矿产资源运输通道概述

全球矿产资源垄断格局使得中国很多重要进口矿产资源来源较为集中,而中国对进口资源的运输通道控制力较弱,影响矿产资源供应安全。本文对中国矿产资源管道运输、海运及陆运进行了概述,分析目前存在的问题,并提出建议：开辟多元进口油气运输通道,加强科技创新,降低远距离运输安全风险;北极航线的开辟将使世界矿产资源贸易和战略格局产生重大调整;加快推进＂丝绸之路经济带＂和＂海上丝绸之路＂等。     

Architecture,formation and implication of active structure-controlled intraslope channel system southeast offshore Sendai,Tohoku, Japan

Located off the Pacific coast of central Tohoku (NE Japan), the Ishinomaki slope channel (ISC) provides an excellent opportunity to study a structure-controlled intraslope channel and downslope sedimentation along the active margin. The seismic reflection data across ISC show an extensive basal surface and overlying channel complexes between the basement structures of the Abukuma ridge to the south and Kitakami massif to the north, indicating that the formation of the intraslope basin, channelization of ISC and sedimentation of the downstream channel-lobe transition zone (CLTZ) are very likely to be structure-controlled. The oblique channel stacking pattern, faulting of the seafloor and subsurface Abukuma ridge in the upper and lower domains of ISC, collectively suggest that ISC has migrated northward and is currently under the influence of active compression. Differences in styles of accommodation space between the upper and lower domains of ISC suggest that differential subsidence occurred along the strike-slip tectonic line. Based on the regional strike-slip tectonic line, we propose that a Kitakami-Abukuma ridge existed before the formation of ISC. The strike-slip faulting divided the Kitakami-Abukuma ridge into the Kitakami massif to the north and the Abukuma ridge to the south, and an intervening fault trough as the precursor of the intraslope basin and ISC. As the subduction of the Pacific Plate and associated compressional events continued, the Abukuma ridge was reactivated to narrow the intraslope basin into a confined channel. Located near the epicentre of the devastating 2011 Tohoku earthquake event, the ISC, downstream CLTZ and underlying intraslope basin provide information on active basement structure and the evolving sediment routing system on the tectonically active margin.     

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Edelvang, Karen; Larsen, Michael; Pejrup, Morten: Tidal Variation in Field Settling Velocities of Suspended Sediment in a Tidal Channel. Geografisk Tidsskrift 92:116–121. Copenhagen 1992.

Particles of silt and clay may form large, low density floes when suspended in salt water. The sediment floes have settling velocities much higher than the single small particles constituting them and therefore, the flocculation process may strongly influence the transport of cohesive sediment in estuarine environments. will be described in this paper, the field settling velocities of suspended sediment were investigated in a large tidal channel with tidal current velocities up to 1.3 m/s and depths of about 10 m. The analyses of suspended sediment were made on both bottom and surface samples. For the bottom samples, equivalent median fall diameters in the range 26–98 μm were measured. For surface samples, the range was 15–40 μm. During most of the tidal period, the occurrence of much larger settling diameters near the bottom was due to the suspension of individual sand and silt particles. For the investigated periods, high-tide was the only possible time to observe flocculation influencing the vertical distribution of finegrained sediment in the water column.     

Hydrologic and geomorphic flow thresholds in the Lower Brazos River,Texas, USA

Abstract

River science and management often require a design or reference discharge. The common (and sometimes unavoidable) use of such discharges may, however, obscure the fact that the magnitude and frequency of critical flows can differ due to various hydrological, geomorphological, and ecological criteria. Threshold stages and discharges were identified for six lower Brazos River, Texas gaging stations corresponding to thalweg connectivity, bed inundation, high sub-banktop flows, channel–floodplain connectivity (CFC), and overbank flooding. Critical flows were also identified for estimated thresholds for sandy bedform and medium gravel mobility, critical specific stream power for potential channel modifications, and cohesive-bank channel erosion. These thresholds have variable relationships to mean, median, and maximum flows. For four of the six stations, daily recurrence probabilities for all but flood flows are at least 1%, and as high as 11%. All stations achieve channel–floodplain connectivity at stages less than banktop. Estimated threshold flows for sediment mobility and channel erosion occur relatively frequently, with daily probabilities of 2–77%. Critical flows for bank erosion occur least often, and for sandy bedform and gravel mobility most often. Thalweg connectivity is always maintained at all sites, while bed inundation flows have a daily probability of about 80% or more. Overall, results suggest that no single flow level is dominant in hydrological or geomorphic dynamics, and that the frequency of a given threshold varies considerably even along a single river. The results support the idea that multiple flow levels and ranges are necessary to create and maintain the hydrological, geomorphological, and ecological characteristics of rivers, and that no single flow level is a reliable determinant of fluvial state.

Editor Z.W. Kundzewicz; Associate editor Q. Zhang     

Geomorphic coupling between hillslopes and channels in the Swiss Alps

The coupling relationships between hillslope and channel network are fundamental for the understanding of mountainous landscapes' evolution. Here, we applied dendrogeomorphic methods to identify the hillslope–channel relationship and the sediment transfer dynamics within an alpine catchment, at the highest possible resolution. The Schimbrig catchment is located in the central Swiss Alps and can be divided into two distinct geomorphic sectors. To the east, the Schimbrig earth flow is the largest sediment source of the basin, while to the west, the Rossloch channel network is affected by numerous shallow landslides responsible for the supply of sediment from hillslopes to channels. To understand the connectivity between hillslopes and channels and between sources and sink, trees were sampled along the main Rossloch stream, on the Schimbrig earth flow and on the Rossloch depositional area. Geomorphic observations and dendrogeomophic results indicate different mechanisms of sediment production, transfer and deposition between upper and lower segments of the channel network. In the source areas (upper part of the Rossloch channel system), sediment is delivered to the channel network through slow movements of the ground, typical of earth flow, shallow landslides and soil creep. Contrariwise, in the depositional area (lower part of the channel network), the mechanisms of sediment transfer are mainly due to torrential activity, floods and debris flows. Tree analysis allowed the reconstruction of periods of high activity during the last century for the entire catchment. The collected dataset presents a very high temporal resolution but we encountered some limitations in establishing the source‐to‐sink connectivity at the catchment‐wide scale. Despite these uncertainties, for decennial timescales the results suggest a direct coupling between hillslopes and neighbouring channels in the Rossloch channel network, and a de‐coupling between sediment sources and sink farther downstream, with connections possible only during extraordinary events. Copyright © 2012 John Wiley & Sons, Ltd.     

Wood dynamics in upland streams under different disturbance regimes

This paper presents reach scale large wood (LW) budgets of 12 upland streams in the Okanagan Basin of British Columbia. The study included 100 m long reaches at three wildfire sites and three undisturbed sites in the Interior Douglas‐fir (IDF) biogeoclimatic zone, and three recent Mountain Pine Beetle (MPB) infestation sites and three undisturbed sites in the Montane Spruce (MS) zone. Detailed information on wood recruitment, output and storage were obtained from repeated annual surveys. Recruitment from the riparian zone was found to dominate wood inputs, with fluvial import of secondary importance. In undisturbed streams, wood exhumation was found to be of tertiary importance, but was not observed in disturbed streams. Relative wood length was found to be a strong predictor of wood stability, with wood length to channel width and wood diameter to channel depth ratios of 1:1 forming an approximate maximum threshold of wood mobility. Volumetric decomposition was, on average, a third of the value of fluvial export, and the average residence time of wood in the channels was 20 years. In undisturbed reaches, wood storage indicated a slow depletion of wood from the channels. In the disturbed reaches, wildfire was found to significantly increase annual wood recruitment by more than an order of magnitude over undisturbed or control streams. MPB had not significantly increased LW recruitment, but is expected to increase over the coming decades. Storage rates at the disturbed streams indicated a net accumulation of wood over the study period. Copyright © 2012 John Wiley & Sons, Ltd.     

CHANGES IN THE FOREST-ALPINE TUNDRA ECOTONE: COLORADO FRONT RANGE

On Niwot Ridge, alpine climatic factors dominate today within the upper part of the forest-alpine tundra ecotone on the east slope of the Colorado Front Range. This study provides evidence that the climatic conditions controlling the distribution of the upper limit of tree species and growth forms within the ecotone have changed through time. It appears that much of the present forest-alpine tundra ecotone is a relict of past warm climate episodes. There is much evidence that, in the past, tree forms were more symmetrical and less deformed, tree trunks with larger diameters existed, and the trees were more extensive in areal coverage. However, no evidence exists to show that the upper limit of tree species growth was more than marginally higher in the past than today. The treeline appears to be stable to historical and Holocene climatic fluctuations, but the altitudinal limits of seedling establishment and survival are not stable. The liming of climatic changes in the Front Range and their possible influence on the distribution of the trees within the ecotone are reviewed. Because of its extreme easterly location, slight but significant climatic variations may be observed within the forest-alpine tundra ecotone of Niwot Ridge, but are not observed elsewhere.     

WEATHERING PIT CHARACTERISTICS AND TOPOGRAPHY ON STONE MOUNTAIN,GEORGIA

A detailed analysis of weathering-pit distribution on Georgia's Stone Mountain granite dome reveals a complex relationship between pit size and density, compared with slope aspect and angle. The uniform nature of the lithology provides an ideal natural laboratory for the analysis of weathering pits. Through the random establishment of 32 dome-encircling, ten-by-ten meter study plots within an elevational range from 610 to 650 meters, the distribution, size, aspect, slope and lithology of pit features were mapped, measured, and analyzed. Thematic maps were used in the visual representation of pit distribution and dimension data. Correlation coefficients, ANOVA, and multiple regression analyses were utilized to determine the relationships of these variables. Pits showed a dimensional and density increase toward a southwestern aspect as well as a dimensional and density increase with decreasing slope angle. Greatest pit dimensions were found at approximately the 200° N azimuth. These findings lead the authors to conclude that insolation weathering may be a more important process in granite pit formation on Stone Mountain than commonly believed because afternoon temperature maxima accelerate weathering through increased chemical constituent dissolution and/or crystal constituent disintegration. [Key words: weathering pits, gnammas, granite weathering, Stone Mountain.]     

Migration of channel heads following wildfire in the Colorado Front Range,USA

The High Park Fire burned ~35 300 ha of the Colorado Front Range during June and July 2012. In the areas of most severe burn, all trees were killed and the litter and duff layers of soil were completely removed. Post‐fire erosion caused channel heads to develop well upslope from pre‐fire locations. The locations of 50 channel heads in two burned catchments were documented and the range of drainage areas contributing to these channel heads to drainage areas of unburned channel heads in the region measured previously were compared. Mean drainage area above channel heads in the burned zone decreased by more than two‐orders of magnitude relative to unburned sites. Drainage area above channel heads between the two burned catchments does not differ significantly with respect to slope, likely as a result of differences in surface roughness between the two sites following the fire. Copyright © 2013 John Wiley & Sons, Ltd.     

Discrimination of alluvial and mixed bedrock–alluvial multichannel river networks

This paper explores the use of planview morphological metrics to quantitatively describe and distinguish mixed bedrock–alluvial multichannel networks from alluvial multichannel networks. The geometries of the channel planforms of two bedrock‐constrained networks (Mekong and Orange rivers) are compared with the classic alluvial anastomosed Upper Columbia River and the wandering Ganga River. Widely recognized indices utilized include: channel link count and channel sinuosity, with additional emphasis being given to the less common metrics: network bifurcation angles and island shape characteristics (i.e. aspect ratio, compactness, roundness and convexity). Link count data, with one notable exception, conform to theoretical expectations. Bifurcation angles for all four multichannel rivers are significantly greater than angles reported for braiding rivers. Island convexity clearly discriminates the two alluvial rivers from the two bedrock‐influenced rivers. The width of the macrochannel, in which each network develops, has a positive influence on the number of channel links and is further related to channel slope variations which, in turn, are influenced by terrain structure revealed using trend‐surface analysis. The geometry of multichannel networks are often laterally constrained such that the values of channel bifurcation angles and link sinuosity values reduce as the network intensifies and channel links are shortened. These latter observations go some way to explain the oft‐noted relatively ‘straight’ links seen within multichannel networks which are a necessary adjustment to space‐filling constraints placed on a network. Copyright © 2013 John Wiley & Sons, Ltd.