23 research outputs found
Future Response of the Wadden Sea Tidal Basins to Relative Sea-Level rise—An Aggregated Modelling Approach
No full textClimate change, and especially the associated acceleration of sea-level rise, forms a serious threat to the Wadden Sea. The Wadden Sea contains the world’s largest coherent intertidal flat area and it is known that these flats can drown when the rate of sea-level rise exceeds a critical limit. As a result, the intertidal flats would then be permanently inundated, seriously affecting the ecological functioning of the system. The determination of this critical limit and the modelling of the transient process of how a tidal basin responds to accelerated sea-level rise is of critical importance. In this contribution we revisit the modelling of the response of the Wadden Sea tidal basins to sea-level rise using a basin scale morphological model (aggregated scale morphological interaction between tidal basin and adjacent coast, ASMITA). Analysis using this aggregated scale model shows that the critical rate of sea-level rise is not merely influenced by the morphological equilibrium and the morphological time scale, but also depends on the grain size distribution of sediment in the tidal inlet system. As sea-level rises, there is a lag in the morphological response, which means that the basin will be deeper than the systems morphological equilibrium. However, so long as the rate of sea-level rise is constant and below a critical limit, this offset becomes constant and a dynamic equilibrium is established. This equilibrium deviation as well as the time needed to achieve the dynamic equilibrium increase non-linearly with increasing rates of sea-level rise. As a result, the response of a tidal basin to relatively fast sea-level rise is similar, no matter if the sea-level rise rate is just below, equal or above the critical limit. A tidal basin will experience a long process of ‘drowning’ when sea-level rise rate exceeds about 80% of the critical limit. The insights from the present study can be used to improve morphodynamic modelling of tidal basin response to accelerating sea-level rise and are useful for sustainable management of tidal inlet systems.Coastal Engineerin
An evaluation of aeolian sand transport models using four different sand traps at the Hors, Texel
No full textThis report shows the result of an evaluation of how 12 aeolian sand transport models perform on a beach in Northwest-Europe. Their predictions are compared to measured rates of sand transport using four different traps. The efficiency of the different types of traps was also evaluated. From this it followed that the Sarre-trap performed best with an efficiency of ~100%. It is also very practical in its usage. The measured rates of transport with the Sarre-trap were best predicted by the White-, Bagnold- and Chepil-models.
The ratio betweep creep-transport and the total transport was also studied. It turned out that this ratio is not constant as was previously assumed, but depends on the shear velocity. Assuming a constant efficiency of the traps, the ratio decreases with increasing shear velocities. The larger impact of landing saltating grains during higher shear velocities is most likely such that instead of creep saltation is initiated
A NEW SEDIMENT BUDGET FOR THE NETHERLANDS; THE EFFECTS OF 15 YEARS OF NOURISHING (1991-2005)
No full textTechnisch rapport Duinafslag
No full textDe TAW Leidraad Duinafslag van 1984 is vervangen door dit Technisch Rapport Duinafslag 2006 (TRDA2006). De hoofdreden daarvoor is dat er indertijd bij het opstellen van de Leidraad 1984 niet voldoende rekening is gehouden met het effect dat de golfperiode heeft op de mate van duinafslag. Metingen van golfkarakteristieken hebben inmiddels laten zien dat er tijdens zware stormvloedomstandigheden langere golfperioden kunnen voorkomen (Tp ? 16 - 20 s) dan waar indertijd rekening mee werd gehouden (Tp = 12 s). Met de procedures die in het TRDA2006 worden beschreven, wordt wel met het effect van deze langere golfperioden rekening gehouden. Daarnaast zijn er enkele andere nieuwe inzichten in het TRDA2006 verwerkt.TAW/EN
The ‘Research for Policy’ cycle in Dutch coastal flood risk management: The Coastal Genesis 2 research programme
No full textThe development of the Coastal Genesis 2 research programme and its role in contributing to Dutch coastal policy are described in the paper. The organisation of policy development related to coastal flood risk and erosion in The Netherlands is addressed, highlighting the division of responsibilities between the policy and operational directorates of the Ministry of Infrastructure and Water Management. A conceptual model of the long term sediment budget of the Dutch coast that underpins the current Coastal Flood and Erosion Risk Management policy is detailed. The role of the operational directorate Rijkswaterstaat in coordinating a ‘Research for Policy’ cycle as a means of generating new insights on the coastal system and ensuring their subsequent inclusion in a new/revised conceptual model, is highlighted. By detailing the new conceptual model of the long term sediment budget, the paper demonstrates how key uncertainties related to this model guided the determination of the research agenda for Coastal Genesis 2. The paper concludes by reflecting briefly on the outcomes of the research programme and the role of the ‘Research for Policy’ cycle in ensuring the sustainable future of the Dutch coast.Policy Analysi
Sediment budget and morphological development of the Dutch Wadden Sea: Impact of accelerated sea-level rise and subsidence until 2100
No full textThe Wadden Sea is a unique coastal wetland containing an uninterrupted stretch of tidal flats that span a distance of nearly 500 km along the North Sea coast from the Netherlands to Denmark. The development of this system is under pressure of climate change and especially the associated acceleration in sea-level rise (SLR). Sustainable management of the system to ensure safety against flooding of the hinterland, to protect the environmental value and to optimise the economic activities in the area requires predictions of the future morphological development.The Dutch Wadden Sea has been accreting by importing sediment from the ebb-tidal deltas and the North Sea coasts of the barrier islands. The average accretion rate since 1926 has been higher than that of the local relative SLR. The large sediment imports are predominantly caused by the damming of the Zuiderzee and Lauwerszee rather than due to response to this rise in sea level. The intertidal flats in all tidal basins increased in height to compensate for SLR.The barrier islands, the ebb-tidal deltas and the tidal basins that comprise tidal channels and flats together form a sediment-sharing system. The residual sediment transport between a tidal basin and its ebb-tidal delta through the tidal inlet is influenced by different processes and mechanisms. In the Dutch Wadden Sea, residual flow, tidal asymmetry and dispersion are dominant. The interaction between tidal channels and tidal flats is governed by both tides and waves. The height of the tidal flats is the result of the balance between sand supply by the tide and resuspension by waves.At present, long-term modelling for evaluating the effects of accelerated SLR mainly relies on aggregated models. These models are used to evaluate the maximum rates of sediment import into the tidal basins in the Dutch Wadden Sea. These maximum rates are compared to the combined scenarios of SLR and extraction-induced subsidence, in order to explore the future state of the Dutch Wadden Sea.For the near future, up to 2030, the effect of accelerated SLR will be limited and hardly noticeable. Over the long term, by the year 2100, the effect depends on the SLR scenarios. According to the low-end scenario, there will be hardly any effect due to SLR until 2100, whereas according to the high-end scenario the effect will be noticeable already in 2050.Coastal Engineerin
Zandsluitingen: State of the art
No full textGezien het unieke karakter en de omvang van vooral de sluitingen van het Tholensche Gat en het Krammer werd al in een vroeg stadium besloten deze zandsluitingen te evalueren. De doelstelling van deze evaluatie was tweeledig. Op de eerste plaats heeft de evaluatie een beschrijvend en documenterend karakter. Dit komt vooral tot uiting in de bij deze nota gevoegde deelnota's bij deze nota waarin hydraulische, grondmechanische en morfologische gegevens zijn vastgelegd. ook onderwerpen als zuigerprodukties en gemeten zandverliezen komen daar aan de orde. Het gaat hierbij om gegevens die zowel voorafgaand, tijdens, als na de zandsluitingen zijn verzameld. Samen geven deze deelnota's een zo goed mogelijk beeld van het verloop van-het ontwerp en de uitvoering van de genoemde werken. Het documenteren en presenteren van (meet)gegevens neemt daarbij een belangrijke plaats in. De tweede doelstelling was om, op grond van de nieuwe ervaringen, de beschikbaar gekomen nieuwe meetgegevens en het daardoor toegenomen inzicht in de problematiek van zandsluitingen, de in het verleden gevolgde ontwerpmethodiek nog eens kritisch te bezien en daar waar mogelijk te verbeteren. Getracht is deze tweede doelstelling te verwezelijken in de voor u liggende nota waarin een overzicht wordt gegeven van de laatste inzichten in de techniek van zandsluitingen. Het interpreteren van de in de deelnota's gepresenteerde gegevens en de integratie daarvan tot een samenhangend geheel stond dan ook voorop bij het schrijven van deze samenvattende hoofdnota. uit de in deze nota geformuleerde conclusies en aanbevelingen moge overigens blijken dat nog lang niet alle vragen zijn beantwoord en dat een aantal fenomenen zich nog moeilijk kwantitatief laat beschrijven. Aan de andere kant kan worden vastgesteld dat veel nieuwe waardevolle kennis is verkregen en bestaande inzichten zijn verdiept. In ieder geval is getracht alle beschikbare kennis omtrent de techniek van zandsluitingen in het onderhavige rapport samen te vatten. Hetgeen in dit rapport is geschreven dient dan ook te worden opgevat als een "state of the art" van de techniek van zandsluitingen.KWP-collectio
Una introducción al derecho de comunicación y contenidos por Internet
No full textCommunication on the internet is unprecedented in its scale, scope, speed, and anonymity. Online words immediately reach the whole globe, can have tremendous impact, and the author is not always known. Our legal system is not naturally fit to deal with these characteristics of the internet. In this paper we address internet communication and content issues from a legal angle. Our discussion reveals the struggle of the law with getting control over what happens on the internet. It is no matter of favouring the law or the internet, the two should act in tandem to realize a safe and just society. The final word on how strict or free legal control should be, has not been said determined. We contribute to this discussion in our paper by discussing UK and Dutch case law and doctrine on threats, defamation, grooming, and ISP blocking.La comunicación en internet no tiene precedentes en cuanto a su escala, diseño, velocidad y anonimato. Las palabras puestas online alcanzan inmediatamente el globo entero pudiendo tener tremendo impacto y el autor no siempre es conocido. Nuestro sistema legal no es naturalmente apropiado para tratar con las características de internet. En este artículo, abordamos las cuestiones de comunicación y contenidos de internet desde un punto de vista jurídico. Nuestra discusión revela la batalla del derecho para conseguir control sobre lo que sucede en internet. No se trata de favorecer el derecho o el Internet, los dos deben actuar en conjunto para lograr una sociedad justa y segura. La última palabra sobre cómo debiera ser un control legal estricto o libre, no ha sido dicha aún. Aquí contribuimos a esa discusión presentando casos jurídicos tanto de Holanda como del Reino Unido sobre amenazas, difamación, engaño a menores y bloqueo de ISP (Internet Service Providers)
Developing a long-term management strategy to prepare the Dutch coast for the future, editorial of the VSI future Dutch coast
No full textCoastal EngineeringPolicy Analysi
