云南楚雄盆地西部浅水风暴岩与珊瑚条砾灰岩的成因   总被引：2，自引：0，他引：2  

韩征  余素玉 《地球科学》1989,14(6):593-598

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Improvements in long-core measurement techniques: applications in palaeomagnetism and palaeoceanography     

Robin Weeks  Carlo Laj  Lionel Endignoux  Michael Fuller  rew Roberts  René Manganne  Erick Blanchard  William Goree 《Geophysical Journal International》1993,114(3):651-662

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Modeling solute transport in river channels using dispersion theory     

T. Morales-Juberias  P. Zafra  M. Olazar  I. Antigüedad  I. Arrate 《Environmental Geology》1994,24(4):275-280

Carrying out a series of field tracer experiments in river channels allows recognition of river behavior in different flow conditions and thus investigation of the evolution of a solute, tracer, or pollutant over the range of flow rates considered. In this paper, data from tracing tests conducted on the Artibai River in northern Basque Country are used to demonstrate the approach. In all experiments the tracer used was lithium and it was added to the river as an input pulse. An analytical solution to the instantaneous injection model that accounts for the effective initial amount of tracer injected, calculated from the tracer breakthrough curve, instead of the conventional initial injection concentration, is used. The technique is applied to estimate travel times, Péclet numbers, and dispersion coefficients using an optimization algorithm with the aim of characterizing the tracer movement in the stream and analyzing its evolution. Subsequently, considering the results of various tracer experiments, conducted over different flow rates, empirical relationships between dispersion, velocity, and flow rates may be determined. This information allows characterization of the river behavior and can be used to model transportation and dispersion of a tracer or pollutant.  相似文献   

A Review of “Eden on the Charles,The Making of Boston”     

Arthur Krim 《The Professional geographer》2013,65(3):470-472

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杭州湾北部潮流深槽区细颗粒物质输运与再悬浮过程   总被引：2，自引：0，他引：2       下载免费PDF全文

杨旸  高抒  汪亚平 《海洋学报》2008,30(2):92-101

于2005年5月大潮期间在杭州湾北部潮流深槽区的4个站位进行潮周期观测,获得了流速、悬沙等数据,并对其进行了分析,计算了水沙通量和再悬浮通量。分析结果表明,该深槽区涨潮流速大于落潮流速,涨潮历时小于落潮历时,潮差自湾口向湾内方向增大;悬沙的组分以粉砂为主,分选较差,偏态以负偏为主,这些特征与底质一致;深槽中部和东部的悬沙沿岸线向湾内方向输运;深槽西部和东部外侧的悬沙输运方向与余流方向一致,分别向湾内和南部输运;除转流和流速加速初期外,垂线流速分布符合Kûrmûn-Prandtl模型,摩阻流速与垂线平均流速变化趋势一致。计算得到的表观粗糙长度在涨落潮时段的水流加速或减速阶段都呈增大趋势,且数值较大,这难以把它简单地归结为床面形态的作用,表观粗糙长度的变化趋势可能是高悬沙浓度和浓度成层性共同作用的结果,但对这一假说的验证还有待于进一步的现场观测和机制分析。计算所得的再悬浮发生的周期性与实测悬沙浓度的周期性相符,而且最大悬沙浓度的出现滞后于最大再悬浮通量,说明再悬浮作用对水层中悬沙浓度的变化具有重要影响。  相似文献   

STUDY ON FREQUENCY CODING ANTI—INTERFERENCE SYSTEM FOR DATA TRANSMISSION IN SHALLOW WATER ACOUSTIC CHANNELS     

许肖梅  粘宝卿  刘志鑫  许鹭芬  黄衍镇 《中国海洋湖沼学报》2002,20(4):309-315

Achieving reliable underwater communication in shallow water acoustic channels is a difficult because of the random time-varying nature of multipath propagation,severe amplitude fluctuation,and spatial variability of the channel conditions.This paper describes a new signal processing technique-frequency coding and decoding by means of real-time measurement of signal width,jamming and suppressing multipath interference and using redundant coder.The application of the technique to thd model ZTY-1 status monitor for underwater system of seabed is introduced in this paper.The main principle,the technique specifications and the key techniques of the system are discussed here.Theoretical estimations and experimental results proved that the performance of the system is excellent.The method can be used for some other related low-data-rate data transmission detecting in shallow water acoustic channel.  相似文献   

Abandoned channel fill sequences in the tidal estuary of a small mountainous,dry‐summer river          下载免费PDF全文

Andrew B. Gray  Gregory B. Pasternack  Elizabeth B. Watson  Miguel A. Goñi 《Sedimentology》2016,63(1):176-206

This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub‐centimetre resolution stratigraphic analyses to describe depositional processes and their resultant sedimentary deposits. Both abandonment sequences recorded quasi‐annual scale fluvial/tidal deposition couplets. In both cases, tidal deposits contained very little sand, were higher in organic and inorganic carbon content than the sandier, fluvially dominated deposits, and possessed millimetre‐scale horizontal laminations. The two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. Aerial photographic analysis showed that the first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ¹³C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (one to five times mean discharge), while those of the second phase were consistent with suspended sediment from higher flows (seven to ten times mean discharge). When considered together, the results indicate that the early fill sequence recorded a reach experiencing regular fluvial deposition through flow conditions during the wet season, while the latter fill sequence records a reach more disconnected from the main stem in terms of flow and sediment. The major factor affecting the difference in sedimentation between the two fill periods appears to have been the morphology of the upstream river bend in relation to the position of the bifurcation node. During the first fill period, the upstream entrance to Ropers Slough seems to have remained open, in part due to the placement of its entrance on the outside of the mainstem river bend, and despite stronger tidal effects caused by a larger tidal prism and closer proximity to the tidal inlet. By the second fill sequence, the upstream bend morphology had altered, placing the entrance to Ropers Slough on the inner bank of the mainstem bend, which resulted in more rapid plug bar formation. The role of tidal effects in the geomorphic trajectory of the two abandonment sequences is unclear, but appears to have been less important than local bifurcation geometry.  相似文献   

水下机器人视频图像高效压缩方法研究     

李庆忠  王冰 《热带海洋学报》2009,28(4):1-5

水下视频图像压缩一直是有限带宽水声信道实时传输海量视频数据的关键技术之一。本文首先介绍了目前水下机器人和水下视频图像压缩研究存在的主要问题，并综合分析了目前几种高效视频压缩方法的特点并探讨了进一步研究的方向。此外，根据水下视频的成像特点，提出了高效的全局与局部运动混合补偿方案和基于小波变换的预处理方法。初步实验结果表明：本文提出的预处理方法可以有效去除视频图像中存在的大量视觉冗余和空间冗余，提出的混合运动补偿方案可以获得很高的压缩编码效率；但必须进一步研究快速、有效的全局运动估计方法。  相似文献   

A model of submarine channel-levee evolution based on channel trajectories: Implications for stratigraphic architecture   总被引：3，自引：0，他引：3  

Zoltán SylvesterAlessandro Cantelli 《Marine and Petroleum Geology》2011,28(3):716-727

Channel-levee systems are frequently interpreted as having a long history of cut-and-fill by channel-shaped features of different scales. Results from a simple geometric model based on a centerline migration algorithm combined with a vertical channel trajectory show that an incising-to-aggrading trajectory of a single channel can produce realistic morphologies similar to systems observed on the seafloor and subsurface, including features such as a basal erosional surface, coeval inner and outer levees, internal erosional boundaries, and terraces draped by inner levee deposits. Channel migration results in composite erosional surfaces that are distinct from topographic surfaces, and their formation does not require larger than usual erosional flows. Many submarine channels interpreted as underfit were probably carved by flows similar to the ones that eroded and deposited the entire channel system. We suggest that the features of most submarine channel-levee systems do not require large temporal variations in flow magnitude but can be explained by a simpler model whereby incision, migration and aggradation of a single channel form over time results in an apparently complex system.  相似文献   

Hydraulic modelling of fish habitat in urban rivers during high flows     

D. J. Booker 《水文研究》2003,17(3):577-599

In urban rivers, flow regime and channel morphology are the drivers of physical habitat quality for aquatic species. Peak discharges are increased at high flows as a result of impermeable catchments and channel engineering for flood protection schemes. Hazardous conditions and flashy hydrographs mean that measurement of velocities at high flows is a difficult task. This research uses a three‐dimensional computational fluid dynamics (3D‐CFD) model to simulate hydraulic patterns in two urban river channels. A 3D‐CFD code, called SSIIM, was used to simulate hydraulic conditions in two engineered river reaches of the River Tame, Birmingham, UK. These two sites represent channels with different levels of engineering. Models were calibrated and tested using field measurements. Results show that modelled water surface levels and velocity profiles are well simulated. Calibrated roughness heights are compared with those derived from field measurement of sediment size. Numerical experiments are used to assess the relationship between grid resolution in the vertical dimension and the form of the modelled velocity profiles. Biologists have used laboratory experiments to determine maximum sustainable swimming speeds (MSSS) of fish, often in order to assess what level of a particular pollutant may be tolerable. In this work, simulations of high‐flow hydraulic patterns are used to compare velocity patterns with fish MSSS. Results show that when the water levels rise to fill the first channel of the two‐stage channels at the sites, which occurred 16 times in 2000, MSSS are surpassed in the majority of available habitat, suggesting that excessive velocities at high flows are one factor that limits fish habitat. A comparison between the two reaches shows that there is less available habitat in the more modified reach. Conclusions suggest that an approach that integrates water quality issues and physical channel characteristics must be taken in river rehabilitation schemes, as improvements to water quality alone may not be sufficient to improve habitat quality to the desired level. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献