Saraswati Thapa, Hugh D. Sinclair, Maggie J. Creed, Alistair G. L. Borthwick, C. Scott Watson, Manoranjan Muthusamy
{"title":"Sediment Transport and Flood Risk: Impact of Newly Constructed Embankments on River Morphology and Flood Dynamics in Kathmandu, Nepal","authors":"Saraswati Thapa, Hugh D. Sinclair, Maggie J. Creed, Alistair G. L. Borthwick, C. Scott Watson, Manoranjan Muthusamy","doi":"10.1029/2024wr037742","DOIUrl":null,"url":null,"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 <span data-altimg=\"/cms/asset/e8aa5bf6-5a8c-4281-ae9f-df9d782c62f2/wrcr27519-math-0001.png\"></span><mjx-container ctxtmenu_counter=\"85\" ctxtmenu_oldtabindex=\"1\" jax=\"CHTML\" role=\"application\" sre-explorer- style=\"font-size: 103%; position: relative;\" tabindex=\"0\"><mjx-math aria-hidden=\"true\" location=\"graphic/wrcr27519-math-0001.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-mo data-semantic- data-semantic-operator=\"infixop,/\" data-semantic-parent=\"5\" data-semantic-role=\"division\" data-semantic-type=\"operator\" rspace=\"1\" space=\"1\"><mjx-c></mjx-c></mjx-mo><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-0001\" display=\"inline\" location=\"graphic/wrcr27519-math-0001.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><mo data-semantic-=\"\" data-semantic-operator=\"infixop,/\" data-semantic-parent=\"5\" data-semantic-role=\"division\" data-semantic-type=\"operator\">/</mo><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>${\\mathrm{m}}^{3}/\\mathrm{s}$</annotation></semantics></math></mjx-assistive-mml></mjx-container> and by 15% (from 28.8 to 24.4 ha) for the 1000-year return period flood discharge of 95 <span data-altimg=\"/cms/asset/4acabe9e-bbf7-4a15-a936-f628bd6a1873/wrcr27519-math-0002.png\"></span><mjx-container ctxtmenu_counter=\"86\" ctxtmenu_oldtabindex=\"1\" jax=\"CHTML\" role=\"application\" sre-explorer- style=\"font-size: 103%; 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. It is recommended that sediment transport effects be factored into embankment design and floodplain planning.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":"21 1","pages":""},"PeriodicalIF":4.6000,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Water Resources Research","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1029/2024wr037742","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
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 and by 15% (from 28.8 to 24.4 ha) for the 1000-year return period flood discharge of 95 (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.
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.