Inter-basin Water Transfer Projects Research Articles

Environmental planning and the evolution of inter-basin water transfers in the United States

The uneven spatial distribution of water resources and demands across the US have motivated a wide range of inter-basin water transfers. By redistributing water resources, Inter-basin water transfer projects can lead to specific environmental changes such as altered river flows, changes in water quality, and loss of ecologically important habitats, impacts which depend on project scale and management. Early water transfer projects were undertaken prior to legislation Since the primary focus is not on the environmental impacts of these projects, they are often not documented historically. We provided a comprehensive inventory of inter-basin water transfer projects (built, incomplete, proposed) in the US, identified patterns of these projects’ characteristics, analyzed the growing role of environmental planning in these projects, and drew lessons to inform future proposals. We categorized historical US water transfer projects into three periods: 1900–1930, 1930–1970, and 1970–2020, analyzing projects over 40 km long and 50 MCM/year using diverse sources, to assess their development from an environmental planning perspective. Results of this study show that the early projects, mostly gravity-driven and smaller-in-scale, grow in scale and require more pumping stations (energy-intensive) to lift the water over high elevations. California and Colorado are the most active, using these transfers for the first time. Federal agencies have reduced funding for most transfers due to a growing recognition of the environmental impacts, which were not adequately addressed in planning of early projects. Environmental impacts are crucial for the planning and operation of inter-basin water transfer projects. We recommend that assessments of climate change vulnerability should also be considered essential for future project proposals.

Ecological impacts and supply demand evolution of the Yangtze to Huaihe water transfer project in Anhui section

Human activities have profound impacts on land use and the supply–demand balance of ecosystem services (ESs). Various activities, such as urban construction, urban and rural planning, and inter-basin water transfer projects, continuously reshape land use patterns. This is a case study of the Anhui section of the Yangtze-Huaihe Water Diversion Project. Data from 2000, 2010, and 2020 is analyzed. Additionally, the patch-generating land use simulation (PLUS) model is utilized to quantify the specific impacts of the water diversion project construction on the supply and demand of ESs. The results indicate that the comprehensive dynamic attitude of land use during the project construction period significantly increased, rising from 0.16 to 13.79%, and mainly affected forest, water areas, construction land, and unused land. Specifically, the construction of the project led to significant changes in water purification, biodiversity, and, especially, hydrological regulation services. Additionally, the migration of residents significantly impacted the demand for ESs. The study also found a significant correlation between land use changes and the balance of ES supply and demand: the proportion of cultivated land and construction land is positively correlated with the balance, while the proportion of forest, grassland, and water areas is negatively correlated. This study provides empirical data for understanding the environmental and socio-economic impacts of large-scale water diversion projects and offers a scientific basis for local mitigation and control of adverse impacts. Through quantitative analysis and model prediction, this research effectively bridges the gap between theory and practice, providing important references for sustainable regional development.

Optimization Study on Sequential Emptying and Dredging for Water Diversity Reservoir Group

Reservoir sediment severely impacts water supply in water-scarce regions, making reservoir dredging an urgent global issue. The investment required for deep-water dredging far exceeds that for dry land dredging. Therefore, against the backdrop of the national water network construction, this study focuses on a typical inter-basin water transfer project in Northern China. To increase the proportion of dry land dredging volume and save costs, this study uses compensation reservoirs to replace the emptied reservoir in undertaking water supply tasks as a constraint. Single-objective optimization models for single reservoirs and multi-objective optimization models for reservoir groups are established, using game theory comprehensive subjective and objective weighting methods to select the optimal solution. The following conclusions are drawn from comparing the water supply effects under various emptying sequences: the optimal sequence for emptying reservoirs should be determined through precise quantitative analysis; as the dredging is completed, the water supply tends to stabilize; the satisfaction with the water supply and the variance of the water shortage rate are primarily related to reservoirs with a large inflow and storage capacity; dredging occurs according to the descending order of the storage capacity of reservoirs; and the startup proportion of pump stations shows an increasing trend.

Beyond immediate relief: Investigating multi-faceted water management in inter-basin water transfer projects

Water scarcity is a compelling and complex global challenge that has far-reaching implications for both ecological systems and human societies. In response, inter-basin water transfer initiatives have been advocated as potential remedies. Though effective in providing immediate relief, the long-term viability of these initiatives is disputed. Notably, recurring scarcity can result from increased water demand in the recipient basin due to transferred water. Addressing this requires balancing water demand and supply. Beyond supply-focused measures such as water transfers, a crucial strategy involves adopting demand-focused approaches to reduce reliance on such transfers. This study centers on the Gavkhouni basin in Iran, where despite repeated water transfers, water scarcity remains persistent due to climate fluctuations, population growth, agricultural activities, and economic development. The research developed a comprehensive system dynamic model, integrating environmental, social, and economic variables impacting water balance in the region in order to assess the effectiveness of three distinct demand-focused water management strategies, namely, technology-based, cropping pattern-based, and land-based policies, both individually and in synergy. This analysis was conducted across a set of scenarios encompassing climate change, population growth, GDP dynamics, and water transfer patterns. The findings revealed a satisfactory accuracy of the water management system model, with a 6.2% mean absolute error. In addition, findings highlighted the advantages of a multifaceted strategy, with technology-driven interventions and optimized cropping patterns emerging as particularly effective. However, the economic dimensions of these policies warrant comprehensive exploration due to the significant impact they have on the feasibility and effectiveness of the policies. The study emphasizes the need to combine demand-side policies with supply strategies like water transfers. This comprehensive approach is vital for effective water management and long-term water security.

Tiny-Machine-Learning-Based Supply Canal Surface Condition Monitoring.

The South-to-North Water Diversion Project in China is an extensive inter-basin water transfer project, for which ensuring the safe operation and maintenance of infrastructure poses a fundamental challenge. In this context, structural health monitoring is crucial for the safe and efficient operation of hydraulic infrastructure. Currently, most health monitoring systems for hydraulic infrastructure rely on commercial software or algorithms that only run on desktop computers. This study developed for the first time a lightweight convolutional neural network (CNN) model specifically for early detection of structural damage in water supply canals and deployed it as a tiny machine learning (TinyML) application on a low-power microcontroller unit (MCU). The model uses damage images of the supply canals that we collected as input and the damage types as output. With data augmentation techniques to enhance the training dataset, the deployed model is only 7.57 KB in size and demonstrates an accuracy of 94.17 ± 1.67% and a precision of 94.47 ± 1.46%, outperforming other commonly used CNN models in terms of performance and energy efficiency. Moreover, each inference consumes only 5610.18 μJ of energy, allowing a standard 225 mAh button cell to run continuously for nearly 11 years and perform approximately 4,945,055 inferences. This research not only confirms the feasibility of deploying real-time supply canal surface condition monitoring on low-power, resource-constrained devices but also provides practical technical solutions for improving infrastructure security.

Do Water Transfer Projects Promote Water Use Efficiency? Case Study of South-to-North Water Transfer Project in Yellow River Basin of China

With a huge capital and labor input influx, inter-basin water transfer (IBWT) projects have been shown to effectively mitigate water stress and ensure the water demand for social and economic development in the receiving area. Whether they have promoted the improvement of regional water use efficiency (WUE) is crucial for sustainable management of regional water resources. Targeting the South-to-North Water Transfer Project (SNWTP), the largest and most ambitious inter-basin water transfer project in China, this study establishes quantitatively econometric models to analyze the impact of different water diversion projects, specifically the eastern route of the SNWTP (ER-SNWTP), middle route of the SNWTP (MR-SNWTP), and diversion from the main stream of the Yellow River (DYR), on the regional water consumption per unit of GDP; regional water stress, water use structure, economic structure, and urbanization level are used as control variables in different types of cities in the Yellow River Basin, and some intriguing results are found. While the overall water transfer project demonstrates a positive impact on water use efficiency, the effects of the three water transfer measures vary significantly. The ER-SNWTP does not exhibit a notable positive effect on regional water use efficiency, whereas the MR-SNWTP demonstrates a significant positive impact. Interestingly, the DYR has a notable negative influence on water use efficiency in developed cities. The water use structure, shaped by the pricing, scale, and policies of different projects, emerges as a pivotal factor in explaining these differences. Finally, this paper suggests that the impact of water transfer projects on the improvement of regional water use efficiency be viewed from a more comprehensive and developmental perspective.

Investigating the Economic Impacts of Inter-Basin Water Transfer Projects with a Water- Embedded Multi - Regional Computable General Equilibrium Approach

Investigating the Economic Impacts of Inter-Basin Water Transfer Projects with a Water- Embedded Multi - Regional Computable General Equilibrium Approach

Risk assessment of inter-basin water transfer plans through integration of Fault Tree Analysis and Bayesian Network modelling approaches

Inter-basin water transfer projects are a common method used to balance water resources and meet regional demand, particularly in the drinking water supply sector. The potential failure risk associated with inter-basin water transfer projects was examined using Fault Tree Analysis (FTA) and Fuzzy Fault Tree Analysis (FFTA) methodologies in this study. Additionally, the conversion of Fault Tree models into Bayesian Network (BN) and Fuzzy Bayesian Network (FBN) models was explored. Ten basic events were identified as factors that could affect the success of inter-basin water transfer plans, including socio-political, environmental, water resource, economic, and technical criteria. Fault Tree and Fuzzy Fault Tree models were utilized to conduct a risk analysis, which was then converted into crisp and fuzzy FTA-BN through an integrated approach. This approach was applied to evaluate inter-basin water transfer scenarios from the Great Karun basin to the Central Iran Plateau. The superior scenario among eight water transfer scenarios was found to be water transfer from the Behesht-Abad Basin to Isfahan province and from the Khersan Basin to Kerman and Yazd provinces, with a failure risk of 0.649 and 0.601 respectively, based on the crisp and fuzzy integrated models. Basic events were ranked based on their contribution to the occurrence of the top event using two FIM and BI indices in the Fault Tree model and two indices of MI and SI in the Bayesian Network. Furthermore, after considering the correlation between basic events and risk factors, the risk obtained by crisp and fuzzy integrated models was found to increase to 0.811 and 0.789 respectively. The results of this study demonstrate that an integrated approach can assist decision-makers and stakeholders in evaluating inter-basin water transfer projects.

Study on the methodology of emergency decision-making for water transfer project contingencies: A case-based reasoning and regret theory approach.

To tackle the global water imbalance problem, a multitude of inter-basin water transfer projects have been built worldwide in recent decades. Nevertheless, given the complexity and safety challenges associated with project operation, effective emergency decision-making is crucial for addressing unforeseen incidents. Hence, this research has developed a two-stage emergency decision-making framework to tackle the uncertainty in the development trends of emergencies in inter-basin water transfer projects. (1) The first stage mainly utilizes case-based reasoning techniques to extract historical case information and disposal plans for inter-basin water transfer projects. Subsequently, a holistic similarity model is built by employing structural similarity and local attribute similarity algorithms to identify highly similar historical cases. (2) The second stage involves the optimization and adjustment of decision-making plans based on the dynamic evolution characteristics of emergencies. It utilizes the theory of decision-makers regret psychology and combines it with practical case studies to verify the scientific rationality of the method. This enables it to achieve effective multidimensional expression and rapid matching of scenarios, satisfying the decision-making requirements of "scenario response". Finally, this study compares the results obtained from this method with those computed using the traditional TOPSIS method and fuzzy comprehensive evaluation method, further validating its feasibility and effectiveness. In practice, this method can provide effective support for decision-makers work.

Joint optimal operation of the South-to-North Water Diversion Project considering the evenness of water deficit

Abstract. Inter-basin water transfer projects are the main measure to address the water deficit crisis caused by uneven distribution of water resources. The current water transfer operation mainly tends to be present in areas with small water transfer costs and is prone to encounter the problem of spatial and temporal imbalances in water allocation. To address these issues, this paper defines a water deficit evenness index (WDEI), aimed at minimizing regional differences in water scarcity and sharing the pressure of water scarcity as a social demand objective. This index is incorporated into a joint optimization model for the Jiangsu section of the South-to-North Water Diversion Project (J-SNWDP), which comprises both the ecological objective of the total water deficit (TWD) and the economic objective of the pumping water (PW). Further, the Nondominated Sorting Genetic Algorithm III (NSGA-III) and multi-attribute decision-making were applied to solve the model and obtain an optimal operation strategy. The results showed the following: (1) the WDEI defined in this paper can mitigate the synchronized water scarcity in certain water users. In typical normal years (wet year and dry year), the WDEI shows a reduction of 94.2 % (81.8 %, 76.7 %) compared to the historical operation strategy. (2) The optimized operation strategy can significantly reduce TWD and PW by 82.06% (37.69 %, 52.36 %) and 45.13 % (3.25 %, 21.51 %) compared with the historical values, respectively, which can improve the water supply satisfaction and reduce the project cost. At the same time, the lake storage capacity of the optimal operation strategy performs well, and the water transfer efficiency of the river is significantly improved. (3) In this paper, targeted optimal operation strategies and potential ways to secure the project tasks are proposed for different natural flow. Overall, it is of great significance to study the water supply equity in the J-SNWDP to alleviate the concentrated water deficit in Jiangsu Province and other similar regions.

Simulation of the Entire Process of an Interbasin Water Transfer Project for Flow Routing

The flow routing process plays a crucial role in underpinning the execution of real-time operations within interbasin water transfer projects (IWTPs). However, the water transfer process within the supplying area is significantly affected by the time lag of water flow over extended distances, which results in a misalignment with the water demand process in the receiving area. Hence, there is an imperative need to investigate the flow routing patterns in long-distance water transfer processes. While MIKE11(2014 version) software and the Muskingum method are proficient in simulating flow routing within a water transfer network, they fall short in addressing issues arising from mixed free-surface-pressure flows in water transfer pipelines. This study enhanced the capabilities of the MIKE11(2014 version) software and the Muskingum method by introducing the Preissmann virtual narrow gap method to tackle the challenge of simulating mixed free-surface-pressure flows, a task unattainable by the model independently. This approach provides a clear elucidation of hydraulic characteristics within the water transfer network, encompassing flow rates and routing times. Furthermore, this is integrated with the Muskingum inverse method to compute the actual water demand process within the supplying area. This methodology is implemented in the context of the Han River to Wei River Diversion Project (HTWDP). The research findings reveal that the routing time for the Qinling water conveyance tunnel, under maximum design flow rate conditions, is 12.78 h, while for the south and north main lines, it stands at 15.85 and 20.15 h, respectively. These results underscore the significance of the time lag effect in long-distance water conveyance. It is noteworthy that the average errors between simulated and calculated values for the south and north main lines in the flow routing process are 0.45 m3/s and 0.51 m3/s, respectively. Compared to not using the Preissmann virtual narrow gap method, these errors are reduced by 59.82% and 70.35%, indicating a significant decrease in the discrepancy between simulated and calculated values through the adoption of the Preissmann virtual narrow gap method. This substantially improves the model’s fitting accuracy. Furthermore, the KGE indices for the flow routing model are all above 0.5, and the overall trend of the reverse flow routing process closely aligns with the simulated process. The relative errors for most time periods are constrained within a 5% range, demonstrating the reasonability and precision of the model.

Assessment of Multi-Regional Comprehensive Benefits of the South-to-North Water Diversion Project in China

Inter-basin water transfer (IBWT) projects are an effective means of addressing regional water resource imbalances. However, owing to the long construction cycle, large investment amount, and wide impact range, water diversion projects exhibit delayed and complex benefits, often lacking clear comprehension. In this study, we established a multi-regional comprehensive benefit assessment framework for the IBWT, considering spatiotemporal and multi-dimensional value effects. Using the South-to-North Water Diversion Project (SNWDP) in China as an example, we assessed its comprehensive benefits from 2003 to 2020. The results showed that the comprehensive benefits of the project were USD 207 billion, encompassing economic and ecological benefits, accounting for 71.6% and 28.4%, respectively. In 2020, the benefits of the SNWDP amounted to USD 39.3 billion, with a per-unit area benefit range of USD −1.03 to 4.27. The operation of the SNWDP effectively alleviated groundwater overexploitation in water-receiving areas. However, without the SNWDP, the total loss caused by industrial development limitations due to water scarcity would have been USD 154.3 billion. These results indicate the importance of a practical framework for assessing IWBT project benefits, aiding managers in assessment tasks, and facilitating the prediction and adjustment of project benefits.

Multi-objective cooperative optimization of reservoir scheduling and water resources allocation for inter-basin water transfer project based on multi-stage coupling model

The efficient coupling of a water allocation model with a reservoir operation model is key to maximizing the benefits of inter-basin water transfer (IBWT) projects. Most existing studies of IBWT operations and management do not account for matching water transfer and demand, and instead seek to optimize either the water allocation model or the reservoir scheduling model. In this paper, we propose a multi-stage joint optimization framework for reservoir scheduling and water allocation models that considers the key operation indicators of the project in the water source area and the multi-dimensional objectives in the receiving area. We derived a functional relationship that balances considerations regarding water, the economy, and ecology (WEE) in the receiving area and applied it to the water allocation model. The reservoir operation model was developed by considering the multiple benefits of water transfer and power generation in the water resource area. To reduce the complexity of the model and the tightness of its coupling, the model was divided into multiple stages of optimization and solved using the Multi-objective Evolutionary Algorithm Based on Decomposition (MOEA/D) algorithm. The results showed the allocation schemes of water resources influenced the competition between the economic and ecological benefits. Using the WEE model, a more reasonable water transfer and allocation method can be selected according to different development needs. As such, the water shortage rate of each user in the receiving area is kept below 8%, and there is significant improvement in all indicators compared with the conventional scheme. In addition, this model enables the reservoir group to achieve a power generation capacity of more than 5.64 kWh with the goal of meeting the water transfer demand, maintaining the reservoir empty rate at about 10%, and reducing the risk of water shortages. Our study can serve as a reference for effectively addressing the challenges associated with IBWT projects, and it can inform socioeconomic development in receiving areas while optimizing water transmission and allocation.

Inter‐Basin Water Transfer Effectively Compensates for Regional Unsustainable Water Use

AbstractGlobally, a persistent decline of freshwater availability has been identified over a number of intensively irrigated agricultural regions. Large‐scale inter‐basin water transfer (IBWT) has been suggested as a key tool for stabilizing regional terrestrial water storage (TWS). However, IBWT projects are prohibitively expensive, and their large‐scale cost effectiveness remains unclear. Here we quantify the IBWT impacts on TWS trends in the North China Plain (NCP), a global hotspot for TWS depletion and IBWT. Based on in‐situ observations, remote sensing, and water balance principles, we provide a framework to disentangle complex climate and anthropogenic impacts on NCP TWS. Results show that the NCP TWS depletion rate was significantly attenuated in 2015–2021, which is primarily attributable to recently enhanced IBWT. Otherwise, the average NCP TWS would currently be 94.9 ± 4.9 mm (or 12.2 ± 0.6 km3) lower. However, the positive effect of IBWT is partly offset by increased crop water consumption (−24.1 ± 5.2 mm or −3.1 ± 0.7 km3). IBWT and agricultural management (i.e., reducing crop density) are both necessary for stabilizing future NCP TWS. Otherwise, a TWS declining trend exceeding 100 mm/year may occur under elevated CO2 conditions. As such, this study verifies the feasibility and effectiveness of IBWT for mitigating regional water shortages, as well as the crucial role of agricultural management in stabilizing regional TWS.

Application of Impact Elastic Wave Method in Quality Inspection of Concrete Lining

As the main part of inter-basin water transfer project, water tunnel plays an important role in long-distance water conveyance. In water tunnel, the lining quality problem is one of the important potential safety hazards of the tunnel engineering. It is very necessary to detect the internal defects of concrete lining. In this paper, a multi-parameter comprehensive interpretation method based on impact elastic wave is proposed to quickly detect the internal defects of lining. The common offset time domain analysis method, frequency domain analysis method and two-dimension Rayleigh wave method are used for data processing. The detection method has the characteristics of single data acquisition and multi-parameter joint interpretation. The physical model of concrete lining is tested and compared with the result of GPR method to verify the accuracy of this method. The coring results show the reliability and stability of this method in practical application.

Challenges of typical inter-basin water transfer projects in China: Anticipated impacts of climate change on streamflow and hydrological drought under CMIP6

Inter-basin water transfer projects are critical for economic development in water scarcity regions. However, the streamflow reduction and the frequent dry extremes in a warming environment raise significant concerns regarding the sustainability of such projects. Based on the latest CMIP6 data, hydrological model, Standardized Streamflow Index (SSI), and run theory, this study systemically examined the future streamflow and hydrological drought changes in the Hanjiang to Weihe River Water Diversion Project (HWWDP) area, China. Significantly, as the most challenging project management scenario, the response of spatially compound hydrological drought (i.e., concurrent hydrological drought in both the water intake and receiving area) was further revealed. This analysis offers the potential to yield novel insights into the prospective management strategies for the HWWDP. The investigation covers the baseline period (1971–2014) and future periods (2021–2100) under SSP245 and SSP585 scenarios. The outcomes demonstrate a decline in annual average streamflow of 5.0–6.4 (SSP245) hundred million cubic meters in the water receiving area and 4.6–7.5 (SSP245) and 3.4–8.1 (SSP585) hundred million cubic meters in the water intake area, respectively, compared to the baseline period. Furthermore, hydrological drought frequency may increase in both the water receiving and source areas, particularly in the summer under SSP585. The duration, severity, and peak intensity of hydrological drought events in the receiving area are expected to exacerbate due to climate change, while those impacts on water intake area should be relatively minor. The spatially compound hydrological drought is expected to occur more frequently in different months except April. The conditional probabilities of spatially compound hydrological drought occurrence may rise by 5.2%-18.7% (SSP245) and 5.9%-20.4% (SSP585) in different months when drought occurs in the water intake area. Moreover, higher probabilities are expected to be observed from April to October when the water receiving area experiences drought. These findings underscore the necessity for adaptive climate change management of the HWWDP to address the future reduction in streamflow and more severe hydrological drought.

Complex network-based analysis of inter-basin water transfer networks

Driven by water resources scarcity, inter-basin water transfer (IBWT) projects have emerged and evolved, thereby shaping the current water supply framework. As IBWT projects increase, they gradually acquire network characteristics, giving rise to IBWT networks. However, the impact of the development of IBWT networks on water-supply patterns remains unclear? Analyzing the spatial and temporal growth patterns of IBWT networks through the lens of complex network theory can help answer this question. This study established a framework for analyzing IBWT networks using complex network analysis (CNA). Within this framework, we analyzed the spatial and temporal development characteristics of the IBWT network by quantifying its global properties across three dimensions: efficiency, elasticity, and coordination. Six centrality indicators were employed to measure the significance of individual nodes. Finally, the Infomap method was employed for network community detection. The results demonstrated that the CNA-based framework effectively captured the comprehensive development of the IBWT network, which underwent six stages from inception to high-speed, near-term, and long-term Stages. IBWT network efficiency, elasticity, and coordination all showed growth, which was most pronounced in 2013–2022, where the scaled global efficiency, network efficiency, average node connectivity, and average betweenness centrality metrics all grew by a factor of greater than 4. Importantly, the total percentage of centrality greater than 0.2 in the Huang-Huai-Hai-Chang Basin was 63.0%. The 125 initial IBWT projects in the IBWT network contained 58 communities, while the subsequent construction of 57 projects added only 12 communities. Future new IBWT network projects will tend to joined existing communities.

Spatiotemporal evolution of dissolved organic matter (DOM) and its response to environmental factors and human activities.

The South-to-North Water Diversion East Project (SNWDP-E) is an effective way to realize the optimal allocation of water resources in China. The North Dasha River (NDR) is the reverse recharge section that receives water from the Yufu River to the Wohushan Reservoir transfer project line in the SNWDP. However, the dissolved organic matter (DOM) evolution mechanism of seasonal water transfer projects on tributary waters has not been fully elucidated. In this paper, the NDR is the main object, and the changes in the composition and distribution of spectral characteristics during the winter water transfer period (WT) as well as during the summer non-water transfer period (NWT) are investigated by parallel factor analysis (PARAFAC). The results showed that the water connectivity caused by water transfer reduces the environmental heterogeneity of waters in the basin, as evidenced by the ammonia nitrogen (NH4+-N) and total phosphorus (TP) in the water body were significantly lower (p<0.05, p<0.01) during the water transfer period than the non-water transfer period. In addition, the fluorescence intensity of DOM was significantly lower in the WT than the NWT (p<0.05) and was mainly composed of humic substances generated from endogenous sources with high stability. While the NWT was disturbed by anthropogenic activities leading to significant differences in DOM composition in different functional areas. Based on the redundancy analysis (RDA) and multiple regression analysis, it was found that the evolution of the protein-like components is dominated by chemical oxygen demand (COD) and NH4+-N factors during the WT. While the NWT is mainly dominated by total nitrogen (TN) and TP factors for the evolution of the humic-like components. This study helps to elucidate the impact of water transfer projects on the trunk basin and contribute to the regulation and management of inter-basin water transfer projects.

The Optimization of Water Storage Timing in Upper Yangtze Reservoirs Affected by Water Transfer Projects

To alleviate regional disparities in water resource distribution and consequent scarcity, China has initiated and planned a series of inter-basin water transfer projects using the Yangtze River Basin as the source. These projects are expected to divert approximately 33.4 billion cubic meters of water annually from the Yangtze River Basin. The implementation of these water transfer projects will inevitably alter the hydrological conditions in the upper reaches of the Yangtze River, impacting the reservoir storage strategies of cascading hydroelectric stations under current end-of-flood-season operational plans. This study quantitatively assesses the impact of water transfer projects on end-of-flood-season reservoir storage in cascading systems using the reservoir fullness ratio as an indicator. Employing reservoir storage analysis models, optimization techniques, and flood risk assessment methods, we simulated reservoir storage processes to evaluate associated flood risks and derive an optimized timing strategy for cascading reservoir storage. The results indicate that advancing the reservoir filling schedule by five days for both the Baihetan and Three Gorges dams can offset the adverse impacts of water transfer projects on reservoir storage efficiency. This adjustment restores the reservoir fullness ratio to levels observed in scenarios without water transfers while still meeting flood control requirements. After optimizing the timing of reservoir filling, the electricity generation capacity for the Baihetan and Three Gorges dams increased by 1.357 and 3.183 billion kWh, respectively, under non-transfer scenarios. In water transfer scenarios, the electricity generation for the Baihetan and Three Gorges dams increased by 1.48 and 2.759 billion kWh, respectively. By optimizing reservoir filling schedules, we not only improved the reservoir fullness ratio but also enhanced the electricity generation efficiency of the cascading systems, offering valuable insights for future reservoir operation optimization.

Flow backward alleviated the river algal blooms

Mechanistic understanding and prediction of river algal blooms remain challenging. It is generally believed that these blooms are formed by the slowdown of water dynamics in tributaries due to the support of the main stream. However, few studies have investigated the impact of flow backward caused by the difference in water dynamics between the main stream and tributaries. Here, we focus on the eutrophication issue in the middle-lower reaches of the Han River, which is affected by the Middle Route of the South-to-North Water Diversion Project (SNWDP), the largest inter-basin water transfer project in Asia. We discover that the reversal of the Yangtze River water level could effectively alleviate the occurrence of Han River water blooms. The Yangtze River frequently back flows into the lower reaches of the Han River, with the probability of such events increasing as it nears the confluence (20km from the Yangtze: 9.5%, 10 km: 19.0%, 8 km: 28.6%). This flow backward carries nutrients that reduce the nitrogen to phosphorus ration (N:P), leading to a shift in the nutrient structure of the Han River. This change is concomitant with a significant decline in algae biomass (Chlorophyll-a=11.19 µg·L-1 and algae density=0.41×107 cells·L-1 under natural flow, Chlorophyll-a=5.19 µg·L-1 and algae density=0.18×107 cells·L-1 under flow backward), as well as a weakening of the correlation (R) between diatom density and chlorophyll-a concentration, i.e., R=0.38 (p>0.05) under flow backward conditions versus R=0.72 (p<0.01) under natural flow conditions. As phosphorus limitation typically suppresses algae growth, the correlation between diatom density and chlorophyll-a concentration can help to reveal the dominance of diatoms, with stronger correlations indicating greater diatom dominance. Consequently, our study provides evidence that the flow backward can alleviate river algal blooms by weakening the growth advantage of diatoms. This study could prove valuable in investigating the eutrophication mechanism within the complex hydrodynamic conditions of rivers. SYNOPSIS: Flow backward caused by the water level difference between the main streams and tributary alleviated the occurrence of river algal blooms in the confluence area.