A Study of High-Temperature and High-Pressure Experiment of Correlativity between Deformational System of Au-Bearing Rocks and Element Adjustment

Modelling of migration and accumulation of elements Au and Ag in rocks under temperatures of350-450℃ and a confining pressure of 300 MPa and axial pressure of 100-150 MPa is conducted. It is found thatthe contents of gold and silver get higher in metallic sulphides such as pyrite, chalcopyrite and sphalerite as well asin quartz and muscovite, and get lower in chlorite, biotite, sericite, albite and calcite, showing that tectono-dynamicsis one of the important factors for petrogenesis and metallogenesis.     

Geomorphic response of the Jingjiang Reach to the Three Gorges Project operation

Upstream damming often causes significant downstream geomorphic adjustments. Remarkable channel changes have occurred in the Jingjiang Reach of the Middle Yangtze River, since the onset of the Three Gorges Project (TGP). Therefore, it is important to investigate the variations in different fluvial variables, for better understanding of the channel evolution characteristics as an example of the Jingjiang Reach. Recent geomorphic adjustments in the study reach have been investigated quantitatively, including variations in sediment rating curve, fluvial erosion intensity, channel deformation volume and bankfull channel geometry. These fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the TGP operation. A focus of this study has been especially on variation in the bankfull channel geometry. Calculated bankfull dimensions at section‐ and reach‐scale indicate that: (i) there were significant bank‐erosion processes in local regions without bank‐protection engineering, with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections; (ii) the variation in the reach‐scale channel geometry occurred mainly in the component of bankfull depth, owing to the construction of large‐scale bank‐revetment works, with the depth increasing from 13.7 m in 2002 to 15.0 m in 2014, and with an increase in the corresponding bankfull area of about 11%; and (iii) the reach‐scale bankfull channel dimensions responded to the previous 5‐year average fluvial erosion intensity during flood seasons at Zhicheng, with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002–2012. Furthermore, these relations developed for the section‐ and reach‐scale bankfull channel geometry were also verified by the observed data in 2013–2014, with encouraging results being obtained. Copyright © 2016 John Wiley & Sons, Ltd.     

CHANNEL ADJUSTMENT OF AN UNSTABLE COARSE-GRAINED STREAM: OPPOSING TRENDS OF BOUNDARY AND CRITICAL SHEAR STRESS,AND THE APPLICABILITY OF EXTREMAL HYPOTHESES

Channel adjustments in the North Fork Toutle River and the Toutle River main stem were initiated by deposition of a 2.5 km³ debris avalanche and associated lahars that accompanied the catastrophic eruption of Mount St. Helens, Washington on 18 May 1980. Channel widening was the dominant process. In combination, adjustments caused average boundary shear stress to decrease non-linearly with time and critical shear stress to increase non-linearly with time. At the discharge that is equalled or exceeded 1 per cent of the time, these trends converged by 1991–1992 so that excess shear stress approached minimum values. Extremal hypotheses, such as minimization of unit stream power and minimization of the rate of energy dissipation (minimum stream power), are shown to be applicable to dynamic adjustments of the Toutle River system. Maximization of the Darcy–Weisbach friction factor did not occur, but increases in relative bed roughness, caused by the concomitant reduction in hydraulic depths and bed-material coarsening, were documented. Predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991–1992 geometries and bed-material characteristics measured in the field. It is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision, retreat of stream-side hummocks, and establishment of riparian vegetation to limit the destabilizing effects of large floods. Further, prediction of energy slope (and consequently stream power) by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained (sand and gravel) bank materials (relative to the coarsened channel bed) from bank retreat and from upstream terrace erosion.     

坐标系转换中全国高精度高分辨率格网改正量的确定

确定全国1980西安坐标系向2000国家大地坐标系转换改正量是实现1980西安坐标系测绘成果向2000国家大地坐标系转换的一项重要的基础性工作。本文在对全国已有大地控制点资料进行整理、分析的基础上,通过大量试算与研究,在国内首次提出了利用全国高精度高分辨率格网改正量实现1980西安坐标系测绘成果向2000国家大地坐标系转换的理念与改正量计算方法 -移动转换法,同时利用全国127 210个高精度的控制点成果,在椭球面上建立了控制点上误差很小、能满足大比例尺地形图转换精度要求的全国高精度高分辨率格网1980西安坐标系测绘成果向2000国家大地坐标系转换改正量模型,该模型现已应用于全国多个省、市不同比例尺基础地理信息数据转换实际生产中。     

MITIGATION OF SEDIMENTATION HAZARDS DOWNSTREAM FROM RESERVOIRS

1 INTRODUCTION Increasing attention is being given to sedimentation hazards downstream from reservoirs as dams built during the past century accumulate progressively greater volumes of sediment. The sediment storage both decreases reservoir capacity and operating efficiency of the dam, and creates a 搒ediment-shadow?downstream where sediment-starved flows commonly erode channel boundaries and create long-term channel instabilities. Numerous studies have documented downstream channel change…     

Recent channel adjustments in alluvial rivers of Tuscany,central Italy

Drastic channel adjustments have affected the main alluvial rivers of Tuscany (central Italy) during the 20th century. Bed‐level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations. Changes in channel width were investigated by comparing available aerial photographs (1954 and 1993–98). Bed incision represents the dominant type of vertical adjustment, and is generalized along all the fluvial systems investigated. The Arno River system is the most affected by bed‐level lowering (up to 9 m), whereas lower incision (generally less than 2 m) is observed along the rivers of the southern part of the region. Human disturbances appear to be the dominant factors of adjustments: the main phase of vertical change occurred during the period 1945–80, in concomitance with the phase of maximum sediment mining activity at the regional scale. The second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel. Based on measurements of channel width conducted on aerial photographs, 38% of the reaches analysed experienced a narrowing greater than 50% of the initial channel width. The largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region. A regional scheme of channel adjustments is derived, based on initial channel morphology and on the amounts of incision and narrowing. Different styles of channel adjustments are described. Rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing; in contrast, sinuous‐meandering channels mainly adjusted vertically, with a minor amount of narrowing. Copyright © 2003 John Wiley & Sons, Ltd.     

Modelling the effect of form and profile adjustments on channel equilibrium timescales

A model for describing river channel pro?le adjustments through time is developed and applied to a river responding to base‐level lowering in order to examine the effect of channel widening and downstream aggradation on equilibrium timescales. Across a range of boundary conditions, downstream aggradation controlled how quickly a channel reached equilibrium. Channel widening either increased or decreased the equilibrium timescale, depending on whether or not sediment derived from widening was deposited downstream. Results suggest that pro?le adjustments are more important than channel width adjustments in controlling equilibrium timescales for a channel responding to base‐level lowering. Copyright © 2003 John Wiley & Sons, Ltd.     

The Changing Geography of Export Trade in Ghana under Structural Adjustment Programs: Some Socioeconomic and Spatial Implications

Like many other countries in Africa, Ghana has traditionally depended on a few export products—namely, cocoa, timber, and mineral resources—as the mainstays of its economy. The often‐volatile nature of the world market price of these products made the economy very vulnerable to fluctuations in the prices of export commodities. Moreover, the geographical distribution of these resources meant that only a few regions could participate in their production and export. This resulted in wide spatial and socioeconomic disparities between the producing and nonproducing regions. Within the past eighteen years, however, a shift seems to have taken place. Under the auspices of the ongoing structural adjustment programs, emphasis is being placed on nontraditional export goods. This is not only helping to reduce the vulnerability of the economy by diversifying the sources of export earnings, but also engendering participation in the export trade by regions that have been traditionally left behind. This study analyses the changing geography of the export trade of Ghana using data from the International Monetary Fund/World Bank, the Ghanaian government, the World Trade Organization, and field observation. The study argues that while these new trends and efforts are laudable, they cannot bridge the gap between the export producing and nonproducing areas and cushion the economy against the vagaries of the export market unless deliberate attempts are made to improve transportation and other basic infrastructure in the less‐endowed areas.     

城市河流形态及稳定性演变研究进展

人为干扰导致的城市河流退化在地理科学和水文学领域引发了广泛关注, 针对城市河流形态及演变过程的研究成为退化河流生态修复的一项重要内容, 然而, 目前国内相关基础理论的系统梳理相对缺乏。本文回顾了半个多世纪以来城市河流形态及稳定性演变的研究成果, 从研究内容和方法两方面对不同城市化阶段河流形态及稳定性变化的特征和原因进行总结, 同时评述了不同研究方法的特点与局限。本文认为, 城市化进程改变了河流自然演化过程, 破坏了河流原有形态及稳定性, 其中, 沉积和径流体系变化是其根本原因。为了更好地运用河流演变机理进行河流修复, 学者们发展了河流分类体系, 主要包括形态导向法、过程导向法和综合分类法, 重点从河流退化的地貌形态、沉积和径流变化过程、河流演变的时间周期等方面概述各分类体系的优缺点, 阐述具有预测功能的河流分类体系不断完善的过程。本文通过梳理城市河流演变的研究成果, 以期为中国城市河流修复与管理提供科学依据和现实借鉴。     

Processing of strong-motion accelerograms: needs, options and consequences

Recordings from strong-motion accelerographs are of fundamental importance in earthquake engineering, forming the basis for all characterizations of ground shaking employed for seismic design. The recordings, particularly those from analog instruments, invariably contain noise that can mask and distort the ground-motion signal at both high and low frequencies. For any application of recorded accelerograms in engineering seismology or earthquake engineering, it is important to identify the presence of this noise in the digitized time-history and its influence on the parameters that are to be derived from the records. If the parameters of interest are affected by noise then appropriate processing needs to be applied to the records, although it must be accepted from the outset that it is generally not possible to recover the actual ground motion over a wide range of frequencies. There are many schemes available for processing strong-motion data and it is important to be aware of the merits and pitfalls associated with each option. Equally important is to appreciate the effects of the procedures on the records in order to avoid errors in the interpretation and use of the results. Options for processing strong-motion accelerograms are presented, discussed and evaluated from the perspective of engineering application.