In this paper the safety of a double-dike system (or twin dikes) is assessed. Such a system consist of two parallel lines of flood defences. During storms the combined strength of the parallel flood defences must prevent flooding of the hinterland. A culvert can be implemented for the tidal exchange of sea water to enable new land-uses in the area between the dikes such as aquaculture, saline agriculture, salt marsh restoration and clay extraction. We develop a general framework for assessing the safety of such double dike systems and apply a simplified version to the Double Dike between Eemshaven and Delfzijl (The Netherlands) to test this method. In doing so, we aim to quantify the flood protection benefits of parallel flood defenses and enable their use in multifunctional flood protection strategies. Within the framework the transmission of hydraulic loads by the seaward dike to the landward dike in the case-study was described by overtopping, overflow and erosion of the outer slope, alongside discharge through the culvert in the event of a non-closure. For the subset of coastal double dike systems with a tall seaward dike (as in the case-study), the results show only a negligible improvement in flood protection compared to a single dike system. With the addition of a culvert in the first dike, flood risk will only be reduced by the second landward dike if its height is sufficient to retain water in the event of a non-closure during common storm events. These double dike systems are implemented for potential uses of the inter-dike zone, e.g. for nature restoration, rather than as a measure to primarily improve flood protection.

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In this paper, we introduce and test a framework to qualitatively assess the environmental impact of climate adaptation innovations with the ambition to facilitate the implementation of these adaptations. The framework was designed to enable continuous environmentally conscious benchmarking based on three environmental performance indicators: sustainable design, environmental impact and ecological impact. It was pilot tested by uninvolved experts and key-persons for two large-scale nature-based flood adaptation innovations in the Netherlands and discussed with environmental assessment professionals. Our findings indicate how the inclusion of our framework helps to identify important knowledge gaps regarding environmental co-benefits and trade-offs, and can be beneficial to both those developing the innovation and the local authorities charged with assessing the suitability of innovations. We conclude by noting how the incorporation of environmental impact assessment from the design stage of adaptations could supplement existing environmental assessment regulations pre-empting concerns rather than reacting to them.

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Integrating natural components in flood defence infrastructure can add resilience to sea-level rise. Natural foreshores can keep pace with sea-level rise by accumulating sediment and attenuate waves before reaching the adjacent flood defences. In this study we address how natural foreshores affect the future need for dike heightening. A simplified model of vertical marsh accretion was combined with a wave model and a probabilistic evaluation of dike failure by overtopping. The sensitivity of a marsh-dike system was evaluated in relation to a combination of processes: (1) sea-level rise, (2) changes in sediment concentration, (3) a retreat of the marsh edge, and (4) compaction of the marsh. Results indicate that foreshore processes considerably affect the need for dike heightening in the future. At a low sea-level rise rate, the marshes can accrete such that dike heightening is partially mitigated. But with sea-level rise accelerating, a threshold is reached where dike heightening needs to compensate for the loss of marshes, and for increasing water levels. The level of the threshold depends mostly on the delivery of sediment and degree of compaction on the marsh; with sufficient width of the marsh, lateral erosion only has a minor effect. The study shows how processes and practices that hamper or enhance marsh development today exacerbate or alleviate the challenge of flood protection posed by accelerated sea-level rise.

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Effective adaptation to sea-level rise is critical for future flood protection. Nature-based solutions including salt marshes have been proposed to naturally enhance coastal infrastructure. A gently sloping grass-covered dike (i.e. Wide Green Dike) can be strengthened with clay accumulating locally in the salt marsh. This study explores the feasibility of extracting salt-marsh sediment for dike reinforcement as a climate adaptation strategy in several sea-level rise scenarios, using the Wide Green Dike in the Dutch part of the Ems-Dollard estuary as a case study. A 0-D sedimentation model was combined with a wave propagation model, and probabilistic models for wave impact and wave overtopping. This model system was used to determine the area of borrow pits required to supply clay for adequate dikes under different sea-level rise scenarios. For medium to high sea-level rise scenarios (>102 cm by 2100) thickening of the clay layer on the dike is required to compensate for the larger waves resulting from insufficient marsh accretion. The model results indicate that for our case study roughly 9.4 ha of borrow pit is sufficient to supply clay for 1 km of dike reinforcement until 2100. The simulated borrow pits are refilled within 22 simulation years on average, and infilling is projected to accelerate with sea-level rise and pit depth. This study highlights the potential of salt marshes as an asset for adapting flood defences in the future.

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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.@en

This article describes and analyzes the reintroduction of the “wide green dike” in the Netherlands. It is a noteworthy example of implementation of an innovation in long-term strategic delta planning. The Dutch Delta Program was central herein. Pursuing its ambition to make the Netherlands climate-proof, the Delta Program invited a diverse set of actors to participate in developing a long-term adaptation plan, and also to propose innovative short-term measures to help realize that plan. The wide green dike was actively promoted by a local water board, with involvement of scientists and nature conservation organizations. A stepwise participatory process resulted in national-level recognition of the potential of the wide green dike, particularly due to its “green” and “adaptability” characteristics. Alignment of flood protection and climate adaptation goals with nature conservation objectives, as well as collaboration with new actors, were all crucial in the reintroduction of this innovation.@en

Since climate adaptation entered the political agenda, numerous efforts on the international as well as on the national, regional and local scale have been made to stimulate and support mechanisms for climate adaptation. The EU, for instance, stimulates the development of adaptation strategies by Member States, as well as the development of innovative climate adaptation measures (which may fit in the adaptation strategy) and decisioncentered applications of climate research. The development of innovative adaptation measures is funded by both EU’s LIFE Programme and Horizon2020. A special type of innovative adaptation measures are Nature Based Solutions. Nature Based Solutions deliberately use nature or natural processes (or mimic natural processes) and the services they provide to address societal challenges such as climate change or natural disasters. They also fit in EU policies to protect, preserve and improve the environment, including nature and biodiversity, for present and future generations. Although Nature Based Solutions fit in multiple policies and serve multiple objectives, implementation of these innovative climate adaptation measures is still limited. In 2016 the EU project BRIGAID commenced. BRIGAID is a 4-year project under EU Horizon2020 aimed to effectively bridge the gap between innovators of climate adaptation measures and end-users of these adaptation innovations. One of BRIGAIDs objectives is to develop a comprehensive, standardized methodology (the TIF) for testing and implementing climate adaptation measures, in particular to assess their potential to reduce risks from floods, droughts and extreme weather, and guidelines for assessing an innovation’s social readiness and impact across various geographic scales and socio-economic and environmental sectors. The goal of testing and assessing is to increase the technology readiness level (TRL) of the innovation, while simultaneously evaluating its societal acceptance and its potential for implementation. TRLs are a well-accepted measurement of the maturity level of particular technologies, and ranges from 1 (basic principles observed) through 9 (total system used successfully in project operations). BRIGAID’s TIF Tool covers TRL 1-3 and consists of a desk intended functionality (e.g., design criteria), the identificationstudy which will result in a description of the climate adapatation innovation of possible failure modes, a preliminary theoretical social acceptance assessment, and an initial screening of the potential impact of the innovation on the environment and on important socio-economic sectors. This helps innovators to identify possible societal, technical, environmental and sectoral concerns that their innovations could raise early on – and iteratively throughout the development – so that they can modify their designs. In this paper the potential of the TIF Tool to promote Nature Based Solutions is explored by applying the TIF tool on the Wide Green Dike concept and by analysing how the ex-ante impact assessment of this adaptation innovation could help to overcome the gap between the initial concept and the application of this measure.@en

Rural areas face major challenges in adapting to the impacts of climate change, in particular to floods and droughts. This calls for both adaptation of rural functions and climate-proof and water-resilient design of the rural area, often implying improvement of water retention and flood protection. Implementation of such climate change-related goals in spatial planning often involves adaptations in water management, perhaps even leading to land consolidation. Water management and land consolidation thus form important tools for spatial adaptation. Land consolidation is also a tool to support the integration of other claims that need room, such as agriculture, nature, landscape and tourism functions. This paper investigates the history of and approaches to land consolidation and water management in Poland and the Netherlands, and illustrates the integration of land consolidation and water management to realize a multifunctional climate resilient rural area by two examples in each country. We qualitatively compared the extent to which the planned activities in water retention and flood protection were realized and planned results were achieved for other functions. We found that the two adaptation measures, water retention and flood protection, were more effective in the Netherlands, stemming from ample attention for the impact of climate change and the incorporation of climate change adaptation goals in water policy. Furthermore, the water retention and flood protection measures in the Netherlands better serve multiple functions: agriculture, nature, recreation, landscape and infrastructure. Reasons for this are the multidisciplinary and participatory approach, attention to public awareness and communication and promotion of the process. On the other hand, the Dutch have much to learn from Poland's vast, undisturbed natural areas, which contribute to a climate resilient landscape. Both Poland and the Netherlands could therefore benefit from bringing together ideas and experiences regarding climate proofing the rural area.

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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

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 paper analyses the effect of observed vegetation characteristics on modelled wave heights. Detailed information on species composition, as well as on height, number of stems, and diameter of the plant species of a restored salt marsh on the Wadden barrier island of Terschelling was used to parameterize and apply the Simulating Waves Nearshore-Vegetation wave model to a schematized restored salt-marsh zone in front of the dike. The results indicate that wave damping by vegetated forelands is strongly related to vegetation heterogeneity and salt-marsh zonation. The modelling works suggest that at the study site under storm conditions with a frequency of 5-10 times/y, a vegetated foreland of some 90 m in width will dampen the wave height more than 80%, whereas under extreme conditions (1/2000 y) a foreland covered with dense vegetation will dampen the wave height up to 50%. These results imply that at the study site a vegetated foreland in front of the dike leads to reduced wave attack on the dike, which may result in changed requirements for both height and revetment of the dike while maintaining the required safety level. Although there are still many questions concerning dimensions, management, and performance, developing a vegetated foreland seems an interesting strategy to adapt existing flood protection works to the effects of climate change.
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In the Netherlands, the concept of a multifunctional dike has already often been implemented, and has been identified as a promising climate adaptation measure. In a multifunctional dike, functions like urban development, transport infrastructure, recreation, agriculture or nature are deliberately combined with its primary flood protection function. This means that the design must be based on the requirements and life span of all different functions, while in a monofunctional dike only the flood protection function is considered. By accommodating other functions, a multifunctional dike may easier fit into, or even contribute to the quality of the landscape. Moreover, these other functions may help in financing the flood protection works, but governance is more complicated. To avoid costly adjustments forthcoming from changed safety standards, incorporation of multiple functions can require a more "robust" flood defence than a monofunctional flood defence. A robust flood defence can withstand more extreme situations than required by the present safety standards, and has a substantially lower flooding probability. Therefore, a multifunctional dike may be attractive in view of the uncertainties regarding the effects of climate change and a changing world. Moreover, it will result in reduced flood risk. As part of the Dutch Delta programme, several explorative studies on multifunctional dikes were initiated. Most studies focused on urban areas, but also in the rural area interest emerged for multifunctional dikes, e.g. for the integration of salt marshes into the flood defences. Marshes provide valuable habitat for vegetation and invertebrate species, and are important for wading birds. Furthermore, under condition of abundant sediment availability they can keep pace with sea level rise. Explorative modelling results indicate that vegetated forelands affect wave heights, even under extreme conditions. However, the inclusion of a vegetated foreland into the dike design does not automatically mean that nature values and flood protection are well integrated. Flood protection imposes rather different requirements on the extent and features of marshes than nature conservation and development. Wave damping is most effective with a high and stable marsh, while nature thrives with dynamic processes and differences in elevation. Therefore, only a design that allows natural marsh dynamics and includes different marsh zones could combine nature values with flood protection. In practice, this means a dike design with an uncertain foreland, that offers space for natural processes. The uncertainty in foreland development reduces the possible flood risk reduction. In our paper we describe the critical points of interest concerning risk reduction in this system.

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