波浪作用下缓坡近岸海域沿岸流分布影响因素分析

本文研究了均匀岸坡地形条件下．规则波及不规则波浪作用下缓坡近岸海域沿岸流的分布规律。采用数学模型与物理模型相结合，分析了波浪要素，地形坡度等因素对沿岸流分布的影响。提出了表征沿岸流分布特征参数的经验公式。研究结果表明，缓坡近岸海域，波浪作用下沿岸流的分布主要受到入射波浪波高、入射角度及地形坡度的影响。不规则波浪作用下沿岸流的速度分布相对平缓。     

Simulation of wind-driven circulation and temperature in the near-shore region of southern Lake Michigan by using a channelized model

To enhance the efficiency of a pathogen forecasting model in the beach areas of southern Lake Michigan and to reduce the computation time, the near-shore current is approximated as a channelized flow parallel to the shorelines in clockwise or anti-clockwise direction within the accuracy tolerance range. A channelized model with a curvilinear boundary can significantly reduce the computation effort, and at the same time achieve a good agreement between the predicted and measured water surface elevations, currents, and water temperatures. The sensitivity analysis results show that the suitable channel width for the near-shore region of southern Lake Michigan should be no less than 10 km. The modeling results of the water temperature are much less sensitive to the channel width than those of the current velocity and the water surface elevation. The modeling results also show a close correlation between the speeds of the wind and the near-shore current. The current may fully respond the wind stress with a time lag of several hours. The correlation may provide an approximate estimation of the lake circulation under some wind conditions for a practical forecasting purpose. More complex wind-current relationships need to be described with a more sophisticated hydrodynamic model. This verified model can be used for the pathogen forecasting in the near-shore regions of southern Lake Michigan in the future.     

A field study of nearshore environmental changes in response to newly-built coastal structures in Lake Michigan

In this study, we monitored changes of cohesive nearshore environment including bluff and lake bottom/bed response to newly-built coastal structures with a thousand-meter-long revetment in Lake Michigan shoreline over a six-year study period. Sequential aerial photos showed that excessive slumping occurred only on the south bluffs and no bluff recession in the middle areas with coastal structures. Field measurements using our recently developed integrated geophysical techniques provided information on bathymetry, sand layer thickness, and lakebed downcutting over the nearshore reach of Concordia University in Lake Michigan. During the study period, the bathymetry profiles at the study site fluctuated dynamically, especially in the regions outside the shoreline structures, suggesting continuous and ongoing sediment erosion and deposition. The lakebed downcutting in front of the newly-built coastal structures is correlated with CWIH (cumulative wave impact height). Significant differences of lakebed downcutting in the north and south natural beach regions were revealed and may be associated with the nearshore sediment budget. The southwardly dominant longshore current maintains the equilibrium state of beach profiles in the north region, but the coastal structures prevent sediment supply from the well-protected bluffs in the middle region to the south region. The possible source of sediment supply in the south region is therefore from lakebed or bluff materials, supported by excessive bluff failures and lakebed downcutting. Overall the newly-built coastal structures seem to pose negative impacts on bluff stability at the south shore of the coastal structures.     

NUMERICAL SIMULATION OF TOPOGRAPHY CHANGE IN RECLAIMED LAND ALONG COAST OF SOUTH CHINA SEA

1. INTRODUCTIONThe geomorphology of beach is controlled by natural and unnatural effects. In coastal reclaimed land, the topography change is based on suspended sediment transport and near-bed sediment transport. No matter whether the topography change is…     

洋山港南北汊道水体和悬沙输运变化

汊道封堵是洋山港建设的规划方案之一,是后续码头建设的基础工程,其实施也是对港区水动力变化和海床冲淤演变产生影响的主要工程。迄今为止,港区北部颗珠山-小洋山汊道和南部双连山-大山塘汊道及大山塘-大洋山汊道保持畅通。这几个汊道是否封堵一度成为热点问题。本文通过通量分析方法,分析汊道位置水沙输运年际变化。结果表明,颗珠山汊道单宽净输沙通量逐年增强,保留颗珠山汊道是必要的。     

Sand exchange between groyne‐field beaches and the navigation channel of the Dutch Rhine: the impact of navigation versus river flow

The morphodynamics of groyne‐field beaches along the Dutch Rhine was studied from in situ measurements of hydrodynamics and sand transport, aerial photographs, and bed‐level time series. From the analyses, it appeared that groyne‐field beaches experience an alternation of periods of erosion and deposition. The erosion is due to navigation at low to moderate discharge; the deposition is due to floods. On a time scale of a few decades, periods of erosion and deposition are in equilibrium. Navigation‐induced erosion is mainly due to vessels >60 m. The impact of passing vessels on the currents near the banks and the erosion of the beaches increases as underwater volume increases. Individually, loaded barge‐tows have the greatest influence on groyne‐field hydrodynamics and sand transport. On a yearly basis, however, the relatively strong influence of push towing is superseded by the higher frequency of passing motorized vessels. The erosion on a yearly basis, therefore, is driven by the effects of the large motorized vessels. The effects of push towing are negligible. Underwater volume and passing distance from the bank are the most important parameters of passages, insofar as their effect on groyne‐field beaches is concerned. The effect of underwater volume is clearly reflected in the different behaviour of groyne‐field beaches on the north and south banks. Loaded vessels sailing along the south bank from Rotterdam to Germany have a much greater effect on the beaches on the south bank than do returning vessels, often empty or partly loaded, on the beaches of the north bank. As a result, beach erosion on the south bank is twice as pronounced as the erosion on the north bank. Remarkably, the greater erosion of the beaches observed on the south bank was compensated by a similarly larger deposition during the flood of 1998. The impact of navigation on groyne‐field beach erosion increased strongly from 1970 to 2001, and probably will have doubled from 1970 to 2010. Copyright © 2004 John Wiley & Sons, Ltd.     

海南岛西南岸沿岸输沙特性及防波堤影响

通过海南岛西南岸东方海洋观测站波浪观测资料验证,建立八所海域波浪数学模型,计算确定八所新港沿岸水域各向破波要素。采用3种沿岸输沙率计算公式,确定海南岛西南岸八所新港周边海岸沿岸输沙率。分别探讨风浪、涌浪对海南岛八所新港沿岸输沙率的贡献,对比分析防波堤工程建设前后八所新港及附近沿岸输沙率特征。研究表明,海南岛西南岸向北的沿岸输沙能力大于向南的;风浪、涌浪对八所新港附近海岸沿岸输沙能力的贡献率与其出现的频率略有区别;八所新港建港后南北两侧出现淤积且南侧淤积强度大于北侧;防波堤长度的增加对沿岸输沙能力影响的范围和强度有所增大。     

毛里塔尼亚友谊港岸线演变及防护工程

毛里塔尼亚友谊港所处海域为典型沙质海岸,面向大西洋,波浪作用下自北向南的沿岸输沙是其主要泥沙运动方式。该海岸泥沙中值粒径0.25 mm,年平均输沙约100万m~3。因为港口建设拦截了沿岸输沙,原本平直海岸线形成了港口北侧淤积和南侧冲刷的岸线形态。为保护堆场免受侵蚀,港口南侧于1991年建成了南挑丁坝,至2009年其南侧岸线已后退至根部,再度危及堆场和陆地设施安全。根据实测岸线资料,采用一线理论岸线演变数学模型,对港口南侧海岸不同防护方案进行了计算。结果显示,现有南挑丁坝与其南侧续建的T型丁坝之间岸线能很快调整至稳定状态,可对该岸段陆地设施起到保护作用。在现有丁坝南侧2 000 m处新建T型丁坝,平行于岸线的横头部分置于-2 m等深线,作为港口南侧岸线防护的推荐方案。沿岸输沙未得到补给的情况下,新的岸线防护工程在稳定上游岸线的同时,下游岸线的冲刷后退不可避免。考虑较长期限和更大范围的岸线稳定,还需采取每隔一定年限新建防护工程的措施。     

盐城市侵蚀性海岸防护设计

介绍盐城市侵蚀性海岸防护概况,以及海岸防护设计中应正确处理的2种关系,即宏观蚀退和微观保护的关系以及保堤、保脚、保滩的关系。对常见的防护、保滩(促淤)工程的结构形式及其特点进行总结。以盐城市海岸侵蚀最为严重的滨海县六合庄为例,进行典型岸段海岸防护效果分析。指出:在盐城市侵蚀性海岸防护设计中,应在宏观蚀退条件下构建侵蚀性海岸整体防护体系,保护沿岸地区工程的安全;工程措施不能在宏观上改变海洋与地质条件,但能够在局部改善水沙条件,起到消浪与阻止沿岸流冲刷的作用;保堤必须保脚,保脚必须保滩。     

波浪通过斜坡上潜堤的波能演化实验研究

潜堤是防止海岸侵蚀的常用护岸建筑物,准确的掌握潜堤前后波浪的传播变形规律十分必要.该文以斜坡上梯形潜堤为研究对象,基于波浪水槽实验,通过谱分析探求线性波、非线性波、非规则波通过斜坡上潜堤内部组成能量的变化规律,分析相同的入射波情况下波浪倍频能量演变与堤顶水深大小的关系,得出堤顶水深越小主频能量衰减越大的规律.同时,比较研究线性波与非线性波作用下潜堤前后波能的变化,发现非线性波高倍频能量产生更加剧烈.     

近海人工岛及沙坝工程与潮流的响应特征研究

北戴河新区位于最具发展潜力的环渤海经济圈中心地带,为满足旅游业发展需要而建的人工岛和保护旅游海滩而建的人工沙坝对近海潮流动力有不同程度的影响。该文基于MIKE21 FM模块通过大、中、小模型三层嵌套的方式建立洋河-葡萄岛近岸海域潮流数学模型,研究分析人工岛及沙坝工程建设前后的潮流动力变化特征,得到下列主要结论:工程建设后研究区域的主体潮流特征仍为顺岸往复流,流速变化量涨潮大于落潮;人工岛工程对流速场的影响范围和程度均明显大于沙坝工程,其中人工岛工程引起的流速变化量是沙坝工程的4倍;人工岛的建设使其内部形成一个相对封闭的水域,流速近乎为零,而养滩工程区在两侧水工建筑物和水下人工沙坝的掩护作用下流速基本减小至0.10 m/s以下。     

A numerical study of pumping effects on flow velocity distributions in Mosul Dam reservoir using the HEC‐RAS model

Water flow direction and velocity affect and controls erosion, transport and deposition of sediment in rivers, reservoirs and different hydraulic structures. One of the main structures affected is pumping stations within the dams wherein the velocity distribution near the station intake is disturbed. The two‐dimensional (2‐D) HEC‐RAS 5.01 model was utilized to study, analyse and evaluate the effects of pumping rates and flow depth on the flow velocity distribution, flow stream power and their effects in the Mosul Dam reservoir. The pumping station was considered as a case study. The station is suffering from sediment accumulation around, and in, its intake and suction pipes. The main inflow sources to the reservoir are the Tigris River and run‐off from the valleys within its basin. The reservoir was divided into two parts for the present study, including the upper part near the pumping station (analysed as a two‐dimensional zone), while the lower part was analysed as a one‐dimensional flow to reduce the simulation period computation time (1986–2011). Different operation plans (i.e. pumping rate and water depth) were considered. The results of the depth‐averaged velocity model indicated that when the pumping station was working at a range from the designed full capacity (100% to 25% of its full capacity), the maximum flow velocity increased from 75 to 4 times the normal velocity when there is no pumping dependent on pumping rate and flow depth. For the same operation plans, the flow stream power varied from around zero values to 400 times at full pumping capacity and low flow depth. For sediment routing along the reservoir, the considered statistical criteria indicated the model performance in estimating the total sediment load deposition and invert bed level is much better than in the case of erosion and deposition areas for different considered bed sections of the reservoir.     

Modeling the Transport of Sediments and Hydrophobic Contaminants in the Lower Saginaw River

A study of processes that are significant in the transport and fate of sediments and hydrophobic contaminants in the lower Saginaw River over long periods of time, up to 25 years, has been made. The numerical model used in the analysis consists of a two-dimensional, vertically-integrated, time-dependent hydrodynamic and sediment transport model coupled (a) with a three-dimensional, time-dependent model of the dynamics of the sediment bed and its properties and (b) with a model of the transport and fate of hydrophobic contaminants. Calculations of sediment transport for different magnitude flow events demonstrate the variations in erosion and deposition at different sites and the dependence of this erosion and deposition on the flow rate. These calculations also illustrate the inherent variability, or uncertainty, in any long-term predictions since the results depend to a great extent on the times of occurrence of the largest flow events, times which can not be predicted but are only known statistically. The transport and fate of PCBs were also investigated with the emphasis on the effects of (a) large flow events, (b) incoming upstream PCB loads, and (c) burial of contaminated sediments by clean sediments with subsequent erosion of sediments by a large flow event. The analysis clearly shows that the major erosion of contaminated sediments occurs at the edge of the river channel with little erosion of contaminated sediments in the near-shore area.     

长江河口南槽近期滩槽水沙输移特性分析

为了深刻认识近期长江河口演变趋势,依据2005,2006年和2010年长江口南槽滩槽洪枯季实测水文泥沙数据,分析了主槽与浅滩的水动力条件及悬沙浓度的时空分布特征。利用机制分解法,研究了河口滩槽间泥沙输移及交换机制。研究结果表明,长江口南槽主要以往复流为主,落潮流速大于涨潮流速。随着水深变浅,水流流速过程线存在差异,使不同区域的水流挟沙能力和输沙过程不同。输沙以平流项输沙通量为主,但潮泵作用在南槽地区泥沙输移中也占有重要地位,形成"主槽出沙、浅水进沙"的输沙模式,促使南汇边滩前缘缓慢淤涨。     

长江扬中河段河势演变及治理研究

为进一步稳定长江中下游扬中河段的河势,归纳分析了新水沙条件下段内江心洲的历史治理情况,发现洲头崩坍后退、沿程阻力的减小等问题仍然存在。在现有河势控制工程的基础上,提出太平洲“裹头”及两缘护岸、落成洲右缘护岸和禄安洲“裹头”及两缘护岸的合理治理方案,模拟了治理方案实施前后的流量流速,分析了各治理方案下的治理效果。首先,太平洲近岸流速减小幅度在 0.01～0.05 m/s 之间,汊道分流基本无变化;其次,落成洲近岸流速均减小 0.02～0.04 m/s,对于该部位岸线的坍塌起到有效的控制作用;最后,禄安洲近岸流速总体减小 0.01～0.04 m/s,有利于洲头以及左右侧汊道分流的稳定。结果表明,所提出的治理方案能够有效降低区域内近岸流量及流速,有利于洲滩及汊道分流的稳定,对遏制岸线崩退和坍塌有至关重要的作用,以期为长江中下游江心洲的治理提供参考。     

杭州湾北沿上海段水下地形冲淤变化特征

基于2005—2020年上海市滩涂实测地形、气象数据及开发建设资料,以杭州湾北沿上海段为研究区,定性与定量、整体与局部相结合,分析其水下地形冲淤变化特征,探寻演变原因及影响。结果表明：杭州湾北沿上海段近16年整体呈强度渐弱的冲刷态势,共冲刷1.482亿m³,年均冲刷深度为2.886 cm,金山深槽虽受强潮及圈围工程的影响兼具强冲刷及强淤积,但整体表现为冲淤均衡略显冲刷,冲刷强度仅为研究区域冲刷的12.1%;上游来水来沙的减少使得杭州湾北沿维持冲刷态势,潮流挟沙补充作用随涨潮潮差增大而增强,冲刷强度减弱,圈围区域岸线稳定,贴岸冲刷较强,地形变化较为剧烈。     

黄河洪水的非恒定性对输沙及河床冲淤的影响

本文根据黄河主要干支流冲积河段实测高含沙洪水的输沙资料，从黄河下游河道比降、河宽、流速沿程调整、洪水非恒定性等方面分析研究了冲积河道输沙特性与河床冲淤特性。分析了动床阻力与输沙特性间的关系。当水流流速大于1．8～2．0m/s时，床面进入高输沙动平整状态，河道输沙特性呈现“多来多排”状态，是形成河床沿程冲刷的水流动力条件。从洪水期作用在床面上的剪力或功率的变化，引起底沙输移强度的变化，论证了涨水期河床强烈冲刷与落水时迅速淤积的必然性。指出底沙运动速度比洪水波传播慢是造成河道长距离冲刷的根本原因。     

远破波作用下堤前冲淤形态及冲淤机理

远破波作用下堤前海床冲刷较为严重，对建筑物的安全更具威胁，国外尚无专门研究，。本文通过试验，重点研究远破波作用下堤前冲淤规律，并对冲淤机理进行分析。     

Modeling impact of culture facilities on hydrodynamics and solute transport in marine aquaculture waters of North Yellow Sea

An increasing number of marine aquaculture facilities have been placed in shallow bays and open sea, which might significantly affect hydrodynamic and solute transport processes in marine aquaculture waters. In this study, a coupled hydrodynamic and solute transport model was developed with high-resolution schemes in marine aquaculture waters based on depth-averaged shallow water equations. A new expression of drag force was incorporated into the momentum equations to express the resistance of suspended culture cages. The coupled model was used to simulate the effect of suspended structures on tidal currents and the movement of a contaminant cloud in the marine aquaculture of the North Yellow Sea, China. The simulation results showed a low-velocity area appearing inside the aquaculture cage area, with a maximum reduction rate of velocity close to 45% under high-density culture. The results also showed that tidal currents were sensitive to the density of suspended cages, the length of cages, and the drag coefficients of cages. The transport processes of pollutants inside aquaculture facilities were inhibited away from the vicinity of the culture cage area because of the diminished tidal currents. Therefore, the suspended cages significantly affected the transport processes of pollutants in the coastal aquaculture waters. Furthermore, the reduced horizontal velocity significantly decreased the food supply for the aquaculture areas from the surrounding sea.     

太湖梅梁湾、贡湖套网格风生流数值模拟

对太湖梅梁湖、贡湖湖流进行套网格数值模拟。根据1998年8月太湖富营养化水质监测水文物理资料,绘制出梅梁湖、贡湖各站点位置分布图和其流速大小和方向。模拟计算与实测结果吻合较好,证明其套网格数值模型的建立是合理和有效的。分析结果表明,太湖各水域流速相差很大,近岸区域流速高于远岸区域,存在明显的近岸流。但流速值不大,即梅梁湖、贡湖和大太湖的水体交换量不大,通过流场分布可初步判断污染物质在水体中的扩散与迁移情况。