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<p>Coastal erosion poses a significant threat to ecosystems and coastal communities on Indonesia’s islands, including Bali. While wave and tidal forces are widely recognized as primary drivers of shoreline change, the contribution of large-scale oceanic currents, particularly the Indonesian Throughflow (ITF), remains poorly understood. This study aims to assess the long-term shoreline changes along the eastern coast of Bali and to evaluate the potential role of the ITF in driving coastal erosion in this region. To achieve this, we analyzed shoreline positions from 1973 to 2024 using multitemporal Landsat imagery and the Digital Shoreline Analysis System (DSAS), which was integrated with reanalysis datasets, including wave height, tidal range, sea level anomalies, and ocean current velocities. Severe erosion was identified in the Klungkung and Gianyar Regencies (KGR), with an average shoreline retreat of 121&#xa0;m and a land loss of approximately 258 hectares. Despite low wave energy and tidal influence, erosion is strongly linked to a westward ITF branch that flows parallel to the KGR coastline, facilitating longshore sediment transport. Coastal infrastructure and steep bathymetry exacerbate this process further. Erosion intensifies during boreal summer when the ITF strengthens. Long-term analysis reveals a positive correlation between ITF strength and Indo-Pacific climate modes, including the El Niño-Southern Oscillation (<i>r</i> = 0.54) and the Indian Ocean Dipole (<i>r</i> = 0.51), suggesting an indirect influence of climate on coastal erosion in eastern Bali. Overall, these findings highlight that the combined effects of ITF variability, steep coastal morphology, and human interventions are the dominant causes of shoreline retreat along the KGR coastline. This study presents the first evidence of ITF-driven shoreline retreat in Bali and underscores the importance of integrating offshore current dynamics into erosion risk assessments. Future work should focus on high-resolution modeling that couples ocean-coast interactions to quantify sediment transport pathways, as well as on regional-scale adaptive coastal management strategies that account for ITF variability and climate-induced forcing.</p>

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Coastal erosion in Eastern Bali: impacts of the Indonesian throughflow

  • 期刊论文

  • 发表日期：

    2026年2月2日

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  • Fuad Azminuddin,
  • Aloysius Bagyo Widagdo,
  • Mardi Wibowo,
  • Hanah Khoirunnisa,
  • Reno Arief Rachman,
  • Hamzah Haru Radityo Suharyanto

摘要

Coastal erosion poses a significant threat to ecosystems and coastal communities on Indonesia’s islands, including Bali. While wave and tidal forces are widely recognized as primary drivers of shoreline change, the contribution of large-scale oceanic currents, particularly the Indonesian Throughflow (ITF), remains poorly understood. This study aims to assess the long-term shoreline changes along the eastern coast of Bali and to evaluate the potential role of the ITF in driving coastal erosion in this region. To achieve this, we analyzed shoreline positions from 1973 to 2024 using multitemporal Landsat imagery and the Digital Shoreline Analysis System (DSAS), which was integrated with reanalysis datasets, including wave height, tidal range, sea level anomalies, and ocean current velocities. Severe erosion was identified in the Klungkung and Gianyar Regencies (KGR), with an average shoreline retreat of 121 m and a land loss of approximately 258 hectares. Despite low wave energy and tidal influence, erosion is strongly linked to a westward ITF branch that flows parallel to the KGR coastline, facilitating longshore sediment transport. Coastal infrastructure and steep bathymetry exacerbate this process further. Erosion intensifies during boreal summer when the ITF strengthens. Long-term analysis reveals a positive correlation between ITF strength and Indo-Pacific climate modes, including the El Niño-Southern Oscillation (r = 0.54) and the Indian Ocean Dipole (r = 0.51), suggesting an indirect influence of climate on coastal erosion in eastern Bali. Overall, these findings highlight that the combined effects of ITF variability, steep coastal morphology, and human interventions are the dominant causes of shoreline retreat along the KGR coastline. This study presents the first evidence of ITF-driven shoreline retreat in Bali and underscores the importance of integrating offshore current dynamics into erosion risk assessments. Future work should focus on high-resolution modeling that couples ocean-coast interactions to quantify sediment transport pathways, as well as on regional-scale adaptive coastal management strategies that account for ITF variability and climate-induced forcing.