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Caris A.,Hasselt University | Caris A.,Research Foundation Flanders FWO | Macharis C.,Vrije Universiteit Brussel | Janssens G.K.,Hasselt University
Computers in Industry | Year: 2013

This paper proposes new research themes concerning decision support in intermodal transport. Decision support models have been constructed for private stakeholders (e.g. network operators, drayage operators, terminal operators or intermodal operators) as well as for public actors such as policy makers and port authorities. Intermodal research topics include policy support, terminal network design, intermodal service network design, intermodal routing, drayage operations and ICT innovations. For each research topic, the current state of the art and gaps in existing models are identified. Current trends in intermodal decision support models include the introduction of environmental concerns, the development of dynamic models and the growth in innovative applications of Operations Research techniques. Limited data availability and problem size (network scale) and related computational considerations are issues which increase the complexity of decision support in intermodal transport. © 2012 Elsevier B.V.


Maetens W.,Catholic University of Leuven | Poesen J.,Catholic University of Leuven | Vanmaercke M.,Catholic University of Leuven | Vanmaercke M.,Research Foundation Flanders FWO
Earth-Science Reviews | Year: 2012

The effects of soil and water conservation techniques (SWCTs) on annual runoff (R a), runoff coefficients (RC a) and annual soil loss (SL a) at the plot scale have been extensively tested on field runoff plots in Europe and the Mediterranean. Nevertheless, a comprehensive overview of these effects and the factors controlling the effectiveness of SWCTs is lacking. Especially the effectiveness of SWCT in reducing R a is poorly understood. Therefore, an extensive literature review is presented that compiles the results of 101 earlier studies. In each of these studies, R a and SL a was measured on field runoff plots where various SWCTs were tested. In total, 353 runoff plots (corresponding to 2093 plot-years of data) for 103 plot-measuring stations throughout Europe and the Mediterranean were considered. SWCTs include (1) crop and vegetation management (i.e. cover crops, mulching, grass buffer strips, strip cropping and exclosure), (2) soil management (i.e. no-tillage, reduced tillage, contour tillage, deep tillage, drainage and soil amendment) and (3) mechanical methods (i.e. terraces, contour bunds and geotextiles). Comparison of the frequency distributions of SL a rates on cropland without and with the application of SWCTs shows that the exceedance probability of tolerable SL a rates is ca. 20% lower when SWCT are applied. However, no notable effect of SWCTs on the frequency distribution of RC a is observed. For 224 runoff plots (corresponding to 1567 plot-year data), SWCT effectiveness in reducing R a and/or SL a could be directly calculated by comparing measured R a and/or SL a with values measured on a reference plot with conventional management. Crop and vegetation management techniques (i.e. buffer strips, mulching and cover crops) and mechanical techniques (i.e. geotextiles, contour bunds and terraces) are generally more effective than soil management techniques (i.e. no-tillage, reduced tillage and contour tillage). Despite being generally less effective, no-tillage, reduced tillage and contour tillage have received substantially more attention in the literature than the other SWCTs. Soil and water conservation techniques are generally less effective in reducing R a than in reducing SL a, which is an important consideration in areas where water is a key resource and in regions susceptible to flooding. Furthermore, all SWCTs show a more consistent and effective reduction of both R a and SL a with increasing R a and SL a magnitude, which is attributed to the reduced influence of measurement uncertainties. Although some significantly negative correlations between SWCT effectiveness and plot slope length, slope gradient or annual precipitation were found, the importance of these factors in explaining the observed variability in effectiveness seems limited. Time-series analyses of R a during multiple years of SWCT application strongly indicate that no-tillage and conservation tillage become less effective in reducing R a over time. Such an effect is not observed for SL a. © 2012 Elsevier B.V.


Vannoppen W.,Catholic University of Leuven | Vanmaercke M.,Catholic University of Leuven | Vanmaercke M.,Research Foundation Flanders FWO | De Baets S.,University of Exeter | Poesen J.,Catholic University of Leuven
Earth-Science Reviews | Year: 2015

Living plant roots modify both mechanical and hydrological characteristics of the soil matrix (e.g. soil aggregate stability by root exudates, soil cohesion, infiltration rate, soil moisture content, soil organic matter) and negatively influence the soil erodibility. During the last two decades several studies reported on the effects of plant roots in controlling concentrated flow erosion rates. However a global analysis of the now available data on root effects is still lacking. Yet, a meta-data analysis will contribute to a better understanding of the soil-root interactions as our capability to assess the effectiveness of roots in reducing soil erosion rates due to concentrated flow in different environments remains difficult. The objectives of this study are therefore: i) to provide a state of the art on studies quantifying the effectiveness of roots in reducing soil erosion rates due to concentrated flow; and ii) to explore the overall trends in erosion reduction as a function of the root (length) density, root architecture and soil texture, based on an integrated analysis of published data. We therefore compiled a dataset of measured soil detachment ratios (SDR) for the root density (RD; 822 observations) as well as for the root length density (RLD; 274 observations). A Hill curve model best describes the decrease in SDR as a function of R(L)D. An important finding of our meta-analysis is that RLD is a much more suitable variable to estimate SDR compared to RD as it is linked to root architecture. However, a large proportion of the variability in SDR could not be attributed to RD or RLD, resulting in a low predictive accuracy of these Hill curve models with a model efficiency of 0.11 and 0.17 for RD and RLD respectively. Considering root architecture and soil texture did yield a better predictive model for RLD with a model efficiency of 0.37 for fibrous roots in non-sandy soils while no improvement was found for RD. The unexplained variance is attributed to differences in experimental set-ups and measuring errors which could not be explicitly accounted for due to a lack of additional data. Based on those results, it remains difficult to predict the effects of roots on soil erosion rates. However, by using a Monte Carlo simulation approach, we were able to establish relationships that allow assessing the likely erosion-reducing effects of plant roots, while taking these uncertainties into account. Overall, this study demonstrates that plant roots can be very effective in reducing soil erosion rates due to concentrated flow. © 2015 Elsevier B.V.


Vanmaercke M.,Catholic University of Leuven | Vanmaercke M.,Research Foundation Flanders FWO | Poesen J.,Catholic University of Leuven | Broeckx J.,Catholic University of Leuven | Nyssen J.,Ghent University
Earth-Science Reviews | Year: 2014

Several studies have compiled and analysed measured contemporary catchment sediment yield (SY, [tkm-2 y-1]) values for various regions of the world. Although this has significantly contributed to our understanding of SY, Africa remains severely underrepresented in these studies. The objective of this article is therefore: (1) to review and compile available SY data for Africa; (2) to explore the spatial variability of these SY data; and (3) to examine which environmental factors explain this spatial variability. A literature review resulted in a dataset of SY measurements for 682 African catchments from 84 publications and reports, representing more than 8340 catchment-years of observations. These catchments span eight orders of magnitude in size and are relatively well spread across the continent. A description of this dataset and comparison with other SY datasets in terms of spatial and temporal distribution and measurement quality is provided. SY values vary between 0.2 and 15,699tkm-2y-1 (median: 160tkm-2y-1, average: 634tkm-2y-1). The highest SY values occur in the Atlas region with SY values frequently exceeding 1000tkm-2y-1. Also the Rift region is generally characterised by relatively high SY values, while rivers in Western and Central Africa have generally low SY values. Spatial variation in SY at the continental scale is mainly explained by differences in seismic activity, topography, vegetation cover and annual runoff depth. Other factors such as lithology, catchment area or reservoir impacts showed less clear correlations. The results of these analyses are discussed and compared with findings from other studies. Based on our results, we propose a simple regression model to simulate SY in Africa. Although this model has a relatively low predictive accuracy (40%), it simulates the overall patterns of the observed SY values well. Potential explanations for the unexplained variance are discussed and suggestions for further research that may contribute to a better understanding of SY in Africa are made. © 2013 Elsevier B.V.


Vanderlinde R.,Ghent University | Vanderlinde R.,Research Foundation Flanders FWO | Van Braak J.,Ghent University | Dexter S.,University of Virginia
Computers and Education | Year: 2012

Researchers and policy makers around the world are increasingly acknowledging the importance of developing a school-based ICT policy plan to facilitate the integration of information and communication technology (ICT) in education. Despite this interest, not much is known about how schools can develop their local ICT policy capacity and how to establish an ICT policy plan. In order to fill the gap in research on ICT policy planning, a multiple case study analysis with a mixed-method design was carried out with three Flemish primary schools. Primary schools in Flanders are encouraged by the government to develop local ICT policy planning in a context of ICT curriculum reform. Data from multiple sources (e.g. interviews with school leaders and ICT coordinators, focus group interviews with teachers, school policy document analysis, and a teacher questionnaire) were gathered and analyzed. The results indicate that ICT policy planning in schools should be considered as a multifaceted phenomenon grounded in school culture. ICT policy consists of different policy domains: vision development, financial policy, infrastructural policy, continuing professional development policy, and curriculum policy. Each policy domain can be described in terms of policy artifacts (tools, routines, and structures), and differences exist between schools concerning the involvement of teachers in the policy planning process and in the distribution of management tasks. As such, the study illustrates a distributed leadership perspective on ICT school policy planning. The results are of particular importance for school leaders, ICT coordinators and professional development trainers, and illustrates that ICT school policy is as much about developing shared meanings among stakeholders for ICT, and coordinating their relations and interactions in keeping with the school's culture as it is about content related decisions. © 2012 Elsevier Ltd. All rights reserved.

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