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Lefebvre A.,University of Bremen | Paarlberg A.J.,HKV Consultants | Winter C.,University of Bremen
Water Resources Research | Year: 2014

Large asymmetric bed forms commonly develop in rivers. The turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers. This paper uses the Delft3D modeling system to investigate the effects of bed form geometry and forcing conditions on flow separation length and associated turbulence, and bed form shear stress over angle-of-repose (30 lee side angle) bed forms. The model was validated with lab measurements that showed sufficient agreement to be used for a systematic analysis. The influence of flow velocity, bed roughness, relative height (bed form height/water depth), and aspect ratio (bed form height/length) on the variations of the normalized length of the flow separation zone, the extent of the wake region (where the turbulent kinetic energy (TKE) was more than 70% of the maximum TKE), the average TKE within the wake region and the form shear stress were investigated. Form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region (extent of the wake region/extent of water body above the bed form) and the average TKE within the wake region. The results add to understanding of the hydrodynamics of bed forms and may be used for the development of better parameterizations of small-scale processes for application in large-scale studies. Key Points A numerical model is set and validated to simulate flow over bed forms Separation zone extent is affected by relative bed form height and length Bed form shear stress relates to the extent and turbulence in the wake region ©2014. American Geophysical Union. All Rights Reserved.


Westerhoff R.S.,Deltares | Kleuskens M.P.H.,Deltares | Winsemius H.C.,Deltares | Huizinga H.J.,HKV Consultants | And 2 more authors.
Hydrology and Earth System Sciences | Year: 2013

This paper presents an automated technique which ingests orbital synthetic-aperture radar (SAR) imagery and outputs surface water maps in near real time and on a global scale. The service anticipates future open data dissemination of water extent information using the European Space Agency's Sentinel-1 data. The classification methods used are innovative and practical and automatically calibrated to local conditions per 1 × 1° tile. For each tile, a probability distribution function in the range between being covered with water or being dry is established based on a long-term SAR training dataset. These probability distributions are conditional on the backscatter and the incidence angle. In classification mode, the probability of water coverage per pixel of 1 km × 1 km is calculated with the input of the current backscatter - incidence angle combination. The overlap between the probability distributions of a pixel being wet or dry is used as a proxy for the quality of our classification. The service has multiple uses, e.g. for water body dynamics in times of drought or for urgent inundation extent determination during floods. The service generates data systematically: it is not an on-demand service activated only for emergency response, but instead is always up-to-date and available. We validate its use in flood situations using Envisat ASAR information during the 2011 Thailand floods and the Pakistan 2010 floods and perform a first merge with a NASA near real time water product based on MODIS optical satellite imagery. This merge shows good agreement between these independent satellite-based water products. © Author(s) 2013.


Wesselink A.,University of Leeds | Warner J.,Wageningen University | Kok M.,HKV Consultants
Environmental Science and Policy | Year: 2013

In this paper we show how applying an analytical framing of hegemony to policy making can draw out strategic positioning and negotiation of the actors involved that would remain hidden with a more rationalistic analysis. We show how long established flood protection management from the Dutch lowlands was imported into Limburg after two major flood events (1993/1995) and we argue this case highlights how existing hegemony is easily replicated in new situations. With the shock caused by these floods came a securitising discourse that transformed the portrayal of flood risks in Limburg as 'safety' rather than 'costly nuisance'. After an intense lobby by Limburg, the Meuse and its floodplains were included into the Dutch Flood Defence Law in 2005, becoming a national responsibility. While most Limburg inhabitants see increased protection against flooding as beneficial, the new law also meant strict design procedures and planning restrictions. Water expertise plays an important role in setting the new rules that determine which local ambitions are compatible with the national laws and policies. While securitisation helped to actively reproduce the existing (perception of) hegemonic relations in this case, the relationship between securitisation and hegemony is context-dependent, and both hegemon and non-hegemon can use a securitisation strategy to their advantage. Exactly how this will happen cannot be predicted, but 'securitization' and 'hegemony' are important sensitising concepts that can alert the observer to mechanisms of power re-distribution in other situations and settings. © 2012 Elsevier Ltd.


Terpstra T.,HKV Consultants | Lindell M.K.,Texas A&M University
Environment and Behavior | Year: 2013

Although research indicates that adoption of flood preparations among Europeans is low, only a few studies have attempted to explain citizens' preparedness behavior. This article applies the Protective Action Decision Model (PADM) to explain flood preparedness intentions in the Netherlands. Survey data (N = 1,115) showed that hazard-related attributes (e.g., perceived efficacy in protecting persons) were positively correlated, but failed to show that resource-related attributes (e.g., perceived costs) were negatively correlated with preparedness intentions. Although respondents rated the hazard-related attributes as more important than the resource-related attributes, moderated regression failed to detect practically meaningful interaction effects. Risk perception was also positively correlated with preparedness intentions but explained less variance than did the hazard-related attributes. Among the demographic characteristics, only female gender was consistently correlated with higher risk perception and the hazard-related attributes. Finally, risk area was correlated with perceived flood likelihood and consequences as well as the hazard-related attributes. Implications are discussed. © The Author(s) 2012.


Kolen B.,HKV Consultants | Helsloot I.,Radboud University Nijmegen
Disasters | Year: 2014

A traditional view of decision-making for evacuation planning is that, given an uncertain threat, there is a deterministic way of defining the best decision. In other words, there is a linear relation between threat, decision, and execution consequences. Alternatives and the impact of uncertainties are not taken into account. This study considers the 'top strategic decision-making' for mass evacuation owing to flooding in the Netherlands. It reveals that the top strategic decision-making process itself is probabilistic because of the decision-makers involved and their crisis managers (as advisers). The paper concludes that deterministic planning is not sufficient, and it recommends probabilistic planning that considers uncertainties in the decision-making process itself as well as other uncertainties, such as forecasts, citizens responses, and the capacity of infrastructure. This results in less optimistic, but more realistic, strategies and a need to pay attention to alternative strategies. © 2014 The Author(s).


Kolen B.,HKV Consultants | Kolen B.,Radboud University Nijmegen | Helsloot I.,Radboud University Nijmegen
Disasters | Year: 2012

On 30 May 2008, the Government of the Netherlands informed the national parliament about the effectiveness of preventive evacuation of coastal and river areas in case of flooding. Analysis of a case study showed that it is impossible to evacuate coastal areas preventively within a 48-hour time span preceding a worst credible scenario flood caused by a storm surge. This fact illustrates the need for alternative evacuation strategies, such as vertical evacuation (evacuating to safe havens, inside the flood zone) or shelter-in-place (hiding), to reduce loss of life and the impact of the evacuation. This paper defines these strategies and demonstrates, by returning to the case study used by the Dutch government, that they require different measures, methods of approach, and crisis management processes. In addition, it addresses the need for flexible and scalable preparation so that after detecting and understanding the threat, authorities and citizens can make decisions about different evacuation strategies. © 2012 The Author(s). Journal compilation © Overseas Development Institute, 2012.


De Jong M.,HKV Consultants | Helsloot I.,University of Amsterdam
Procedia Engineering | Year: 2010

This study presents and analyses data about choices citizens made in their evacuation response during three days of the Dutch national flooding exercise 'Waterproef'. It explores the link of this response with the provided information and communication during the exercise by comparing the risk awareness, information experience and information needs of the individuals to their evacuation behavior in three different flooding scenarios. Overall this study shows that communication and information has an effect on the response of individuals but not necessarily in the way that is expected. Government can influence people's response but the effect of this communication seems to have limits. Also some aspects in responses are more susceptible for this influence by information then others.


De Boer J.,VU University Amsterdam | Wouter Botzen W.J.,VU University Amsterdam | Terpstra T.,HKV Consultants
Risk Analysis | Year: 2014

This article proposes an approach to flood risk communication that gives particular emphasis to the distinction between prevention and promotion motivation. According to E. Tory Higgins, the promotion system and the prevention system are assumed to coexist in every person, but one or the other may be temporarily or chronically more accessible. These insights have far-reaching implications for our understanding of people's reasoning about risks. Flood risk communication framed in terms of prevention involves the notions of chance and harm, woven into a story about particular events that necessitate decisions to be more careful about safety issues and protect one's family and oneself from danger. The article describes how the insights worked out in practice, using a flood risk communication experiment among a sample from the general population in a highly populated river delta of the Netherlands. It had a posttest-only control group design (n = 2,302). The results showed that risk communication had a large effect on the participants' responses and that this effect was higher among chronic prevention-focused people than among others. Any information that increased the fit between a prevention-framed message and a person's chronic prevention motivation produced stronger situationally induced, prevention-focused responses. This may significantly improve communication about risks. In contrast, the notion of water city projects, featuring waterside living, had more appeal to promotion-focused people. © 2013 Society for Risk Analysis.


Kuijper B.,HKV Consultants | Kallen M.J.,HKV Consultants
Structure and Infrastructure Engineering | Year: 2012

Decisions regarding the maintenance of structures subject to uncertain deterioration are usually made on the basis of expected costs. For example, the optimal frequency of preventive replacements is the one which entails the lowest expected costs. For this kind of investment strategy, the variance of costs can be large. However, the variance can only be easily calculated in a few simple cases. It is therefore not common to include the uncertainty about the outcome of the optimal strategy in the final decision. The variance of costs for maintenance strategies was one of the subjects professor Jan M. van Noortwijk worked on during his career. His research shows that the variance in the costs of an optimal strategy can be larger than in the case of less optimal strategies. This article reports on one particular application of this research, namely, the periodic heightening of the many dikes that protect the Netherlands against coastal and fluvial flooding. Two existing models for dike heightening are reviewed, and the variance of the costs is determined by assuming that floods occur in time according to a non-homogeneous Poisson process. © 2012 Copyright Taylor and Francis Group, LLC.


Kallen M.J.,HKV Consultants
Reliability Engineering and System Safety | Year: 2011

In problems of maintenance optimization, it is convenient to assume that repairs are equivalent to replacements and that systems or objects are, therefore, brought back into an as good as new state after each repair. Standard results in renewal theory may then be applied for determining optimal maintenance policies. In practice, there are many situations in which this assumption cannot be made. The quintessential problem with imperfect maintenance is how to model it. In many cases it is very difficult to assess by how much a partial repair will improve the condition of a system or object and it is equally difficult to assess how such a repair influences the rate of deterioration. In this paper, a superposition of renewal process is used to model the effect of imperfect maintenance. It constitutes a different modelling approach than the more common use of a virtual age process. © 2011 Elsevier Ltd.All rights reserved.

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