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Electrical resistivity tomography (ERT), a geophysical imaging method, is commonly used on flood embankments (dykes or levees) to characterize their internal structure and look for defects. These surveys often use a single line of electrodes to enable 2-D imaging through the embankment crest, an approach that enables rapid and efficient surveying compared to 3-D surveys. However, offline variations in topography can introduce artefacts into these 2-D images, by affecting the measured resistivity data. Such topographic effects have only been explored on a site-specific basis. If the topographic effects can be assessed for a distribution of embankment geometries (e.g. slope angle and crest width) and resistivity variations, it would allow for targeted correction procedures and improved survey design. To investigate topographic effects on ERT measurements, we forward-modelled embankments with different trapezoidal cross-sections sat atop a flat foundation layer with contrasting resistivity values. Each was compared to a corresponding flat model with the same vertical resistivity distribution. The modelling workflow was designed to minimize the effect of forward modelling errors on the calculation of topographic effect. We ran 1872 unique embankment forward models, representing 144 geometries, each with 13 different resistivity contrasts. Modelling results show that offline topography affects the tested array types (Wenner–Schlumberger, Dipole–Dipole and Multiple–Gradient) in slightly different ways, but the magnitudes are similar, so all are equally suitable for embankment surveys. Three separate mechanisms are found to cause topographic effects. The dominant mechanism is caused by the offline topography confining the electrical current flow, increasing the measured transfer resistance from the embankment model. The two other mechanisms, previously unidentified, decrease the measured transfer resistances from the embankment model compared to a layered half-space but only affect embankments with specific geometries and resistivity distributions. Overall, we found that for typical embankment geometries and resistivity distributions, the resistivity distribution has a greater control on the magnitude of the topographic effect than the exact embankment geometry: the subsurface resistivity distribution cannot be neglected. 2-D inversions are suitable when both the embankment is more resistive than the foundations and when the embankment's cross-sectional area is greater than 4 m2 m−2 (area scaled to an embankment with a height of 1 m). Topographic corrections, 3-D data acquisition or 3-D forward models are required when these conditions are not met. These are demonstrated using field data from an embankment at Hexham, Northumberland, UK. Improving the accuracy of the resistivity values in ERT models will enable more accurate ground models, better integration of resistivity data with geotechnical data sets, and will improve the translation of resistivity values into geotechnical properties. Such developments will contribute to a better characterized and safer flood defence network. [ABSTRACT FROM AUTHOR]

Currently, the alarm functions of existing levee seepage monitoring systems are limited to single-parameter monitoring and lack rate-of-change alarms and correlation alarms. This can lead to false alarms, missed alarms, equipment failures, or unnecessary downtime. To enhance the intelligence of levee safety monitoring and seepage alarms, a levee seepage intelligent alarm system based on a Bidirectional Long Short-Term Memory (BILSTM) network model was designed and implemented. Firstly, data cleaning and preprocessing are carried out on the engineering safety monitoring operation data to reduce the influence of dirty data such as outliers and repetitive values on the accuracy of alarms. Secondly, for the correlation between the piezometric tube water levels of the levee and the Yangtze River water levels, a correlation analysis based on Mutual Information (MI) theory was conducted to minimize the effect of piezometric tube water level change delays on correlation. Finally, the BILSTM model was used to predict trends in these potentially abnormal data intervals. Based on engineering application requirements, alarm thresholds were established, and a multi-level alarm module was developed. Field operation test results show that the proposed method can accurately predict the piezometric tube water levels of levees, achieving intelligent alarms within the engineering safety monitoring system. [ABSTRACT FROM AUTHOR]

Backward erosion piping (BEP) is a leading cause of levee and dam failures and generally occurs when seepage flow breaks through a defect in the downstream low-permeability blanket layer, causing a shallow erosion channel to form and extend toward the seepage source. Unfortunately, to our best knowledge, limited research has been conducted on the effects of blanket defect properties (i.e., size or material properties) on BEP processes because of the existence of a preset exit in most experiments. In this study, a laboratory testing apparatus was designed and constructed to investigate BEP initiation with respect to the blanket defect size. During the BEP initiation process, three failure morphologies were identified within the samples: shear failure; bending failure; and bending–shear failure. The results indicated that the failure morphology and critical gradient were not only a function of the unit weight of the soil and water but also highly influenced by the geometrical proportions and thickness of the defects. The findings of this study identified measures that may be applied in the field for seepage protection against BEP. [ABSTRACT FROM AUTHOR]

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]

Microplastics are widely distributed in deep oceans, with some of the highest concentrations reported in submarine canyons, which are thought to be closely related to turbidity currents. However, the turbidity current role in microplastic transport and deposition is poorly understood. Here, we present temporal variation in microplastic abundance and settling flux from sediment trap observations on the levee of Gaoping Canyon, offshore Taiwan, where turbidity currents occur frequently. The results showed that relatively high microplastic abundance and flux were consistent with the increases of near-bottom suspended sediment concentration caused by turbidity currents. The microplastics, dominated by polypropylene (59%) and polyethylene (21%), were probably derived from Taiwan coastal resuspension and river input and then transported into the submarine canyon by typhoon- or earthquake-triggered turbidity currents. During the turbidity currents, the average microplastic abundance and flux was 4137 particles per kilogram and 40.11 particles per square meter per day, respectively, showing an increase of 49% and 270%, respectively, compared to non–turbidity current periods. The total microplastic flux during the turbidity currents accounted for ∼76% of annual flux. Our study highlights turbidity currents to be the major hydrodynamic process in regulating microplastic transport and settling in a submarine canyon. [ABSTRACT FROM AUTHOR]

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In recent years, earthquakes have caused several types of damage to residential embankments. To assess the integrity of residential embankments and ascertain necessary countermeasures following ground disasters, it is crucial to accurately define the boundary of cutting and filling. Although surface wave methods nondestructively unveil the S-wave velocity VS across a broad spectrum, there are currently no methods available to predict the boundary of cutting and filling based on VS. In this investigation, surface wave measurements were conducted in an area thought to be an embankment, according to aerial topographic interpretation. The acquired VS data were used to ascertain the soil characteristics of the unaffected residential embankment. Furthermore, the applicability of a method for predicting the boundary of cutting and fillings was examined. When the mode value of VS within the embankment was selected as the threshold for the boundary of cutting and filling, some agreement was confirmed with the outcomes calculated through aerial topographic interpretation. In addition, a straightforward technique for calculating ground subsidence based on VS was considered. It was found that it may be feasible to determine the estimated seismic settlement of residential levees swiftly and nondestructively throughout a sizable region. These results indicate that the use of the surface wave method has the potential to advance residential embankment health assessment systems. [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]

Levees/earth dams are critical infrastructures for supplementing clean water, flood management, and energy production, prone to progressive failures due to internal erosion. Current inspection methods are unable to detect internal erosion until its exterior manifestation when it is too late to prevent the often-catastrophic failures. Therefore, finding innovative methods for the early detection of internal erosion is crucial. Despite the knowledge about the general mechanism of internal erosion, its early detection (and prevention) has remained a gap. This study introduces a novel artificial intelligence (AI) method to identify the temporal patterns within the passive seismic monitoring data, which can be associated with internal erosion initiation in earth dams. The proposed approach implements Convolutional AutoEncoders, an emerging deep-learning algorithm for anomaly detection in time-series data. Through an unsupervised learning framework, the AutoEncoders are trained using passive seismic monitoring data collected from a full-scale test embankment. In addition to the approximate initiation time, this algorithm can evaluate the initiation location by identifying the first sensors demonstrating internal erosion signs. The proposed deep learning framework combined with continuous seismic monitoring can serve as a basis for developing advanced early warning systems for internal erosion in earth dams. [ABSTRACT FROM AUTHOR]

The morphometric indices (MI) have been calculated along the Gavilgarh/Salbardi Fault (G/SF) to investigate active deformation, tectonic uplift, and basin tilt to find out its impact on the late Quaternary landscape. To explore the tectonic intensity, we computed MI such as stream-length gradient index (SL), hypsometric integral (HI), transverse topographic symmetry factor (T), asymmetry factor (Af), basin elongation ratio (Re), mountain front sinuosity (Smf) and valley floor width to valley height ratio (Vf). The necessary field investigations were carried out on the evolution of the Quaternary landscape to ascertain the various morphometric indices. The evaluated values of SL, HI, Re, Smf, and Vf show the high uplift of the northern block exists as opposed to the southern block, and the tilt and asymmetric character of the basins are shown by T and Af values. The presence of sedimentary landscapes like Quaternary alluvium, triangular facets, natural levees, and boulder-pebbly beds, indicates that the area has recently experienced tectonic activity. The assessed values of MI with supporting field evidence proposed that the northern block is uplifted and the basins are tilted because of the effect of G/SF. [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]

In recent years, the increasing frequency of climate change and extreme weather events has significantly elevated the risk of levee breaches, potentially triggering large-scale floods that threaten surrounding environments and public safety. Rapid and accurate measurement of river surface velocities is crucial for developing effective emergency response plans. Video image velocimetry has emerged as a powerful new approach due to its non-invasive nature, ease of operation, and low cost. This paper introduces the Dynamic Feature Point Pyramid Lucas–Kanade (DFP-P-LK) optical flow algorithm, which employs a feature point dynamic update fusion strategy. The algorithm ensures accurate feature point extraction and reliable tracking through feature point fusion detection and dynamic update mechanisms, enhancing the robustness of optical flow estimation. Based on the DFP-P-LK, we propose a river surface velocity measurement model for rapid levee breach emergency response. This model converts acquired optical flow motion to actual flow velocities using an optical flow-velocity conversion model, providing critical data support for levee breach emergency response. Experimental results show that the method achieves an average measurement error below 15% within the velocity range of 0.43 m/s to 2.06 m/s, demonstrating high practical value and reliability. [ABSTRACT FROM AUTHOR]

The intensity of an atmospheric river (AR) is only one of the factors influencing the damage it will cause. We use random forest models fit to hazard, exposure, and vulnerability data at different spatial and temporal scales in California to predict the probability that a given AR event will cause flood damage, as measured by National Flood Insurance Program (NFIP) claims. We first demonstrate the usefulness of data-driven models and interpretable machine learning to identify and describe drivers of AR flood damage. Hazard features, particularly measures of AR intensity such as total precipitation, increase the probability of damage with increasing values up to a threshold point, after which the probability of damage saturates. Although hazard is generally the most important risk dimension across all models, exposure and vulnerability contribute up to a third of the explanatory power. Exposure and variability features generally increase the probability of damage with increasing values, apart from a few instances which can be explained by physical intuition, but tend to affect the probability of damage less for the largest AR events. Comparisons between random forest models at different spatial and temporal scales showed general agreement. We then examine limitations inherent in publicly available exposure, vulnerability, and loss data, focusing on the difference in temporal resolution between variables from different risk dimensions and discrepancies between NFIP claims and total flood losses, and describe how those limitations may affect the model results. Overall, the application of interpretable machine learning to understand the contributions of exposure and vulnerability to AR-driven flood risk has identified potential community risk drivers and strategies for resilience, but the results must be considered in the context of the data that produced them. [ABSTRACT FROM AUTHOR]

The Bounty Channel is a large-scale submarine channel system located in the eastern continental margin of New Zealand. Extending along the axis of the Bounty Trough, the channel system comprises three main tributaries (C1–C3) at its head, which merge downstream into a trunk channel leading to a terminal submarine fan. In this study, we use high-quality two-dimensional multichannel seismic data to investigate the formation and evolution of tributary channels C1 and C2. Four types of seismic facies are identified in the tributary channels: fill-type, mounded divergent, wavy, and subparallel facies. These seismic facies are correspondingly interpreted as topographic depression or channel fills, levees, sediment waves, and hemipelagic deposits. The Late Miocene tributary channels were developed above a pre-existing NE–SW-oriented depression. The Pliocene to Quaternary tributary channels are characterized by preferential development of higher levees on their left hand, and the presence of sediment waves on the lower levees of their right-hand, signaling an effect of the Coriolis force. The formation and evolution of the tributaries are primarily linked to regional tectonics, including increased convergence rate between the Pacific and Australian plates along the Alpine Fault in the Late Miocene and enhanced uplift and erosion at the Southern Alps during the Pliocene. [ABSTRACT FROM AUTHOR]

Background: Oncomelania hupensis is the exclusive intermediate host of Schistosoma japonicum in China. Snail control is an essential component of schistosomiasis elimination programme. With 70 years of continuous efforts, the range of O. hupensis had reduced significantly, but slowed down in last decades. A large number of levees against flooding were constructed along Yangtze River and its affiliated lakes in the middle and lower reaches, which influenced the hydrology and ecology in the alluvial plains. The purpose of this study was to assess the impact of levees on the distribution of O. hupensis in the middle and lower reaches of the Yangtze River. Methods: The snail habitats were digitalised by hand-held GPS system. The years for discovery and elimination of snail habitats were extracted from historical records. The accumulated snail-infested range for each habitat was calculated on the basis of annual reports. The current distribution of O. hupensis was determined by systematic and environmental sampling. The geographical distribution of levees was obtained from satellite imagery. To assess the impact of levees, the data pertaining to O. hupensis were divided into two parts: inside and outside the Yangtze River. Joinpoint regression was utilised to divide the study time span and further characterise the regression in each period. The 5-year-period moving averages of eliminated area infested by snails were calculated for the habitats inside and outside Yangtze River. The moving routes of corresponding geographical median centres were simulated in ArcGIS. Hotspot analysis was used to determine the areas with statistical significance clustering of O. hupensis density. Results: Three periods were identified according to Joinpoint regression both inside and outside Yangtze River. The area infested by O. hupensis increased in the first two periods. It decreased rapidly outside Yangtze River year over year after 1970, while that inside the Yangtze River did not change significantly. Furthermore, the latter was significantly higher than the former. It was observed that the present density of O. hupensis inside Yangtze River was lower than outside the Yangtze River. The median centre for eliminated ranges inside Yangtze River wavered between the east (lower reach) and the west (middle reach). In contrast, the median centre for eliminated ranges continuously moved from the east to the west. Conclusions: Our findings indicated that the levees had a considerable negative impact on the distribution of O. hupensis outside Yangtze River. Some hotspots observed in the irrigation areas need a sluice system at the inlet of branch for snail control. The major distribution of O. hupensis located in Hubei might be caused by severe waterlogging. The intensive surveillance should be implemented there. The biggest two freshwater lakes, the major endemic regions historically, were identified as cold spots. The long-term impact of Three Gorges Dam on the distribution of O. hupensis in the lakes should be monitored and evaluated. [ABSTRACT FROM AUTHOR]

Seepage is a typical hydraulic factor that can initiate the breaching process in a levee system. If not identified and treated on time, seepages can be a severe problem for levees, weakening the levee structure and eventually leading to collapse. Therefore, it is essential always to be vigilant with regular monitoring procedures to identify seepages throughout these levee systems and perform adequate repairs to limit potential threats from unforeseen levee failures. This paper introduces a fully convolutional neural network to identify and segment seepage from the image in levee systems. To the best of our knowledge, this is the first work in this domain. Applying deep learning techniques for semantic segmentation tasks in real-world scenarios has its own challenges, especially the difficulty for models to effectively learn from complex backgrounds while focusing on simpler objects of interest. This challenge is particularly evident in the task of detecting seepages in levee systems, where the fault is relatively simple compared to the complex and varied background. We addressed this problem by introducing negative images and a controlled transfer learning approach for semantic segmentation for accurate seepage segmentation in levee systems. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of removing 3D effects as one of the most challenging problems related to 2D electrical resistivity tomography (ERT) monitoring of embankment structures. When processing 2D ERT monitoring data measured along linear profiles, it is fundamental to estimate and correct the distortions introduced by the non-uniform 3D geometry of the embankment. Here, I adopt an iterative 3D correction plus 2D inversion procedure to correct the 3D effects and I test the validity of the proposed algorithm using both synthetic and real data. The modelled embankment is inspired by a critical section of the Parma River levee in Colorno (PR), Italy, where a permanent ERT monitoring system has been in operation since November 2018. For each model of the embankment, reference synthetic data were produced in Res2dmod and Res3dmod for the corresponding 2D and 3D models. Using the reference synthetic data, reference 3D effects were calculated to be compared with 3D effects estimated by the proposed algorithm at each iteration. The results of the synthetic tests showed that even in the absence of a priori information, the proposed algorithm for correcting 3D effects converges rapidly to ideal corrections. Having validated the proposed algorithm through synthetic tests, the method was applied to the ERT monitoring data in the study site to remove 3D effects. Two real datasets from the study site, taken after dry and rainy periods, are discussed here. The results showed that 3D effects cause about ±50% changes in the inverted resistivity images for both periods. This is a critical artifact considering that the final objective of ERT monitoring data for such studies is to produce water content maps to be integrated in alarm systems for hydrogeological risk mitigation. The proposed algorithm to remove 3D effects is thus a rapid and validated solution to satisfy near-real-time data processing and to produce reliable results. [ABSTRACT FROM AUTHOR]

The principle of detecting seepage anomalies in water-retaining earthen structures through temperature monitoring has yet to gain extensive acceptance in modern field applications. As such, this study demonstrated the practical detection of seepage anomaly from fiber optic distributed temperature sensing (DTS) through physical and numerical modeling. A high-resolution DTS, capturing temperature at a sub-cm interval, was embedded in a laboratory-scale earth dam featuring normal and anomalous seepage conditions (induced by artificial defect). Then, a fluctuating reservoir thermal load was applied, and the internal temperature of the dam was monitored. Evaluation of the temperature lag time showed a quicker detection of temperature changes on the DTS sensing locations traversed by the anomalous seepage flow. The disparity in temperature lag times across the DTS increased significantly when a severe seepage anomaly was induced by systematically channeling the reservoir water directly into the artificial defect through a small tube tapping into the reservoir. Further insight into the heat-seepage interaction was achieved through coupled hydrothermal numerical modeling using COMSOL Multiphysics. Numerous dam and levee failures worldwide linked to poor conditions and erosion have caused much damage and loss of life. This study practically demonstrated temperature analysis as a robust indicator for identifying potential issues related to seepage in earthen water infrastructures, such as dams and levees. This methodology facilitates efficient early detection, allowing for proactive intervention to avert potential failures and improve public safety. Moreover, the research findings are expected to lay the groundwork for a proof of concept, cultivating an improved understanding and appreciation of the technique among practicing engineers. Building on the success of this study, future laboratory investigations are planned to explore deeper into seepage-heat interactions and optimize the technique for enhanced practical applications, including determining factors such as the ideal location and embedment depth for the distributed temperature sensing system. [ABSTRACT FROM AUTHOR]

In this paper, the use of vacuum consolidation to improve soft ground and increase its undrained shear strength (Su) is discussed. Since peat and organic clay have very low Su values, the construction of embankments and structures on these soils often cause ground failure. For the trial embankment conducted in this research project, soft ground composed of peat, organic clay and clay was improved by using vacuum consolidation, resulting in a significant increase in Su values, and an embankment 10.7 m high could be constructed on the improved ground without causing ground failure. It was demonstrated that the increased Su was the result of synergy of the relatively high normalised strength (Su/σ′v, where σ′v is the effective overburden stress) of peat and organic clay, and the unique loading mechanism of vacuum consolidation. It was also demonstrated that in the case of a relatively narrow embankment (e.g. road embankment and river levee), the effect of isotropic consolidation also contributes to increase the stability of the vacuum consolidated peaty ground. It was also found that if the (Su/σ′v)NC of the original ground and the overconsolidation ratio are known, the (Su/σ′v)OC of the given ground overconsolidated by vacuum consolidation can be predicted. [ABSTRACT FROM AUTHOR]

This technical paper investigates the influence of sample size and geologic characteristics on the geotechnical design of levee embankments. Sample quality plays a vital role in quantifying engineering properties for levee embankment projects, and numerous studies have highlighted the impact of sample disturbance on such engineering properties. Despite this evidence, conventional tube and piston samplers of different diameters continue to be widely used, potentially leading to underestimation of shear strength. The paper focuses on comparing 7.6 cm and 12.7 cm diameter undisturbed Shelby tube samples and CPT data collected from three levee sites in the Greater New Orleans Area, Louisiana, USA, which encompass diverse geologic histories. The study aims to assess the effect of industry used samples size and geology on levee construction costs. The findings provide valuable insights into optimizing sample collection methods and improving geotechnical design for earthen embankments. [ABSTRACT FROM AUTHOR]

Floodplain societies decide whether to protect themselves against floods (fight), live with floods (adapt), or adopt an approach that represents some combination of the two. The formation of a levee system is an important factor in determining whether a society fights or adapts to floods; however, these factors have been considered fixed boundaries in previous studies in human–flood interactions. We analyze a levee system transformation process covering the past century, from the indigenous ring-type levee system with floods to modern continuous levees against floods in the Kiso River basin in Japan by applying a historical sociohydrological approach. The results show degradation processes of the indigenous levee system and traditional communities alongside the installation of modern continuous levees, and a trade-off relationship was observed between the lengths of both. There are interactions between the levee systems and the human–water system through various water uses and different-scale components, and the dynamics within the region are connected to external socioeconomic trends through the installed modern levees and institutions. [ABSTRACT FROM AUTHOR]

The river levee settlement derived from shield tunnel excavation face instability is an anticipated safety issue. Serious engineering safety hazards may occur if it is not restricted. Thus, this study selected six influence indicators to quantify the stability level of the excavation face using the AHP-Fuzzy method. A database of the levee settlement prediction indicators containing tunneling speed, supporting pressure, grouting pressure, horizontal distance, lagging distance, and stability coefficient of excavation face was built by collecting 60 samples from a river-crossing shield tunnel project in China. Five models were carried out for predicting the levee settlement, i.e., modified Peck formula, RF, SVM, BPNN, and PSO-BPNN. Their prediction performance was verified by comparing the prediction results with the measured ones in a shield tunnel engineering application. The analytical results indicated that the PSO-BPNN model has the highest correlation coefficient, i.e., 0.8831(in training) and 0.8657(in testing) and the lowest error, i.e., RMSE = 1.901, and MAE = 0.8412, respectively. Thus the PSO-BPNN model has the best ability to capture the nonlinear relationship between the independent and dependent variables compared with the abilities of the RF, SVM, and BPNN model in this case study. The modified Peck formula performed unsatisfactory results (RMSE = 3.2588, MAE = 3.1172). The correlation analysis results of the input characteristic parameters of the model also indicate that the stability of the levee settlement is significantly related to the excavation face stability. The results indicate that the hybrid model is a very useful and powerful means to investigate the levee settlement caused by shield tunneling and can be improved by gathering more data from tunneling operations over time. [ABSTRACT FROM AUTHOR]

A rainfall-induced debris flow occurred on 30 September 2022, closing the A87 trunk (strategic) road on the Isle of Skye for around 2 h. Ground-based and aerial drone inspections were used to describe the event and a comprehensive rainfall analysis was undertaken. It is concluded that the event was triggered by overland water flow from the slopes above the source zone as a result of high rainfall. The resulting translational slide transitioned into a debris flow that reached a pre-existing channel where entrained superficial deposits were deposited, adding to pre-existing levee structures before reaching the road. The rainfall that led to the debris flow was high intensity–low duration; the rainfall analysis encompasses annual, monthly, daily, hourly and 15 min data, each aiding understanding of the climate of the area and/or the event rainfall. Comparison is made with a rainfall event the following month, which was of a greater magnitude but of longer duration and lower intensity. The hazard at this location is a concern but the risk is emphasized by the proximity of the road to the steep slopes above and the lack of a viable detour. Thematic collection: This article is part of the Geo-resilience and infrastructure collection available at: https://www.lyellcollection.org/topic/collections/geo-resilience-and-infrastructure [ABSTRACT FROM AUTHOR]

The two-dimensional gravity-driven motion of a relatively dense viscous liquid at the base of a granular mush is investigated using a model that exploits the relative shallowness of the flow. The granular mush obeys a $\mu (I)$ -rheology, and we assume that the two phases are segregated throughout the motion. The viscous liquid spreads under gravity, carrying the granular mush above and transporting it outwards as levees at either end of the flow. The accumulation of granular material away from the centre of the deposit produces hydrostatic pressure gradients that retard the viscous gravity current. At later times, the granular mush is quasi-static relative to the moving liquid owing to the balance of outward granular transfer by the liquid and inward hydrostatic pressure gradients associated with the granular free surface. The viscous liquid exhibits a Poiseuille-like flow structure with negligible velocity at both the base and the granular interface. The flow of a fixed volume of viscous liquid becomes self-similar with the effective viscosity quadrupled relative to a classical viscous gravity current owing to the retarding effects of the granular mush. The case of constant input flux of viscous liquid is also analysed. The qualitative features are akin to the fixed volume case with the granular mush forming levees and slowing the viscous spreading. The case in which the upper medium is a Bingham material rather than a granular mush is also discussed, and the same features are observed, demonstrating the importance of the yield criterion in the upper medium. [ABSTRACT FROM AUTHOR]

The authors of the discussed paper presented an interesting study in which a moat is introduced just downstream of an overflowing levee for reducing the energy of the overflowing water. The authors investigated the effect of the geometric parameter of the moat downstream of the overflowing levee on its hydraulic characteristics and energy reduction. The Reynolds-Averaged Navier-Stokes and Volume of Fluid methods were implemented to simulate and measure water depths and flow structures in order to optimize the geometric parameters of the moat, including dimensionless depths and lengths, and then to explore the effect of downstream slope, upstream slope, levee crest length, and levee height on energy reduction. Following the turbulence model validation and mesh convergence analysis were both satisfactory, an enormous amount of numerical simulations for overflowing levees with a moat under various hydraulic circumstances were conducted. The present discussion paper shows that when the dimensionless overflow depth is less than 0.81, the ideal dimensionless length of the moat is 1.50 and the optimal dimensionless depth is 0.35, which may fulfill energy dissipation requirements while saving construction costs. Moreover, when the dimensionless overflow depth is larger, it can be beneficial to reduce downstream energy by improving the overflow levee structure, which primarily involves steepening the upstream slope, reducing the downstream slope, increasing the levee crest length, and decreasing the levee height. However, when the dimensionless overflow depth decreases, the effect of these factors diminishes gradually. [ABSTRACT FROM AUTHOR]

Coastal flood risk is a serious global challenge facing current and future generations. Several disaster risk reduction (DRR) measures have been posited as ways to reduce the deleterious impacts of coastal flooding. On a global scale, however, efforts to model the future effects of DRR measures (beyond structural) are limited. In this paper, we use a global-scale flood risk model to estimate the risk of coastal flooding and to assess and compare the efficacy and economic performance of various DRR measures, namely dykes and coastal levees, dry-proofing of urban assets, zoning restrictions in flood-prone areas, and management of foreshore vegetation. To assess the efficacy of each DRR measure, we determine the extent to which it can limit future flood risk as a percentage of regional GDP to the same proportional value as today (a "relative risk constant" objective). To assess their economic performance, we estimate the economic benefits and costs of implementing each measure. If no DRR measures are implemented to mitigate future coastal flood risk, we estimate expected annual damages to exceed USD 1.3 trillion by 2080, directly affecting an estimated 11.5 million people on an annual basis. Low- and high-end scenarios reveal large ranges of impact uncertainty, especially in lower-income regions. On a global scale, we find the efficacy of dykes and coastal levees in achieving the relative risk constant objective to be 98 %, of dry-proofing to be 49 %, of zoning restrictions to be 11 %, and of foreshore vegetation to be 6 %. In terms of direct costs, the overall figure is largest for dry-proofing (USD 151 billion) and dykes and coastal levees (USD 86 billion), much more than those of zoning restrictions (USD 27 million) and foreshore vegetation (USD 366 million). These two more expensive DRR measures also exhibit the largest potential range of direct costs. While zoning restrictions and foreshore vegetation achieve the highest global benefit–cost ratios (BCRs), they also provide the smallest magnitude of overall benefit. We show that there are large regional patterns in both the efficacy and economic performance of modelled DRR measures that display much potential for flood risk reduction, especially in regions of the world that are projected to experience large amounts of population growth. Over 90 % of sub-national regions in the world can achieve their relative risk constant targets if at least one of the investigated DRR measures is employed. While future research could assess the indirect costs and benefits of these four and other DRR measures, as well as their subsequent hybridization, here we demonstrate to global and regional decision makers the case for investing in DRR now to mitigate future coastal flood risk. [ABSTRACT FROM AUTHOR]

Coastal levees play a role in protecting coastal areas from storm surges and high waves, and they provide important input information for inundation damage simulations. However, coastal levee data with uniformity and sufficient accuracy for inundation simulations are not always well developed. Against this background, this study proposed a method to extract coastal levees by inputting high spatial resolution optical satellite image products (RGB images, digital surface models (DSMs), and slope images that can be generated from DSM images), which have high data availability at the locations and times required for simulation, into a deep learning model. The model is based on U-Net, and post-processing for noise removal was introduced to further improve its accuracy. We also proposed a method to calculate levee height using a local maximum filter by giving DSM values to the extracted levee pixels. The validation was conducted in the coastal area of Ibaraki Prefecture in Japan as a test area. The levee mask images for training were manually created by combining these data with satellite images and Google Street View, because the levee GIS data created by the Ibaraki Prefectural Government were incomplete in some parts. First, the deep learning models were compared and evaluated, and it was shown that U-Net was more accurate than Pix2Pix and BBS-Net in identifying levees. Next, three cases of input images were evaluated: (Case 1) RGB image only, (Case 2) RGB and DSM images, and (Case 3) RGB, DSM, and slope images. Case 3 was found to be the most accurate, with an average Matthews correlation coefficient of 0.674. The effectiveness of noise removal post-processing was also demonstrated. In addition, an example of the calculation of levee heights was presented and evaluated for validity. In conclusion, this method was shown to be effective in extracting coastal levees. The evaluation of generalizability and use in actual inundation simulations are future tasks. [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]

Managing the levee system of a river network is an essential aspect to reduce the flood risk and protect communities and urbanised areas. Too many times, the viewpoint of the managing institution in charge of the restoration of river levees is of an emergency type so that the restoration works are conducted only after flood occurrence, without the consideration for a complete and necessary overview of priority criteria at a basin scale. The present work aims to develop a basin-scale methodology to analyse the current state of the Ombrone Pistoiese River (Italy) levees, so as to identify targeted solutions for breakage prevention. By applying a vulnerability index, producing maps of flooded areas and counting the exposed elements induced by levees breaks, this study wants to provide a decision support procedure able to define a priority scale of interventions. [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]

Levees founded on peaty organic soils in the Sacramento-San Joaquin Delta region of California are vital infrastructure that supply much of the state with fresh drinking water and protects Delta islands from inundation. Therefore, the damage or breach of a levee as a result of an earthquake has the potential for catastrophic impacts. Peaty-organic soils affect the seismic demand and ground deformation potential associated with risk assessment, but existing ground motion models (GMMs) are not calibrated for such soft soils. In this ongoing study, we develop empirical data on small-strain site amplification in the Delta through expansion of the NGA-West2 ground motion database and investigate and adjust an NGA-West2 GMM for regional path effects. A regional site response model is developed using a dataset developed from 45 instrumented sites located within the Delta, as well as 55 sites outside of the Delta. The combination of accounting for regional path effects and local site response holds the potential to significantly improve GMM predictions and significantly reduce epistemic uncertainty.

Two-dimensional (2D), depth-averaged shallow water equation (SWE) models are routinely used to simulate flooding in coastal areas – areas that often include vast networks of channels and flood-control topographic features and/or structures, such as barrier islands and levees. Adequately resolving these features within the confines of a 2D model can be computationally expensive, which has led to coupling 2D simulation tools to less expensive one-dimensional (1D) models. Under certain 1D–2D coupling approaches, this introduces internal constraints that must be considered in the generation of the 2D computational mesh used. In this paper, we further develop an existing automatic unstructured mesh generation tool for SWE models, ADMESH+, to sequentially (i) identify 1D constraints from the raw input data used in the mesh generation process, namely the digital elevation model (DEM) and land–water delineation data; (ii) distribute grid points along these internal constraints, according to feature curvature and user-prescribed minimum grid spacing; and (iii) integrate these internal constraints into the 2D mesh size function and mesh generation processes. The developed techniques, which include a novel approach for determining the so-called medial axis of a polygon, are described in detail and demonstrated on three test cases, including two inland watersheds with vast networks of channels and a complex estuarine system on the Texas, USA, coast. [ABSTRACT FROM AUTHOR]

In the low-lying, river-rich Pearl River Delta in South China, an extensive network of flood defense levees, spanning over 4400 km, plays a crucial role in urban flood management. These levees are designed to withstand floods and storm surges, yet their failure can lead to significant human and economic losses, highlighting the need for robust urban flood defense strategies. This necessitates the development of a sophisticated geographic information system for the levee network and rapid, accurate assessment methods for levee conditions to support water management and flood mitigation efforts. This study focuses on the levees along the Hengmen waterway in the Pearl River Delta, utilizing airborne Light Detection and Ranging (LiDAR) technology to gather 3D spatial data of the levees. Employing the Cloth Simulation Filter (CSF) algorithm, non-ground point cloud data were extracted. The study improved upon the region-growing algorithm, using a seed point set approach for the automatic extraction of levee point cloud data. The accuracy and completeness of levee extraction were evaluated using the quality index. This method achieved effective extraction of four levee types, showing significant improvements over traditional algorithms, with extraction quality ranging from 72% to 83%. Key research outcomes include the development of a novel method for detecting localized levee depressions based on the computation of the variance of angles between normal vectors in single-phase levee point cloud data. An adaptive optimal neighborhood approach was utilized to accurately determine the normal vectors, effectively representing the local morphology of the levee point clouds. Applied in three levee depression detection experiments, this method proved effective, demonstrating the capability of single-phase data in identifying regions of levee depression deformation. This advancement in levee monitoring technology marks a significant step forward in enhancing urban flood defense capabilities in regions such as the cities of the Pearl River Delta in China. [ABSTRACT FROM AUTHOR]

Earthen levees are critical civil infrastructure of coastal regions for flood protection. Earthquakes can cause significant deformation and damage to earthen levees. Seismic performance of such levees under the earthquake hazards is a major concern in their safety evaluation. However, there are significant uncertainties in assessing the seismic behavior of earthen levees and geotechnical uncertainties play a critical role in the probabilistic assessment of earthquake-induced deformation and failures. This paper presents a simplified probabilistic framework for assessing the seismic performance of earthen levees with dynamic analysis and finite element modeling. In this framework, the effects of geotechnical uncertainties are explicitly considered in the uncertainty propagation for probabilistic evaluation of seismic deformations of earthen levees under earthquake hazards. The probability curves are developed to describe the correlations among the probability of exceedance, limiting deformation value, and input peak ground acceleration. The derived probability curves can provide valuable information for risk assessment and risk-informed decision-making of earthen levee infrastructure. The effectiveness of the proposed probabilistic framework is demonstrated through a case study of earthen levee example. [ABSTRACT FROM AUTHOR]

Breach geometry is one essential feature for flood modelling in the channel–levee–floodplain system. It is hard to accurately predict the breach geometry because of its high uncertainty. However, due to the fact that breach geometry direct impacts the flow through the breach, the water surface profile in the channel and the flood hazard factors within the floodplain are changed with the breach geometry. To explore the impacts of breach width (one feature of the breach geometry) on the channel–levee–floodplain system, we took the Cinan Feiyou Flood Control Protection Area (CNFY-FCPA) in the middle reach of the Huaihe River Basin as the study area. We constructed a coupled 1D-2D hydrodynamic model to simulate the flooding with a series of breach-width scenarios. According to the simulation results of the models, we quantitatively analyzed the impacts of breach width on the inflow through the breach, fluvial flood process, and flood hazard factors in the CNFY-FCPA. The results indicate that (i) the relationship between the peak discharge (and inflow volume) and breach width was approximate to an S-shaped curve, while the peak discharge, inflow volume, and duration per unit width decreased with the wider breach; (ii) the breach caused a decrease in the water surface profile along the entire river sections; and (iii) while the breach width exceeded a certain width, the inundation area was nearly stable without changing with wider breach. The certain width was not the same in different rivers of 300 m in the Yinghe River and of 500 m in the Huaihe River. The research results can provide a scientific basis for flood-control and disaster-reduction decision making. [ABSTRACT FROM AUTHOR]

In this study, overtopping-induced levee breach experiments were conducted to explore the effect of differences in levee structure on levee breach characteristics, considering the heterogeneity of the levee material and the flow outside the levee. A homogeneous levee composed of silica sand No. 7 and a heterogeneous levee composed of silica sand No. 5 and No. 7 overlapped by two levees were subjected to overtopping-induced levee breaches in the presence of flow outside the dike. Comparison of these processes revealed that the downstream progress of erosion is more plausible than the upstream side due to flow outside the levee. The shape of the breach opening was different during the levee breach process between the levee made of a heterogeneous structure and that made of a single material. Moreover, the rate of widening of the breach opening on the back slope increased at an earlier stage in the former case than in the latter, resulting in a larger overflow rate. To the best of our knowledge, few studies have simultaneously considered the heterogeneous structure of an actual levee and the flow outside the levee. [ABSTRACT FROM AUTHOR]

The stability of the ancient flood control levees is mainly influenced by water level fluctuations, groundwater concentration and rainfalls. This paper takes the Lanxi ancient levee as a research object to study the evolution laws of its seepage, displacement and stability before and after reinforcement with the upside-down hanging wells and grouting curtain through numerical simulation methods combined with experiments and observations. The study results indicate that the filled soil is less affected by water level fluctuations and groundwater concentration after reinforcement. A high groundwater level is detrimental to the levee's long-term stability, and the drainage issues need to be fully considered. The deformation of the reinforced levee is effectively controlled since the fill deformation is mainly borne by the upside-down hanging wells. The safety factors of the levee before reinforcement vary significantly with the water level. The minimum value of the safety factors is 0.886 during the water level decreasing period, indicating a very high risk of the instability. While it reached 1.478 after reinforcement, the stability of the ancient levee is improved by a large margin. [ABSTRACT FROM AUTHOR]

Decreases in shallow-water habitat area (SWHA) in the Lower Columbia River and Estuary (LCRE) have adversely affected salmonid populations. We investigate the causes by hindcasting SWHA from 1928 to 2004, system-wide, based on daily higher high water (HHW) and system hypsometry. Physics-based regression models are used to represent HHW along the system as a function of river inflow, tides, and coastal processes, and hypsometry is used to estimate the associated SWHA. Scenario modeling is employed to attribute SWHA losses to levees, flow regulation, diversion, navigational development, and climate-induced hydrologic change, for subsidence scenarios of up to 2 m, and for 0.5 m fill. For zero subsidence, the system-wide annual-average loss of SWHA is 55 ± 5%, or 51 × 105 ha/year; levees have caused the largest decrease ( 54 - 14 + 5 %, or ~ 50 × 105 ha/year). The loss in SWHA due to operation of the hydropower system is small, but spatially and seasonally variable. During the spring freshet critical to juvenile salmonids, the total SWHA loss was 63 - 3 + 2 %, with the hydropower system causing losses of 5–16% (depending on subsidence). Climate change and navigation have caused SWHA losses of 5 - 5 + 16 % and 4 - 6 + 14 %, respectively, but with high spatial variability; irrigation impacts have been small. Uncertain subsidence causes most of the uncertainty in estimates; the sum of the individual factors exceeds the total loss, because factors interact. Any factor that reduces mean or peak flows (reservoirs, diversion, and climate change) or alters tides and along-channel slope (navigation) becomes more impactful as assumed historical elevations are increased to account for subsidence, while levees matter less. [ABSTRACT FROM AUTHOR]

Floodplain societies decide whether to protect themselves against floods (fight), live with floods (adapt), or a combination of the two. The formation of a levee system is an important factor in determining whether a society fight or adapt to flood; however, these factors have been considered as fixed boundaries in previous studies in human-flood interaction. We analyse a levee system transformation process covering the past century, from the indigenous ring-type levee system with floods to modern continuous levees against floods in the Kiso River basin, Japan, by applying a historical sociohydrological approach. The results show degradation processes of the indigenous levee system and traditional communities alongside the installation of modern continuous levees, and a trade-off relationship was observed between the lengths of both. There are interactions between the levee systems and the human-water system through various water uses and different scale components, and the dynamics within the region are connected to external socioeconomic trends through the installed modern levees and institutions. [ABSTRACT FROM AUTHOR]

Investigating the sedimentary architecture and evolution of sand-rich submarine fans is vital for comprehending deep-water sedimentary processes and enhancing the success rate of hydrocarbon resource exploration. Recent drilling activities in the Qiongdongnan Basin, northern South China Sea, have unveiled significant gas hydrate and shallow gas potential. However, exploration in this area faces substantial challenges due to the limited understanding of sandy reservoirs. Leveraging extensive newly acquired extensive 3D seismic data (~9000 km²) and well data, our study reveals five distinct deep-water depositional systems in the Quaternary Ledong Formation, including a submarine fan system, mass transport deposits, deepwater channel-levee systems, slope fans, and hemipelagic sediments. Notably, the targeted sandrich submarine fan lies within the abyssal plain, situated at a water depth of 1300-1700 m. This fan exhibits a unique tongue-shape configuration and a SW-NE flow direction within the plane and spans an expansive area of ~2800 km² with maximum length and width reaching 140 km and 35 km, respectively. Vertically, the fan comprises five stages of distributary channel-lobe complexes, progressing from Unit 1 to Unit 5. Their distribution ranges steadily increase from Unit 1 to Unit 3, followed by a rapid decrease from Unit 4 to Unit 5. Our results suggest that the occurrence and evolution of the submarine fan are primarily controlled by sea level fluctuation, confined geomorphology, and sediment supply. Specifically, sea level fluctuation and sediment supply influenced the occurrence of the submarine fan. Concurrently, the confined geomorphology in the abyssal plain provided accumulation space for sediments and shaped the fan into its distinct tongue-like form. In contrast to the deepwater channels within the deepwater channel-levee systems, the distributary turbidite channels within the submarine fan are marked by lower erosion depth with "U" shapes, greater channel width, and higher ratios of width to depth. The comparative analysis identifies turbidite channels as the focal points for offshore gas hydrate and shallow gas exploration in the Qiongdongnan Basin. Furthermore, the temporal evolution of submarine fan offers valuable insights into Quaternary deep-water sedimentary processes and hydrocarbon exploration within shallow strata of marginal ocean basins. [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 Bounty Channel is a large-scale submarine channel system located in the eastern continental margin of New Zealand. Extending along the axis of the Bounty Trough, the channel system comprises three main tributaries (C1–C3) at its head, which merge downstream into a trunk channel leading to a terminal submarine fan. In this study, we use high-quality two-dimensional multichannel seismic data to investigate the formation and evolution of tributary channels C1 and C2. Four types of seismic facies are identified in the tributary channels: fill-type, mounded divergent, wavy, and subparallel facies. These seismic facies are correspondingly interpreted as topographic depression or channel fills, levees, sediment waves, and hemipelagic deposits. The Late Miocene tributary channels were developed above a pre-existing NE–SW-oriented depression. The Pliocene to Quaternary tributary channels are characterized by preferential development of higher levees on their left hand, and the presence of sediment waves on the lower levees of their right-hand, signaling an effect of the Coriolis force. The formation and evolution of the tributaries are primarily linked to regional tectonics, including increased convergence rate between the Pacific and Australian plates along the Alpine Fault in the Late Miocene and enhanced uplift and erosion at the Southern Alps during the Pliocene.

The morphology of river levees and floodplains is an important control on river-floodplain connectivity within a river system under sub-bankfull conditions, and this morphology changes as a river approaches the coast due to backwater influence. Floodplain width can also vary along a river, and floodplain constrictions in the form of bluffs adjacent to the river can influence inundation extent. However, the relative controls of backwater-influenced floodplain topography and bluff topography on river-floodplain connectivity have not been studied. We measure discharge along the lower Trinity River (Texas, USA) during high flow to determine which floodplain features are associated with major river-floodplain flow exchanges. We develop a numerical model representing the transition to backwater-dominated river hydraulics, and quantify downstream changes in levee channelization, inundation, and fluxes along the river-floodplain boundary. We model passive particle transport through the floodplain, and compute residence times as a function of location where particles enter the floodplain. We find that bluff topography controls flow from the floodplain back to the river, whereas levee topography facilitates flow to the floodplain through floodplain channels. Return flow to the river is limited to locations just upstream of bluffs, even under receding flood conditions, whereas outflow locations are numerous and occur all along the river. Residence times for particles entering the floodplain far upstream of bluffs are as much as two orders of magnitude longer than those for particles entering short distances upstream of bluffs. This study can benefit floodplain ecosystem management and restoration plans by informing on the key locations of lateral exchange and variable residence time distributions in river-floodplain systems.