3805 resultaten

  • Development of a new case-based reasoning tool for the comparison of water stress related information in Europe

    Auteurs: Kukuric, N.; Robijn, F.; Griffioen, J. (2009)

    Many regions across Europe are exposed to a water stress. Consequently, various stress mitigation measures are planned and implemented. Water stress specifics and environmental setup wherein the stress occurs can be comparable among certain regions. It is therefore useful to search for similar ‘cases’ and to (re)use the experience on stress behaviour and mitigation measures gained elsewhere. In de framework of AQUASTRESS, a long-term European research project, a methodology has been developed for a comparison of water-stress related information in Europe. Environmental (or ‘natural’) conditions and stress specifics are described by a set of attributes at a sub-catchment level. A significant effort has been made to collect environmental- and stress-related information and define the attributes for each sub-catchment in Europe. A new Case-Based Reasoning (CBR) tool has been developed for the comparison of cases among the sub-catchments. The tool can be used as a stand-alone application or coupled with other AQUASTRESS software applications. This paper contains a detailed description of developed software, presented in context of its application for the solving of water stress related problems.

  • Composite modelling by applying an inverse technique in analysing interactions between beaches and structures

    Auteurs: Boogaard, H.F.P. van den; Gerritsen, H.; Caires, S.; Gent, M.R.A. van (2009)

    Composite modelling aims to combine the best properties of physical scale modelling and numerical modelling and so provide a more efficient modelling infrastructure. The paper analyses this for the case of wave attack on the sea defence at Petten, the Netherlands, which has a typical foreshore with a bar. An error correction model is created for the results of the numerical simulations. Inverse application of the correction model on the results of a range of efficiently realised numerical simulations provides corresponding “pseudo” scale model experiments of higher accuracy than the uncorrected numerical results. Benefits are enhanced flexibility, efficiency and accuracy.

  • Root architecture of six tropical seagrass species, growing in three contrasting habitats in Indonesian waters

    Auteurs: Kiswara, W.; Erftemeijer, P.L.A. (2009)
    Gepubliceerd in: Aquatic botany, volume 90 (2009) nummer 3, pagina 235-245

    Although several recent studies point at the importance of seagrass roots for nutrient acquisition in oligotrophic tropical ecosystems, remarkably little is known about the root architecture of tropical seagrasses. The present study provides a detailed description of the root architecture of six seagrass species that were extracted from three sites differing in sediment type and nutrient availability (i.e., except for one species that was not present at one of the sites). Number of roots per node, order of root branching, length and diameter per root order, root hair density and length were determined and used to calculate a topological index for the different species and habitats. Root architecture differed strongly between species. The relatively long-lived and slowly-growing species Thalassia hemprichii and Enhalus acoroides were characterised by short internodes with relatively few unbranched roots per node and a high root hair density. More fast growing species such as Cymodocea rotundata, Cymodocea serrulata and Syringodium isoetifolium had many roots per node, the majority of which were branched. Surprisingly, differences in sediment type and nutrient availability, as present between locations, had little effect on root architecture. We expect this to be due to a relatively homogeneous nutrient distribution at the small scale within water saturated sediments. Overall, all seagrass species had relatively simple branching (topological index > 0.7), comparable to angiosperms of the low temperate salt marsh. We speculate that relatively simple root architecture of plants in flooded systems reflects the need for a minimal path length for oxygen transport from shoots to roots.

  • Quantification methods of black carbon : comparison of Rock-Eval analysis with traditional methods

    Auteurs: Poot, A.; Quik, J.T.K.; Veld, H.; Koelmans, A.A. (2009)

    Journal of Chromatography A, 1216 (2009) pp. 613-622.

  • Finite element simulation of a slow moving natural slope in the Upper-Austrian Alps using a visco-hypoplastic constitutive model

    Auteur: Ham, G. van den (2009)

    A large-size creeping natural slope was simulated with the Finite Element (FE) method, using a viscohypoplastic material model, which describes the mechanical behaviour of cohesive soils, allowing for viscous effects (i.e. creep, relaxation and rate-dependence of stiffness). First, the required material parameters were determined by means of standard geotechnical laboratory tests using representative soil samples taken from the slope. Then a FE mesh of a slope section was constructed and boundary conditions were established. The slope movements were simulated and compared with inclinometer measurements, which were available for a period of 16 years. The calculation results are in good agreement with the observed velocities. A parameter study was carried out in order to assess the influence of slope angle, initial void ratio, material parameters as well as their spatial distribution.

  • Investigation of the influence of a low-tide terrace on wave loads using the Boussinesq-type model TRITON

    Auteurs: Caires, S.; Gent, M.R.A. van (2009)

    Computations of the Boussinesq-type wave model TRITON of wave propagation over a shallow foreshore with a varying low-tide terrace configuration were carried out. The results were compared with Scheldt flume physical experiments, using the same settings and post processing. The comparisons show that TRITON can model the wave propagation along shallow foreshores quite accurately as long as highly nonlinear effects do not play a significant role. Furthermore, the level of the low-tide terrace was found to influence the wave conditions at the toe of a fictive structure as follows: a) As the level of the low-tide terrace increases there is more energy dissipation and the significant wave height at the toe decreases, decreasing the hydraulic load. b) On the other hand, as the waves dissipate low-frequency energy is released and the spectral wave period at the toe increases, increasing the hydraulic load.

  • The use of a Boussinesq-type wave model to determine the surf quality of artificial reefs

    Auteurs: Hout, A.J. van der; Borsboom, M.J.A. (2009)

    In this study the use of a Boussinesq-type wave model in the integral design of an artificial surf reef (ASR) is investigated. Until now ASR’s are mainly designed using physical scale models. Already several steps have been taken to predict the surf quality of a reef design with the use of numerical models. Nonlinear refractiondiffraction models and surfbeat models can respectively reproduce wave heights and rip currents adequately, but both lack the capability to combine the two within a single model. The use of a Boussinesq-type wave model (TRITON) , capable of computing waves and horizontal flow simultaneously, is therefore proposed to determine the surf quality of an ASR in a design stage. With the use of TRITON wave propagation has been simulated in the time domain for bichromatic wave conditions. From the simulations four parameters have been determined that are a measure of the surf quality: wave height, inshore Iribarren number, wave velocity along the breaker line, and current. The predictive capabilities of TRITON have been verified against physical measurements for a wedge-shaped ASR. TRITON is capable to predict integral wave height parameters (Hm0) within 10%-15% accuracy. Also the development of a rip current is predicted by TRITON. The calculated wave pattern and the breaking process are in good agreement with the measurements. The aforementioned parameters that determine the surf quality are resolved with sufficient accuracy to give a reliable prediction of the quality of waves produced by an ASR. It is concluded that a Boussinesq-type wave model like TRITON can be a valuable tool in the design of a surf reef.

  • Comparison of soil moisture simulated by HBV96 and estimated from TRMM passive microwave observations for a catchment in Southern NSW, Australia

    Auteurs: Liu, Y.; Dijk, A.I.J.M.; Weerts, A.H.; Jeu, R.A.M. de (2007)

  • Weather-induced temporal variations in nitrate concentrations in shallow groundwater

    Auteurs: Rozemeijer, J.C.; Broers, H.P.; Geer, F.C. van; Bierkens, M.F.P. (2009)

    For the evaluation of policy action programs to improve groundwater quality, research institutes and governmentsintensively monitor nitrate concentrations in shallow or near surface groundwater.

  • Seasonal-scale nearshore morphological evolution : field observations and numerical modeling

    Auteurs: Ruggiero, P.; Walstra, D.J.R.; Ormondt, M. van (2009)

    The role offully three-dimensional cell circulation patterns in explaining the observed morphological variability alsoappears to be minor, at least in the case investigated here.

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