The 2021 summer floods in the Netherlands: some findings and lessons

Hydraulic Structures and Flood Ris

Overview and Design Considerations of Storm Surge Barriers

The risk of flooding in coastal zones is expected to increase due to sea level rise and economic development. In larger bays, estuaries, and coastal waterways, storm surge barriers can be constructed to temporarily close off these systems during storm surges to provide coastal flood protection. Worldwide, 18 storm surge barriers have been constructed thus far, but they are increasingly being considered as a future solution for other coastal locations. This study provides a systematic overview of existing storm surge barriers. It analyzes informationabout the main functions of each barrier, the type of gates used, and the associated costs. It also shows that functional requirements determine the design and layout of the barrier. The main design challenges are discussed. The study results may be of use in future planning and preliminary storm surge barrier designHydraulic Structures and Flood Ris

Wave attenuation by salt marsh vegetation

Salt marshes are a characteristic feature of estuaries and coastal seas. They are found in the upper coastal intertidal zones between land and water, which are regularly flooded by tides and surges. They are covered with salt-tolerant vegetation types, such as herbs and grasses. Sheltering from continuous intense hydrodynamic forcing by waves and currents and sufficient supply of (fine) sediment are the two main requirements for salt marsh development. The presence of vegetation accelerates the sediment settlement by reducing the wave forces on the bed material. Addition-ally, the roots of the plants stabilize the accumulated sediments and amplify the process of subsoil drainage, consoli-dation and compaction. Salt marshes and the intertidal flats in front form a coherent system with many mutual dependencies.Coastal flood risk reduction by creating and restoring ecosystems is increasingly seen as a promising supplement to conventional coastal engineering methods. Salt marshes, mangrove forests and reed fields can act as a vegetated foreshore in front of a coastal dike. In such a combined dike-foreshore system, the foreshore plays a role in attenuating storm waves, whereas the dike retains the surge and the remaining wave energy. The current study focuses on the process of wave attenuation by vegetation and, vice versa, the process of breakage of vegetation due to wave action.Hydraulic Structures and Flood Ris

How does the risk-based approach work?

Hydraulic Structures and Flood Ris

Global mortality from storm surges is decreasing

Changes in society's vulnerability to natural hazards are important to understand, as they determine current and future risks, and the need to improve protection. Very large impacts including high numbers of fatalities occur due to single storm surge flood events. Here, we report on impacts of global coastal storm surge events since the year 1900, based on a compilation of events and data on loss of life. We find that over the past, more than eight thousand people are killed and 1.5 million people are affected annually by storm surges. The occurrence of very substantial loss of life (>10 000 persons) from single events has however decreased over time. Moreover, there is a consistent decrease in event mortality, measured by the fraction of exposed people that are killed, for all global regions, except South East Asia. Average mortality for storm surges is slightly higher than for river floods, but lower than for flash floods. We also find that for the same coastal surge water level, mortality has decreased over time. This indicates that risk reduction efforts have been successful, but need to be continued with projected climate change, increased rates of sea-level rise and urbanisation in coastal zones.Hydraulic Structures and Flood Ris

Flood risk reduction for Galveston Bay: Preliminary design of a coastal barrier system

Many coastal areas around the world are densely populated and at risk from flooding, but utilize different strategies to deal with coastal hazard. This chapter summarizes how Dutch concepts for coastal flood risk reduction have been explored for Galveston Bay. Firstly, it is shown how risk-based screening methods can help to evaluate various alternative strategies based on metrics such as costs, risk reduction and (societal and environmental) impacts. Application of this approach for Galveston Bay that a coastal spine alternative would entail a large investment, but it would provide the greatest risk reduction by maximizing the protected area. Secondly, a preliminary design for the coastal spine (also known as the Ike Dike) has been elaborated for protection of the region against storm surges, with involvement of Dutch and international students and experts. It includes storm surge barriers at Bolivar Roads and San Luis Pass, and several alternatives for the land barrier—including a fortified dune. Important aspects for future work are discussed, such as the cost estimation, in-bay measures, and the need for integral and proactive planning.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Hydraulic Structures and Flood Ris

Advances in reliability analysis of the piping failure mechanism of flood defences in the Netherlands

Piping is one of the main failure mechanisms for flood defences. This paper gives an overview of recent developments in the reliability analysis for this mechanism in the Netherlands. These comprise new approaches in the treatment of heterogeneity of the subsoil with respect to the failure process, the inclusion of information from field observations and monitoring by means of Bayesian Updating. Also, a framework is presented for including the effects of taking emergency flood fighting measures in reliability analysis. In essence, incorporation of each of these aspects in modelling piping reliability can change the probability of failure considerably, depending on the local conditions and amount of information available a-priori.Hydraulic Structures and Flood Ris

Bending Vibrations of the Afsluitdijk Gates Subjected to Wave Impacts: A Comparison of two Design Methods

This paper describes a first case study of the application of a newly developed fluid-structure interaction model to the design of flood gates. The gates in the Afsluitdijk, that will be replaced in the coming years, are considered. Due to the presence of a concrete beam in front of the gates breaking wave can occur, leading to high impact pressures acting on the gate. For this case both a quasi-static approach and a more detailed semi-analytical model representing the dynamic behaviour including fluid-structure interac-tion are applied to determine the maximum deflection of the gate. Results show the capability of the model to efficiently quantify flood gate vibrations while considering the involved fluid-structure interaction. For the Afsluitdijk case this leads to a slightly lower maximum deflection of the gate, and therefore potentially al-lows a more economical design.Hydraulic Structures and Flood Ris

The influence of deviating conditions on levee failure rates

This study introduces a method for assessing the annual failure rate of levees based on information from historical floods, while also considering the return period of these past events. Also, an approach has been developed to quantify the influence of deviating conditions on failure rates. The presence of deviating conditions at failed and survived levee sections is analyzed based on satellite observations. Bayesian techniques and likelihood ratios are used to update the failure rate as a function of the presence of deviations. The river system of Sachsen-Anhalt, Germany, is used as a case study. It experienced severe floods with many levee failures in the years 2002 and 2013. It is found that the presence of geological deviations had a significant influence on the observed failure rate and that failure rate increases with the magnitude of the hydraulic loading. It is also discussed how the expected number of failures in a system during a flood event with a certain magnitude can be estimated. The results of this study can be used to further optimize soil investigations, calibrate the results of more advanced reliability analyses and complement risk assessments, particularly in data-poor environments.Hydraulic Structures and Flood Ris

Temporal Development of Backward Erosion Piping in a Large-Scale Experiment

This paper presents a large-scale backward erosion piping experiment aimed at studying the erosion rate. This temporal aspect of piping complements previous research that focused on the critical head. To study the progression rate in realistic conditions, an experiment was carried out on a 1.8 m high levee with a cohesive blanket on a sandy foundation. The pipe was guided along a row of pore pressure transducers in order to measure its temporal development. Pipe development in space and time was successfully derived from pore pressure changes, showing an average progression rate of 8  m/day during the progressive erosion phase. The results show a relation between upstream gradient and progression rate. Furthermore, analysis of the eroded sand mass shows a relatively large pipe volume compared to existing lab tests, and an approximately linear relation between pipe length and volume. The results and insights from this study can be used to validate and improve transient piping models, leading to more accurate dam and levee safety assessments.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Hydraulic Structures and Flood Ris