Qualitative and quantitative applications of LiDAR imagery in fluvial geomorphology     

Bastiaan Notebaert  Gert Verstraeten  Gerard Govers  Jean Poesen 《地球表面变化过程与地形》2009,34(2):217-231

The potential for geomorphological mapping and quantitative calculations of light detection and ranging (LiDAR) data within fluvial geomorphology was studied for two river catchments within Belgium (Dijle and Amblève), which differ in physical settings and floodplain morphology. Two commercial, of‐the‐shelf LiDAR datasets with different specifications (horizontal resolution and vertical accuracy) were available for parts of the floodplains of both catchments. Real‐time kinematic (RTK) Global Positioning System (GPS) data were used as ground truth for error calculations. Qualitative analysis of LiDAR data allowed the identification of former channel patterns, levees, colluvial hillslope and fan deposits. These results were confirmed by field data, topographic surveys and historical maps. The pixel resolution proved to be an important factor in the identification of small landforms: only features with a width equal to or larger than LiDAR resolution can be detected. This poses limits on the usability of regionally available LiDAR data, which often have a horizontal resolution of several metres. The LiDAR data were also used in a quantitative analysis of channel dynamics. In the study area, the width of the Dijle River channel increased 3 m on average between 1969 and 2003. A sediment budget of channel processes for the period 1969–2003 indicated a total river bank erosion of 16·1 10³ m³ and a total within channel deposition of 7·1 10³ m³, resulting in a net river erosion of 9·0 10³ m³ or c. 0·4 Mg year^?1 per metre river length. Sequential LiDAR data can in theory be used to calculate vertical sedimentation rates, as long as there is control on the error of the reference levels used. Copyright © 2008 John Wiley and Sons, Ltd.  相似文献   

Facies variation in Waulsortian buildups,Part 1; A model from Belgium     

A. Lees  V. Hallet  D. Hibo 《Geological Journal》1985,20(2):133-158

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Transatlantic latest Cretaceous mosasaurs (Reptilia,Lacertilia) from the Maastrichtian type area and New Jersey     

Mulder  Eric W.A. 《Geologie en Mijnbouw》1999,78(3-4):281-300

Cranial and postcranial elements of the mosasaurid reptiles Mosasaurus hoffmanni Mantell 1829 and Plioplatecarpus marshi Dollo 1882 from the Maastrichtian type area, and of Mosasaurus maximus Cope 1869 and Plioplatecarpus depressus (Cope 1869) from New Jersey are compared. Views held by previous authors are discussed. It is concluded that these European and North American taxa are conspecific.  相似文献   

Sensitivity analysis for the EPIK method of vulnerability assessment in a small karstic aquifer, southern Belgium   总被引：5，自引：0，他引：5  

Radu Constantin Gogu  Alain Dassargues 《Hydrogeology Journal》2000,8(3):337-345

Applying the EPIK parametric method, a vulnerability assessment has been made for a small karstic groundwater system in southern Belgium. The aquifer is a karstified limestone of Devonian age. A map of intrinsic vulnerability of the aquifer and of the local water-supply system shows three vulnerability areas. A parameter-balance study and a sensitivity analysis were performed to evaluate the influence of single parameters on aquifer-vulnerability assessment using the EPIK method. This approach provides a methodology for the evaluation of vulnerability mapping and for more reliable interpretation of vulnerability indices for karst groundwater resources. Received, March 1999/Revised, December 1999, February 2000/Accepted, February 2000  相似文献   

Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium     

Marc Van Camp  Marleen Coetsiers  Kristine Martens  Kristine Walraevens 《水文科学杂志》2013,58(5):763-779

Abstract

Using a groundwater flow model and long historical meteorological time series data, the evolution of the groundwater flow regime in a multi-layered groundwater flow basin in northern Belgium during the last one and a half centuries (since 1833) is reconstructed. Model output parameters such as piezometric levels, depth to water table, seepage fluxes in the valleys and calculated baseflow to the river system are presented and inter-annual and decadal variations are evaluated against seasonal fluctuations. The main time-varying boundary condition in the model is the aquifer recharge which was estimated using the method of Thornthwaite and Mather based on precipitation and temperature data. The model does not take into account changes in boundary conditions due to changes in land use (deforestation, drainage of cultivated land) or groundwater exploitation. Variations in model output parameters are therefore only due to climatological forcing. Only the natural non-exploited state of the aquifer is considered. Although few historical piezometric measurements are available to verify model output, the results give an indication of the natural hydrodynamic variations on a time scale of decades.

Citation Van Camp, M., Coetsiers, M., Martens, K. & Walraevens, K. (2010) Effects of multi-annual climate variability on the hydrodynamic evolution (1833 to present) in a shallow aquifer system in northern Belgium. Hydrol. Sci. J. 55(5), 763–779.  相似文献   

The relative impact of climate change and urban expansion on peak flows: a case study in central Belgium     

Lien Poelmans  Anton Van Rompaey  Victor Ntegeka  Patrick Willems 《水文研究》2011,25(18):2846-2858

An essential part of hydrological research focuses on hydrological extremes, such as river peak flows and associated floods, because of their large impact on economy, environment, and human life. These extremes can be affected by potential future environmental change, including global climate change and land cover change. In this paper, the relative impact of both climate change and urban expansion on the peak flows and flood extent is investigated for a small‐scale suburban catchment in Belgium. A rainfall‐runoff model was coupled to a hydrodynamic model in order to simulate the present‐day and future river streamflow. The coupled model was calibrated based on a series of measured water depths and, after model validation, fed with different climate change and urban expansion scenarios in order to evaluate the relative impact of both driving factors on the peak flows and flood extent. The three climate change scenarios that were used (dry, wet winter, wet summer) were based on a statistical downscaling of 58 different RCM and GCM scenario runs. The urban expansion scenarios were based on three different urban growth rates (low, medium, high urban expansion) that were set up by means of an extrapolation of the observed trend of urban expansion. The results suggest that possible future climate change is the main source of uncertainty affecting changes in peak flow and flood extent. The urban expansion scenarios show a more consistent trend. The potential damage related to a flood is, however, mainly influenced by land cover changes that occur in the floodplain. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Influence of sedimentary setting on the use of magnetic susceptibility: examples from the Devonian of Belgium   总被引：1，自引：0，他引：1  

A.-C. DA SILVA  C. MABILLE  F. BOULVAIN 《Sedimentology》2009,56(5):1292-1306

Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea‐level variations. This paper explores the link between magnetic susceptibility, depositional setting and environmental parameters. These environmental parameters include distal–proximal transects, microfacies successions and fourth‐order trends on different carbonate platform types (platform, ramp, carbonate mound or atoll) during different Devonian stages (Eifelian, Givetian and Frasnian). Average magnetic susceptibility values over a distal–proximal‐trending facies succession vary markedly with depositional setting. On carbonate platforms, average magnetic susceptibility generally increases towards the top of shallowing‐upward sequences. On a distal–proximal transect, average magnetic susceptibility is intermediate for the deepest facies, decreases for the reef belts and increases to a maximum in the back‐reef zone. In ramps and atolls, magnetic susceptibility trends clearly differ; average magnetic susceptibility generally decreases towards the top of shallowing‐upward sequences and is highest in the deepest facies. The strong relationship between magnetic susceptibility, facies and sequences implies a strong environmental influence. However, the different responses in the different platform types suggest that sea‐level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values. Other primary or secondary processes also probably influenced magnetic mineral distribution. Primary processes such as carbonate production and water agitation during deposition are probably key factors. When carbonate production is high, the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases. High water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values. These parameters explain the lowest values observed on the reef platform, inner ramp and atoll crown, which are all in areas characterized by higher carbonate production and greater water agitation during deposition. The lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown. However, other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal. Diagenesis can change magnetism by creating or destroying magnetic minerals. However, the influence of diagenesis probably is linked strongly to the primary facies (permeability, amount of clay or organic matter) and probably enhanced the primary signal. The complexity of the signal gives rise to correlation problems between different depositional settings. Thus, while magnetic susceptibility has the potential to be an important correlation tool, the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control.  相似文献   

Large-scale GIS-based hydrogeological modeling of Flanders: a tool for groundwater management     

Jan Cools  Yves Meyus  Solomon Tuccu Woldeamlak  Okke Batelaan  Florimond De Smedt 《Environmental Geology》2006,50(8):1201-1209

For the implementation of the European Union Water Framework Directive (WFD), technological and scientific support are required. This paper presents a methodology to support a first step of the implementation of WFD, which is the delineation of groundwater bodies. The methodology consists of (1) the development of a complete and generally-accepted hydrogeological classification system for Flanders, named the HCOV code, (2) the development of a geographic information systems (GIS)-managed borehole database, and (3) the development of aquifer and aquitard models by means of a solid modeling approach. For each unit of the hydrogeological classification code for Flanders unit, GIS maps are generated for the three basic characteristics of hydrogeological layers: extent, base level and thickness, such that combined, the volume and extent of a hydrogeological layer is unambiguously defined. This GIS-based hydrogeological database has become a useful tool for groundwater management purposes and to provide the input for groundwater modeling.  相似文献   

Origin of deviations between the remanent magnetisation and inducing geomagnetic field direction in kilns and implications on archaeomagnetic dating     

J. Hus  R. Geeraerts 《Studia Geophysica et Geodaetica》2005,49(2):233-253

Standard secular variation curves of the geomagnetic field direction for the last few millennia for different countries in Europe, based mainly on baked materials discovered in archaeological sites, are reaching sufficient accuracy and reliability that archaeomagnetic dating within this timespan in these areas is becoming feasible now. Orientation errors during sampling and sample preparation can be kept to a minimum and measurement errors of baked materials are in general very small. Nevertheless, even when the secular variation in the site to be dated is similar to that in the reference site, systematic or regular deviations between the remanence vector and geomagnetic field direction in kilns, due to internal and external factors, may result in biased average magnetisation directions and consequently in diverging archaeomagnetic dates. In more or less circular kilns, important non-random deviations of the remanence direction in the walls, in function of the relative azimuth as seen from the centre of the kilns, have been noticed in spite of precise and highly reliable average kiln magnetisation directions. The effect was revealed in the walls of the combustion chambers of roman pottery kilns and of mediaeval brass melting and working kilns, of different shape, lined with refractory bricks. Several hypotheses for the origin of these deviations were examined and anisotropy and/or magnetic refraction are unlikely to be the principal causes. The regular component of these deviations may be responsible for a strongly biased average magnetisation direction when only part of the kiln wall is preserved or when sampling is limited to certain parts of it and consequently result in unreliable dates when applying the archaeomagnetic dating method.  相似文献   

Politicization of research and the relevance of geography: some experiences and reflections for an ongoing debate     

Justin Beaumont  Maarten Loopmans  Justus Uitermark† 《Area》2005,37(2):118-126

In this paper we address the revival of interest in recent years in the relevance of geographical research and highlight problems of politicization faced by researchers through cases of policy-oriented research in the UK and Belgium. We argue that geographers should be aware of the possibilities and constraints for critical engagement in the context of policy-oriented research. We identify at least two important opportunities for researchers to avoid clientelistic relationships with contractors and enhance their political relevance. First, researchers can stick to letter of the contract and maintain academic standards while at the same time interpreting their tasks according to their own ethical and political judgements. Second, relevance can be increased by forming alliances within and beyond the formal hierarchies of the state and the academy. The identification and utilization of these 'spaces of relevance' can be seen as the first step towards an approach that strategically seeks a balance between societal engagement on the one hand and contractual obligations, policy relevance and academic standards on the other.  相似文献