A novel analytical solution for constant‐head test in a patchy aquifer

A mathematical model describing the hydraulic head distribution for a constant‐head test performed in a well situated at the centre of a patchy aquifer is presented. The analytical solution for the mathematical model is derived by the Laplace transforms and the Bromwich integral method. The solution for the hydraulic head has been shown to satisfy the governing equations, related boundary conditions, and continuity requirements for the hydraulic head and flow rate at the interface of the patch and outer regions. An efficient numerical approach is proposed to evaluate the solution, which has an integral covering an integration range from zero to infinity and an integrand consisting the product and square of the Bessel functions. This solution can be used to produce the curves of dimensionless hydraulic head against dimensionless time for investigating the effect of the contrast of formation properties on the dimensionless hydraulic head distribution. Define the ratio of outer‐region transmissivity to patch‐region transmissivity as α. The dimensionless hydraulic head for α=0.1 case is about 2.72 times to that for α=10 case at dimensionless large time (e.g. τ?10⁶) when the dimensionless distance (ρ) equals 10. The results indicate that the hydraulic head distribution highly depends on the hydraulic properties of two‐zone formations. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatially-integrated estimates of net ecosystem exchange and methane fluxes from Canadian peatlands

Background

Peatlands are an important component of Canada’s landscape, however there is little information on their national-scale net emissions of carbon dioxide [Net Ecosystem Exchange (NEE)] and methane (CH₄). This study compiled results for peatland NEE and CH₄ emissions from chamber and eddy covariance studies across Canada. The data were summarized by bog, poor fen and rich-intermediate fen categories for the seven major peatland containing terrestrial ecozones (Atlantic Maritime, Mixedwood Plains, Boreal Shield, Boreal Plains, Hudson Plains, Taiga Shield, Taiga Plains) that comprise >?96% of all peatlands nationally. Reports of multiple years of data from a single site were averaged and different microforms (e.g., hummock or hollow) within these peatland types were kept separate. A new peatlands map was created from forest composition and structure information that distinguishes bog from rich and poor fen. National Forest Inventory k-NN forest structure maps, bioclimatic variables (mean diurnal range and seasonality of temperatures) and ground surface slope were used to construct the new map. The Earth Observation for Sustainable Development map of wetlands was used to identify open peatlands with minor tree cover.

Results

The new map was combined with averages of observed NEE and CH₄ emissions to estimate a growing season integrated NEE (±?SE) at ??108.8 (±?41.3) Mt CO₂ season^?1 and CH₄ emission at 4.1 (±?1.5) Mt CH₄ season^?1 for the seven ecozones. Converting CH₄ to CO₂ equivalent (CO₂e; Global Warming Potential of 25 over 100 years) resulted in a total net sink of ??7.0 (±?77.6) Mt CO₂e season^?1 for Canada. Boreal Plains peatlands contributed most to the NEE sink due to high CO₂ uptake rates and large peatland areas, while Boreal Shield peatlands contributed most to CH₄ emissions due to moderate emission rates and large peatland areas. Assuming a winter CO₂ emission of 0.9 g CO₂ m^?2 day^?1 creates an annual CO₂ source (24.2 Mt CO₂ year^?1) and assuming a winter CH₄ emission of 7 mg CH₄ m^?2 day^?1 inflates the total net source to 151.8 Mt CO₂e year^?1.

Conclusions

This analysis improves upon previous basic, aspatial estimates and discusses the potential sources of the high uncertainty in spatially integrated fluxes, indicating a need for continued monitoring and refined maps of peatland distribution for national carbon and greenhouse gas flux estimation.

     

Historical water resources in South Asia: the hydrological background

Abstract

The development of historical water resources in the South Asian subcontinent has been largely dependent on the hydrological background. The runoff patterns are derived from climate statistics and the historical developments in different areas are related to these patterns.

Citation Sutcliffe, J., Shaw, J. & Brown, E. (2011) Historical water resources in South Asia: the hydrological background. Hydrol. Sci. J. 56(5), 775–788.     

Poro-viscoelasticity modelling based on upscaling quasistatic fluid-saturated solids

In this paper, quasistatic models are developed for the slow flow of compressible fluids through porous solids, where the solid exhibits fading memory viscoelasticity. Problems of this type are important in practical geomechanics contexts, for example, in the context of fluid flow through unconsolidated reservoir sands and of wellbore deformation behaviour in gas and oil shale reservoirs, all of which have been studied extensively. For slow viscous fluid flow in the poro-viscoelastic media we are able to neglect the dynamic effects related to inertia forces, as well as the dissipation associated with the viscous flows. This is in contrast to the vast body of work in the poro-elastic context, where much faster flow of the viscous fluids may give rise to memory effects associated with microflows in pores of the solid media. Such problems have been treated extensively in both the dynamic and quasistatic cases. We are taking a specific type of the porous medium subject to slow deformation processes possibly inducing moderate pressure gradients and flow rates characterised by negligible inertia effects. As the result of homogenisation of such a two-phase medium, we observe the fading memory behaviour in the Biot modulus which controls the pressure increase due to skeleton macroscopic deformation and pore fluid content. Although our derivation leads to a result which is consistent with the formal phenomenological approach proposed by Biot (J Appl Phys 23:1482–1498, 1962), we offer the reader more insight into the structure of the poro-viscoelastic constitutive relations obtained; in particular, we can show that the Biot compressibility evolves in time according to the creep function while the skeleton stiffness is driven by the relaxation function.     

A less‐is‐more approach to geovisualization – enhancing knowledge construction across multidisciplinary teams

The ‘less‐is‐more’ concept in interface design for computer applications has recently gained ground. In this article, the concept is adopted for a user‐centered design of geovisualization application. The premise is that using simple and clear design can lead to successful applications with improved ease of use. Over the last three decades, the development of GIS and geovisualization has seen a marked increase in the levels of interaction between the user, the system and the information. However, these enthusiastic advances in technology have not resulted in a significant increase in the number of users.

This article suggests that types of user interaction should not simply emphasize traditional GIS functions such as zooming and panning but move towards interaction based on facilitating the knowledge construction process. Considerations are made for the complexity of the system, the task at hand and the skills and limitations of the users. These elements are particularly important when maps act as the mediators in collaboration with users across disciplinary backgrounds. In such cases, the emphasis on simplicity and usability becomes as important as functionality. In these situations a geovisualization application designed for specific uses can maximize effective development of geographic knowledge.

In this article, a minimalistic design approach to geovisualization is adopted by creating a geographic profiling tool which shifts the emphasis from technological advances or interaction with the map to the interaction elements key to building the spatial knowledge of GIS experts and non‐experts alike. To evaluate this notion of ‘less‐is‐more geovisualization’ the profiling tool is evaluated according to usability matrices: efficiency, effectiveness and learnability. How well the Suburban Profiler contributes to these elements is assessed by conducting a video analysis of the types and forms of user interaction available. The video analysis demonstrates the usefulness and usability of the Suburban Profiler, providing proof of concept for ‘less‐is‐more geovisualization’.     

Exploring potential human activities in physical and virtual spaces: a spatio‐temporal GIS approach

Today, the opportunity for potential human activity has gone beyond physical space to virtual space. Based on a proposed conceptual framework that models the relationships between physical and virtual spaces, this paper presents an attempt to adjust the space–time prism concept of Hägerstrand's time geography to identify potential activity opportunities in virtual space, focusing on the virtual space access channels available in physical space. A three‐dimensional (3D) spatio‐temporal Geographic Information System (GIS) design has been developed in this research to accommodate the adjusted space–time prism concept to support the representation, visualization, and analysis of potential human activities and interactions in physical and virtual spaces using the prism representation. Following the design, a prototype system has been successfully implemented in a 3D GIS environment. Such a system can provide powerful analytical tools for studies related to potential human activities and applications such as location‐based services (LBS) and accessibility analysis in the information age.     

晚古生代冈瓦纳的演化长逾13500 km的基墨利超级地体的裂离及其向亚洲的漂移

The Cimmerian terrane forms an almost unbroken chain stretching >13,500 km, from central southern Europe to western Indonesia, via SE Europe, the Middle East, Afghanistan, Tibet, SW China and Myanmar. Ar-guably, it is Earth’s most spectacular example of a “sliver” terrane, dwarfing in size more recently devel-oped examples, for instance the Palawan Block in the western Philippines, and the Lord Howe Rise in the Tasman Sea. The presentation will first outline the in-triguing geological features associated with this unique tectonic entity. Following that, recently obtained results following paleomagnetic investigations of two lower Permian rift-related basalt suites will be summarized (Abor Volcanics in northeastern India and Woniusi Ba-salts in Yunnan, China). The two studies are part of a larger programme of ongoing research aimed at deducing (I) the geodynamic configuration that generated the un-usual rifting system, and (II) exactly how Cimmeria fit-ted against Gondwana prior to its dispersal in the Early Permian. The critical unit is Baoshan, which we fit against Gondwana within a narrow longitudinal belt close to where northern India and northwestern Australia were once in close proximity (Fig. 1). Furthermore, we suggest that Sibumasu lay to directly the east, offshore of Australia; Qiangtang and Lhasa almost certainly sat to the west (off northern Greater India-SE Arabia), but we are uncertain as to their exact configuration. Our findings will be compared with several rather different models that have been published in recent years. The new pa-leomagnetic constraint highlights the flexibility authors currently have in reconstructing the region, principally because of the overall lack of similar high-quality data from the various blocks. We explain how new data could resolve these ambiguities, thereby offering more robust explanations for eastern Gondwana’s late Paleozoic de-velopment.     

Improved Gabor Deconvolution and Its Extended Applications

In log time-frequency spectra, the nonstationary convolution model is a linear equation and thus we improved the Gabor deconvolution by employing a log hyperbolic smoothing scheme which can be implemented as an iteration process. Numerical tests and practical applications demonstrate that improved Gabor deconvolution can further broaden frequency bandwidth with less computational expenses than the ordinary method. Moreover, we attempt to enlarge this method’s application value by addressing nonstationary and evaluating Q values. In fact, energy relationship of each hyperbolic bin (i.e., attenuation curve) can be taken as a quantitative indicator in balancing nonstationarity and conditioning seismic traces to the assumption of unchanging wavelet, which resultantly reveals more useful information for constrained reflectivity inversion. Meanwhile, a statistical method on Q-value estimation is also proposed by utilizing this linear model’s gradient. In practice, not only estimations well agree with geologic settings, but also applications on Q-compensation migration are favorable in characterizing deep geologic structures, such as the pinch-out boundary and water channel.     

Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs.