analysis System (DSAS) software. The results of the analysis showed that the southwest part of Saba Beach experienced accretion, while the northeastern part experienced significant abrasion. The average area of accretion that occurs on Saba Beach is 94,8 m2 while the average area of abrasion is 41,8 m2. In the 2017-2021 period, Saba Beach experienced accretion with a rate of change of 9,1 m/year and abrasion with a rate of change of 4,9 m/year. The change in shoreline is caused by high waves hitting the coast of Saba Beach. The simulation results of wave propagation using Delft 3D-Wave indicate that the incoming wave forms an angle and triggers a longshore current. The movement of sediment along the coast towards the northeastern part of Saba Beach is hampered so that abrasion occurs. Abrasion mitigation can be done by planting nonmangrove vegetation and coastal structures in the form of groynes combined with beach nourishment activities.