22,673 research outputs found

    Key Note: Living with droughts?

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    The Netherlands Center for River Research (NCR) in its first 10 years of existence has focused its activities on flooding. Climate change might cause that droughts will become as important as or even more important than floods. The dry year 2003 in Europe has shown the huge socio-economic impacts of droughts. New concepts are emerging on how to deal with droughts. This key-note addresses the issues of droughts and scarcity and makes a plea to include more drought research in NCR

    Numerical modelling of erosion and sedimentation around offshore pipelines

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    In this paper a numerical model is presented for the description of the erosion and sedimentation near pipelines on the sea bottom. The model is based on the Navier-Stokes equations and the equation of motion and continuity of sediment.\ud \ud The results of the simulations have been compared with the results of tests in a large-scale facility. The agreement between the results of the simulations and the experimental results is good.\ud \ud The applicability of the method is twofold: firstly, the processes of erosion and sedimentation around bodies on the sea bottom can be simulated; secondly, the method can be used for the design of pipelines, including erosion stimulating elements, such as spoilers

    Functional Valuation of Ecosystem Services on Bonaire: an ecological analysis of ecosystem functions provided by coral reefs

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    This research is a semi-quantitative analysis of the functional value of coral reef habitats on Bonaire to support ecosystem services. It is part of an economic valuation study of marine and terrestrial ecosystem services on Bonaire

    Key principles for foster carers and adopters who are helping a child to move to adoption

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    When children cannot safely return home from care, adoption provides legal security, love and belonging in a new family. But adoption also means that the child must be separated from a foster family where he or she has felt secure and loved, as well as from familiar routines and surroundings. In order to manage these losses, children of all ages will need the sensitive support and understanding of the adults around them before, during and after the move. This leaflet outlines six important principles for foster carers and adopters to hold in mind as they work together to help children to move to adoption

    Test data from pullout experiments on vetiver grass (Vetiveria zizanioides) grown in semi-arid climate

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    The data set presented in this article includes the results of pullout tests carried out on vetiver grass (Vetiveria zizanioides) growing on an abandoned terrace slopes in Spain. The results comprise tables showing the resistance of each tested vetiver plant to pullout forces applied to it at various angles. The dataset also contains the measurements of the displacement at each pullout force increment. The dataset also includes the plots of the pullout resistance of each vetiver plant against the measured displacement

    Nitrous oxide emissions from fertilized and unfertilized grasslands on peat soil

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    Emissions of nitrous oxide (N2O) from managed and grazed grasslands on peat soils are amongst the highest emissions in the world per unit of surface of agriculturally managed soil. According to the IPCC methodology, the direct N2O emissions from managed organic soils is the sum of N2O emissions derived from N input, including fertilizers, urine and dung of grazing cattle, and a constant ‘background’ N2O emission from decomposition of organic matter that depends on agro-climatic zone. In this paper we questioned the constant nature of this background emission from peat soils by monitoring N2O emissions, groundwater levels, N inputs and soil NO3 -–N contents from 4 grazed and fertilized grassland fields on managed organic peat soil. Two fields had a relatively low groundwater level (‘dry’ fields) and two fields had a relatively high groundwater level (‘wet’ fields). To measure the background N2O emission, unfertilized sub-plots were installed in each field. Measurements were performed monthly and after selected management events for 2 years (2008–2009). On the managed fields average cumulative emission equaled 21 ± 2 kg N ha-1y-1 for the ‘dry’ fields and 14 ± 3 kg N ha-1y-1 for the ‘wet’ fields. On the unfertilized sub-plots emissions equaled 4 ± 0.6 kg N ha-1y-1 for the ‘dry’ fields and 1 ± 0.7 kg N ha-1y-1 for the ‘wet’ fields, which is below the currently used estimates. Background emissions were closely correlated with groundwater level (R 2 = 0.73) and accounted for approximately 22% of the cumulative N2O emission for the dry fields and for approximately 10% of the cumulative N2O emissions from the wet fields. The results of this study demonstrate that the accuracy of estimating direct N2O emissions from peat soils can be improved by approximately 20% by applying a background emission of N2O that depends on annual average groundwater level rather than applying a constant valu

    Piping in loose sands: the importance of geometrical fixity of grains

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    Piping is one of the possible failure mechanism for dams and levees with a sandy foundation. Water flowing through the foundation causes the onset of grain transport, due to which shallow pipes are formed at the interface of the sandy layer and an impermeable blanket layer. In the past, the mechanism has been investigated predominantly in densely packed sands, in which the process was observed to start at the downstream side (backward erosion). Recently performed experiments in loose sand (van Beek et al. 2009) showed a different failure mechanism (forward erosion). In this article additional experiments of piping in loose sands are described for investigating the relevance of the forward process for practice. In these experiments the type of process was found to be dependent on the presence of shear resistance between sand box cover and top sand grains, that causes grains to be fixed geometrically. Without this shear resistance the process was found to be forward, whereas with this shear resistance the process was found to be backward oriented. The change in degree of fixity and relative density as a result of loading is investigated with electrical density measurements. The experiments show that the forward process is not relevant for levees in practice, in which the cohesive blanket layer causes the sand grains to be fixed properly

    Feed additives : annual report 2009 of the National Reference Laboratory

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    This report of the National Reference Laboratory (NRL) for feed additives describes the activties employed in 2010. The main tasks of the NRL are: giving assistance to the European Union Reference Laboratort (EU-RL) on their request and advice and support the competent authority, the Dutch Ministry of Economic Affairs, Agriculture and Innovation - Department of Food, Animal and Consumer (EL&I-VDC
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