Requirements for Topology in 3D GIS

Topology and its various benefits are well understood within the context of 2D Geographical Information Systems. However, requirements in three-dimensional (3D) applications have yet to be defined, with factors such as lack of users' familiarity with the potential of such systems impeding this process. In this paper, we identify and review a number of requirements for topology in 3D applications. The review utilises existing topological frameworks and data models as a starting point. Three key areas were studied for the purposes of requirements identification, namely existing 2D topological systems, requirements for visualisation in 3D and requirements for 3D analysis supported by topology. This was followed by analysis of application areas such as earth sciences and urban modelling which are traditionally associated with GIS, as well as others including medical, biological and chemical science. Requirements for topological functionality in 3D were then grouped and categorised. The paper concludes by suggesting that these requirements can be used as a basis for the implementation of topology in 3D. It is the aim of this review to serve as a focus for further discussion and identification of additional applications that would benefit from 3D topology. © 2006 The Authors. Journal compilation © 2006 Blackwell Publishing Ltd

The need for improved management of the subsurface

The subsurface is used intensively to support economic stability and growth. Human interaction with the shallow subsurface ranges from exploitation of resources, accommodation of utilities, harnessing of energy (ground source heat pumps) and storage of waste. Current practice of managing these shallow subsurface zones is far from ideal. Many subsurface interventions are preceded by feasibility studies, predictive models or investigative measures to mitigate risks or predict the impacts of the work. However, the complex interactions between the anthropogenic structures and natural processes mean that a holistic impact assessment is often not achievable. By integrating these subsurface infrastructures within three dimensional framework models, a comprehensive assessment of the potential hazards in these shallow subsurface environments may be made. Some Geological Survey Organizations (GSOs) are currently developing subsurface management systems that will aid decision making in the shallow subsurface [1]. The British Geological Survey (BGS) is developing an open Environmental Modeling Platform [2] to provide the data standards and applications to link models, numerical simulations and ultimately socio-economic models so as to generate predictive responses to questions concerning sustainable us of the subsurface

Tectonic interpretation of the connectivity of a multiscale fracture system in limestone

This paper studies the statistics and tectonism of a multiscale natural fracture system in limestone. The fracture network exhibits a self‐similar characteristic with a correlation between its power law length exponent a and fractal dimension D, i.e., a ≈ D + 1. Contradicting the scale‐invariant connectivity of idealized self‐similar systems, the percolation state of trace patterns mapped at different scales and localities of the study area varies significantly, from well to poorly connected. A tectonic interpretation based on a polyphase fracture network evolution history is proposed to explain this discrepancy. We present data to suggest that the driving force for fracture formation may be dissipated at the end of a tectonic event when the system becomes connected. However, the “effective” connectivity can successively be reduced by cementation of early fractures and reestablished by subsequent cracking, rendering a variable “apparent” connectivity that can be significantly above the percolation threshold.ISSN:0094-8276ISSN:1944-800

Design, Implementation, and Evaulation of GIS-Based Learning Materials in an Introductory Geoscience Course

Little is known about how well GIS-based learning lives up to its potential for improving students' skills in problem solving, analysis, and spatial visualization. This article describes a study in which researchers determined ways to quantify student learning that occurred with a GIS-based module on plate tectonics and geologic hazards, and to improve the materials design with the use of classroom observations and field testing. The study found that student difficulties in working with GIS-based activities can be overcome by making some features of the GIS transparent to the user, that a lack of basic geography skills can interfere in the progression of a GIS-based activity, and that some conceptual difficulties can be overcome by providing guiding questions that help students interrogate visual data. In addition, it was noted that some misconceptions in interpretation of two-dimensional maps and three-dimensional block diagrams can persist even after direct instruction. In general, a positive correlation was noted between spatial thinking and GIS-based learning. Educational levels: Graduate or professional

Knowledge-based systems and geological survey

This personal and pragmatic review of the philosophy underpinning methods of geological surveying suggests that important influences of information technology have yet to make their impact. Early approaches took existing systems as metaphors, retaining the separation of maps, map explanations and information archives, organised around map sheets of fixed boundaries, scale and content. But system design should look ahead: a computer-based knowledge system for the same purpose can be built around hierarchies of spatial objects and their relationships, with maps as one means of visualisation, and information types linked as hypermedia and integrated in mark-up languages. The system framework and ontology, derived from the general geoscience model, could support consistent representation of the underlying concepts and maintain reference information on object classes and their behaviour. Models of processes and historical configurations could clarify the reasoning at any level of object detail and introduce new concepts such as complex systems. The up-to-date interpretation might centre on spatial models, constructed with explicit geological reasoning and evaluation of uncertainties. Assuming (at a future time) full computer support, the field survey results could be collected in real time as a multimedia stream, hyperlinked to and interacting with the other parts of the system as appropriate. Throughout, the knowledge is seen as human knowledge, with interactive computer support for recording and storing the information and processing it by such means as interpolating, correlating, browsing, selecting, retrieving, manipulating, calculating, analysing, generalising, filtering, visualising and delivering the results. Responsibilities may have to be reconsidered for various aspects of the system, such as: field surveying; spatial models and interpretation; geological processes, past configurations and reasoning; standard setting, system framework and ontology maintenance; training; storage, preservation, and dissemination of digital records

Derivation of lowland riparian wetland deposit architecture using geophysical image analysis and interface detection

For groundwater-surface water interactions to be understood in complex wetland settings, the architecture of the underlying deposits requires investigation at a spatial resolution sufficient to characterize significant hydraulic pathways. Discrete intrusive sampling using conventional approaches provides insufficient sample density and can be difficult to deploy on soft ground. Here a noninvasive geophysical imaging approach combining three-dimensional electrical resistivity tomography (ERT) and the novel application of gradient and isosurface-based edge detectors is considered as a means of illuminating wetland deposit architecture. The performance of three edge detectors were compared and evaluated against ground truth data, using a lowland riparian wetland demonstration site. Isosurface-based methods correlated well with intrusive data and were useful for defining the geometries of key geological interfaces (i.e., peat/gravels and gravels/Chalk). The use of gradient detectors approach was unsuccessful, indicating that the assumption that the steepest resistivity gradient coincides with the associated geological interface can be incorrect. These findings are relevant to the application of this approach in settings with a broadly layered geology with strata of contrasting resistivities. In addition, ERT revealed substantial structures in the gravels related to the depositional environment (i.e., braided fluvial system) and a complex distribution of low-permeability putty Chalk at the bedrock surface—with implications for preferential flow and variable exchange between river and groundwater systems. These results demonstrate that a combined approach using ERT and edge detectors can provide valuable information to support targeted monitoring and inform hydrological modeling of wetlands

High-resolution truncated plurigaussian simulations for the characterization of heterogeneous formations

Integrating geological concepts, such as relative positions and proportions of the different lithofacies, is of highest importance in order to render realistic geological patterns. The truncated plurigaussian simulation method provides a way of using both local and conceptual geological information to infer the distributions of the facies and then those of hydraulic parameters. The method (Le Loc'h and Galli 1994) is based on the idea of truncating at least two underlying multi-Gaussian simulations in order to create maps of categorical variable. In this manuscript we show how this technique can be used to assess contaminant migration in highly heterogeneous media. We illustrate its application on the biggest contaminated site of Switzerland. It consists of a contaminant plume located in the lower fresh water Molasse on the western Swiss Plateau. The highly heterogeneous character of this formation calls for efficient stochastic methods in order to characterize transport processes.Comment: 12 pages, 9 figure

Simulating spatial and temporal evolution of multiple wing cracks around faults in crystalline basement rocks

Fault zones are structurally highly spatially heterogeneous and hence extremely complex. Observations of fluid flow through fault zones over several scales show that this structural complexity is reflected in the hydrogeological properties of faults. Information on faults at depth is scarce, hence, it is highly valuable to understand the controls on spatial and temporal fault zone development. In this paper we increase our understanding of fault damage zone development in crystalline rocks by dynamically simulating the growth of single and multiple splay fractures produced from failure on a pre-existing fault. We present a new simulation model, MOPEDZ (Modeling Of Permeability Evolution in the Damage Zone surrounding faults), that simulates fault evolution through solution of Navier's equation with a combined Mohr-Coulomb and tensile failure criteria. Simulations suggest that location, frequency, mode of failure and orientation of splay fractures are significantly affected both by the orientation of the fault with respect to the maximum principal compressive stress and the conditions of differential stress. Model predictions compare well with published field outcrop data, confirming that this model produces realistic damage zone geometries

Extremes in dune preservation: controls on the completeness of fluvial deposits

Understanding sedimentary preservation underpins our ability to interpret the ancient sedimentary record and reconstruct palaeoenvironments and palaeoclimates. Dune sets are ubiquitous in preserved river deposits and are typically interpreted based on a model that that describes the recurrence of erosion in a vertical sequence, but without consideringspatial variability. However, spatial variability in flow and sediment transport will change the recurrence of erosion, and therefore dune preservation. In order to better understand the limits of these Interpretations and outline the causes of potential variability in preservation potential, this paper reviews existing work and presents new observations of an extreme end-member of dune preservation: ?form-sets?, formed by dunes in which both stoss- and lee- slopes are preserved Intact. These form-sets do not conform to models that are based on the recurrence of erosion, since erosion does not recur in their case, and can therefore be used to evaluate the assumptions that underpin sedimentary preservation. New Ground Penetrating Radar data from the Río Paraná, Argentina, show dune fields that are buried intact within larger scale barforms. These trains of form-sets are up to 300 m in length, are restricted to unit-bar troughs in the upper 5 m of the channel deposits, occur in >5% of the mid-channel bar deposits, show reactivation surfaces, occur in multiple levels, and match the size of average-flow dunes. A review of published accounts of form-sets highlights a diversity of processes that can be envisaged for their formation: i) abandonment after extreme floods, ii) slow burial of abandoned dune forms by cohesive clay in sheltered bar troughs and meander-neck cut-offs, iii) fast burial by mass-movement processes, and iv)climbing of dune sets due to local dominance of deposition over dune migration.Analysis of these new and published accounts of form-sets and their burial processes highlights that form-sets need not be indicative of extreme floods. Instead, form-sets are closely associated with surrounding geomorphology such as river banks, meander-neck cutoffs,and bars because this larger-scale context controls the local sediment budget and the nature of recurrence of erosion. Locally enhanced preservation by the ?extreme? dominance of deposition is further promoted by finer grain sizes and prolonged changes in flow stage. Such conditions are characteristic, although not exclusive, of large lowland rivers such as the Río Paraná. The spatial control on dune preservation is critical: although at-a-point models adequately describe near-horizontal sets of freely migrating dunes in uniform flows, they are unsuitable for inclined dune co-sets and other cases where multiple scales of bedforms interact. Spatial and temporal variations in flow and sediment transport betweenthe thalweg and different positions on larger bar-forms can change the preservation potential of dunes within river channels. Therefore, dune set thickness distributions are likely grouped in larger-scale units that reflect both formative dune geometries and bar-scale variations inpreservation potential. The multi-scale dynamics of preservation highlighted herein also provides a useful comparison for other sedimentary systemsFil: Reesink, Arnold J.. University Of Binghamton; Estados UnidosFil: Van den Berg, J. H.. University of Utrecht; Países BajosFil: Parsons, Daniel R.. University Of Hull; Reino UnidoFil: Amsler, Mario Luis. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Best, James L.. University of Illinois. Urbana - Champaign; Estados UnidosFil: Hardy, Richard J.. University Of Durham; Reino UnidoFil: Orfeo, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; ArgentinaFil: Szupiany, Ricardo Nicolas. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentin