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Adaptation to uncertain sea-level rise : how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands
Uncertainties in the rate and magnitude of sea-level rise (SLR) complicate decision making on coastal adaptation. Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase SLR in the second half of this century. The implications of SLR may be existential for a low-lying country like the Netherlands and warrant exploration of high-impact low-likelihood scenarios. To deal with uncertain SLR, the Netherlands has adopted an adaptive pathways plan. This paper analyzes the implications of storylines leading to extreme SLR for the current adaptive plan in the Netherlands, focusing on flood risk, fresh water resources, and coastline management. It further discusses implications for coastal adaptation in low-lying coastal zones considering timescales of adaptation including the decisions lifetime and lead-in time for preparation and implementation. We find that as sea levels rise faster and higher, sand nourishment volumes to maintain the Dutch coast may need to be up to 20 times larger than to date in 2100, storm surge barriers will need to close at increasing frequency until closed permanently, and intensified saltwater intrusion will reduce freshwater availability while the demand is rising. The expected lifetime of investments will reduce drastically. Consequently, step-wise adaptation needs to occur at an increasing frequency or with larger increments while there is still large SLR uncertainty with the risk of under- or overinvesting. Anticipating deeply uncertain, high SLR scenarios helps to enable timely adaptation and to appreciate the value of emission reduction and monitoring of the Antarctica contribution to SLR.
Bacteriën als heipalen : Deltares werkt aan innovatieve, duurzame technieken
Bij twee veelbelovende toepassingen, BioSealing en BioGrout, is een hoofdrol weggelegd voor bacteriën. Met de juiste dosis 'voeding' kurmen zij lekkende dijken dichten of de bodem verstevigen. In situ, zonder grondverzet. Het idee om bacteriën het zware werk te laten doen, komt niet uit de lucht vallen. In de milieugeotechniek worden bacteriën al jaren ingezet om verontreinigde grond schoon te maken. Zouden zij de bodem misschien ook steviger kunnen maken of minder waterdoorlatend, vroegen onderzoekers van Deltares zich af. Dan wordt het mogelijk om te bouwen waar dat nu onverstandig is vanwege een slappe of onvoorspelbare ondergrond. Of er kunnen herstelwerkwerkzaamheden worden uitgevoerd zonder verstoring, bijvoorbeeld onder bestaande bebouwing of infrastructuur.
Testen voor de dijk van de toekomst : Deltares voert full-scale 'piping' test uit op IJkdijk
De IJkdijk is een initiatief van N.V NOM, STOWA, Stichting IDL, Deltares en TNO. Rijkswaterstaat participeert via het programma Sterkte en Belastingen Waterkeringen (SBW) in de 'piping' experimenten. De resultaten van de praktijkproeven kunnen resulteren in een aanpassing van rekenregels om de sterkte van dijken te bepalen, waardoor dijkbeheerders 'piping' in de toekomst wellicht ook beter kunnen voorspellen.
Nederland in zicht : water en ruimtelijke ontwikkeling in Nederland : een analyse van de langetermijnontwikkelingen
In het ontwerp Nationaal Waterplan wordt een aanzet gegeven voor een ruimtelijke strategie voor water in Nederland. Het rapport 'Nederland in Zicht: de diagnose' heeft daaraan bijgedragen. De analyse is door Rijkswaterstaat-Waterdienst, Deltares en H+N+S Landschapsarchitecten uitgevoerd in opdracht van het ministerie van Verkeer en Waterstaat en het Directoraat Generaal Water. 'Nederland in Zicht' is een bundeling en analyse van bestaande kennis en kan gebruikt worden als inspiratiebron voor de regionale planvorming.
Beheerbibliotheek Voorne en Goeree : beschrijvingen van het kustvak ter ondersteuning van het beheer en onderhoud van de kust
De voorliggende beheerbibliotheek van de kustvakken 11, Voorne en 12, Goeree betreft een update van de eerste versie door De Ronde en Van Oeveren (2014). Belangrijke delen van de tekst zijn uit dit document overgenomen, daarnaast zijn de resultaten van nieuwe studies opgenomen en tekst, figuren en tabellen geactualiseerd.
The vulnerability of tidal flats and multi-channel estuaries to dredging and disposal
Shipping fairways in estuaries are continuously dredged to maintain access for large vessels to major ports. However, several estuaries worldwide show adverse side effects to dredging activities, including a shift from multi-channel systems to single-channel systems and the loss of ecologically valuable intertidal flats. We used a time series of bathymetry of the Western Scheldt estuary (the Netherlands), morphodynamic model runs and physical scale-experiments to analyse the effects of dredging. All methods indicate that current dredging and disposal strategies are in the long run unfavourable because dredging increases the imbalance between shallow and deeper parts of the estuary, causing a loss of valuable connecting channels and fixation of the tidal flats and main channel positions. Changing the disposal strategy can be economically and ecologically better for the preservation of the multi-channel system. While future sea-level rise may revive the multi-channel system, further channel deepening will accelerate the adverse side effects.
Mapping the seabed and shallow subsurface with multi-frequency multibeam echosounders
Multi-frequency multibeam backscatter (BS) has indicated, in particular for fine sediments, the potential for increasing the discrimination between different seabed environments. Fine sediments are expected to have a varying signal penetration within the frequency range of modern multibeam echosounders (MBES). Therefore, it is unknown to what extent the multispectral MBES data represent the surface of the seabed or different parts of the subsurface. Here, the effect of signal penetration on the measured multi-frequency BS and bathymetry is investigated. To this end, two multi-frequency datasets (90 to 450 kHz) were acquired with an R2Sonic 2026 MBES, supported by ground-truthing, in the Vlietland Lake and Port of Rotterdam (The Netherlands). In addition, a model to simulate the MBES bathymetric measurements in a layered medium is developed. The measured bathymetry difference between the lowest (90 kHz) and highest frequency (450 kHz) in areas with muddy sediments reaches values up to 60 cm dependent on the location and incident angle. In spatial correspondence with the variation in the depth difference, the BS level at the lowest frequency varies by up to 15 dB for the muddy sediments while the BS at the highest frequency shows only small variations. A comparison of the acoustic results with ground-truthing, geological setting and model indicates that the measured bathymetry and BS at the different frequencies correspond to different parts of the seabed. However, the low-frequency BS cannot be directly related to a subsurface layer because of a significant sound attenuation in the upper layer. The simulation of the MBES bottom detection indicates that the bathymetry measured at the highest and lowest frequency can be used to determine the thickness of thin layers (20 cm). However, with an increasing layer thickness, the bottom detection becomes more sensitive to the incident angle and small variations in the sediment properties. Consequently, an accurate determination of the layer thickness is hampered. Based on this study, it is highly recommended to analyze multi-frequency BS in combination with the inter-frequency bathymetry difference to ensure a correct interpretation and classification of multi-frequency BS data.
Review article: Natural hazard risk assessments at the global scale
Since 1990, natural hazards have led to over 1.6 million fatalities globally, and economic losses are estimated at an average of around $260–310 billion per year. The scientific and policy community recognise the need to reduce these risks. As a result, the last decade has seen a rapid development of global models for assessing risk from natural hazards at the global scale. In this paper, we review the scientific literature on natural hazard risk assessments at the global scale, and specifically examine whether and how they have examined future projections of hazard, exposure, and/or vulnerability. In doing so, we examine similarities and differences between the approaches taken across the different hazards, and identify potential ways in which different hazard communities can learn from each other. For example, we show that global risk studies focusing on hydrological, climatological, and meteorological hazards, have included future projections and disaster risk reduction measures (in the case of floods), whilst these are missing in global studies related to geological hazards. The methods used for projecting future exposure in the former could be applied to the geological studies. On the other hand, studies of earthquake and tsunami risk are now using stochastic modelling approaches to allow for a fully probabilistic assessment of risk, which could benefit the modelling of risk from other hazards. Finally, we discuss opportunities for learning from methods and approaches being developed and applied to assess natural hazard risks at more continental or regional scales. Through this paper, we hope to encourage dialogue on knowledge sharing between scientists and communities working on different hazards and at different spatial scales.
Uncertainties in coastal flood risk assessments in small island developing states
Considering the likely increase of coastal flooding in Small Island Developing States (SIDS), coastal managers at the local and global level have been developing initiatives aimed at implementing Disaster Risk Reduction (DRR) measures and adapting to climate change. Developing science-based adaptation policies requires accurate coastal flood risk (CFR) assessments, which are often subject to the scarcity of sufficiently accurate input data for insular states. We analysed the impact of uncertain inputs on coastal flood damage estimates, considering: (i) significant wave height, (ii) storm surge level and (iii) sea level rise (SLR) contributions to extreme sea levels, as well as the error-driven uncertainty in (iv) bathymetric and (v) topographic datasets, (vi) damage models and (vii) socioeconomic changes. The methodology was tested through a sensitivity analysis using an ensemble of hydrodynamic models (XBeach and SFINCS) coupled with an impact model (Delft-FIAT) for a case study at the islands of São Tomé and Príncipe. Model results indicate that for the current time horizon, depth damage functions (DDF) and digital elevation model (DEM) dominate the overall damage estimation uncertainty. We find that, when introducing climate and socioeconomic uncertainties to the analysis, SLR projections become the most relevant input for the year 2100 (followed by DEM and DDF). In general, the scarcity of reliable input data leads to considerable predictive error in CFR assessments in SIDS. The findings of this research can help to prioritise the allocation of limited resources towards the acquisitions of the most relevant input data for reliable impact estimation.
Evaluating a planning support system’s use and effects in urban adaptation : an exploratory case study from Berlin, Germany
Planning Support Systems (PSS) are increasingly used to support collaborative planning workshops in urban adaptation practice. Research has focused on developing such tools and evaluating their use in workshops but has not measured tools’ effects over time on real planning processes, on the participants involved, and on the final outcomes. The role that tools play in adaptation planning, therefore, remains unclear. A longitudinal case study was made to evaluate a PSS, the Adaptation Support Tool (AST), in a design workshop for sustainable urban water management, in Berlin, Germany. The case study also served to test the evaluation framework and generate insights regarding systematic evaluations of tools in planning processes. The case study was carried out over eighteen months, to capture both the details of the workshop and its longer-term effects on the project and participants. Our results show that the AST’s most evident effects were (1) contributory and less tangible in nature (e.g., supporting learning), than directly causal and concrete (e.g., affecting planning decisions), and (2) a function of the process and context in which the workshop took place. This study demonstrates that making systematic, longitudinal evaluations are valuable for studying the role of PSS in urban adaptation planning.