Search Results (41)

The Seomjin River estuary is a key habitat for the Asian clam (Corbicula fluminea), contributing significantly to the local economy and aquatic biodiversity in South Korea. However, long-term reductions in upstream discharge, geomorphological alterations, land reclamation, and climate change have intensified saltwater intrusion, gradually displacing clam habitats upstream. This study employed the Environmental Fluid Dynamics Code (EFDC) model to simulate salinity distribution and evaluate optimal environmental flow strategies for clam conservation. Simulation results indicated that maintaining a minimum upstream flow of 23 m³/s was essential to prevent salinity levels from exceeding the critical threshold of 20 psu at Seomjin Bridge, a key habitat site. During neap tides, reduced tidal flushing led to prolonged saltwater retention, elevating salinity levels and increasing the risk of mass clam mortality. A historical event in May 2017, when salinity exceeded 20 psu for over four consecutive days, resulted in a major die-off. This study successfully reproduced that event and evaluated mitigation strategies. A combined approach involving increased dam releases and temporary reductions in intake withdrawal was assessed. Notably, a pulse release strategy supplying an additional 9.9–10.37 m³/s (total 30.4 m³/s) over three days during neap tide effectively limited critical salinity durations to fewer than four days. The preservation of Asian clams in the Seomjin River estuary is a sustainability measure not only from an ecological perspective but also from a cultural one. Full article

As an important part of the urban landscape, lakes not only enhance the overall environmental quality of a city, but also strengthen the residents’ sense of well-being and cultural identity. With the acceleration of urbanization, the water quality and ecological health of urban lakes have become increasingly prominent issues. However, there is a lack of quantitative research on the effects of lake shape on the spatial and temporal distribution of hydrodynamics and water quality. Using the Environmental Fluid Dynamics Code (EFDC) model, this study simulates the hydrodynamic characteristics and water quality responses of an urban lake in Tianjin, focusing on the critical role of lake shape in regulating hydrodynamics and water quality. By quantifying the relationship between lake landscape indices (e.g., shape index, Fractal Dimension) and hydrodynamic parameters, this study reveals how lake shape regulates water flow characteristics and nutrient distribution, thereby influencing eutrophication risk. The results show that regular lakes (e.g., Lake B) exhibit higher flow velocities (0.027 m/s) and significantly lower chlorophyll-a concentrations (6–9 μg/L), reducing eutrophication risk, whereas complex-shaped lakes (e.g., Lake X) have lower flow velocities (0.0087 m/s) and higher localized chlorophyll-a concentrations (13–15 μg/L), increasing the risk of eutrophication. This study systematically quantifies the impact of lake shape on hydrodynamic characteristics and water quality distribution, providing a scientific reference for lake shape optimization, precise water replenishment, and water quality management. Full article

South Korea’s River Act mandates the maintenance of instream flow to support river ecosystems. This regulation has evolved from early river management practices to more advanced, systematic approaches, including the Instream Flow Incremental Methodology (IFIM). Despite these advancements, river management in South Korea, particularly in the Seomjin River Basin, continues to face numerous challenges. In this study, a three-dimensional numerical model was developed to simulate the hydrodynamic and salinity conditions of the Seomjin River Estuary. This study proposes optimal instream flows to support critical habitats for the Corbicula bivalve, which has seen a significant decline due to salinity intrusion by environmental changes. Using the Environmental Fluid Dynamics Code (EFDC), the model simulates salinity and river discharge with calibration and validation by incorporating historical data. Subsequently, this study evaluates how river discharge affects salinity in four major Corbicula habitats (Dugok, Shinbi, Mokdo, and Hwamok). Finally, we determine the minimum flow (instream flow) needed to sustain Corbicula habitats. In short, this study found that the minimum flow rates (instream flow) required to meet target salinities varied significantly across these sites and under different tidal conditions. These findings highlight the necessity of adapting river flow management practices to preserve the ecological health for Corbicula in the Seomjin River Estuary. Furthermore, this study suggests integrating an additional water supply to be used with local water management plans by suggesting short-term and long-term alternatives in order to sustain adapting river minimum flow (instream flow). Full article

The quality of freshwater input from tributaries of the Western Mississippi Sound (WMSS) impacts the quality of coastal water. Hydrological and hydrodynamic models can be coupled to assess the impact of freshwater inflow from coastal watersheds. This study aims to compare the performance of a hydrodynamic model and a hydrological–hydrodynamic coupled model in detecting the effect of freshwater inflow from the coastal watersheds of the state of Mississippi into the WMSS. A hydrological model, the Soil and Water Assessment Tool (SWAT), and a hydrodynamic model, the visual Environmental Fluid Dynamics Code (vEFDC), were coupled to evaluate the difference between the hydrodynamical modelling approach, which employs an area-weighted approach to define flow and nutrient concentrations, and the more recent coupling model approach, which uses a hydrological model to determine the flow and nutrient load of the model. Furthermore, a nutrient load sensitivity analysis of the effect of freshwater inflow on water quality in the WMSS was conducted in addition to assessing the repercussions of tropical depressions. Hydrological assessments of the major tributaries watersheds of Saint Louis Bay (SLB) at the WMSS were performed using the SWAT model. After calibration/validation of the SWAT model, the streamflow output from the SWAT was incorporated into the vEFDC model. Finally, hydrodynamic simulation of the SWAT-vEFDC model was conducted, and water quality output was compared at different SLB locations. The salinity, dissolved oxygen, total nitrogen (TN), and total phosphorus (TP) were assessed by comparing the vEFDC and SWAT-vEFDC outputs. The results indicated that hydrological input from the SWAT alters the flow and nutrient concentration results as compared to an area-weighted approach. In addition, a major impact on the concentration of TN and TP occurred at the location where the freshwater flows into SLB. This impact diminishes further away from the point of freshwater inflow. Moreover, a 25% nutrient load variation did not demonstrate a difference in water quality at the WMSS besides TN and TP in a post-tropical depression scenario. Therefore, the SWAT-vEFDC coupled approach provided insights into evaluation of the area-weighted method, and of hydrological model output to the hydrodynamical model, the effect of freshwater inflow into coastal waters, and nutrient sensitivity analysis, which are important for integrated coastal ecosystems management. Full article

Anthropogenic development can strongly influence natural river processes, leading to environmental changes that negatively affect important habitats and biodiversity and consequently reduce economically important natural resources. This study investigated the effects of salinity intrusion on the habitat of the clam Corbicula japonica in the Seomjin River estuarine zone. We employed the Environmental Fluid Dynamics Code (EFDC) model, which incorporates topographic data and hydrological changes, to simulate salinity. Two salinity measurement facilities were installed in Seomjin River estuarine and operated to optimize the EFDC model. The results show that reduced flow rates due to intake have a negligible impact on the increased salinity. Maintaining optimal salinity (15–20 psu) during neap tides at the Seomjin River Bridge requires constant high flow rates, which poses significant challenges. Saltwater stratification is identified as the primary cause of pronounced salinity stratification, particularly during neap tides. Addressing this issue through river discharge and intake facility operation is challenging. Structural measures, including riverbed restoration and underwater barriers, are recommended to improve resistance to seawater intrusion. Future research should aim to develop scenarios to reduce salinity, quantify the reduction efficiency, and propose region-specific measures. Full article

Florida Bay, a large and shallow estuary, serves as a vital habitat for a diverse range of marine species and holds significant environmental, commercial, and recreational value. The Florida Bay ecosystem is under extensive stress due to decades of increased nutrient loads. Based on the Environmental Fluid Dynamics Code (EFDC), a hydrodynamic model was developed in this study. The model was calibrated with a comprehensive dataset, including measurements over 7 years from 34 tidal stations, 42 current stations, and 14 temperature and salinity stations. Key findings include the following: (1) the bay exhibits a shift in the tidal regime, transitioning from macro-tidal in the western region to micro-tidal in the central and eastern/northeast regions; (2) local winds and the subtidal variations from the coastal ocean are the primary drivers for the hydrodynamic processes in the eastern and central regions; (3) salinity changes in the bay are primarily controlled by three processes: the net supply of freshwater, the processes that drive mixing within the estuary (e.g., wind, topography, currents), and the exchange of salinity with the coastal ocean. This hydrodynamic model is essential for providing a comprehensive tool to address environmental challenges and sustain the bay’s ecosystem health. Full article

High concentrations of 2-methylisoborneol (2-MIB) were reported during winter in the Paldang reservoir and North Han River, South Korea. The causes of the unusual taste and odor problems in the regulated river-reservoir system were not understood; however, a short-term solution is to flush out 2-MIB-rich water to secure water sources for over 20 million people. Approximately 150 million tons of water was released from upstream dams for 12 days (late November to early December 2018) to reduce the elevated levels of 2-MIB. Simultaneously, the spatio-temporal variations of the measured concentration of sample 2-MIB from five sites were simulated using a multi-dimensional hydrodynamics-based solute transport model to monitor the flushing effect. A modified environmental fluid dynamics code (EFDC) was adopted as the primary model framework. Five scenarios on the kinetic constants related to the characteristics of 2-MIB transport and behavior, such as conservative, net decay, and net production, were applied, and the results were compared. We found that the simulation errors on the elapsed times to satisfy the Korean drinking water monitoring standard (≤20 ngL⁻¹) were smallest with the conservative dye transport option, indicating that the physical and biochemical characteristics of 2-MIB may not play an essential role. Full article

Harmful algal blooms (HABs) are a serious threat to ecosystems and human health. The accurate prediction of HABs is crucial for their proactive preparation and management. While mechanism-based numerical modeling, such as the Environmental Fluid Dynamics Code (EFDC), has been widely used in the past, the recent development of machine learning technology with data-based processing capabilities has opened up new possibilities for HABs prediction. In this study, we developed and evaluated two types of machine learning-based models for HABs prediction: Gradient Boosting models (XGBoost, LightGBM, CatBoost) and attention-based CNN-LSTM models. We used Bayesian optimization techniques for hyperparameter tuning, and applied bagging and stacking ensemble techniques to obtain the final prediction results. The final prediction result was derived by applying the optimal hyperparameter and bagging and stacking ensemble techniques, and the applicability of prediction to HABs was evaluated. When predicting HABs with an ensemble technique, it is judged that the overall prediction performance can be improved by complementing the advantages of each model and averaging errors such as overfitting of individual models. Our study highlights the potential of machine learning-based models for HABs prediction and emphasizes the need to incorporate the latest technology into this important field. Full article

Harmful algal blooms (HABs) caused by harmful cyanobacteria adversely impact the water quality in aquatic ecosystems and burden socioecological systems that are based on water utilization. Currently, Korea uses the Environmental Fluid Dynamics Code-National Institute of Environmental Research (EFDC-NIER) model to predict algae conditions and respond to algal blooms through the HAB alert system. This study aimed to establish an additional deep learning model to effectively respond to algal blooms. The prediction model is based on a deep neural network (DNN), which is a type of artificial neural network widely used for HAB prediction. By applying the synthetic minority over-sampling technique (SMOTE) to resolve the imbalance in the data, the DNN model showed improved performance during validation for predicting the number of cyanobacteria cells. The R-squared increased from 0.7 to 0.78, MAE decreased from 0.7 to 0.6, and RMSE decreased from 0.9 to 0.7, indicating an enhancement in the model’s performance. Furthermore, regarding the HAB alert levels, the R-squared increased from 0.18 to 0.79, MAE decreased from 0.2 to 0.1, and RMSE decreased from 0.3 to 0.2, indicating improved performance as well. According to the results, the constructed data-based model reasonably predicted algae conditions in the summer when algal bloom-induced damage occurs and accurately predicted the HAB alert levels for immediate decision-making. The main objective of this study was to develop a new technology for predicting and managing HABs in river environments, aiming for a sustainable future for the aquatic ecosystem. Full article

Dam operation is regarded as an effective way to increase water, food, and energy security for society. However, with the increasing water demand and frequent extreme droughts, numerous rivers worldwide go through periods of water scarcity and water ecosystem deterioration to varying degrees. Balancing the water supply and ecological flow of the dam-regulated river network is essential in the context of river restoration. In this study, we proposed a hydrodynamic and water quality model of a dam-regulated river network balancing water supply and ecological flow using the Environmental Fluid Dynamics Code (EFDC). A section of Jinjiang watershed located in the southwestern of China was chosen as the study area. Firstly, the model was calibrated and validated. By comparing the simulated values with the measured values, the statistical analysis results showed that the relative root mean-squared error (RRMSE) values of water level, COD and NH₃-N were 5.5–8.1%, 23.6% and 28.4%, respectively, indicating an adequate degree of agreement between simulation and observation. Based on the established model, dam operation schemes under a dry hydrologic scenario and emergency contamination scenario were formulated to ensure the requirement of ecological water flow and water quality simultaneously. For the dry hydrologic scenario, the ecological water requirement could be satisfied through the dam operation. However, in an emergency contamination scenario, regional water quality requirements cannot be met through dam operation. The dam operation only plays a role in controlling the scope of pollution. This study is expected to provide scientific support for dam-regulated river network management and downstream river ecosystem protection. Full article

In this study, the water quality change in a stagnant controlled river containing hard management structures due to pulsed flow was simulated. The Environmental Fluid Dynamics Code (EFDC) model was used for the water quality change simulation, and the water quality improvement effect caused by pulsed flow was simulated for multiple scenarios. Based on Case 1, in which 274.2–291.8 CMS was discharged for five hours, other scenarios, in which the gate was opened by 0.5 m and 1.0 m while the discharge time was doubled, were simulated. On comparing the water level results with the observed data, a relatively positive result of R2 = 0.82 was obtained. The water quality simulation results showed that the concentrations of Chl-a, COD, and T-P were, respectively, approximately 7.7%, 4.5%, and 4.0% higher in Case 2 than in Case 1, 24 h after the start of discharge. Cases 3 and 4, on the other hand, exhibited decreased concentrations of Chl-a, COD, and T-P 24 h after the start of discharge. These results confirm that pulsed flow leads to different water quality improvement effects depending on the discharge amount and duration. Furthermore, the water quality improvement effect was recorded at close to 0% after 72 h in all scenarios. As the water quality improvement effect due to pulsed flow appears within 24 h and almost disappears after 72 h depending on the scenario, a physical solution to this problem is required. Full article

Water-quality model simulation is the key to understanding hydrological processes and water-quality dynamic(s). In this study, Jingpo Lake, which is the most typical lake in the northern cold region of China, was selected as the research object. A numerical simulation model for transporting and diffusing the chemical oxygen demand (COD_Mn) and ammonia nitrogen (NH₃N) with ice-covered and open-water periods was constructed and calibrated using the Environmental Fluid Dynamics Code (EFDC). Parameters such as the bottom roughness, ice roughness, diffusion coefficient, horizontal momentum diffusivity, molecular eddy viscosity, molecular diffusivity, buoyancy influence coefficient, COD_Mn decay rate and NH₃N decay rate were validated. The research findings show that there were differences in the hydrodynamic water-quality changing process during the ice-covered and open-water periods, as well as for the seasonal ice-covered waterbody. The key parameter decay rates of the COD_Mn and NH₃N in the ice-covered periods were lower than those in the open-water periods due to the water-temperature decline. The R² of the COD_Mn and NH₃N reached 90.71% and 79.79%, respectively. Thus, it may be concluded that the EFDC model could well reflect changes in the water level of Jingpo Lake, as well as the transport and diffusion of the COD_Mn and NH₃N in Jingpo Lake. Full article

Floating treatment wetlands (FTWs) are widely used in surface water. The nutrient removal performance depends on both physical processes and chemical/biological transformations in FTWs. However, research describing the coupling processes of hydrodynamic and water quality in the system remains limited. Therefore, a coupled three-dimensional model of hydrodynamic and water quality for FTWs was developed based on the Environmental Fluid Dynamics Code (EFDC). Additional plant drag terms were added to the momentum equations to simulate the suspended canopy effect, and the chemical/biological processes occurring in FTWs were integrated into the original water quality equations simultaneously. The fully calibrated model was used to compare the hydrodynamic characteristics and nutrient removal performance of seven FTW configurations. The modeling results showed that the main stream would turn to the bottom and side of the plant root zone because of the block in FTWs. The differences in the hydrodynamic characteristics among the seven configurations led to a difference in water quality improvement effects. Segmenting a single FTW into a pair of parallel FTWs could achieve the maximum nitrogen and phosphorus mass removal. The results of the study are useful for designing an optimal FTW configuration in surface water. Full article

Green algae play an important role in ecosystems as primary producers, but they can cause algal blooms, which are socio-environmental burdens as responding to them requires water resources from dam reservoirs. This study proposes an alternative for reducing algal blooms through dam operation without using additional water resources. A novel oscillation flow concept was suggested: oscillating discharge of dam for irregular flow. To examine its effect, the Environmental Fluid Dynamics Code—National Institute of Environment Research (EFDC-NIER) model was constructed and calibrated for the Namhan River, South Korea, from downstream of the Chungju Dam to downstream of Gangcheon Weir. The water quality in the study area were simulated and analyzed for August 2019, which is when the largest number of harmful cyanobacteria had been reported in recent years. Our results showed that the oscillation flow produced significant variance of flow velocity, and algal bloom density in the Namhan River was reduced by 20–30% through the operation of the Chungju Dam. However, further study and investigation are required before practical application. Full article

A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns in external total phosphorus (TP) input and TP concentration, as well as the composition of the phytoplankton community. The model was calibrated to reproduce qualitative features and the succession of phytoplankton communities, and the net primary production was calculated. The modeled daily net primary production (NPP) ranged between −16.89 and 15.12 mg C/m²/d and exhibited significant seasonal variation. The competition for phosphorus and temperature was identified as the primary governing factor of NPP by analyzing the parameter sensitivity and limitation factors of the lake. The simulation of four nutrient loading reduction scenarios suggested high phytoplankton biomass and NPP sensitivity to the external TP reduction. A significant positive correlation was found among NPP, total phytoplankton biomass and TP concentration. Overall, this work offers an alternative approach to estimating lake NPP, which has the potential to improve sustainable lake management. Full article