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1.
Erosion of the intertidal chalk platform in the vicinity of groynes and seawalls is evident to the naked eye along many stretches of the engineered coastline of southeast England, leading to undermining and eventually failure of these structures. However, quantification of the magnitude and spatial extent of the erosion has been difficult to date because of a lack of data about the past elevation of the platform. The application of softcopy photogrammetry makes it possible to recreate past platform elevations from historic air photographs and to compare these with elevations from modern air photographs. Coastal sea defence structures have been installed along the chalk coast east of Brighton at various dates over the past 70 years. During this period, the construction methods have changed from predominantly manual labour to a reliance on heavy machines. The analysis of erosion patterns around structures built since the 1970s using heavy machinery show that surface lowering is 4 to 25 times greater in the vicinity of these structures than across the platform as a whole. In contrast, there is no similar pattern of increased erosion around structures built using predominantly manual labour in the 1930s. A four fold increase in average surface lowering is found also along a vehicle trackway that crosses the mid platform. Depressions developed by enhanced lowering in the front of seawalls generate their own dynamic of increased erosion by trapping pebbles and cobbles that enhance the abrasion of the chalk through bedload transport under standing waves in front of the walls. 相似文献
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海滩养护过程和工程技术 总被引：1，自引：0，他引：1
海滩养护是根据设计方案,向海滩大量抛沙,或者同时辅以硬工程,使受蚀海滩增宽和稳足的工程,是抵御海岸侵袭灾害的最佳措施。上世纪末发达国家已普遍开展,我国目前尚属起步,但近年发展迅速。该工程分调查,重建和修补3个阶段,三者相互补充和制约。重建前必须充分调查目标岸段,以为设计养护方案提供依据;重建阶段应注重抛沙位置、沙成分、抛沙量和沙源选择等工序;重建后应进行多年的剖面监测和再抛沙的修补。在那些浪大,沙少和岩礁裸露的侵蚀岸段,应辅以丁坝或岸外潜坝等硬工程加以抵浪,维持所填沙的稳定。 相似文献
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Xuan Weili Xu Xiongjun Zhao Yongqian
Engineer Zhejiang Provinccial Administration Bureau of the Qiantang River Hangzhou
Senior Engineer Zhejiang Provinccial Administration Bureau of the Qiantang River Hangzhou
Lecturer Dept. of Civil Engineering Zhejiang University Hangzhou 《中国海洋工程》1997,(4)
-The groyne has been used widely in bank protection and river regulation.The plane layoutand structural style of groyne are closely related to the stability of the groyne itself and the effect of bankprotection.In this paper,based on the preliminary summary of the design of bank protection in the boresurging area of Qiantang River,some problems regarding the structure of groyne are pointed out and animproved plan is put forward.Site experiment was carried out combined with an emergency repair.The re-sults of the experiment indicate that the improved project is reliable and successful. 相似文献
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The importance of long‐term storage of heavy metals in groyne fields, functioning over 150 years, is investigated for the River Odra (Oder), western Poland. Construction of groynes along the Odra preceded rapid development of heavy industrialization in the largest coal mine districts in Poland and the Czech Republic that resulted in persistent riverine pollution. The 187 km long Middle Odra reach was repeatedly channelized from the first half of the eighteenth century to the turn of the twentieth century, during which time partially filled groyne fields were dissected by new bank lines and groyne systems, with older groyne fields partially keyed into the floodplain. Consequently, concentrations of zinc, lead, cadmium, and copper within historically deposited groyne field sediments exceed local geochemical background levels by more than 60, 40, 15 and 10 times, respectively. Sediments contaminated with heavy metals occur within three distinctive geomorphic zones: zone I is up to 250 m wide and furthest from the present channel, comprising decimeter‐thick polluted sediments, overlying eighteenth century sand and gravel bars; zone II represents the former nineteenth century groyne fields, with widths between 10 and 100 m, filled with as much as 3 m of polluted sediments; zone III represents the twentieth century groyne fields, which are several to a dozen metres wide and filled with polluted sediments averaging depths of more than 2 m. This investigation indicates that large and extensive sediment quantities of moderately polluted sediments are stored immediately along the banks of the River Odra. These sediments could be a significant secondary pollution source and therefore careful maintenance of contemporary bank protection structures is required. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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This present paper proposes a two-dimensional lattice Boltzmann model coupled with a Large Eddy Simulation (LES) model and applies it to flows around a non-submerged groyne in a channel. The LES of shallow water equations is efficiently performed using the Lattice Boltzmann Method (LBM) and the turbulence can be taken into account in conjunction with the Smagorinsky Sub-Grid Stress (SGS) model. The bounce-back scheme of the non-equilibrium part of the distribution function is used to determine the unknown distribution functions at inflow boundary, the zero gradient of the distribution function is set normal to outflow boundary to obtain the unknown distribution functions here and the bounce-back scheme, which states that an incoming particle towards the boundary is bounced back into fluid, is applied to the solid wall to ensure non-slip boundary conditions. The initial flow field is defined firstly and then is used to calculate the local equilibrium distributions as initial conditions of the distribution functions. These coupled models successfully predict the flow characteristics, such as circulating flow, velocity and water depth distributions. The comparisons between the simulated results and the experimental data show that the model scheme has the capacity to solve the complex flows in shallow water with reasonable accuracy and reliability. 相似文献
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Michael Bhme 《洁净——土壤、空气、水》2006,34(3):201-213
The river Elbe is a large eutrophic lowland river with high primary production and high phytoplankton biomass in the growing season. The objective of the study was to gain basic knowledge of the role of dead zones for phytoplankton distribution and the oxygen balance of the river Elbe. At two sampling stations water temperature, oxygen concentration, conductivity, pH value, turbidity, and chlorophyll fluorescence were measured with high precision to learn about the distribution of these parameters across the cross‐sections. The structures indicate differences in the intensity of physical and biological processes between the shallow waters near the shores, which are characterized by groyne fields, and the deep bulk flow. The conductivity clearly shows the high transverse mixing intensity in the groyne fields in contrast to the bulk flow. Groyne fields and the first, the groyne head near margin lamella of the bulk flow can be regarded as a unit. Groyne field results indicate higher primary production of phytoplankton, oxygen release, and higher pH. The turbidity of water entering the groyne fields decreases rapidly because of sedimentation within a short time. The groyne head lamella of the bulk flow sometimes shows higher chlorophyll fluorescence than the central lamella of the bulk flow and the water of the groyne field. The processes which contribute to the observed distribution are discussed, but could not yet be quantified. A modification of the dead zone model is proposed. 相似文献
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This paper examines a variety of recirculation flow patterns that develop in the groyne fields on rivers. A comprehensive data set was obtained from flume experiments at Delft University of Technology and field measurements performed on the Elbe River in Germany. The analysis focuses on patterns of velocity, scour and deposition, and corresponding change of riverbed morphology. The results show that velocity patterns in the groyne fields depend mainly on the aspect ratio between groyne length and length of groyne field. When the aspect ratio is greater than 0·5, a one‐gyre pattern of recirculation develops, while at groyne fields with aspect ratios less than 0·5 a two‐gyre recirculation pattern emerges. The spatial distribution of fine‐sediment deposition between the groynes coincides with the locations of gyres. Moreover, the thickness of the fine‐sediment layer decreases toward the gyre margins where recirculation velocities are greatest. Although the total concentration of suspended sediment in the river does not change considerably as the flow moves through the groyne field, the biological and gravimetrical composition of the suspended material changes substantially within the groyne field. These changes are due to preferential deposition of coarse mineral particles and the replacement of those minerals with finer organic material. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
10.
防护丁坝抗冲刷失效安全可靠性分析 总被引：1，自引：1，他引：0
分析了防护丁坝冲刷的机理,用概率分析方法研究了在随机因素影响下防护丁坝抗冲刷的可靠性问题.应用Rosen-blatt变换确定防护丁坝抗冲刷破坏的功能函数在随机因素影响下的可靠性指标.提出了用丁坝端部冲刷坑的当量坡度小于冲刷坑坡度的临界值JD作为丁坝抗冲刷破坏的安全（稳定性）准则.分别考虑了水道流速、土颗粒等效直径、冲刷坑半径、冲刷坑后坡度临界值和水流方向角为相关或独立的非高斯随机参数时的可靠性问题.该分析能为防护丁坝系统的抗冲刷可靠性评估和设计提供有实用价值的方法. 相似文献