Search

ABSTRACT Seepage‐induced backward erosion is a complex and significant issue in geotechnical engineering that threatens the stability of infrastructure. Numerical prediction of the full development of backward erosion, pipe formation and induced failure remains challenging. For the first time, this study addresses this issue by modifying a recently developed five‐phase smoothed particle hydrodynamics (SPH) erosion framework. Full development of backward erosion was subsequently analysed in a rigid flume test and a field‐scale backward erosion‐induced levee failure test. The seepage and erosion analysis provided results consistent with experimental data, including pore water pressure evolution, pipe length and water flux at the exit, demonstrating the good performance of the proposed numerical approach. Key factors influencing backward erosion, such as anisotropic flow and critical hydraulic gradient, are also investigated through a parametric study conducted with the rigid flume test. The results provide a better understanding of the mechanism of backward erosion, pipe formation and the induced post‐failure process. [ABSTRACT FROM AUTHOR]

Flash floods can carry substantial sediment, posing significant sedimentation hazards in hilly cities. The sedimentation hazard map can reproduce the sediment thickness and extent of an extreme events scenario, playing an important role in sediment risk management. However, current research primarily focuses on modeling the inundation area and depth of floods, while studying sedimentation hazard caused by flash floods in urban areas remains insufficient. This paper aims to address this gap by utilizing a numerical model that simulates hyperconcentrated flow in hilly urban areas using the two‐dimensional hydro‐sediment‐morphological model to compile the cumulative sedimentation hazard map. The model, built upon the open‐source TELEMAC‐MASCARET framework, incorporates Zhang Hongwu's formula to simulate sediment‐carrying capacity, particularly suitable for hyper‐sediment concentration near the riverbed. This paper uses the data of extreme flash flood events in the Wuding River basin in 2017 to simulate and compile the cumulative sedimentation hazard map. The hazard map delineates the sedimentation hazard extent and level attributable to overbank floodplain sedimentation. Notably, the sediment thickness is highest in areas near the levees on both sides of the Dali River. Moreover, the map illustrates the extent of channel erosion resulting from hyperconcentrated floods, which could jeopardize bank stability. [ABSTRACT FROM AUTHOR]

Levees aim to provide protection during floods, however, these structures can breach, causing significant damage. Flood maps that include levee breaching are often limited to deterministic methods. Where probabilistic breaching is done, it often requires computationally expensive Monte Carlo simulations and an understanding of the geotechnical levee properties that are often limited. In this paper, we combine existing fragility curves and empirical breaching equations with a framework for automating levee breaching in catchments with limited geotechnical information. This method can be adapted and applied to existing 2D flood models to determine the probability of inundation, given that a breach occurs. This ultimately allows for greater emergency responses and land use planning to reduce the flood risk faced by our communities. The method was applied to four case study catchments. The results showed that including levee breaching in one catchment led to an average increase in the inundated area by 48.2% and a tripling in the potentially exposed area. However, breaching in some locations reduced the inundation extent by 12%, illustrating the potential for fuse plug levees and floodways as a flood mitigation strategy. This strategy has seen successful usage internationally. Further investigation is recommended to consider whether these mitigation strategies should be enacted. [ABSTRACT FROM AUTHOR]

Translation abstract More resilient levees using geotextilesFlood events occur regularly in Germany, with the dykes as flood protection structures taking centre stage. Due to the high water levels in conjunction with often long‐lasting flood events, the stability of the dykes, which are usually built as homogeneous earth structures, was often critical, and in some cases the dykes even failed. By using geotextiles, dykes can be reinforced or secured both in the course of new construction or upgrading and immediately before or during flood events in such a way that the typical cases of failure can be prevented or at least significantly delayed. Some possible applications of geotextiles for short and long‐term preventive measures are presented in this article. These are both state‐of‐the‐art applications and innovative applications of geotextiles in dykes. [ABSTRACT FROM AUTHOR]

The spread of morning glory (Ipomoea spp.) in Japanese soybean (Glycine max (L.) Merr.) fields has severely decreased soybean yields. Field levees are believed to be a source of this invasion. The introduction of Zoysia japonica Steud. is expected to suppress weed growth and reduce the required labor for weed management on the levees. In this study, field experiments were conducted on the soybean levees of turf (Z. japonica), bare, and weed (mainly broad leaf weeds such as white clover) from 2017 to 2019 to compare its effects on the occurrence, growth, and seed production of I. hederacea (L.) Jacq. var. integriuscula A. Gray. The canopy height in the turf levee was the lowest, and the vegetation cover rate was the highest. At the flowering and fruiting stage of I. hederacea var. integriuscula (September), the largest number of I. hederacea var. integriuscula that survived were on the turf levee; however, the plant length, dry weight, and the number of fruits were the least. Additionally, the stems of the morning glory on the turf levee were slight and spindly, and their growth and seed productivity were suppressed. Consequently, vegetation conversion to Z. japonica on the soybean field levees can be an effective strategy to suppress the colonization and growth of morning glory, thereby, improving soybean yields. [ABSTRACT FROM AUTHOR]

Relocating levees further back from river channels to increase river–floodplain connection can reduce flood stages and provide a host of co‐benefits. Modeling case studies show the significant potential of large levee setbacks for reducing flood stages; however, the difficulty of comparing between these case studies limits our understanding of how the hydraulic effects of setbacks vary in different settings. We filled this research gap by systematically modeling the hydraulic effects of setbacks across a range of river and flood conditions. We used unsteady, 1D Hydrologic Engineering Center‐River Analysis System models to quantify changes in flood stage, channel velocity, and sediment transport capacity for various setback sizes with different river slopes, widths, floodplain roughness, and flood sizes (peak flows) and durations. Setbacks reduce flood stages within the setback, as well as up‐ and downstream. Channel velocity and sediment transport capacity both increased upstream and decreased within the setback. Channel slope, flood size, and flood duration had the largest influence on hydraulic changes. There are diminishing returns in hydraulic effects with increasing setback size. These results can help guide the design and prioritization of levee setback projects and help set reasonable expectations for the scale of changes to flood hydraulics relative to the size of the reconnected floodplain. [ABSTRACT FROM AUTHOR]

Flood losses have steadily increased in the past and are expected to grow even further owing to climate and socioeconomic change. The reduction of flood vulnerability, for example, through adaptation, plays a key role in the mitigation of future flood risk. However, lacking knowledge about vulnerability dynamics, which arise from the interaction between floods and the ensuing response by society, limits the scope of current risk projections. We present a socio‐hydrological method for flood risk assessment that simulates the interaction between society and flooding continuously, including changes in vulnerability through collective (structural) and private (non structural) measures. Our probabilistic approach quantifies uncertainties and exploits empirical data to chart risk dynamics including how society copes with flooding. In a case study for the commercial sector in Dresden, Germany, we show that increased adaptation is necessary to counteract the expected four‐fold growth in flood risk due to transient hydroclimatic and socioeconomic boundary conditions. We further use our holistic approach to identify solutions for effective long‐term adaptation, demonstrating that integrated adaptation strategies (i.e., combined structural and non structural measures) can reduce the average risk by up to 60% at the study site. Ultimately, our case study highlights the benefit of the model for robust flood risk assessment as it can capture unintended, adverse feedbacks of adaptation measures such as the levee effect. Consequently, our socio‐hydrological method contributes to a more systemic and reliable flood risk assessment that can inform adaptation planning by exploring the possible system evolutions comprehensively including unlikely futures. Plain Language Summary: The rise in flood losses due to climate and societal changes calls for effective strategies to reduce risks. Understanding how floods interact with society and affect vulnerability is crucial in addressing this challenge. However, current flood risk assessments lack this comprehensive insight. We have developed a novel method that integrates floods and society into a single model, enabling us to comprehend how society's vulnerability to floods changes over time. Our approach examines how communities respond to floods, considering both collective (like constructing levees) and private actions (such as individual property precautions). By factoring in uncertainties and utilizing real‐world data, we improve our understanding of societal flood adaptation. Using the commercial sector in Dresden, Germany, as a case study, we reveal a potential four‐fold increase in future flood risk due to climate and socioeconomic shifts. We propose a combination of collective and private measures, potentially reducing flood risk by up to 60% at the study site. In summary, our method is capable of simulating a wide range of potential futures and uncovering unforeseen challenges that may arise when societies attempt to shield themselves from floods. This aids in robust flood risk management and facilitates better planning for adaptation. Key Points: We present a socio‐hydrological model for continuous flood risk projection that captures vulnerability dynamics and quantifies uncertaintyOur case study highlights the need for effective adaptation to intensifying flood risk and the potential of integrated flood risk managementThe robust flood risk assessment method explores the possibility space comprehensively including adverse feedbacks such as the levee effect [ABSTRACT FROM AUTHOR]

Flooding is one of the most frequent and costliest natural hazards around the world. Traditionally, flood risk management has relied on building protective structures such as levees and dams to protect assets based on historical data (e.g., 1% AEP flood), which encourages development on floodplains, provides a potentially false sense of security to communities, particularly in the context of climate change, and increases residual flood risk (the risk remaining after implementing risk reduction measures). This article aims to contribute to the management of residual risk by drawing on empirical findings from a survey carried out with flood risk practitioners from the public and private sector in Aotearoa New Zealand. Findings indicate fundamental concerns relating to how to best manage residual flood risk, despite its long profile and integration in current policy and practice. Other issues revolve around the use of outdated information to guide decisions and the lack of regulatory power to restrict developments in flood‐prone areas protected by hard defense structures. Identified barriers to improving current practice include the lack of national guidance and support, financial resources, public awareness, and some technical constraints such as uncertainties in flood modeling, staff expertise, and data availability. [ABSTRACT FROM AUTHOR]

Animal activities threaten levee stability, especially during flood events, increasing levee failure risk. Indeed, while dens alter hydraulically‐induced failure mechanisms, it is difficult to locate them and to know in advance if critical conditions may be reached. This paper demonstrates that it is possible to perform nondestructive surveys to assess the risk of burrow animal activities in levee systems using a ground penetrating radar (GPR) for effective levee structure control, being GPR a nondestructive, expeditious, and cost‐effective geophysical technique. Here, a flood‐prone area in Sicily, where traditional hydraulic phenomena did not justify past levee failure events, is considered a case study. Through a visual inspection survey, several animal holes were recovered. GPR measurements allowed us to explore the levee interior and to detect the presence, distribution, and configuration of dens inside them. It was found that a complex burrow system crosses the entire embankment. Porcupine was recognized as a builder of such cavities. Although, previous studies established the porcupine presence in semi‐humid environments, for the first time, here we provide evidence of the development, articulation, and extension of porcupine burrows inside the levee system. [ABSTRACT FROM AUTHOR]

Improving protection against fluvial floods requires a better estimation of levee failure. We developed an assessment method of levee failure probabilities for sliding, backward erosion, and overflowing each represented by fragility curves. We tested two approaches to aggregate those fragility curves into a global fragility curve respectively using: an enveloping curve and Monte‐Carlo simulations. We implemented this approach to earthen levee reliability for several flood return periods to the Bow River in Calgary, Canada. We used limit equilibrium method to estimate the safety factor of the levee segment and Monte‐Carlo simulations to estimate sliding probabilities. We used Terzaghi's critical hydraulic gradient to estimate backward erosion failure probabilities. The estimation of overflowing probabilities required expert judgment. We discussed how the choice of the hydraulic gradient area and the consideration of a steady state or transient model impact backward erosion failure probabilities. The results showed for our study case that, even though the transient model is a closer representation of reality, the levee saturation parameter has little impact on hydraulic gradient values, by extension, on sliding and backward erosion failure probabilities. The Monte‐Carlo aggregated fragility curve is more realistic than the envelop curve of the failure mechanisms for an equivalent computation time. [ABSTRACT FROM AUTHOR]

The second generation of Eurocode 7 includes both soil and rock. In addition to the current practice of ground engineering, this document aims at incorporating rock engineering, improving the ease of use, the harmonization of regulations and covering new developments. This paper provides an overview of some of the significant changes to Eurocode 7 in rock engineering design, taking into consideration limit state design, robustness, durability, and reliability. It focuses on the design of slopes, spread foundations, and retaining structures. The clauses focus on soil mechanics, but also include special rock mechanical issues such as the influence of discontinuities and strength anisotropy on the limit states. Many matters associated to verification of rock mechanical design are linked to the use of prescriptive rules and shall be given in National Annexes. For geotechnical structures in rock, it is mentioned that geotechnical mapping and documentation is important to verify the limit states. However, the basic issues with partial factor methods for verification of the ground‐structure interaction of reinforced slopes and retaining structures are not fully resolved. This has caused some difficulties in setting up partial factors and obtaining a sufficient overview of the application of partial factor method, especially in rock engineering. The design of slopes, spread foundations and retaining structures must likewise consider other clauses in the Eurocode. Rock support for slopes and retaining structures is described in Clause 13 "Rock Bolts and Surface Support". Groundwater‐related issues are described in clause 12 "Ground water control" which influence the design and limit states for the actual geotechnical structure. Dams and levees are featured in Clause 4 "Slopes, Cuttings and Embankments". [ABSTRACT FROM AUTHOR]

This research comprehensively examined multiple sources of historical records and the built heritages of flood control construction along the Yongding River surrounding the Marco Polo Bridge section from 1890 to 1899, including stone levees, brick levees, cement dams, distributary channels, steel bridges, and temples dedicated to flood control. We mapped all these construction heritage features by time and geographical location according to historical documents to reveal the cause and intention behind each site. The following new insights were gained. First, the human–river relationship transitioned from utilization to resistance throughout the history of the Yongding River. Second, the philosophy of flood control represented a balance between symptom suppression and condition treatment at the peak of water management in imperial China. Third, the cultural and religious attitudes of humans in regard to flood control gradually shifted from a belief in the supernatural to faith in the ability of humans. Finally, modern technology, materials, and technicians were gradually imported, and water construction was implemented during the late Qing Dynasty, indicating modernization of the human–river relationship. [ABSTRACT FROM AUTHOR]

Infrastructure equity is an immediate concern with levees, constituting the backbone of the U.S. protection against flooding. Flooding patterns are exacerbated by anthropogenic climate change in several regions, posing a significant risk to the economy, safety, and well‐being of the nation. The evolving risk of flooding is shown to disproportionately affect historically underserved and socially vulnerable communities (HUSVCs). Here we compare the sociodemographic and socioeconomic composition of leveed and non‐leveed U.S. communities and show a substantial overrepresentation of HUSVCs in leveed areas at the state, regional, and national levels. Further, we analyze the proportion of communities designated as "disadvantaged" in leveed versus non‐leveed areas, revealing a substantially larger population of disadvantaged communities residing behind levees. Our analyses show that nationally, Hispanic are the most overrepresented population in leveed areas yielding a disparity percentage of 39.9%, followed by Native American (18.7%), Asian (17.7%), and Black (16.1%) communities. Communities characterized by low education, poverty, and disability exhibit a disproportionately higher presentation of 27.8%, 20.4%, and 5.4% in leveed areas across the U.S. In 43 states, disadvantaged communities are overrepresented behind levees, with a national disparity percentage of 40.6%. At the regional level, the highest disparity was observed in the Northeast (57.3%), followed by the West (51.3%), Southeast (38%), Midwest (29.2%), and Southwest (25%). The findings can enable decision‐ and policy‐makers to identify hotspots within HUSVCs that need to be prioritized for enhancing the integrity and climate adaptation of their levee systems. Plain Language Summary: Levees constitute the backbone of the nation's protection system against flooding, which is shown to disproportionately impact historically underserved and socially vulnerable communities (HUSVCs). Here we identify disparities in levee‐protected U.S. communities by comparing several sociodemographic and socioeconomic attributes in non‐leveed areas with tracts behind levees listed in the National Levee Database. Further, we analyze the proportion of leveed versus non‐leveed communities designated as "disadvantaged." We found a substantial overrepresentation of HUSVCs in leveed areas at the state, regional, and national levels. Nationally, the major disparities are found to be Hispanic (39.9%), low education (27.8%), poverty (20.4%), native American (18.7%), Asian (17.7%), and Black (16.1%). Regionally, In the Midwest and Southeast, 60.6% and 40.2%, respectively, more Black populations live behind levees. In the West, the largest disparities are education (40.5%) and Hispanic or Latino (38.6%). In 43 states, disadvantaged communities are overrepresented behind levees, with a national disparity percentage of 40.6%. The highest regional disparity was observed in the Northeast (57.3%), followed by the West (51.3%), Southeast (38%), Midwest (29.2%), and Southwest (25%). The findings can enable decision‐ and policy‐makers to identify hotspots within HUSVCs that need to be prioritized for enhancing the integrity of their levee systems. Key Points: Infrastructure equity is an immediate concern with leveesWe found substantial disparities in race/ethnicity, education, poverty, and disability of leveed‐ versus non‐leveed U.S. communitiesHistorically underserved and socially vulnerable communities are substantially overrepresented in leveed areas compared to non‐leveed areas [ABSTRACT FROM AUTHOR]

For several years, fragility curves have been used to assess the failure probability of flood defences when undertaking probabilistic flood risk assessments. When preparing an editorial, members of the Editorial Board sometimes discuss cases of floods that are topical at the time of writing. [Extracted from the article]

Hyperpycnal flow deposits, one of the most important deep‐water gravity‐flow deposits in lacustrine basins, have become the research focus in recent years. However, the sedimentary characteristics and depositional model of hyperpycnal flow deposits in lacustrine basins remain unclear due to the differences of depositional settings between lacustrine and marine environments. Hyperpycnal flow deposits observed in the middle of the third member of the Shahejie Formation (Es3z) in the Bonan Sag, Bohai Bay Basin, Eastern China, provide a rare case study to reveal the characteristics and depositional model in lacustrine basins. For the first time, detailed core analysis, high‐resolution 3D seismic data, petrology and grain size analysis were used to unravel the characteristics and depositional model of hyperpycnal flow deposits in this study. Twelve lithofacies, six bed types and four bedsets (corresponding to feeder channel, distributary channel, levee and lobe) were recognized from detailed facies analysis. Plant fragment, an important identification mark for hyperpycnal flow deposits, can be classified into three types: completely broken plant fragments, partially broken plant fragments and complete leaves. The proximal part of the deposit develops a small amount of scattered and completely broken plant fragments in massive or spaced stratified pebbly sandstone and massive sandstone due to strong erosion of sustained high‐density turbidity current. The medial part of the deposit is dominated by laminated partially broken plant fragments in planar laminated or rippled sandstone due to suspended settling of sustained high‐density turbidity current and quasi‐steady low‐density turbidity current. Layered partially broken plant fragments with some complete leaves are common in the upper part mud rich division of hybrid event bed and laminated siltstone in the distal part of the deposit. The distribution pattern of hyperpycnites is controlled comprehensively by palaeogeomorphy and sediment supply. Palaeogullies determine the provenance direction of hyperpycnal flow. The formation of synsedimentary faults and troughs control the transport routing patterns. Local micro‐palaeogeomorphy and depression areas further restrict the distribution of sand bodies. During the early stage of deposition with insufficient sediment supply, sediments are transported to the deep basin along confined faulted troughs forming elongated sandy bodies. During the late stage of deposition with sufficient sediment supply, sediments are transported to the deep basin without confinement accumulating fan‐shaped sandy bodies. This study offers insight for enhancing the recognition criteria of hyperpycnites, as well as their depositional model in lacustrine basins. [ABSTRACT FROM AUTHOR]

Contrary to widely used traditional sequence‐stratigraphic models, highstand sublacustrine fans developed in the deep‐water environment in the middle of the third member of the Eocene Shahejie Formation (Es3z, 42–40.5 Ma), Dongying Sag. Using four cores and 3D seismic data, we describe the sequence stratigraphy frameworks, sediment characteristics, depositional elements, and depositional model of the Liangjialou highstand sublacustrine fan. The Es3z is a complete third‐order sequence stratigraphic, bounded by T4 at the top and T6 at the base. Between T4 and T6, there is the maximum flooding surface (MFS) distributed from proximal to distal of the system in the third‐order stratigraphic sequence. Therefore, the Liangjialou Fan at the top of the Es3z, between MFS and T4, is a typical highstand sublacustrine fan as determined from seismic data. This highstand sublacustrine fan is characterised by gravel to fine‐grained sand, abundant amalgamation surfaces, and crude stratifications common in coarse‐grained structureless‐ to normal‐ graded sandstones. Climbing ripples and thin laminae rich in plant debris are common in inverse‐then normal‐graded sandstones. Channel‐levee, channel‐lobe transition zone, and lobes developed in this highstand sublacustrine fan, with clear internal progradation stacking patterns caused by hyperpycnal flow. The sudden increase in sediment supply in an accommodation decrease situation and the narrow shelf width are the primary controlling factors for forming highstand sublacustrine fans. In the late stage of the highstand systems tract, gravity‐flow deposits caused by hyperpycnal flow are developed from another new point source to form this highstand sublacustrine fan. Hyperpycnal flow in lacustrine basins can transport coarse‐grained sediments with the help of strong flood energy and steep slopes. Gravity flow deposits in lacustrine basins are not confined by sequence stratigraphy frameworks, and many additional areas of sand caused by hyperpycnal flow could be found in lacustrine basins. [ABSTRACT FROM AUTHOR]

Understanding the interactions of submarine channels with seafloor deformations is challenging as these channels more often involve a wide variety of responses relying on both autogenic and allogenic factors. The effect of active growing structures on channel pathways is well documented, but the evolution of lateral migration and the internal architectures along the deflected channel bends around ongoing active structures remain poorly constrained. Here, we use 3D seismic interpretation and quantitative geomorphologic methods to examine the channel bend morphology and the kinematics of lateral migration near gravity‐driven tectonic deformation. Using high‐resolution seismic reflection data acquired from the offshore Niger Delta, two‐channel levee systems (Amaku Major System and Amaku Channel Levee System) have been recognized in the seismic survey. Each system consists of three channel complexes, recording five types of deflected channel bends, defined here as: (i) avulsed bend, (ii) confined bend, (iii) chute cut‐off bend, (iv) blocked bend and (v) kinked bend. Geomorphologic parameters including bend sinuosity, bend amplitude, along‐bend length, straight‐bend length, channel depth and width, were considered within the deflected channels. Lateral migration estimators; channel lateral shift (SH), and channel lateral spacing (CS), were assessed throughout the distances of cross‐sectional channel patterns. The lateral migration estimators (SH and CS) were used to estimate the expression of internal architectures and the evolution of lateral migration around seabed deformation at the scale of the channel complex. The results show that the morphology and internal architecture of the deflected bends, although developing in the same structural context, display varied responses to structural deformation. Unlike previously published models of channel‐fold interactions asserting tectonics as the solitary driver, here we demonstrate that the channel deflections around structures are sensitive to the lateral confinement produced by sediment relief of the outer levees, and the autogenic forcing of channel mechanisms. This study provides new insights into the evolution of submarine channels in active tectonic settings, shows detailed mechanisms of channel bends at a small scale and offers a better understanding of the distribution of sediments in the deep sea. [ABSTRACT FROM AUTHOR]

The sedimentary architecture of channelized turbidites can be highly complex as it reflects the response of submarine channels to several interplaying factors. Although intensively investigated through seismic imaging, turbidite channel fills are not convincingly calibrated for sedimentary facies at a sub‐seismic scale. This contribution addresses the sedimentary architecture and the controls on the evolution of a ca 20 m thick channel‐levee complex of the Tachrift turbidite subunit (Upper Miocene, the Melloulou Formation), which accumulated along the southern slope of the Neogene Taza‐Guercif Basin (Rifian Corridor of north‐east Morocco). Facies and architectural analyses indicate that the studied channel‐levee complex is the result of three‐fold evolution. From base to top, it is comprised of: (i) a ca 7 m thick lower mud‐prone interval containing relatively small and vertically stacked channel fills with poorly developed muddy levees; (ii) a ca 4 m thick and >1 km wide sandstone‐rich middle interval made of lateral accretion packages that become progressively less amalgamated and fine‐grained and is overlain by ca 5 m of thin‐bedded mud‐rich turbidites intercalated with hemiplegic marlstones; and (iii) an up to ca 9 m thick upper interval constituted by aggradational channel fills with well‐developed levees and variously directed lateral accretion packages. This organization suggests that, following a phase of inception (lower interval), the channel underwent extensive meandering with very minor vertical aggradation, prior to being blanketed by 'retrogressive' muddy lobes (middle interval) during a phase of reduced sediment input. In turn, the uppermost interval records a late phase of channel re‐establishment and aggradation that likely terminated as a result of up‐dip avulsion. It is suggested that the observed change of architectural style reflected the feedback of changing sediment input, slope equilibrium profile and channel morphodynamics. [ABSTRACT FROM AUTHOR]

Species distribution models (SDMs) are widely applied to understand the processes governing spatial and temporal variation in species abundance and distribution but often do not account for measurement errors such as false negatives and false positives.We describe unmarked, a package for the freely available and open‐source R software that provides a complete workflow for modelling species distribution and abundance while explicitly accounting for measurement errors. Here we focus on recent advances in unmarked functionality to support multi‐species, multi‐state, and multi‐season data, as well as support for fitting models with random effects.For illustration, we present an analysis of Acadian Flycatcher Empidonax virescens abundance on Roanoke River National Wildlife Refuge, North Carolina, USA, over 18 years. We found that Acadian Flycatcher abundance was initially greater in hardwood plantation habitat relative to bottomland hardwood forest along river levees but that abundance declined over time in both habitats.We plan for unmarked development to keep pace with advances in hierarchical modelling in ecology, including better handling of continuous‐time data from camera trap and automated recording units and integrated models for multiple data streams. [ABSTRACT FROM AUTHOR]

This article discusses the levee failure that occurred on 6 December 2020 at Castelfranco Emilia, near Modena (Italy), showing that it cannot be explained without assuming the presence of local heterogeneities or a small cavity. The possible presence of these defects is supported by evidence derived from historical data and site observations. Fully coupled hydromechanical finite element simulations prove that the river embankment assumed without any deficiency had a sufficient level of safety for the considered event, thus it is necessary to hypothesize the presence of a local defect. The presence of a small cavity, in hydraulic communication with the river and buried at shallow depth, is assumed. This could be, for example, a new den, an old animal burrow repaired only partially, or a rotten plant root. Numerical analysis shows that the increase in water pressure within the cavity can trigger local failure of the landside slope, thus starting concentrated erosion. In highly erodible soils, this mechanism can lead very rapidly to the opening of the breach. A new analytical expression for the factor of safety of the soil wedge between the cavity and the surface is proposed. This approach is very simple and easily applicable, for example, to the assessment of levee vulnerability to animal burrows at a large scale. The results of the study are relevant for the management of water retaining structures. [ABSTRACT FROM AUTHOR]

Despite abundant studies on gravel‐sand transitions (GSTs), GST origin and migration in large alluvial channels characterized by significant variations in width, numerous tributary (or distributary) streams, and frequent human disturbances remain difficult to explain. Here, we take the Yangtze River as an example and use field observations and numerical modeling to make progress toward addressing GST origin and migration. The results show that the Yangtze River exhibits a non‐abrupt GST approximately 60 km long. Within the GST and the adjacent area, there are two dramatic decreases in shear stress; the upstream one induces the settlement of sand from suspension, explaining the emergence of the Yangtze River GST, whereas the downstream one induces general cessation of gravel movement. However, the deposited gravel was mostly overwhelmed by sand. We argue that these changes in shear stress in the Yangtze River depended primarily on the combined effects of width variability and distributary systems. Since 1970, the Jingjiang Meander Cut‐off, the Gezhouba Dam, and the Three Gorges Dam (TGD) have been completed in succession, repeatedly altering the flow‐sediment regime within the GST. However, the GST position remained unchanged until the TGD began operation in 2003. The stability of the GST was primarily ascribed to the sufficient upstream sand supply (grain size <0.5 mm), the resistant lithologies upstream of Zhicheng, and the Jingjiang Great Levees constraints. Plain Language Summary: Gravel‐sand transitions (GSTs) connecting gravel channels and sand channels occur in various environments and channel scales; however, morphological changes observed across GSTs vary with worldwide large rivers because of environmental setting differences and anthropogenic modifications. More detailed studies are needed to enrich the data set and improve the understanding of GSTs. The Yangtze River, the third‐largest river in the world, has been frequently disturbed by human activities over the past five decades. The study of the development of the Yangtze River GST is essential to better understand the evolutionary processes of large alluvial rivers and the impacts of channel regulation. Based on detailed field observations and a hydrodynamic model, this study explains the GST origin, describes the GST migration process and determines its primary controlling factors. The results show that the GST in the Yangtze River emerged due to the settlement of coarse sand rather than general gravel cessation and that the GST was stable until the sand supply substantially decreased after the Three Gorges Dam operation. The results also show that two changes in flow properties are a crucial feature of the Yangtze River GST and depend primarily on spatial changes in channel width and the presence of distributary channels. Key Points: The gravel‐sand transition (GST) in the Yangtze River had stabilized until the upstream sand supply was nearly cut off by the Three Gorges Dam operationThe GST emerges due to the settlement of sand rather than general gravel cessationThe changes in shear stress within the GST depend primarily on the controls of channel width and the presence of distributary streams [ABSTRACT FROM AUTHOR]

Submarine channels act as the main conduits for the transport of sediment to deep‐water basins by sediment gravity flows. The interplay between fault‐related deformation and the initiation and development of the channels is poorly known. Here, we present the identification, formation and evolution of the Miocene slope‐parallel channel by employing 3D seismic reflection, wireline‐log and core data in the eastern slope of Yinggehai Basin, South China Sea. Based on the lengths and plan‐view shapes, a total of three different types of fault‐associated slope‐parallel depressions have been identified. The depressions were formed in the fault zone and controlled by the reactivation of the underlying older faults. Among them, Type‐1 depressions are short (<20 km) oval or circle shaped possessing only one depocenter. Type‐2 depressions are elongated (25–70 km), and usually have multiple depocenters. Type‐3 depressions, which are usually connected by slope‐perpendicular channels in the head and middle, are longer (more than 190 km) and connect shallow and deep‐water basins. The analysis of morphology, erosivity and material transport shows that Type‐3 depressions are fully fledged channels. Type‐1 and Type‐2 depressions are channel precursors representing the initial stage of channel evolution. With this motive, a model for the initiation and evolution of slope‐parallel submarine channels controlled by strike‐slip‐extensional faults is presented. Unlike the previous investigations which suggest that erosion takes place at the inception of submarine channel formation, the fault‐controlled slope‐parallel channel is mainly controlled by faulting and has no initial erosive base and does not develop levees. The depressions are extended and elongated by the continuous fault activity. It was not until the slope‐parallel depression connected with large‐scale slope‐perpendicular channels transporting materials into the depression via erosive turbidity currents that it evolved into a channel‐levee system. This study is of global importance for understanding submarine channel generation and evolution since the fault‐controlled slope‐parallel channels have been found in tectonic active basins worldwide. [ABSTRACT FROM AUTHOR]

Channels filled with coarse‐grained sands are one of the hot issues in stratigraphic explorations. However, the sub‐surface uncertainty restricts the prediction of porous channel sandstones using the conventional seismic attributes, which is a concern for the demarcation of stratigraphic plays. The amplitude‐based frequency attributes and seismic‐petrophysical simulation tools were applied to characterize the fluvial channel system from the Indus Basin, Pakistan. The conventional amplitude of the Basal Sand Formation shows limited imaging ability to detect the dimensions of channel‐levee and point bars. The continuous wavelet transforms (CWT) tool distinguishes the whole channel‐levee reservoir system at tuning frequencies of 21, 25, 29, and 34 Hz. The amplitudes extracted along the pseudo‐porosity wells depict the low‐density and low‐velocity profiles within the gas‐bearing zones. The zone between 20% and 30% porosity displays low‐density and low‐velocity compartments within the point bars. Hence, it implicates the zone of deposition for hydrocarbon‐bearing fluvial facies. Based on the porosity constraint, the gas‐bearing fluvial reservoirs have high (>25%) porosity, which implicates the development of aggradational parasequences. The oil‐dominated sandstone facies experience relatively low‐porosity of <12% and negligibly high density and high velocity, which implicates the development of transgressive parasequences. The reservoir system shows an eastward shale‐out zone, where the high‐density and high‐velocity shales mask the channel‐levee systems. Consequently, these stratigraphic configurations are developing into a cost‐effective stratigraphic trap, and hence, this exploration scheme serves as an analogue for global fluvial depositional systems. [ABSTRACT FROM AUTHOR]

Flood hazard assessment is a fundamental step in flood risk mapping. Quantitative assessment requires hydrodynamic modelling of the flooding process in order to calculate the spatial distribution of suitable flood hazard indicators representative of flooding intensity and frequency, hence its potential to result in harm. Flood hazard indicators are usually defined by combining relevant flooding parameters, mainly flood depth and flow velocity, but also flooding arrival time, flooding duration, sediment or contamination load, and so forth. A flood hazard classification is commonly introduced to assign a hazard level to areas potentially subject to flooding. This article presents a systematic review of quantitative methods proposed in the scientific literature or prescribed by government authorities to assess the hazard associated with natural or anthropic flooding. Flood hazard classification methods are listed and compared by specifying their underlying approach (heuristic, conceptual, empirical), the exposed element which they were designed for (people, buildings, vehicles, etc.), and their fields of application (river overflow, dam‐break, levee breach, debris flow). Perspectives and future challenges in quantitative flood hazard analysis are also discussed. This review aims to help modellers and practitioners to select the most suitable flood hazard assessment method for the case study of interest. [ABSTRACT FROM AUTHOR]

Effective coastal management requires a fundamental understanding of the impacts of anthropogenic activities on sediment dynamics, yet it is challenging to isolate individual impacts in heavily altered regions. The Ayeyarwady Delta, Myanmar has been extensively deforested for agriculture but has few levees/polders. In this study, the relative resilience to subsidence was compared between a 45‐year‐old agricultural field and a nearby mangrove‐forest preserve. At both sites, water velocity and turbidity were measured in tidal channels, topography was mapped, and sediment cores were collected during 2018–2019. There was net sediment import at both sites due to sediment trapping by vegetation. Relative elevations were equivalent, suggesting that the field has aggraded at rates similar to the forest (0.7 cm/year). Unleveed fields may be less vulnerable to subsidence than leveed fields. However, uncertainties remain and the decision to replace mangroves with agricultural fields should weigh all the benefits provided by each environment. Plain Language Summary: Many tropical river deltas are densely populated agricultural centers, and these coastal landscapes are threatened by sea‐level rise. In these managed regions, farmers remove mangrove forests to expand fields and construct levees to control the annual inundation of fields. Unfortunately, levees prevent sediment delivery and can contribute to rapid sinking of the land surface. In the Ayeyarwady Delta, Myanmar, there are relatively few leveed agricultural fields. Here, we assess the resilience to sinking of a deforested but unleveed rice field with respect to a nearby, natural mangrove‐forest preserve in the center of the Ayeyarwady Delta. Land‐surface elevation, sediment transport, and sediment accumulation were measured at both sites in 2018–2019. The land‐surface elevation and average flooding per tide were equivalent in the field and forest. There were similar sediment retention rates, suggesting that rice crops can help trap sediment in a manner similar to mangrove trees. Consequently, unleveed fields are less likely to sink than leveed fields, despite mangrove removal. However, mangrove forests can provide additional benefits and should be preserved where possible. Key Points: Elevation and sediment import are equivalent in an unleveed agricultural field and a mangrove preserve in the Ayeyarwady Delta, MyanmarUnleveed agricultural fields in deltas are less vulnerable to subsidence than leveed or poldered fields [ABSTRACT FROM AUTHOR]

River flooding impacts human life and infrastructure, yet provides habitat and ecosystem services. Traditional flood control (e.g., levees, dams) reduces habitat and ecosystem services, and exacerbates flooding elsewhere. Floodplain restoration (i.e., bankfull floodplain reconnection and Stage 0) can also provide flood management, but has not been sufficiently evaluated for small frequent storms. We used 1D unsteady Hydrologic Engineering Center's River Analysis System to simulate small storms in a 5 km‐long, second‐order generic stream from the Chesapeake Bay watershed, and varied % channel restored (starting at the upstream end), restoration location, restoration bank height (distinguishes bankfull from Stage 0 restoration), and floodplain width/Manning's n. Stream restoration decreased (attenuated) peak flow up to 37% and increased floodplain exchange by up to 46%. Floodplain width and % channel restored had the largest impact on flood attenuation. The incremental effects of new restoration projects on flood attenuation were greatest when little prior restoration had occurred. By contrast, incremental effects on floodplain exchange were greatest in the presence of substantial prior restoration, setting up a tradeoff. A similar tradeoff was revealed between attenuation and exchange for project location, but not bank height or floodplain width. In particular, attenuation and exchange were always greater for Stage 0 than for bankfull floodplain restoration. Stage 0 thus may counteract human impacts such as urbanization. [ABSTRACT FROM AUTHOR]

Deep‐water clastic settings frame major stratigraphic plays the world over. The advanced seismic interpretation tools provide prediction of accurate physical characteristics of undiscovered reservoirs, including their lithology, thickness, and porosity. The designed amplitude spectrum (DAS)‐based processing tool on Full spectrum seismic may yield a remarkable stratigraphy. This study deals with the prediction of thick and porous (possibly gas‐rich) litho‐facies using the DAS tool on high‐resolution seismal profiles within the offshore Indus Basin (OIB), SW Pakistan. The seismic and trace envelope magnitudes bound the demarcation of stratigraphic traps. The DAS processing tool on relative acoustic impedance inversion (RAI) magnitude demarcates the aggradational porous sandstone‐filled reservoirs, which are encased within a transgressive non‐porous shale‐filled channel‐levee system. The thickness predicted by band‐limited seismic acoustic impedance (AI) simulation for channels, point bars, and levees is 28, 27, and 24 m, respectively. The DAS‐based RAI processing on AI reservoir simulation accurately resolves the lenses of channel sandstone, point bars and levees, and confirms the channelized basin floor fans (BFFs) with an average 11, 34, 24, and 52 m thickness and a lateral extent between 10 and 25 km. The western zones have implications for basin development, which have accumulated the porous and thickest reservoir facies inside the aggradational parasequences of BFFs of Miocene sedimentary sequences. Hence, the presented scheme of exploration serves as a comparable example for exploring the hydrocarbon‐bearing plays inside OIB and global deep‐water depositional systems. [ABSTRACT FROM AUTHOR]

Debris flow runout poses a hazard to life and infrastructure. The expansion of human population into mountainous areas and onto alluvial fans increases the need to predict and mitigate debris flow runout hazards. Debris flows on unconfined alluvial fans can exhibit spontaneous self‐channelization through levee formation that reduces lateral spreading and extends runout distances compared to unchannelized flows. Here we modify the D‐Claw shallow flow model in two ways that are hypothesized to generate levees. We evaluate these modifications with observations from a large‐scale flume experiment. We investigate model performance when including the effect of two different friction sub‐models, as well as the inclusion of segregation effects on granular permeability. Results show that, for a wide range of plausible model input parameters, simulations including the effects of segregation promoted modeled levee formation, whereas simulations without the effects of segregation did not create levees. Further, using a forward predictive framework, simulations with the effects of segregation were more likely to better model the magnitude of debris flow depth and runout distance, whereas simulation timing of the debris flow was affected by the choice of friction sub‐model. Our results indicate that including the effects of segregation on granular permeability can improve the likelihood of better predictions of debris flow depth and runout prior to an event occurring. Plain Language Summary: Hillsides that receive heavy rainfall sometimes experience a debris flow, a flood‐like mix of water, soil, and rocks. As more people move into mountainous regions, the hazard that debris flows present increases. In this study, we use a computer simulation to model debris flow behavior. We look at different ways to model parts of the physics, specifically, friction and the effects of the debris material size, on the area that debris flow reaches. We find that capturing the effect of different sized debris is important to recreate the self‐forming debris flow channel that can extend the length a debris flow can travel. Including these effects improves the predictive capability of the computer simulations. Improving our understanding and ability to model debris flow runout is important to predicting locations where a potential hazard exists from debris flows. Key Points: Modeling different material properties through the effects of segregation in D‐Claw allows for spontaneous self‐channelizing levee formationIncluding the effects of segregation on granular permeability improves debris flow simulation performance for recreating a large scale experimental debris flow [ABSTRACT FROM AUTHOR]

A robustly calibrated and validated hydrodynamic model depicts flow patterns over a topographically complex floodplain with a heterogeneous main channel levee. Simulations highlight floodplain inundation dynamics for two conditions, the passage of sub-bankfull and overbank flood waves. Sub-bankfull inundation commences with the passage of the flood wave crest beyond the lower elevation levee breaches, and floodplain wetting is guided by the channel network. Hence, the upstream sub-bankfull inundation area expands while much of the downstream floodplain remains dry. The onset of overbank flow is spatially variable but becomes continuous, and the through-bank channels persist as preferential pathways that produce higher velocity flows several kilometers inland. Meanwhile, near-stagnant zones develop between through-bank channel mouths, where water is temporarily stored and routed to the channel network. Also, 48% of the inundation water is from the river while 52% enters the study area from the upstream floodplain. Overall, floodplain wetting and draining processes significantly influence flow direction, and characteristics of the flood wave over the floodplain surface such that a single stage in the main channel does not uniquely define floodplain flow hydraulics. Given these findings we propose that assessments of floodplain hydraulic connectivity account for the effects of heterogeneous levee structure and intra-floodplain exchanges, as well as the typical flow thresholds associated with submergence and emergence of topography. [ABSTRACT FROM AUTHOR]

Levees are the most frequently used flood protection measure worldwide. In central Europe, they have been built systematically since the beginning of the 19th century. After the extreme regional floods in 1997, 2002 and 2013, the need arose for a more systematic and optimised approach to levee design and management, including the decommissioning of ineffective dike reaches. In this paper, a multicriterial algorithm is presented for the optimisation of levee management. The aspects considered are flood risk, economy, technical conditions, environmental issues and the consistency with general documents and principles in water management. The method is demonstrated via a case study of a levee subsystem in the upper Morava River basin. [ABSTRACT FROM AUTHOR]

Flood prone areas are often protected against flooding by an extensive network of flood defenses. To ensure their structural integrity, these flood defenses are periodically assessed. Many levees have been functioning well for decades, and have survived several relatively high hydraulic loads within their lifetime. However, information on survived load conditions is seldom included in levee safety assessments. Observed degradation from levee inspections is also not taken into account. That way, information that is useful to improve the accuracy of estimations of the actual strength of the levee remains unexploited. This study proposes a pragmatic approach to include observations of survived loads and levee degradation in the levee safety assessment. This approach consists of three steps: (1) a prior estimation of the failure probability, based on levee characteristics, (2) a posterior estimation of the failure probability, based on observed hydraulic loads, and (3) correction of the posterior failure probability estimation, based on levee inspections. In a case study, the estimated failure probabilities using this approach were much lower than when information on levee performance was not included. This study demonstrates the value of levee performance observations and how they could be included to improve levee safety assessments. [ABSTRACT FROM AUTHOR]

Between 1998 and 2006 a series of extreme flood events took place on the Tisza River and its tributaries. In Hungary, this triggered the development of flood‐peak polders as a more cost‐efficient solution of defense compared to raising the dikes. The recent analysis applies Monte‐Carlo simulation‐based quantified risk calculations with a cost–benefit type comparison. Results indicate that compared to the originally planned, 100‐year return frequency flood that threats to topple the levees, lower flood levels already provide economic justification for polder use. Apart from the optimal timing of opening the floodgates, the controlled inundation of polders requires the consideration of its cost–benefit effects as well. The development of the economic decision‐support system for the controlled use of the flood‐peak polders along the Tisza River provides an insight into the efficiency gains that a more informed, quantitative economic analysis can offer in risk reduction. The analysis reveals the potential for more efficient management of flood polders. The decision support of controlled polder inundation includes all the necessary information elements for the cross‐sectoral comparability of impacts that is the foundation for any multi‐purpose land management scheme that enables nature‐based solutions. [ABSTRACT FROM AUTHOR]

For the safety assessment and design of levees in the Netherlands probabilistic tools are used, which account for both statistical and model uncertainties in the determination of hydraulic loads. However, climate change induced uncertainties in extreme wind climate or storminess are not yet accounted for. This paper presents a first assessment of the effect of uncertainties in storminess on Dutch levee design. An expert panel was consulted to define a range of plausible trends and uncertainties in extreme wind climate. Three scenarios were defined with variations of the current wind climate, including changes in wind speed high percentiles and in wind direction. For the defined scenarios probabilistic computations were carried out to determine the effect of the wind statistics variations on the water level, wave loads, and required levee height along the Dutch lakes and coast. In the case of an increase in wind percentiles (mean + 5%, standard deviation 12%), the required levee height increases significantly: up to 1.5–4 m along the Dutch coast and up to 1–2 m along the Dutch lakes. Given the large impact of the considered changes, it is first recommended to carry out a more robust assessment of the uncertainties in future storm climate and to measure and monitor evolution of future wind speeds. [ABSTRACT FROM AUTHOR]

The analysis of seepage through earthen levees is fundamental to investigate the levee safety condition, since that the seepage phenomenon can often lead to piping causing the collapse of the levee (Saghaee et al., 2012). This work proposes a new approach for identifying the location of the saturation line through the earthen levee by using a multilayer soil approach that assumes the levee body and the levee foundation as two different layers, characterized by using a different hydraulic conductivity parameter. The main purpose is to investigate the difference in the predicted saturation line identified through the proposed method and the one based on the single layer analytical solution of the seepage flow suggested by Marchi (1961). On comparison of the saturation lines provided by two different approaches, the ratio between the river water head and the groundwater thickness or depth increases; allowing the determination of a ratio threshold above which the Marchi equation should no longer be applied. The proposed multilayer (levee and foundation) soil approach is also used to assess the seepage vulnerability of the methodology proposed by Barbetta et al. (2017). The results show that the differences between the seepage vulnerabilities evaluated using the multilayer approach and the single layer method are quite low. Although notably, significant modifications of the seepage probability are observed when the distance between the ground level and the groundwater table changes. [ABSTRACT FROM AUTHOR]

Streamflow regulation compounded by regional drought has resulted in up to 22% reduction in channel width, changes in channel planform, expansion of riparian vegetation, and alterations to floodplain habitat on the Colorado River in Meander Canyon, Utah. Although some changes in channel width occurred between the 1940s and 1980s, coinciding with major phases of upstream water development, larger decreases in channel width occurred between 1993 and 2006 during periods of exceptionally low annual floods. These findings illustrate that low runoff associated with regional drought and climate change may cause changes in river channel form that accelerate and compound the effects of upstream water development. Declining peak flows have also resulted in disconnection between the wetted channel and floodplains, where inundated back‐levee depressions provide habitat used by two species of threatened and endangered native fish. Despite this disconnection, some back‐levee depressions on the floodplain continue to be inundated by ~1.5‐year recurrence floods via connections created by tributary mouths, floodplain outflow channels, and levee breaches excavated by resident beaver. These changes are shown by analysis of aerial images, high‐resolution bathymetric and topographic measurements, and 2‐dimensional streamflow modeling. [ABSTRACT FROM AUTHOR]

Since 1968 when the Kainji dam was built on the R. Niger in Nigeria, many other large dams, and more than 10 formal, large‐scale irrigation schemes have been constructed in the R. Niger drainage basin. By the early 1990s, a perception had developed in the Niger Delta, the floodplain and tidal region comprising the terminal distributaries of the R. Niger, that the operations of these dams and upstream land use have caused a marked reduction in river discharges in the Delta. Concurrently with the dam construction era (1964–1995), there was a 30‐year (1968–1998) drought particularly in the Sudan‐Sahel Zone of West Africa, a significant section of the R. Niger drainage basin. This negatively impacted the flow regime in the Delta. The long‐term low flow regime appears to have influenced the direction of settlement growth in the region. Rainfall started reverting to pre‐drought levels circa 1995, promoting spate flows on the R. Niger, its tributaries and the Delta. The consequence has been debilitating quasi‐annual flooding also perceived in the Niger Delta as another result of dam operations. This study attempts to elucidate the cause of flooding in the Niger Delta, and particularly the roles of dam operations, local rainfall, and direction of settlement growth on the flooding phenomena. Flooding and flood impact mitigating solutions are proffered. [ABSTRACT FROM AUTHOR]

Land‐surface subsidence is a major contributor to land loss in many river deltas. New approaches yielding high‐resolution data are needed to parse the relevant driving forces. In 2016, we established a novel "subsidence superstation" ∼2 km from the Mississippi River in coastal Louisiana (USA) to measure compaction in a global reference frame as a function of depth in Holocene sediments and deeper subsidence. The site features three borehole optical fiber strainmeters to obtain continuous records of displacement between ∼1.3 m below the surface and depths of ∼11, 25, and 38 m. These data are complemented by an adjacent station providing hydrologic data and near‐surface compaction. We also installed three GPS antennas, one of which is mounted to a rod cemented into the Pleistocene basement. A core from one of the boreholes provides insight into the sediment properties of the entire Holocene succession. Five years of records reveal the compaction rate in the material between 1.3 and 38 m is likely less than 0.25 mm/yr. The GPS records yield a subsidence rate of 2.5 mm/yr regardless of the depth of the anchor, thus corroborating the low compaction rates observed by the strainmeters. The new instrumental records show that current subsidence at this location is governed mostly by deformation of the Pleistocene or underlying strata rather than compaction of Holocene material, with the exception of the uppermost meter. The methodology represents an important new approach to mapping subsidence rates at varying depths, providing insight into the mechanisms governing delta subsidence. Plain Language Summary: It is important to learn about the rate and causes of land subsidence along low‐lying coastlines and deltas where a large fraction of the world's population lives. In the Mississippi Delta, sediment deposited during the last ∼11,000 years (Holocene) has gradually compacted under its own weight. Constraining the path of the Mississippi River with levees over the past century has prevented deposition of new sediment over most of the delta, causing the land surface to drop with respect to sea level, increasing the threat from inundation by seawater. We measured the compaction of a nearly 40 m thick sediment layer at one site in the Mississippi Delta using a combination of optical fiber strainmeters in boreholes to several depths and GPS antennas mounted near the land surface and to deeper points. We found that the subsidence at our site, which occurs at a rate of several mm per year, is caused by very shallow (of order 1 m) and very deep (below 40 m) processes and is not driven by compaction of the bulk of the 38 m thick Holocene layer. Key Points: First integration of multiple coastal subsidence monitoring techniques at one siteHigh‐resolution records from co‐located optical fiber strainmeters and GPS instruments corroborate one anotherThe site exhibits isostatic subsidence with a potential role of fluid extraction and negligible compaction [ABSTRACT FROM AUTHOR]

This paper deals with the simulation of inundated areas for a region of 84,000 km2 from estimated flood discharges at a resolution of 2 m. We develop a modeling framework that enables efficient parallel processing of the project region by splitting it into simulation tiles. For each simulation tile, the framework automatically calculates all input data and boundary conditions required for the hydraulic simulation on‐the‐fly. A novel method is proposed that ensures regionally consistent flood peak probabilities. Instead of simulating individual events, the framework simulates effective hydrographs consistent with the flood quantiles by adjusting streamflow at river nodes. The model accounts for local effects from buildings, culverts, levees, and retention basins. The two‐dimensional full shallow water equations are solved by a second‐order accurate scheme for all river reaches in Austria with catchment sizes over 10 km2, totaling 33,380 km. Using graphics processing units (GPUs), a single NVIDIA Titan RTX simulates a period of 3 days for a tile with 50 million wet cells in less than 3 days. We find good agreement between simulated and measured stage–discharge relationships at gauges. The simulated flood hazard maps also compare well with local high‐quality flood maps, achieving critical success index scores of 0.6–0.79. Key Points: Second‐order accurate scheme discretizing the full shallow water equations at a resolution of 2 m for a stream network of 33,880 km lengthStreamflow adjustment for regionally consistent flood peak probabilities and automatic estimation of boundary conditions for arbitrary domain tilingModel accuracy comparable to local models (critical success index scores of 0.6–0.79) [ABSTRACT FROM AUTHOR]

Floodplains of large rivers are exploited for agricultural production, industrial and municipal development, and transportation infrastructure. Recently, increased frequency of costly floods has prompted consideration of whether offsetting benefits might accrue from management of floodplains for ecosystem services. We employed a simple inundation model for 800 km of the Lower Missouri River, USA, to evaluate spatial and temporal distributions of ecological floodplain inundation metrics and how those distributions might vary with levee removal and climatic change. The model evaluates inundation at 30 × 30 m resolution on a daily basis over 82 years of record. We quantified provisioning of waterfowl habitat and potential denitrification. Spatial variability is affected by ongoing geomorphic adjustments that affect floodplain connectivity. Statistical models indicate that available floodplain area and recent aggradation are predictive of most inundation metrics. Connectivity is sensitive to climate‐change scenarios that predict increased floodplain inundation during spring waterfowl migrations; the greatest sensitivity to future climate exists where channel‐floodplain geomorphology presently enhances floodplain connectivity. Evaluation of floodplain denitrification indicates that on average, the nonleveed part of the floodplain could denitrify 0.05%–1.7% of the mean annual nitrogen load of the river. Levee removal could increase this rate to only 3.6% of the nitrogen load. The capacity of floodplain connectivity to influence certain ecosystem services is highly variable in space along the Lower Missouri River and may be appreciably influenced by climate change. Hence, decisions to optimize management of large‐river floodplains are likely to be highly location dependent. Plain Language Summary: Increased flooding on large, highly engineered rivers has prompted reconsideration of how to increase resiliency to flooding while also increasing net socioeconomic benefits. These concerns have prompted managers to consider how ecosystem services—such as provision of wildlife habitat or nutrient processing—may contribute to bottom‐line decisions about levee system designs. On the Lower Missouri River, USA, ongoing erosion and deposition along the channel exert a strong control on flooding patterns. Recognition of where and when floodplain areas flood, and a full accounting of costs and benefits of flooding, can be a useful component of floodplain management, especially when flooding potential varies substantially along the river. Key Points: Resiliency of large‐river floodplains to floods can be highly spatially variable, dependent on geomorphic channel adjustmentsFloodplain habitat for waterfowl increases significantly in areas of decreased channel conveyance and increased floodplain areaDenitrification potential, on average, is only 3.6% of N flux, showing that nutrient mitigation strategies in the floodplain are limited [ABSTRACT FROM AUTHOR]

Standards-based levee design aims to protect against events with specific probabilities, for example eliminating overtopping from a storm surge with a 1% annual exceedance probability (i.e., a "100-year" event). This allows levee segments to be analyzed independently but ignores interior dynamics and overall risk. We present and implement a framework for calculating optimal riskinformed design heights. Using this design paradigm and multi-objective evolutionary algorithms, we identify levee and floodwall design heights that minimize the total system cost and expected flood losses over 50 years. With our model, decision makers may feasibly evaluate hundreds or thousands of alternative designs over a large ensemble of future states of the world. Comparing to the existing design elevations of the Larose to Golden Meadow Hurricane Protection Project in coastal Louisiana, over multiple climate change scenarios, we identify system configurations of similar cost that reduce the expected value of discounted residual risk of 26%-73% ($8-85 million). We also achieve the same residual risk at 90%-97% of the cost of the existing system (saving $19-73 million). [ABSTRACT FROM AUTHOR]

Although hydraulic infrastructure such as levees remain important for flood risk management in the USA, France, and Quebec (Canada), there is increasing emphasis on nonstructural measures, such as regulatory flood maps, to reduce exposure and vulnerability, for example, preventing people from building in high hazard areas. One key concept related to areas protected by levees is that of "residual risk", that is, the risk from floods greater than the design standard of the levees (levee overtopping) and from levee breach. In this article, we review the legislative framework for regulatory flood maps in the USA, France, and Quebec (Canada) and compare how residual risk behind protective structures is taken into account (or not) in regulatory flood maps. We find big differences in how the USA, France and Canada manage residual risk behind the levees. While in France the area behind levees is part of the regulatory flood prone area, and land use restrictions, building codes, emergency measures and risk communication are mandatory, in the USA the area behind levees is only shown as part of the regulatory flood prone area if the levee is not accredited. In Quebec, regulatory flood maps in general follow the French approach with a few exceptions. [ABSTRACT FROM AUTHOR]

This study introduces a method for assessing the annual failure rate of levees based on information from historical floods, while also considering the return period of these past events. Also, an approach has been developed to quantify the influence of deviating conditions on failure rates. The presence of deviating conditions at failed and survived levee sections is analyzed based on satellite observations. Bayesian techniques and likelihood ratios are used to update the failure rate as a function of the presence of deviations. The river system of Sachsen-Anhalt, Germany, is used as a case study. It experienced severe floods with many levee failures in the years 2002 and 2013. It is found that the presence of geological deviations had a significant influence on the observed failure rate and that failure rate increases with the magnitude of the hydraulic loading. It is also discussed how the expected number of failures in a system during a flood event with a certain magnitude can be estimated. The results of this study can be used to further optimize soil investigations, calibrate the results of more advanced reliability analyses and complement risk assessments, particularly in data-poor environments. [ABSTRACT FROM AUTHOR]

Flooding is New Zealand's most frequent natural hazard, responsible for the highest number of declared civil defence emergencies and greatest regular economic loss. Stopbanks (levees) perform a critical flood protection function in all regions of the country. However, there have been limited and inconsistent records on the location and physical attributes of these stopbanks at a national level. Through collaboration with regional government representatives, we provide the first standardised national inventory of stopbanks, the New Zealand Inventory of Stopbanks (NZIS). The NZIS provides a standardised geospatial overview of New Zealand's 5284 km long stopbank network, enabling spatial reviews and comparisons of flood protection characteristics at national and regional scales. Around 64% of New Zealand's total stopbank length is situated within five regions (Canterbury, Waikato, Southland, Manawatu-Whanganui and Bay of Plenty), while the nation's most densely population region, Auckland, accounts for just 1.9% of the total national stopbank length. Our research uses the NZIS geospatial dataset to conduct a preliminary exposure assessment of New Zealand's stopbank network to seismic and co-seismic hazards; including proximity to known active earthquake faults, ground shaking intensities and susceptibility to liquefaction and landslides. Preliminary exposure assessments provide an example of how the NZIS can be adopted and applied. [ABSTRACT FROM AUTHOR]

Deep‐water mudstones overlying basin‐floor and slope sandstone‐prone deposits are often interpreted as hemipelagic drapes deposited during sand starvation periods. However, mud transport and depositional processes, and resulting facies and architecture of mudstones in deep‐water environments, remain poorly understood. This study documents the sedimentology and stratigraphy of basin‐floor and slope mudstones intercalated with sandstone‐prone deposits of the Laingsburg depocentre (Karoo Basin, South Africa). Sedimentologic and stratigraphic criteria are presented here to distinguish between slope and basin‐floor mudstones, which provide a tool to refine palaeogeographical reconstructions of other deep‐water successions. Several mudstone units were mapped at outcrop for 2500 km2 and investigated using macroscopic and microscopic core descriptions from two research boreholes. Basin‐floor mudstones exhibit a repeated and predictable alternation of bedsets dominated by low‐density turbidites, and massive packages dominated by debrites, with evidence of turbulent‐to‐laminar flow transformations. Slope mudstones exhibit a similar facies assemblage, but the proportion of low‐density turbidites is higher, and no repeated or predictable facies organisation is recognised. The well‐ordered and predictable facies organisation of basin‐floor mudstones suggest local point sources from active slope conduits, responsible for deposition of compensationally stacked muddy lobes. The lack of predictable facies organisation in slope mudstones suggests deposition took place in a more variable range of sub‐environments (i.e. ponded accommodation, minor gully/channel‐fills, levees). However, regional mapping of three mudstone units evidence basinward tapering and similar thicknesses across depositional strike. This geometry is consistent with the distal part of basin margin clinothems, and suggests laterally extensive mud delivery across the shelf edge combined with along‐margin transport processes. Therefore, the sedimentology and geometry of mudstones suggests that mud can be delivered to deep‐water dominantly by sediment gravity flows through point source and distributed regionally, during periods of up‐dip sand storage. These findings challenge the common attribution of deep‐water mudstones to periods of basin‐floor sediment starvation. [ABSTRACT FROM AUTHOR]

Artificial levees are anthropogenic structures designed to hydrologically disconnect rivers from floodplains. The extent of artificial levees in the contiguous United States (CONUS) is unknown. To better estimate the distribution of artificial levees, we tested several different geomorphic, land cover, and spatial variables developed from the National Elevation Dataset, the National Land Cover database, and the National Hydrology Dataset HR Plus. We used known levee locations from the National Levee Database as training data. We tested machine learning and general logistic models' ability to detect artificial levees in a 100‐year hydrogeomorphic floodplain of seven geographically diverse 8‐digit HUC basins. Random forest models outperformed other models in predicting the location of levees using variables representing geomorphic attributes, land cover, and distance from streams ranging in size between stream order one through six. To demonstrate the ability of our approach to detect unknown levees, we conducted a leave‐one‐out cross‐validation in the lower Mississippi Basin using approximately 1,100 artificial levees. This approach detected known levees constituting 94% of the total levee length in the basin. Scaling up to the CONUS, we applied a high performing (overall accuracy of 97%) random forest model using land cover and stream order variables. We detected 182,213 km of potential levees, mostly along streams of order 2–6 in the Mississippi and Missouri River Basins, indicating that the national levee database contains 20.4% of levee length. Potential levees and those documented in the national levee database modify 2% of the total length of streams in the contiguous United States. Plain Language Summary: There has been a lot of research exploring how humans have impacted river systems to include impacts from dams and roads at national and global scales. However, the study of artificial levees has been limited to local studies due to incomplete databases of levee location. Artificial levees are linear dirt mounds, built next to rivers to stop flooding of property built on floodplains. Because the location of every artificial levee is not known in the US, we do not know to what extent floodplains have been separated from their rivers. To ameliorate this, our study explores different methods to detect unknown levees and applies an algorithm that is 97% accurate to the contiguous U.S. Most levees are built within floodplains, so we limited our study to the 100‐year floodplain. We tested different types of algorithms in a limited study with variables explaining levee shape, human land cover, and distance from streams of different sizes. Then, we applied the most effective models to the contiguous U.S. We located over 182,000 km of potential levees, potential areas with artificial levees not identified in the NLD, most of which were built on smaller streams and concentrated in the Mississippi and Missouri River basins. Key Points: An incomplete database of artificial levees inhibits the study of artificial levee impacts to floodplain extent in the contiguous USADifferent methods of detecting artificial levees are tested in case study basins and in the contiguous USAThis study detects 182,000 km of potential levees, along smaller streams in the Mississippi and Missouri Basins [ABSTRACT FROM AUTHOR]

Probabilistic methods are widely adopted for residual flood hazard assessment in flood‐prone areas protected by levees. Such methods can consider various sources of uncertainty, including breach location and flood event characteristics, and allow for the quantification of the result confidence. However, the possible occurrence of multiple levee breaches during the same flood event is usually disregarded. This paper presents a probabilistic method based on levee fragility functions and basic probability rules to estimate the probability of selected breach scenarios, including multiple breaching events. The flood hazard classification is based on inundation variables calculated for flood events of different return periods. A combined 1D‐2D hydrodynamic model is used for flood simulations. Probabilistic inundation extent maps and probabilistic flood hazard level maps are then created. Finally, probabilistic flood hazard estimates are summarized in a map of a suitable central tendency of the hazard level, coupled with a map of the Shannon entropy as an uncertainty indicator. This pair of statistical maps provides concise and effective information on a reference flood hazard along with the associated uncertainty. The method was applied to a region located along the middle reach of the Po River (northern Italy). Comparable central flood hazard estimates are obtained for the two sets of breaching events including or not including multiple breaches, with higher uncertainty if multiple breaches are considered. This result highlights the importance of considering multiple breaching events in flood risk management. Key Points: A probabilistic method is presented for flood hazard mapping in flood‐prone areas protected by levees, considering multiple breachesBreach scenario probabilities for selected return periods are estimated using levee fragility functions and basic probability rulesA "central" hazard level map and an entropy index map are introduced to summarize probabilistic information on flood hazard [ABSTRACT FROM AUTHOR]

While levees are typically the focus of attention during floods, and higher levees are commonly demanded by the public for flood protection, levees alone cannot manage floods. Flood diversions take water from a flooding river to reduce stage in the main river, diverting excess flow to another location, often providing important ecological functions. Flood diversions are critically important complements to levees in managing floods on the Mississippi and Sacramento rivers, and elsewhere, with early examples going back 3000 years. Diversions range widely in design and function, so we propose a typology: flood bypasses, reconnected floodplains, compound channels, backwaters, distributaries, and inter‐basin transfers. Flood bypasses route floodwaters around critical reaches, rejoining the river downstream; they can be tunnels and hard‐engineered channels or wide areas of floodplain designated to convey flood flows, along a continuum of increasing residence time, greater potential for ecological benefit, but also greater land requirements. Managing the flow split (bifurcation) at the start of the flow diversion can be tricky. The flow split will depend on the angle and elevation difference between main channel and diversion, and can be affected by land subsidence, deposition of sediment, and accumulation of debris in either channel or control structures. One of the greatest challenges is keeping flow paths in the diversion free of development incompatible with inundation, but as these are often private lands and local governments are reluctant to withhold building permits, it has proved difficult to prevent such development, especially when the diversion is active only rarely. This article is categorized under: Engineering Water > Sustainable Engineering of WaterWater and Life > Conservation, Management, and AwarenessScience of Water > Water Extremes [ABSTRACT FROM AUTHOR]

Damaging storm events frequently impact the Texas coast. In response, the US Army Corps of Engineers Galveston District (SWG) has undertaken the Sabine‐to‐Galveston (S2G) Coastal Storm Risk Management (CSRM) Project. This approximately $3.9B project includes numerous measures across several counties of the upper Texas coast, including levees, floodwalls, and pump stations. In June 2019, SWG leadership enlisted a team including the paper authors to integrate Engineering With Nature (EWN) strategies into this infrastructure project. EWN strategies intentionally align natural and engineering processes to efficiently and sustainably deliver economic, environmental, and social benefits through collaboration. The first step in this process was to develop potentially relevant EWN strategies. A collaborative workshop included visits to project sites and working sessions where the project team reviewed challenges associated with each site, generated an array of EWN strategies, and began to test design concepts based on those strategies through collaborative drawing sessions. Afterward, prioritized ideas were refined and evaluated in terms of property acquisition, estimated cost, logistics, stakeholder and sponsor interest, constructability, aesthetics, recreational opportunities, and ecological benefit. Design concepts considered feasible for integration into the broader S2G project included horizontal levees, inland floodwater storage areas that double as wildlife habitat, and strategic placement of sediment berms to reduce storm impacts and provide marsh substrate. All these concepts should achieve intended CSRM outcomes while enhancing environmental and social benefits. This assimilation of EWN strategies and landscape architecture techniques into a large CSRM study illustrates a method for expanding overall project value and producing infrastructure that benefits coastal communities. Integr Environ Assess Manag 2022;18:63–73. © 2021 SETAC KEY POINTS: The US Army Corps of Engineers Galveston District has undertaken the Sabine‐to‐Galveston (S2G) Coastal Storm Risk Management (CSRM) project along the upper Texas coast to reduce flood risk from damaging storm events that frequently impact the region. Engineering With Nature (EWN) strategies intentionally align natural and engineering processes to deliver benefits through collaboration, and this process includes developing relevant EWN strategies at a collaborative workshop; testing EWN design concepts based on those strategies; and evaluating them based on their intended benefits. Design concepts feasible for integrating into the S2G project that would achieve intended CSRM outcomes while enhancing co‐benefits included horizontal levees, inland floodwater storage areas that provide wildlife habitat, and strategic sediment placement that reduces storm impacts. This assimilation of EWN strategies and landscape architecture techniques into a large CSRM study illustrates a method for expanding overall project value and producing infrastructure that benefits coastal communities. [ABSTRACT FROM AUTHOR]

Distal slope and basin depositional systems in deep waters of the Pará‐Maranhão Basin, Equatorial Brazil, are investigated using a high‐resolution 3D seismic volume, borehole data and multispectral satellite imagery. A Neogene calciclastic submarine fan and a series of channel‐levee systems are analysed at water depths of 100–3,500 m. Channel‐levee systems have sinuous and straight morphologies and are of different sizes. Their origin is related to turbidity flows sourced and funnelled from the carbonate shelf to submarine canyons and gullies, as well as from areas with marked slope instability. A mixed calciclastic‐siliciclastic sediment input is recognised with autochthonous calcarenites and calcilutites comprising the bulk of sediment on the mid and outer continental shelf. Minor amounts of siliciclastic sediment sourced from small rivers occur on the inner shelf. Sedimentation processes of a distally steepened carbonate ramp are discussed considering a general depositional setting dominated by fluctuations in relative sea‐level. Cross‐sectional and planar parameters of mixed calciclastic‐siliciclastic channel‐levee systems are compared to their siliciclastic counterparts. Morphological results show similarities between calciclastic and siliciclastic channel‐levee systems. As a corollary, three types of channel‐levee systems are described: (a) channels related to calciclastic submarine fans, (b) low‐sinuosity, aggradational channels, and (c) high‐sinuosity channels. [ABSTRACT FROM AUTHOR]

1. Nest mounds are an integral part of many subterranean insect species, and they aid in thermoregulation, gaseous exchange, and flood prevention. Ants living in subterranean nests are prone to nest flooding particularly during monsoons and this will impact the colonies' fitness. 2. Diacamma indicum is a tropical Ponerine ant species that lives in simple, single‐chambered nests with a single entrance. In this study, we characterised the mound architecture and performed field experiments to check functional significance of mounds. 3. On examining mound architecture (n = 19 nests), we found that mounds not only elevated the nest entrance by 3.39 cm on average, but they also made the entrance at the top of the mound significantly smaller than the nest entrance at the base of the mound. Both these features are likely to reduce rainwater from falling directly into the nest's entrance tunnel. 4. Upon performing partial (n = 18 nests) and complete destruction (n = 20 nests) in two different seasons, colonies were observed to actively rebuilt mounds to pre‐destruction levels within 3 days in all cases. 5. Furthermore, examining the amount of water that entered the nest upon flooding in the presence and absence of mounds (n = 18 colonies) revealed that mounds prevented a minimum of 29.2% of water from seeping into the nest from the surrounding area, as mounds could act as a levee. This study highlights the active architectural adaptations to flooding by an organism that dwells in subterranean nests in a tropical habitat. [ABSTRACT FROM AUTHOR]