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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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The effect of fully submerged boulders on the flow structure in channels has been studied by some researchers. However, many natural streams have bed material with boulders that are not fully submerged under water. In many natural streams, boulders cover between 1% and 10% of the area of the stream reach. The effect of non-submerged boulders on the velocity profile and flow characteristics is very important for assessing riverbed deformation. The objectives of this paper are to find the pattern of velocity distribution around a non-submerged boulder and to compare it with the classical studies on flow resistance and Reynolds stress distribution in open channels. Also, by considering the variation in the Reynolds stress distribution at different locations around a non-submerged boulder, the effect of a non-submerged boulder on the estimation of shear velocity and resistance to flow has been investigated. Results indicates that inside the scour hole caused by a non-submerged boulder in a river velocity distributions are irregular. However, velocity distributions are regular outside the scour hole. The presence of the boulder causes a considerable deviation of the Reynolds shear stress from the classic distribution, showing a non-specific distribution with negative values. The classical methods for calculating shear velocity are not suitable because these methods do not give detailed velocity and Reynolds stress distributions in natural rivers with a lot of boulders. Thus, the effect of a non-submerged boulder on the estimation of the resistance to flow by considering the variations in velocity and Reynolds stress distributions at different locations around a non-submerged boulder is important and needs to be studied in a natural river instead of just in laboratory flumes. The negative values in Reynolds stress distribution around a boulder indicate that the classical methods are unable to predict resistance to flow, and also show strong turbulence inside the scour hole where the complex flow conditions present ambiguous Reynolds stress distributions. In the current study, to obtain a reasonable estimation of parameters in natural rivers, the classical method has been modified by considering velocity and Reynolds stress distributions through the boundary layer method. 相似文献
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EXPERIMENTAL INVESTIGATIONS AND NUMERICAL SIMULATIONS OF REDUCING SECONDARY FLOWS AROUND A SPUR DIKE
Xuelin TANG Xiang DING Zhicong CHEN Wenlong WANG 《国际泥沙研究》2006,21(2):145-157
1 INTRODUCTION The Yangtze River at the Three Gorges Project (TGP) site meanders with a complex morphology, including ridges like Jiuling Hill that projects into the approach navigation channel (Fig. 1). The approach navigation channel consists of a 530-m… 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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丁坝在江道整治及护岸工程中已有比较广泛的应用。丁坝的平面布置、结构型式与丁坝自身的稳定性及护岸效果密切相关。本文在对钱塘江涌潮区护岸丁坝的设计作了初步总结的基础上,指出了在丁坝结构上存在的一些问题,提出了相应的改进方案,并结合抢险修复工程,进行了现场原型试验。试验结果表明,本文提出的改进方案是切实可行的。 相似文献