Opportunities and challenges of interdisciplinarity in river water environmental ethics and integrated river basin management

This paper examines the ethical issues of water environment in the context of river management in practical engineering and technological applications. In particular, three important issues are discussed in this paper referring to two actual engineering cases in ancient and modern China, that is, the construction of ancient Dujiangyan irrigation project in Sichuan, China, and the modern practice of integrated operation of flood control and pollution prevention in Huai River Basin. The three issues include how to consider the trade‐offs between flood control and irrigation, how to balance flood control and contamination prevention related to sudden water pollution incident, and how to ensure the protection of water environments and ecology in rivers under the grand challenges of natural environmental changes and high‐intensity human activities. Finally, this paper concludes by emphasizing the future development of water environmental ethics and its interdisciplinary integration with modern science & technology in smart river management in China.


| INTRODUCTION
Rivers are essential natural systems that provide habitats for humans and support their livelihoods.However, intense human activities related to economic and social development, including agriculture, urbanization, and river development, have led to significant concerns regarding river water environments and ecological protection.These issues have emerged as critical concerns for global and regional water security, as well as sustainable socioeconomic development (Braga et al., 2014;Michalak et al., 2023).Sustainable development aims to meet the current needs without compromising the ability of future generations to fulfill their own needs.The United Nations (UN) 2023 Water Conference, held at the UN Headquarters in New York, United States, comprehensively discussed these water security issues, with a specific focus on UN Sustainable Development Goal 6 (SDG6), which aims to ensure the availability and sustainable management of water and sanitation and plays a connecting role to all other SDGs (https://water.org/united-nations-water-conference-2023).To foster sustainable development, environmental ethics need to be seriously considered.
Environmental ethics is a discipline within philosophy that explores the moral relationship of human beings and the environment, as well as the value and moral status of the environment and its nonhuman contents (Aftab et al., 2022;de Wet & Odume, 2019;McShane, 2009).While traditional environmental ethics has primarily been rooted in philosophy, ethics, and law, the field has gained significant attention in recent years due to the growing awareness of environmental issues, including the pressing concerns of water pollution and ecological degradation in river basins.In the face of ethical challenges in integrated river basin management, it is imperative to study water environmental ethics from the perspectives of science and technology using cross-disciplinary approaches.These approaches involve incorporating environmental science problem-solving aspects into the framework of environmental ethics and introducing new scientific questions through an environmental ethics lens when studying environmental issues.
Here we discuss several crucial issues and challenges related to environmental ethics, particularly water environmental ethics.The traditional approach to economic development has resulted in new environmental problems, including water shortage, water pollution and the disruption of aquatic ecosystems, due to the increasing human impact on nature (Braga et al., 2014;Xia, 2023).As industrialization and scientific and technological progress advance, ethical issues arise in the realm of environmental and ecological governance.Examples include China's air pollution and haze problems and their management, the hazards and control of Pharmaceuticals and personal care products at the micro level, water pollution problems and their management, as well as ecological compensation and the ecological balance of rivers and lakes (Blanchfield et al., 2022;Bryan, 2019;Zhang et al., 2023).These issues have become cross-cutting concerns that intersect across science & technology, the economy, the society, and the environment (Grunwald, 2016;Mao et al., 2017;Xia, 2023).Hence, to foster water security and integrated water resources management at river basin scale, there is an immediate need for conducting more intense research focusing on water environmental ethics by considering the dual goals of economic development and environmental protection.This paper will discuss the theoretical and interdisciplinary issues on the construction of water environment ethics for integrated river basins management.Two typical water engineering project examples include (1) China's earliest water conservancy project in river water security and water management, namely the Dujiangyan Water Conservancy Project in Sichuan, and (2) Huai River basin's water management and integrated operation project with the consideration of water quantity, water quality and river ecosystem health.Furthermore, this paper will provide a viewpoint on the importance of scientific and technological advancements at the intersection of natural and social sciences for studying water environmental ethics in river ecosystems for sustainable development.This includes the development of river basin simulators to facilitate the study of water environmental ethics and solutions for integrated water resources management.Finally, it will explore the future prospects of the overlap between water environmental ethics, hydraulic engineering, and smart river management, while considering new challenges and opportunities in a changing world.

| THE CASE OF DUJIANGYAN WATER CONSERVANCY PROJECT AND ITS RIVER ETHICS IN ANCIENT CHINA
The world-renowned Dujiangyan Water Conservancy Project (also known as Dujiangyan Irrigation System) situated along the Minjiang River of Sichuan Province, a major tributary of Yangtze River in China, was constructed between 256 and 251 BC and has been in continuous operation for more than 2000 years (Bangben, 2008; Figure 1).During the era of its inception, this area confronted major water environmental challenges in flood and drought control as well as agricultural irrigation needs in the Chengdu Plain.During the flood season, the Chengdu Plain, located in the Sichuan Basin, was prone to flooding caused by the Minjiang River and Dadu River, posing substantial threats that adversely affected agricultural production and daily lives of local residents.On the other hand, agriculture in the Chengdu Plain demanded a reliable water management system to secure a consistent and adequate water supply during the dry season.This was pivotal for effective farmland irrigation and crop cultivation, with the overarching goal of enhancing agricultural yield and ensuring food security.The construction of the Dujiangyan irrigation system aimed to address both issues.Through a sophisticated water diversion and irrigation system, it not only regulates water flow to prevent floods but also furnishes a dependable water source for irrigation across the Chengdu Plain.This engineering marvel played a historic role in mitigating water-related disasters and meeting the agricultural needs of the region.It is so far, the world's oldest and the sole remaining ancient river water management project featuring natural water diversion without artificial dams, and still play a huge benefit at present for people in the Chengdu Plain as the majestic long-term grand ecological water conservancy project with continuous operation for over two millennia.
From the perspective of environmental ethics, the case of Dujiangyan Water Conservancy Project, which was built in ancient China, has several features that are worth revealing: 1. Righteousness: The Dujiangyan Water Conservancy Project eliminates the flood disaster in the region of the Chengdu Plain.2. Accountability and Fairness: This project exemplifies water conservation engineering that maintains the ecological sustainability of rivers without dam construction.3. Scientificity: This project scientifically solves the difficulty in automatic diversion of river water, automatic sand discharge, and control of the inflow for irrigation.Smart Engineering and Advanced Science & technology support human being's responsibility in balancing the prevention of disasters and the welfare of food production.
The Dujiangyan water conservancy project is an excellent case of implementing water environmental ethics by finding effective balanced solutions to the comprehensive dilemma of irrigation, flood discharging and sands reduction.This project transformed Chengdu plain into the "Land of Abundance" and embodied a deep philosophical idea and approach to integrating environmental ethics with science and technology, therefore can serve as a valuable inspiration and lesson in environmental ethics for the construction of modern ecological water conservancy projects.

| THE CASES ON RIVER ETHICS AND INTEGRATED WATER MANAGEMENT IN MODERN CHINA
China faces a unique set of challenges in ensuring water security, including issues related to water supply, floods and droughts, water pollution, and the degradation of aquatic ecosystems due to rapid industrialization and socioeconomic development.In response, traditional water resources management has shifted into a new stage of integrated river basin management that requires taking into account the multiple needs of reducing water disasters and guaranteeing the security of water supply, while simultaneously combating water pollution and protecting water ecology (Biswas, 2004;Xia & Takeuchi, 1999).River ethics, especially those related to the water environment and water ecology, have become increasingly crucial, with the support of science and technology serving as important tools and keys.The author and his team have been researching the issue of integrated water management related to changing environment and water environmental ethics in the river basin system in China (Xia & Chen, 2001;Xia & Takeuchi, 1999;Xia et al., 2021).Huai River is a unique case on how to present solution for such complex system (Xia et al., 2009;Xia et al., 2011).This section presents a case study related to the integrated operation for water quantity, water quality, and water ecology in the Huai River Basin, highlighting the challenges at the intersection of environmental ethics and science and technology, including the contradictions and controversies surrounding engineering measures and water management.This exploration underscores China's evolving water management landscape, emphasizing the need to balance competing demands on water resources while upholding ethical considerations and leveraging scientific advancements for sustainable practices.

| BACKGROUND OF HUAI RIVER BASIN
The Huai River Basin (HRB), spanning an area of 270,000 km 2 , and strategically positioned at the convergence of southern and northern parts of China, confronts significant challenges from floods and droughts (Figure 2).To address these challenges, an extensive hydraulic engineering network of 11,000 sluices and dams have been implemented in the river basin for flood control, water supply, and other purposes.Additionally, the HRB exhibits an average population density of 611 people/km 2 , surpassing China's average by 4.8 times and ranking highest among major river basins in China, highlighting the vulnerability of water security (Xia et al., 2009).The basin's socioeconomic development, particularly the burgeoning growth of small and medium-sized enterprises in the 1990s, has brought forth a pressing concern about water quality in numerous tributaries and water environmental protection at the river basin scale.This is exacerbated during heavy rainstorm events, elevating the risk of severe water pollution incidents in the Huai River (Bai & Shi, 2006;Xia et al., 2009Xia et al., , 2011)).
For instance, in July 1994, a significant water pollution incident occurred in the Huai River, resulting in significant socioeconomic impacts and losses.The incident's primary causes were twofold: first, an abrupt heavy rainfall on the Huai River Basin led to substantial runoff into sluices and dams, prompting authorities to employ them for floodwater drainage beyond the flood control level.Second, the release of stored sewage from sluices and reservoirs accumulated during the non-rainy season resulted in a 9 km long sewage mass, with 200 million cubic meters of sewage flowing into the river.This forced waterworks along the mainstream of Huai River to cease water collection for 54 days, leaving 1.5 million people without access to clean tap water and incurring direct economic losses totaling hundreds of millions of Chinese yuan.

| ENVIRONMENTAL ETHICS RELATED TO WATER MANAGEMENT ISSUE OF HUAI RIVER
Facing to the challenges and to ensure effective water governance and management in the Huai River Basin, it is essential to not only strengthen control of polluted sources entering the river and remediate polluted water bodies but also address the issue of coordinating flood control and pollution prevention.This is a significant challenge that requires reducing the occurrence of major water pollution incidents at the basin scale.Achieving this objective is a key goal and requires the development of key technologies in Huai River water management.Furthermore, this issue is closely linked to environmental ethics and requires further research to address this critical challenge and meet national demands for effective water governance and management in the river basin.Thus, the research and practice primarily focus on three key scientific and technological issues: 1. Understanding the coupling mechanism of the basin water cycle and water quality and quantity processes under the influence of high-intensity human activities.2. Identifying the systematic relationship between multiple factors in the river, such as pollution loads, sluice and dam regulation, and the interaction between the river's hydrological processes and changes in water quality.
Additionally, the analysis of sluice & dam regulation capacity is considered.3. Establishing an early warning and forecasting system to monitor changes in water quality and quantity in the Huai River.This involves the implementation of integrated flood prevention with pollution control to reduce the risk of flood disaster loss and major water pollution accidents.
From the perspective of environmental ethics, there are three important principles that support the operation of this system and guide smart water management, that is, 1. Justice: Justice plays a crucial role in the environmental ethics of the Huai River case, particularly when addressing sudden basin-scale floods and the resulting water pollution incidents.In such situations, the primary objective is to prevent any loss of life or, at the very least, minimize the loss of human lives, prioritizing the safety and well-being of people affected.2. Responsibility: In addition to justice (i.e., protecting people's lives), responsibility is another crucial aspect when addressing the risk of flood disasters in the Huai River basin with the primary focus on minimizing the occurrence of sudden water pollution incidents.This involves the implementation of early warning and forecasting systems to monitor changes in the water quality and quantity of the Huai River, coupled with the coordinated operation scheduling of sluices and dams, to the greatest extent possible.On the other hand, during non-flood periods in basin management, there is a focus on the transformation of the industrial structure in the basin and the control of water pollution at its source.Additionally, measures need to be taken to enhance water circulation in the river network and improve the connectivity of the water system, aiming to reduce pollution sources and prevent the cumulative accumulation of pollutants in the river.3. Fairness: Fairness is a key consideration in response to the demands of all residents living along the upstream and downstream of the Huai River with the consideration of environmental governance, ecological protection, and the improvement of quality standards.In other words, the economic development of some parts shall not be obtained by sacrificing the ecological environment of other parts.To achieve fairness, it is essential to transform the traditional joint management of water quality and quantity to the enhanced integrated management by coordinating not only water quality and quantity, but also aquatic ecology in the river basin.This involves enhancing ecological governance in the basin, including the conservation of wetlands, the improved connectivity of water systems, and the implementation of institutional innovations such as the River Chief and Lake Chief systems (among which the chiefs, i.e., the heads of local governments are fully responsible for the ecological environments of rivers or lakes in their territories).Ultimately, the goal is to achieve sustainable development in the basin, aligning with the objectives of the Sustainable Development Goals (SDGs) for economic, social, and environmental aspects.
The Huai River has seen significant improvements in pollution control over the past 20 years.The hard work and dedication have led to remarkable achievements, including the absence of large-scale sudden water pollution incidents since 2005.This has effectively guaranteed the safety of water usage in towns located along the river.In 2020, the water quality in the entire basin reached a historic milestone, transitioning from mild pollution to good quality for the first time ever.The proportion of excellent and good quality river sections reached an impressive 78.9%, marking a comprehensive elimination of water quality deterioration (Wang & Ongley, 2004;Xia et al., 2011;Xia, 2023).

| PERSPECTIVES ON INTERDISCIPLINARITY OF WATER ENVIRONMENT ETHICS AND SMART WATER MANAGEMENT
1.As the pursuit of a happy life and the importance of environmental issues and ecological conservation continue to grow, the need for high-quality development of the economy and society become increasingly prominent.One particular area that demands attention is the issue of sustainable development goals, especially as it relates to water security and environmental ethics.on philosophical and legal aspects, will shift to science and technology-based ethics, that urgently require intersection and integration with natural sciences, particularly with modern scientific and technological developments.This integration, a crucial direction for future development, will strengthen the intersection between water sciences, environmental sciences, ecological sciences, and social sciences as they apply to environmental ethics in water security and integrated river basin management.Supported by technology and scientific knowledge, such as Digital Twin Technologies and River Basin Simulators and so forth, can bridge the gap between environmental ethics and smart water management.For the sustainable use of water resources and the achievement of SDG6, research and practice on the relationship between environmental ethics and sustainable development can effectively address questions such as harmonizing the equity of unbalanced regional development, balancing the spatial equity problem of mismatch in the spatial distribution for economic, resource, and ecological relationships, and sustaining the issue of intergenerational equity in the face of changing population size and total economic growth.
In conclusion, the intersection between the social sciences of environmental ethics and the natural sciences of watershed water resources management is very important.The river basin system approach build upon hydrological sciences plays a key role for supporting these intersections.This field is poised for future growth, and it is crucial to enhance research, practice, application, and theory to address the resource and environmental challenges posed by global change and sustainable development.By doing so, we can contribute to the development of interdisciplinary theories and methodologies, as well as the application and cases for the promotion of the sustainable development at global and regional scales.