Key Note: Living with droughts?

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

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

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

Numerical modelling of erosion and sedimentation around offshore pipelines

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

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

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

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

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

3D character of backward erosion piping

Backward erosion piping is an important failure mechanism for cohesive water-retaining structures which are founded on a sandy aquifer. Nowadays, piping research and safety assessments are often based on experimental or numerical modelling using arbitrary model widths or even two-dimensional (2D) assumptions. This technical note shows the influence of this limitation through a series of small-scale experiments with varying model widths. The flow pattern proves to be highly three-dimensional (3D), influencing both the pipe geometry and critical gradients leading to piping failure. A 2D model is unable to capture the important aspects of the erosion mechanism and a correction factor needs to be applied if the minimum width for correctly simulating a 3D situation is not accomplished

Developments in modelling of backward erosion piping

One of the failure mechanisms that can affect the safety of a dyke or another water-retaining structure is backward erosion piping, a phenomenon that results in the formation of shallow pipes at the interface of a sandyor silty foundation and a cohesive cover layer. Themodels available for predicting the critical head at which the pipe progresses to the upstreamside have been validated and adapted on the basis of experiments with two-dimensional (2D) configurations. However, the experimental base for backward erosion in three-dimensional (3D) configurations in which the flow concentrates towards one point, a situation that is commonly encountered in the field, is limited. This paper presents additional 3D configuration experiments at two scales with a range of sand types. The critical gradients, the formed pipes and the erosion mechanism were analysed for the available experiments, indicating that the erosion mechanism is more complex than previously assumed, as both erosion at the tip of the pipe (primary erosion) and in the pipe (secondary erosion) are relevant. In addition, a 3D configuration was found to result in significantly lower critical gradients than those predicted by an accepted calculation model calibrated on the basis of 2D experiments, a finding that is essential for the application of the model in the field

Kennisbasis WOT Fisheries 2011 - what is in the Programme?

The KBWOT Fisheries programme is core to the maintenance and development of the expertise that underpins the statutory obligations of fisheries monitoring and advice for the Netherlands. The structure of the KBWOT Fisheries programme for 2011 changed to reflect the recent discussions on the research direction between IMARES, CVO and EL&I. One of the strengths of the structure of the KBWOT Fisheries programme was the bottom up approach to calls for projects to fulfil the research priorities. This however was seen as giving the programme the potential to miss strategic needs of both the science development within IMARES and the research questions of EL&I, thus the programme now also contains a specific project request on an research subject relevant to IMARES and EL&I needs. The KBWOT Fisheries programme will fund 12 projects in 2011. The projects will investigate competition in exploited fish communities, long term changes in eel populations, the spawning habitat of mackerel, sub-stock structure in fish, trawling impact on benthic communities, quality assurance in fish aging, surveys of shellfish, maturity staging of fish and acoustic methods. Plus a targeted project specifically designed to research needs of IMARES and EL&I will be carried out into the trade-offs in FMSY targets for North Sea flatfish fisheries