大风对金山湖水动力影响的数值模拟研究

为研究大风对金山湖水利调度过程的影响,使用SMS软件的RMA2二维水动力模型,模拟了东南向45° 8级大风作用下金山湖调水过程的水动力特性,并和无风作用时的水动力特性进行比较分析。结果表明大风作用下金山湖注水过程发生明显的增水现象,换水过程增水现象较弱;大风对金山湖水流流向影响不大,增加了水流沿岸流动的趋势,增强了注水过程西部湖区的涡流现象;大风增大了金山湖的流速,入流断面和出流断面流速的增大比主湖区大。研究成果为金山湖多闸站联合调度提供了水动力学依据。     

基于GPS的洪泽湖水流流场质点示踪及数值模拟

针对不同水文气象条件下湖泊真实流场描述的难题,通过在洪泽湖主要入口分别投放GPS示踪器,实现了对湖泊表层水流轨迹、方向的实时监测,形成洪泽湖初步流场图。野外示踪实验结果表明:流经湖泊中心区域的水流运动轨迹均为自西向东的曲线;入湖流量较小时水流难以进入湖泊中心流场,入湖流量较大时流速空间分布不均,流场较复杂;小流量入湖条件下水流运动受到湖泊表面风场的影响,流量较大时水流流动的主要影响因素为湖泊自身的流场。同时,构建了不同入湖流量条件下的洪泽湖二维水动力数值模型,水动力模型模拟的流场分布基本符合水流质点GPS示踪实验的结果,两者拟合较好。本次研究揭示了洪泽湖的真实流场,基于GPS的示踪方法可用于分析河流湖泊的水动力空间变化,为泥沙、污染物质的输移和扩散提供了重要参考依据。     

三峡水库香溪河库湾水华水动力调控初步研究

针对三峡水库蓄水运行后支流库湾春季水华频现问题,利用CE-QUAL-W2模型建立了香溪河-三峡库区整体立面二维水动力数学模型,对三峡水电站不同开机数量和春季不同水文条件下的香溪河库湾流速进行了数值模拟。计算结果表明:香溪河上游来流量较小时,滞留区表层流速小于香溪河库湾水华的临界流速0.05 m/s;而香溪河上游来流量增大到合适的值时,香溪河滞留区表层流速可大于0.05 m/s;仅利用三峡电站小幅度日调节对支流库湾流速的改善效果十分有限,而利用干支流水库对香溪河库湾流速的联合调控效果明显,可控制三峡水库香溪河库湾水华爆发。     

A Semi-Lagrangian Study of Circulation and Transport in Lake Ontario

A particle tracking model (PTM) is linked with a hydrodynamic model to evaluate mean seasonal circulation patterns in Lake Ontario, and also to provide a basis for predicting movement of algal blooms. The PTM is based on a random walk algorithm that combines a deterministic advective component with a stochastic component associated with the turbulent diffusivity field to calculate trajectories of neutrally buoyant particles, where both the advective and diffusive velocities are obtained from the hydrodynamic model. Mean circulation is calculated using 30-year average meteorological forcing data collected from five stations around the lake. Seasonal variations in lake circulation are demonstrated, and a clockwise flow in the eastern basin during summer and early fall is identified, contrary to some previous observations that suggest counterclockwise flow. The impacts of Niagara and St. Lawrence river flows on general lake circulation are found to be small, except within approximately 10 km of the river mouth. Development and application of the PTM demonstrate its potential to provide calculations of (Lagrangian) movements as determined from the hydrodynamic output, and to serve as a first step toward development of an algal transport model. Particle tracking helps to visualize flow patterns and provides a means of evaluating the probability a bloom will reach a specified area, given an initial position and the predicted velocity and diffusivity fields. This capability, when set up for real-time applications, can provide an important tool to support management decisions that may be needed when a bloom is observed, for example in predicting potential impacts of the bloom on a beach or a water intake.     

Circulation and mixing in Sodus Bay due to water exchange with Lake Ontario

Embayments on large lakes may be affected by water exchange with the lake that, in turn, impact water quality in the embayment. In this study we examine the influence of hydrodynamic factors that may play a role in controlling water quality in Sodus Bay, the largest enclosed embayment on the U.S. shoreline of Lake Ontario. The motivation for this study was the occurrence of a blue-green algal (cyanobacterial) bloom in 2010, and the need to understand the factors that influence this and other water quality issues. A hydrodynamic model with high spatial and temporal resolution was applied and calibrated to field data collected in a detailed sampling program in 2013. The model, along with field data collected over several additional years, was then used to develop a comprehensive understanding of the hydrodynamic impacts on physical conditions in the bay. A primary result of this process is a determination of the importance of flow exchange between Lake Ontario and Sodus Bay, particularly during lake upwelling periods that cause colder water to enter the bay as an underflow. Hydrodynamic features identified to have played a potential role in the bloom formation of 2010 include a lake upwelling event, strong stratification, and relatively warm conditions throughout much of the summer. Lack of continuous monitoring in 2010 precludes a specific comparison of the model and data when the bloom formed, but the model clearly shows conditions that would have led to a bloom, assuming other preconditions were in place. The customized hydrodynamic model provides opportunities for future ecological modeling, hypothesis development, and what-if scenario testing. This study reinforces the importance of hydrodynamic interactions between lakes and embayments, and their impacts on water quality.     

水库潮汐式调度对支流水动力影响研究——以三峡库区支流小江为例

三峡水库蓄水运行后,库区支流在春夏季时有水华暴发,对水质造成了一定影响。大量研究表明,通过水库调度改变库区支流水动力条件,抑制水华发生是可行的。采用Delft3D模型对三峡库区支流小江渠马-双江大桥段进行模拟研究,以探明潮汐式调度对库区支流水动力的影响,为抑制库区支流水华发生进行生态调度提供理论支撑。研究结果表明：三峡水库开展潮汐式调度对小江的水流具有扰动作用,整体趋势表现为水位抬升期回水区中、下游段流速值均有所减小,水位下降时流速值有所增加,基本与河口水位变化的步调保持一致;调度期水位变幅越大,流速的扰动越大;水位抬升期表现为流速减小幅度随调度水位变幅的增加而增加,水位下降期表现为流速增加幅度随调度水位变幅的增加而增加。     

调水对巢湖市河道水质的改善效果及对浮游藻类的影响

以巢湖市封闭河道为研究对象,采用水动力模型和生态动力学模型方法,结合野外围隔试验,探讨了调水对河道水质改善和水华抑制的作用效果,并通过调水试验对模拟结果进行了验证。计算出最优的调水周期,提出了合理的涵闸工程改造与科学的引排结合的措施。结果表明:调水能够使河道的水动力条件得到显著提高,平均流速均大于0.10 m/s,高于浮游植物生长临界流速,换水频率在21 d以内。通过一次调水试验表明模型的计算结果比较合理,科学合理的调水能达到抑制有害蓝藻水华在夏季暴发的目的。     

Algal bloom transport in Lake Erie using remote sensing and hydrodynamic modelling: Sensitivity to buoyancy velocity and initial vertical distribution

In this study, we simulate three-dimensional transport of algal blooms in Lake Erie using a combination of remote sensing and hydrodynamic modelling. The remote sensing algorithms use data from the Sentinel-3 OLCI satellite sensor to derive chlorophyll-a concentration from cyanobacteria blooms in Lake Erie. The derived chlorophyll-a concentration initializes an algal bloom transport model driven by the lake component of the Water Cycle Prediction System for the Great Lakes, a system of coupled atmosphere-lake-hydrological models operated out of Environment and Climate Change Canada. The bloom is modelled as Microcystis aeruginosa, a buoyant species that is often dominant in harmful algal blooms in western Lake Erie. Short-term (a few days) predictions of algal bloom transport from July 27 to October 8, 2017 are modelled in both Eulerian and Lagrangian frameworks. The Eulerian framework is used to evaluate the sensitivity of model results to the initial vertical distribution of the bloom. In this work, the Lagrangian framework is limited to two-dimensional surface confined particles. We use several error metrics to evaluate model predictions. We find that results are sensitive to the buoyancy velocity for cases where the bloom was initially distributed over a large portion of the water column. An initial vertical distribution selected from modelled chlorophyll-a half depth shows the highest accuracy for the entire range of buoyancy velocities tested. We also find that the Pierce skill score is difficult to interpret, particularly in cases where bloom intensity is greatly overpredicted by the model.     

An analysis of satellite-derived chlorophyll and algal bloom indices on Lake Winnipeg

Lake Winnipeg has experienced dramatic increases in nutrient loading and phytoplankton biomass over the last few decades, accompanied by a marked shift in community composition towards the dominance of cyanobacteria. Comprehensive lake-wide observations of algal blooms are critical to assessing the lake's health status, its response to nutrient management practices, and an improved understanding of the processes driving blooms. We present an analysis of the spatial and temporal variability of algal blooms on Lake Winnipeg using satellite-derived chlorophyll and indices for algal bloom intensity, spatial extent, severity, and duration over the period of ESA's MERIS mission (2002–2011). Imagery documented extensive blooms covering as much as 93% of the lake surface. Bloom conditions were analysed in the context of in-lake and watershed processes to gain further insight on the drivers of bloom events. Day to day bloom variability was driven primarily by intermittent wind mixing events, with quiescent periods leading to the formation of dense surface blooms. Seasonal bloom distribution was consistent with light limitation in the south basin and lake circulation transporting bloom material towards the north-east shore. Inter-annual variability in average bloom severity was related to both total phosphorus (TP) loadings and summer lake surface temperatures. Results provide a valuable historical time series of bloom conditions to which ongoing observations from Sentinel-3's OLCI sensor can be added for longer term monitoring and change detection.     

新疆博斯腾湖二维水动力数学模型研究

风场是影响湖泊水动力的重要因素,它可以改变水体运动速度和方向,影响各种物质在湖泊内的输移扩散。通过分析博斯腾湖大湖区风场,准确估算出风力、风向变化情况,构建了博斯腾湖平面二维水动力模型。应用计算模型对博斯腾湖水动力进行模拟预测,分析不同风向、风速对湖泊流场结构的影响,为进一步研究博斯腾湖水动力和污染物输移扩散提供理论依据。     

Experiment study of the effects of hydrodynamic disturbance on the interaction between the cyanobacterial growth and the nutrients

The eutrophication of shallow lakes is sensitive to dynamic currents(i.e., disturbances) because of their shallow depths and high contents of nutrients in bed sediments. The relation between the sediment resuspension and the algae bloom is not well understood in the field scale because the interwoven influencing factors cannot be examined individually. By combining the laboratory experiment and the field observation, this paper proposes a sediment-water-algae concept to simulate the effects of hydrodynamic disturbances on the algae growth in the Taihu Lake located in east China. The sediments are sampled from the Taihu Lake while the Microcystis aeruginosa(M. aeruginosa) algae is cultured in the laboratory and then transplanted into the experiment cylinders. The temperature and the light intensity in the experiment are adjusted to be similar with the prevalent in situ conditions. The results indicate that the M. aeruginosa populations under the disturbance condition of the rotational speed ?300 rad/min in the experiment(corresponding to the bottom velocity flow ?0.059 m/s, the shear stress 2?0.069 N/m, or the wind speed ?4 m/s in the field) are higher than those under the disturbance condition of the rotational speed is 400 rad/min(corresponding to the bottom flow velocity 0.079 m/s, the shear stress 0.124 N/m2). It is suggested that a low to moderate disturbance prompts the release of the nitrogen as well as the phosphate nutrients from the bed sediments, amplifying the eutrophication of the Taihu Lake.     

Numerical study of hydrodynamic process in Chaohu Lake

In this paper, the hydrodynamic characteristics of water flow in Chaohu Lake are studied by using the finite volume coastal ocean model(FVCOM), which is verified by the observed data. The typical flow field and the 3-D flow structure are obtained for the lake. The flow fields under extreme conditions are analyzed to provide a prospective knowledge of the water exchange and the transport process.The influence of the wind on the flow is determined by the cross spectrum method. The results show that the wind-driven flow dominates most area of the lake. Under prevailing winds in summer and winter, the water flows towards the downwind side at the upper layer while towards the upwind side at the lower layer in most area except that around the Chaohu Sluice. The extreme wind speed is not favorable for the water exchange while the sluice's releasing water accelerates the process. The water velocity in the lake is closely related with the wind speed.     

Reporting on the status,trends, and drivers of algal blooms on Lake of the Woods using satellite-derived bloom indices (2002–2021)

Despite significant declines in external phosphorus loads, Lake of the Woods continues to experience severe recurring cyanobacterial harmful algal blooms (cHABs) covering as much as 80% of the lake surface area. Satellite-derived bloom indices were used to assess the status, trends, and drivers of cHAB conditions for the period 2002 to 2021 in support of developing ecosystem objectives and response indicators for the lake. Areas of greatest potential concern, with the most prolonged bloom occurrences, were in the southeast of the lake. Significant decreases in bloom indices suggest the lake may now be responding to historical nutrient reductions. The greatest rates of decrease were within the main water flow paths, with little change in the more isolated embayments, suggesting flushing plays a key role in regulating regional bloom severity. Significant inter-annual variability in bloom phenology was observed, with blooms peaking later in recent years, which may be in response to climate-induced changes in the lake and watershed. The absence of a direct relationship between external phosphorus loads and annual bloom severity reflects the complexity of the lake’s response to eutrophication and the potential roles of other drivers including climate and a strong legacy effect of sedimentary nutrients. A case study of the 2017 bloom season captures the compounding interaction of meteorological variability and seasonal nutrient delivery in regulating the bloom response. Results highlight the need for greater understanding of seasonal and regional variability of bloom drivers to aid in forecasting the lake’s recovery under both nutrient management and climate change scenarios.     

大型浅水湖泊纳污能力核算的风场设计条件分析

分析了东南风、西北风及东北风3种不同主导风场下太湖的风生湖流形态特征、环流结构及湖流流速大小变化,研究了不同风生湖流特征条件下环湖入湖污染物的输移扩散规律和湖区水质空间分布特征差异,以及在不同主导风场和常年主导风向下风速变化对太湖各主要湖湾纳污能力的影响。同时,参照水情设计条件要求,选择相对不利的主导风向和保证率为90％时的风速,对太湖进行了纳污能力计算。计算结果表明：在平均风速1.0m/s的西北风和枯水年型设计来水条件下,太湖的CODMn、TP、TN指标纳污能力分别为29732t/年、393t/年和7550t/年,较常年主导风向及多年平均风速条件下的纳污能力分别减小13.5％、 11.3％、23.6％。     

调水引流对太湖无锡水域湖流的影响

2007年望虞河和梅梁湖泵站联合引调工程,在保障太湖水源地水质水量方面取得了一定的成效。在介绍贡湖与梅梁湖湖流监测工作情况的基础上,对湖流测验结果进行了初步分析,分析了贡湖、梅梁湖湖流分布状况,风场对湖流的影响,特殊区域和位置的流场变化,得出以下结论：联合引调工程,改善了两湖水体的流动状态,特别是在梅梁湖泵站调水情况下,湖区流速明显增加,这一流动状态对贡湖取水口和梅梁湖水源地的水质改善是非常有利的。     

洪泽湖换水能力的时空分布特征EI北大核心CSCD

为研究洪泽湖换水能力的时空分布特征,基于MIKE21建立洪泽湖二维水动力模型,模拟分析了洪泽湖不同湖区的换水周期;考虑洪泽湖的流场呈现风生流和吞吐流双重特点,分析了不同季节和不同风场条件下换水周期的空间变化特征。结果表明:洪泽湖换水周期空间异质性明显,从南到北梯度递增,冬季和春季全湖平均换水周期较长,分别为75 d和60 d,秋季和夏季的全湖平均换水周期较短,分别为49 d和31 d;实际风场对洪泽湖的换水能力起到正向作用,东南风对洪泽湖的换水能力起正向作用,东北风对洪泽湖的换水能力起到抑制作用。     

洞庭湖地形变化对洪水过程的影响研究

为了更好地理解地形变化对湖泊洪水过程的影响,采用已构建的长江-洞庭湖二维水动力模型,在洞庭湖2003及2011年实测地形的基础上,以2003年型洪水为例,定量分析了湖泊地形变化对洞庭湖洪水过程的影响。结果表明：2003—2011年洞庭湖超过40%的区域地形下降值大于0.10 m,特别是湘江洪道,其深泓线地形高程平均下降了5.72 m。通过对2003年洪水过程模拟发现,相比于2003年,在2011年地形情况下,以“四水”来流为主导的洪水过程中,南洞庭湖内洪峰水位下降超过0.40 m,西洞庭湖内洪峰水位下降约0.20 m,东洞庭湖内仅在南部地形变化较大区域的水位变化明显;斗米咀-城陵矶河段水面坡降变缓,南洞庭湖内洪道水面坡降变陡。而对于以长江来流为主导的洪水过程,由于长江洪水位的顶托作用,洞庭湖内洪峰水位下降了0.15 m,斗米咀-城陵矶河段及南洞庭湖内水面坡降下降不明显。因此,2003—2011年洞庭湖地形变化对“四水”来流型洪水影响较大,湖盆下切导致湖容增大,可有效缓解洞庭湖内防洪形势,但对长江来流主导的洪水影响较小。研究结果可为洞庭湖内疏浚扩容等防洪工程的开展提供参考。     

荆江河段地形变化对洞庭湖水文情势的影响

基于实测数据分析了荆江河段冲淤变化特征,采用数值模拟方法定量分析了三峡水库建库前后荆江河段地形变化对2008—2018年8—11月洞庭湖水文情势的影响。结果表明：荆江河道地形变化导致洞庭湖区8—11月水位下降,地形变化对洞庭湖区水位的影响程度随着与城陵矶距离增加而减弱;荆江河段和三口洪道冲刷下切削弱了长江与洞庭湖的水力联系,导致同样来水条件下荆南四河入湖和城陵矶出湖水量减少,从而间接降低了洞庭湖的调蓄能力;在枝城站来水一定的条件下,荆南四河分流量减少导致沙市—螺山河段的流量增加,同流量下螺山站中低水水位有一定的抬高。     

Response of Hydrodynamics and Water-quality Conditions to Climate Change in a Shallow Lake

Lake water resources operation and water quality management come up with higher challenges due to climate change. The frequency and intensity of extreme hydrological events are increasing under global warming, which may directly lead to more uncertainty and complexity for hydrodynamic and water-quality conditions in large shallow lake. However, studies about effects of climate change on lake hydrodynamic and water-quality conditions are not enough. Thus, a coupled model is es-tablished to investigate the potential responses of lake water level, flow field and pollutant migra-tion to the changing climatic factors. The results imply that water flow capacity and self-purification in the Hongze Lake can be improved by west, northwest, north, south and southeast winds indi-cating wind filed change has a great effect on the hydrodynamic and water-quality conditions in large shallow lake. It is further observed that both hydrodynamics and water quality are more sensitive to rainfall change than to temperature change; compared to the effect from temperature and rainfall, the effect from wind field appear to be more pronounced. Moreover, the results verify the feasibility of coupling basin hydrological model with lake hydrodynamic and water quality model. To the best of knowledge, the coupled model should not be used until independent calibra-tions and verifications for hydrodynamics and water quality modeling, the hydrological model and the coupled model.

     

Relationships between wind-driven and hydraulic flow in Lake St. Clair and the St. Clair River Delta

A three-dimensional hydrodynamic forecasting model of the Great Lakes Huron-Erie Corridor is used to investigate mixing and the relationship between hydraulic and wind-induced currents in a shallow lake system in which lake inflows come through several channels of a river delta. The hydrodynamics in Lake St. Clair and the channels of the St. Clair River Delta are evaluated for (1) a one-year simulation from 1985 including water age calculation, (2) 8 different wind direction scenarios, and (3) a storm event. Observations and model simulations show distinct regions in the lake in which currents are forced by either hydraulic flow from the river system or from wind stress over the lake. However, during severe storm events, these regions are found to shift or even disappear due to changes in the delta channel inputs into the lake. These changes underscore the need for realistic, unsteady river flow boundary conditions at interfaces between a shallow lake and river delta. Steady inflow conditions will not allow for potential shifting of these current zones, and will also fail to resolve flow retardation or reversals during storm events.