Flood Protection Structures Research Articles

Effectiveness and applicability of flood barriers for risk mitigation in flash-flood prone Mediterranean area

The new policy of flood risk management is to give more attention to non-structural measures, allowing people to “live with floods” rather than “fight floods”. To protect existing buildings there are two main mitigation strategies: dry proofing and wet proofing. One measure of dry proofing is the shielding, consisting in the use of flood barriers, which can be installed at the entrance of the buildings or at a certain distance from them (including the placing along the banks or crossing a street). These flood protection structures are easier and faster to install rather than sandbags. This paper shows the results applied to a case study in the city of Barcellona, Sicily, Italy that is crossed by a river and suffered a severe inundation in November 2011. To study the effectiveness of using these flood barriers, a 2D hydrodynamic model has been used: the barriers has been placed along a road to inhibit the flow from flooding the protected area. While in North Europe these types of barriers are commonly used, because those areas are typically interested in clear water floods, in Italy flash floods and mud-debris-flows are more frequent and limit their use. The purpose of this work is to verify if these types of barriers are effective when placed along Mediterranean river courses and, especially, to be sure about their stability while subjected to the hydrodynamic effects of these kind of events. To gain this aim, the computed stresses from the modelling have been compared with the stability values of the barriers provided by the producers, evaluating barriers’ stability against overturning and sliding. Simulations show how the flood barriers can mitigate the hydraulic risk, being able to withstand the hydrodynamic pressures and managing to divert the flow of water, thus avoiding that the flood water hits very exposed areas.

Innovating Disaster Risk Reduction (DRR) Framework for Ensuring Urban Resilience: A Study on Coastal Delta Cities

Coastal delta cities are at risk to hydro meteorological hazards especially from flooding. To reduce this risk many cities have built extensive flood defence system that can only reduce the probability of flood occurrence. So, the study is focusing on developing a framework for selecting the most suitable flood risk reduction policies according to the local situation which will ensure resilience. First, from the physical and environmental point of view 10 DRR policies have been identified under three broad approaches based on the DRR initiatives by eleven precedent (model) cities. After that few explanatory variables are selected on the basis of geography, climate, flood hazard, risk magnitude and economic aspects. Then a correlation has been established among DRR policies and explanatory variables and then the pattern of correlations have been explained. The findings of this study show a framework from where appropriate DRR policies can be selected. It has been observed that in a stable political situation, a city can decide to adopt various DRR policies based on geography and climate, hazard pattern, magnitude and experience. The study further reveals that along with structural flood protection, practicing environmental and planning management can reduce the flood risk in coastal cities. Journal of Bangladesh Institute of Planners, Vol. 8, Dec 2015, pp. 123-134

ASSESSMENT OF CHANGES OF EXTREME WAVE CONDITIONS AT THE GERMAN BALTIC SEA COAST ON THE BASIS OF FUTURE CLIMATE CHANGE SCENARIOS

Information on possible changes in extreme wave heights is needed to determine the future effectiveness and safety of coastal and flood protection structures. In this study, an assessment of possible changes in the extreme wave heights at selected locations along the German Baltic Sea coast has been carried out on the basis of numerical simulations of waves in the western Baltic Sea and regional climate model data for the past and the future (1961-2100). The future climate change signal of significant wave heights with a return period of 200 years mainly depends on: (i) the location, (ii) the climate change scenario run, (iii) the time period of the comparison, and (iv) the approach adopted to calculate the wave climate. The results show increases of up to +0.5 m and decreases of up to -0.5 m of the extreme wave heights. The increases might have considerable effect on the constructional design of coastal and flood protection structures-such as breakwaters, sea dykes, and vertical walls-because the extreme wave heights are used as input parameters for the design of the structures.

Benchmarking flood risk reduction in the Elbe River

AbstractThe past decade has seen the development and overall acceptance of the concept of Integrated Flood Risk Management. This approach strives to balance positive and negative effects of riverine floods and combines it with risk management concepts. In practice, this has led to a diversification of flood management practices that go beyond traditional structural flood protection measures towards non‐structural measures. These include giving more space for rivers, backwards location of dykes, re‐naturalisation of flood plains and a suite of improved information systems including improved flood forecasting services, promoting flood risk awareness and self‐help capabilities. The paper describes in some detail the process of benchmarking to support effective planning, implementation and monitoring of integrated flood risk management activities that require a set of quantifiable measures, against which progress in flood risk management can be referenced. The case of the extreme Elbe River floods in 2002 and 2013 triggered the development and implementation of the Elbe Flood Protection – Action Plan that in large parts has been implemented. The paper shows the basic concepts of the Elbe Flood Protection Plan and its actions and puts these in the context of a benchmarking framework. The paper concludes that although elements of a benchmarking concept are outlined in the Action Plan, the establishment of benchmarking practices as a tool in flood risk management is in its infancy. The development of a consistent benchmarking procedure would have the potential to improve further the effectiveness of Integrated Flood Risk Management practices in national and international river basins.

Lulling Effect of Public Flood Protection: Case of Benhe Community in Kaohsiung during Typhoon Fanapi

AbstractMany people believe that once structural public flood protection is completed, disasters are completely prevented. Benhe community was the only place in Taiwan where a flood detention pond had been built in 2005. After that, the community was developed intensively. However, when Typhoon Fanapi brought record-high rainfall of 345.5 mm in 3 h to the Kaohsiung area in 2010, Benhe residents suffered severe flooding because the rainfall exceeded the capacity of the pond’s pumping station. Based on interviews with residents, the authors discovered that the incomplete risk information provided by the local government and previous no-damage experiences of the detention pond lowered the risk perception and created a false image that the area was fully secured against any type of rainfall. Therefore, a future risk-communication and disaster-preparedness plan should adopt a proactive approach to increasing the awareness of flood risk by taking into account how public flood protection structures influence the...

Development of an expert‐led GIS‐based approach for assessing the performance of river levees: the Digsure method and tool

AbstractFrance and other regions around the world frequently undergo devastating flood events. Any failure of a flood protection structure can lead to human casualties and material damage. Unfortunately, such long linear structures are often poorly maintained and have shown repeated signs of weakness. Therefore, river levee management raises a number of substantial issues for the decision‐makers responsible for ensuring maximum safety for the surrounding population at a reasonable management cost. The aim of the Digsure project is to provide levee managers with scientific methods and information technology (IT) tools for levee management. The Digsure method is a levee assessment method based on a probabilistic pattern. It produces levee performance indicators and integrates data and the uncertainty on results. Digsure is a geographic information system tool that implements the Digsure method. It estimates and displays levee performance and associated uncertainty intervals throughout levee assessments.

Debates—Perspectives on socio‐hydrology: Capturing feedbacks between physical and social processes

AbstractIn flood risk assessment, there remains a lack of analytical frameworks capturing the dynamics emerging from two‐way feedbacks between physical and social processes, such as adaptation and levee effect. The former, “adaptation effect”, relates to the observation that the occurrence of more frequent flooding is often associated with decreasing vulnerability. The latter, “levee effect”, relates to the observation that the non‐occurrence of frequent flooding (possibly caused by flood protection structures, e.g. levees) is often associated to increasing vulnerability. As current analytical frameworks do not capture these dynamics, projections of future flood risk are not realistic. In this paper, we develop a new approach whereby the mutual interactions and continuous feedbacks between floods and societies are explicitly accounted for. Moreover, we show an application of this approach by using a socio‐hydrological model to simulate the behavior of two main prototypes of societies: green societies, which cope with flooding by resettling out of flood‐prone areas; and technological societies, which deal with flooding also by building levees or dikes. This application shows that the proposed approach is able to capture and explain the aforementioned dynamics (i.e. adaptation and levee effect) and therefore contribute to a better understanding of changes in flood risk, within an iterative process of theory development and empirical research.

Application of remote sensing and GIS in sinuosity and river shifting analysis of the Ganges River in Uttarakhand plains

Sinuosity and river shifting analysis of the Ganges River in Uttarakhand plains between Haridwar and Balawali has been done using topographic maps and various Landsat images during 1972 to 2005. The transect method was used for the river shifting measurement. The study area consists of a stretch characterized by uneven meandering and shifting. Consequently, the adjacent areas are susceptible to frequent flooding that causes significant losses of crops, property, livestock, and human lives. During the study period, different channel patterns were observed such as straight single-channel river, braided multi-channel river, etc. It was found that the west bank of the Ganges River was subjected to more erosion and that the river is shifting towards the west. The width of the meander belt ranged from 1 to 3.5 km with an average of about 2 km. Based on the findings of this study, it is suggested that the flood protection structures are crucial for the west bank. It is further suggested that these structures be constructed outside the meander belt of the river.

Lessons learnt from adaptation planning in four deltas and coastal cities

Deltas and coastal cities around the world face the need to adapt to uncertain future changes. We compared adaptation planning on flood risk management in four cases based on three main elements of adaptive planning: to prepare for a wide range of plausible future scenarios; to respond to change with robust and flexible actions; and to monitor critical changes to be able to reassess the plan accordingly. Differences can be observed in the implementation of these elements. Good practices could be distinguished: cases consider a wide range of future scenarios; short-term decisions are coupled with long-term options while envisioning these options and possibilities for switching between them through adaptation pathways; opportunities originating from other agendas to achieve multiple objective investments are seized; and the system's resilience is improved by a wide variety of measures. At the same time some barriers for using adaptive planning approaches were identified: the use of a wide range of scenarios is only accepted in an exploratory phase of planning. Structural flood protection measures taken in the past do constrain future choices. The potential for monitoring and reassessment of options is hampered by the fact that trends in some variables cannot be detected.

Geosynthetics for waterways and flood protection structures – Controlling the interaction of water and soil

The interaction of water and soil has been both a blessing and a curse in all times within living memory. Water is the origin of life but is also threatening life when appearing unboundedly. Therefore mankind has always worked hard to benefit from water resources on one hand and to deal with the threat of flooding on the other hand. For both, to protect the land and to allow for beneficial uses like irrigation or navigation, often special measures are necessary to keep the water within certain bounds. Structures to achieve a permanently stable situation like irrigation and navigational canals, river training or flood protection measures need suitable material, carefully thought out design and accurate execution. Often a decision has to be made among competitive approaches to optimize such structures. In many cases, geosynthetics can support or improve the functionality and sometimes only with geosynthetics the desired result can be achieved.Geosynthetics can provide strength and flexibility, imperviousness and drainage, durability and robustness or controlled degradation. All these properties can be of use to handle the many occurrences of interaction of water and soil. Surface water has to be guided or to be kept off; percolating water should be controlled to avoid internal erosion effects should be restrained by appropriate filtration. To guarantee well functioning in general, also chemical and biological aspects have to be considered like ochre formation, root penetration and population by any kind of species. The German Federal Waterways Engineering and Research Institute (BAW) has gathered experience with geosynthetics in hydraulic applications since more than 40 years. These years revealed the capabilities of geosynthetic solutions and simultaneously emphasized the need of careful selection, design and execution.A large variety of geosynthetic fabric and structures is available. To control the interaction of water and soil many different attributes are required, e.g. membranes for impervious lining, filter sheets for erosion control, different kinds of mattresses or wrap-around structures, voluminous elements from sandbags to mega containers for protection, training or immediate repair. In many cases geosynthetics can be designed to control the interaction of water and soil according to the individual and local requirements to allow for an excellent execution of waterways and flood protection structures.

Insights from socio-hydrology modelling on dealing with flood risk – Roles of collective memory, risk-taking attitude and trust

The risk coping culture of a community plays a major role in the development of urban floodplains. In this paper we analyse, in a conceptual way, the interplay of community risk coping culture, flooding damage and economic growth. We particularly focus on three aspects: (i) collective memory, i.e., the capacity of the community to keep risk awareness high; (ii) risk-taking attitude, i.e., the amount of risk the community is collectively willing to be exposed to; and (iii) trust of the community in risk reduction measures. To this end, we use a dynamic model that represents the feedback between the hydrological and social system components. Model results indicate that, on the one hand, by under perceiving the risk of flooding (because of short collective memory and too much trust in flood protection structures) in combination with a high risk-taking attitude, community development is severely limited because of high damages caused by flooding. On the other hand, overestimation of risk (long memory and lack of trust in flood protection structures) leads to lost economic opportunities and recession. There are many scenarios of favourable development resulting from a trade-off between collective memory and trust in risk reduction measures combined with a low to moderate risk-taking attitude. Interestingly, the model gives rise to situations in which the development of the community in the floodplain is path dependent, i.e., the history of flooding may lead to community growth or recession.

Floods and societies: the spatial distribution of water‐related disaster risk and its dynamics

This opinion article posits that the current lack of understanding of the dynamic interactions among the different components of risk (e.g., hazard, exposure, vulnerability, or resilience) is one of the main obstacles for the implementation of effective risk prevention measures. In state‐of‐the‐art methods for risk assessment, natural and social systems are typically treated separately by using different approaches. In flood risk studies, for instance, hydrological scientists typically focus on flood hazard, whereas socioeconomic scientists mainly examine the exposure, vulnerability, or resilience to flood events. However, we argue that these different components are deeply interconnected: for example, changes in flood hazard often trigger changes in vulnerability, and vice versa. These interconnections between the different components of risk remain largely unexplored and poorly understood. This lack of knowledge is of serious concern as it limits our ability to plan appropriate risk prevention measures. To design flood protection structures, for example, current methods can indeed provide quantitative assessments of the corresponding risk reduction associated to the reduced flood hazard. Nevertheless, traditional methods cannot estimate how, and to what extent, the reduced frequency or magnitude of floods might trigger increases of exposure or vulnerability to flooding (e.g., ‘levee effect’). Thus, while many progresses have been made in the static assessment of flood risk, the dynamics of risk are still poorly investigated. We think that this is a major issue in a rapidly changing world, and we therefore propose a transdisciplinary research agenda as a possible way out.This article is categorized under: Science of Water > Water Extremes

Can Material Pits in the Vicinity of a Polder Threaten its Safety?

Abstract The frequent occurrence of floods recently has motivated discussions by experts on reviewing the safety of flood protection structures. The simulation of flood discharges belongs among transient flow tasks. Due to the randomness of the phenomenon, as well as the often unknown geological composition of the environment in which the flooding occurs, this question has become very complicated. The finite element method (FEM) is one of the methods for reviewing risk factors endangering the stability of hydraulic structures. In this article the application of FEM is mentioned in assessing the stability of the subsoil of the Borša polder in Slovakia.

Derivation of a representative piping resistance parameter based on random field modelling of erosion paths

The piping mechanism is a dangerous failure mechanism for dikes and other flood protection structures in the world. A dike fails due to piping in case a head difference causes a water flow below the dike that, in case the flow is strong enough, causes the soil particles to erode. The progressing erosion ultimately results in the collapse of the dike. The grain size d 70 (determining piping resistance) is highly variable in space. The resistance of a dike stretch with respect to piping is not determined by the smallest value of d 70 in the sand layer that is susceptible to piping but by the largest d 70 in the erosion path (d 70,mech). The ultimate goal of this paper is to find the relation between (measured) point variability of d 70, which follows from collected samples, and the ‘mechanism variability’ d 70,mech, which follows from an analysis of erosion paths. Based on this relation, a new representative design value of d 70 can be derived. The spatial variability in d 70 is modelled with random field simulations. A model is developed that captures the formation of an erosion path in a generated d 70 random field, using an erosion criterion which combines the representative grain size d 70 and groundwater flow velocity near the tip of the backward developing erosion path. The model captures the search for the weakest path under flow influence. By applying the model to multiple random field realisations and to various assumed scales of fluctuation of d 70, the distribution of d 70,mech is obtained for various scales of fluctuation. The main outcome of the new model is that the smaller the scale of fluctuation, the larger the characteristic value of d 70,mech, whereas smaller characteristic values may be found for larger scales of fluctuation. This has some important implications for the design of dikes with respect to piping. If a detailed analysis shows a small scale of fluctuation of d 70, a larger representative design value of d 70 may be used, based on the distribution of d 70,mech. Hence, this may result in significant smaller dike (or berm) designs and lower dike construction costs.

Historical development and future outlook of the flood damage potential of residential areas in the Alpine Lech Valley (Austria) between 1971 and 2030

In the recent past, the Alpine Lech valley (Austria) experienced three damaging flood events within 6 years despite the various structural flood protection measures in place. For an improved flood risk management, the analysis of flood damage potentials is a crucial component. Since the expansion of built-up areas and their associated values is seen as one of the main drivers of rising flood losses, the goal of this study is to analyze the spatial development of the assets at risk, particularly of residential areas, due to land use changes over a historic period (since 1971) and up to possible shifts in future (until 2030). The analysis revealed that the alpine study area was faced to remarkable land use changes like urbanization and the decline of agriculturally used grassland areas. Although the major agglomeration of residential areas inside the flood plains took place before 1971, a steady growth of values at risk can still be observed until now. Even for the future, the trend is ongoing, but depends very much on the assumed land use scenario and the underlying land use policy. Between 1971 and 2006, the annual growth rate of the damage potential of residential areas amounted to 1.1 % (‘constant values,’ i.e., asset values at constant prices of reference year 2006) or 3.0 % (‘adjusted values,’ i.e., asset values adjusted by GDP increase at constant prices of reference year 2006) for three flood scenarios. For the projected time span between 2006 and 2030, a further annual increase by 1.0 % (‘constant values’) or even 4.2 % (‘adjusted values’) may be possible when the most extreme urbanization scenario ‘Overall Growth’ is considered. Although socio-economic development is regarded as the main driver for increasing flood losses, our analysis shows that settlement development does not preferably take place within flood prone areas.

FUTURE EXTREME WAVES AT THE GERMAN BALTIC SEA COAST DERIVED FROM REGIONAL CLIMATE MODEL RUNS

Information about possible changes of extreme wave heights are essential for the future safe design of coastal and flood protection structures likes dykes, flood protection dunes, revetments etc. In this study, scenarios of regional climate change up to 2100 are used for the evaluation of changes of wave conditions. Analyses on calculated significant wave heights derived from extreme value statistics are showing a different signal of change for the selected locations along the German Baltic Sea Coast. The results are showing that extreme wave heights with a return level of 200 years can increase up to +14%. But also a decrease of down to -14% were found compared to actual conditions, depending on the location and climate change scenario applied. At the location of Warnemunde a slight increasing trend for the change of extreme wave heights could be found for 3 of 4 scenario runs with a maximum increase of +7%.

THE KOKEMÄENJOKI RIVER BASIN FLOOD RISK MANAGEMENT PLAN––A NATIONAL PILOT FROM FINLAND IN ACCORDANCE WITH THE EU FLOODS DIRECTIVE

ABSTRACTThe Kokemäenjoki River Basin is the fourth largest in Finland. The city of Pori at the delta of the river is the most significant flood risk area in Finland. The preparation of a flood risk management plan (FRMP) for the Kokemäenjoki River Basin as a national pilot began in 2007 and will be finalised during 2011.The main challenges of the FRMP are the reconciliation of flood risks and various interests in different parts of the river basin, and adaptation to climate change. It has been predicted that climate change will alter the flood dynamics of the Kokemäenjoki River: the highest flow peaks will shift from spring to late autumn and winter and the risk of ice jam floods will increase.Development of the existing early warning systems and adaptive lake regulation practices are the two most important non‐structural measures for preventing and mitigating flood damage. A new channel in the mid‐river reach would help to manage the increasing winter flows. Also robust structural flood protection measures will be needed in the city of Pori. Nevertheless, close collaboration among authorities, municipalities and water body regulators will be critical in successful flood risk management in the Kokemäenjoki River Basin. Copyright © 2011 John Wiley & Sons, Ltd.

금강 상류 유역의 저수지 홍수저감지수 산정

최근 기후변화 등으로 인하여 홍수의 위험이 증대되고 있고, 이에 대한 대비로 홍수조절을 위한 댐 및 저수지 등의 역할이 강조되고 있다. 그러나 국내에서는 유역 내 중소규모의 저수지등에 의한 홍수저감효과에 대한 지수가 제시되어있지 않아, 이의 객관적인 비교가 어려운 실정이다. 본 연구에서는 국내 유역의 저수지 홍수저감효과를 지수화한 유역특성인자의 산정을 위하여, 영국의 홍수량산정방법(Flood Estimation Handbook)의 저수지 및 호수의 홍수저감지수를 금강 상류 15개의 소규모 유역(총 739개의 저수지를 대상)에 적용하였다. 이를 위하여 국가수자원관리포탈(WAMIS)의 유역의 자료, 소재 저수지 제원, 유역수문자료 등을 바탕으로 저수지 홍수저감지수를 산정하였다. 대상 유역의 홍수저감지수는 0.859~0.990의 분포를 보이고 있으며 저수지에 의한 홍수저감효과가 가장 큰 유역은 진천 유역이다. 영동유역을 대상으로 2001년에 완공된 용담댐의 준공 전후의 홍수저감지수를 산정한 결과 준공 전 0.98에서 준공 후 0.894로 산정되어 지수반영 효과를 확인 하였다. 향후 국내 유역의 홍수저감 특성인자로 활용가능성이 높음을 확인하였다. Dams and reservoirs have been charged as important flood protection structures; likewise, attenuation effects of flooding have been highlighted due to recent climate change. However, it is difficult to generalize effects of flood attenuation by reservoirs in catchment scale because the flood attenuation index has not yet been used in Korea. This study estimates Reservoirs Flood Attenuation Index (RFAI) for catchment based on 739 reservoirs in 15 upper Geumgang catchments. The RFAI employs the method of Flood Attenuation by Reservoir and Lakes index (FARL), Flood Estimation Handbook, UK. All hydrological data for RFAI are provided by Water Management Information System (WAMIS) and Korea Meteorological Administration (KMA). The value of RFAI range from 0.859 to 0.990; The Jincheon catchment with the lowest RFAI values (0.859) shows the highest attenuation effects in study catchments, while the Sangjocheon has 0.990 which indicates the low influence of attenuation effects. Yeongdong catchment is examined for the effects of built of large reservoir on RFAI; The RFAI is changed 0.894 from 0.980 due to the built of Yongdam Dam, which was constructed in 2001. In this study RFAI is shown as an useful index in assessing flood characteristics for catchment managements.

The role of deep processes in late 20th century subsidence of New Orleans and coastal areas of southern Louisiana and Mississippi

[1] Geodetic leveling observations from Biloxi, MS, to New Orleans, LA, and water level gauge measurements in the New Orleans–Lake Pontchartrain area were analyzed to infer late 20th century vertical motions. These data were used to test the validity of previous subsidence rate measurements and the models that predict the location and causes of subsidence. Water gauges attached to bridge foundations and benchmarks affixed to deep rods that penetrate Holocene strata subsided as much as 0.8 m locally between 1955 and 1995. The observed deep-seated subsidence far exceeds model predictions and demonstrates that shallow processes such as compaction and consolidation of Holocene sediments are inadequate by themselves to explain late 20th century subsidence. Deep-seated subsidence occurring east and north of the normal faults marking the Gulf of Mexico basin margin can be explained by local groundwater withdrawal, and regional tectonic loading of the lithosphere by the modern Mississippi River delta (MRD). Sharp changes in subsidence coincide with strands of the basin margin normal faults. Displacements are consistent with activity and show motions consonant with fault creep. Deep subsidence of the region to the south, including New Orleans, can be explained by a combination of groundwater withdrawal from shallow upper Pleistocene aquifers, the aforementioned lithospheric loading, and perhaps, nongroundwater-related faulting. Subsidence due to groundwater extraction from aquifers ∼160 to 200 m deep dominated urbanized areas and is likely responsible for helping to lower local flood protection structures and bridges by as much as ∼0.8 m.

A probabilistic finite element analysis of embankment stability under transient seepage conditions

Flood protection structures lend themselves to probabilistic design given the large uncertain variables. Taking into account the historical discharge statistics of rivers, the annual probability of failure by slope instability of an embankment along the river Elbe in Eastern Germany is determined using a finite element analysis. The effect of transient seepage within the embankment and its effect on embankment stability are considered. Whereas a steady-state seepage line is most critical for the embankment stability, a transient seepage calculation including the rise and drop of the river water level reveals stability reserves. It has been demonstrated that the First-Order Reliability Method with Adaptive Response Surface is an efficient calculation technique for coupling numerical simulations to a reliability analysis.