Overtopping Probability Research Articles

Relative sea level rise contributions to flood construction levels in British Columbia

This paper proposes an updated approach to incorporating relative sea level rise in the estimation of flood construction levels in British Columbia, which are required in coastal planning and infrastructure development. Initially, current guidelines for British Columbia are outlined, and recent information on projected relative sea level rise is summarized. Then, recognizing the uncertainty in sea level rise projections, a probabilistic model of estimating the contribution of relative sea level rise to the flood construction level is described, relying on an available theoretical formulation that is corroborated by the application of a Monte Carlo simulation method. An updated approach to incorporating relative sea level rise in the estimation of flood construction levels is thereby recommended, relying on available data portals for relative sea level rise. Finally, the estimation of the probability of overtopping is described, and the implications of this for making informed decisions on flood construction levels with respect to risk assessments are indicated.

Data-Driven Model for Estimating the Probability of Riverine Levee Breach Due to Overtopping

Breach due to overtopping is the most common failure mode of earthen levees. Historic records and future projections consistently show exacerbating patterns in the frequency and severity of floods in several regions, which can increase the probability of levee overtopping. The main objective of this study is twofold: (1) to present a comprehensive data set of levee overtopping events, and (2) to develop a data-driven model for determining the probability of levee breach due to overtopping that can support risk assessment. For this purpose, we first assessed available performance data to develop a refined data set of 185 riverine levee overtopping events within the portfolio of levee systems maintained by the US Army Corps of Engineers. The data set includes several geometric, geotechnical, and hydraulic variables for each overtopping incident. We then employed the data set along with logistic regression to develop, train and validate a model for calculating the probability of levee breach due to overtopping. Among several variables and functional forms examined, levee construction history, overtopping depth, overtopping duration, embankment erosion resistance, and duration of levee hydraulic loading prior to overtopping were found to be statistically significant, thus were included in the proposed model. The model was validated through k-fold cross validation and tested against a separate performance data set aside for validation purposes. The data set presented in this study can be used for identifying key factors controlling overtopping behavior, validation of model results, and providing new insight into the phenomenon of levee overtopping. The proposed model offers a practical yet robust tool for levee risk analysis that can be readily employed in practice.

Changes of Chinese Coastal Regions Induced by Land Reclamation as Revealed through TanDEM-X DEM and InSAR Analyses

Chinese coastal topography has changed significantly over the last two decades due to human actions such as the development of extensive land reclamation projects. Newly-reclaimed lands typically have low elevations (<10 m) and often experience severe ground subsidence. These conditions, combined with the more frequent occurrence of extreme sea-level events amplified by global climate change, lead to an increased risk of flooding of coastal regions. This work focuses on twelve Chinese coastal areas that underwent significant changes from 2000 to 2015 in their environments, correlated to relevant land reclamation projects. First, the ground changes between 2000 and 2015 were roughly computed by comparing the TanDEM-X and the Shuttle Radar Topography Mission (SRTM) digital elevation models of the investigated areas. These results indicate that six of the analyzed coastal zones have reclaimed more than 200 km2 of new lands from 2000 to 2015, with five of them in northern China. Second, we focused specifically on the city of Shanghai, and characterized the risk of flood in this area. To this purpose, two independent sets of synthetic aperture radar (SAR) data collected at the X- and C-band through the COSMO-SkyMed (CSK) and the European Copernicus Sentinel-1 (S-1) sensors were exploited. We assumed that the still extreme seawater depth is chi-square distributed, and estimated the probability of waves overtopping the coast. We also evaluated the impact on the territory of potential extreme flood events by counting the number of very-coherent objects (at most anthropic, such as buildings and public infrastructures) that could be seriously affected by a flood. To forecast possible inundation patterns, we used the LISFLOOD-FP hydrodynamic model. Assuming that an extreme event destroyed a given sector of the coastline, we finally computed the extent of the flooded areas and quantified its impact in terms of coherent structures potentially damaged by the inundation. Experimental results showed that two coastline segments located in the southern districts of Shanghai, where the seawalls height is lower, had the highest probability of wave overtopping and the most significant density of coherent objects potentially subjected to severe flood impacts.

Observations and Preliminary Vulnerability Assessment of a Hybrid Dune-Based Living Shoreline

A novel hybrid (e.g., vegetation, sand, cobble, rip-rap) nature-based dune structure was constructed at Cardiff State Beach in Encinitas, California, to protect a critical transportation artery from undermining and frequent flooding. A collaboration between regulators, funders, state agencies, professional practice and academia developed a high resolution robust unmanned aerial vehicle (UAV) based monitoring strategy to observe dune construction and evolution. Fifteen construction surveys were conducted to observe each substrate element for future morphodynamic modeling efforts. Six post-construction surveys were conducted to observe seasonal and storm-by-storm dune evolution. Backshore vulnerability was assessed using a sixty-one year time series of tides and hindcast wave forcing fit to a general extreme value distribution. The dune crest is above calculated 100-year water levels; however, the dune remains vulnerable to mass wasting caused by swash interaction at the toe of the dune. Sea-level rise will substantially increase the probability of dune erosion, breaching, and overtopping.

A novel simulation–optimization strategy for stochastic‐based designing of flood control dam: A case study of Jamishan dam

AbstractThis study presents a novel stochastic simulation–optimization approach for optimum designing of flood control dam through incorporation of various sources of uncertainties. The optimization problem is formulated based on two objective functions, namely, annual cost of dam implementation and dam overtopping probability, as those are the two major concerns in designing flood control dams. The nondominated solutions are obtained through a multi‐objective particle swarm optimization (MOPSO) approach. Results indicate that stochastic sources have a significant impact on Pareto front solutions. The distance index (DI) reveals the rainfall depth (DI = 0.41) as the most significant factor affecting the Pareto front and the hydraulic parameters (DI = 0.02) as the least. The dam overtopping probability is found to have a higher sensitivity to the variability of stochastic sources compared to annual cost of dam implementation. The values of interquartile range (IQR) indicate that the dam overtopping probability is least uncertain when all stochastic sources are considered (IQR = 0.25%). The minimum annual cost of dam implementation (2.79 M$) is also achieved when all stochastic sources are considered in optimization process. The results indicate the potential of the proposed method to be used for better designing of flood control dam through incorporation of all sources of uncertainty.

Enhancing climate resilience of vertical seawall with retrofitting - A physical modelling study

Coastal defence structures are playing a vital role in protecting coastal communities from extreme climatic conditions and flooding. With climate change and sea-level rise in the next decades, the freeboard of existing coastal defences is likely to be reduced and the probability of wave overtopping for these coastal defences will increase. The wave overtopping from coastal defences increases the probability of coastal inundation and flooding, imposing threat to the communities which are living in low-lying coastal areas. Retrofitting of existing seawalls offers the potential to enhance coastal resilience by allowing them to adapt and respond to changing climatic conditions. This study investigates a range of possible physical configurations and optimum retrofit geometry to maximize the protection of existing seawalls from wave overtopping. A comprehensive physical modelling study of four retrofit prototypes, including recurve wall, model vegetation, reef breakwater and diffraction pillars, was conducted to examine their performance in mitigating wave overtopping, when placed in front of a vertical seawall. All the tests were conducted on 1:20 smooth beach slope. Each test case consisted of approximately 1000 pseudo-random waves based on the JONSWAP spectrum. The physical modelling experiments were designed to include both impulsive and non-impulsive wave conditions. This study provides new predictive relations and decision support tool needed to evaluate overtopping risks from existing seawalls with retrofits under various hydrodynamic conditions. The analysis of experimental measurements demonstrates that wave overtopping from retrofitting structures can be predicted with similar relations for vertical seawalls, and by using a reduction factor which varies with geometric shapes. Statistical measures and sensitivity analysis show that recurve walls have the best performance in reduction of wave overtopping volume followed by model vegetation and reef breakwater. The measurements show the insignificance of diffraction pillars, at least for the selected configurations investigated, in mitigating wave overtopping.

A case study on asphalt core construction rate for the Zhaobishan embankment dam

Traditional construction practices showed that asphalt core construction rate was commonly 2 layers/day (0.4 m/day) before the year 2000. More than 2 layers/day has been concerned as it would be difficult to compact the third layer to reach the required density (void content of maximum 3%) as the sublayers are soft. However, the Zhaobishan embankment dam was located at a very special dam site and high construction rate was required. Based on reviewing successfully high construction rates of asphalt core test section with 0.8 m/day (4 layers/day) and 0.9 m/day (3 layers/day) extensive laboratory tests and 4 trial test sections near the Zhaobishan dam site were carried out to gain asphalt mix parameters and construction techniques before constructing the asphalt core. The 63.6 m high asphalt core for the 71 m high dam was completed in 159 days with intensively quality control during construction. The maximum construction rate was 0.92 m/day (4 layers/day). The dam with asphalt core has performed well since the completion year 2005. The dam case study has documented that asphalt core dam can be constructed in a high rate without compromising core quality. Based on practical experience, field observations, and investigations in recent years, one can now build asphalt core dams faster and more economically than before. The fact that one can significantly reduce the probability of overtopping during construction by increasing the construction rate, may be an important point in many situations.

Levee Overtopping Risk Assessment under Climate Change Scenario in Kao-Ping River, Taiwan

With the growing concern about the failure risk of river embankments in a rapidly changing climate, this study aims to quantify the overtopping probability of river embankment in Kao-Ping River basin in southern Taiwan. A water level simulation model is calibrated and validated with historical typhoon events and the calibrated model is further used to assess overtopping risk in the future under a climate change scenario. A dynamic downscaled projection dataset, provided by Meteorological Research Institute (MRI) has been further downscaled to 5-km grids and bias-corrected with a quantile mapping method, is used to simulate the water level of Kao-Ping River in the future. Our results highlighted that the overtopping risk of Kao-Ping River increased by a factor of 5.7~8.0 by the end of the 21st century.

Construction Diversion Risk Assessment for Hydropower Development on Sediment-Rich Rivers

Hydropower is an important renewable energy, and Construction Diversion Risk (CDR) should be highlighted and assessed during hydropower development. Since sediment-rich rivers are widely existing around the world and have great hydro-energy potential, assessing CDR for hydropower development on sediment-rich rivers in terms of engineering feasibility is of significance. This paper proposes a CDR assessment method for the sediment-rich hydropower development environment. The method is concise and practical, reflects diversion uncertainties and correlation, and mainly adopts the Gumbel–Hougaard Copula and the Monte Carlo Simulation. Through simulating flood evolution and sediment impact during diversion, the method can assess CDR basing on the cofferdam overtopping probability. Case results show that the proposed method can achieve CDR assessment on a sediment-rich river and highlights sediment impact on the diversion risk. Through results discussion, the risk feature of construction diversion on sediment-rich rivers is revealed, that sediment impact causes the dynamic and yearly-risen CDR. Hence, our conclusions are: (1) the proposed method is feasible, effective and has industrial potential, and (2) a diversion scheme on sediment-rich rivers is suggested that adopts the design with high or yearly-heightening cofferdams, based on the advanced CDR assessment to cope with the risk features of sediment-rich diversion environments.

Empirical Tool for the Assessment of Annual Overtopping Probabilities of Dams

AbstractThis paper presents a simple tool for the assessment of maximum overtopping probabilities of dams. The tool is based on empirical relations between the overtopping probability and the basic...

Dealing with uncertainty in the probability of overtopping of a flood mitigation dam

Abstract. In recent years, copula multivariate functions were used to model, probabilistically, the most important variables of flood events: discharge peak, flood volume and duration. However, in most of the cases, the sampling uncertainty, from which small-sized samples suffer, is neglected. In this paper, considering a real reservoir controlled by a dam as a case study, we apply a structure-based approach to estimate the probability of reaching specific reservoir levels, taking into account the key components of an event (flood peak, volume, hydrograph shape) and of the reservoir (rating curve, volume–water depth relation). Additionally, we improve information about the peaks from historical data and reports through a Bayesian framework, allowing the incorporation of supplementary knowledge from different sources and its associated error. As it is seen here, the extra information can result in a very different inferred parameter set and consequently this is reflected as a strong variability of the reservoir level, associated with a given return period. Most importantly, the sampling uncertainty is accounted for in both cases (single-site and multi-site with historical information scenarios), and Monte Carlo confidence intervals for the maximum water level are calculated. It is shown that water levels of specific return periods in a lot of cases overlap, thus making risk assessment, without providing confidence intervals, deceiving.

Numerical Study on the Effects of Submerged Breakwater on Wave Overtopping

ABSTRACT Wang, Z.; Yin, Z.; Chen, Y., and Yang, B., 2017. Numerical study on the effects of submerged breakwater on wave overtopping. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 264–248. Coconut Creek (Florida), ISSN 0749-0208. In order to protect beach or mud coastlines, submerged breakwaters are built in the world widely. When the submerged breakwater is designed, one important issue having to be analyzed is wave overtopping of coastlines or coastal preventing structures since the wave overtopping is very dangerous for people or structures on the potential coastal zones with probability of wave overtopping appearing. A 2-D numerical wave flume has been established based on Flow-3D software to investigate effects of incident wave parameters in front of the submerged breakwaters, slope of the beach and the submerged breakwaters themselves, respectively. The numerical wave flume...

A resilience loss assessment framework for evaluating flood-control dam safety upgrades

Dams that were designed and built decades ago may not meet current design standards that reflect our improved knowledge of extreme rainfall events. When comparing dam safety upgrades, cost-efficient options that reduce the probability of overtopping are preferred. However, these criteria neglect flood damage costs resulting from controlled water flow inherent to the design of the safety upgrades. Therefore, to address this shortcoming, we apply the concept of resilience to evaluate dam safety upgrade options from a flood damage mitigation perspective through a resilience assessment framework. In this study, resilience is defined as the ability to provide flood-control service after an extreme rainfall event and to recover a desired level of functionality as soon as practicable. This framework features four main steps: estimating the probable maximum flood for the dam under investigation, calculating the dam discharge for each of the upgrade options, quantifying the loss in system resilience, and converting the losses into monetary units. This framework is applied to two dam safety upgrade options (constructing an emergency spillway and increasing dam crest height) for a large dam in Andong, South Korea. In practice, the former option is typically preferred as it is cost-efficient. However, we find that the latter option is superior when accounting for flood damage costs caused by water that is intentionally released from the dam during a probable maximum flood event. This study will help to ensure sound decision making when evaluating dam safety upgrade options by considering not only construction costs but also flood damage costs.

Multiobjective Optimal Operation of Gated Spillways

AbstractThis paper develops an optimal, multistage operation of gated spillways for the Karkheh Reservoir, Iran. In each stage of the proposed method, the opening of the gates is proportional to the water level of the reservoir. Two novelties are introduced in this work. The first one is consideration of the absence of a spillway or the existence of blocked spillway gates as two operation scenarios. The second novelty is attributed to using improvement of dam safety as an objective function rather than a constraint of the optimization problem. A genetic algorithm (GA) was implemented for determining the optimal opening of gates to minimize downstream damages. The nondominated sorting genetic algorithm-II (NSGA-II) was applied to optimize the two objectives of minimizing downstream damages and reducing the probability of dam overtopping. This paper’s results reveal that increasing the number of stages of gate opening improved the value of the objective functions. On the other hand, the lack of spillways or...

Systemic Estimation of Dam Overtopping Probability: Bayesian Networks Approach

AbstractDam overtopping is one of the major causes of dam breach accidents. Many studies have focused on the estimation of dam overtopping probability. However, the occurrence of a dam overtopping incident is subject to many factors including hydrologic and management factors. In this paper, a model for estimating dam overtopping probability considering spillway gate maintenance activity is established based on Bayesian networks (BN). The interactions between factors that can form a loop in causality are decomposed, and the probability representing the feedback effect is calculated for BN construction. The model is applied to an arch dam with three spillway gates. Statistical data and expert domain knowledge are used to quantify the relationships between variables. The results of a case study demonstrate that gate maintenance activity can significantly influence the occurrence probability of dam overtopping. Inspection frequency and individuals’ situational awareness are important factors that need to be ...

A non-traditional approach to the analysis of flood hazard for dams

The traditional and still prevailing approach to characterization of flood hazards to dams is the inflow design flood (IDF). The IDF, defined either deterministically or probabilistically, is necessary for sizing a dam, its discharge facilities and reservoir storage. However, within the dam safety risk informed decision framework, the IDF does not carry much relevance, no matter how accurately it is characterized. In many cases, the probability of the reservoir inflow tells us little about the probability of dam overtopping. Typically, the reservoir inflow and its associated probability of occurrence is modified by the interplay of a number of factors (reservoir storage, reservoir operating rules and various operational faults and natural disturbances) on its way to becoming the reservoir outflow and corresponding peak level—the two parameters that represent hydrologic hazard acting upon the dam. To properly manage flood risk, it is essential to change approach to flood hazard analysis for dam safety from the currently prevailing focus on reservoir inflows and instead focus on reservoir outflows and corresponding reservoir levels. To demonstrate these points, this paper presents stochastic simulation of floods on a cascade system of three dams and shows progression from exceedance probabilities of reservoir inflow to exceedance probabilities of peak reservoir level depending on initial reservoir level, storage availability, reservoir operating rules and availability of discharge facilities on demand. The results show that the dam overtopping is more likely to be caused by a combination of a smaller flood and a system component failure than by an extreme flood on its own.

Avaliação da probabilidade de galgamento da barragem da PCH de Cajuru por simulação de Monte Carlo

The concept of risk related to the potential breaching of a dam is a current problem in engineering. Dams have an important role in society and the collapse of such structures may bring about large disasters. This research aims to summarize a numerical technique of risk analysis, namely a Monte Carlo Simulation, to evaluate the probability of a dam overtopping, caused by events of hydraulic and hydrological nature and apply then in a case study. The simulation was used with the objective of evaluating the probability of overtopping of Cajuru dam, located in the Brazilian state of Minas Gerais, due to a flood of a certain return period, considering the uncertainties from the local frequency analysis of annual maximumdis charges. The Monte Carlo method, which account for the uncertainties of quantile estimates of a given return period, showed that it can be useful in providing a full evaluation of the probability of overtopping. For the case reported herein, the simulation showed that Cajuru dam has a non-negligible degree of vulnerability to rare and extreme events. In addition to floods, the impact of the wind on the upstream face of the dam was also analyzed. Wind waves and consequent reductions in existing freeboard, in between the full-pool elevation and the dam crest elevation, were also taken into account in computing the probability of dam failure

Reduction of the Expected Wave Overtopping Probability and Its Rate upon Seawall Utilizing STB(Steel Type Breakwater)

Kweon, H.M.; Choi, Y.H.; Kang, J.W.; Lee, W.D.; Hong, S., and Park, S.K., 2014. Reduction of the expected wave overtopping probability and its rate upon seawall utilizing STB(Steel Type Breakwater).Wave overtopping damages at seawalls, which separate lands from coastlines, are increasing as residences and commercial facilities are recently becoming concentrated near coastlines. The wave overtopping volume or probability can be decreased by increasing the crest elevation or width of the existing structure. Crest elevation or width increase of structures like seawalls, however, violates the citizens' view rights, and public water reclamation leads to an increase in the construction cost. The STB (Steel Type Breakwater) is a submerged-type non-reclamation structure, can be quickly constructed at a very low cost, and incurs almost no additional responding costs for the sea level rise. The feasibility of the new economical areal protection combination construction method that can reduce the EWOP (Expected Wave Overtopping Probability) without violating the citizens' view rights was validated in this study.

The role of offshore boundary conditions in the uncertainty of numerical prediction of wave overtopping using non-linear shallow water equations

The paper examines the variability of wave overtopping parameters predicted by numerical models based on non-linear shallow water equations, due to the boundary conditions obtained from wave energy density spectra. Free surface elevation time series at the boundary are generated using the principle of linear superposition of the spectral components. The components' phases are assumed to be random, making it possible to generate an infinite number of offshore boundary conditions from only one spectrum.A reference case was provided by carrying out overtopping tests on a simple concrete structure in a wave flume. Numerical tests using the measured free surface elevation at the toe of the structure were carried out. Three parameters were analysed throughout the paper: the overtopping discharge, the probability of overtopping and the maximum overtopping volume. These showed very good agreement between the numerical solver prediction and the overtopping measurements. Subsequently, the measured spectra at the toe were used to generate a population of reconstructed offshore boundary time series for each test, following a Monte Carlo approach. A sensitivity analysis determined that 500 tests were suitable to perform a statistical analysis on the predicted overtopping parameters. Results of these tests show that the variability in the predicted parameters is higher for the smaller number of overtopping waves in the modelled range and decreases significantly as overtopping becomes more frequent. The characteristics of the distributions of the predictions have been studied. The average value of the three parameters has been compared with the measurements. Although the accuracy is lower than that achieved by the model when the measured time series are used at the boundary, the prediction is still fairly accurate above all for the highest overtopping discharges. The distribution of the modelled probability of overtopping was found to follow a normal distribution, while the maximum value follows a GEV one. The overtopping discharge shows a more complex behaviour, values in the middle of the tested range follow a Weibull distribution, while a normal distribution describes the top end of the range better.Results indicate that when the probability of overtopping is smaller than 5%, a sensitivity analysis on the seeding of the offshore boundary conditions is recommended.

Optimal design of drainage channels using probabilistic search

Optimal design of artificial drainage channels is essential for the planning and management of irrigation projects. In this paper a special class of drainage channel with horizontal bottom and parabolic sides (HBPS) is designed using a recent meta-heuristic optimisation tool, namely probabilistic global search Lausanne (PGSL). The solutions of different models are found to be competitive with those obtained by classical optimisation procedures and particle swarm optimisation (PSO). The trend and sensitivity analyses show that more attention is needed in maintaining the design bed slope while implementing channels in real field conditions. Uncertainties associated with channel design parameters are incorporated in the design by applying first-order second-moment (FOSM) formulations. Two probabilistic channel design models are considered, one with overtopping probability constraint and another with a channel capacity constraint, and the solutions are obtained in the PGSL environment. To improve practical usefulness, both the models are further modified by adding geometric constraints on top width and flow depth and solutions are obtained. The presented PGSL approach is found to be capable of handling varying degrees of complexity and is proven to be suitable even for channels with more complex profiles than that of simple trapezoidal channels.