Flood Safety Research Articles

Flood Risk and Resilience in the Netherlands: In Search of an Adaptive Governance Approach

In the Netherlands, dealing with the risk of flooding in the face of the current climate change requires a governance approach that is less based upon the long-standing tradition of prevention and protection, and more oriented toward ideas of resilience and adaptivity. Such an approach is assumed to be more resilient compared to static approaches and better equipped to deal with the indeterminate character of a problem like flood risk. This article presents the Dutch attempt to introduce a more polycentric and adaptive governance approach in flood management, called multilayered safety (MLS). We studied this approach via interviews and an extensive document study, and analyzed the institutions governing the issue using the Institutional Analysis and Development (IAD) framework of Elinor Ostrom. For years, the issue was in the hands of a small network of actors, mainly occupied by water experts and governed by a strong lead organization and permanent bodies. While introducing a new, more adaptive policy concept the government encountered both resistance and inability within the existing policy regime. This article shows that the issue of flood safety was successfully ‘tamed’ for decades. Adopting a more adaptive and polycentric approach necessitates ‘untaming’ the issue of flood safety.

Assessing stakeholder perceptions of landscape and place in the context of a major river intervention: a call for their inclusion in adaptive management

AbstractAdaptive management strategies are required to manage multi-actor and multifunctional river landscapes. Such strategies need to be inclusive of perspectives of different stakeholders. We present a case study of a pilot engineering project in the Dutch river Waal, which drastically changed the appearance of the river landscape. We study perceptions of four stakeholder groups (residents, recreational anglers, recreational boaters and shipping professionals) regarding the impacts of this intervention on landscape values, including aesthetics, naturalness, biodiversity, flood safety and accessibility. Results show that stakeholders differ in which functions of the river landscape they find important and how they perceive the longitudinal dams to influence the landscape. They also differ in levels of place attachment and trust in the responsible authority. Shipping professionals stand out for their more negative evaluations of the dams compared to the other stakeholders, while especially residents demonstrate high levels of place identity and connection with nature. Residents also feel that the dams are improving flood risk safety in the area, and they positively evaluate knowledge and skills of Dutch water managers. These results provide water managers with much needed insights into landscape functions valued by different stakeholder groups and those perceived as most endangered by landscape interventions.

Peak flow rate response to vegetation and terraces under extreme rainstorms

Soil and water conservation measures such as vegetation cover and terraces effectively reduce runoff and sediment yield. However, there is little information available on how vegetation cover and terraces affect peak flow under extreme rainstorm conditions. The purpose of this study was to investigate the effect of vegetation cover and terraces on peak flow rate in small catchments under “7.26” extreme rainstorm conditions on the Chinese Loess Plateau. Thirty-two small watersheds located in Chabagou Watershed, Zizhou County, Shaanxi Province, were selected. The watershed areas ranged from 0.03 to 1.55 km2. An aerial image with a resolution of 0.2 m was used to determine the land use and engineering practice by means of visual interpretation. The cross-section at the watershed outlets were investigated. At each cross-section, the flow depth, cross-sectional area of flow, wetted perimeter, and slope gradient of the channel were measured. Then, flow velocity was calculated using Manning’s equation. Peak flow rate was calculated based on flow velocity and cross-sectional area of flow. The results showed that peak flow rates varied from 0.35 to 79.89 m3/s. Unit flood peak ranged from 4.3 to 153.0 m3/(km2·s). Peak flow rate was significantly correlated with watershed area, main channel length of the watershed, mean slope gradient of the watershed, and area percentage of the grassland at p < 0.01. The unit flood peak in the grassland and woodland decreased by 36% and 64%, respectively, compared with that in the watershed with the largest cropland component. Terraces reduced the unit flood peaks in the farmland and grassland by 48% and 39%, respectively. Thus, vegetation cover and terraces effectively reduced peak flow rate, and the susceptibility of the sampled watersheds to flood generation was evaluated as “average’’ under extreme storm conditions. Our findings indicate that vegetation cover and terraces play an important role in soil conservation onsite and flood safety offsite under extreme rainstorm conditions.

Er kommunene forpliktet til å bruke klimapåslagved flomfarevurdering?

Climate change is causing greater precipitation. The Planning and Building Act and technical regulations control flood safety requirements, but in recent years the specialist authorities have recommended an additional climate impact factor to minimize future damage. County-level climate profiles incorporate a climate impact factor, and a new national planning guideline bolsters the impression that the climate impact factor should be a mandatory part of the flood hazard assessment. This change has consequences for municipal case processing, both in terms of enforcement of the rules and in the event of any claims for damages. The article briefly discusses the legal significance of technical guides and national planning guidelines, and assesses the use of a climate impact factor in flood hazard assessment in relation to these.

On the feasibility of managed retreat in the Wadden Sea of Schleswig-Holstein

Sea embankments along the mainland coastline in the Schleswig-Holstein Wadden Sea safeguard 130,000 people and 19 billion € of capital assets from flooding during storm surges. Due to climate change induced sea-level rise, these defences will become exposed to higher storm surges and adaptation becomes inevitable. As an alternative to strengthening, managed retreat is discussed in literature as a coastal risk management option for climate change adaptation. Based on an evaluation of examples from the Wadden Sea, this paper elaborates managed retreat as alternative climate change adaptation from a coastal risk management perspective. This paper concludes that, conform the principles of integrated coastal zone management, one precondition for successful implementation of managed retreat is local acceptance. With respect to natural resilience to sea-level rise, managed retreat may counteract the loss of Wadden Sea structures and habitats due to coastal squeeze. However, the effectiveness depends on the surface elevation in the opened polder. If large volumes of sediment are needed to restore a natural elevation, regional resilience against SLR-induced drowning may deteriorate. With respect to coastal flood risk management in Schleswig-Holstein, opened polders have no significance as flood retention rooms and managed retreat does not reduce the hazard of flooding in surrounding polders. Further, removal of primary embankments requires large efforts to secure flood safety in adjacent polders. Under certain conditions, removal or opening of embankments may constitute sustainable coastal risk management, e.g., if retreat leads to a shorter line of defence or if other win-win-situations like securing of NATURA 2000 coherence arise.

Adjusting the water-sediment matching relationship to reduce sedimentation in the flow rate constraint reach of the Lower Yellow River, China

The bank-full discharge along the Dongbatou-Aishan river reach of the Lower Yellow River is significantly lower than that of the upper reach and is the flow rate constraint reach that dictates the flood safety of the Lower Yellow River. The water and sediment matching relationship is the important factor that affects scour and siltation along this reach. It is necessary to control the relationship between water and sediment by retaining a portion of sediments in the upper reach in order to increase the overflow capacity in this reach. We first analyse the relationship between the water and sediment processes of the Lower Yellow River and the scouring and siltation of the constraint reach and verify the water and sediment conditions that require sediment retention in the upper reach. By analysing the characteristics of the river, we determined the area of sediment retention to be the reach that stretches from Xiaolangdi to Huayuankou. The relationship between the incoming sediment coefficient at Huayuankou Station and the percentage of sediment discharged and deposited in the lower reach is analysed. The results showed that when the incoming sediment coefficient is more than 0.04 kg.s/m6, sediment should be retain in the Xiaolangdi-Huayuankou river reach to maintain non-siltation in the constraint reach. Using bank-full discharge in the river reach from Xiaolangdi to Huayuankou and the channel stability as constraints we propose that the sediment retention in this river reach should be less than 0.144 billion m3.

Modelling of the Impact of the Retention Reservoir on the Flood Protection of the City – A Case Study for the City of Kalisz (Central Poland)

Floods are natural phenomena related to the circulation of water in nature and they cannot be avoided. Despite the methods of predicting floods, technological development and civilization progress, the flood risk has been still increasing. The relevant hydrotechnical advancement, rational spatial development and optimal water management have a significant impact on reducing the consequences of flooding. Particularly retention reservoirs are decisive to rising flood safety and living conditions of urban residents who are at risk of flooding. The construction of a retention reservoir is a serious engineering, economic and eco-scale challenge. It must be preceded by numerous studies and analyses necessary to carry out the entire construction process and subsequent operation in an optimal way. At present, a number of engineering and environmental analyses are supported by the use of forecasting and computational tools based on the mathematical description of a given physical phenomenon. With their use, it is possible to determine, at the design level, the impact of a technical facility on various elements of the natural or the human environment. The paper presents the impact analyses of a planned retention reservoir located on the Prosna river in the flood protection system in Kalisz (Poland). The flood protection system is insufficient in Kalisz and its weakness was demonstrated, among others, by flood in May, 2010. Analyses were based on data received from the unsteady flow numerical modelling system and optimisation methods to support the management process of retention reservoir resources for extreme periods. The formulated task of dynamic optimisation due to its non-linearity was simplified to a static task by discretisation of an independent variable.

Risk Assessment of Dam Overtopping Based on The Extended Three-parameter Distribution and Stochastic Differential Equation

For earth and rockfill dam, overtopping is intolerable especially for those dams where cascade hydropower stations exist in the river basin. The flood safety of control reservoir directly relates to the safety of the dam. It is necessary to carry out an accurate analysis for flood risk. Based on the extended three-parameter Burr XII distribution of the maximum reservoir inflow design flood computation, the results are larger than the design standard using analysis method which is also based on Person O distribution. The flood risk analysis of uncertainty factors is considered based on the stochastic differential equation. Combination of these two methods, dam overtopping risk is calculated, greater risk is obtained than the traditional JC method, and the conclusion is much more rational. When determining the crest elevation in water conservancy engineering, the design of dam safety evaluation and risk analysis should be considered using more uncertain factors involved, and the new method is more feasible and reasonable than traditional methods.

Mapping Land Cover Damages in Mega Floods through Integration of Remote Sensing and GIS Techniques

Today we are encircled by multiple problems, such as global warming, drought, wildfires, Hurricanes and tropical storms etc; among them flooding is one of the major problems; however, the flood hazards are probably rising due to an amalgamation of environmental and socio-economic effects. Therefore, flood safety measurements are more essential to avoid barriers toward major development in society associated to environment, which requires modern and accurate steps for preventing the impacts of flood on population and properties. Floods are among the most destructive physical vulnerabilities on earth’s surface, which cause major economic and social damages rather than any other natural incidence. However, the flood problem begins because the human beings are using river floodplains. In this research our focus is to identify and measure extent and impacts such as Infrastructural, loss of Agriculture, Built-up (Houses), natural vegetation and property along Indus river due to heavy flooding of 2010, to achieve our purpose, two different years landsat imageries before and after flood i.e September 2009 and September 2010 have been applied and the desire results were achieved through integration of Remote Sensing (RS) and Geographical Information System (GIS) techniques. With the help of RS data, hazardous impacts of flooding 2010 have been observed on the bases of different factors which were performed on Arc Map 10.3.1, Erdas Imagine 9.2, eCognition Developer 64. After performing different analysis, the major losses have been observed which are shown in table 1to4 and further highlighted in Figure 5a to 8g.

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.

Re-evaluating safety risks of multifunctional dikes with a probabilistic risk framework

Abstract. It is not uncommon for a flood defence to be combined with other societal uses as a multifunctional flood defence, from housing in urban areas to nature conservation in rural areas. The assessment of the safety of multifunctional flood defences is often done using conservative estimates. This study synthesizes new probabilistic approaches to evaluate the safety of multifunctional flood defences employed in the Netherlands and explores the results of these approaches. In this paper a case representing a typical Dutch river dike combining a flood safety function with a nature and housing function is assessed by its probability of failure for multiple reinforcement strategies considering multiple relevant failure mechanisms. Results show how the conservative estimates of multifunctional flood defences lead to a systematic underestimation of the reliability of these dikes. Furthermore, in a probabilistic assessment uncertainties introduced by multifunctional elements affect the level of safety of the dike proportional to the reliability of the dike itself. Hence, dikes with higher protection levels are more suitable to be combined with potentially harmful uses for safety, whereas dikes with low protection levels can benefit most from uses that contribute to safety.

Life cycle assessment of point source emissions and infrastructure impacts of four types of urban stormwater systems

The implementation, operation and decommissioning of stormwater management systems causes environmental damage, while at the same time reducing pollutant loads in receiving waters by treating stormwater. The focus in research has been either on assessing impacts caused by stormwater infrastructure, or risks associated with stormwater discharges, but rarely have these two sources of environmental impacts been combined to allow a comprehensive environmental evaluation of stormwater management. We assess the environmental sustainability of four different generic stormwater management systems for a catchment of 260ha by a) modelling the flow of pollutants in stormwater, and resulting point source emissions to freshwater, and b) quantifying emissions and resources for all relevant processes associated with the life cycle of the infrastructure. Using life cycle impact assessment, we quantify the resulting environmental impacts and consequent damage to two areas of protection – ecosystems (expressed in time-integrated species loss) and natural resource availability (expressed in extra costs for future resource extraction). Our assessment shows that combined stormwater management causes the highest damage to both ecosystems (1.4E-03 species.yr/yr) and resource availability (8.8E+03 USD/yr). Separate systems using only green infrastructure were found to avoid damage to resource availability (−3.7 to −5.2 USD/yr) and cause lower ecosystem damage (1.1–1.3E-03 species.yr/yr). Stormwater discharges contribute significantly to the total ecosystem damage of the different systems (36–88%), and the sustainability of separate systems can be further improved by optimizing the removal efficiency of low-tech elements like surface basins and filter soil. The systems are designed according to engineering standards. Choosing different criteria, e.g. identical flood safety levels, would result in substantial changes of the relative performance of the systems. The findings highlight the importance of including point source emissions into the assessment to allow comparative conclusions and minimisation of environmental damage of stormwater management.

Is Bangkok becoming more resilient to flooding? A framing analysis of Bangkok's flood resilience policy combining insights from both insiders and outsiders

The rapidly urbanizing cities in Southeast Asia experience increasing flood impacts due to the consequences of climate change. In these cities, policy efforts to build flood resilience are gaining momentum. The aim of this paper is to understand and assess flood resilience policy development, particularly in cities in developing countries. Bangkok is one of the cities that participates in the 100 Resilient Cities Programme (100RC) - the international policy platform for building resilient cities. In 2017, the Bangkok Metropolitan Administration (BMA) launched the ‘Bangkok Resilience Strategy’ to translate the resilience concept to its urban context. A framing perspective is adopted to reconstruct the strategy, process and anticipated outcome of Bangkok's flood resilience policy. We studied data obtained from ‘insiders’ (involved policy makers, experts and consultants) and ‘outsiders’ (local communities, civil society organizations and news media). Findings indicate that the economic growth frame is prevailing in the development of Bangkok's flood resilience policy, prioritizing structural flood protection with little attention for flood adaptation measures and related social impacts among vulnerable communities. The role of local communities and civil society in the formulation of Bangkok's flood resilience policy is limited. This paper therefore recommends cities in developing countries and cities in the 100RC Programme to organize a more inclusive resilience building process for addressing social problems regarding urban poor communities along with increasing flood safety and protection.

Numerical Simulation and Engineering Application of a Dovetail-Shaped Bucket

Flip trajectory buckets are widely used in hydraulic engineering. With the rapid development of water conservation projects, an increasing number of these projects are located in complex topography. As a result, the energy dissipation and anti-scour abilities of the outlet structures in such projects have become the focus of research. This study used FLOW-3D fluid computation software with a renormalization group turbulence model and a volume of fluid free surface tracking technique. The bank of the ShiZiYa reservoir is steep and is located in a narrow river valley, in which the downstream angle is approximately 70°. The system was modeled under the conditions of this special terrain with the flow energy dissipation scheme having dovetail drainage characteristics, and the results were verified experimentally. With adjustments of the angles of the left and right walls, the width and jet angle of the dovetail-shaped sill were optimized in the model to ensure that the downstream flow fell into the main channel, and the hydraulic characteristics of the water jet were analyzed. The results showed that this scheme can meet the flood safety requirements of the ShiZiYa reservoir.

A hazai árvízvédelmi stratégia főbb irányai

Formulation of a country’s flood protection s trategy in every case depends on the technical-socio-economic conditions of the given country. The flood safety requirements are highly influenced by the country’s performance and financial situation. On the Hungarian rivers, flood safety is based on the 100-year return period maximum flood events and the flood safety requirements must be developed accordingly. The state must guarantee the success of the flood protection up to this flood safety level. The water management sector has also formed the Hungarian flood protection strategy to this flood safety level as an operator of primary flood protection structures. In the past decades, due the changes in socio-economic conditions and the rise of extremities caused by climate change have caused that flood protection strategy had to be changed several times. In my article I show the changes and the effects of changes on the operational flood protection activities and preventive flood protection strategy.

Effects of Shoal Margin Collapses on the Morphodynamics of a Sandy Estuary.

Shoal margin collapses of several million cubic meters have occurred in the Western Scheldt estuary, the Netherlands, on average five times a year over the last decades. While these collapses involve significant volumes of material, their effect on the channel‐shoal morphology is unknown. We hypothesize that collapses dynamicize the channel‐shoal interactions, which could impact the ecological functioning, flood safety, and navigation in the estuary. The objective is to investigate how locations, probability, type, and volume of shoal margin collapse affect the channel‐shoal dynamics. We implemented an empirically validated parameterization for shoal margin collapses and tested its effect on simulated estuary morphological development in a Delft3D schematization of the Western Scheldt. Three sets of scenarios were analyzed for near‐field and far‐field effects on flow pattern and channel‐shoal morphology: (1) an observed shoal margin collapse of 2014, (2) initial large collapses on 10 locations, and (3) continuous collapses predicted by our novel probabilistic model over a time span of decades. Results show that a single shoal margin collapse only affects the local dynamics in the longitudinal flow direction and dampen out within a year for typical volumes, whereas larger disturbances that reach the seaward or landward sill at tidal channel junctions grow. The direction of the strongest tidally averaged flow determined the redistribution of the collapsed sediment. We conclude that adding the process of shoal margin collapses increases the channel‐shoal interactions and that in intensively dredged estuaries shoal margins oversteepen, amplifying the number of collapses, but because of dredging the natural morphological response is interrupted.

Designing Model of Serious Game for Flood Safety Training

Serious games have the potential to increase motivation among users in the aspect of safety training. Additionally, serious games can also positively impact training outcomes when the knowledge and skills acquired during a serious game training are transferred to a real-world application. The development of a serious game is based on the game elements and theories determined according to the goals or objectives of the game being developed. There are existing serious games that have been used for training but less usage of scenarios and feedback element render the game less effective for training purposes. Besides that, existing serious games for training purposes fail in delivering domain content to achieve the game objectives since they are more focused on entertainment. This is because the games do not involve experts in providing game domain content. The objective of this paper is to design a serious game model for flood safety training. Preliminary study and literature review are used in this study as the research method. The result of this study is a model of a serious game for flood safety training. In conclusion, this study focuses on the design of a serious game model for flood safety training that includes the elements of serious game identified and adapted to psychology readiness based on the flood training module by Malaysian Defense Force (APM). This makes the serious game more attractive and can give intrinsic motivation to players. For future studies, every single element serious game and theory of psychology readiness in the model developed in this study will be validated with the expert game and expert psychology.

FRS4: options for wave freeboard

The fourth edition of flood and reservoir safety (FRS4) published in 2015 included the change that where an existing dam failed to meet the defined engineering standard, then a risk-based approach could be used as an aid to assessing the value (cost against reduction in risk) of undertaking works to meet the standard, or the extent of works required, if any, to reduce risk to ‘as low as reasonably practicable’. This paper summarises the key aspects of a case history with a risk-based approach to assessing the adequacy of freeboard, which was presented at the FRS workshop at the BDS conference at Swansea.

Sand Spit Elongation and Sediment Balance at Cua Lo Inlet in Central Vietnam

Duy, D.V.; Tanaka, H.; Mitobe, Y.; Anh, N.Q.D., and Viet, N.T., 2018. Sand spit elongation and sediment balance at Cua Lo Inlet in Central Vietnam. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 32–39. Coconut Creek (Florida), ISSN 0749-0208.Erosion is significant on the downdrift beach of Cua Lo Inlet, which is located in Central Vietnam. The elongation of Cua Lo Inlet's updrift sand spit together with severe erosion of the downdrift bank is raising numerous social problems such as flood safety and land loss. In this study, a series of Landsat and Google Earth images were used to analyze and investigate the inlet recent morphological changes and evolution. Since 1970 the inlet has constantly migrated towards the sediment transport pathway, and its traveling distance has reached 1700 m. In order to quantitatively investigate such characteristics, the tip coordinates and the area of the sand spit updrift of the inlet were calculated. In particular, the area of the sand spit has increased remarkably, and the increasing rate is almost constant. Using this value, the rate of sand volume transported along the updrift sand spit by the waves was estimated and it is in good agreement with the longshore sediment transport rate of the surrounding beach.