Two-dimensional numerical algorithm for water quality modeling in the topographically complicated river

In this paper, a two dimensional numerical calculation algorithm for the water quality modeling in the Hengyang City section of the Xiangjiang River is researched considering the effect of the Dayuandu navigational key project. The research river is winding and has two branches resulted from an isle. The numerical calculation algorithm for the water quality modeling is set up on the basis of applying topographic map of the river course and the finite element method. The calculation result for the water quality modeling includes the concentration fields for various pollutants. The numerical calculation algorithm for the water quality modeling set up in this paper can be applied to shallow river with similar topographically complicated river course.

An alternating direction implicit （ADI） numerical model for two－dimensional hydrodynamic equations

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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.

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.

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.

Numerical study on water waves and wave-induced longshore currents in Obaky coastal water

In this paper, the water waves and wave-induced longshore currents in Obaky coastal water which is located at the Mediterranean coast of Turkey were numerically studied. The numerical model is based on the parabolic mild-slope equation for coastal water waves and the nonlinear shallow water equation for the wave-induced currents. The wave transformation under the effects of shoaling, refraction, diffraction and breaking is considered, and the wave provides radiation stresses for driving currents in the model. The numerical results for the water wave-induced longshore currents were validated by the measured data to demonstrate the efficiency of the numerical model. Then the water waves and longshore currents induced by the waves from main directions were numerically simulated and analyzed based on the numerical results. The numerical results show that the movement of the longshore currents was different while the wave propagated to a coastal zone from different directions.

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 relationships 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.

Modelling of water quality of Minjiang estuary

In order to establish economic development region at Mawei districtwhich is nearby downstream of Minjiang river and to answer the question of impact of economic development on water quality of Minjiang estuary, the analyses of hydrologic and hydraulic characteristics of Mawei reach of Minjiang tidal river, a two-dimensional mathematical model has been established and simulation of water quality was studied. The results show that the flushing time of a conservative pollutant during dry and raining period are 12 and 7 days respectively from Mawei to Minjiang mouth, the decay rate constants of BOD and NH3-N are 0.1 to 0.4 and 0.18 to 0.45 d-1 respectively. The capacity of dilution and assimilation for pollutants is larger.

A three-dimensional prediction system for water quality polluction in coastal waters

The hydrodynamics and water quality in Hakata Bay, Japan are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three\|dimensional hydrodynamics and water quality model has been developed to simulate the long\|term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal waters. It is a 3\|dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay.

Evaluation, prediction, and protection of water quality in Danjiangkou Reservoir, China

The water quality in the Danjiangkou Reservoir has attracted considerable attention from the Chinese public and government since the announcement of the Middle Route of the South to North Water Diversion Project(SNWDP), which commenced transferring water in 2014.Integrated research on the evaluation, prediction, and protection of water quality in the Danjiangkou Reservoir was carried out in this study in order to improve environmental management. Based on 120 water samples, wherein 17 water quality indices were measured at 20 monitoring sites, a single factor evaluation method was used to evaluate the current status of water quality. The results show that the main indices influencing the water quality in the Danjiangkou Reservoir are total phosphorus(TP), permanganate index(COD Mn), dissolved oxygen(DO), and five-day biochemical oxygen demand(BOD5), and the concentrations of TP, BOD5, ammonia nitrogen(NH3e N), COD Mn, DO, and anionic surfactant(Surfa) do not reach the specified standard levels in the tributaries. Seasonal Mann e Kendall tests indicated that the COD Mn concentration shows a highly significant increasing trend, and the TP concentration shows a significant increasing trend in the Danjiangkou Reservoir. The distribution of the main water quality indices in the Danjiangkou Reservoir was predicted using a two-dimensional water quality numerical model,and showed that the sphere of influence from the tributaries can spread across half of the Han Reservoir if the pollutants are not controlled.Cluster analysis(CA) results suggest that the Shending River is heavily polluted, that the Jianghe, Sihe, and Jianhe rivers are moderately polluted, and that they should be the focus of environmental remediation.

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。

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 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.

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.

A NUMERICAL MODEL OF FLOW FIELD AND WATER QUALITY FOR TIDAL REGIONS BASED ON TRIANGULAR MESHES

In tidal areas, natural land boundary is complex and underwater topography varies acutely due to influence of upstream runoff and outer tide. The simulation and forecast of water current and mass transport play an important role in practical engineering. According to the situation of irregular natural boundaries in tidal region, unsturctured triangular grid arrangement is applied to suit for complex conditions. A finite difference method with alternating directional implicit scheme for triangular grid is established in this paper. The model has been applied in calculation of flow and concentration fields for Nantong reach of the Yangtze River. It is satisfied that the calculated values are in agreement with observed data.

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。

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。

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。

基于断面水质达标的污水处理厂尾水排放浓度确认研究

我国在建设项目准入中实行“三线一单”生态环境分区管控制度,“环境质量底线”是其重要要素之一。研究以苏中水网地区某工业污水处理厂为例,遵循地表水环境质量底线要求,在满足控制断面(排污口下游2 km)主要水质污染因子浓度达标并预留安全余量的要求下,通过构建一维河网水动力水质耦合模型,建立污染源与水质响应关系,模拟分析丰、枯水期控制断面水质稳定达标时污水处理厂尾水的允许排放浓度,为区域水环境保护和管理工作提供技术支撑。