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Lessons of past disasters and preparedness actions to cope with future hydrological extreme events in the Netherlands
The Netherlands, being a low-lying delta of the rivers Rhine, Meuse and Scheldt, have grappled for centuries in coping with water-related disasters: floods originating from both storm surges and high river discharges. Projected climate change scenarios learned the country to prepare for even more frequent and more intense extreme events. We realized the need for new solutions: automatically heightening the levees to protect against flooding was no longer a sustainable solution. We had to change the system we worked with for centuries and broaden its goals. The Netherlands revisited their safety standards for protection against flooding, now incorporating a risk-based approach. We introduced nature-based solutions like “Room for the River” to enable higher river discharges and the “Sand Engine” for beach nourishment to complement traditional engineering for protective disaster resilient infrastructure. The Netherlands embraced system thinking to future proof the country, and we incorporated cultural and ecological values into adaptive decision making. The Netherlands has proven it can shift the fundamentals of its strategy to prepare for a changing climate. Essentially, we have addressed the synergies between the agendas of water-related disaster risk reduction and climate adaptation in a coherent way, both of which are essential in reaching the integrated goals of the nation’s long-term vision for sustainable development.
HELP global report on water and disasters 2019
The focus of HELP is to promote concrete actions by governments and stakeholders and to help achieve transformative changes to drastically improve preparedness and readiness for water-related disasters as well as provision of safe water and sanitation at emergency. Learning from experiences, lessons, and good practices of disasters that have already happened will enable the transformation fast and effectively. That is the very reason why HELP decided to start compiling and sharing lessons and experiences of major disasters on regular basis. This document is a major part of HELP’s flagship initiatives. The Report will be published on annual basis.
Parallellisatie van MODFLOW 6
Sinds eind 2017 werkt Deltares in opdracht van de United States Geological Survey (USGS) aan de parallellisatie van de open-source rekencode MODFLOW 6. Dit artikel geeft kort de gekozen concepten van de parallellisatie weer en de eerste numerieke experimenten op de Nationale Supercomputer Cartesius. De experimenten tonen aan dat aanzienlijke versnellingen in rekentijd kunnen worden behaald en dat de MODFLOW 6 rekenkern in de basis geschikt is voor zeer grote, hoge-resolutie, grondwatermodellen.
Global potential for the growth of fresh groundwater resources with large beach nourishments
Whether a coastal area is suitable for beach nourishments and can induce a growth in fresh groundwater resources depends on the appropriateness of the intended site for beach nourishments, and the attainable growth in fresh groundwater resources. In this study we presume that all eroding sandy beaches are suitable for large beach nourishments, and focus on the impact of these nourishments on fresh groundwater in various coastal settings. The growth in fresh groundwater resources -as a consequence of the construction of a beach nourishment- was quantified with 2-D variable-density groundwater models, for a global range in geological parameters and hydrological processes. Our simulation results suggest that large beach nourishments will likely lead to a (temporary) increase of fresh groundwater resources in most settings. However, for a substantial growth in fresh groundwater, the coastal site should receive sufficient groundwater recharge, consist of sediment with a low to medium hydraulic conductivity, and be subject to a limited number of land-surface inundations. Our global analysis shows that 17% of shorelines may consist of erosive sandy beaches, and of these sites 50% have a high potential suitability. This shows a considerable potential worldwide to combine coastal protection with an increase in fresh groundwater resources.
Value of information of Structural Health Monitoring in asset management of flood defences
One of the most rapidly emerging measures in infrastructure asset management is Structural Health Monitoring (SHM), which aims at reducing uncertainty in structural performance by using monitoring equipment. As earthen flood defence structures typically have large strength uncertainties, such techniques can be particularly promising. However, insight in the key characteristics for successful SHM for flood defences is lacking, which hampers the practical implementation. In this study, we explore the benefits of pore pressure monitoring, one of the most promising SHM techniques for earthen flood defences. The approach is based on a Bayesian pre-posterior analysis, and results are evaluated based on the Value of Information (VoI) obtained from different monitoring strategies. We specifically investigate the effect on long-term reinforcement decisions. The results show that, next to the relative magnitude of reducible uncertainty, the combination of the probability of having a useful observation and the duration of a SHM effort determine the VoI. As it is likely that increasing loads due to climate change will result in more frequent future reinforcements, the influence of scenarios of different rates of increase in future loads is also investigated. It was found that, in all considered possible scenarios, monitoring yields a positive Value of Information, hence it is an economically efficient measure for flood defence asset management both now and in the future.
Watching the beach steadily disappearing : the evolution of understanding of retrogressive breach failures
Retrogressive breach failures or coastal flow slides occur naturally in the shoreface in fine sands near dynamic tidal channels or rivers. They sometimes retrogress into beaches, shoal margins and river banks where they can threaten infrastructure and cause severe coastal erosion and flood risk. Ever since the first reports were published in the Netherlands over a century ago, attempts have been made to understand the geo-mechanical mechanism of flow slides. In this paper we have established that events, observed during the active phase, are characterized by a slow and steady retrogression into the shoreline, often continuing for many hours. This can be explained by the breaching mechanism, as elaborated in this paper. Recently, further evidence has become available in the form of video footage of active events in Australia and elsewhere, often publicly posted on the internet. All these observations justify the new term ‘retrogressive breach failure’ (RBF event). The mechanism has been confirmed in small-scale flume tests and in a large-scale field experiment. With a better understanding of the geo-mechanical mechanism, current protection methods can be better understood and new defense strategies can be envisaged. In writing this paper, we hope that the coastal science and engineering communities will better recognize and understand these intriguing natural events.
To advance sustainable stewardship, we must document not only biodiversity but geodiversity
Despite many facets of sustainable development being underpinned by access to geological assets, key elements of geodiversity are yet to be incorporated into policy documents and international conventions. We, therefore, propose essential geodiversity variables (EGVs) describing features and processes of Earth’s abiotic surface and subsurface to advance science and sustainable stewardship, complementing the existing essential variables. These EGVs will enable more holistic and better-informed monitoring efforts, decision making, and responses to global change.
Mekong delta much lower than previously assumed in sea-level rise impact assessments
Deltas are low-relief landforms that are extremely vulnerable to sea-level rise. Impact assessments of relative sea-level rise in deltas primarily depend on elevation data accuracy and how well the vertical datum matches local sea level. Unfortunately, many major deltas are located in data-sparse regions, forcing researchers and policy makers to use low-resolution, global elevation data obtained from satellite platforms. Using a new, high-accuracy elevation model of the Vietnamese Mekong delta, we show that quality of global elevation data is insufficient and underscore the cruciality to convert to local tidal datum, which is often neglected. The novel elevation model shows that the Mekong delta has an extremely low mean elevation of ~0.8m above sea level, dramatically lower than the earlier assumed ~2.6 m. Our results imply major uncertainties in sea-level rise impact assessments for the Mekong delta and deltas worldwide, with errors potentially larger than a century of sea-level rise.
Governance bodemdaling : handelingsperspectieven
Als gevolg van bodemdaling staan diverse maatschappelijke functies onder druk en worden de grenzen van het bodem- en watersysteem bereikt. Het Planbureau voor de Leefomgeving heeft inmiddels duidelijk gemaakt dat er hoge kosten met bodemdaling gemoeid zijn. Met name in het stedelijk gebied kunnen de kosten van herstel van schade en frequenter onderhoud aan infrastructuur oplopen tot EURO 5,2 miljard in het jaar 2020. Bodemdaling, door de hoge mate van complexiteit met zowel interne als externe afhankelijkheden in het socio-technisch systeem en de betrokkenheid van verschillende actoren, wordt als gevolg hiervan een steeds belangrijker (en gevoeliger) onderwerp binnen beleidsontwikkeling. In een onderzoek dat is uitgevoerd door Deltares en de Erasmus Governance Design Studio in opdracht van het Uitvoeringsprogramma Bodem en Ondergrond is antwoord gegeven op de vraag ‘Welke handelingsperspectieven t.a.v. governance zijn te ontwikkelen en bruikbaar voor omgaan met bodemdaling in stedelijk en landelijk gebied?’ Hierbij is een methodiek uitgewerkt waarmee handelingsperspectieven voor bodemdaling kunnen worden ontwikkeld. De term handelingsperspectief wordt gedefinieerd als: een samenspel van bestuurlijk-juridische, technische en ruimtelijke maatregelen. Elk handelingsperspectief bevat de rolverdeling, stijl van sturing en een set maatregelen, waardoor de handelingsruimte voor het omgaan met -in dit geval- bodemdaling verkend wordt. De aanpak is ontwikkeld en getoetst in twee praktijkcases: Zaanstad en Rotterdam.
Large scale flood hazard analysis by including defence failures on the Dutch river system
To make informed flood risk management (FRM) decisions in large protected river systems, flood risk and hazard analyses should include the potential for dike breaching. ‘Load interdependency’ analyses attempt to include the system-wide effects of dike breaching while accounting for the uncertainty of both river loads and dike fragility. The intensive stochastic computation required for these analyses often precludes the use of complex hydraulic models, but simpler models may miss spatial inundation interactions such as flows that ‘cascade’ between compartmentalised regions and overland flows that ‘shortcut’ between river branches. The potential for these interactions in the Netherlands has previously been identified, and so a schematisation of the Dutch floodplain and protection system is here developed for use in a load interdependency analysis. The approach allows for the spatial distribution of hazard to be quantified under various scenarios and return periods. The results demonstrate the importance of including spatial inundation interactions on hazard estimation at three specific locations, and for the system in general. The modelling approach can be used at a local scale to focus flood-risk analysis and management on the relevant causes of inundation, and at a system-wide scale to estimate the overall impact of large-scale measures.