1,720,954 research outputs found
Technisch 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
Short Term Morphological Impact of the Eierlandsedam
No full textAfter decades of coastal erosion in the north-west area of the Island of Texel, the shore-normal `Eierlandse Dam` had been built in 1995. The dam, situated in the outer delta of the Eierlandse Gat tidal inlet, resulted in a remarkable short-term morphological development of the adjacent coast. Four years following completion of the dam, large sedimentation rates were measured on both sides of the dam. On the updrift (south) side, sedimentation was predicted as a result of the blocked alongshore sediment transport. However, on the downdrift (north) side of the dam, no sedimentation was predicted. Today, almost two decades later, it remains unclear which processes contributed to the sediment accumulation on the north side of the dam. The increased functionalities and capabilities of the present-day modelling software enable a re-evaluation of the morphological processes around the dam in particular, and gain insights in the complex short-term morphodynamics in this area. To capture the driving mechanism(s) of the net sediment transport towards the northern area of the Eierlandse dam, the state-of-the-art process-based computational model Delft3D is applied. To investigate the influence of various conditions and processes on the morphological development around the dam, simulations are performed with various boundary conditions, model processes and formulations. After calibration of the model, one-year morphological predictions show large similarities with the observed bed level development at both sides of the dam. The ebb tidal currents seem responsible for the large amounts of sedimentation at the north side of the dam, predominantly during spring tides when flow velocities and tidal excursion increase. The ebb tidal channel `Robbengat` is located along the northern tip of the Island of Texel and curves from the inlet around the Eierlandse dam. The Robbengat channel has been eroding by strong ebb tidal currents since 1985. The eroded sediments of the channel are transported by the flow towards the outer delta. Before the channel curves, the flow is partly deflected towards the northern area of the Eierlandse dam. The flow enters a shallow area and decelerates, resulting in deposition of sediment. This conclusion rejects the conclusions drawn by previous studies regarding the same area, where complex hydrodynamics such as eddy forming and spiral flow in the channel bend were drawn as possible causes of the sedimentation.Hydraulic EngineeringCivil Engineering and Geoscience
Paleogeografie en veiligheid tegen overstromen
No full textPaleogeografie is de wetenschap van het beschrijven van de landschapsontwikkeling op basis van de opbouw van de ondergrond en de dynamiek van het voormalige landschap. Haar kennis en methodieken kunnen worden ingezet voor de reconstructie van overstromingen in de Nederlandse delta in het recente geologische verleden. Dit vooronderzoek is een inventarisatie van de bruikbaarheid van de huidige paleogeografische inzichten voor de verbetering van de veiligheid tegen overstromen, en een verkenning van de mogelijkheden dit inzicht op korte termijn te vergroten. De inventarisatie heeft tot doel: 1. Inzichtelijk te maken welke mogelijkheden kennis en inzicht in de paleogeografie van Nederland biedt voor het verbeteren van de veiligheid tegen overstromen; 2. Een overzicht geven van de huidige kennis op het gebied van extreme overstromingen in de laatste 5000 jaar; 3. Inzichtelijk te maken wat op korte en langere termijn te verwachten is van paleogeografische resultaten, voor herhalingsfrequentieschattingen van piekafvoeren. 4. Het doen van een schatting van de verwachte inspanningen en doorlooptijd, bij voorgestelde aanpakken van gekoppeld onderzoek naar overstromingen en veiligheid
Modeling the effects of hard structures on dune erosion and overwash
No full textMany of the most densely populated areas are located near the coast. Climate change and population growth put more and more pressure on these coastal areas. As free space is becoming sparse, coastal disaster risk reduction plans need to be spatially efficient. In this thesis the sandy coast with hard structures, such as buildings or dune revetments, is addressed. These structures can either provide additional protection or enhance erosion. Field measurements and experimental data featuring these phenomena are scarce, but the measurements of the devastating impact of Hurricane Sandy (October 2012) on the New Jersey shore provide new model validation possibilities. Hard structures in the barrier have three effects: 1) The main effect of a structure is the impact on the sand balance (both cross-shore and longshore), by cutting of (part) of the supply of sediment (WL | Delft Hydraulics, 1987). 2) In cross-shore direction a structure may result in the development of scour at the toe as a result of higher energetic conditions at the toe. However, in the post-Sandy bathymetry at the (buried) seawall at Bay Head, NJ, no scour holes were found. XBeach (Roelvink et al., 2009) simulations have reproduced these profiles and suggests this is the result of infilling of scour after the peak of Sandy. 3) In longshore direction a hard element will result in the extra erosion at the sides of the structure as a result of exchange of sediment and locally higher short waves. XBeach simulations have shown that the presence of a condo at Camp Osborne, NJ, during Sandy resulted in 32% additional erosion in adjacent locations However, these effects are no reason to state on forehand that multifunctional use of the barrier is not possible. Its applicability needs to be addressed case-by-case. Process-based models, like XBeach, can accurately reproduce the effects noticed in the field. Calculation rules, like Deltares and Arcadis (2013), do not reflect the true complexity, but can give a rough first indication of the longshore effect.Coastal EngineeringHydraulic EngineeringCivil Engineering and Geoscience
Morphological behaviour of shoreface nourishments along the Dutch coast: Data analysis of historical shoreface nourishments for a better understanding and design
No full textTo counteract relative sea level rise, Rijkswaterstaat nourishes the Dutch coast with sand. This sand spreads out over the shoreface zone, beach and dunes. One of the nourishment types is the shoreface nourishment. In this thesis, data of historical shoreface nourishments along the Dutch coast is analysed to find the factors that influence this behaviour. This research showed that there are two main categories in the migration of shoreface nourishments. The first one migrates only in cross-shore direction and alongshore migration is negligible, this mainly occurs at beaches without influence of surrounding structures and the outer delta of the Wadden Sea. The second one migrates onshore and in alongshore direction, this category occurs mainly southward of the outer delta of the Wadden Sea. The migration can be predicted by the behaviour of the original bar system. The first one exists at coasts with primarily cross-shore bar behaviour and the second one at coasts with primarily alongshore or no bar behaviour. For future application of shoreface nourishments, it is recommended to analyse the original bar system and determine the location of execution on this analysis. If the location is determined, even the prediction for the migration can be determined based on the behaviour of the original bar system.Civil Engineering and GeosciencesHydraulic Engineerin
Dutch experience with sand nourishments for dynamic coastline conservation – An operational overview
No full textThe Dutch coast is one of the most heavily nourished coasts globally. An average of 12 mln. m3 is annually added to the coastline of only 432 km for dynamic coastline conservation. This study provides an overview of the operational aspects of the more than 300 nourishments for coastline maintenance that have been performed since the 1990s and discusses the evolution of the nourishment approach and lessons learned with regard to the nourishment design. The first nourishments were beach and dune nourishments to repair local beach and dune erosion. In the 1990s the nourishment efforts increased when nourishing the coastline was set in policy as the formal strategy to dynamically preserve the coastline. Simultaneously shoreface nourishments emerged, which aim to feed the coast gradually over a longer period than beach nourishments. In 2001 the volume of sand used for nourishments increased from 6.4 to 12 mln. m3 per year, to enable the coastal zone to stay in equilibrium with sea level rise. Channel wall nourishments were introduced around that time because they can slow down the landward migration of tidal channels and can accommodate large volumes of sediment. Nowadays, underwater nourishments are preferred because of the lower costs associated, but the decision for a beach, shoreface, or channel wall nourishment also depends on the morphology, the local setting, and the purpose of the nourishment. All nourishments combined have succeeded in conserving the coastline at its desired position over the past 30 years.Policy Analysi
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
ASMITA modelling of the Wadden Sea with focus on the Groningerwad: Assessing how the Groningerwad will respond to accelerated sea level rise
No full textSome of the sediment which is eroded from the Dutch coast ends up in the Wadden Sea. Because of this the morphological development of the Wadden Sea is important, not only for the Wadden Sea itself but also for the maintenance programs of the adjacent coastlines. This is one of the reasons that the morphological development of the Wadden Sea is extensively studied. Some of these studies use the ASMITA model to make predictions of the morphological development with accelerating sea level rise. The Groningerwad is a part of the Wadden Sea consisting of a number of smaller tidal basins which has not been modelled with ASMITA. It has not yet been necessary to structurally nourish the coastlines surrounding the Groningerwad. However, as sea level rise increases it might well be possible that the coastal profiles surrounding the Groningerwad require nourishment. Therefore this thesis aims to study the Groningerwad with ASMITA to make a prediction of how the area will develop with accelerating sea level rise. To do this a morphological study is performed to determine the current morphological developments. This morphological study, based on available literature and bathymetry measurements of the area, finds that the Groningerwad is a highly dynamic area. It also determined the area and characterizing volume of each of the tidal basins, which have been used to set up the ASMITA model. For each basin in the Groningerwad an ASMITA model is set up using the information from the morphological study. The ASMITA model is used to make predictions for the development of the intertidal, channel and delta volumes of each of the Groningerwad its basins. The required parameters for the model have been derived from relevant formulas and the assumption that the Groningerwad is currently in a morphodynamic equilibrium. This was done because the time period for which bathymetrical measurements are available are to short to allow for a proper calibration procedure for these parameters. With this setup the ASMITA models show that all basins will lose intertidal sediment volume with rising sea levels. The larger basins of the Groningerwad also will not reach a new dynamic equilibrium state with large levels of sea level rise rate increase. When comparing these results to other basins in the Wadden Sea, it appears that the basins in the Groningerwad respond a lot slower than other Wadden Sea basins. Given the difference between the Groningerwad and the Wadden Sea and the fact that the time period over which bathymetrical data is available was to short to fully calibrate the model the recommendation is made to revisit this study when more data is available and it is possible to calibrate the relevant parameters.Civil Engineerin
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