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Experiences in developing and applying decision support systems for strategic flood risk management
Decision support systems (DSSs) have been developed for many years. Their main goal was originally to support decision-makers. Reviews show, however, that the actual use of most DSSs did fall short of these ambitions. The goal of DSSs has gradually shifted to enhancing stakeholder engagement for better informed and societally supported decisions. In this paper, we present and discuss a DSS which has been extensively used by a large and diverse group of stakeholders. This so-called Planning Kit Room for the River did successfully support the development of alternative strategies for flood risk management of the riverine area in the Netherlands. Based on these strategies a major investment programme was developed, which has been implemented recently, within time and budget. In the paper, we explore the key factors for its successful application. Based on this analysis and our experience with both interactive planning processes and DSSs, we propose a typology of DSSs for strategic planning of flood risk management. We outline three types of DSSs with different set-ups and associated users, including a DSS based on an integrated model system. The paper concludes with a discussion of the main characteristics and the potential and limitations of these types of DSSs from both a user and a hydro-informatics perspective.
Assessment of critical infrastructure resilience to flooding using a response curve approach
Following a flood the functioning of critical infrastructure (CI), such as power and transportation networks, plays an important role in recovery and the resilience of the city. Previous research investigated resilience indicators, however, there is no method in the literature to quantify the resilience of CI to flooding specifically or to quantify the effect of measures. This new method to quantify CI resilience to flooding proposes an expected annual disruption (EADIS) metric and curve of disruption versus likelihood. The units used for the EADIS metric for disruption are in terms of people affected over time (person days). Using flood modelling outputs, spatial infrastructure, and population data as inputs, this metric is used to benchmark CI resilience to flooding and test the improvement with resilience enhancing measures. These measures are focused on the resilience aspects robustness, redundancy and flexibility. Relative improvements in resilience were quantified for a case study area in Toronto, Canada and it was found that redundancy, flexibility, and robustness measures resulted in 44, 30, and 48% reductions in EADIS respectively. While there are limitations, results suggest that this method can effectively quantify CI resilience to flooding and quantify relative improvements with resilience enhancing measures for cities.
Faalkansanalyse bij dijkontwerp Zeeburgereiland met parallelle waterleiding : POV Kabels & Leidingen
De POV Kabels en Leidingen (POV K&L) wordt uitgevoerd binnen het Hoogwaterbeschermingsprogramma (HWBP) met als belangrijkste doel om de risico’s van kabels en leidingen bij dijkversterkingsprojecten te minimaliseren. De POV K&L heeft aan Deltares gevraagd om onderzoek te doen naar de toepassing van een integrale faalkansanalyse van de waterveiligheid voor het referentieproject dijkversterking Zeeburgereiland. Het referentieproject betreft een ontwerp van een multifunctionele primaire waterkering met ter plaatse van de binnenkruin aan te leggen parallelle leidingen.
Human-caused avulsion in the Rhine-Meuse delta before historic embankment (The Netherlands)
Although the shifting of deltaic river branches (avulsion) is a natural process that has become increasingly influenced by humans, the impact of early human activities as a driver of avulsion success has remained poorly explored. This study demonstrates how two important avulsions in the downstream part of the Rhine-Meuse delta, The Netherlands, were stimulated by human activities in the first millennium CE, before historic embankment constrained the river courses. Peatland reclamation induced land subsidence in the lower delta. This effect, together with a human-induced increase in suspended fluvial sediments and tidal backwater effects, allowed for a gradual ingression of tidal creek channels and progradation of fluvial crevasse channels into human-occupied and drained peatlands, where they eventually connected. We reconstructed the initial situation and identified the feedback loops among overbank sedimentation, tidal incursion, and land drainage subsidence that led to avulsion success. The processes and feedbacks resulting from human activities are generic and hence relevant to many other deltas today where human-induced subsidence results in tidal ingression, potentially connecting to rivers and causing unexpected avulsions.
Low-hanging fruits in large-scale fluvial landscaping measures: trade-offs between flood hazard, costs, stakeholders and biodiversity
Adapting densely populated deltas to the combined impacts of climate change and socioeconomic developments presents a major challenge for their sustainable development in the 21st century. Decisions for the adaptations require an overview of cost and benefits and the number of stakeholders involved, which can be used in stakeholder discussions. Therefore, we investigated the balance between multi-faceted costs and benefits of common landscaping measures to compensate for changes in discharge and sea level rise on the basis of relevant, but inexhaustive, quantitative variables for physical, ecological and societal costs and benefits. We modelled the largest delta distributary of the Rhine River with adaptation scenarios driven by (1) the choice of seven measures, (2) the areas owned by the two largest stakeholders (LS) versus all stakeholders (AS), and (3) the ecological or hydraulic design principle. We evaluated measures by their efficiency in flood hazard reduction, potential biodiversity, number of stakeholders as a proxy to governance complexity, and measure implementation cost. We found that only floodplain lowering over the whole study area can offset the altered hydrodynamic boundary conditions; for all other measures, additional dike raising is required. LS areas comprise low hanging fruits for water level lowering due to the governance simplicity and hydraulic efficiency. Measures implemented in LS areas are 3 to 74% more efficient than in AS areas. Clear trade-offs were revealed between evaluation parameters, but no single measure represented the optimal combination on all aspects. The multidimensional evaluation space provides a frame for the co-creation of adaptation paths for climate-proofing deltas.
Urban water security dashboard : systems approach to characterizing the water security of cities
Urban water security is a major concern in the context of urbanization and climate change. Water security goes beyond having good infrastructure or good governance. Systems thinking can help in understanding the mechanisms that influence the long-term water security of a city. Therefore, we developed a dashboard of 56 indicators based on the pressure-state-impact-response (PSIR) framework. We applied the dashboard to ten cities to capture different characteristics of their water security and ranked the cities based on their overall water security index score. We found the highest levels of water security in wealthy cities in water-abundant environments (Amsterdam and Toronto), in which security is determined by the ability of the city to mitigate flood risks and the sustainability of hinterland dependencies for water supply. The lowest security was found in developing cities (Nairobi, Lima, and Jakarta). Here, the combination of large socio-economic pressures (e.g., rapid population growth, slums, low GDP, polluting industries) and an inadequate response (weak institutions, and poor planning and operational management) leads to inappropriate fulfilment of all functions of the urban water system.
How to model algal blooms in any lake on earth
Algal blooms increasingly threaten lake and reservoir water quality at the global scale, caused by ongoing climate change and nutrient loading. To anticipate these algal blooms, models to project future algal blooms worldwide are required. Here we present the state-of-the-art in algal projection modelling and explore the requirements of an ideal algal projection model. Based on this, we identify current challenges and opportunities for such model development. Since most building blocks are present, we foresee that algal projection models for any lake on earth can be developed in the near future. Finally, we think that algal bloom projection models at a global scale will provide a valuable contribution to global policymaking, in particular with respect to SDG 6 (clean water and sanitation).
Lessons learned from dike failures in recent decades
The paper describes five different dike failures that occurred in recent decades. The case histories were located on different rivers and involved different loading conditions. The observed failure mechanisms involved erosion and stability problems. The types of erosion observed were both internal erosion due to extreme groundwater flow and external erosion caused by the river flow and wave action. The case involving instability was caused by uplift, i.e., increased hydraulic head led to a sharp reduction in maximum shear strength between subsoil layers. Two cases demonstrate the importance of dike management and maintenance. Despite the variations in the loading conditions and failure mechanisms, all the cases show that the strength of a dike depends not only on the material used to build the dike but also on the strength of the subsoil.
Een Nederlandsch Waterbouwkundig Laboratorium
Waterloopkundig Laboratorium te Delft (architect ir. H. Kammer)