Three-Dimensional Tidal Model and Its Application to Numerical Simulation of Water Quality in Coastal Waters

The turbulence mechanism plays an important part in the mixing process and momentum transfer of turbulence. A three-dimensional Prandtl mixing length tidal model has been developed to simulate tidal flows and water quality. The eddy viscosities and diffusivities are computed from the Prandtl mixing length model. In order to model the water quality of an estuary or coastal area many interdependent processes need to be simulated. These may be conveniently separated into three main groups: transport and mixing processes, biochemical interaction of water quality variables and the utilization and re-cycling of nutrients by living matter. The model simulates full oxygen and nutrient balance, primary productivity and the transport, reaction mechanism and fate of pollutants over tidal time-scales. The model is applied to numerical simulation of tidal flows and water quality in Dalian Bay. The model has been calibrated against a limited data set of historical water quality observations and in general demonstrates excellent agreement with all available data.

A Three-Dimensional Water Quality Model and Its Application to Jiaozhou Bay, China

A three-dimensional coupled physical and water quality model was developed and applied to the Jiaozhou Bay to study water quality involving nutrients, biochemical oxygen demand, dissolved oxygen, and phytoplankton that are closely related to eutrophication process. The physical model is a modified ECOM-si version with inclusion of flooding/draining processes over the intertidal zone. The water quality model is based on WASP5 which quantifies processes governing internal nutrients cycling, dissolved oxygen balance and phytoplankton growth. The model was used to simulate the spatial distribution and the temporal variation of water quality in the Jiaozhou Bay for the period of May 2005 to May 2006. In addition, the effect of reduction of riverine nutrients load was simulated and evaluated. The simulated results show that under the influence of nutrients discharged from river, the concentrations of nutrients and phytoplankton were higher in the northwest and northeast of the bay, and decreased from the inner bay to the outer. Affected by strong tidal mixing, the concentrations of all state variables were vertically homogeneous except in the deeper regions where a small gradient was found. Obvious seasonal variation of phytoplankton biomass was found, which exhibited two peaks in March and July, respectively. The variation of riverine waste loads had remarkable impact on nutrients concentration in coastal areas, but slightly altered the distribution in the center of the bay.

Three-Dimensional Water-Quality Simulation for River Based on VOF Method

In the present study, considering the transport and transformation processes of variables, a threedimensional water quality model for the river system was established, which coupled the volume of fluid(VOF) method with the k-ε turbulence mathematical model. Then, the water hydrodynamic characteristics and transport processes for BOD_5, NH_(3^-)N and TP were analyzed. The results showed that the water surface of convex bank was a little lower than that of concave bank due to the centrifugal force near the bend, and most concentrations were inferior to the type Ⅴ standard indexes of surface water environmental quality. The model validation indicated that the errors between the simulated and monitored values were comparatively small, satisfying the application demands and providing scientific basis and decision support for the restoration and protection of water quality.

Water Quality Model Establishment for Middle and Lower Reaches of Hanshui River,China

With the development of industry and agriculture,nitrogen,phosphorus and other nutrients in the Hanshui River greatly increase and eutrophication has become an important threat to the water quality of the Hanshui River,especially in the middle and lower reaches.The primary objective of this study was to establish the water quality model for the middle and lower reaches of the Hanshui River based on the model of MIKE 11.The main pollutants migration and transformation process could be simulated using the water quality model.The rainfall-runoff model,hy-drodynamic model and water quality model were established using MIKE 11.The pollutants,such as chemical oxygen demand(COD),biochemical oxygen demand(BOD),ammonia nitrogen,nitrate nitrogen,phosphorus,dissolved oxy-gen(DO),were simulated and predicted using the above three models.A set of methods computing non-point source pollution load of the Hanshui River Basin was proposed in this study.The simulated and observed values of COD,BOD5,ammonia,nitrate,DO,and total phosphorus were compared after the parameter calibration of the water quality model.The simulated and observed results match better,thus the model can be used to predict water quality in the fu-ture for the Hanshui River.The pollution trend could be predicted using the water quality model according pollution load generation.It is helpful for government to take effective measures to prevent the water bloom and protect water quality in the river.

An integrated measurement and modeling methodology for estuarine water quality management

This paper describes research undertaken by the authors to develop an integrated measurement and modeling methodology for water quality management of estuaries. The approach developed utilizes modeling and measurement results in a synergistic manner. Modeling results were initially used to inform the field campaign of appropriate sampling locations and times, and field data were used to develop accurate models. Remote sensing techniques were used to capture data for both model development and model validation. Field surveys were undertaken to provide model initial conditions through data assimilation and determine nutrient fluxes into the model domain. From field data, salinity re- lationships were developed with various water quality parameters, and relationships between chlorophyll a concentrations, transparency, and light attenuation were also developed. These relationships proved to be invaluable in model development, particularly in modeling the growth and decay of chlorophyll a. Cork Harbour, an estuary that regularly experiences summer algal blooms due to anthropogenic sources of nutrients, was used as a case study to develop the methodology. The integration of remote sensing, conventional fieldwork, and modeling is one of the novel aspects of this research and the approach developed has widespread applicability.

Water quality changing trends of the Miyun Reservoir

In order to simulate changes in the water quality of the Miyun Reservoir dueto continuous descent of surface water level, a 3-D ecological hydrodynamic model was developedthrough coupling the water quality analysis simulation program (WASP) with the environmental fluiddynamics code (EFDC). The model was then calibrated and verified. Four scenarios (S1, S21, S22 andS23) were simulated using the model. Results show that the water quality of the Miyun Reservoirunder conditions of low surface water level is apparently affected by different amounts of inflowand different total phosphorus (TP) loadings. The chlorophyll-a concentration might exceed 10 μg/Lin many areas of the Miyun Reservoir (This limitative value is seen as a critical value ofeutrophication) when large loadings of TP enter due to the amount of inflow increasing. Results ofscenario S23 indicate that control of TP loadings can decrease chlorophyll-a concentrationeffectively, and the water quality of the Miyun Reservoir will improve or retain its status quo.

Three-dimensional hydrodynamic and water quality model for TMDL development of Lake Fuxian,China

Lake Fuxian is the largest deep freshwater lake in China. Although its average water quality meets Class I of the China National Water Quality Standard （CNWQS）, i.e., GB3838-2002, monitoring data indicate that the water quality approaches the Class II threshold in some areas. Thus it is urgent to reduce the watershed load through the total maximum daily load （TMDL） program. A three-dimensional hydrodynamic and water quality model was developed for Lake Fuxian, simulating flow circulation and pollutant fate and transport. The model development process consists of several steps, including grid generation, initial and boundary condition configurations, and model calibration processes. The model accurately reproduced the observed water surface elevation, spatiotemporal variations in temperature, and total nitrogen （TN）, total phosphorus （TP）, and chemical oxygen demand （COD） concentrations, suggesting a reasonable numerical representation of the prototype system for further TMDL analyses. The TMDL was calculated using two interpretations of the water quality standards for Class I of the CNWQS based on the maximum instantaneous surface and annual average surface water concentrations. Analysis of the first scenario indicated that the TN, TP and COD loads should be reduced by 66%, 68% and 57%, respectively. Water quality was the highest priority; however, local economic development and cost feasibility for load reduction can pose significant issues. In the second interpretation, the model results showed that, under the existing conditions, the average water quality meets the Class I standard and therefore load reduction is unnecessary. Future studies are needed to conduct risk and cost assessments for realistic decision-making.

The Hydrodynamic Behaviour of Euboean Gulf Coastal Areas and the Mixing of the Physico-Chemical Characteristics of Urban Sewage Discharged into Them under the Influence of Climate Change

The hydrodynamic circulation within the marine environment is a complex phenomenon, characterized by the interplay of strong tidal forces, atmospheric influences, and bathymetric features. The physical and hydrodynamic attributes of this flow play a pivotal role in promoting vertical mixing of seawater masses, thereby facilitating the integration of their physical and chemical parameters, including nutrients and oxygen. Additionally, they are instrumental in governing the dispersion and diffusion of pollutants originating from urban sewage, contributing to the overall water renewal process and environmental quality. This study investigates the potential impact of anticipated increases in average air temperatures on water column stratification in coastal regions susceptible to these dynamic influences. These areas receive treated urban sewage, and the study aims to assess how these temperature changes might influence the dispersion and mixing of pollutant loads present in these coastal waters.

核电工程异形水箱流固耦合分布式参数模型与效用研究

在流固耦合动力分析领域,传统的Housner模型在工程设计中发挥重要作用。但其理论推导仅适用于规则水箱,采用集中质量总体模型描述液体晃动的整体效应,难以有效模拟异形水箱储液结构的局部精细响应,亟须建立适用于不规则水体晃荡的分布式附加质量模型。基于势流理论推导了一种模态综合法模型,实现了分布质量与储液器壁激振加速度的解耦。该模型能够有效剥离分布式的脉冲质量与对流质量;同时,实体网格的振型分析适用于任意形状水体的动力分析。通过算例的形式将该模型与精细声学-结构耦合(Acoustic-Structural coupling,CAS)模拟法进行了比较,验证了模型的精确性与可靠性。最后,基于本文的模型研究了核电异形的安全水箱在不同水位和减晃格栅分布下的动力响应规律,并检验了其在工程中的适用性。

平原河网水动力优化调度与水环境改善的响应关系研究

平原河网河道流动性较差是引起水环境污染严重的主要原因,引调水是改善平原河网地区水环境的重要措施之一。本文以佛山市三山围为例,基于实测资料构建了河网水动力水质耦合模型,采用15天的连续水动力水质监测数据对模型进行了验证,并将NSE和RMSE模型评价指标用于模型评价。同时结合地势、潮汐规律和景观水位等设计了4种闸控模式和7种景观控制水位,共28种模拟工况,模拟分析了不同条件下的水动力水质改善与内外江潮位变化、引排水流量及其空间分布、闸控方式和景观水位等综合响应机理。结果表明:构建的模型合理可靠。研究区域受引排水路径的影响,河道流动性差异较为显著。综合考虑河道流量分布、水流路径、分汊河道分流作用和外江污染物浓度等对河道水质的作用效果并有效结合潮汐河网的动态水环境容量和污染源排放的时空分布对水环境的改善作用将非常显著。与低景观控制水位相比,高景观控制水位的内江动态水环境容量相对较大,污染物浓度较低。景观控制水位从0.2 m上升至0.8 m时,不同引调水路径的引水流量上升28.00%~64.70%,断面氨氮浓度削减了0.85~5.50 mg/L,削减比例达到28.89%~67.23%。本研究为平原潮汐河网水环境优化调度研究提供了新的思路,为相关部门对平原河网的水环境改善提供了重要的参考。

Three-dimensional numerical modelling of water quality in Dahuofang Reservoir in China

A three-dimensional eutrophication model was applied to assist the management of Dahuofang Reservoir in China.Transport processes were obtained from the three-dimensional,finite volume hydrodynamic model.The hydrodynamic model was verified for a one-year time period in 2006.Our simulation reproduced intra-annual variation of stratification.The simulated variation of vertical thermal structures also matched observations.The water quality model included 8 state variables,including dissolved oxygen,phytoplankton as carbon,carbonaceous biochemical oxygen demand,ammonium nitrogen,nitrate and nitrite nitrogen,ortho-phosphorus,organic nitrogen,and organic phosphorus.Sensitivity of the parameters has been analyzed to decide which process would affect the water quality in the simulation.The water quality verification suggested the model successfully computed the temporal cycles and spatial distributions of key water quality components.The comparison between water quality components before and after the first phase of the water conveyance project suggests that the project has a slight effect on the reservoir ecosystem.The model could be used as a tool to guide physico-biological engineering design or management strategies for Dahuofang Reservoir.

考虑水动力条件及水系连通的平原河网圩区畅流活水方案

针对平原河网地区水动力条件不足等问题,以嘉兴市新塍镇为例,探究不同畅流活水方案对河道水质的改善效果。构建MIKE11水动力学水质耦合模型,分析“引水/水系连通—水质”驱动响应规律,以NH3-N浓度为主要指标,分析不同活水方案的水质改善效果,并提出优化调控方案。结果表明,集中引水对区域水质改善影响较小,分散设置多个引水点可明显提高水质;直接对水质较差河道进行补水,污染物消减率在8%~30%之间,水质改善效果较明显;合理的水系连通工程可进一步增加畅流活水方案水质改善效果。

THREE－DIMENSIONAL MODELLING OF HYDRODYNAMICS AND WATER QUALITY IN COASTAL WATERS

Dalian Bay is a large coastal embayment situated in the Yellow Sea. The bay is heavily industrialised and the surrounding water they receives large amounts of industrial effluent. A numerical model of water quality in Dalian Bay has been developed to study the long-term transport and fate of pollutants in the system. In order to model the water quality of an estuary or coastal area many interdependent processes need to be simulated. These may be conveniently separated into three main groups: transport and mixing processes, biochemical interaction of water quality variables and the utilization and re-cycling of nutrients by living matter.The waters of Dalisn Bay are stratified due to the density variations resulting from the seasonal variations in meteorological conditions. In order to simulate the vertical structure of the hydrodynamics and pollutant transport in the bay the three-dimensional segmented and layered hydrodynamic model has been utilised. The results are used to drive the water quality model which simulates full oxygen and nutrient balance, primary productivity and the transport,reaction mechanism and fate of pollutants. The model has been used to study seasonal effects.The model has been calibrated against a limited data set of historical water quality observations and in general demonstrates excellent agreement with all available data.

基于Delft3D的大辽河水动力水质数值模拟

近年来,大辽河流域工业化发展迅速,带来了一系列水质恶化问题。因此,通过实测大辽河水文和水质数据,基于Delft3D建立大辽河二维水动力模型,对其进行水位和水温验证,计算值与实测值基本吻合;在水动力模型的基础上建立水质模型,对其进行NH^(+)_(4)-N(氨氮)和DO(溶解氧)验证,计算结果基本能够反映真实水质变化趋势。通过验证后的水动力水质耦合模型分析大辽河水动力水质输移特征。结果表明,大辽河具有明显的半日潮特征,河口处的流速低于内陆河道的流速;NH^(+)_(4)-N浓度年际分布较为均匀,DO浓度夏季较低,冬季较高;涨潮时,河口处NH^(+)_(4)-N浓度降低,落潮时河口处NH^(+)_(4)-N浓度升高;汛期排放的污染物浓度峰值高于枯水期的值,峰现时间也早于枯水期,在枯水期,污染物更容易在河口处滞留;整合排污口和减排两种方式均能降低河道内污染物浓度,靠近河道上游整合排污口方式优于减排方式,靠近河口减排方式略优于整合排污口。研究成果可为大辽河水质管理提供参考。

数字孪生丹江口水质模型关键技术与应用

数字孪生技术作为近年来的创新技术,通过构建精确的虚拟模型实现了对实际物理世界的高度映射,为解决传统水质安全管理中的难题提供了全新的视角和方法。水质模型是实现数字孪生湖库水质安全精准映射和虚实互动的核心。围绕南水北调中线工程的水源地——丹江口水库的水质安全管理需求,针对传统模型存在的模拟失真、误差累积、计算速度慢及无法满足突发污染事件实际决策要求等各种技术难题,提出了一种新型三维水动力水质模型,并利用实地流场观测和水质监测数据进行了模型校验。结果表明:该模型主要改进了组合σ/z网格、总磷本构方程、突发污染投药处置模拟、OpenMP并行计算、水动力预计算和双时间步长模式、污染团扩散轨迹示踪等关键技术,显著提升了模型的计算效率和模拟精度;通过在2023年汉江秋汛期间对丹江口水库水质安全管理的实际应用,证明了该模型能有效支持水质安全“四预”功能(预报、预警、预演、预案),模拟结果为汉江秋汛防御及汛后蓄水水质安全保障提供了重要技术支撑。

汉江中下游水质时空特征及环境流量确定

近年来,汉江中下游水质问题频发,且河道内环境流量尚未明确,严重威胁沿岸用水安全。为探明汉江中下游水质时空分布特征和河道环境流量,收集调研了2015—2019年汉江中下游黄家港、襄阳、皇庄、沙洋、潜江、仙桃和汉川等7个控制断面的pH、溶解氧、高锰酸盐指数、氨氮、总磷5项水质指标,基于水质单因子评价方法分析了水质时空变化特征。通过建立一维水动力-水质模型,构建了基于保障各控制断面水质的环境流量计算方法;根据不同水源的输入,计算了汉江中下游河道环境流量,并提出了保障方案。结果表明,汉江中下游丰水期氨氮和枯水期总磷在皇庄以下断面均未达到Ⅱ类水标准,氨氮沿程变化不明显,总磷从上游至下游逐渐升高。环境流量保障需结合引江济汉补水工程和丹江口下泄流量,丰水期和枯水期当引调长江水分别为500 m^(3)/s和350 m^(3)/s时,还需丹江口水库分别下泄214 m^(3)/s和315 m^(3)/s才能满足河道内的环境流量。研究为汉江中下游水质安全保障和合理分配丹江口水资源提供了参考。

不同调水方案对沙湖水动力及水质影响研究

由于地处降雨量少、蒸发量大的特殊地理环境,沙湖每年都需要调水引流以达到改善水质和维持总体水量的目的。因此调水水量及调水路线的选取对沙湖水质改善有关键的影响。文章基于环境流体力学模型(Environmental Fluid Dynamic Code,EFDC)模型构建了沙湖水动力-水质模型,模拟沙湖水动力、总氮和总磷的时空分布特征,发现与实际数值拟合度较高;并基于沙湖实际调水方案,设置四种调水方案,探究了不同调水方案对沙湖水动力及水质的影响。结果表明调水引流工程能有效加快沙湖水体流速同时降低总氮、总磷浓度,但也会造成沙湖水质波动。相较于减水方案,增水方案对提高沙湖水体流速和降低总氮、总磷浓度的效果更好;与八一渠入流相比,东干渠入流更利于提升沙湖水体流速和降低沙湖总氮、总磷浓度。总体而言,4种调水方案中方案一(增水方案)是改善沙湖水动力条件和水质的最佳方案。

北江下游河道地形演变及其对物质输运的影响分析

基于1998、2012和2020年三期河道实测地形数据,较为系统地研究了北江下游石角-三水河段近20年来河道地形的时空变化特征,同时采用有限体积法建立研究区域二维水动力水质耦合模型,定量研究了不同地形和洪水量级下石角-三水河段水力滞留时间的空间分布。研究结果表明,1998-2012年该段河道存在明显冲刷,研究区域平均高程降低2.9 m,平均深泓点高程降低7.8 m,河道断面存在显著的由宽浅向窄深发展的趋势;2012-2020年,研究区域平均高程降低0.7 m,平均深泓点高程增加0.4 m,变幅显著低于1998-2012年,河道断面形态趋于稳定。研究区域水力滞留时间的空间分布表现为从上游至下游逐渐增大,且河道中心的水力滞留时间一般低于两岸。在同一地形条件下,洪水量级越大,研究区域水力滞留时间越小,物质输运速度越快;在2020年地形条件下,P=1%时出口位置水力滞留时间为11.99 h,低于P=5%时的12.69 h及P=20%时的13.08 h;从时间尺度来看,1998-2020年研究区域平均水力滞留时间增加0.72~0.75 h,出口位置水力滞留时间增加2.20~2.35 h。通过对比出口位置水力滞留时间与区间内各水文站点平均流速,发现二者呈显著的负相关性,并最终采用幂函数建立水力滞留时间的估算公式。相关研究成果可为今后北江下游突发污染事故的预警和管理提供科学参考。

基于MIKE21研究生态补水对巢湖水质时空分布的影响

选取引江济淮工程中引江济巢段的2条生态补水路线,设计3种生态补水方案:方案一为西兆线、菜巢线双线引入巢湖,经裕溪河巢湖闸流出;方案二为兆河单线引入巢湖,由白石天河的白山节制枢纽流出;方案三为生态补水经兆河单线进入巢湖,经裕溪河巢湖闸流出。利用MIKE21软件建立巢湖水动力水质耦合模型,模拟巢湖水动力和水质时空变化过程及4个敏感区域(南淝河入湖口、峔山岛、忠庙和饮用水水源地)的水质改善效果。总体看来,方案二对南淝河入湖口、峔山岛、忠庙水质改善效果最优,而方案三使饮用水水源地总磷(TP)浓度降幅最大。方案二降低了峔山岛、忠庙区域蓝藻暴发的潜在风险,使总氮(TN)/TP分别从14.7、13.4降至7.4、4.0;方案三使饮用水水源地的TN/TP从10.0降至4.8,降低了饮用水水源地蓝藻暴发的潜在风险,但3个生态补水方案中南淝河入湖口区域的TN/TP均在15~20,表明蓝藻暴发风险依然较高。引江济巢工程对巢湖水环境改善有积极的效果,可以保证巢湖市饮用水水源地的水质安全,但由于西半湖的水动力环境未得到改善,蓝藻暴发的潜在风险依然较高,因此,要优化生态补水方案,并有效控制入湖河流流域的地表径流污染、农业面源污染及城市合流制系统的溢流污染。

长江下游河湖水系连通的生态效应与联合调度

现行的水系连通工程规划和实施普遍侧重于水资源调度、防洪抗旱和航运畅通等需求,对连通河湖水生态环境质量的影响机制和协同管理措施仍不明确。引江济太等水系连通工程在恢复长江下游水系连通性的同时,会引起河湖水位、水动力、水沙输移、水质等要素变化,促使水体和底质生境条件改变,导致河湖关键生物种群、生态系统结构及“清水草型”/“浊水藻型”生态类型动态演替,从而深刻影响河湖生态环境。在梳理河湖水系连通联合调度方法的基础上,提出开展长江下游河湖水系连通工程的科学调控,需将水文水动力联动、生境条件变化、生态系统响应、水系连通动态调控有机结合起来,系统分析水系连通下相连河湖的生态响应机理,建立水动力-水质-水生态耦合模型进行仿真模拟,提出保障防洪安全、生态流量、循环畅通的多目标联合调度方案,充分发挥其在水网建设、河湖生态环境复苏等方面的成效。