46 research outputs found
Integrated analysis of global lakes and reservoirs: Global reservoirs modeling database, climate-driven changes in thermal stratification, depth-area-volume relationships, dam operation, and downstream phosphorus export
No full textInland freshwater bodies, including lakes, reservoirs, and wetlands, are critical components of the global freshwater system. They play essential roles in water storage, flow regulation, biodiversity, nutrient cycling, and many other ecosystem services including food production and local climate regulation. However, human interventions such as dam construction, urbanization, intensive agriculture, and climate change significantly alter their hydrological and ecological functions. This underscores the importance of data integration and modeling tools to predictively understand and effectively manage these water bodies to ensure their sustainability and resilience under changing climate and environmental conditions.
With this thesis, I aim to contribute to the comprehensive, global-scale analysis of inland water bodies. I present a new global reservoir water modeling database, abbreviated GRM, that can be coupled with hydrodynamic and water quality simulations. The use of GRM is illustrated by computing temperature changes in nearly 7000 large reservoirs between 1980 and 2019. I also present a database of depth-area-volume (D-A-V) relationships for over 1.4 million lakes and reservoirs worldwide. These relationships provide easy access to essential bathymetric information to users interested in carrying out modeling studies. The D-A-V database is complemented by a Python package that generates bathymetric representations for multidimensional water quality modeling. Lastly, for a reservoir in southern Ontario, I analyze how controlling water level, and the positioning of dam outflow gates can be used to reduce the outflow of total and bioavailable phosphorus, which, more generally, opens the possibility of considering dam operation strategies that help protect downstream water bodies from eutrophication impacts.
Chapter 1 provides an overview of the significance of inland water bodies and the impacts of anthropogenic activities on their biogeochemical dynamics. The chapter reviews existing global databases on lakes and reservoirs, highlighting their strengths and limitations. I further argue that existing global-scale biogeochemical modeling studies of inland waters have primarily relied on simple box models and empirical relationships that lack the ability to capture the complex temporal and multidimensional physical-geochemical-biological interactions in these ecosystems. This gap sets the stage for developing the comprehensive global multidimensional model database presented in Chapter 2.
Chapter 2 describes the development of the Global Reservoir Modeling (GRM) database that integrates multiple existing global datasets to facilitate reservoir hydrodynamic and water quality modeling on a global scale. The current GRM database version brings together 40 years (1980-2019) of diverse data series for nearly 7,000 reservoirs worldwide. The corresponding data are extracted from the following datasets: GRanD for reservoir attributes, ReGeom for bathymetric data, WaterGAP for streamflow, and ERA5 for meteorological parameters. With these data, GRM can generate compatible input files for hydrodynamic and water quality simulations with the popular CE-QUAL-W2 model. Thus, GRM offers researchers a practical and readily usable tool to model changes in reservoir water temperature and mixing regimes and their impacts on water quality, whether for a single or a large selection of the GRanD reservoirs.
Chapter 3 offers an example of the type of global-scale assessments that can be performed with GRM by calculating the temporal trajectories of the thermal gradients in all the reservoirs included in GRM from 1980 to 2019. For each reservoir, a 30×30 depth-length bathymetry is generated by GRM, which is then used in the multithreaded, process-based CE-QUAL-W2 model to calculate the temperature distribution as a function of space and time. The results are illustrated globally by mapping both the surface-to-bottom temperature difference and the distributions of thermocline depth for 1980, 2000, and 2019. The findings confirm not only a widespread increase in surface-to-bottom temperature differences (on average by 0.39 ℃ per decade) but also a generalized deepening of the thermocline, on average by 1.2 m (around 0.3 m per decade) between 1980 and 2019. The results confirm that global reservoir thermal stratification has both intensified and migrated downward over the past four decades.
Chapter 4 compiles depth–area–volume (D-A-V) relationships for over 1.4 million lakes and reservoirs by merging HydroLAKES and GLOBathy. The resulting GLRDAV database contains > 17 million equations—five polynomial functions (orders 1–5) and one power function for both depth–area and depth–volume—evaluated at 0.1 m depth increments. Validation against ReGeom, GRDL, and in-situ Texas Water Development Board surveys show that 4th- and 5th-order polynomials deliver the highest accuracy. Lower-order polynomials and the power function perform adequately for small, simple basins but not for large waterbodies. A Python package, named “Global Waterbody Calculator”, provides streamlined access to all 17 million equations and coefficients, facilitating rapid bathymetric reconstruction for hydrodynamic and water-quality models. The tool rasterizes shoreline
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polygons at 1 arcsecond (~30 m) resolution and rapidly generates full 3-D GeoTIFF bathymetry on a standard desktop, enabling immediate visualization and 3-D model-ready inputs.
Chapter 5 applies the CE-QUAL-W2 model to Fanshawe Reservoir (Ontario, Canada) to test how 33 dam operation scenarios—three dam withdrawal elevations crossed with eleven water-level elevations from 0 to +10 m relative to the current conditions—alter phosphorus retention by the reservoir. Under baseline operation (normal withdrawal, 0 m water level) the reservoir retains only 13% of incoming total phosphorus (TP) annually and can become a net TP and dissolved phosphorus (DRP) source in summer. Switching to surface withdrawal alone boosts the annual TP retention to 20 %, while combining surface withdrawal with a +10 m pool-raise pushes summer retention of TP above 78% and the annual retention to 52%. These gains stem from a four-fold lengthening of the water residence time (peaking at 149 days) and the hydraulic isolation of the P-rich hypolimnion. However, these dam operation and water level conditions also prolong bottom-water hypoxia (with dissolved oxygen < 2 mg/l for around 48 days). The modeling highlights the trade-off between maximizing phosphorus retention and avoiding in-reservoir deoxygenatiom, underscoring the need for seasonally targeted, adaptive dam management.
Finally, Chapter 6 synthesizes the thesis’s key insights and charts a path forward. It emphasizes how the new global datasets (GRM and GLRDAV) and the Fanshawe case study together advance our understanding of the links between hydrodynamics, nutrient cycling, and dam operation. Looking ahead, this chapter calls for coupling “big-data” archives with process-based and machine-learning models, building reservoir-scale digital twins, and incorporating sediment and groundwater interactions to assess long-term climate and management impacts. Strengthening this predictive framework will be instrumental in safeguarding lakes and reservoirs under accelerating environmental change
Modeling Phosphorus Cycling in a Seasonally Stratified Reservoir (Fanshawe Reservoir, Ontario, Canada)
No full textHuman activities, such as mining, sewage discharge, fertilizer usage and dam construction for electricity and flood controll, have significantly disturbed the biogeochemical cycling of nutrients, such as carbon, phosphorus, and nitrogen, in atmospheric, terrestrial, and aquatic systems. Globally, negative effects of the excess inputs of nutrients have been observed in freshwater and saline surface water environments. Phosphorus (P) is an essential nutrient for primary production, and due to intensive anthropogenic activities, including rapid agricultural intensification and urban development, excess P has been loaded into the Thames River Watershed (TRW), Ontario, Canada for around 45 years. Water quality in the TRW has been significantly affected by inputs of P and other nutrients. These eutrophic waters could have significant and chronic negative effects on the downstream and nearby aquatic environment, such as Lake St. Clair and Lake Erie. This thesis focuses on Fanshawe Reservoir, located in the Northern TRW, where Fanshawe Dam has been built to control potential flood events that may damage the City of London. However, excess nutrients could accumulate in the reservoir sediments and slowly release over a long period, posing significant difficulties for water quality management. During summertime, blue-green algae and elevated bacterial concentrations have been frequently observed by the Upper Thames River Conservation Authority (UTRCA). However, the existing field data cannot explain the seasonal variation of the algal blooms or the long-term scale interaction between the external loading of P and internal loading of P. To provide a computational framework to analyse existing field data and relate P availability in Fanshawe Reservoir to external and internal P loading, I developed a two-dimensional model for Fanshawe Reservoir using the CE-QUAL-W2 software. The model combines hydrodynamic, water quality, and sediment diagenesis modules. The simulation results imply a major role of internal P loading during the summer when the reservoir stratifies. Retention of P mainly occurs during wintertime, while the reservoir is a source of P during summertime. In a scenario where external P input to the reservoir is instantaneously reduced by 40%, the annual downstream export of P from the reservoir only decreases by 22%, because of continued internal P loading from the sediments. Due to the legacy P stored in the sediments, it would take on the order of 22 years for P export from Fanshawe Reservoir to drop to 36.5% of its current value. In another biomass scenario, the sediment P loading has 40.1% larger effects on algal growth than the external loading of P during summertime. Furthermore, to provide feasible and fast water quality modeling applications, a back propagation artificial neural network (BP-ANN) model was successful developed and calibrated for the future modeling works
GlobalReservoirModel V1.0 A new global reservoir modeling database
No full textWith increasing of population and socioeconomic development during the last decades, global constructions of dams and reservoirs have surged in diverse applications, such as flood control, and hydropower generation etc. As the acceleration of human activities, reservoirs and dam management, such as quantitative analysis of biogeochemical cycling, dam spatiotemporal outflow regulations, and greenhouse gas emissions etc., become interdisciplinary scientific hotspots. Available databases provided uncoupled global databases, such as dam attributes, and climate variations etc. The lack of user-friendly systematic modelling databases for many two-dimensional (2D) and three-dimensional (3D) global reservoir models, resulting in researchers and governments cannot obtain timely water quality information. Here, we have developed a novel 2D global reservoir modelling usable database (GRM V1.0) that integrated multiple global databases, including Global Reservoir and Dam database (GRanD), reservoir storage-area-depth dataset (ReGeom), WaterGAP V2.2D, FutureStreams, ERA5 reanalysis databases. GRM V1.0 generated and provided global simplified reservoir bathymetry with user defined segment and layer numbers for each reservoir, as well as long-term water discharge (from 1901 to 2019) and water temperature (from 1979 to 2005) model usable files. Additionally, GRM V1.0 have generated model usable meteorological daily data (from 1959 to 2019) which contain air temperature, wind speed and direction, and cloud information. These output files can be directly implemented in CE-QUAL-W2 model which is a laterally 2D hydrodynamic and water quality model through GRM intelligent multithreading module.
GRM V1.0 could be dynamic modified through user demand and overcome the gaps between conventional datasets and water quality modelling research. Furthermore, GRM V1.0 offers a multiple range of applications. For instance, the simulation of dissolved oxygen (DO) concentrations with reservoir thermal stratifications from individual reservoirs to several reservoirs in a watershed. Our findings suggested that GRM V1.0 can be a crucial component of process-based water quality model and it will potentially enable new insight into how reservoir responds to climatic variability.This research was undertaken thanks, in part, to support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF
Prediction and Prevention of Edge Waves in Continuous Cold Forming of Thick-Wall High-Strength Welded Pipe
No full textIn order to reduce the edge waves and defects of the strip in the forming process and obtain better properties of the strip, it is urgent to establish a better flexible cold forming process. In this paper, a finite element model of the production line was established to simulate the forming process, and the effective stress distribution at the corner of the strip was simulated. The effect of cold working hardening was basically consistent with that calculated by the analytical method and tensile test results. A mathematical model of the maximum normal strain along the tangent direction of the strip’s outer edge of each pass was established. With the constraint conditions that the maximum value of the normal strain value of each pass is less than the critical value and the upper and lower limit of the horizontal value of each test factor, and the maximum value of the normal strain of each pass as the goal, the number of cold forming passes, the bending angle of each pass and the working roll diameter of the roll have been determined. The optimized process parameters were used in the simulations. No edge wave at the strip edge and no “Bauschinger effect” in forming before high-frequency induction welding was found. The method proposed in this paper can optimize the key process parameters before the production line is put into operation, minimize the possible buckling of the strip edge during the forming process, and reduce the possible loss caused by design defects
Research on Risk Assessment and Refined Improvement of Traffic Safety Facilities for Low Volume Rural Highways in China
No full textBased on an extensive investigation, this paper conducts a comprehensive analysis of the existing safety facilities on rural roads with low traffic volume in China. It quantifies the indicators for identifying high-risk sections and provides a detailed description of these common high-risk areas. Furthermore, this study proposes engineering measures to enhance the traffic safety facilities specifically designed for these vulnerable road sections. Additionally, practical design examples based on engineering practices in China are presented, which are both simple and user-friendly
Research on equipment supportability assessment based on agent-oriented colored petri nets
No full textThe Impact of the Three Gorges Reservoir Operations on Hydraulic Characteristics in the Backwater Region: A Comprehensive 2D Modeling Study
No full textThe Three Gorges Reservoir (TGR), a landmark of human engineering, has significantly altered the hydrodynamics and ecology of its surrounding environment. Our research explores the hydrodynamic and ecological changes in the TGR, focusing on their implications for reservoir-induced water quality and water resource issues. We designed a 2D hydrodynamic and water quality model and implemented 15 operational scenarios with an advanced dynamic storage capacity method for the TGR during flood season, drawdown and impoundment periods. Our simulations well reproduced and predicted water levels, discharge rates, and thermal conditions of the TGR, providing critical insights. The dynamic storage capacity method significantly improved the precision of water level simulations. This approach achieved modeling errors below 0.2 m when compared to real measurements from seven stations. We performed a detailed analysis of the sensitive, sub-sensitive, and insensitive areas during three reservoir operation periods. The drawdown period showed the most extensive impact range (468 km river channel), while the impoundment period had the least impact range (76 km river channel). Furthermore, we quantified the delay of temperature waves during these periods, observing a maximum delay of approximately 120 km and a minimum delay of less than 10 km, which underscores the variability in hydrodynamic responses under different operational scenarios. Our findings reveal the complex sensitivities of the TGR to varied operational modes, aiding in the development of eutrophication and water resources control strategies. Our modeling application provides different operational scenarios and insights for ecological management strategies in large dam systems globally, informing future water resource management and policy-making, ensuring sustainable and effective management of large reservoir systems
