Dike Breach Research Articles

The wave overtopping load on landward slopes of grass-covered flood defences: Deriving practical formulations using a numerical model

Overtopping waves exert a high hydraulic load on the landward slopes of flood defences leading to erosion of the grass cover and finally to a dike breach. The hydraulic load is an important variable in erosion models and a detailed description of the load is necessary to determine where and when the grass cover erodes. We use a numerical model to simulate the flow of a single overtopping event over a flood defence with a grass-covered crest and landward slope. The model results show that the flow velocity, the shear stress and the pressure are maximal at the landward toe and can be used to describe grass erosion by shear forces. For steep slopes, the flow separates at the crest line and impacts on the upper slope. The normal stress is maximal at the location of impact and describes the grass erosion by normal forces. Practical formulations are developed for the maximum flow velocity, the maximum pressure, the maximum shear stress, the maximum normal stress and the impact location using three main design parameters for the landward slope: the overtopping volume, the slope steepness and the slope length. The formulations are able to accurately predict the overtopping load with Nash–Sutcliffe model efficiency factors between 0.41 and 0.90. The model output and these new formulations are used to calculate the erosive power of the overtopping waves predicted by eight erosion indices to show how the simulated load can be used in erosion models.

Predicting Outflow Hydrographs of Potential Dike Breaches in a Bifurcating River System Using NARX Neural Networks

Early flood forecasting systems can mitigate flood damage during extreme events. Typically, the effects of flood events in terms of inundation depths and extents are computed using detailed hydraulic models. However, a major drawback of these models is the computational time, which is generally in the order of hours to days for large river basins. Gaining insight in the outflow hydrographs in case of dike breaches is especially important to estimate inundation extents. In this study, NARX neural networks that were capable of predicting outflow hydrographs of multiple dike breaches accurately were developed. The timing of the dike failures and the cumulative outflow volumes were accurately predicted. These findings show that neural networks—specifically, NARX networks that are capable of predicting flood time series—have the potential to be used within a flood early warning system in the future.

Inundation Analysis of the Dike Breach of the Chikuma River Taking Drainage Process and House Damage into Consideration

Heavy rain and river flooding due to Typhoon No. 19 in October 2019 led to overflow and a dike breach on the left bank of the Chikuma River that caused large-scale inundation damage in Nagano City, Japan. To devise countermeasures, an inundation analysis model is an important tool. In this study, an inundation analysis model was developed to examine the inundation water behavior. The calculated inundation water depth and inundation area showed good agreement with the observed inundation water depth and the inundated area, confirming the validity of the analysis model. In addition, temporal changes of the inundation state were calculated considering the drainage process. However, the sewerage system, waterway, and drainage pump car were not taken into consideration in this analysis, and future issues for model improvement were also revealed. In addition, an analysis model with a 2 m grid was developed in the dike breach site, and the inundation water flow on roads and the fluid force around houses were obtained after taking into consideration the effect of houses. In paticular, the calculated value of the specific force exerted on damaged houses was very high. Moreover, it was proposed that house hazard should be evaluated while taking into consideration the loss of houses around the dike.

Sea-Level Rise in Northern Germany: A GIS-Based Simulation and Visualization

The future sea-level rise caused by climate change will lead to coastal regions being flooded and ecological and socio-economic systems being disrupted. This study examines the question of how the sea-level rise in Northern Germany can be simulated on a regional level and visualized as a media map. The simulation is based on the TanDEM-X digital elevation model, IDW interpolated current measurements of the sea level and the vertical land movement, as well as regional sea surface elevation projections for the year 2100. Two different climate scenarios were applied based on IPCC forecasts. Particular attention was paid to transforming elevation systems into orthometric heights. In addition, the uncertainties existing in the simulation of future developments were quantified and visualized. Depending on the applied scenario, an area between 1061 and 9004 km2 will be inundated. Accordingly, the affected population varies between 5477 and 626,880 people. The calculation of the inundated areas reveals serious differences; between the various climate scenarios, as well as between the North and Baltic coasts, but above all between the assumption of a stable coastal protection on the one hand and a dike breach on the other. Based on the requirements of journalistic cartography and the specific requirements of the German broadcasting company Norddeutscher Rundfunk (NDR), static maps were developed, which will be shown as a sequence starting with the least and ending with the most severe possible impact.

Continuous Monitoring of Fluvial Dike Breaching by a Laser Profilometry Technique

AbstractA nonintrusive, high‐resolution laser profilometry technique (LPT) has been developed for continuous monitoring of the three‐dimensional (3‐D) evolving breach in laboratory models of noncohesive fluvial dikes. This simple and low‐cost setup consists of a commercial digital video camera and a sweeping red diode 30 mW laser projecting a sheet over the dike. The 2‐D image coordinates of each deformed laser profile incident on the dike are transformed into 3‐D object coordinates using the direct linear transformation (DLT) algorithm. All 3‐D object coordinates computed over a laser sweeping cycle are merged to generate a cloud of points describing the instantaneous surface. The DLT‐based image processing algorithm uses control points and reference axes, so that no prior knowledge is needed on the position, orientation, and intrinsic characteristics of the camera, nor on the laser position. Because the dike is partially submerged, ad hoc refraction correction has been developed. Algorithms and instructions for the implementation of the LPT are provided. Reconstructions of a dike geometry with the LPT and with a commercial laser scanner are compared in dry conditions. Using rigid dike geometries, the repeatability of the measurements, the refraction correction, and the dike reconstruction have been evaluated for submerged conditions. Two laboratory studies of evolving fluvial dike breaching due to flow overtopping have been conducted to demonstrate the LPT capabilities and accuracy. The LPT has advantages in terms of flexibility and spatiotemporal resolution, but high turbidity and water surface waves may lead to inaccurate geometry reconstructions.

Impact evaluation of geomorphic changes caused by extreme floods on inundation area considering geomorphic variations and land use types

Extreme floods caused by dam breaches, dike breaches, and rainstorms cause significant erosion and deposition in the flooded area. Furthermore, geomorphic changes have various impacts on different land use types, which is an important aspect extreme flood outcomes. The impact type and degree depend on geomorphic variations and land characteristics. However, neither the amount of geomorphic variations nor its impact on the inundation area have been fully understood. Firstly, we propose the use of a numerical simulation method to calculate erosion and deposition depths of the whole inundation area caused by extreme floods. Secondly, combined with the characteristics of erosion, deposition, and land use types, the impact type of geomorphic changes on different land use types were divided into positive, negative, and negligible impacts, and the impact degree was expressed by two indices of impact grade and impact score. In addition, the calculation methods of the two indices were put forward. Then, we propose a method for evaluating the impacts of geomorphic changes on the whole inundation area from five aspects of mesh, land use type, overall erosion region, overall deposition region, and overall inundation area. Combined with the simulation of the flood process caused by dam breach of Luhun Reservoir in China, this method was verified, and the results showed that: (a) geomorphic changes had a negative impact on 94.7% of the inundation area, and only part of the water bodies were positively affected and the towns were not affected, accounting for 2.1% and 3.2% respectively; (b) the negative impact degree of each land use type in descending order was grassland, town, cropland, forest, shrubland and water body; and (c) the area of deposition was larger than that of erosion, whereas the severity of negative impact was opposite.

Large-scale stochastic flood hazard analysis applied to the Po River

Reliable hazard analysis is crucial in the flood risk management of river basins. For the floodplains of large, developed rivers, flood hazard analysis often needs to account for the complex hydrology of multiple tributaries and the potential failure of dikes. Estimating this hazard using deterministic methods ignores two major aspects of large-scale risk analysis: the spatial–temporal variability of extreme events caused by tributaries, and the uncertainty of dike breach development. Innovative stochastic methods are here developed to account for these uncertainties and are applied to the Po River in Italy. The effects of using these stochastic methods are compared against deterministic equivalents, and the methods are combined to demonstrate applications for an overall stochastic hazard analysis. The results show these uncertainties can impact extreme event water levels by more than 2 m at certain channel locations, and also affect inundation and breaching patterns. The combined hazard analysis allows for probability distributions of flood hazard and dike failure to be developed, which can be used to assess future flood risk management measures.

Experimental Study on Sand Dike Breaching by Wave Overtopping

A series of large-scale experiments are conducted to investigate the breaching process of sand dikes under wave overtopping. The dikes are constructed with uniform sand, covered with a thin clay layer on the upstream slope to prevent seepage during breaching. Wave height, wave period and dike slopes are systematically varied to examine their effects on the breaching process. Morphological development of the breach is recorded using a 3D laser scanner. The results indicate that erosion starts at the downstream edge of dike crest and the downstream dike slope gradually flattens. The breach cross-section is observed to be of a trapezoidal shape. Breach flow increases at an accelerating rate after initial overtopping until a peak flow is attained. The breach dimension and peak flow rate increase with increasing wave height, wave period, and upstream and downstream dike slopes. A dimensionless dike breach parameter is proposed to establish regression relations for the breach geometry and flow characteristics.

Discussion of “Consequences of dike breaches and dike overflow in a bifurcating river system” by Anouk Bomers, Ralph M. J. Schielen and Suzanne J. M. H. Hulscher

In this discussion, the authors will point out that even if Bomers et al. (Nat Hazards 97:309–334, 2019) tackle an important problem, ignoring the uncertainties related to the roughness coefficients, Manning coefficients, the downstream boundary and most importantly the errors of the chosen software, HEC-RAS, are serious shortcomings of their study.

Apparent cohesion effects on overtopping-induced fluvial dike breaching

Flow overtopping can lead to the initiation of breaching and failure of fluvial dikes, causing severe inundations and damage in the protected areas. For flood risk management and prevention, the accurate estimate of flow discharge across the fluvial dike breach is paramount, requiring precise understanding of the breach expansion. Laboratory experiments were conducted to analyse the effects of fine sand, inducing apparent cohesion in the dike material, on breach development and outflow. Tests were conducted under controlled inflow discharge and dike material composed of either homogeneous non-cohesive coarse sand or heterogeneous fine sand/coarse sand mixtures. Based on the non-intrusive laser profilometry technique, high temporal and spatial resolution of the three-dimensional breach geometry evolution was measured, indicating a small effect of the fine material on the overall breach dynamics. A detailed analysis revealed, however, that fine sand induces less frequent slope collapses but larger sliding/failing lumps compared to homogenous non-cohesive coarse sand.

Numerical Study of Storm Surge Inundation in the Southwestern Hangzhou Bay Region During Typhoon Chan-Hom in 2015

Storm surge inundation is a major concern in marine hazard risk assessment during extreme weather conditions. In this study, a high-resolution coupled model (the ADVanced CIRCulation model + the Simulating WAves Nearshore model) was used to investigate the storm surge inundation in the southwestern Hangzhou Bay region during Typhoon Chan-hom in 2015. The simulated hydrodynamic processes (sea surface wave and storm tide) were validated with measured data from wave buoys and tide gauges, indicating that the overall performance of the model was satisfactory. The storm surge inundation in the coastal area was simulated for several idealized control experiments, including different wave effects (wave-enhanced wind stress, wave-enhanced bottom stress, and wave radiation stress). Dike overflowing cases with different dike heights and dike breaking cases with different dike breach lengths were considered in the simulation. The results highlight the necessity of incorporating wave effects in the accurate simulation of storm surge inundation. Dike height significantly influences the magnitude and phase of the maximum inundation area in the dike overflowing cases, and dike breach length is an important factor impacting the magnitude of the maximum inundation area in the dike breaking cases. This study may serve as a useful reference for accurate coastal inundation simulation and risk assessment.

Historic Flood Reconstruction With the Use of an Artificial Neural Network

AbstractThe uncertainty in flood frequency relations can be decreased by adding reconstructed historic flood events to the data set of measured annual maximum discharges. This study shows that an artificial neural network trained with a 1‐D/2‐D coupled hydraulic model is capable of reconstructing river floods with multiple dike breaches and inundations of the hinterland with high accuracy. The benefit of an artificial neural network is that it reduces computational times. With this network, the maximum discharge of the 1809 flood event of the Rhine River and its 95% confidence interval was reconstructed. The study shows that the trained artificial neural network is capable of reproducing the behavior of the hydraulic model correctly. The maximum discharge during the flood event was predicted with high accuracy even though the underlying input data are, due to the fact that the event occurred more than 200 years ago, uncertain. The confidence interval of the prediction was reduced by 43% compared to earlier predictions that did not use hydraulic models.

Large Scale Flood Hazard Analysis by Including Defence Failures on the Dutch River System

To make informed flood risk management (FRM) decisions in large protected river systems, flood risk and hazard analyses should include the potential for dike breaching. ‘Load interdependency’ analyses attempt to include the system-wide effects of dike breaching while accounting for the uncertainty of both river loads and dike fragility. The intensive stochastic computation required for these analyses often precludes the use of complex hydraulic models, but simpler models may miss spatial inundation interactions such as flows that ‘cascade’ between compartmentalised regions and overland flows that ‘shortcut’ between river branches. The potential for these interactions in the Netherlands has previously been identified, and so a schematisation of the Dutch floodplain and protection system is here developed for use in a load interdependency analysis. The approach allows for the spatial distribution of hazard to be quantified under various scenarios and return periods. The results demonstrate the importance of including spatial inundation interactions on hazard estimation at three specific locations, and for the system in general. The modelling approach can be used at a local scale to focus flood-risk analysis and management on the relevant causes of inundation, and at a system-wide scale to estimate the overall impact of large-scale measures.

Consequences of dike breaches and dike overflow in a bifurcating river system

Currently, the effect of dike breaches on downstream discharge partitioning and flood risk is not addressed in flood safety assessments. In a bifurcating river system, a dike breach may cause overland flows which can change downstream flood risk and discharge partitioning.This study examines how dike breaches and overflow affect overland flow patterns and discharges of the rivers of the Rhine delta.For extreme discharges, an increase in flood risk along the river branch with the smallest discharge capacity was found, while flood risk along the other river branches was reduced. Therefore, dike breaches and resulting overland flow patterns must be included in flood safety assessments.

Impact of including interdependencies between multiple riverine flood defences on the economically optimal flood safety levels

In risk analysis of riverine flood defence systems, sections of flood defences are often considered separately, herewith ignoring their interdependence, e.g. due to the hydraulic response following dike breaches in the system. In previous studies it has been found that such interdependence can have a significant influence on flood risk estimates and the spatial distribution. In this paper a method is proposed for the economic optimisation of riverine flood defence safety levels from a river system perspective. In order to deal with the computational challenge of integrating the hydraulic interactions in an economic optimisation, a surrogate model was developed. Despite the many simplifications, this model yields reasonably accurate results within acceptable time. The application of the model to a case study in the Netherlands has shown that taking into account interactions between flood defences has significant influence on optimal long term strategies for flood defences. The results suggest that accounting for interdependence in setting safety standards and reinforcement prioritisation yields a significant return on investment both in terms of lower investment cost and in terms of reduced risks.

Flow and detailed 3D morphodynamic data from laboratory experiments of fluvial dike breaching

This paper presents a dataset obtained from fifty four laboratory experiments of the breaching of fluvial dikes due to flow overtopping. Data were collected on two complementary experimental setups, each consisting of a main channel representing the river, an erodible lateral dike and a floodplain. The dataset covers seven test series, involving varying hydraulic boundary conditions (e.g. inflow discharge, downstream boundary conditions), main channel dimensions, as well as bottom and dike material. The following experimental data were produced: time series of water levels in the main channel, time series of flow discharges in the main channel and through the breach, as well as high resolution 3D reconstructions of the breach geometry during its expansion. The latter measurements were performed using a novel non-intrusive laser profilometry technique developed for this research. Reuse of the collected data will support efforts to improve our understanding of the physical processes underpinning fluvial dike breaching. It will also enable benchmarking the accuracy of conceptual or detailed numerical models for the prediction of dike breaching, which is central to flood risk management.

Real-time hybrid dike breach model: simulating reservoirs of arbitrary shape and volume in laboratory tests

ABSTRACT Dikes and earthen embankments are common parts of modern infrastructure. Dike breaches resulting from extreme weather conditions and a lack of maintenance have caused significant damage to populated and agricultural areas in the past. Despite recent research findings, the effects of the parameters reservoir water volume and reservoir shape have not been properly assessed due to limitations in laboratory channel size and/or a lack of adequate test methodology. Furthermore, repeatability during the breach initiation phase has proved difficult to achieve when applying standard test methods. Therefore, a novel pump regulation method is introduced with the objective of simulating reservoirs of arbitrary size and shape during dike breach tests. This real-time, fully coupled hybrid modelling approach reduces test limitations due to limited laboratory space and considerably improves repeatability during the breach initiation phase. The pump regulation method, its limitations, test results and possible applications in the hydraulic laboratory are presented.

Influence of surface lining type on the probability of dike breaching due to overtopping

AbstractThe reliability analysis of a flood protection dike depends on the probability of its failure. In this context, the surface lining covering the landside slope of the dike plays a considerable role, as it protects the dike against failure due to overtopping. A mathematical model describing the overtopping and erosion processes is proposed. The overtopping is simulated using simple surface hydraulics equations while the erosion initiation is linked to the lining resistance. For the modelling of erosion, a simple transport equation was used with erosion parameters. In order to obtain a probabilistic solution, the uncertainty in the involved parameters was taken into account and the Latin Hypercube Sampling method was used. Eight different types of lining material were tested for a chosen dike. Typical phases of the dike breaching due to overtopping were distinguished. The final results take the form of probabilities for those typical phases for each lining material.

Flood risk assessment due to cyclone-induced dike breaching in coastal areas of Bangladesh

Abstract. Bangladesh, one of the most disaster-prone countries in the world, has a dynamic delta with 123 polders protected by earthen dikes. Cyclone-induced storm surges cause severe damage to these polders by overtopping and breaching the dikes. A total of 19 major tropical storms have hit the coast in the last 50 years, and the storm frequency is likely to increase due to climate change. The present paper presents an investigation of the inundation pattern in a protected area behind dikes due to floods caused by storm surges and identifies possible critical locations of dike breaches. Polder 48 in the coastal region, also known as Kuakata, was selected as the study area. A HEC-RAS 1-D–2-D hydrodynamic model was developed to simulate inundation of the polder under different scenarios. Scenarios were developed by considering tidal variations, the angle of the cyclone at landfall, possible dike breach locations and sea level rise due to climate change according to the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). A storm surge for a cyclone event with a 1-in-25-year return period was considered for all the scenarios. The primary objective of this research was to present a methodology for identifying the critical location of dike breaching, generating a flood risk map (FRM) and a probabilistic flood map (PFM) for the breaching of dikes during a cyclone. The critical location of the dike breach among the chosen possible locations was identified by comparing the inundation extent and damage due to flooding corresponding to the developed scenarios. A FRM corresponding to the breaching in the critical location was developed, which indicated that settlements adjacent to the canals in the polders were exposed to higher risk. A PFM was developed using the simulation results corresponding to the developed scenarios, which was used to recommend the need of appropriate land use zoning to minimize the vulnerability to flooding. The developed hydrodynamic model can be used to forecast inundation, to identify critical locations of the dike requiring maintenance and to study the effect of climate change on flood inundation in the study area. The frequency and intensity of the cyclones around the world are likely to increase due to climate change, which will require resource-intensive improvement of existing or new protection structures for the deltas. The identification and prioritization of the maintenance of critical locations of dike breaching can potentially prevent a disaster. The use of non-structural tools such as land use zoning with the help of flood risk maps and probabilistic flood maps has the potential to reduce risk and damage. The method presented in this research can potentially be utilized for deltas around the world to reduce vulnerability and flood risk due to dike breaching caused by cyclone-induced storm surge.

Applying tidal landform scaling to habitat restoration planning, design, and monitoring

Tidal channels are structurally and functionally prominent features in tidal marshes, so their restoration is central to marsh restoration. Prominent design questions in tidal marsh restoration include: How many tidal channels can a restoration site support, and thus, how many dike breaches should be made to restore tidal inundation and tidal channels? How much total channel surface area will be supported by a restored marsh, and thus, how many fish, shrimp, or other organisms can be supported by restored channel habitat? These basic design questions can be addressed by landscape allometry, which describes the proportional relative rates of change in a system between two entities of particular interest—in the case of marsh restoration, between the amount of marsh area to be restored and a wide variety of measures of tidal channel network geometry. This paper briefly reviews the development of landscape allometry, insights that it provides into landforms and related ecological patterns, and its utility and application to marsh restoration planning, design and monitoring. Its practical application is illustrated in a conceptual restoration design that is the basis for a current restoration project.