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<p>Flood zonation mapping of different return periods is one of the vital non-structural mitigation measures for flood-induced disasters. This study delineates restricted zones for developmental activities along the selected stretch of the Rangit River based on estimated return period water surface elevation. This novel approach contributes to mitigating site-specific flood-induced disasters and exposure of lives and properties to flood hazard at the selected stretch of the Rangit River from Legship bazar to a few kilometers upstream of Jorethang bazar with a total length of 24&#xa0;km. Also recommend threshold elevation values for developmental activities and land use plannings. Return period peak discharge was calculated using an empirical equation based on topographical and meteorological parameters. The estimated peak discharge was simulated downstream with hydraulic 1D steady flow modeling using Hydraulic Engineering Center’s River Analysis System (HEC-RAS) software. The study found that the Legship, the Rothak-Nayabazar, and the Birdang areas are three critical locations with high flood risk. As per the findings, to mitigate flood-induced disasters along the study area, developmental activities shall be restricted below 600&#xa0;m above msl in the Legship area, below 390&#xa0;m at this densely populated Rothak-Naya bazar area, below 450&#xa0;m amsl at Birdang area. The main risk-fostering factors are urbanization, commercialization along and adjacent to river channels, lower terraces, and mid-terraces, huge channel sedimentation, bank failure, and bank erosion.</p>

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Assessment of flood risk zones in the Rangit Basin of the Sikkim Himalaya

  • 期刊论文

  • 发表日期：

    2025年7月1日

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  • Dakshina Tamang,
  • Rajesh Kumar

摘要

Flood zonation mapping of different return periods is one of the vital non-structural mitigation measures for flood-induced disasters. This study delineates restricted zones for developmental activities along the selected stretch of the Rangit River based on estimated return period water surface elevation. This novel approach contributes to mitigating site-specific flood-induced disasters and exposure of lives and properties to flood hazard at the selected stretch of the Rangit River from Legship bazar to a few kilometers upstream of Jorethang bazar with a total length of 24 km. Also recommend threshold elevation values for developmental activities and land use plannings. Return period peak discharge was calculated using an empirical equation based on topographical and meteorological parameters. The estimated peak discharge was simulated downstream with hydraulic 1D steady flow modeling using Hydraulic Engineering Center’s River Analysis System (HEC-RAS) software. The study found that the Legship, the Rothak-Nayabazar, and the Birdang areas are three critical locations with high flood risk. As per the findings, to mitigate flood-induced disasters along the study area, developmental activities shall be restricted below 600 m above msl in the Legship area, below 390 m at this densely populated Rothak-Naya bazar area, below 450 m amsl at Birdang area. The main risk-fostering factors are urbanization, commercialization along and adjacent to river channels, lower terraces, and mid-terraces, huge channel sedimentation, bank failure, and bank erosion.