Spatial Delineation of the Water Boundary Dynamics with Band Ratio and MNDWI Comparison from Multitemporal Satellite Imagery based on the DSAS Method (Case Study: Duriangkang Reservoir, Batam City)

Abstract

The Duriangkang Reservoir is the city of Batam's primary source of raw water and must be regularly monitored to ensure its long-term sustainability. One indicator that can be used to determine changes in the reservoir’s condition is the shoreline's dynamics over time. This study aims to analyse the shoreline dynamics of the Duriangkang Reservoir from 2016 to 2025 using multitemporal satellite imagery, and to compare the results of feature extraction using both the Band Ratio method and the Modified Normalized Difference Water Index (MNDWI). Data consist of Landsat 8 OLI/TIRS images from 2016–2018 and Sentinel-2A images from 2019–2025, which were processed using Google Earth Engine. Shoreline change analysis was conducted using the Digital Shoreline Analysis System (DSAS), and the accuracy test was performed using a confusion matrix based on 100 validation sample points. The results of the study show that both methods produced similar patterns of change and identified a trend of the water’s edge shifting toward land at the Duriangkang Reservoir during the observation period. The Band Ratio method yielded the following average values: 185.29 m for SCE, -63.58 m for NSM, -7.06 m/year for EPR, and -6.07 m/year for LRR. The MNDWI method yielded the following average values: 142.50 m for SCE, 79.32 m for NSM, -8.81 m/year for EPR, and -9.38 m/year for LRR. These negative values indicate a shift of the water boundary toward land during the study period. Accuracy test results show that the band ratio method yielded an overall accuracy of 94.00% and a kappa coefficient of 0.88, while the MNDWI method yielded an overall accuracy of 95.00% and a kappa coefficient of 0.90. Based on the validation results and analysis of changes in the water boundary, the MNDWI method demonstrated slightly better performance than the Band Ratio method in extracting the water boundary in the study area.