Sediment Transport and Flood Risk: Impact of Newly Constructed Embankments on River Morphology and Flood Dynamics in Kathmandu, Nepal

IF 4.6 1区 地球科学 Q2 ENVIRONMENTAL SCIENCES
Saraswati Thapa, Hugh D. Sinclair, Maggie J. Creed, Alistair G. L. Borthwick, C. Scott Watson, Manoranjan Muthusamy
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Using the CAESAR-Lisflood landscape evolution model based on a 2-m digital elevation model, we simulate four flood scenarios with and without embankments and sediment transport: a historical 25-year return period flood event used to design the embankments, 50-year, 100-year, and 1000-year return period flood events forecast using the Generalized Logistic Model (using data from 1992 to 2017). 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position: relative;\" tabindex=\"0\"><mjx-math aria-hidden=\"true\" location=\"graphic/wrcr27519-math-0002.png\"><mjx-semantics><mjx-mrow data-semantic-children=\"2,4\" data-semantic-content=\"3\" data-semantic- data-semantic-role=\"division\" data-semantic-speech=\"normal m cubed divided by normal s\" data-semantic-type=\"infixop\"><mjx-msup data-semantic-children=\"0,1\" data-semantic- data-semantic-parent=\"5\" data-semantic-role=\"latinletter\" data-semantic-type=\"superscript\"><mjx-mi data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic- data-semantic-parent=\"2\" data-semantic-role=\"latinletter\" data-semantic-type=\"identifier\"><mjx-c></mjx-c></mjx-mi><mjx-script style=\"vertical-align: 0.363em;\"><mjx-mn data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic- data-semantic-parent=\"2\" data-semantic-role=\"integer\" data-semantic-type=\"number\" size=\"s\"><mjx-c></mjx-c></mjx-mn></mjx-script></mjx-msup><mjx-mi data-semantic-font=\"normal\" data-semantic- data-semantic-operator=\"infixop,/\" data-semantic-parent=\"5\" data-semantic-role=\"division\" data-semantic-type=\"operator\"><mjx-c></mjx-c></mjx-mi><mjx-mi data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic- data-semantic-parent=\"5\" data-semantic-role=\"latinletter\" data-semantic-type=\"identifier\"><mjx-c></mjx-c></mjx-mi></mjx-mrow></mjx-semantics></mjx-math><mjx-assistive-mml display=\"inline\" unselectable=\"on\"><math altimg=\"urn:x-wiley:00431397:media:wrcr27519:wrcr27519-math-0002\" display=\"inline\" location=\"graphic/wrcr27519-math-0002.png\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><semantics><mrow data-semantic-=\"\" data-semantic-children=\"2,4\" data-semantic-content=\"3\" data-semantic-role=\"division\" data-semantic-speech=\"normal m cubed divided by normal s\" data-semantic-type=\"infixop\"><msup data-semantic-=\"\" data-semantic-children=\"0,1\" data-semantic-parent=\"5\" data-semantic-role=\"latinletter\" data-semantic-type=\"superscript\"><mi data-semantic-=\"\" data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic-parent=\"2\" data-semantic-role=\"latinletter\" data-semantic-type=\"identifier\" mathvariant=\"normal\">m</mi><mn data-semantic-=\"\" data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic-parent=\"2\" data-semantic-role=\"integer\" data-semantic-type=\"number\">3</mn></msup><mi data-semantic-=\"\" data-semantic-font=\"normal\" data-semantic-operator=\"infixop,/\" data-semantic-parent=\"5\" data-semantic-role=\"division\" data-semantic-type=\"operator\" mathvariant=\"normal\">/</mi><mi data-semantic-=\"\" data-semantic-annotation=\"clearspeak:simple\" data-semantic-font=\"normal\" data-semantic-parent=\"5\" data-semantic-role=\"latinletter\" data-semantic-type=\"identifier\" mathvariant=\"normal\">s</mi></mrow>${\\mathrm{m}}^{3}\\mathrm{/}\\mathrm{s}$</annotation></semantics></math></mjx-assistive-mml></mjx-container> (similar to a 25-year maximum mid-future). The presence of embankments increases downstream sediment transport by more than 32% for all flood scenarios considered. Inclusion of sediment transport leads to a fivefold increase in predicted inundation area for a 25-year maximum mid-future flood compared to the no-sediment case in the embanked channel. Changes in channel geometry due to sedimentation significantly reduce conveyance capacity increasing overtopping flood risk, particularly where the channel is sinuous or located on flat terrain. Our results indicate that sediment erosion in outer meanders may threaten embankment stability by promoting undercuts. 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引用次数: 0

Abstract

Floodplain encroachment by embankments heightens flood risk. This is exacerbated by climate change and land-use modifications. This paper assesses the impact of embankments on sediment transport, channel geometry, conveyance capacity, and flood inundation of a reach of the Nakkhu River, Nepal. Using the CAESAR-Lisflood landscape evolution model based on a 2-m digital elevation model, we simulate four flood scenarios with and without embankments and sediment transport: a historical 25-year return period flood event used to design the embankments, 50-year, 100-year, and 1000-year return period flood events forecast using the Generalized Logistic Model (using data from 1992 to 2017). Our results indicate that flow confinement by embankments reduces inundation by 99% (from 22.5 to 0.3 ha) for the historical 25-year flood discharge of 42.23 m3/s${\mathrm{m}}^{3}/\mathrm{s}$ and by 15% (from 28.8 to 24.4 ha) for the 1000-year return period flood discharge of 95 m3/s${\mathrm{m}}^{3}\mathrm{/}\mathrm{s}$ (similar to a 25-year maximum mid-future). The presence of embankments increases downstream sediment transport by more than 32% for all flood scenarios considered. Inclusion of sediment transport leads to a fivefold increase in predicted inundation area for a 25-year maximum mid-future flood compared to the no-sediment case in the embanked channel. Changes in channel geometry due to sedimentation significantly reduce conveyance capacity increasing overtopping flood risk, particularly where the channel is sinuous or located on flat terrain. Our results indicate that sediment erosion in outer meanders may threaten embankment stability by promoting undercuts. It is recommended that sediment transport effects be factored into embankment design and floodplain planning.
沉积物迁移与洪水风险:新建堤坝对尼泊尔加德满都河流形态和洪水动态的影响
堤坝对洪泛区的侵占加剧了洪水风险。气候变化和土地使用的改变加剧了这种情况。本文评估了堤坝对沉积物输运、河道几何形状、输送能力以及尼泊尔纳库河某河段洪水淹没的影响。利用基于 2 米数字高程模型的 CAESAR-Lisflood 景观演变模型,我们模拟了有堤防和无堤防以及泥沙输运的四种洪水情景:用于设计堤防的 25 年一遇历史洪水,利用广义逻辑模型预测的 50 年一遇、100 年一遇和 1000 年一遇洪水(使用 1992 年至 2017 年的数据)。我们的研究结果表明,对于历史上 25 年一遇的 42.23 m3/s${mathrm{m}}^{3}//\mathrm{s}$的情况下,洪水淹没面积减少了 15%(从 28.8 公顷减少到 24.4 公顷);1000 年重现期洪水排放量为 95 m3/s${mathrm{m}}^{3}/\mathrm{s}$(类似于 25 年最大中洪水)的情况下,洪水淹没面积减少了 15%(从 28.8 公顷减少到 24.4 公顷)。在考虑的所有洪水情景中,堤坝的存在都会使下游泥沙输移增加 32% 以上。与无沉积物情况相比,在有堤防的河道中,沉积物运移导致 25 年一遇的未来中期最大洪水的预测淹没面积增加了五倍。沉积作用导致的河道几何形状变化大大降低了河道的输送能力,增加了倾覆洪水的风险,尤其是在河道蜿蜒曲折或地势平坦的情况下。我们的研究结果表明,外侧蜿蜒处的泥沙侵蚀可能会促进下切,从而威胁堤坝的稳定性。建议在堤坝设计和洪泛区规划中考虑泥沙输移的影响。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Water Resources Research
Water Resources Research 环境科学-湖沼学
CiteScore
8.80
自引率
13.00%
发文量
599
审稿时长
3.5 months
期刊介绍: Water Resources Research (WRR) is an interdisciplinary journal that focuses on hydrology and water resources. It publishes original research in the natural and social sciences of water. It emphasizes the role of water in the Earth system, including physical, chemical, biological, and ecological processes in water resources research and management, including social, policy, and public health implications. It encompasses observational, experimental, theoretical, analytical, numerical, and data-driven approaches that advance the science of water and its management. Submissions are evaluated for their novelty, accuracy, significance, and broader implications of the findings.
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