Estimating impacts of changed land use on recharge: review of modelling and other approaches appropriate for management of dryland salinity     

Glen R. Walker  Lu Zhang  Tim W. Ellis  Tom J. Hatton  Cuan Petheram 《Hydrogeology Journal》2002,10(1):68-90

To manage dryland salinity, one needs to know how changed land use affects groundwater recharge. Few techniques are available for comparing 'deep drainage' under different land uses. Soil-tracer methods, although good for replication and remote field sites, are subject to spatial variability. Lysimeters are good for comparisons but are difficult for drier areas and sloping land. Agronomic water-balance studies, where appropriate soil-water measurements exist, may be used with a soil-vegetation model to estimate long-term deep drainage. Complex models are required to analyze specific land-use differences, such as perenniality and root and leaf area dynamics, but models require intensive and extensive data for calibration. This approach is time-consuming, labour-intensive, and difficult in remote locations. Because of the one-dimensionality of most soil-vegetation models and the small fraction of the total water balance that is deep drainage, little success has occurred in extrapolating beyond the research plot, or to spatially heterogeneous systems such as alley farming. Some 'top-down' modelling and landscape disaggregation approaches have been partially successful in making catchment or regional-scale predictions. The direction for further work depends on the level of recharge reduction that is required for most groundwater systems and difficulties that it imposes. Electronic Publication  相似文献   

Is the Ventersdorp Rift System of Southern Africa related to a continental collision between the Kaapvaal and Zimbabwe Cratons at 2.64 Ga ago?     

Kevin Burke  W.S.F. Kidd  Tim Kusky 《Tectonophysics》1985,115(1-2)

Rocks of the Ventersdorp Supergroup were deposited in a system of northeast trending grabens on the Kaapvaal Craton approximately 2.64 Ga ago contemporary with a continental collision between the Kaapvaal and Zimbabwe Cratons. We suggest that it was this collision that initiated the Ventersdorp rifting. Individual grabens strike at high angles toward the continental collision zone now exposed in the Limpopo Province where late orogenic left-lateral strike-slip faulting and anatectic granites are recognized. We relate the Ventersdorp rift province to extension in the Kaapvaal Craton associated with the collision, and see some analogy with such rifts as the Shansi and Baikal Systems associated with the current India-Asia continental collision.  相似文献   

The concealed Caledonide basement of Eastern England and the southern North Sea — A review     

Tim Pharaoh  Richard England  Mick Lee 《Studia Geophysica et Geodaetica》1995,39(3):330-346

Summary Field mapping, analysis of borehole core and studies of geophysical potential field and seismic data can be used to demonstrate the existence of a number of distinct crustal blocks within Eastern Avalonia beneath eastern England and the southern North Sea. At the core of these blocks is the Midlands Microcraton which is flanked by Ordovician volcanic arc complexes exposed in Wales and the Lake District. A possible volcanic arc complex of comparable age in eastern England is concealed by late Palaeozoic and Mesozoic cover. These volcanic arc complexes resulted from subduction of oceanic lithosphere beneath Avalonia prior to collision with Baltica and Laurentia in late Ordovician and Silurian time, respectively. The nature of the crust north and east of the concealed Caledonides of Eastern England and south of the lapetus Suture/Tornquist Sea Suture, which forms the basement to the southern North Sea, is unclear. Late Ordovician metamorphic ages from cores penetrating deformed metasedimentary rocks on the Mid-North Sea High suggest these rocks were involved in Avalonia-Baltica collision before final closure of the lapetus Ocean between Laurentia and Avalonia.  相似文献   

IGS Near Real-Time Products and Their Applications   总被引：2，自引：2，他引：2  

Peng Fang  Gerd Gendt  Tim Springer  Tony Mannucci 《GPS Solutions》2001,4(4):2-8

The primary IGS products, including precise GPS orbits, Earth orientation parameters, and estimated and predicted GPS satellite clocks, are no longer used exclusively for essential geodetic support of scientic research. They are increasingly being used by a wide range of non-academic applications. In these applications, timeliness is extremely critical. To address the timeliness issue, the strengths and weaknesses of current IGS production processes are discussed, new ways to improve the timeliness and quality are explored, and recommendations are proposed to fulfill the application requirements. ? 2001 John Wiley & Sons, Inc.  相似文献   

Modeling Transport of a Degradable Chemical and Its Metabolites in the Unsaturated Zone     

Udoyara S. Tim  Saied Mostaghimi 《Ground water》1989,27(5):672-681

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Fundamental issues in quantitative estimation of mineral resources     

Guocheng Pan  DeVerle P. Harris  Tim Heiner 《Natural Resources Research》1992,1(4):281-292

Several issues considered to be fundamental in quantitative estimation of mineral resources and selection of mineral targets are addressed. Integration of multiple data sets, either by experts or by statistical methods, has become a common practice in estimation of mineral potential. Several major problems in data integration must be solved to significantly improve mineral resource estimation. Issues related to randomness of mineral endowment, basic statistical tools, exceptionalness of ore, and economic truncation and translation are discussed in the first part of the article. A number of important technical problems in data integration are also identified; they include data compilation, information enhancement, information synthesis, and target selection.  相似文献   

Consequences of thrusting and intraplate stress fluctuations for vertical motions in foreland basins and peripheral areas   总被引：1，自引：0，他引：1  

Tim Peper  Fred Beekman  Sierd Cloetingh 《Geophysical Journal International》1992,111(1):104-126

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Variability of bedload transport and channel morphology in a braided river hydraulic model     

Jeff Warburton  Tim Davies 《地球表面变化过程与地形》1994,19(5):403-421

This paper investigates variability in bedload transport and channel morphology for 11 replicate experimental runs in an approximately 1:50 braided river model. The experiments, each of 90 h duration, were carried out in a 20 × 3m tilting flume. All the experiments started with the same initial conditions. Bedload transport was measured at 5 min intervals in a collection drum at the exit from the flume. The model showed reasonable hydraulic similarity when compared to prototype rivers. Results show that mean bedload transport rates for the 11 runs vary in the range 0·98 to 1·49gs^?1 (mean + 1·21, coefficient of variation 11 per cent). Within-run transport rates commonly vary from close to zero, to two and occasionally three or four times the mean rate. Within the bedload series, several irregular phases of transport intensity can be observed, but time series analysis of the data show little underlying serial structure (an AR(2) autoregressive model is appropriate). Channel patterns are narrow/braided, are established quickly and remain relatively stable throughout the runs, although channel widths increase between 20 and 103 per cent over the 11 runs. Channel behaviour varies from aggradational to transitional between aggradation and degradation. Time-averaged bedload transport rate is weakly correlated with braiding intensity. In general, these results demonstrate that for a given set of controlling variables, bedload transport and channel morphology can be approximately replicated.  相似文献   

Remote sensing of capelin and other biological features in the North Pacific using lidar and video technology     

Brown  Evelyn D.; Churnside  James H.; Collins  Richard L.; Veenstra  Tim; Wilson  James J.; Abnett  Kevin 《ICES Journal of Marine Science》2002,59(5):1120-1130

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Dealing with interests displaced by marine protected areas: A case study on the Great Barrier Reef Marine Park Structural Adjustment Package     

Andrew Macintosh  Tim Bonyhady  Debra Wilkinson 《Ocean & Coastal Management》2010,53(9):581-588

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