均质土岸坡崩塌与河床冲淤交互过程试验

在弯道水槽中展开系列试验,研究水力冲刷过程中均质土岸坡冲刷崩塌输移与河床冲淤过程及其影响因素。该过程及变化特征可描述为:水下坡面侵蚀及坡脚淘刷导致岸坡失稳崩塌;暂时堆积在凹岸坡脚处的崩塌体加剧附近水流紊动程度利于其输运与分解;分解后较粗的颗粒随弯道螺旋流以推移质形式被输移至下游凸岸落淤,较细的颗粒大部分都随水流以悬移质形式被携带至下游出口;水流结构随岸坡及河床变形而调整;如此循环往复。试验成果进一步表明:冲刷状态下,试验材料黏性越小、近岸流速越大、作用时间越长,岸坡冲刷崩塌量及河床冲刷量都越大;同条件下岸坡冲刷崩塌总量大于河床冲刷总量,且河床相对冲刷率随岸坡冲刷崩塌量的增大而减小,数值范围为0.40~0.92。     

轨道交通整体床道测量

本文从地铁床道测量的意义出发,结合轨道交通八号线二期工程,介绍了轨道交通整体床道测量技术设计、作业方法、数据采集、成果分析,以及在作业过程中的注意事项.     

Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland,Northern Baffin Island,Canadian Arctic Archipelago

Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.     

Changeability of Movable Bed‐Surface Particles in Natural,Gravel‐Bed Channels and Its Relation to Bedload Grain Size Distribution (Scott River,Svalbard)

The presented paper analyses the variability of grain size distribution parameters of bedload transported by the gravel‐bed Scott River (Svalbard) draining a glacier catchment with an area of 10 km². The grain size distribution analysis is one of the basic elements of identification of the fluvial transport mechanisms in gravel‐bed rivers. It is used for the determination of threshold values for bedload movement. It is also treated as an important indicator of the origin, routes of distribution, and conditions of transport and deposition of fluvial bedload. The field study in a natural proglacial gravel‐bed channel was carried out at two reaches in the mouth section of Scott River. The study revealed relatively high temporal variability and similar mean parameters of grain size distribution in conditions of low discharges. Bedload transport rates reached a mean of 71.9–76.0 kg d^?1 in channel cross‐section. Bedload texture was dominated by gravels with a proportional contribution of the fine‐grained fraction along with very fine‐grained gravels (8‐2 mm) of 38.8%. The medium‐grained fraction (16‐8 mm) constituted 33.7%, with a lower contribution from the coarse‐grained fraction (32‐16 mm) of 23.2%, and the very coarse‐grained fraction (64‐32 mm) of 4.4%. Two periods in the course of bedload transport and distribution of grain size distribution parameters were distinguished based on variation of hydro‐meteorological conditions. The first half of the measurement period was distinguished by significantly higher values of daily loads and increased contribution of the coarse‐grained and very coarse‐grained fraction (28–31% and 6.2–6.6%, respectively). During this time, the river discharged up to 94% of bedload. This resulted in a clear tendency for riverbed scouring. The second half was distinguished by generally low daily bedload transport rates (<10 kg d^?1), an increase in contribution of fine‐ and very fine‐grained gravels (42–55.6%), and a change in the tendency to aggradation. Grain size indices were more varied, and grains were usually finer and better sorted. Selective transport processes, often related to redeposition, were dominant in the channel. Along with an increase in flow velocity, conditions for material deposition became more variable. This was manifested in weaker sorting and an increase in grain diameter.     

Elemental composition and its environmental significance for the varicolored hills in the northern foothills of the Qilian Mountains of Sunan Yugur Autonomous County, China

The varicolored hills in the northern foothills of the Qilian Mountains of northern China, in the Hexi Corridor of Gansu Province's Sunan Yugur Autonomous County, have given this region a unique geomor...     

Amber‐bearing Bed in a Shallow Marine Setting,an Example from the Lower Cretaceous Miyako Group,Northeastern Japan

A previously unknown amber‐bearing bed in the Lower Cretaceous Miyako Group, northeastern Japan, was deposited within a sequence that contains abundant marine macrofossils and wave‐generated sedimentary structures that suggest deposition in an open shallow marine environment. How the amber was transported from its terrestrial origin to the marine environment is unclear, but sedimentary gravity flow is a strong candidate. Our observations suggest that the occurrence of amber clasts in sediments deposited in open and closed shallow marine environments is not uncommon. Thus, in addition to terrestrial sediments, sediments of marine origin have potential as targets for amber exploration.     

Radio‐tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by Einstein

Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio‐tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain‐diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain‐diameters and 6·1 m or 120 grain‐diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D₅₀ of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd.     

EVOLUTION OF RAPIDS OF CREEK MOUTH－BAR AT GEZHOUBA RESERVOIR AND THE IMPACTS ON NAVIGABLE CHANNEL IN THE UPPER REACHES OF THE CHANGJIANG RIVER

ＥＶＯＬＵＴＩＯＮＯＦＲＡＰＩＤＳＯＦＣＲＥＥＫＭＯＵＴＨ－ＢＡＲＡＴＧＥＺＨＯＵＢＡＲＥＳＥＲＶＯＩＲＡＮＤＴＨＥＩＭＰＡＣＴＳＯＮＮＡＶＩＧＡＢＬＥＣＨＡＮＮＥＬＩＮＴＨＥＵＰＰＥＲＲＥＡＣＨＥＳＯＦＴＨＥＣＨＡＮＧＪＩＡＮＧＲＩＶＥＲ￥ＬｉｎＣ...     

Problems of reservoir sedimentation in China

As there are many heavily sediment-laden rivers in China, with high sediment concentration and a large quantity of sediment load, the sedimentation problems of the reservoirs built on those rivers are so serious that the amount of sediment deposited in the reservoirs is great and the rate of sedimentation is accelerated. According to the statistics, up to the end of 1981, a total amount of 11.5×10⁹m³ of sediment were accumulated in those reservoirs, i.e. 14.2% of the total designed capacity were lost. The average annual loss in storage capacity reached 2.3 percent, being the highest in the world. Silting of impounding lakes not only has an effect on the benefits of the reservoirs and seriously threatens the life of reservoirs, but also results in many environmental problems which were not fully estimated in the planning of the reservoirs. In this paper, the situation of reservoir deposition in China are described from the following aspects: 1) the characteristics of hydrology and sediment of the rivers; 2) the seriousness of reservoir sedimentation in China; 3) problems caused by reservoir deposition; 4) the methods of minimizing sediment deposition, etc.