Hasil untuk "River protective works. Regulation. Flood control"

Wenbin Wu, Chunliu Wang, Zheng Zhao et al.

Sediments had emerged as a significant repository of MPs (microplastics) and biomass accumulation in eutrophic lakes, yet the mechanisms by which these particles impact sediment stability remained elusive. This study aimed to investigate the effect of MPs on the structural stability of sediments during the accumulation of biomass, as these properties could affect the formation of fluid sediment and trigger resuspension. A coaxial cylindrical rheometer was used to explore changes in the rheological properties of sediments under the influence of MPs. Within 30-day experiments, it was found that MPs could decrease sediment viscosity, yield stress, and flow point shear stress (τtau) by up to 61.2 %, 57.9 % and 54.3 %. In the early stage of the experiment, MP addition led to a significant decrease on sediment rheological properties, but then this effect decreased gradually. Subsequently, the variations in EPS (extracellular polymeric substances), organic matter, and microbial communities influenced by MPs were suggested to relate with the change in sediment rheology properties. These findings suggested that MPs could facilitate the degradation of biomass and decrease sediment rheological properties by altering sediment microbial activities. On this basis, the decline in sediment stability would increase the risk of sediment re-suspension under wind and wave disturbance. Overall, this study sheds light on the environmental challenges posed by MPs under biomass accumulation, offering a fresh perspective that deepens our comprehension of the environmental behavior of MPs in sediment ecosystems.

Baolong Zhao, Qinghui Zeng, Jianhua Wang et al.

Cascade reservoirs construction has modified the nutrients dynamics and biogeochemical cycles, consequently affecting the composition and productivity of river ecosystems. The Jinsha River, as the predominant contributor to runoff, suspended sediment (SS), and nutrients production within the Yangtze River, is a typical cascade reservoir region with unclear transport patterns and retention mechanisms of nutrients (nitrogen and phosphorus). Furthermore, how to regulate nutrients delivery in the cascade reservoirs region is also an urgent issue for basin water environment study. Therefore, we monitored monthly variations in nitrogen and phosphorus concentrations from November 2021 to October 2022 in the cascade reservoirs of the Jinsha River. The results indicated that the concentrations and fluxes of total phosphorus (TP) and particulate phosphorus (PP) decreased along the cascade of reservoirs, primarily due to PP deposited with SS, while opposing trends for total nitrogen (TN) and dissolved total nitrogen (DTN), which might be the consequences of human inputs and the increase of dissolved inorganic nitrogen discharged from the bottom of the reservoirs. Moreover, the positive average annual retention ratios for TP and PP were 10% and 16%, respectively, in contrast to the negative averages of -8 % for TN and -11% for particulate nitrogen (PN). The variability in runoff-sediment and hydraulic retention time (HRT) of cascade reservoirs played crucial roles in the retention of TP and PP. A regulatory threshold of HRT = 5.3 days in the flood season was obtained for controlling the balance of TP based on the stronger relationship between HRT and TP retention ratio. Consequently, the HRT of these reservoirs could be managed to control nutrients delivery, which was of particular significance for basin government institutions. This study enhances our comprehension of how cascade reservoirs influence the distribution and transport patterns of nutrients, offering a fresh perspective on nutrients delivery regulation.

Li Huang, Zhicheng Yu, Wei Wang et al.

Abstract Flood disasters are a hot topic in the field of disaster prevention and control. To reduce the high‐density economic losses caused by floods, it is necessary to effectively and reasonably distribute emergency supplies to disaster sites during the emergency cycle. This article describes setting up a comprehensive multirescue site, multidisaster site, and multiobjective programming model to measure the total amount of time taken to transport supplies and economic losses endured in the response and recovery. Moreover, we use the evolutionary algorithm based on the Pareto concept and simulate the calculation using computer simulation. Finally, a case study is carried out based on various supply data of the historical flood disaster and the flood control supply reserves in the Jiangsu Province. The optimization results are discussed using the sorting method that approaches the ideal solution, and three feasible emergency plans are given, which can provide a reference for emergency supply transportation for urban flood control.

Isaac Besarra, Aaron Opdyke, Diocel Harold Aquino et al.

Abstract The Philippines experiences frequent flooding, but, despite expansive tools for risk reduction, there remain gaps in understanding generalised relationships between flood events and damage to residential structures for regions outside the nation's capital. This gap has limited the ability to model flood risk and damage without robust functions to link hazards and housing vulnerability. This research draws on 394 household surveys to empirically derive a suite of flood fragility and vulnerability functions for residential structures in the Province of Leyte for light material, elevated light material and masonry structures. The results showed that masonry construction was more resilient to floods compared to light material counterparts. Elevated light material structures also exhibited lower damages at low inundations but tend to fail abruptly at flood depths greater than 3 m. By empirically deriving flood damage functions, the findings contribute to a more localised approach to quantifying housing vulnerability and risk that can be used for catastrophe and risk modelling, with applications for government agencies, the insurance industry and disaster risk researchers. This research lays the foundation for future flood risk mapping with growing significance under climate change.

Haksoo Kim, Hojun Keum

ABSTRACT A laboratory‐based physical modeling environment has great potential to reproduce the complex physical hydrologic phenomena and understand the interactions of rainfall‐runoff processes in a visual and informative manner. In this study, a three‐layer physical modeling environment was developed to represent the dynamics of runoff production from the urban drainage system. The three‐layer physical modeling environment consists of a rainfall simulator (the 1st layer), a surface drainage network (the 2nd layer) and a subsurface rainwater pipe network (the 3rd layer). The degree of homogeneity of the spatial rainfall distribution produced by the rainfall simulator ranged from 78.6% to 84.0%, which lies within an acceptable range in the rainfall uniformity. The physical catchment model accurately represented the dynamic characteristics of the catchment response in a natural system associated with differing rainfall intensities within a controlled laboratory modeling environment, particularly the magnitude, volume, and shape of the discharge hydrographs. The three‐layer physical modeling setup was implemented to identify the effects of stormwater management facilities such as the rooftop detention storage and the permeable road pavement on the urban rainfall‐runoff responses. The runoff reduction rates for the peak discharge and the total discharge volume showed a strong linearity with the percentage coverages of the stormwater management facilities. Functional relationships between the variables were established to provide intuitive criteria for the runoff reduction rates for a specific coverage percentage of the rooftop detention storage and the permeable road pavement. These results demonstrate the effectiveness of the three‐layer physical setup for modeling rainfall‐runoff processes within the urban drainage network.

Abderraman R. Amorim Brandão, Dimaghi Schwamback, Frederico C. M. deMenezes Filho et al.

ABSTRACT Researchers have widely applied discharge simulation using artificial neural networks (ANNs) and have gained prominence in water resources. Morphological features, watershed urbanization, and climate change influence hydrological variables. Thus, data‐driven models need to be able to identify the hydrological relationships without explicitly stating the physical processes. The main objectives of this work were (i) to evaluate an ANN Multilayer Perceptron for flood forecasting in an urban basin and its efficiency for several lead times; (ii) to evaluate discharge variation considering climate change scenarios. The study applied the methodology in a basin occupied by the Cerrado biome, with its intermediate outlet in an urban area that suffers from recurrent floods. The selection of climate change models followed from the Coupled Model Intercomparison Project Phase 6 scenarios Shared Socioeconomic Pathway (SSP)2‐4.5 and SSP5‐8.5 for two futures: 2021–2050 and 2071–2100, with the period of 1976–2019 as reference. The model obtained satisfactory results for the discharge prediction at the current time and for a horizon of up to 4 days. However, forecasts for longer lead times led to metrics deterioration. Furthermore, future projections suggest decreased discharges, more extreme events, and increased short return‐period floods. The developed model is valuable for short‐term forecasting and water resources management in the face of changing climates.

Anna Heidenreich, Heather J. Murdock, Annegret H. Thieken

ABSTRACT In July 2021, a flash flood event affected hilly watersheds in Western Germany and neighbouring countries. Many people reported being surprised by the event and in Germany, there were 190 fatalities recorded, pointing to failures in the flood early warning system. We analyze the warning situation based on the results of an online survey with 1351 participants from the most affected areas in two German federal states, Rhineland‐Palatinate (RLP), and North Rhine‐Westphalia (NRW). Among other topics, the survey addressed whether and when residents received a flood warning and if they knew what to do in response to a flood. We look at differences in the performance of the warning system at the district level and at the watershed segment level from upstream to downstream. We find significant differences between the districts but also due to the location of districts within different federal states and the presence of operational flood forecasting systems. We find some differences between watershed segments; however, the severity of the flood is more important than location within the watershed. Results show that timely warnings through official channels based on operational flood forecasting can help close the warning gap for flash floods.

Soon Ho Kwon, Seungyub Lee, Donghwi Jung

ABSTRACT Global climate change exacerbates urban floods, making their projection into future uncertainties more challenging. Identifying flood impact factors in urban areas is necessary for effective urban flood risk management. However, studies investigating the priority determination among flood impact factors based on an integrated decision‐making tool are limited. This study proposes an integrated flood risk matrix combining two methods. The proposed tool comprises quantitative and qualitative approaches to comprehensively investigate the priorities among flood impact factors. The quantitative approach examines the “uncertainty,” and the qualitative approach investigates the “importance”. The proposed tool, combined with two measures, performs priority determination with respect to hydrological and hydraulic flood risk factors. Pipe roughness and curve number were identified as the key drivers (i.e., high priority). In addition, the proposed matrix demonstrated how priority determination among flood impact factors can help improve decision‐making for urban infrastructure projects. This study improves knowledge of project decision‐making by providing a mechanism that integrates two different methods while providing reliable results.

Mandy Paauw, Glen Smith, Ann Crabbé et al.

Abstract Flood risks worldwide are increasing due to climate change. Managing these risks is ever more necessary. Although flood risk management (FRM) is often understood as a technical challenge, it also involves decisions about the distribution of resources and risks in floods, which can be inherently unfair. People are disparately affected by floods due to their location. Because of their various socioeconomic and demographic characteristics, they also differ in their capacity to deal with floods. These differences need to be recognised in FRM to prevent disproportionate impacts on vulnerable communities. However, at present, a knowledge gap exists on how to make FRM more inclusive and just, and discussions on recognition justice in the context of FRM are scarce. This article therefore examines recognition of differences in the capacity of people to deal with floods in FRM in England (United Kingdom), Finland, Flanders (Belgium) and France. We analyse if, and how, these differences are recognised in FRM policy and practice and through decision‐making procedures, drawing on examples from the implementation of five FRM strategies in each country (flood risk prevention, flood defence, flood risk mitigation, flood preparation and flood recovery). Furthermore, we aim to highlight opportunity spaces to strengthen recognition justice in future FRM.

Ozge Naz Pala, Irem Daloglu Cetinkaya, Mahir Yazar

ABSTRACT Cities striving to adapt to the impacts of climate change must recognize the significant variability in flood vulnerability across different communities. By examining the interplay between physical and socio‐demographic factors, this paper provides a comprehensive overview of the multidimensional aspects of flood exposure and vulnerability in Istanbul's Pendik District. The Pendik District, situated within the Istanbul Metropolitan Area, was chosen for this study as it regularly faces floods exacerbated by climate change. Utilizing a mixed‐methodology approach, ranging from the analytic hierarchy process (AHP) to surveys and census data, we find that areas classified as flood‐prone have residential units with lower land market values. Additionally, these high flood‐prone areas within the district tend to be populated by elderly individuals, refugees, and citizens with low education levels. In sum, this study reveals that there is a sharp correlation between socio‐economically disadvantaged communities and their exposure and vulnerability to urban flooding in Pendik District. As long as the current urban design and building stock fail to address the high level of flood exposure among the most disadvantaged urban communities, there is a critical need for inclusive urban planning and disaster management strategies.

Bastien Bourlier, Franck Taillandier, Charlotte Heinzlef et al.

ABSTRACT Flash floods and coastal flooding are more and more frequent and damaging in the context of climate change. In addition, the concentration of the population in urban areas contributes to increasing flood risk in these areas. Furthermore, not all territories are at the same level in their risk and resilience management approaches. Regarding this, the French overseas territories have been identified as particularly vulnerable to flood risk. This is the case for Tahiti, the main island of French Polynesia where the capital is located. It is a dense urban area subject to coastal and river flooding hazards, largely exacerbated by the physical environment. Our goal is to propose a method to assess flood resilience in Tahiti. We developed an indicator‐based method and used GIS to produce and represent a spatial analysis of territorial resilience. We developed a list of comprehensive spatial indicators that take into account three main dimensions: a structural dimension (e.g., building resilience), an organisational dimension (e.g., the resilience of actions during crisis) and a socio‐economic dimension (e.g., human economic capital). The final objective of this research is to design decision‐making tools for territorial stakeholders to help them in long‐term reflection and collaboration.

Stephen Grey, Ye Liu, Jeffrey Simmons

Abstract A hurricane surge and inundation risk assessment has been carried out for Grand Bahama and Eleuthera in The Bahamas. 10,000 years of synthetic hurricane tracks were generated based on a statistical analysis of historical hurricanes from 1979 to 2020 inclusive. The surge and inundation were modelled using a hydrodynamic TELEMAC‐2D model covering sea around The Bahamas and the land of the two islands. Predictions of flood extents and depths were mapped for return periods of up to 1000 years for present day conditions and three climate change scenarios to 2100. The flooding experienced over Grand Bahama during Hurricane Dorian in 2019, was estimated to have a return period of up to approximately 450 years. Under the climate change scenarios the likelihood of flooding similar to Hurricane Dorian was estimated to be approximately 1.7 times more likely in 2050 and up to 3.4 times as likely in 2100 under a high greenhouse gas emissions scenario. The storm surge maps can be used by the Bahamas Department of Meteorology and other government agencies for emergency management, planning of infrastructure and building resilience in response to climate change.

Wencong Qiu, Yanlong Li, Wei Zhao et al.

Irina Stefanović, Ratko Ristić, Nada Dragović et al.

The aim of this research was to analyze the impact of implemented erosion control works (ECW) on soil erosion intensity in the watershed of the Ćelije reservoir (Rasina River) in the period between 1968 and 2022. The Erosion Potential Method was used to calculate the annual gross erosion (W), sediment transport (G), and erosion coefficient (Z) in the study area. As a result of the performed ECW there was a general decreasing trend in the intensity of soil erosion processes in the last 54 years. The specific annual gross erosion was 1189.12 m3/km-2/year-1 in 1968, while in 2022 it was 554.20 m3/km-2/year-1. The specific sediment transport was 540.18 m3/km-2/year-1 in 1968 and 253.55 m3/km-2/year-1 in 2022. Due to the changes in the intensity of erosion processes the specific annual gross erosion decreased by 634.92 m3/km-2/year-1, and the specific sediment transport by 286.63 m3/km-2/year-1. The erosion coefficient was reduced from Z=0.62 to Z= 0.35. A dependence between the slope of siltation and the natural bed slope was defined. The results show a significant correlation between erosion intensity and performed ECW, providing a basis for future watershed management and defining a strategy for soil erosion control in the Ćelije reservoir watershed.

محمد مهدی آرتیمانی, حسین زینی وند, ناصر طهماسبی پور

مقدمه ناهمگنی موجود در آبخیزها و غیر‌‌خطی بودن رفتارهای هیدرولوژیکی، شناخت کامل روابط موجود در آنها را بسیار پیچیده و مشکل ساخته است. از این رو، ارزیابی این سیستم‌‌ها، نیاز به فرایند مدل‌‌سازی دارد. با توجه به توسعه زبان‌های برنامه‌‌نویسی و ارائه الگوریتم‌های بهینه و کارا جهت حل مسائل دیفرانسیلی در چند دهه اخیر، مدل‌های هیدرولوژیکی/هیدرولیکی جایگاه خاصی در مطالعات هیدرولوژی پیدا کرده و بر این اساس، به‌کارگیری مدل‌‌های شبیه‌‌سازی بارش-رواناب، برای پیش‌‌بینی سیل مورد توجه محققین قرار گرفته است. این امر سبب شده تا مدل‌های متنوعی جهت شبیه‌‌سازی فرایند بارش-رواناب توسعه یابند. یکی از مدل‌‌های موفق در این زمینه، مدل TOPKAPI-X است. این مدل در دهه 90 میلادی در دانشگاه بولونیا توسط پروفسور Todini به‌صورت یک مدل بارش-رواناب توزیعی مکانی قابل کاربرد در سطح حوزه‌ آبخیز توسعه داده شد. از ویژگی‌های مهم مدل‌های توزیعی مکانی این است که می‌توان نتایج شبیه‌سازی مدل را در هر نقطه از حوزه ‌‌آبخیز استخراج نموده و بر خلاف مدل‌های یکپارچه که کل حوزه‌‌ آبخیز را یک واحد در نظر می‌گیرند، اجازه تفکیک‌‌بندی در هر نقطه از حوضه را می‌دهد. بنابراین، در این پژوهش بعد از واسنجی و اعتبارسنجی مدل فیزیکی-توزیعی TOPKAPI-X در حوزه‌‌‌ آبخیز گاماسیاب، نسبت به بهینه‌‌سازی مدل در منطقه پژوهش جهت برآورد دبی روزانه اقدام می‌‌شود.   مواد و روش‌‌ها حوزه‌‌ آبخیز گاماسیاب در غرب کشور و در نواحی شمالی رشته کوه زاگرس، در شمال حوضه سد کرخه و عمدتاً در محدوده استان‌‌های همدان و کرمانشاه قرار دارد. مناطق کوهستانی این حوضه بیشتر در قسمت‌های شمالی و جنوبی متمرکز شده‌اند و مناطق پست و جلگه‌ای آن بیشتر در بخش‌های میانی و جنوب غربی حوضه قرار دارند. در این پژوهش از مدل TOPKAPI-X برای شبیه‌سازی رواناب در حوزه‌‌‌آبخیز گاماسیاب استفاده شد. برای این منظور، ابتدا مرز حوضه با استفاده از مدل رقومی ارتفاعی (DEM) با وضوح 30 متر، نقشه کاربری اراضی، بافت خاک، شبکه آبراهه حوزه ‌‌آبخیز و مولفه‌‌های اقلیمی در مدل TOPKAPI-X وارد شد. پس از معرفی مکان حوضه، از محل خروجی حوضه (ایستگاه هیدرومتری) برای شبیه‌‌سازی جریان استفاده شد. در این مدل بارش-رواناب، داده‌‌های سری زمانی پیوسته در گام زمانی روزانه در نظر گرفته شد. برای اجرای مدل در حوضه، سری زمانی دبی، بارش و دمای روزانه در دوره آماری 21 ساله در 13 ایستگاه هواشناسی و یک ایستگاه هیدرومتری داخل و خارح حوضه طی سال‌‌های 1999 تا 2020 بهره‌‌ برده شد. پس از چندین بار اجرای مدل، هر بار پارامترهای کلی مدل به‌صورت دستی و سعی و خطا تغییر می‌‌کرد تا در نهایت، با در نظر گرفتن مقادیر مناسب معیارهای ارزیابی ناش-ساتکلیف و اریب مدل برای حوضه، مقادیر بهینه پارامترهای مدل به‌دست آمد.   نتایج و بحث این پژوهش، به‌منظور تحلیل بارش-رواناب یکی از زیرحوضه‌‌های اصلی حوضه آبخیز سد کرخه با استفاده از مدل TOPKAPI-X در مقیاس زمانی روزانه انجام شده است. در محیط نرم‌افزار TOPKAPI-X با استفاده از نقشه‌‌های ورودی و داده‌‌های مشاهداتی بارش، دما و دبی، واسنجی مدل انجام شد. مقایسه ظاهری هیدروگراف‌‌های مشاهداتی و شبیه‌‌سازی شده، امکان ارزیابی کلی و سریع دقت مدل‌‌ها را فراهم می‌‌کند. نتایج گرافیکی مقایسه دبی حاصل از اجرای مدل TOPKAPI-X با پارامترهای واسنجی شده و دبی اندازه‌‌گیری شده در حوضه گاماسیاب نشان داد که این مدل، توانایی خوبی در برآورد دبی روزانه این حوضه را دارد. اما در برخی موارد دبی‌‌های شبیه‌‌سازی شده بیشتر از دبی مشاهده شده است. چهار معیار NSE، R، BIAS و RMSE برای ارزیابی مدل استفاده شده است. برای حوزه آبخیز گاماسیاب مقدار معیار ناش-ساتکلیف در دوره واسنجی (2014-1999) برابر 0.697 و در دوره اعتبارسنجی (2020-2014) برابر 0.660 محاسبه شد. بنابراین، می‌‌توان نتیجه گرفت که این مدل در حوضه مورد مطالعه، در شبیه‌‌سازی جریان عملکرد خوبی دارد.   نتیجه‌‌گیری اهمیت مدل‌‌های هیدرولوژیکی برای مدیریت منابع آب، ارزیابی کیفیت مطالعات اجرایی و درک فرایندهای هیدرولوژیکی کاملاً مشخص است. مدل‌‌های هیدرولوژیکی ابزارهای مهمی هستند که به دانشمندان و همچنین سیاستگذاران اجازه می‌‌دهد تا بر اساس شبیه‌‌سازی رفتار حوضه، تصمیم‌‌گیری کنند. بنابراین، با توجه به افزایش تقاضا برای آب و تأثیر تغییرات آب و هوایی، شبیه‌‌سازی هیدرولوژیکی توسط مدل‌‌ها از ابزارهای مدیریت آب در آینده خواهند بود. نتایج مطالعه حاضر نشان داد که مدل TOPKAPI-X پتانسیل بالایی در شبیه‌سازی رواناب در حوزه‌‌‌آبخیز انتخابی دارد. بنابراین، با توجه به قابلیت‌‌های آن، استفاده از این محیط به عنوان یک ابزار مدل‌‌سازی برای حوزه‌‌های آبخیز پیشنهاد می‌‌شود.

Baoling Li, Lihu Yang, Xianfang Song et al.

Identifying groundwater (GW)-surface water (SW) interactions in riparian zones is important for assessing the transport pathways of pollutants and all potential biochemical processes, particularly in rivers with artificially controlled water levels. In this study, we constructed two monitoring transects along the nitrogen-polluted Shaying River, China. The GW-SW interactions were qualitatively and quantitatively characterized through an intensive 2-y monitoring program. The monitoring indices included water level, hydrochemical parameters, isotopes (δ18O, δD, and 222Rn) and microbial community structures. The results showed that the sluice altered the GW-SW interactions in the riparian zone. A decrease in river level occurs during the flood season owing to sluice regulation, resulting in discharge of riparian GW into the river. The water level, hydrochemistry, isotopes, and microbial community structures in near-river wells were similar to those in the river, indicating mixing of the river water with the riparian GW. As the distance from the river increased, the percentage of river water in the riparian GW decreased, whereas the GW residence time increased. We found that nitrogen may be easily transported through the GW-SW interactions, acting as a sluice regulator. Nitrogen stored in river water may be removed or diluted by mixing GW and rainwater during the flood season. As the residence time of the infiltrated river in the riparian aquifer increased, nitrate removal increased. Identifying the GW-SW interactions is crucial for water resource regulation and for further tracing the transport of contaminants such as nitrogen in the historically polluted Shaying River.

Xilin Wu, Xiaoming Feng, B. Fu et al.

Human regulations are involved in the hydrogeomorphic processes of silt-laden rivers with unprecedented intensity, and further, affect the structures and functions of the riverine social-ecosystem. The braided reach (BR) of the lower Yellow River is one of the world's most sediment-rich and dynamic rivers. In the recent twenty years, the Xiaolangdi Reservoir constructed upstream and the growing river training works have deeply changed the conditions of the BR, however, the behaviors of the fluvial system under multiple human influences and their mechanisms remain unexplored. Here we systematically analyze the changes in the BR in the past four decades from the view of a coupled human and natural system. We find that compared with the pre-dam period, the channel of the BR in the post-dam period is 60 % narrower and 122 % deeper. Meanwhile, the lateral erosion rate and lateral accretion rate have decreased by 164 m yr-1 and 236 m yr-1, and the flood transport capacity has increased by nearly 79 %. These changes were mainly caused by anthropic flow regime changes and boundary modifications, whose relative contributions were 71 ± 10 % and 29 ± 10 %, respectively. The interactions among channel morphology change, regional flood risk and human activities underpinned the evolution of the fluvial system by shifting the human-river relationship. Reach-scale stabilization of a silt-laden river needs the effective management of erosion and deposition processes, which calls for integrated management of soil conservation, dam regulation, and floodplain governance at a basin scale. Lessons from the lower Yellow River have important implications for other rivers faced with siltation problems, especially in the Global South.

Yuan‐Shun Chang, Hao‐Che Ho, Li‐Ya Huang

Abstract Low impact development (LID) is a common approach to storm water management aimed at mitigating the impact of flooding in urban areas. Most previous studies on this topic focused solely on the qualitative assessment of urban resilience. The lack of operational or quantitative resilience indicators has made it difficult to elucidate the degree to which LID affects resilience to flooding. This study established a quantitative flood resilience index (FRI) to assess the resilience of specific locations to flooding. We then used a 3Di hydrodynamic model to simulate time‐variant inundation conditions under an extreme weather event (799 mm in 72 h) in Tainan, Taiwan. Physical and socioeconomic factors were identified as the important factors in calculating the FRI in areas affected by LID. Our results revealed that LID can reduce inundation area and depth during short‐duration (sub‐daily) rainfall events; however, its effectiveness in reducing the effects of flooding during long‐duration (>1 day) events is negligible. Nonetheless, LID could enhance urban resilience to flooding by reducing the duration of flooding events and thereby making it possible to initiate recovery efforts earlier.

Hongyu Ji, Shenliang Chen, Chao Jiang et al.

River dynamics and sediment budget play a crucial role in shaping geomorphic variability of river channels and deltaic environments. Basin-scale human activities, including dam construction, induce alterations in river flow and sediment dynamics in the downstream channels and to the delta, and quantification of sediment source shift along downstream fluvial-deltaic systems is often uncertain. This study analyzed the river regime changes and sediment dynamics of a typical sediment-laden fluvial-deltaic system—the lower Yellow River (LYR) and the Yellow River Delta (YRD) —to assess the integrated effects of dam impoundment and dam-based river regulation schemes on downstream hydrogeomorphic transition processes. The Xiaolangdi (XLD) Reservoir, which was completed in 2000 with a total storage of 12.7 km3, is the final reservoir located in the middle Yellow River and plays an important role in flood control and energy supply. Following the full operation of XLD Reservoir, the relationship between water and sediment in the LYR became more balanced, with a drastic decline of sediment input and seasonal migrations of floodwaters. The interannual variability of water levels at downstream hydrological stations indicated a geomorphic transition in the LYR from net deposition to erosion state. The building of the XLD Reservoir caused a downstream shift of river-originated sediment source and 48% of the total sediment delivered to the YRD was derived from the LYR. However, the reduced sediment delivery since 2000 has still triggered net land loss regarding the YRD system, with a strong spatial variability which is dominated by the reduced accretion at the active delta front and erosion at the abandoned river mouth and coastal engineering zone. Compared with other environmental factors, the construction of upstream dams contributed the most to the decline of downstream sediment delivery over the past decades. The challenge for sustainable sediment management is the gradual decline of scouring efficiency as the riverbed sediment is coarsening. Our study suggests that future river regulation strategies should consider the geomorphic sustainability of both the LYR and the YRD system.