Modelling radionuclide transport in large fractured-media systems: the example of Forsmark, Sweden

The planned high-level nuclear waste repository at Forsmark, Sweden, will accommodate 6,824 containers with a total of 13,920 tonnes of uranium in burnt fuel at approximately 400 m depth in a fractured-granite aquifer. The transport of radionuclides, which may be released from the disposed waste, is simulated with the TOUGHREACT code for a three-dimensional model with 305,571 elements. The model performs coupled flow-transport simulations. It aims to achieve more realistic simulations of contaminant transport than the commonly used decoupled procedure consisting of three-dimensional flow and one-dimensional transport simulations. The model has a relatively small problem size because it is designed as a double-porosity model (one matrix continuum) that is the parameterised equivalent of a much larger multiple-interacting continua (MINC) model, i.e. a model with a finely discretised matrix (several matrix continua). The parameterisation is performed with two-dimensional models. Only one or two variables among three variables (diffusive transport distance between fracture and matrix, retardation factor and effective diffusivity) have to be parameterised. The results obtained with the parameterised three-dimensional model are very close to those that can be obtained with a much larger MINC model but may be quite different from those that can be obtained with the conventional decoupled procedure.     

基于多源共享数据的北极航道海域冰情分析

随着全球气候变暖,北冰洋季节性大规模通航已经可以预见。为开辟北极航道服务,保障航道航行安全,采集航线所经海域及沿岸国家和地区基础地理信息,建立基础数据库是基础。以东北航道所经海域海冰覆盖为例,获取多国海洋信息服务网络的海冰共享数据,按照空间信息系统要求,相互校验,提高数据时效和空间覆盖频率,处理成适用于保障北极航道安全航行的信息,讨论了东北航道所经海区的海冰对航道开通时间的影响,实现航道水域海冰信息的通航期(7月1日到11月30日)逐日发布,非通航期(12月1日到次年6月30日)半月发布一次,为北极航道大规模通航积累经验和基础信息。     

The function of the freight distribution systems

Summary To sum up it can be said that new or further developed systems of haulage must be found, especially in conurbations, in order to be able to cope efficiently with freight transport. The scheme here presented for freight distribution centres is one possibility which has been much discussed. The establishment of such a freight distribution centre in Koblenz by the end of 1976 could be regarded as a first step towards its realization. By means of this model which was generally planned by Dornier and which is open to visit, provides solutions for many problems. It is yet too early for a final evaluation of the entire system but approaches have been made to the Federal Ministry of Research and Technology for a research project and thus to a good starting point for realization.     

Sediment transport analysis as a component of coastal management— a UK example

Detrimental effects of engineering works on the coast and a wish to conserve parts of the coastline have increased realization among coastal managers of the need to examine shoreline problems and proposals for protection in a wider spatial context than the site itself and over a longer time scale than the past few years. This paper outlines the approach taken in one region of the United Kingdom, the central south coast of England, to provide that wider perspective. Authorities responsible for coastal protection and sea defenses formed a coastal group, which, among other activities, commissioned research aimed at providing a greater understanding on which to base shoreline management decisions. A major project undertaken was a sediment transport study in which all existing information relating to coastal sediment processes in the region was collated and analyzed. All inputs, flows, and outputs of sediment were documented. Links between processes were examined for each part of the region. Finally, nine littoral cells of sediment circulation were identified and were suggested as forming a framework for shoreline management. The methods of compilation and analysis are outlined here and are exemplified for one area in the region. The approach is recommended as a cost-effective basis for strategic management of the coast in developed regions.     

Some problems in planning the office economy in a third world city: the example of Tunis

While the office economy has been studied extensively in the advanced industrial nation, it has been overlooked in the context of the developing country. Based on a case-study of Tunis it is shown how the growth of office activities in the central area has exacerbated the planning problems of the city's core. Planning policies designed to control the rate of office growth in the central area and encourage its suburban decentralization have been introduced. However, achievements to date on either of these two aims have been limited, reflecting political, administrative and fiscal problems which limit the effectiveness of planning in the city as a whole.     

Detrital transport of metals by glaciers, an example from the Pinchi Mine, central British Columbia

 Abundant cinnabar (HgS) mineralization is associated with the Pinchi Fault in central British Columbia. Two formerly producing mercury mines have been developed on this fault: Pinchi and Bralorne Takla. The mercury content of till (a sediment type directly deposited by glaciers) in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock and the direction of ice flow. Cinnabar-bearing bedrock was eroded by glaciers, transported in the direction of ice flow, and deposited "down-ice" from its source. An example of such a dispersal train is documented for the Pinchi Mine area where mercury ore was transported over a distance of 12 km, as measured in the clay-sized fraction (< 0.002 mm) of till, and could have been transported over 24 km according to heavy mineral concentrates (specific gravity >3.3) of this same sediment. Antimony, chromium, and nickel dispersal trains were also detected in the region. These data indicate that natural glacial processes can result in the "mobilization" of metals in the surficial environment, a factor which has to be considered at mine sites in glaciated terrain, where mine reclamation and remediation measures are now required. Received: 31 October 1996 · Accepted: 27 May 1997     

声波透射法在检测大直径灌注基桩的分辨率及应注意的几个问题

讨论了声波透射法检测大直径灌注基桩的分辨率问题。并以工程实例，说明声波透射法在检测大直径灌注基桩工作过程中应注意的问题，以避免给检测工作带来不必要的损失，防止对检测大直径灌注基桩质量的错判和误判。     

Flow and transport model of a polder area in the Belgian coastal plain: example of data integration

Tracer data can serve to derive parameters related to groundwater systems or can be used in the calibration of transport and flow models. Temperature, ³H/³He (age dating) and hydrochemical data, together with head measurements, borehole logs and an aquifer test, were used to obtain insight into the flow and transport of a Quaternary aquifer system located in the Belgian polder area. Flow and transport model code SEAWAT acted as the integration medium for the different data. Each type of data has its own interpretation technique and adds components to the model. Additionally, different types of data aid in verification of the results. For instance, fluxes from temperature logs (used with the SEAWAT model), and water quality and age dating all provide information on flow to and velocities in the vicinity of drainage ditches. Different data also provide information on different scales. Temperature logs and aquifer tests act on a small scale, groundwater age is influenced by larger-scale flow, and water quality is determined by the general flow of the area. Integration of different kinds of geological, hydrological, geophysical and geochemical data is shown to be an important way forward in the efforts to model real-world cases.     

大变形黏土防渗层中的污染物迁移和转化规律研究

国内湖泊疏浚污染底泥堆场一般以较厚的黏土层作为主要防渗层,由于在上覆底泥作用下黏土层会发生较大的固结变形,因此,在研究黏土防渗层中的污染物运移和转化规律时,应该考虑土体变形的影响。基于Gibson一维大变形固结理论和饱和多孔介质中的污染物对流扩散方程,建立了二者耦合的可变形多孔介质中污染物的运移和转化模型,其中首次考虑了土体自重和生物降解作用的影响。利用所建立模型的数值解,研究了在可变形黏土防渗层中的污染物运移和转化规律,同时分析了模型中不同项和主要参数的作用和影响。研究结果表明,土体大变形对黏土防渗层中污染物的运移有着较复杂的影响,一方面土体变形会加速污染物的运移;另一方面土体固结带来的渗透性减小会增加污染物的穿透时间,二者的不同作用取决于众多的影响因素,如土层厚度和吸附作用等。研究结果对于评估天然黏土防渗层对污染物的阻隔作用有重要的指导意义。     

The impact of shipping on the invasion of alien plants to Norway

Important agencies responsible for the invasion of alien plants to Norway by means of shipping were ballast thrown ashore from sailing ships and contaminants in imported grain. Most ballast-plants were casuals, which disappeared when the ballast traffic ceased at the time of World War I. Changes in the origin of imported grain are reflected in the grain mill flora.     

The sedimentary coastal basin of Togo: example of a multilayered aquifer still influenced by a palaeo-seawater intrusion

In Togo, the hydrogeology of the sedimentary coastal aquifers along the Gulf of Guinea has been studied for the last three decades to define the recharge processes and the origin and evolution of the salinity. Isotope hydrology and fluid geochemistry suggest that the current recharge of all aquifers, both confined and unconfined, occurs through the crystalline basement and the Plio-Quaternary deposits. Two main groundwater mineralization processes are observed: the first one, in recharge areas, is due to farming, village and city life and concerns unconfined aquifers (crystalline basement, Continental Terminal and Quaternary sediments); the second one is a mixing process between recent freshwater and fossil saline water still present in the deep confined aquifers inland, several kilometers away from the coast. Brackish water was trapped in low-permeability lenses of confined aquifers (Eo-Palaeocene and Maastrichtian) during the Quaternary, in periods of low recharge, notably during the last glacial maximum (LGM), and has not yet been flushed out. Hydrodynamic simulations indicate that, at that time, the aquifers experienced a maximum seawater intrusion as far as 20–22 km inland, depending on the palaeo-recharge value at the outcrops.     

Impacts of a large Sahelian city on groundwater hydrodynamics and quality: example of Niamey (Niger)

The management of groundwater resources is very important in the semiarid Sahel region, which is experiencing rapid urban development. Impacts of urbanization on groundwater resources were investigated in the unconfined aquifer of the Continental Terminal beneath the city of Niamey, Niger, using water level and chemical data. Hydrodynamic and chemical changes are best described by a combination of factors including the historical development of the city, current land use, water-table depth and topography. Seasonal groundwater recharge occurs with high spatial variability, as indicated by water-level monitoring in all wells, but there was no interannual trend over the 5-year study period. Groundwater salinity shows high spatial variability and a minor rising trend. The highest salinity is in the old city centre, with Na–NO₃ dominant, and it increases seasonally with recharge. Salinity is much lower and more variable in the suburbs (Ca–HCO₃, Ca–NO₃, and Na–NO₃ dominant). Nitrate is the main ionic contaminant and is seasonally or permanently above the international guidelines for drinking water quality in 36 % of sampled wells, with a peak value of 112 mg L^?1 NO₃–N (8 meq L^?1). Comparison of urban and rural sites indicates a long-term increase in groundwater recharge and nitrate enrichment in the urban area with serious implications for groundwater management in the region.     

关于峨眉山大火成岩省一些重要问题的讨论

峨眉山大火成岩省(ELIP)近几年来取得了许多新的进展,但在一些重要的问题上仍存在着争论,笔者列举了ELIP火山喷发的时间、分布范围、高钛和低钛玄武岩、层状岩体与玄武岩以及成矿作用的关系、大火成岩省与生物绝灭的关系以及与地幔柱的关系等方面存在的问题,以及由此引发的相关争论.这些问题的解决对于大火成岩省研究的深入将会起到重要作用.     

Kinematics of large syn-orogenic intrusions: example of the Lower Proterozoic Saraya batholith (Eastern Senegal)

The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major crustal fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body. This model could be extended to the other large Birimian batholiths of the Lower Proterozoic in Eastern Senegal.