Resilience and flood risk management: A systems approach applied to lowland rivers

Floods along lowland rivers still cause a lot of damage and casualties although centuries of experience with flood risk management have passed. In order to reduce flood impacts and to prevent flood waves from causing disasters, the current and alternative flood risk management strategies need to be reconsidered. As a potential solution the Dutch policy makers propose to increase the resilience of systems, since resilient systems are expected to be able to cope better with disturbances such as flood waves. In their policies, however, resilience and resilient water systems are not clearly defined. Resilience has a positive connotation although it is difficult to explain exactly what the positive aspects of resilient systems for water management are. In this thesis this positive connotation of resilience was verified. The objective of this research was to establish whether applying the resilience concept facilitates the development of comprehensive strategies for flood risk management of large lowland river systems. To study the potential benefits resulting from the application of the resilience concept first resilience was defined and quantified by indicators. Secondly, case studies were carried out on the lowland parts of the Rhine, Meuse and Mekong Rivers.Civil Engineering and Geoscience

Influence of load interdependencies of flood defences on probabilities and risks at the Bovenrijn/IJssel area, The Netherlands

In the Netherlands, flood risk analysis is usually carried out for a location, without considering potential flood defence failures in upstream areas. This may result in significant over- or underestimation of flood risks. The effect of upstream failures on failure probabilities and flood risks in other areas is called load interdependence of flood defences. This effect can be both positive and negative: loads on a certain defence can increase and decrease due to failures upstream. In this research a framework was developed which enables the consideration of these interdependencies in a probabilistic framework. This was done by using Monte Carlo with Importance Sampling and a fast inundation model, which enables considering many scenarios with many different breaches. The case considered was the Bovenrijn/IJssel area in the Netherlands, a lowland river area where dike breaches can have both positive and negative effects on the loads on other flood defence elements. The risk estimates and changes in water level probabilities in the considered area show a clear interrelation between loads on different elements of the flood defence system and demonstrate that the effects of dike breaches on loads and risks on other locations cannot be ignored in flood risk analysis.Hydraulic EngineeringCivil Engineering and Geoscience

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.Hydraulic Structures and Flood Ris

Experimental determination of pressure coefficients for flood loading of walls of Dutch terraced houses

Failure of residential buildings during floods is an important cause of damage and loss of life. In the case of the Netherlands, the collapse of buildings is implicitly included in current damage and mortality curves since these are generated from historical data. However, the Netherlands has not experienced destructive flooding since 1953, so damage functions for modern buildings do not exist. Therefore, this paper assesses the effect of floods on modern Dutch residences with laboratory tests and structural models in order to formulate physically-based fragility curves. The results gathered are also applicable to similarly-built masonry and cavity-wall rowhouses elsewhere. Almost half of the Dutch population live in terraced houses (also known as townhouses or rowhouses), of which the critical failure mechanism during a flood is out-of-plane bending of the load-bearing walls. Failure of these structural elements should be analysed with the pressure coefficient, Cp, instead of the currently used drag coefficient, CD, because wall collapse is more likely than displacement of the entire structure. This paper describes the quantification of both coefficients by conducting flume experiments on rectangular boxes with different geometries and orientations. Higher drag coefficients are derived from the experiments than provided by FEMA, resulting in higher hydrodynamic loads on the residences. The physical approach to evaluate the collapse of residences is exemplified with a case study of the three most common type of residences in the Netherlands. Structural analyses of their load-bearing walls subjected to a hydrostatic and hydrodynamic load perpendicular to the wall show failure due to milder flood conditions than the current damage curves do for all case study residences. A sensitivity analysis shows an important influence of wall thickness, initial axial loading of the wall, and the flood water level inside the residence.Applied MechanicsHydraulic Structures and Flood Ris

Assessing quick-wins to protect critical urban infrastructure from floods: Case study (three urban communities) Bangkok, Thailand

Hydraulic EngineeringCivil Engineering and Geoscience