Groundwater flow through Pleistocene glacial deposits in the rapidly urbanizing Rouge River–Highland Creek watershed,City of Scarborough,southern Ontario,Canada

The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern coastline of Lake Ontario. The City has a population of 500,000 and is presently one of the fastest growing communities in Canada. The City is expanding northwards onto rural land on the south slope of the large Pleistocene glacial Oak Ridges Moraine system. The moraine system is underlain by a thick (150 m) succession of tills, sands and gravels and is a regionally-significant recharge area for three principle aquifer systems that discharge to numerous watercourses that flow to Lake Ontario. Protection of deeper aquifers from surface-generated urban contaminants is a particular concern. A groundwater flow model using Visual MODFLOW was developed for the 350-km² Rouge River–Highland Creek (RRHC) drainage basin using an extensive GIS-based collection of subsurface geological, geophysical and hydrogeological data, maps of land use and surficial geology. The RRHC model was calibrated against point water level data, known potentiometric surfaces of the principal aquifers and baseflow measurements from streamflow gauging stations and determined to be within acceptable limits. Water balance calculations indicate that 70% of the basin recharge (106,000 m³/day) enters the Upper Aquifer along the crest and immediate flanks of the Oak Ridges Moraine. To the south, Upper Aquifer water moving through fractured till aquitards accounts for more than 75% of recharge to deeper aquifers. Water quality data confirm previous observations that urban- and rural-sourced contaminants (chlorides and nitrates) present in Upper Aquifer waters are moving rapidly into deeper aquifers. Some 83% of total RRHC recharge water is ultimately discharged as baseflow to creeks draining to Lake Ontario; the remainder discharges to springs and along eroding lakeshore bluffs. Model results demonstrate that deeper aquifers are poorly protected from urban contaminants and that long-term protection of ground and surface water quality has to be a priority of municipal planners if the resource is not to be severely degraded. Electronic Publication     

天文科技论文计量单位存在的一些问题

叙述了我国天文科技期刊论文中计量单位存在的问题 ,提出了正确使用计量单位的看法     

东海及邻近地区岩石圈三维结构研究

文中首先对两条剖面的岩石圈结构进行了论述。以两条剖面的岩石圈结构作为约束,采用小波分解、全磁纬变倾角化极和地热场反演岩石圈底界等项技术,获取了研究区沉积基底面、莫霍面和岩石圈底界面在三维空间的展布以及岩浆岩的分布。在此基础上论述了岩石圈各层的展布及岩石圈三维结构单元的划分,认为东海陆架盆地的东部凹陷带为寻找油气最有利的地区,冲绳海槽为弧后盆地,钓鱼岛岩浆岩带为中酸性岩浆岩带,吐嘎喇火山带为当今火山弧,琉球岛弧为欧亚板块裂离部分,琉球岛弧东部斜坡为古东海大陆架的陆坡,位于此陆坡上的凹陷为弧前盆地。     

Evaluation of heterogeneity and field-scale groundwater flow regime in a leaky till aquitard

Recent work in southern Ontario, Canada, demonstrates anomalously high vertical groundwater flow velocities (>1 m/year) through a thick (as much as 60 m), sandy silt till aquitard (Northern till), previously assumed to be of very low permeability (hydraulic conductivity <10^–10 m/s). Rapid recharge is attributed to the presence of fractures and sedimentary heterogeneities within the till, but the field-scale flow regime is poorly understood. This study identifies the nature of physical groundwater pathways through the till and provides estimates of the associated groundwater fluxes. The aquitard groundwater flow system is characterized by integrating details of the outcrop and subsurface sedimentary characteristics of the till with field-based hydrogeologic investigation and numerical modeling. Outcrop and subsurface data identify a composite internal aquitard stratigraphy consisting of tabular till beds (till elements) separated by laterally continuous sheet-like sands and gravels (interbeds) and boulder pavements. Individual till elements contain sedimentary heterogeneities, including discontinuous sand and gravel lenses, vertical sand dikes, and zones of horizontal and vertical fractures. Hydrogeologic field investigations indicate a three-layer aquitard flow system, consisting of upper and lower zones of more hydraulically active and heterogeneous till separated by a middle unit of relatively lower hydraulic conductivity. Groundwater pathways and fluxes in the till were evaluated using a two-dimensional aquitard/aquifer flow model which indicates a step-wise flow mechanism whereby groundwater moves alternately downward along vertical pathways (fractures, sedimentary dikes) and laterally along horizontal sand interbeds within the till. This model is consistent with observed hydraulic-head and isotope profiles, and the presence of tritiated pore waters at various depths throughout the till. Simulations suggest that a bulk aquitard vertical hydraulic conductivity on the order of 1×10^–9 m/s is required to reproduce observed hydraulic-head and tritium profiles. Electronic Publication     

Evolution of an incised valley system in the southern Adriatic Sea (Apulian margin): an onshore–offshore correlation

Seismic surveys with sub‐bottom profiler were carried out in the Manfredonia Gulf in the southern Adriatic Sea. Here, a buried surface was recognized on which three valleys, located about 80 km from the shelf edge, were deeply incised. Beneath this surface, a pre‐upper Würm seismic unit (PW) was identified. Above, two seismic units were recognized: the transgressive system tract (TST) and highstand system tract (g₂)_. On the basis of regional correlation with onshore and offshore data, these units and their boundaries were dated and correlated with phases of the last glacial–interglacial cycle. The incised valley system was attributed to the Marine Isotopic Stage (MIS) 2. The TST and g₂ units fill the valleys and were attributed to the post‐glacial sea‐level rise and highstand. The incised valleys are anomalous with respect to published models; despite having many characteristics that would have limited the fluvial incision (the lowstand shoreline that remained on the shelf, the low gradient of the shelf, the subsidence that affected the study area since MIS 5), the valleys appear to be deeply incised on the shelf, with valley flanks that can exceed 40 m in height. The model to explain the formation of the valleys comprises enhanced river discharge as the key factor in increasing river energy and promoting erosion across the low gradient shelf. Copyright © 2014 John Wiley & Sons, Ltd.     

国外深地震反射研究之现状

本文概括地总结和回顾了深地震反射研究成果,并针对存在的一系列问题进行了讨论。许多国家利用深地震反射法来研究大陆地壳和上地幔的内部结构。研究成果表明,大陆地壳和上地幔的反射特征具有显著的差异,这些差异反映了不同的构造单元和状态。     

Ex ante evaluation of the costs and benefits of individual transferable quotas: A case-study of seven Australian commonwealth fisheries

Individual transferable quotas (ITQs) have been introduced in a number of different countries, including Australia. Using seven Australian commonwealth fisheries the paper undertakes an ex ante cost–benefit analysis whether to introduce ITQs into these fisheries. The analysis uses five cost–benefit criteria, and in particular the gross value of production (GVP), to evaluate whether ITQs should be introduced or not. For fisheries where the net benefits do not currently justify ITQs, a pathway is provided to improve management outcomes with the use of individual transferable efforts units (ITEs).     

Delineating floodplain and upland areas for hydrologic models: a comparison of methods

A spatially distributed representation of basin hydrology and transport processes in hydrologic models facilitates the identification of critical source areas and the placement of management and conservation measures. Floodplains are critical landscape features that differ from neighbouring uplands in terms of their hydrological processes and functions. Accordingly, an important step in watershed modelling is the representation of floodplain and upland areas within a watershed. The aim of this study is (1) to evaluate four floodplain–upland delineation methods that use readily available topographic data (topographic wetness index, slope position, uniform flood stage, and variable flood stage) with regard to their suitability for hydrological models and (2) to introduce an evaluation scheme for the delineated landscape units. The methods are tested in three U.S. watersheds ranging in size from 334 to 629 km² with different climatic, hydrological, and geomorphological characteristics. Evaluation of the landscape delineation methods includes visual comparisons, error matrices (i.e. cross‐tabulations of delineated vs reference data), and geometric accuracy metrics. Reference data were obtained from the Soil Survey Geographic (SSURGO) database and Federal Emergency Management Agency (FEMA) flood maps. Results suggest that the slope position and the variable flood stage method work very well in all three watersheds. Overall percentages of floodplain and upland areas allocated correctly were obtained by comparing delineated and reference data. Values range from 83 to 93% for the slope position and from 80 to 95% for the variable flood stage method. Future studies will incorporate these two floodplain–upland delineation methods into the subwatershed‐based hydrologic model Soil and Water Assessment Tool (SWAT) to improve the representation of hydrological processes within floodplain and upland areas. Copyright © 2016 John Wiley & Sons, Ltd.     

湖南省地形地貌与地质灾害分布关系分析

湖南是我国地质灾害比较严重的省份之一,属地质灾害高易发区,地质灾害分布和发育程度具有一定的地域性,地形地貌对地质灾害的发生起着主控作用。本文根据湖南省地形地貌特点,结合全省1∶10万县市地质灾害调查数据,从区域上研究了不同地貌特征对不同地质灾害的影响,并选取了典型地形地貌进行分析。