439 research outputs found
Karst, GIS and geological hazard planning and management in Great Britain
The British Geological Survey (BGS) database of karst features for the United Kingdom include dolines, cave entrances, stream sinks, resurgences and building damage; data for approximately half of the country has so far been gathered. BGS makes and utilises digital geological map data, which includes lithological and stratigraphical information for bedrock and superficial deposits. By incorporating this digital map data with digital elevation slope models and karst data, BGS has generated a derived dataset assessing the likelihood of subsidence due to karst collapse. This dataset is informed and verified by the karst database and marketed as part of its GeoSure suite; the karst layer includes areas of limestone, chalk, gypsum and salt. It is currently used by environmental regulators, the insurance and construction industries plus the BGS semi-automated enquiry system. The karst database and GeoSure datasets can be combined and manipulated using GIS to make other datasets that deal with specific problems. Sustainable drainage systems, some of which use soak-aways into the ground are being encouraged in the UK, but in karst areas they can cause problems. Similarly, open loop ground source heat pumps may induce subsidence if installed in certain types of karst such as chalk with overlying sand deposits. Groundwater abstraction also has the potential to trigger subsidence in karst areas. GIS manipulation of the karst information will allow the UK to be zoned into areas suitable, or unsuitable, for such uses; it has the potential to become part of a suite of planning management tools for local and National Government to assess the long term sustainable use of the ground
Superficial geology and hydrogeological domains between Durham and Darlington. Phase 1, (Durham South)
The North East Region’s Groundwater Modelling Strategy has identified the need for the
development of a conceptual model for the Magnesian Limestone aquifer. In line with the
Environment Agency R&D Technical Report W214 (Environment Agency Framework for
Groundwater Resources Conceptual and Numerical Modelling), a scoping study was produced,
that identified areas of uncertainty and work required for the development of the conceptual
model.
The purpose of this project is to give the Environment Agency (EA) a regional understanding of
the geology and hydrogeology of the Magnesian Limestone and overlying superficial deposits in
the North East Region, using information presently held by the British Geological Survey (BGS).
This report contributes to the conceptual model and understanding of the Magnesian Limestone
aquifer.
There is uncertainty in the amount of recharge that the Magnesian Limestone receives from
rainfall. The project is designed to gain a greater understanding of the geology of the superficial
deposits and their hydrogeological properties. These are the key factors for the calculation of
recharge to the Magnesian Limestone aquifer from rainfall. This element of the conceptual
model is essential in understanding the potential water resource available within this aquifer
Superficial geology and hydrogeological domains between Durham and Darlington. Phase 2, (Durham North)
The North East Region’s Groundwater Modelling Strategy has identified the need for the
development of a conceptual model for the Magnesian Limestone aquifer. In line with the
Environment Agency R&D Technical Report W214 (Environment Agency Framework for
Groundwater Resources Conceptual and Numerical Modelling), a scoping study was produced,
that identified areas of uncertainty and work required for the development of the conceptual
model.
The purpose of this project is to give the Environment Agency (EA) a regional understanding of
the geology and hydrogeology of the Magnesian Limestone and overlying superficial deposits in
the North East Region, using information held by the British Geological Survey (BGS). This
report contributes to the conceptual model and understanding of the Magnesian Limestone
aquifer.
There is uncertainty in the amount of recharge that the Magnesian Limestone receives from
rainfall. The project is designed to gain a greater understanding of the geology of the superficial
deposits and their hydrogeological properties. These are the key factors for the calculation of
recharge to the Magnesian Limestone aquifer from rainfall. This element of the conceptual
model is essential in understanding the potential water resource available within this aquifer
Vale of York 3-D borehole interpretation and cross-sections study
The Vale of York between Doncaster and Scunthorpe in the south and York and Bugthorpe in
the north is largely underlain by bedrock of the Sherwood Sandstone Group – one of the regions
principal aquifers. Significant superficial deposits of Quaternary age overlie the Sherwood
Sandstone. This study aims to investigate the nature of these superficial deposits with respect to
their relationship with the underlying aquifer.
The Vale of York project area represents a varied glaciated terrain, consisting of pro-glacial finegrained
sediments, coarser glaciofluvilal sediments and extensive glacial tills. These diverse
superficial units vary in thickness throughout the project area. The hydrogeological nature of the
natural superficial sequence is consequently highly variable. Units may be considered as
aquitards, while others may act as aquifers, providing a potential pathway to the underlying
sandstone. The classification of lithologies as aquifer or aquitard is described in detail in this
report.
To investigate the hydrogeological nature of the superficial sequence, six east-west and three
north-south lithostratigraphical cross-sections were constructed. A range of geoscientific
information was considered, including existing geological mapping and over 3000 fully
attributed and coded boreholes. The cross-sections show a subdivision of the superficial
sequence into lithostratigraphical units. Each unit is described in detail in this report.
In addition, a series of thematic maps were generated from the lithological component of the
digital borehole data. Total superficial aquifer and superficial aquitard maps show how the
lithological nature of the superficial sequence varies across the area. Rockhead elevation and
superficial thickness maps indicate where the sandstone aquifer outcrops at the ground surface.
In summary, four main lithostratigraphical units overlie the Sherwood Sandstone Group aquifer
in the project area: a basal sequence of glaciofluvial sand and gravel (interpreted as a superficial
aquifer), glaciolacustrine laminated silt & clay (aquitard), glacial till comprising sandy gravelly
clay (aquitard), and a cover sequence of fluvial and aeolian sand, clay and peat (aquifer /
aquitard). The correlations illustrate that in certain areas, superficial deposits are thin or absent
and that in these areas the Sherwood Sandstone aquifer comes directly to ground surface
Double-Layer Systems at Zero Magnetic Field
We investigate theoretically the effects of intralayer and interlayer
exchange in biased double-layer electron and hole systems, in the absence of a
magnetic field. We use a variational Hartree-Fock-like approximation to analyze
the effects of layer separation, layer density, tunneling, and applied gate
voltages on the layer densities and on interlayer phase coherence. In agreement
with earlier work, we find that for very small layer separations and low layer
densities, an interlayer-correlated ground state possessing spontaneous
interlayer coherence (SILC) is obtained, even in the absence of interlayer
tunneling. In contrast to earlier work, we find that as a function of total
density, there exist four, rather than three, distinct noncrystalline phases
for balanced double-layer systems without interlayer tunneling. The newly
identified phase exists for a narrow range of densities and has three
components and slightly unequal layer densities, with one layer being spin
polarized, and the other unpolarized. An additional two-component phase is also
possible in the presence of sufficiently strong bias or tunneling. The
lowest-density SILC phase is the fully spin- and pseudospin-polarized
``one-component'' phase discussed by Zheng {\it et al.} [Phys. Rev. B {\bf 55},
4506 (1997)]. We argue that this phase will produce a finite interlayer Coulomb
drag at zero temperature due to the SILC. We calculate the particle densities
in each layer as a function of the gate voltage and total particle density, and
find that interlayer exchange can reduce or prevent abrupt transfers of charge
between the two layers. We also calculate the effect of interlayer exchange on
the interlayer capacitance.Comment: 35 pages, 19 figures included. To appear in PR
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
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