Levee Failure Research Articles

Numerical Analysis of Levee Failure Characteristics for Flood Hydrograph Patterns

Recent climate change has significantly affected the magnitude and frequency of rainfall, which critically affects the safety of levees and leads to severe flooding damage when levees fail. This study aimed to analyze the impact of the shape of flood hydrographs on levee failure characteristics using numerical analysis. Three types of flood hydrographs derived from lognormal, beta, and Weibull probability density functions (PDFs) were utilized, with each showing differences in the timing and magnitude of the peak flows. Levee overtopping and failure phenomena were simulated using a three-dimensional numerical analysis model, namely, FLOW-3D. The simulation results indicate that the failure patterns of levees vary, depending on the PDF used, with the lognormal PDF showing significant levee failure, owing to relatively high initial flows. These results suggest that a rapid increase in the flow at the onset is a direct factor that causes levee failure. These numerical analysis results highlight the importance of understanding the characteristics of each probability density function to accurately predict and effectively respond to levee failure risk. Future research should focus on a more precise analysis of levee failure mechanisms as well as the propagation and impacts of flood waves resulting from such failures.

Effect of Seepage on Sand Levee Failure Due to Lateral Overtopping

Recent increases in rainfall duration and intensity due to climate change have heightened the importance of levee stability. However, previous studies on levee failure, primarily caused by seepage and overtopping, have mostly examined these causes independently owing to their distinct characteristics. In this study, we conducted lateral overtopping failure experiments under seepage conditions that closely resembled those in experiments conducted in previous studies. Seepage was monitored using water pressure sensors and a distributed optical fiber cable that provided continuous heat for temperature monitoring in the levee. Τhe analysis of levee failure due to lateral overtopping, in the presence of seepage, was conducted using image analysis with digitization techniques and machine learning-based color segmentation techniques on the protected lowland side of the levee, targeting the same area. The results revealed that levee failure occurred more than twice as fast in experiments where seepage conditions were considered compared to the experiments where they were not. Thus, levees weakened by seepage are more vulnerable to overtopping and breaching. Consequently, employing a comprehensive approach that integrates various monitoring and analysis methods for assessing levee stability is preferable to relying on a single method alone.

Integrating Multiple Levee-Breaching Scenarios and Flood Events to Develop a Probabilistic Spatial Flood-Hazard Map of Etobicoke Creek in Toronto, Canada

Forecasting flood characteristics (e.g., water levels and velocity) is a growing concern due to climate change. It is therefore necessary to consider the stability conditions of earthen levees used to mitigate floods during a flood risk assessment. This technical note presents a method to assess probabilistic flood hazard that takes into account levee failures, for a levee located along Etobicoke Creek in Toronto, Canada. We compute flood scenario probabilities resulting from multiple flood scenarios that accounts for both the levee failures across the length of the levee, and different levee-failure mechanisms (e.g., backward erosion and overtopping). Then, for each location of the flooded area, we compute a cumulative flood exceedance probability curve for flood depth and velocity. This method provides a flood-hazard map (depth and velocity) for a given probability and probabilistic maps for given values of depth or velocity.

Evaluating levee setback distance for the co-benefits of groundwater recharge and riparian ecosystem function

Constructed levees are designed to protect anthropogenic developments from destructive flooding events, but their construction has reduced groundwater recharge, increased flood risk severity under levee failure, increased the incision of river channels, and deteriorated riparian habitat. To reverse these impacts, levee setbacks are often designed to reduce flood risk and provide the opportunity to restore ecohydrological function, while groundwater recharge is rarely considered because it may require relatively detailed groundwater system analysis. In this study, we evaluated 100 heterogeneous hydrogeology realizations to estimate recharge with high-conductivity pathways (HCPs) under varying flood flows for a range of levee setback distances to identify the trade-offs in groundwater recharge and floodplain habitat. We find that on a regional scale, total recharge potential increases with setback distance, with the largest gains up to 1,400 m where there are outcropping HCPs and sufficient flow to inundate more of the setback area. In contrast, the recharge per unit area (i.e., the average daily recharge divided by setback area) generally decreases as levee setback increases, but there are local increases in the recharge per unit area at 1,400 m where HCP recharge may sufficiently offset the larger area. There is a median 10%–40% reduction in peak streamflow with increasing setback distance, which would aid flood risk reduction, but the increased area leads to decreasing depth due to flow losses and increased spreading of flood water. Ultimately, the decision for levee setback distance will depend on local conditions and management goals, as we find that increasing recharge will reduce the floodplain depth necessary for ecosystem function. Our results highlight the opportunity to consider groundwater recharge benefits in levee setback feasibility studies in semi-arid regions impacted by floods and groundwater overdrafts so that setback distance designs can achieve integration of flood risk reduction, riparian habitat, and groundwater recharge.

From manual to UAV-based inspection: Efficient detection of levee seepage hazards driven by thermal infrared image and deep learning

Levee failures are caused mainly by river water seepage erosion inside the levee, manifesting as slope leakage and foundation piping phenomena. To address the urgent need for levee safety monitoring during flood seasons and extreme rainfall events, unmanned aerial vehicles (UAVs) equipped with thermal infrared imagers can quickly detect leakage and piping hazards based on temperature differences between damaged areas and their surroundings. In this study, we collected 5995 UAV thermal infrared images of leakage and piping on levees in four floodplains under various weather, time, and surface coverage conditions to evaluate the applicability of combining thermal infrared imaging with a deep learning model in complex natural environments. We categorized levee hazards into water piping, ground piping, and slope leakage, and developed a Mask R-CNN segmentation model. The results revealed that thermal infrared levee inspection was affected by vegetation occlusion and subtle temperature differences caused by continuous rainstorms and water body depth. The Mask R-CNN demonstrated strong generalizability to hazards with significant variability in shape, size, and temperature difference, making it suitable for detecting evolving and expanding damaged area. The mean average precision, recall, and precision of the Mask R-CNN were 0.977, 0.982, and 0.897, respectively, and the detection time was 0.015 s per image. Moreover, Eigenvector-based class activation mapping (Eigen-CAM) was used to visualize the decision basis and failure modes of the Mask R-CNN to improve interpretability. Seepage damage is a progressive process, so timely hazard identification can provide valuable time for levee repair.

Prediction of Backward Erosion, Pipe Formation and Induced Failure Using a Multi‐Physics SPH Computational Framework

ABSTRACTSeepage‐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.

Quantifying risk contagion of fluvial flood disaster chain

ABSTRACT The fluvial flood disaster (FFD) poses a great threat to human civilisation. The high water level can cause overtopping, piping, and even breach of the levees, which, in turn, further results in urban flood. These secondary disasters form a disaster chain with multipaths that amplify the risk of the fluvial flood. This work develops a stochastic multi-path network method to quantify the risk contagion for the FFD chain. First, the multi-path network structure for the chain was identified, characterised by reflecting the uncertainties of levee failure modes. Second, a model for the evolutionary probabilities of the chain was proposed by combining the directed network technique with the network structure. Finally, the systematic risk of the chain was quantified by considering the consequence of the disasters. A risk contagion factor was proposed to quantify the attenuation or amplification effect of the risk during the evolution of the chain. A case study in Huizhou, China, shows that the FFD chain is characterised by “small probability” but “extremely high risk”. The most likely path is overtopping-urban flooding, indicating the priority of the area is to heighten the levees. This work paves the way for a more entrepreneurial future on disaster prevention and mitigation.

Application of Deep Learning for Segmenting Seepages in Levee Systems

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.

Modeling the flood protection services of levee setbacks, a nature-based solution

Levee setbacks are an intuitive nature-based solution that can improve the flood protection services provided by levees and help rehabilitate levee-stressed ecosystems. Their application in professional practice is in part limited by a lack of guidance on how to size setbacks to balance different interests in floodplain land use. To help address this application barrier, we demonstrate how flood hazard and levee failure risk reduction may be modeled with a numerical hydraulic model of a leveed river in the Midwestern USA, as well as how to calculate scaling relationships between levee failure risk reduction and setback size. Our results suggest setbacks can greatly reduce the severity of flood hazards, for example, by alleviating flow bottlenecks and lowering flood heights. Our results also suggest that improvements in levee reliability scale non-linearly with setback size and exhibit diminishing returns. We conclude with a discussion of design insights and cautions to support the application of setbacks in practice.

Observation of the effect of soil-structure boundaries using transparent soil technology

The predominance of water flow at strata boundaries often triggers dam and levee failures. However, research on the porosity and water flow at soil-structure boundaries is insufficient despite the fact that the fact that their significant influence on water flows through soil is due to high porosity caused by compaction difficulties in the boundary region. Additionally, observing the interior of soil by conventional experimental methods is challenging, making it difficult to precisely determine the exact differences between the boundary area and surrounding grounds. Therefore, transparent soil techniques were employed to investigate the interior of the soil and the impact of soil-structure boundaries on flow path formation. The experiment identified two critical properties at the soil-structure boundary: relatively high porosity and the maximum average velocity of the fluid during permeability, both occurring at the interface. The good connectivity of the pores at the boundary is due to the barrier effect of the flat wall, which causes water to flow vertically upward along the boundary. In contrast, water flows meanderingly upward in the interior area of the soil, resulting in a two-dimensional movement at the boundary compared to a three-dimensional movement in the interior of the soil.

Revisiting emergencies, disasters, & catastrophes: Adding duration to the hazard event classification

Disaster researchers have long sought to classify hazard events using various characteristics. Despite varying perspectives on how hazard events differ, the most commonly used classification in disaster scholarship categorizes hazard events as either emergencies, disasters, or catastrophes, which generally are described as being distinguished based on impacts, needs, stakeholder involvement, and management approach. Although this hazard event classification is useful, disaster scholars have noted it needs further refinement and development. In an effort to address these calls from disaster scholars and create a more robust hazard event classification, the traditional classification is revisited and expanded. Specifically, this article proposes the addition of a second dimension, response duration, to the existing hazard event type classification, which to this point has largely been defined by scale of impacts, needs, stakeholder involvement, and management approach. This paper argues short and long-duration emergencies, disasters, and catastrophes are categorically different and therefore require different management approaches, and can be used to categorize and distinguish between events such as COVID-19 and Hurricane Katrina and the Levee Failure. The proposed change would have important implications for emergency management practice and policy and would encourage a re-evaluation of the kinds of hazard events considered to be part of the academic purview of emergency management.

Reducing flood risk and improving system resiliency in Sacramento, California: overcoming obstacles and emerging solutions

Sacramento, the capital of California, has a population of over 2 million and is one of the most flood prone regions in the nation. Its problems exemplify those of many urban communities built near riverine and deltaic systems, that are subject to climate change. The city and its surrounding communities are protected by an elaborate system of levees and flood bypasses; but aging infrastructure, expected increases in extreme wet weather, and projected sea level rise are increasing the risk of levee failures. We explore how flood management approaches including social/institutional (non-structural), traditional structural, and ecological based approaches are being implemented in the Lower Sacramento/North Delta Region amid significant obstacles, to build resilient flood management systems. We review four case studies, one structural levee project and three multi-benefit projects that are only recently being implemented. We also examine the barriers, constraints, and challenges for implementing flood protection projects, and how project proponents are collectively working through these obstacles. We conclude that significant progress has been made in building flood resiliency since the 2008 Central Valley Flood Protection Act and the release of the 2012 Central Valley Flood Protection Plan. Informational tools and policies are being developed to educate the public and prepare for floods. Structural levee investments are substantial and are being implemented through partnerships. Statewide policies and investments are increasingly supporting multi-benefit projects that incorporate ecological restoration/enhancement while expanding flood volume capacity. Progress on implementing multi-benefit projects has been slow, due to land acquisition, easements, funding, regulatory and construction challenges; however, solutions to these impediments are emerging to facilitate more rapid progress. It is essential to continue and intensify the progress made in the last two decades, by learning from past projects, and improving on existing pathways to implement sustainable projects at a faster rate.

Experimental Investigation of Levee Erosion during Overflow and Infiltration with Varied Hydraulic Conductivities of Levee and Foundation Properties in Saturated Conditions

This study investigated erosion during infiltration and overflow events and considered different grain sizes and hydraulic conductivity properties; four experimental cases were conducted under saturated conditions. The importance of understanding flow regimes during overflow experiments including their distinct flow characteristics, shear stresses, and erosion mechanisms in assessing the potential for levee failure are discussed. The failure mechanism of levee slopes during infiltration experiments involves progressive collapse due to piping followed by increased liquefaction and loss of shear stress, with the failure progression dependent on the permeability of the foundation material and shear strength. The infiltration experiments illustrate that the rate of failure varied based on the permeability of the foundation material. In the case of IO-E7-F5, where the levee had No. 7 sand in the embankment and No. 5 sand in the foundation (lower permeability), the failure was slower and limited. It took around 90 min for 65% of the downstream slope to fail, allowing more time for response measures. On the other hand, in the case of IO-E8-F4, with No. 8 sand in the embankment and No. 4 sand in the foundation (higher hydraulic conductivity), the failure was rapid and extensive. The whole downstream slope failed within just 18 min, and the collapse extended to 75% of the levee crest. These findings emphasize the need for proactive measures to strengthen vulnerable sections of levees and reduce the risk of extensive failure.

Non‐invasive surveys to assess animal burrows as potential causes of levee instability

AbstractAnimal 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.

A probabilistic approach to levee reliability based on sliding, backward erosion and overflowing mechanisms: Application to an inspired Canadian case study

AbstractImproving 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.

Assessing 40 Years of Flood Risk Evolution at the Micro-Scale Using an Innovative Modeling Approach: The Effects of Urbanization and Land Planning

The present work is aimed at assessing the change in time of flood risk as a consequence of landscape modifications. The town of San Donà di Piave (Italy) is taken as a representative case study because, as most parts of the North Italy floodplains, it was strongly urbanized and anthropized in the last several decades. As a proxy for flood risk, we use flood damage to residential buildings. The analysis is carried out at the local scale, accounting for changes to single buildings; GIS data such as high-resolution topography, technical maps, and aerial images taken over time are used to track how the landscape evolves over time, both in terms of urbanized areas and of hydraulically relevant structures (e.g., embankments). Flood hazard is determined using a physics-based, finite element hydrodynamic code that models in a coupled way the flood routing within the Piave River, the formation of levee failures, and the flooding of adjacent areas. The expected flood damage to residential buildings is estimated using an innovative method, recently proposed in the literature, which allows estimating how the damage evolves during a single flood event. The decade-scale change in the expected flood damage reveals the detrimental effect of urbanization, with flood risk growing at the pace of a fraction of urbanized areas. The within-event time evolution of the flood damage, i.e., how it progresses in the course of past or recent flood events, reflects changes in the hydrodynamic process of flooding. The general methodology used in the present work can be viewed as a promising technique to analyze the effects on the flood risk of past landscape evolution and, more importantly, a valuable tool toward an improved, well-informed, and sustainable land planning.

Failure of levees induced by toe uplift: Investigation of post-failure behavior using material point method

Levees are essential structures in flood defense systems, and their failures can lead to devastating consequences on the surrounding territories. One of the failure mechanisms mostly controlled by the foundation soil stratigraphy is the instability of the land side slope, triggered by the development of high uplift pressures in the foundation. This complex phenomenon has been investigated experimentally with centrifuge tests or large-scale tests and numerically with the limit equilibrium method (LEM) and the finite element method (FEM). In this work, we applied a multiphase formulation of the material point method (MPM) to analyze the development of toe uplift instability mechanism, from the onset of failure to large displacements. The numerical model is inspired by an experiment carried out in a geotechnical centrifuge test by Allersma and Rohe (2003). The comparison with the experiment allows for understanding critical pore pressure triggering large displacements in the foundation soils. Moreover, we numerically evaluated the impact of different values of foundation soils' hydraulic conductivity on the failure mechanism. The results show that hydraulic conductivity mainly influences the time of failure onset and the extension of shear localization at depth. Finally, the advantages of using large displacement approaches in the safety assessment of earth structures are discussed. Unlike FEM, there are no issues with element distortions generating difficulties with numerical convergence, allowing for full post-failure reproduction. This capability permits precise quantification of earth structure damages and post-failure displacements. The ensuing reinforcement systems' design is no longer over-conservative, with a significant reduction in associated costs. ©2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The effect of heterogeneities and small cavities on levee failures: The case study of the Panaro levee breach (Italy) on 6 December 2020

AbstractThis 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.

Semi-quantitative evaluation of levees risk within the context of hydrology uncertainty

Risk assessment is necessary to understand whether a levee is safe and able to prevent flood invasion. Most previous assessment methods attempted to quantitatively assess the risks posed by hydraulic structures using probabilistic analysis from a research perspective. The kind of method depends on the probability density function of factors but sometimes difficult to determine either a priori or posteriori in practice. On the other hand, current semi-quantitative methods despite the convenience are somewhat subjective in their implementation. This study sought to rectify the shortcomings of previous quantitative and semi-quantitative approaches to assessing the risk of levee failure wherein the uncertainty of risk factors is presented within a semi-quantitative framework, in accordance with ISO assessment procedures. The risk of levee failure discussed in this work is mainly related to overtopping and erosion of its foundation. This study proposed a semi-quantitative approach to maintain the exactness and objectivity of the risk assessment of levees and use Puzih river in Taiwan as a case study. In this study, we tried to add uncertainty facts and developed a risk assessment framework for levee management using a risk map according to our semi-quantitative methods. This study firstly defines the risk and associated factors within the context of government regulations, then implement a series of risk assessment tasks using the widely used hydraulic and sedimentation transport model, HEC-RAS, to simulate the risk of inundation, where hydrological events are used as a proxy for uncertainty. This study considers that consequence of levee failure and compute representative qualitative indices by which to evaluate hazards using a risk map and risk matrix in order to illustrate potential economic losses under given flood scenarios. After gaining the levee assessment results, the risk map is also built which can be applied on the practical engineering works. Our results reveal that the most secure levees along Puzih river should be able to withstand flood events with a 100-year return period; however, the levees in a several areas fail to provide suitable protection. Accordingly, this work developed a risk map and corresponding flood prevention strategies to decrease the risk in specific regions for the consideration of rive management administration.

Impact of Sediment Deposition on Flood Carrying Capacity of an Alluvial Channel: A Case Study of the Lower Indus Basin

Impacts of climate change and human-made interventions have altered the fluvial regime of most rivers. The increasingly uncertain floods would further threaten the flow delivery system in regions such as Pakistan. In this study, an alluvial reach of the Indus River below Kotri barrage was investigated for the geomorphologic effects of sediments deposited over the floodplain as well as the influences on the downstream flood-carrying capacity. The hydrodynamic modeling suite HEC-RAS in combination with ground and remotely sensed data were used to undertake this analysis. Results suggest that the morphology of the river reach has degraded due to depleted flows over a long period and hydrological extremes that have led to excessive sediment deposition over the floodplain and an enhancement in flood water extension possibility over the banks. A deposition of 4.3 billion cubic meters (BCM) of sediment increased the elevation of the channel bed which in turn reduced a 17.75% flood-carrying capacity of the river reach. Moreover, the excessive deposition of sediments and the persistence of low flows have caused a loss of 48.34% bank-full discharges over the past 24 years. Consequently, the river’s active reach has been flattened, with a live threat of left levee failure and the inundation of the populous city of Hyderabad. The study would gain insights into characterizing the impacts associated with a reduction in the flood-carrying capacity of the alluvial channel on account of the inadequate sediment transport capacity after heavy flow regulations.