Flood prone areas are often protected against flooding by an extensive network of flood defenses. To ensure their structural integrity, these flood defenses are periodically assessed. Many levees have been functioning well for decades, and have survived several relatively high hydraulic loads within their lifetime. However, information on survived load conditions is seldom included in levee safety assessments. Observed degradation from levee inspections is also not taken into account. That way, information that is useful to improve the accuracy of estimations of the actual strength of the levee remains unexploited. This study proposes a pragmatic approach to include observations of survived loads and levee degradation in the levee safety assessment. This approach consists of three steps: (1) a prior estimation of the failure probability, based on levee characteristics, (2) a posterior estimation of the failure probability, based on observed hydraulic loads, and (3) correction of the posterior failure probability estimation, based on levee inspections. In a case study, the estimated failure probabilities using this approach were much lower than when information on levee performance was not included. This study demonstrates the value of levee performance observations and how they could be included to improve levee safety assessments.

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Flood risk reduction can be provided by interventions such as raising land or constructing flood defences. This paper introduces an approach to optimise the selection of risk reduction strategies. It expands existing economic optimization approaches for flood defences, by introducing (largely) analytical formulations to include the effects of approaches to mitigate flood consequences. The method considers the size of the protected area and associated damages, the costs and dimensioning of interventions and the likelihood of flooding. It is applied in several practical cases. Within the context of this economic model, we conclude that a system of flood defences is more economical than a landfill for larger areas. Fills are preferred for small areas and/or for low costs. A combination of strategies is preferred when the value protected by the flood defence is low compared to the value protected by the fill, or when the high value development is relatively small in size. The sensitivity of outcomes to the choice of the main input parameters is presented, as well as implications of the results and selection of strategies in developing and developed countries. Overall, this approach supports decision makers in developing effective strategies to manage and reduce flood risk.

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The application of risk-based approaches for the design of flood infrastructure has become increasingly common in flood management. This approach, based on risk reduction and reliability, is used to assess the performance of conventional interventions (e.g., flood defences and dams) and to support decisions regarding their implementation. However, for more innovative solutions, performance has often not been quantified by means of these metrics and, therefore, end-users are hesitant to implement them in existing flood risk reduction systems. To overcome the gap between innovators and end-users, we present a framework based on four performance indicators, to ensure the required insights in risk and reliability are provided. The four indicators: effectiveness, durability, reliability and costs, allow end-users to evaluate, select, and implement flood adaptation innovations, and provide innovators with insight into the performance of the technology and the criteria and information necessary for successful market uptake of their innovation. The practical application of the framework is demonstrated for a (hypothetical) case of a hospital complex built in an area that has subsided below the surrounding area, which is subject to tropical rain showers. The following innovations are considered: an early flood warning system, a green roof, and a temporary flood barrier.

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Polders in the Netherlands are protected from flooding by flood defence systems along main water bodies such as rivers, lakes or the sea. Inside polders, canal levees provide protection from smaller water bodies. Canal levees are mainly earthen levees along drainage canals that drain excess water from polders to the main water bodies. The water levels in these canals are regulated. During the last decades, probabilistic approaches have been developed to quantify the probability of failure of flood defences along the main water bodies. This paper proposes several extensions to this method to quantify the probability of failure of canal levees. These extensions include a method to account for (i) water-level regulation in canals, (ii) the effect of maintenance dredging on the geohydrological response of the canal levee and (iii) survival of loads in the past. The results of a case study demonstrate that the proposed approach is capable of quantifying the probability of failure of canal levees and is useful for exploring the relative benefit of risk mitigating measures for canal levees.

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Flood risk reduction systems are applied worldwide to reduce flood risk and provide protection of flood prone areas. More and more, decision makers use risk-based approach for the design and implementation of interventions in these systems. This dissertation advances existing risk-based approaches for specific interventions within a flood risk reduction system. Highlights of this dissertation include i) quantifying the reliability of canal levees, ii) evaluating the effectiveness of emergency measures, iii) optimizing portfolios (of combinations) of risk reduction strategies: flood defences and/or land fills and iv) assessing the performance of innovative interventions for flood risk reduction. @en

Floods are the costliest and deadliest weather-related disaster globally. With higher population density in flood prone areas, increased urban development, and projected climate impacts, the frequency and severity of flooding in Europe is predicted to rise. While permanent flood defences have been shown to be more economically effective and reliable in the long-term than temporary flood barriers, they are expensive upfront, socially and politically complex, and time-consuming to build (Lendering et al., 2015). To adapt to climate change and mitigate flooding in the short term, it will be necessary to identify and test temporary flood barriers which can be quickly deployed during a flood event to mitigate risk. Moreover, in some areas, where permanent structures may be phsyically (or socially) infeasible, temporary (or semi-permanent) flood barriers may become a permanent strategy for mitigating floods.@en

Currently there is no internationally accepted framework for assessing the readiness of innovations that reduce disaster risk. To fill this gap, BRIGAID is developing a standard, comprehensive Testing and Implementation Framework (TIF). The TIF is designed to provide innovators with a framework for innovation and guidelines for assessing an innovation’s technical effectiveness, its social acceptance, and its impact on key socio-economic and environmental sectors. The vision is that the TIF will become the standard framework used to assess the effectiveness of climate adaptation innovations and the European quality label for testing.@en

This report focuses on the methodological development of the testing and implementation framework (TIF) for increasing the socio-technical readiness of climate adaptation innovations and assessing their impact on different socio-economic and environmental sectors. It is designed to be read by innovators and used as a supporting document for the application of different toolboxes made available through BRIGAID. In this report, Chapter 2 provides an overview of the different components of the TIF, including an overview of the planned testing phases. Definitions for the Performance Indicators (PI) are provided in Chapter 3, which also includes a description of how the test results which are to be integrated into the Climate Innovation Window (CIW) (in WP7). Elaborated guidelines for testing are provided in Chapters 4-6. Specifically, guidelines for assessing the technical effectiveness of innovations are provided in Chapter 4; guidelines for assessing the impact of an innovation on the environment and socio-economic sectors that will feel direct consequences of climate change are provided in Chapter 5; guidelines for assessing the societal acceptance of innovations in Chapter 6.@en

On August 25, 2017, Hurricane Harvey made landfall near Rockport, Texas as a Category 4 hurricane with maximum sustained winds of approximately 200 km/hour. Harvey caused severe damages in coastal Texas due to extreme winds and storm surge, but will go down in history for record-setting rainfall totals and flood-related damages. Across large portions of southeast Texas, rainfall totals during the six-day period between August 25 and 31, 2017 were amongst the highest ever recorded, causing flooding at an unprecedented scale. More than 100,000 residential properties are estimated to have been affected in southeast Texas. It is likely that Harvey will rank among the costliest storms in U.S. history. In the wake of Hurricane Harvey, Delft University of Technology has initiated a Harvey Research Team to undertake a coordinated multidisciplinary investigation of the events with a focus on the greater Houston area. This ‘fact-finding’ research is based on information available from public sources during and in the first weeks after the event. Results are therefore preliminary, but aim to provide insight into lessons that can be learned for both Texas and the Netherlands. As part of the investigations, a hackathon with more than 80 participants was organized to collect and analyze available public information. Houston was especially hard hit by flooding. During the event, all 22 watersheds in the greater Houston area experienced flooding. Many of Houston’s creeks and bayous exceeded their channel capacities, reaching water levels never before recorded. Across large portions of Harris County, rainfall totals exceeded the 1000-year return period. In addition, the water from the two reservoirs protecting downtown Houston (Addicks and Barker) were opened on August 28 to prevent catastrophic damages to the dams and further flooding in upstream communities. The releases exacerbated flooding in the areas downstream of the dams and an estimated 4,000 homes in neighborhoods downstream of the dams were impacted by flooding. The consequences of the event in the greater Houston area have been characterized in terms of economic damages, loss of life and impacts on critical infrastructure, airports and industry. In total, more than 100,000 homes were affected more than 70 fatalities were reported in the greater Houston area. The event highlighted the vulnerability of industrial facilities, as several cascading impacts (releases of toxic materials and explosions) were reported. Emergency response has been assessed. No large-scale mandatory evacuation was ordered before or during Harvey. However, it appeared that several local evacuations were ordered for areas with specific risks and circumstances. During the event, many people were trapped by rising waters necessitating a major rescue operation. In total, more than 10,000 rescues were made by professional and volunteer rescuers. Social media played an important role during the event and recovery, as an additional source of information, to inform emergency managers and as a means to organize community response e.g. for clean-up. Also, messages were conveyed through social media, e.g. a report of a levee breach that appeared to be incorrect afterwards. Major flooding is a problem that has multiple causes from both physical and social origin. Based on the investigations, recommendations for future research and lessons for flood management have been formulated. A better understanding of the issues studied in this report is expected to contribute to a knowledge basis for further in-depth investigations and future directions for flood risk reduction. Data collection and Report production funded by DIMI and DSys Special Case 'Houston Galveston Bay Region, Texas, USA' Project 'Harvey hackathon' and follow-up research @en

Polders in the Netherlands are protected from flooding by primary and regional flood defence systems. During the last decade, scientific research in flood risk focused on the development of a probabilistic approach to quantify the probability of flooding of the primary flood defence system. This paper proposed a methodology to quantify the probability of flooding of regional flood defence systems, which required several additions to the methodology used for the primary flood defence system. These additions focused on a method to account for regulation of regional water levels, the possibility of (reduced) intrusion resistance due to maintenance dredging in regional water, the probability of traffic loads and the influence of dependence between regional water levels and the phreatic surface of a regional flood defence. In addition, reliability updating is used to demonstrate the potential for updating the probability of failure of regional flood defences with performance observations. The results demonstrated that the proposed methodology can be used to determine the probability of flooding of a regional flood defence system. In doing so, the methodology contributes to improving flood risk management in these systems.@en