Environmental Fluid Dynamics Code Research Articles

Influences of increased daily repeated upstream releases and varying meteorological conditions on temperature distributions in a river-reservoir system

Temperature distribution in a river-reservoir system was simulated using a calibrated three-dimensional Environmental Fluid Dynamics Code model under various hypothetical weather conditions and daily repeated large releases (DRLRs) from the upstream boundary. Both DRLRs and weather conditions affect and control the formation and spread of density currents and then affect the bottom-layer temperatures. The DRLRs with longer durations (e.g., 6 or 8 hours) can relatively quickly push cooler release water to the Gorgas upstream monitoring station (GOUS) and the river intake. With the air temperature drops in the first 6 days, simulated bottom temperatures at GOUS for 6- and 8-hr DRLRs are lower than one under 4-hr DRLR, but relatively larger bottom-layer temperature drops only primarily occur during the air-temperature drop and rise period. The release with larger flow rate can also maintain the cooler water temperature downstream. Releasing the same amounts of water, with different release durations and flow rates, has a very similar effect on the downstream water temperatures.

Identification of optimal water transfer schemes for restoration of a eutrophic lake: An integrated simulation-optimization method

This research developed an integrated simulation-optimization method (ISOM). This model incorporated eutrophication modeling, water resource allocation and trophic status assessment within a general modeling framework. In ISOM, the simulation effort [i.e. environmental fluid dynamics code (EFDC)] was used to forecast the concentration of water quality variables to evaluate the lake trophic status under various conditions, while the optimization studies were used to identify the optimal water transfer strategies from a number of alternatives. To solve the model, a surrogate-based genetic algorithm (GA) was proposed in which the support vector regression (SVR) was used to create a set of easy-to-use and rapid-response surrogates for identifying the functional relationships between water transfer and lake trophic status. By replacing the EFDC and the corresponding trophic state index (TSI) equations with the surrogates, the computation efficiency could be improved. The developed ISOM was applied to the inter-basin water transfer management of the Niulanjiang-Dianchi Water Transfer Project (NDWTP) to support the eutrophication restoration of Lake Dianchi. Optimal water transfer schemes for three different remediation durations were generated from the model. The results demonstrated that NDWTP could exert a positive influence on the ecology and environment of Lake Dianchi, and that the trophic level for the Lake Dianchi could be effectively mitigated through the adoption of optimal water transfer schemes.

Modeling the impacts of water transfer on water transport pattern in Lake Chao, China

Water transport pattern plays an important role in determining water and pollution transport, and is worth our investigation. In this study, a hydrological model (Xinanjiang) and a hydrodynamic model (Environmental Fluid Dynamics Code, EFDC) were coupled to investigate the impacts of a water transfer project on the water transport pattern of Lake Chao, China. The Xinanjiang model simulated the inflow discharges for the EFDC model. The validation results were acceptable with a Nash–Sutcliffe coefficient of 0.74 and 0.84 for the Xinanjiang and EFDC models. Based on the calibrated models, four simulations were implemented and compared to evaluate the impacts of the water transfer project on the water transport pattern, described by water age and residence time. The simulation results revealed that the water transfer project had the potential to shorten water age and residence time of the lake, however, should be carried out by considering the influences of wind conditions and water transfer route. This study demonstrated a successful adaption of water age and residence time for describing water transport pattern, and highlighted the importance of model coupling approach in addressing multidisciplinary questions from the complex natural ecosystem.

Analysis of optimum grid determination of water quality model with 3-D hydrodynamic model using environmental fluid dynamics code (EFDC)

This study analyzes guidelines to select optimum number of grids to represent behavior of a given water system appropriately. The EFDC model was chosen as a 3-D hydrodynamic and water quality model and salt was chosen as a surrogate variable of pollutant. The model is applied to an artificial canal that receives salt water from coastal area and fresh water from a river from respective gate according to previously developed gate operation rule. Grids are subdivided in vertical and horizontal (longitudinal) directions, respectively until no significant changes are found in salinity concentrations. The optimum grid size was determined by comparing errors in average salt concentrations between a test grid systems against the most complicated grid system. MSE (mean squared error) and MAE (mean absolute error) are used to compare errors. The CFL (Courant-Friedrichs-Lewy) number was used to determine the optimum number of grid systems for the study site though it can be used when explicit numerical method is applied only. This study suggests errors seem acceptable when both MSE and MAE are less than unity approximately.

Response of the turbidity maximum zone in the Yangtze River Estuary due to human activities during the dry season.

The interaction between a river and the sea results in a turbidity maximum zone (TMZ) within the estuary, which has a great impact on the local ecosystem. In the Yangtze River Estuary, the magnitude and extent of the TMZ vary with water discharge. In this study, the cumulative human activity altered the water discharge regime from the river to the estuary. In the post-Three Gorges Dam (TGD) period, water discharge increased by 35.10% at Datong in February compared with that in the pre-TGD period. The effects of water discharge variation on the characteristics of the TMZ were analyzed during spring and neap tidal periods using the three-dimensional environmental fluid dynamic code (EFDC) model. The area of the TMZ decreased by 3.11 and 17.39% during neap and spring tides, respectively. In addition, the upper limit of the TMZ moved 11.68km seaward during neap tide, whereas the upper limit of the TMZ in the upstream and downstream areas moved seaward 9.65 and 2.34km, respectively, during spring tide. These findings suggest that the area and location of the TMZ are more sensitive to upstream runoff during spring tide than during neap tide. These changes in the TMZ will impact the biochemical processes in the Yangtze River Estuary. In the foreseeable future, the distribution characteristic of TMZ will inevitably change due to variations in the Yangtze River discharge resulting from new human activities (i.e., new dams), which are being constructed upstream in the Yangtze River system.

Simulating the thermal behavior in Lake Ontario using EFDC

The thermal behavior of Lake Ontario (spring warming, thermal bar formation, and summer stratification) is simulated using the three-dimensional thermo-hydrodynamic model, Environmental Fluid Dynamics Code (EFDC). The model is forced with hourly meteorological data from weather stations around the lake and flow data from Niagara and St. Lawrence Rivers. The simulation is performed from April to July 2011 on a curvilinear grid, with cells approximately 2 × 2 km2 and bathymetry interpolated onto the grid. We implement model improvements by (a) updating the evaporation algorithm to ensure accurate simulation of evaporation rates and latent heat fluxes and (b) specifying appropriate solar radiation attenuation coefficients to ensure sufficient absorption of incoming solar radiation by the water column. The study also calibrated horizontal and vertical mixing coefficients. Results show that the model accurately simulated the overall surface temperature profiles with RMSEs between 1 and 2 °C and the vertical temperature profiles during the lake mixed phase with RMSEs < 0.5 °C. Overall, the modified EFDC model successfully replicated thermal bar evolution.

A Bayesian approach for evaluation of the effect of water quality model parameter uncertainty on TMDLs: A case study of Miyun Reservoir

Facing increasingly serious water pollution, the Chinese government is changing the environmental management strategy from solely pollutant concentration control to a Total Maximum Daily Load (TMDL) program, and water quality models are increasingly being applied to determine the allowable pollutant load in the TMDL. Despite the frequent use of models, few studies have focused on how parameter uncertainty in water quality models affect the allowable pollutant loads in the TMDL program, particularly for complicated and high-dimension water quality models. Uncertainty analysis for such models is limited by time-consuming simulation and high-dimensionality and nonlinearity in parameter spaces. In this study, an allowable pollutant load calculation platform was established using the Environmental Fluid Dynamics Code (EFDC), which is a widely applied hydrodynamic-water quality model. A Bayesian approach, i.e. the DiffeRential Evolution Adaptive Metropolis (DREAM) algorithm, which is a high-efficiency, multi-chain Markov Chain Monte Carlo (MCMC) method, was applied to assess the effects of parameter uncertainty on the water quality model simulations and its influence on the allowable pollutant load calculation in the TMDL program. Miyun Reservoir, which is the most important surface drinking water source for Beijing, suffers from eutrophication and was selected as a case study. The relations between pollutant loads and water quality indicators are obtained through a graphical method in the simulation platform. Ranges of allowable pollutant loads were obtained according to the results of parameter uncertainty analysis, i.e. Total Organic Carbon (TOC): 581.5–1030.6t·yr−1; Total Phosphorus (TP): 23.3–31.0t·yr−1; and Total Nitrogen (TN): 480–1918.0t·yr−1. The wide ranges of allowable pollutant loads reveal the importance of parameter uncertainty analysis in a TMDL program for allowable pollutant load calculation and margin of safety (MOS) determination. The sources of uncertainty are discussed and ways to reduce the uncertainties are proposed.

Modelling and Analysis of Hydrodynamics and Water Quality for Rivers in the Northern Cold Region of China.

In this study, the Mudan River, which is the most typical river in the northern cold region of China was selected as the research object; Environmental Fluid Dynamics Code (EFDC) was adopted to construct a new two-dimensional water quality model for the urban sections of the Mudan River, and concentrations of CODCr and NH3N during ice-covered and open-water periods were simulated and analyzed. Results indicated that roughness coefficient and comprehensive pollutant decay rate were significantly different in those periods. To be specific, the roughness coefficient in the ice-covered period was larger than that of the open-water period, while the decay rate within the former period was smaller than that in the latter. In addition, according to the analysis of the simulated results, the main reasons for the decay rate reduction during the ice-covered period are temperature drop, upstream inflow decrease and ice layer cover; among them, ice sheet is the major contributor of roughness increase. These aspects were discussed in more detail in this work. The model could be generalized to hydrodynamic water quality process simulation researches on rivers in other cold regions as well.

Water age prediction and its potential impacts on water quality using a hydrodynamic model for Poyang Lake, China.

The water quality in Poyang Lake, the largest freshwater lake in China, has deteriorated steadily in recent years and local governments have made efforts to manage the potential eutrophication. In order to investigate the transport and retention processes of dissolved substances, the hydrodynamic model, Environmental Fluid Dynamics Code (EFDC) was applied by using the concept of water age. The simulated results showed agreement with the measured water level, discharge, and inundation area. The water age in Poyang Lake was significantly influenced by the variations of hydrological conditions. The annual analysis revealed that the largest averaged water age was observed during the wet year (2010) with 28.4days at Hukou, the junction of the Yangtze River and Poyang Lake. In the normal season (April), the youngest age with 9.1days was found. The spatial distribution of water quality derived from the remote sensing images suggested that a higher chlorophyll-a concentration, lower turbidity, and smaller water age in the eastern area of Poyang Lake might threaten the regional aquatic health. The particle tracking simulation reproduced the trajectories of the dissolved substances, indicating that the water mass with greater nutrient loading would further lead to potential environmental problems in the east lake. Moreover, the water transfer ability would be weakened due to dam (Poyang Project) construction resulting in the rising water levels in periods of regulation. Generally, this study quantified an indicative transport timescale, which could help to better understand the complex hydrodynamic processes and manage wetland ecosystems similar to Poyang Lake.

섬진강 하구역 Mobile MGIS 구축 연구

Abstract The study of Mobile MGIS (Marine Geographic Information System) based on the Android Mobile Platform is mainly performed on effective methodologies which transform real world data to computing world data. Mobile GUI system has its own target on reliable data service by acquisition of geometric information using EFDC (Environmental Fluid Dynamics Code) Model, accurate measurement and graphical visualization. Even simple visualizations can aid in the interpretation of complex hydrodynamic relationships that are frequently encountered in the marine environment.The Mobile MGIS provides an easy way for hydrodynamics geoscientists to construct complex visualizations that can be viewed with free software. This study proposes a Mobile GUI MGIS using EFDC Model result of Seomjin River estuary. Finally, we design a Seomjin River estuarine Coastal Waters Mobile MGIS integrating above data models. It must adds more ecological information and the various service item for approach more easily in order to user.Key words : Marine Geographic Information System, Graphic User Information, Android, Mobile Platform, Seomjin River, Environmental Fluid Dynamics Code ModelCorresponding author : 061-659-7155, kimjk@chonnam.ac.kr( ( )(2 )).

Analysis and numerical simulation of natural and human-caused low dissolved oxygen in the Minjiang River Estuary.

The Minjiang River, a typical tidal channel in Southeast China, plays an important role in the supply of drinking water, flood control and drought relief, farming and navigation, as well as shipping and other functions. Dissolved oxygen (DO), as a basic living condition for aquatic biota, has been deteriorating in the Minjiang River in recent years. In order to understand how the spatial distribution of DO responds to river discharge, nutrient loading and water temperature, a three-dimensional Environmental Fluid Dynamics Code model was used to simulate water age and the distribution of DO in the Minjiang River. The model presented in this paper was used for water resource and water quality simulations under various physical, chemical, and biological scenarios. Sensitivity simulation results indicated that the three factors had a significant impact on the spatial distribution variation of DO in the Minjiang River. Increased river discharge or split ratio of the North Channel resulted in decreased water age and increased DO. Increased nutrient loading and water temperature caused lower DO. In order to protect coastal environments in the Minjiang River, river discharge should be increased and pollutants of local cities should be reduced during the high temperature and drought period.

Global sensitivity analysis of a three-dimensional nutrients-algae dynamic model for a large shallow lake

Sensitivity analysis is a primary approach used in mathematical modeling to identify important factors that control the response dynamics in a model. In this paper, we applied the Morris sensitivity analysis method to identify the important factors governing the dynamics in a complex 3-dimensional water quality model. The water quality model was developed using the Environmental fluid dynamics code (EFDC) to simulate the fate and transport of nutrients and algal dynamics in Lake Dianchi, one of the most polluted large lakes in China. The analysis focused on the response of four water quality constituents, including chlorophyll-a, dissolved oxygen, total nitrogen, and total phosphorus, to 47 parameters and 7 external driving forces. We used Morris sensitivity analysis with different sample sizes and factor perturbation ranges to study the sensitivity with regard to different output metrics of the water quality model, and we analyzed the consistency between different sensitivity scenarios. In addition to the analysis with aggregate outputs, a spatiotemporal variability analysis was performed to understand the spatial heterogeneity and temporal distribution of sensitivities. Our results indicated that it is important to consider multiple characteristics in a sensitivity analysis, and we have identified a robust set of sensitive factors in the water quality model that will be useful for systematic model parameter identification and uncertainty analysis.

Impacts of Forest to Urban Land Conversion and ENSO Phase on Water Quality of a Public Water Supply Reservoir

We used coupled watershed and reservoir models to evaluate the impacts of deforestation and l Niño Southern Oscillation (ENSO) phase on drinking water quality. Source water total organic carbon (TOC) is especially important due to the potential for production of carcinogenic disinfection byproducts (DBPs). The Environmental Fluid Dynamics Code (EFDC) reservoir model is used to evaluate the difference between daily pre- and post- urbanization nutrients and TOC concentration. Post-disturbance (future) reservoir total nitrogen (TN), total phosphorus (TP), TOC and chlorophyll-a concentrations were found to be higher than pre-urbanization (base) concentrations (p &lt; 0.05). Predicted future median TOC concentration was 1.1 mg·L−1 (41% higher than base TOC concentration) at the source water intake. Simulations show that prior to urbanization, additional water treatment was necessary on 47% of the days between May and October. However, following simulated urbanization, additional drinking water treatment might be continuously necessary between May and October. One of six ENSO indices is weakly negatively correlated with the measured reservoir TOC indicating there may be higher TOC concentrations in times of lower streamflow (La Niña). There is a positive significant correlation between simulated TN and TP concentrations with ENSO suggesting higher concentrations during El Niño.

Impact of representation of hydraulic structures in modelling a Severn barrage

In this study, enhancements to the numerical representation of sluice gates and turbines were made to the hydro-environmental model Environmental Fluid Dynamics Code (EFDC), and applied to the Severn Tidal Power Group Cardiff–Weston Barrage.The extended domain of the EFDC Continental Shelf Model (CSM) allows far-field hydrodynamic impact assessment of the Severn Barrage, pre- and post-enhancement, to demonstrate the importance of accurate hydraulic structure representation. The enhancements were found to significantly affect peak water levels in the Bristol Channel, reducing levels by nearly 1m in some areas, and even affect predictions as far-field as the West Coast of Scotland, albeit to a far lesser extent.The model was tested for sensitivity to changes in the discharge coefficient, Cd, used in calculating discharge through sluice gates and turbines. It was found that the performance of the Severn Barrage is not sensitive to changes to the Cd value, and is mitigated through the continual, rather than instantaneous, discharge across the structure.The EFDC CSM can now be said to be more accurately predicting the impacts of tidal range proposals, and the investigation of sensitivity to Cd improves the confidence in the modelling results, despite the uncertainty in this coefficient.

English

English

3차원 수치모델을 이용한 섬진강 하구역의 염수침입 특성

The behavior characteristics of the saltwater intrusion in the Seomjin River Estuary by the inflow of fresh water were analysed by the field observation using CTD in the neap tide in January, June, and August 2013 as well as a numerical model, EFDC (Environmental Fluid Dynamics Code). As a result, Seomjin River Estuary is found that the saltwater intrusion is sensitive to the tide and tidal and freshwater flow. The results of field observation and numerical model were similar in the range of salt, but the results of salt wedge distribution were quite different. The observation of tide and tidal current as well as hydrographic surveying the Seomjin River Estuary will be jointly conducted for the accurate analysis.

Modelling of suspended sediment in a weir reach using EFDC model.

Construction of hydraulic structures often leads to alteration of river dynamics and water quality. Suspended solids entering the upstream of the weir cause adverse effects to the hydroecological system and, therefore, it is necessary to build a modelling system to predict the changes in the river characteristics for proper water quality management. In this study, the discharges and total suspended solids upstream and downstream of the Baekje Weir installed in Geum River, Korea, was modelled using the environmental fluid dynamics code (EFDC) model. The resulting trend of four rainfall events shows that as rainfall increases, the total suspended solids (TSS) concentration increases as well. For the two larger events, at the upstream of the weir, TSS was observed to decrease or remain constant after the rainfall event depending on the lowering of the open gate. At the downstream, TSS supply was controlled by the weir during and after the rainfall event resulting in decline in the TSS concentration. The modelling produced good results for discharge based on %Diff. (4.37-6.35), Nash-Sutcliffe efficiency (NSE) (0.94-0.99) and correlation coefficient (r) (0.97-0.99) values as well as for TSS with acceptable values for %Diff. (12.08-14.11), NSE (0.75-0.81) and r (0.88-0.91), suggesting good applicability of the model for the weir reach of the river in the study site.

Integrated urban hydrologic and hydraulic modelling in Chicago, Illinois

With rapidly growing urbanization, urban flooding and water quality control are becoming a vital component of sustainable urban infrastructure. Integrated urban hydrologic and hydraulic modelling represents a potential framework for capturing system interactivity and optimizing the design, operation, and engineering of urban systems. This work describes how a widely-used hydrodynamic model, the Environmental Fluid Dynamics Code (EFDC), was made compliant with the Open Modelling Interface (OpenMI) standard. The new version of the EFDC has potential to be coupled with any OpenMI-compliant model for various studies. As an example, this paper presents an application of the OpenMI version of EFDC coupled with InfoWorks-CS for a representative highly urbanized area in the city of Chicago, Illinois, United States. The integrated modelling simulates the two-way linkage between the sewer network and the Chicago Area Waterway System (CAWS). This interaction between the river and sewer pipe systems can not be described by decoupled models. By coupling the models, it is possible to observe the interaction between the sewer system overflow discharge and the hydraulic head in the pipe network. This is particularly important since higher water levels in the pipe system increase the potential for flooding.

Sensitivity Analysis of Flow and Temperature Distributions of Density Currents in a River-Reservoir System under Upstream Releases with Different Durations

A calibrated three-dimensional Environmental Fluid Dynamics Code model was applied to simulate unsteady flow patterns and temperature distributions in the Bankhead river-reservoir system in Alabama, USA. A series of sensitivity model runs were performed under daily repeated large releases (DRLRs) with different durations (2, 4 and 6 h) from Smith Dam Tailrace (SDT) when other model input variables were kept unchanged. The density currents in the river-reservoir system form at different reaches, are destroyed at upstream locations due to the flow momentum of the releases, and form again due to solar heating. DRLRs (140 m3/s) with longer durations push the bottom cold water further downstream and maintain a cooler bottom water temperature. For the 6-h DRLR, the momentum effect definitely reaches Cordova (~43.7 km from SDT). Positive bottom velocity (density currents moving downstream) is achieved 48.4%, 69.0% and 91.1% of the time with an average velocity of 0.017, 0.042 and 0.053 m/s at Cordova for the 2-h, 4-h and 6-h DRLR, respectively. Results show that DRLRs lasting for at least 4 h maintain lower water temperatures at Cordova. When the 4-h and 6-h DRLRs repeat for more than 6 and 10 days, respectively, bottom temperatures at Cordova become lower than those for the constant small release (2.83 m3/s). These large releases overwhelm the mixing effects due to inflow momentum and maintain temperature stratification at Cordova.

Parameterizing suspended canopy effects in a three-dimensional hydrodynamic model

ABSTRACTThis paper presents an amendment of an existing three-dimensional hydro-environmental model (Environmental Fluid Dynamics Code) to incorporate effects of suspended canopies on the vertical flow structure. Five different modelling approaches are investigated, encompassing hydrodynamic form drag imparted by the suspended canopy, an amended two-equation turbulence scheme representing turbulence generated locally by elements within the canopy, and three separate formulations for vertical profiles of drag coefficients. Data from laboratory experiments with rigid cylinders are used to validate the calculations of velocity and shear stresses. The results show that the most accurate reproduction of the canopy flow was obtained using a vertically varying drag coefficient along with a two-equation turbulence closure scheme that includes additional turbulence production and dissipation terms. The numerical model reproduced velocity profiles accurately, but the shear stresses are slightly overestimated.