Uncertainties in the rate of sea level rise, coupled with ongoing urban expansion, are a challenge for city planners designing flood risk adaptation strategies. This study quantifies flood exposure in Rotterdam's unembanked areas from 1970 to 2150. We modelled flood hazards for 10-, 100-, and 1000-year return periods under both low- (RCP2.6) and high-emission (RCP8.5) scenarios while assessing exposure using historic and planned urban development data. Temporal variations in exposure rates are attributed to three factors: urban development, sea level rise, and the construction of the Maeslant storm surge barrier. Without adaptation measures, flood exposure in Rotterdam's unembanked areas is projected to increase. Under RCP8.5, exposure rates for 10-year flood events are expected to increase 7-fold by 2150 compared to 2020. For RCP2.6, a 3-fold increase is projected for 10-year events, reflecting uncertainties in long-term sea level rise. A retrospective analysis reveals a decrease in flood exposure: exposure levels observed in 2020 were approximately half those observed in 1996, due to construction of the Maeslant barrier. Exposure rates are primarily influenced by the Maeslant barrier, followed by sea level rise and urban development. Understanding the interplay of these three factors is crucial for urban planning and flood risk management in delta cities.

‘Water en bodem sturend’ is op zich een goed uitgangspunt voor ruimtelijke inrichting. In de uitwerking dreigt dat echter meer ‘dicterend’ te worden, vinden Friso de Zeeuw en Ties Rijcken. Zij laten aan de hand van praktijkvoorbeelden zien hoe uitstekende gebiedsontwikkelingen dan kopje onder gaan, onder meer door vergaande juridisering.

Sea level rise necessitates the upgrade of coastal flood protection including storm surge barriers. These large movable hydraulic structures are open in normal conditions, but close during a storm surge to prevent coastal floods in bays and estuaries. Barrier improvements lower their susceptibility to operational, structural, or height-related failures. However, there is no method to determine the relative importance of these three barrier failure types. Here, we present a probabilistic method to systematically organize barrier failures and storm conditions to establish exceedance frequencies of extreme water levels behind the barrier. The method is illustrated by an assessment of extreme water level frequencies at Rotterdam (The Netherlands), which is protected by the Maeslant barrier. Four combinations of barrier states and storm conditions were analyzed and prioritized in the following order: (1) an operational failure with 1/100 year storm conditions, (2) a successful closure with an extreme (~1/1000 year) river discharge accumulating behind the barrier, (3) structural failure, and (4) insufficient height both with extreme storm conditions (10^–6 year). The case study confirmed the method's ability to systematically explore promising barrier improvements to adapt to sea level rise, in this case, lowering the susceptibility toward operational failures.

Storm surge barriers are large movable hydraulic structures which close during a storm surge to prevent coastal floods. In the regions they protect, a failure to close the barrier is often the most likely cause for a catastrophic flood. Nevertheless, flood risk assessments usually only focus on raising flood defences behind the barrier. Despite its importance, there is no general method to assess the costs and benefits of improving the closure reliability. This paper presents a model that optimises investments considering both closure reliability improvements and raising flood defences behind the barrier, using the region protected by the Maeslant barrier as a case. We substantiate that constructing the Maeslant barrier was an optimal economic decision. Moreover, we demonstrate large investments such as a redundant barrier already being economically sound with a few decimetres of sea level rise. Based on our experience with this case study, we expect the model is useful in finding strategies to adapt to rising sea levels and other developments that cause coastal flood risk to rise worldwide.

The central proposal in Ties Rijcken’s talk at the NCR river days is to have future river management and science revolve around the concept of beauty – on various levels: beauty in the way the river system serves the needs of society, beauty in the way it is studied, beauty in the way it is perceived through the senses and beauty in the way all this is visualised and communicated among experts and between experts and stakeholders. The talk builds on his dissertation Emergo (written between 2012 and 2017) and the internet platform Flows (under development since 2015).

PART I | A RESEARCH AND DESIGN PROJECT ABOUT FLOOD RISK POLICY SINCE 1986 The period between the Dutch flood disaster of 1953 and the year 2016 can be divided into two eras, separated by the year 1986, when the famous Eastern Scheldt barrier was completed. The perspective of water professionals on flood risk policymaking during the three decades before 1986 was dominated by the reconstruction approach of the Delta Works and has frequently been studied. The three decades after 1986 have a less obvious general approach, which has not yet been studied in depth as a whole. This dissertation attempts to develop a coherent perspective on flood risk policy during the last 30 years. This thesis’s research objective is to develop a comprehensive flood risk and water systems analysis framework, to be used for two purposes. First, providing a historical interpretation of flood risk policy by answering the main research question: how can the development of the Dutch flood risk system since 1986 be characterised fundamentally? In the core of the thesis, three main historical trends are identified. The first trend results from a study of systematic approaches to flood risk through the years, the second main trend addresses the relevance to flood risk of additional flood risk-related water system objectives (freshwater conveyance, shipping, nature/ecotopes and landscape quality) and the third trend involves additional new ideas or narratives which have been influential during the studied period. The second purpose of the water systems analysis framework is to meet the design objective of the thesis: to design an internet platform to represent the systems analysis framework and illustrate historical and future development of the Dutch flood risk system. The aim of the platform is to systematically organize and visualize the available studies and design projects, to educate about water systems, to inspire users to add contributions and monitor user behaviour to help indicate new research and design opportunities and support policy decisions. Acknowledged criteria for scientific and societal relevance guide the design throughout the thesis. Chapter 2 introduces the platform, which was called SimDelta in 2012 and renamed Flowz in 2017. A brief survey of approaches to water system planning and ‘serious games’ concludes that a graphic interface to visualise technical-physical complexity and socio-political complexity (or: supply and demand of analyses and ideas) is increasingly recognised to contribute to effective policymaking. A structure for the platform is proposed, consisting of six stackable software blocks: the base block contains interactive maps generated in a systems model, the top block involves communication between stakeholders to make choices in a virtual problem-solution space. Usage over the internet makes it possible to record preferences, and ‘crowdsource’ corrections, improvements and new ideas. The extent to which the concept can contribute to policymaking can only be tested by developing it step-by-step. Chances for success will depend on how the platform relates to existing ways information is obtained and existing types of decision support. PART II | AN INTEGRATED FLOOD RISK AND WATER SYSTEMS ANALYSIS FRAMEWORK (not added here…) PART III | STRUGGLING IN ‘MASLOW’S HIERARCHY FOR WATER INFRASTRUCTURE (not added here…).

Zacht van buiten, hard van binnen – Rondje IJsselmeer (1) stelde dat regelwerken goed samen gaan met de wens naar meer dynamiek en daarmee ruimtelijke kwaliteit. Maar het beheersen van dynamiek en het inbouwen van onverwachte interessante gebeurtenissen, vergt inzicht in probabilistiek. En dat is moeilijke materie. Hoe ver moeten ruimtelijk ontwerpers gaan om de verbinding te kunnen leggen tussen techniek en beleving?

Zacht van buiten, hard van binnen – een goed waterproject leunt op doordacht waterbeheer maar wordt dagelijks beoordeeld op landschapsbeleving. Deze verbinding vraagt om een dialoog die niet vanzelfsprekend is. Ties Rijcken reist op de WaterViewer het IJsselmeer rond en vraagt Frits Palmboom naar het raakvlak tussen techniek en beleving.

Zacht van buiten, hard van binnen – in Rondje IJsselmeer (2) contrasteerde Frits Palmboom de in beleidsanalyses veronderstelde uitwisselbaarheid van effecten tussen alternatieven met door ruimtelijk ontwerpers nagestreefde uniciteit. De Afsluitdijk bijvoorbeeld, wordt die versterkt vanwege kwantificeerbare en uitwisselbare risicoreductie, of speelt er meer, op het raakvlak tussen techniek en beleving?

Zacht van buiten, hard van binnen – Ties Rijcken reisde op de WaterViewer het IJsselmeer rond en correspondeerde met Frits Palmboom over het sleutelen aan de afvoerverdeling, over optimaliseren versus verhalen vertellen en over rood voor blauw voor groen - of andersom?  Tot slot de vraag wie van de drie - ontwerpers, modelleerders of procesmanagers - de boventoon verdient in het spanningsveld tussen techniek en beleving.

Zacht van buiten, hard van binnen – een goed waterproject leunt op doordacht waterbeheer, maar wordt dagelijks beoordeeld op landschapsbeleving. Deze verbinding vraagt om een dialoog die niet vanzelfsprekend is. Ties Rijcken reist via de projecten op de WaterViewer het IJsselmeer rond en vraagt Frits Palmboom naar het raakvlak tussen techniek en beleving.

Elk groot waterproject kent zowel voordelen als bezwaren, zo ook het bejubelde Ruimte voor de Rivier. Door de nieuwe graafpartijen worden bij hoogwater de sedimentatiepatronen in het zomerbed onregelmatiger, waardoor er meer baggerwerk voor de scheepvaart nodig is. Gelukkig is er voor elk probleem een oplossing – op naar de genormaliseerde natuurlijke rivier?

Sinds de motie-Geurts leidt het onderzoek naar de Rijnmond afsluiting (Plan Sluizen) tot verwarring bij kamerleden en discussies tussen deskundigen. Ontstaat er een polarisatie tussen afsluiten of openhouden, of zit er nog iets tussenin? En wat is de relevantie voor het heden, of is het slechts toekomstmuziek? Het raamwerk van Adaptief Deltamananagement geeft houvast.

Decisions on measures to improve a flood risk system are in part supported by general ideas about how the system works and should work. After the completion of the Dutch Delta Works around 1990, such new ideas regarding flood risk emerged. Some of these may be appealing at first, but appear debatable after a closer look. In this paper, fourteen such debatable ideas, familiar to most Dutch water professionals, are formulated and criticised, in order to find out what can be learned from them. The most important Dutch national flood risk policy documents since 1990 are reviewed for quotes that illustrate these ideas, complemented by scientific papers and other documents. These quotes present different expressions of these ideas, and their number can suggest whether they are broadly shared or marginal. In twelve of the twenty most important government documents, 47 quotes were found; in 26 documents of other types, another 39. Eleven quotes describe the idea that ‘water should not be our enemy, but our friend’. Fifteen quotes were based on the idea that flood protection entraps us in a dangerous ‘spiral of risk’, which can be stopped, 44 quotes are related to the idea that flood risk reducing measures should be ‘natural’ or ‘move with nature’. The remaining quotes illustrate other debatable ideas, such as ‘water should lead spatial planning’ and ‘rivers should not be squeezed into a corset’. The frequency of such quotes suggests that ideas about ‘water as a friend’, the ‘spiral of risk’ and ‘moving with nature’ have not been marginal. It is however difficult to determine how influential they have been in decision-making, since general ideas are not the only factors leading to decisions. The general critique to the three ideas is that they present preferred measures as generally logical conclusions without a systematic comparison of alternatives for particular situations. Behind the new ideas lies increasing societal interest for objectives like an attractive water landscape (water as a friend), reducing our dependence on technology (spiral of risk) and nature conservation and development (moving with nature). This analysis further suggests a couple of final remarks, which are hard to prove and are open for discussion.

In the spring of 2008, Delft University of Technology wrote a report for the Second Delta Committee, a body set up to advise the Dutch government and parliament on the Netherlands’ long-term flood risk policy. The Delft report included a colourful drawing of a solution for Rotterdam and the Drecht Cities, and the Delta Committee used this image to illustrate their ‘closable-but-open’ recommendation for the Rhine-Meuse estuary and explicitly recommended further research.

Wie niet meer de grootste is, moet de slimste zijn. En onder druk van de klimaatverandering betekent dat vooral schoon en energieneutraal. Rotterdam is allang niet meer de grootste haven ter wereld. Die positie werd in 2004 overgenomen door Singapore, die de plaats een jaar later moest afstaan aan Sjanghai. Inmiddels staat Rotterdam op de vijfde plaats, gemeten in aantal tonnen vracht dat jaarlijks wordt doorgevoerd. Maar ook al is