Environmental Fluid Dynamics Code Research Articles

Modeling the transport of titanium dioxide nanomaterials from combined sewer overflows in an urban river

Combined sewer overflows (CSOs) occur frequently in the United States, discharging an estimated 3.2 billion cubic meters of untreated sewage into receiving waters every year. These discharges contain a variety of contaminants including engineered nanomaterials (ENMs), yet ENMs discharged through CSOs have not been taken into account in ENM fate and transport models. This study fills this knowledge gap by developing a new integrated model that links an urban hydrologic-hydraulic model, using the Storm Water Management Model (SWMM), with a three-dimensional hydrodynamic and water quality model of rivers, using the Environmental Fluid Dynamics Code (EFDC). The modeling framework was applied to predict the concentrations of titanium dioxide (TiO2) ENMs in the Buffalo River in Buffalo, New York, as a result of CSO events. CSOs are shown to have a potential for transient high concentrations of ENMs and thus potentially high localized risk near the CSO outfalls and deposition zones in the river. The present approach provides a promising modeling framework to simulate ENM fate and transport in urban waterways. The model presented in this study can help build a management tool to predict temporally and spatially varying concentrations of ENMs introduced into receiving waters through CSOs.

Modelling the Impacts of Bathymetric Changes on Water Level in China’s Largest Freshwater Lake

A recent dramatic decline in water level during the dry season in China’s largest freshwater lake (Lake Poyang) significantly influenced water availability and biogeochemical processes. To learn the potential causes of water level decline, this study investigated the hydrodynamic response to bathymetric changes during three typical hydrological years by scenario simulation using Environmental Fluid Dynamics Code (EFDC). The simulation results indicated that bathymetric changes resulted in a water level decrease during a low water level period. Inter-annual variation in the decrease rate implied that water level in typical dry and wet years were influenced more significantly than that in moderate hydrological years. A spatial gradient in the distribution of water level changes was also observed, which was mainly concentrated in the main channel. Water velocities also slowed down, weakly corresponding to the decrease in water level during the low water level period. Overall, bathymetric changes caused by sand mining contributed to water level and velocity variations, influencing the stability and sustainability of the lake ecosystem. This study can potentially enhance our understanding of the hydrodynamic processes in Lake Poyang and support water resource management.

Drag coefficient parameter estimation for aquaculture systems

The flow conditions in and around a suspended canopy, resembling those formed by aquaculture structures such as rafts cages and longlines, were modeled using an augmented version of the hydrodynamic model Environmental Fluid Dynamics Code. The model was calibrated using vertical profiles of horizontal velocities, Reynolds stresses, and turbulent kinetic energies obtained from prior laboratory flume experiments. The parameter estimation code, PEST, was used to optimize various model parameters including horizontal momentum diffusivity, vertical eddy viscosity, turbulence closure constants, and, most importantly, depth-dependent drag coefficients. An increasing average drag coefficient was observed with decreasing canopy blockage ratio, and an empirical relationship for the vertical variation of drag coefficient was developed that may be appropriate for use in full-scale models of aquaculture systems. Overall, the calibrated canopy-turbulence parameters and drag-coefficient empiricisms may yield improved predictions of alterations to hydrodynamic and nutrient-transport conditions due to various aquaculture structures. Such predictions will help develop methods to minimize environmental impacts and to increase production from aquaculture farms.

Optimization and Effect of Inner Water Diversion and Distribution in the West Lake of Hangzhou

West Lake is a world-famous landscape in Hangzhou, listed on the World Heritage list. In 2003, Hangzhou municipal government implemented the project of water diversion project, which diverted 400,000t/d water from Qiantang River into West Lake, thus, improved the overall water quality of West Lake significantly. However, due to the zigzag lakeshore line and the inlake embankment separation, the diverted water could not fully exchange among different regions of the lake, therefore, high concentration region of nutrient and cyanobacteria outbreak risk still existed in some lake bays. On the basis of spatial water quality analysis, this study put forward the internal water diversion and distribution scheme of the West Lake. Total phosphorus (TP) model with Environmental Fluid Dynamic Code (EFDC) was built to study the optimum water diversion quantity and distribution layout. According to the numerical result, the recommended water diversion scale was 70,000t/d, the layout of diversion and distribution recommended was “2 in 3 out”. The internal water diversion and distribution project was complemented in October 2015. According to the comparison of water quality before and after the project construction, the improvement rates of TP, TN and Chlorophyll A were 26.0%, 8.9% and 25.9% respectively, and the dead water area was reduced from 35% to 13%, which greatly improved the water environment of the water diversion area.

Integrated sediment transport process modeling by coupling Soil and Water Assessment Tool and Environmental Fluid Dynamics Code

Reservoir sedimentation is a major environmental issue, and integrated sediment modeling provides a holistic picture of the sediment transport processes in watershed management planning. This study proposes a sediment modeling framework by coupling a watershed loading model, Soil and Water Assessment Tool (SWAT), with a receiving water-body model, Environmental Fluid Dynamics Code (EFDC). In the proposed framework, upstream sediment load estimates made by SWAT are dynamically linked to EFDC to predict sediment deposition in a reservoir, facilitating multiple model runs required for what-if scenario analyses in developing sediment management plans and for optimization using sampling-based search algorithms. The modeling framework was applied to predict the spatial distributions of sediment depositions in an agricultural reservoir and quantify their uncertainty. This article introduces how the two models, SWAT and EFDC, are linked for integrated sediment modeling and demonstrates how the proposed framework can be applied in a case study.

Spatial–temporal distribution and limiting factor variation of algal growth: three-dimensional simulation to enhance drinking water reservoir management

Although algal growth in drinking water reservoirs has attracted worldwide attention, its spatial–temporal distribution and limiting factor variation are still not well described. In this study, three-dimensional environmental fluid dynamic code of Miyun reservoir had been established and numerical simulation was conducted to reveal the detailed temporal–spatial variation and interrelationship of temperature, total nitrogen, total phosphorous, chlorophyll a at specific time points and locations in a drinking water reservoir in China. The limiting effect of light, temperature, nitrogen and phosphorus on algae growth was also quantified throughout the year. The results suggested that thermal stratification and internal sources of nutrients played an important role in the algal bloom development; the surface layer of shallow regions was identified as the originating algal habitat. The dominant controlling factors for algal growth varied throughout the year. Temperature was the main limiting factor before May 4 and after November 25, while total phosphorous became the dominant limiting factor from May 4 to November 25. Variation of chlorophyll a and phosphorous concentration was closely related during the phosphorous limiting period. This study suggests that comprehensive measures, including external nutrient reduction, internal nutrient reduction and mixing condition improvement, should be implemented to reduce algal bloom events.

Mass balance analysis and calculation of wind effects on heat fluxes and water temperature in a large lake

Abstract Modeling applications often ignore the water mass balance for hydrodynamic simulations in large lakes such as the Great Lakes. However, evaluation of the water budget can be of interest, especially when water surface calculations are important, and also as it relates to the heat budget. In this study Lake Ontario is modeled using the Environmental Fluid Dynamics Code for the heating seasons in 2008–2013, with calibration focused on 2008, for which more data are available. The model is used to test both water mass and heat budgets, and various interpolation schemes for meteorological data are tested to determine the degree of sensitivity of results to the interpolation method used. The water budget incorporates flow from major tributaries and precipitation/evaporation, and it is shown that these processes alone cannot provide a balance. Missing water quantities include direct runoff and flows from smaller, probably ungauged tributaries. In 2008 the calculated quantity is 1.61 × 1010 m3 during April to September, which is equivalent to a change in water surface level of 0.7 m and represents an average flow rate of 1018 m3/s, which is larger than the inflow of any tributary to the lake except the Niagara River. Latent and sensible heat flux calculations are highly affected by wind, and interpolation of wind data is found to impact model calculations of those quantities, though different interpolation schemes do not have a strong effect on surface water temperatures. In general, the natural neighbor interpolation method is preferred over inverse distance methods.

Effect of low temperature water discharged from large reservoir on aquatic ecosystem and agricultural production

Low temperature water discharged from large reservoirs caused a lot of environmental problems, which consist of the impairment of downstream aquatic ecosystem and agricultural production. In order to quantify the impact of low temperature water discharged from large reservoir, an ecological survey and water temperature measurements were carried out on Gangkouwan Reservoir in Anhui province China. The Environmental Fluid Dynamics Code (EFDC) was employed to study the vertical water temperature profile and estimate the temperature of water released from Gangkouwan Reservoir in different hydrological year. And a measure was proposed for alleviation of the negative effects of the low temperature water.

The spatial and temporal distribution of metals in an urban stream: A case study of the Don River in Toronto, Canada

Abstract Widespread growth of cities, the association of trace metals with urban runoff, and the potentially deleterious effect of metals on aquatic ecology have made it important to understand the distribution and transport of metals through surface water channel networks. The Don River in Toronto, Canada has been identified as an Area of Concern for pollution to Lake Ontario, with historically high levels of metal contamination. Sampling programs are sparse, therefore a model is needed to understand the spatial and temporal variability of metals in the river network. The objectives of the current study are to: i) describe the sampled spatial and temporal variability of metals in the Don River and ii) develop a modelling strategy to describe within flood metal transport dynamics. A model setup tool is developed that links Storm Water Management Model (SWMM) with the Environmental Fluid Dynamics Code (EFDC) to allow a seamless transition from catchment hydrology to in-stream hydraulic and chemical processes. Results show that lead pollution in the Don River is decreasing, likely as a result of policy changes and sediment dredging in the mouth of the river. However, zinc and copper pollution are increasingly problematic, with copper exceeding recommended lower guidelines, particularly during floods. Model results confirm that most of the sediment and metals are transported in relatively short bursts within longer flood durations and are stored in depositional hotspots within the Lower Don River. A better monitoring strategy is needed to understand and more accurately parametrize these processes in an urban river system.

Developing an EFDC and Numerical Source-Apportionment Model for Nitrogen and Phosphorus Contribution Analysis in a Lake Basin

The numerical source-apportionment model is an efficient and useful method for analyzing water-quality responses to nutrient loading in rivers and lakes. In this study, the Environmental Fluid Dynamic Code (EFDC) and numerical source-apportionment model were applied to Lake Bali in Jiujiang City, China to predict the contributions of various pollution sources to the lake at any time and position. We calibrated and validated the model by comparing its predictions with observed hydrodynamic and water-quality parameters from 2014 to 2015. Application of the calibrated model to simulate water-quality responses to a pollution source showed that the contribution of a pollution source to water quality in the lake has strong spatial heterogeneity. The results provide useful information for the optimization of pollution load reduction in Lake Bali and can be used to determine the most effective implementation of its pollution-control plan. The model built in this study can also be used for pollution source-apportionment in other urban lakes and is superior to other traditional source-apportionment models.

Numerical simulation of water age and its potential effects on the water quality in Xiangxi Bay of Three Gorges Reservoir

After the impoundment of Three Gorges Reservoir, algal blooms frequently occurred in the tributaries of the reservoir, which has posed a great challenge for the local aquatic environment and ecology. To investigate the main causes and key factors of the algal blooms, the Environmental Fluid Dynamics Code (EFDC) model is applied to the simulation of the three-dimensional hydrodynamics and water quality in the Yangtze River and Xiangxi Bay, and the concept of water age is adopted to quantitatively analyze the effects of hydrodynamics on the water quality by linking water age and phytoplankton levels, which has seldom been explored in previous studies. The model results show good agreement with the field data, and the simulation reproduces the thermal stratification and density current in Xiangxi Bay. The results show that Xiangxi Bay exhibits quite complicated hydrodynamic characteristics, and could be divided into different zones according to the transport process. In the upper reach, the water quality is mainly affected by the upstream inflows, while it is mainly affected by the intrusion flow from the mainstream near the river mouth. Water age and water temperature are found to be the key factors influencing the algal blooms in Xiangxi Bay. Besides, a significant positive correlation has been found between the chlorophyll a (chl-a) concentration in the surface layer and the water age of the dominant water source. This conclusion can be adopted to interpret the longitudinal distribution of chl-a concentration and to explain why Xiangxi Bay is susceptible to algal blooms. The correlation between water age and chl-a concentration is further used to evaluate the effectiveness of water level fluctuation in preventing algal blooms. The analyses and findings in this study could help to better understand the complicated hydrodynamic and water quality processes in Xiangxi Bay following the impoundment, and provide insights into ecological and environmental management of Three Gorges Reservoir.

Numerical Simulation of Fortnightly Modulations of the Convergence Zone by Residual Volume Transport in a Macrotidal Estuary

ABSTRACT Woo, S.-B. and Yoon, B.I., 2018. Numerical simulation of fortnightly modulations of the convergence zone by residual volume transport in a macrotidal estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 606–610. Coconut Creek (Florida), ISSN 0749-0208. This study examines the fortnightly modulation of convergence zone by residual volume transport of main channel using a numerical model in the tidally dominated Han River estuary (HRE), South Korea. The numerical model, EFDC (Environmental Fluid Dynamics Code), was simulated for 124 days, from May to August 2009, and used observed freshwater discharge for major rivers of HRE. The residual volume transport discharged into the HRE from the Yeomha channel and Seokmo channel had a ratio of 44:56 over thirty days under normal freshwater conditions. The model results show that a temporal variation of the ...

An Integrated Method for Accounting for Water Environmental Capacity of the River–Reservoir Combination System

The security of drinking water is a serious issue in China and worldwide. As the backup source of drinking water for the Changde City in China, the Huangshi Reservoir suffers from the threat of eutrophication due to the water quality of the reservoir ecosystem being affected by the tributaries that carry Non-Point Source (NPS) pollutants. The calculation of the water environmental capacity (WEC) can provide a scientific basis for water pollution control, which refers to the maximum amount of pollutants that the water can accommodate. In this paper, according to the hydrological characteristics of the river–reservoir combination system, a one-dimensional (1-D) water quality model and the Environmental Fluid Dynamics Code (EFDC) model were chosen to calculate the water environmental capacity of each functional zone in this basin. The quantity control of pollution from the tributaries was conducted based on the combined results of the water environmental capacity calculation from the EFDC model and a one-dimensional (1-D) river water quality model. The results show that total water environmental capacity of the tributaries included a chemical oxygen demand (COD) of 421.97 tons; ammonia nitrogen (NH3-N) of 40.99 tons; total nitrogen (TN) of 35.94 tons; and total phosphorus (TP) of 9.54 tons. The water environmental capacity of the Huangshi Reservoir region accounts for more than 93% of the total capacity. The reduction targets of the major pollutants in the Huangshi Reservoir and its four major input rivers, which are, namely, the Bamao River, the Longtan River, the Fanjiafang River, and the Dongtan River, have been determined to achieve the water quality objectives for the reservoir in 2020 and 2025. The results will be helpful for the local water quality management and will provide a valuable example for other similar water source reservoirs.

Parameter uncertainty and sensitivity analysis of water quality model in Lake Taihu, China

Lake Taihu was chosen as a case for parameter uncertainty and sensitivity analysis of water quality simulation in large shallow lakes. Forty parameters in Environmental Fluid Dynamic Code model (EFDC) were filtered and analyzed. The results showed that parameters had a considerable influence on simulation and three groups of parameters related to algal kinetics (i.e. PMc, BMRc and PRRc), light (KeChl) and temperature (KTG1c) were very sensitive. For shallow lakes with frequent algal blooms, light extinction due to Chlorophyll-a is also a sensitive parameter. While the temperature effect coefficient for algal growth is sensitive for lakes with seasonal temperature variation. Sensitive parameters and their relevant uncertainty varied spatially. For high nutrients and algae concentration subareas, temperature was more likely to be a limiting factor, whereas sensitive factors could be light in lower concentration subareas. Since most sensitive parameters were related to algae, uncertainty in simulation increased with increasing algal kinetic processes over time and varied in different subareas. Lower nutrients and algae concentration subareas were more easily influenced by model parameters while nearshore areas were highly influenced by boundary conditions. For better simulation of water quality, variable stoichiometry phytoplankton models should be considered and zooplankton need to be integrated into the model explicitly rather than a fixed predation rate.

Analysis and modeling of algal blooms in the Nakdong River, Korea

The purpose of this study is to improve the prediction accuracy of algal blooms in the Nakdong River, Korea, to support improved management practices. To improve algal bloom predictions, it is necessary to consider the microbiological characteristics of algal groups. Therefore, Korean governmental data, including water quality, flow rate, and meteorological data, over 12 years (2004–2015) were analyzed to characterize chlorophyll a (Chl-a) concentration dynamics in the Nakdong River, as the primary indicator of algae. The correlation between water temperature and Chl-a concentration differed by region at the study site. While a positive correlation (R = 0.63) was found in the relatively clean (i.e., mesotrophic) upstream area, a negative correlation (R = −0.51) was found in the more eutrophic downstream area. These results indicate that nutrients are a dominant factor of algal blooms in mesotrophic upstream areas, but other factors may have greater impacts in eutrophic downstream areas. Moreover, the dominance of different algal groups differed spatially and temporally at the study site. The three-dimensional hydrodynamics and water quality modeling-capable Environmental Fluid Dynamics Code model was applied to represent the hydrodynamics and kinetics of water quality variables, including Chl-a. Four statistics, the coefficient of determination (R2), Nash–Sutcliffe model efficiency (ME), percentage model bias (Pbias), and cost function (CF), were used to evaluate the model prediction accuracy against field observation data. Compared to the case in which only a single algal group was modeled, modeling multiple algal groups together improved the R2, ME, Pbias, and CF values from 0.25 to 0.50, 0.15 to 0.50, 30.43 to 4.98, and 0.56 to 0.48, respectively. The degree of improvement in the model prediction accuracy was greater for more eutrophic regions at the study site. These results show that there should be greater focus on studying multiple algal groups together when modeling algal bloom predictions to support the development of alternative management practices.

Using the EFDC model to evaluate the risks of eutrophication in an urban constructed pond from different water supply strategies

Managers of urban lakes are faced with the challenge of finding a balance between saving water resources and preventing eutrophication. One way to address both of these issues is to use the unconventional water source s such as stormwater and reclaimed water to maintain the water supply in urban constructed ponds. We validated and calibrated the Environmental Fluid Dynamics Code and then evaluated the risks of eutrophication from various water supply scenarios, such as different proportions of stormwater (SW), reclaimed water (RW), and tap water (TW). We found that the different types of water influenced the nutrient or Chla levels in the constructed ponds, but that there was little difference between different hydrological years. The range of the trophic state index in the study pond increased from 5.55% to 68.17% in the urban ponds as the proportion of RW increased from 0% to 100%. Stormwater collection strategies had a clear effect on the trophic state of TW-fed ponds but not of RW-fed ponds. Using an index that integrated the eutrophication risks, eutrophication state, and economic costs, we found that the optimal water supply strategy was to collect treated SW and use TW to replenish the water supply.

Environmental Flow for Sungai Johor Estuary

Sungai Johor estuary is a vital water body in the south of Johor and greatly affects the water quality in the Johor Straits. In the development of the hydrodynamic and water quality models for Sungai Johor estuary, the Environmental Fluid Dynamics Code (EFDC) model was selected. In this application, the EFDC hydrodynamic model was configured to simulate time varying surface elevation, velocity, salinity, and water temperature. The EFDC water quality model was configured to simulate dissolved oxygen (DO), dissolved organic carbon (DOC), chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N), nitrate nitrogen (NO3-N), phosphate (PO4), and Chlorophyll a. The hydrodynamic and water quality model calibration was performed utilizing a set of site specific data acquired in January 2008. The simulated water temperature, salinity and DO showed good and fairly good agreement with observations. The calculated correlation coefficients between computed and observed temperature and salinity were lower compared with the water level. Sensitivity analysis was performed on hydrodynamic and water quality models input parameters to quantify their impact on modeling results such as water surface elevation, salinity and dissolved oxygen concentration. It is anticipated and recommended that the development of this model be continued to synthesize additional field data into the modeling process.

Comparative Study on Assimilating Remote Sensing High Frequency Radar Surface Currents at an Atlantic Marine Renewable Energy Test Site

A variety of data assimilation approaches have been applied to enhance modelling capability and accuracy using observations from different sources. The algorithms have varying degrees of complexity of implementation, and they improve model results with varying degrees of success. Very little work has been carried out on comparing the implementation of different data assimilation algorithms using High Frequency radar (HFR) data into models of complex inshore waters strongly influenced by both tides and wind dynamics, such as Galway Bay. This research entailed implementing four different data assimilation algorithms: Direct Insertion (DI), Optimal Interpolation (OI), Nudging and indirect data assimilation via correcting model forcing into a three-dimensional hydrodynamic model and carrying out detailed comparisons of model performances. This work will allow researchers to directly compare four of the most common data assimilation algorithms being used in operational coastal hydrodynamics. The suitability of practical data assimilation algorithms for hindcasting and forecasting in shallow coastal waters subjected to alternate wetting and drying using data collected from radars was assessed. Results indicated that a forecasting system of surface currents based on the three-dimensional model EFDC (Environmental Fluid Dynamics Code) and the HFR data using a Nudging or DI algorithm was considered the most appropriate for Galway Bay. The largest averaged Data Assimilation Skill Score (DASS) over the ≥6 h forecasting period from the best model NDA attained 26% and 31% for east–west and north–south surface velocity components respectively. Because of its ease of implementation and its accuracy, this data assimilation system can provide timely and useful information for various practical coastal hindcast and forecast operations.

Algal bloom prediction of the lower Han River, Korea using the EFDC hydrodynamic and water quality model

The lower part of the Han River, which flows through Seoul, Korea, experienced excessive toxic cyanobacterial growth in 2015. Modeling of algal bloom occurrence patterns in the lower part of this river was performed using the Environmental Fluid Dynamics Code (EFDC) to understand algal dynamics and thus better develop management alternatives. For a 71km long river section, 1175 horizontal 2-D grid elements were developed. This grid system was determined adequate, as the maximum values of the Courant–Friedrichs–Lewy condition and orthogonality deviation were 0.5 and 20.1, respectively. Chlorophyll-a (Chl-a) was chosen as the primary indicator for the likelihood of algal blooms. Calibration and verification of EFDC were performed by comparing the model results to three years of field data collected from 2013 to 2015. Calibration accuracy was verified not only for physical variables, including the mean water level and temperature, but also for other water quality variables in various locations of the study area. To improve the prediction accuracy of Chl-a, three dominant groups of algae were considered: diatoms, green algae, and cyanobacteria. The optimum growth temperature ranges were selected based on field data for the study area. It was found necessary to apply different maximum growth rates for algal groups for the upstream and downstream regions of the study area to appropriately reflect field observations. This result indicates that more than three algal groups need to be included to improve Chl-a calibration accuracy for the study area, yet the current EFDC model can consider only up to three phytoplankton groups. Although this problem could be overcome by assigning different maximum growth rates for different regions, it may be necessary to improve EFDC so that it can include more phytoplankton groups.

Assessment of Water Quality Improvements Using the Hydrodynamic Simulation Approach in Regulated Cascade Reservoirs: A Case Study of Drinking Water Sources of Shenzhen, China

Water quality safety is of critical importance in environmental improvement, particularly with respect to drinking water resources worldwide. As the main drinking water sources in Shenzhen, China, the cascade reservoirs comprising the Shiyan, Tiegang, and Xili Reservoirs are highly regulated and have experienced water quality deterioration in recent years. In this study, a three-dimensional hydrodynamic and water quality model was established using the Environmental Fluid Dynamics Code (EFDC) for the cascade reservoirs. The relationships between water quality and improvement measures were quantified and the main pollution sources for individual reservoirs were identified. Results showed that the hydrodynamic and water quality model well captured the spatial and temporal variations of water level, the permanganate concentration index (CODMn), and total nitrogen (TN), with high resolution in the cascade reservoirs. The correlation coefficients between simulations and observations were close to 1.00 for water levels, and over 0.50 for CODMn and TN concentrations. The most effective methods for water quality improvement were the reduction of the runoff load for TN and transferred water load for CODMn in the Shiyan Reservoir, reduction of the transferred water load in the Tiegang Reservoir, and an increase in transfer water volume, especially in the flood season, in the Xili Reservoir. Internal pollution sources also played an important role in water pollution, and thus sedimentation should be cleaned up regularly. This study is expected to provide scientific support for drinking water source protection and promote the application of hydrodynamic model in water quality management.