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Apeldoorn, Netherlands

Leenders J.K.,HKV Consultants | Leenders J.K.,Wageningen University | Sterk G.,University Utrecht | Van Boxel J.H.,University of Amsterdam
Earth Surface Processes and Landforms | Year: 2011

Wind erosion is an important soil erosion and hence a soil degradation problem in the Sahelian zone of West Africa. Potentially, the characteristic dryland vegetation with scattered trees and shrubs can provide for soil erosion protection from wind erosion, but so far adequate quantification of vegetation impacts is lacking. The aim of this study was to develop a model of windblown soil erosion and sediment transport around a single shrub-type vegetation element. Starting with the selection of a suitable transport equation from four possible sediment transport equations, the effects of a single vegetation element on wind speed were parameterized. The modified wind speed was then applied to a sediment transport equation to model the change in sediment mass flux around a shrub. The model was tested with field data on wind speed and sediment transport measured around isolated shrubs in a farmer's field in the north of Burkina Faso. The simple empirical equation of Radok (Journal of Glaciology 19: 123-129, 1977) performed best in modelling soil erosion and sediment transport, both for the entire event duration and for each minute within an event. Universal values for the empirical constants in the sediment transport equation could not be obtained because of the large variability in soil and roughness characteristics. The pattern of wind speed, soil erosion and sediment transport behind a shrub and on either side of it was modelled. The wind speed changed in the lee of the vegetation element depending on its porosity, height and downwind position. Wind speed was recovered to the upstream speed at a downwind distance of 7·5 times the height of the shrub. The variability in wind direction created a 'rotating' area of influence around the shrub. Compared to field measurements the model predicted an 8% larger reduction in sediment transport in the lee of the vegetation element, and a 22% larger increase beside the vegetation element. © 2011 John Wiley & Sons, Ltd. Source

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. Source

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). Source

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. Source

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. Source

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