NUMERICAL STUDY ON THE THREE-DIMENSIONAL CHARACTERISTICS OF THE TIDAL CURRENT AROUND HARBOR ENTRANCE

A three-dimensional (3-D) numerical model is established to investigate the tidal current motion characteristics around the harbor entrance. Computational approaches consist of the finite difference method, time-splitting technique, C-grid, and a high-order turbulence closure model. The Ocean General Circulation Model (OGCM) inundation scheme is incorporated in the model. An engineering application, Lianyungang Harbor, China, is used as a real-life case. The model is validated by showing that the simulated results agree well with the field data. In the approach channel, the tidal current shows a deflection effect especially in the bottom layer. As for Lianyungang Harbor, a jet flow forms at the tip of the northern breakwater, which drives a circulation flow at the inner side of the harbor entrance. In the vertical, the flow is significantly stratified at the entrance section within the channel, where the flow direction varies between layers and the speed distribution is quite uniform. These 3-D features become less evident to the offshore. Additionally, the sensitivity analysis shows that the flow deflection is related to the channel depth. Simulation results also imply that the siltation rate at the entrance section of the approach channel tends to be more uniform by the 3-D flow motion feature, and could be more significant with the increase of the channel depth.     

Wind-driven Summertime Upwelling in a Fjord-type Lake and its Impact on Downstream River Conditions: Quesnel Lake and River,British Columbia,Canada

Observations and modeling results are presented to explore the response of a multi-basin, fjord-type lake to episodic wind forcing. Field observations show that abrupt cooling and warming events (magnitude greater than 5°C d-1) lasting 3–6 days in a large, salmon-bearing river (Quesnel River) are due to upwelling in its upstream lake (Quesnel Lake) during the summer, stratified season. Within the lake, vertical displacement of isotherms in the vicinity of the river mouth associated with this upwelling is shown to be forced by wind events longer than one quarter of the fundamental seiche period and of sufficient magnitude that the Wedderburn number approaches one. Upwelling occurs nearly-simultaneously throughout a smaller basin adjacent to the outflow (West Basin) that is separated from the Main Basin of Quesnel Lake by a sill and contraction. Wind-driven water fluxes across the sill are estimated using a conceptual model based on volume and heat budgets. These estimates provide an upper bound for flow across the sill and suggest that exchange flow may at times be internally hydraulically controlled, with epilimnetic velocities of up to ∼25 cm/s. Computed fluxes suggest the West Basin hypolimnion has a residence time of 6-8 weeks during the summer stratified period with each upwelling episode irreversibly exchanging 25–30% of the hypolimnetic volume with the rest of the lake. Implications of such events are profound for salmon bearing rivers wherein the thermal habitat is critical to migration success.     

Social differences in leisure behavior: Measurement and interpretation

This article examines how three major dimensions of leisure behavior, i.e., rates of leisure participation, money expenditure for leisure goods and services and discretionary time available for leisure pursuits, are distributed across various socio‐demographic and socio‐occupational groups. The money expenditures for leisure, it is argued, follow traditional class lines most closely; the rates of leisure participation are characterized by a more egalitarian distribution; and the amounts of leisure time are often inversely related to social centrality and social status. The article interprets these varying patterns of leisure inequalities as a function of the cumulative nature of leisure participation as opposed to the “finite” nature of leisure time, and as a reflection of the complex relationship between leisure, work, income, leisure class, and leisure status.     

大流量调度过程对水库缺氧区抑制阈值条件研究

大型水库在热分层期间出现的底部缺氧问题将严重影响湖库底层水体水质,威胁水库供水安全。水库大流量调度引起的强水动力条件可有效削弱甚至完全消除库区缺氧现象。本文以引滦入津源头工程——大黑汀水库为例,采用三维水动力-水质模型复演了水库缺氧区的演化过程,发现大黑汀全库在缺氧区稳定发展时段的8月份有2/3区域出现缺氧现象。为应对缺氧引起的供水安全风险,本文基于多情景分析方法给出了大流量调度过程抑制大黑汀水库缺氧现象的分级调度阈值条件。当大流量调度过程日均流量达到96.5 m³/s且持续时长15～30 d时,大黑汀水库约70%～90%的缺氧区可得到抑制;当流量达到115.7 m³/s且持续时长15~30 d时,90%~100%的缺氧区可得到抑制,库区缺氧现象将基本消除。     

前置挡墙对董箐水库下泄水温的影响

为明确前置挡墙对水库下泄水温及坝前水温分布的影响,以董箐水库为例,构建三维水温-水动力数学模型。模拟不同挡墙高程下的下泄水温和坝前水温分布,分析前置挡墙高程与下泄水温、坝前水温分布间的变化规律。结果表明,下泄水温的改善效果与挡墙高程密切相关:挡墙高程低于取水口高程时,挡墙高程的变化对下泄水温几乎无影响;挡墙高程高于取水口高程一定高度时,挡墙高程越高,下泄水温越高;挡墙高程480 m时,4月下泄水温最大升温1.11 ℃。下泄水温的提高度与挡墙和取水口位置对应的坝前垂向水温差线性相关。坝前垂向水温分布也受挡墙的影响,挡墙高程高于取水口高程一定高度时,随着挡墙高程的增加,分层期温跃层厚度增加位置上升。下泄水温的改善效果与挡墙高程的关系较为复杂,下泄水温提高度增长较快位置分别出现在挡墙高程471 m和475 m处。考虑方案的工程可行性,挡墙高程471 m为改善下泄水温的最优选择。研究可为前置挡墙的设计及工程优化提供方法和参考。     

ENVIRONMENTAL GRADIENTS ALONG A LOWLAND WEIR POOL IN THE SOUTHERN MURRAY‐DARLING BASIN,AUSTRALIA

The 60‐km‐long pool created by the Mildura weir exhibits pronounced physical, chemical and biological gradients along its length. As the river deepens and widens downstream along the weir pool, the flow velocity decreases and the potential for thermal stratification (intensity and duration of stratification) increases. Most nutrient concentrations (TN, NO_x, FRP) as well as the euphotic depth increased in the downstream direction whereas TP and turbidity decreased. The increase in bioavailable nutrients co‐occurred with an increase in electrical conductivity suggesting the presence of relatively more saline groundwater inflows to the weir pool. Throughout the summer (12 December 2003–18 March 2004), with the exception of 8 days, the water column throughout the weir pool mixed completely on a diurnal basis in the deeper sections and was continuously mixed in the shallower upstream sections. This mixing substantially reduced the mean irradiance experienced by the phytoplankton near the weir. Maximum cyanobacteria concentrations were observed in the mid‐weir pool where the range of conditions was most suitable. Diatom abundance increased along the most downstream 20 km of the pool where the water column was deeper and slower flowing yet still mixed completely on a diurnal basis. Peaks in cyanobacteria biomass are not expected in the lower weir pool until lower discharges promote persistent thermal stratification and increase the mean irradiance in the surface mixed layer. Copyright © 2011 John Wiley & Sons, Ltd.     

Factors influencing thermal structure in a tributary bay of Three Gorges Reservoir

To better understand the factors influencing the thermal structure of tributaries in the Three Gorges Reservoir(TGR),a well validated three-dimensional hydrodynamic and water temperature model was proposed to simulate the water temperature distribution in the Xiangxi Bay, a representative tributary of TGR.The numerical results show that water temperature stratification seasonally occurred in the Xiangxi Bay, with stable vertical temperature profiles.It is found from the numerical experiments that three key factors are responsible for the formation of water temperature structure:(1) very often,the locations of thermocline are mainly determined by wind speeds, and the higher the wind speed is, the deeper the thermocline is located beneath the water surface,which could be expressed by a fitted exponential function,(2) the thermal structure is affected by static stability of water column, and the thermocline becomes closer to the water surface and its thickness increases with the increase of temperature, (3) due to the effect of the thermal density inflow, the water temperature of the hypolimnion tends to be uniform, however, even under the condition of larger inflow discharge,the influence of the inflow on the epilimnion and the thermocline is not significant.     

基于Delft3D-flow模型的长江口盐度扩散规律模拟

为了研究长江口环流动力过程下的河口盐度扩散和分层混合机制,采用河口三维模型(Delft3D-flow)模拟了长江口盐度分层扩散规律和扩散系数变化对河口分层的影响。通过模拟实际水文情况下的长江口水动力过程,反映了该区域受到较强的径潮流动力作用后,对盐度在涨落潮周期内的垂向混合分层产生了重要影响,进一步验证了分层河口紊动扩散系数对盐度的水平扩散输移、垂向非稳定层化和混合的影响均较大。模拟结果较好地反映了河口在复杂水动力过程下盐度扩散和分层规律。     

适合多目标种群的窄深型仿自然鱼道研究

传统的仿自然鱼道断面以宽浅型为宜,但对于某些水头较高、河道狭窄的水电站,为了降低工程造价,并增加过鱼目标种群数量,需要建成窄深型的仿自然鱼道。窄深型仿自然鱼道内各项水力参数受边壁及内部结构影响较大,水流结构复杂,易产生流速集中、旋涡等不利流场,为了形成满足多种群鱼类上溯的水流条件,需要开展全面的研究。按照将流场“垂向分层、横向分区”的研究思路,有效利用窄深型断面的特点,结合理论分析、三维数值模拟和物理模型试验的方法,分层分区地满足不同鱼类的上溯条件,在解决了工程问题的基础上,实现了对窄深型仿自然鱼道水力学特性的初步探索研究,增加了仿自然鱼道建设的选择多样性。     

表层排放温水在陡岸型深水中温度层化的测量与模拟

为了研究水体温度分层现象与规律,针对表层排放温水在陡岸型深水中的温度分层现象进行了测量和模拟。首先建立一个表层排放温水在陡岸型深水环境中对流扩散的试验模型,利用温度同步测量系统测量了模型中水体温度场随时间的变化。然后,利用TELEMAC-3D软件建立了一个相应的三维流场与温度场数值模型。根据试验数据对模型进行率定,并开展与试验对应的模拟。结果表明,温度分层后水体从上至下可分为表层同温层、密度跃层和下部滞温层。数值模拟结果与试验结果吻合,所建立的数值模型可作为研究水体温度分层现象和规律的工具。通过分析模拟结果中水体温度分层与理查德森数(Ri)的关系,验证得到判断温度场分层与混合的理查德森数(Ri)临界值为0.25。