Especially for the current situation evaluation of the Danjiangkou reservoir water environment and the needs of environmental protection design work.

**Key words**: Protection, water source quality, methods and countermeasures, Central Route of South-to-North Water Diversion Project

**Abstract**: Starting from the current status of water source quality along the Central Route, this paper analyzes the problems existing in water resources protection and management, explains the importance of water environment monitoring and protection in the water source area, and then proposes methods and countermeasures to combine basin and regional management, strengthen unified water resource management, and ensure the water quality of the Central Route at a macro level.

**1. Geography and Natural Environment**

**1.1 Geographic Location**

The Danjiangkou Reservoir is the water source for the Central Route of the South-to-North Water Diversion Project, located in Hubei and Henan provinces. It administratively belongs to six counties and cities in these two provinces, with a water area of 750 square kilometers. About 50% of the reservoir's area is within Hubei Province, and its upstream length extends 177 km along the Han River and 83 km along the Dan River.

**1.2 Natural Environment**

The Danjiangkou Reservoir is a comprehensive reservoir for flood control, power generation, irrigation, shipping, and aquaculture, formed by the Han River and Dan River (referred to as "Han Reservoir" and "Dan Reservoir"). The general trend of the reservoir slopes from northwest to east. It is located in the subtropical zone, with mild weather and abundant rainfall. The average annual precipitation is about 1,000 mm, with 70-80% occurring between May and October. The average annual inflow volume is 39.5 billion cubic meters, and the normal storage capacity is 17.5 billion cubic meters, making it a water-rich reservoir.

**2. Water Environment Status**

**2.1 Water Environment Quality**

(1) The main water sources of the Danjiangkou Reservoir are the Han River, the Dan River, and their major tributaries. The Han River accounts for over 75% of the total inflow. For more than 30 years, water quality monitoring data analysis has shown that, except for some sections where individual parameters exceed the III category standard of groundwater environmental quality, most of the water quality in the upper reaches of the Han River (above the Danjiangkou Reservoir) meets or exceeds II category standards. The river sections meeting I-III category standards account for 90.3%, while the Dan River sections meeting I-III category standards account for 93.2%.

(2) Currently, the Danjiangkou Reservoir serves as a drinking water source for Danjiangkou City and provides partial industrial and agricultural irrigation water for Henan and Hubei provinces. Based on recent monitoring data, 86% of the monitoring sections meet I-II category standards, 10% meet III category standards, and 4% meet IV category standards. Overall, the water quality is good. As Asia's largest artificial lake, the Danjiangkou Reservoir has an extremely strong self-purification capacity and is considered an ideal water source for the Central Route of the South-to-North Water Diversion Project.

**2.2 Water Environment Monitoring**

(1) The responsibility for water environment monitoring of the Danjiangkou Reservoir lies with the Hanjiang Water Environment Monitoring Center under the Yangtze River Commission. Since the construction of the Danjiangkou Reservoir began in 1958, the Yangtze River Commission has been conducting water quality monitoring and analysis along various sections of the Han River upstream to study the impact of water conservancy projects on the water environment. After the reservoir began storing water in 1967, timely water quality monitoring and analysis were added at dam-related sections. To investigate water pollution, multiple pollution source surveys have been conducted in eight counties and cities within the reservoir basin, collecting extensive basic pollution source data. Additionally, three large-scale sampling analyses have been carried out to understand the changes in water quality and sediment conditions after reservoir storage. Currently, the Yangtze River Commission has set up eighteen water quality monitoring sections in the Danjiangkou Reservoir, analyzing over 50 items. Due to the reservoir's involvement in three provinces, cross-provincial boundary monitoring tasks have also been initiated. Monthly water environment monitoring data is provided to the state for use in the Central Route of the South-to-North Water Diversion Project and the national "Status of National Water Environment" information report.

(2) To meet the needs of the Central Route of the South-to-North Water Diversion Project, especially for the evaluation of the current water environment status of the Danjiangkou Reservoir and the requirements of environmental protection design, in recent years, key efforts have been made to monitor the water environment at Taocha, the starting point of the Central Route channel. Extensive water environment investigations and evaluations have been conducted around the reservoir and its tributaries, along with biological monitoring in the reservoir area. Over the decades, the Hanjiang Water Environment Monitoring Center has conducted extensive water quality surveys, monitoring, and evaluations, accumulating detailed and reliable water environment data for the analysis of water quality conditions in the water source area of the Central Route. This data provides a reliable basis for water source protection and environmental impact assessments.

**2.3 Existing Problems**

(1) Increasing point-source pollution poses a potential threat to the reservoir area.

According to long-term monitoring data, due to its large water volume, high storage capacity, and strong dilution and self-purification ability, the water quality of the Danjiangkou Reservoir has consistently remained at I-II category standards. However, with the development of local industries, particularly the increase in private and privately-owned enterprises, some tributaries of the reservoir have been polluted to varying degrees, posing pollution risks to the reservoir area. For example, the Shending River, whose upper reaches include Shiyan City—a new city developed due to the automobile industry—is the largest industrial city in the upstream basin of the Danjiangkou Reservoir, accounting for about 70% of the reservoir's pollution load. Although industrial wastewater pollution has somewhat eased in recent years, according to monitoring results, the main pollutants in the Shending River—ammonia nitrogen, COD, BOD, and fecal coliform bacteria—still exceed standards, indicating severe domestic sewage pollution. Seventy percent of urban sewage in the city flows into the Han River through the Shending River, making it one of the largest pollution sources for the Danjiangkou Reservoir. Although the proportion of inflowing water is small, the ratio of pollution to runoff is high, and there is a possibility of increasing pollution. Another example is the Laoguan River, which experiences lighter pollution during the wet season when water levels are high but significantly heavier pollution during the dry season, with water quality reaching IV-V category standards.

Local polluting enterprises continue to illegally discharge wastewater despite repeated bans, closely related to local interests. Since the upstream and surrounding areas of the Danjiangkou Reservoir are mostly mountainous regions with inconvenient transportation and weak environmental awareness, pollution accidents frequently occur. For instance, the cyanide spill incidents in the Xun River of the upper Han River and the Tie River of the upper Dan River in 2000 caused serious impacts.

(2) Lack of unified and effective mechanisms for water resource management.

Currently, the South-to-North Water Diversion Central Route project has begun, but as the water source area, the Danjiangkou Reservoir still faces issues of decentralized water resource protection and management. The reservoir and its upstream areas involve three provinces—Henan, Hubei, and Shaanxi—with overlapping water resource management and monitoring departments and monitoring sections, leading to unnecessary waste and even conflicts between provinces, localities, and systems. Without coordination from a unified water resource management institution, there is a lack of emergency response capabilities to deal with pollution accidents, failing to meet the needs of modern water resource protection and management work. There is also a lack of a unified mechanism for water resource management prioritizing national interests.

(3) Unreasonable layout of water environment monitoring, failing to play its due role.

The Danjiangkou Reservoir is vast, covering an area of 750 square kilometers with over 20 major tributaries. Currently, some water areas lack monitoring, failing to meet the needs of water resource protection and management. At the same time, when evaluating water resources across the entire reservoir basin, the representativeness is insufficient, leading to inaccurate evaluations. In some water areas, monitoring overlaps, with significant differences in monitoring methods and capabilities among different places and departments, making it difficult to conduct scientific and effective evaluations. On one hand, this leads to waste, and on the other hand, it fails to effectively resolve disputes related to water resource management, thus not truly fulfilling the supervisory and management role for water resource protection.

**3. Methods and Countermeasures for Water Resource Protection**

**3.1 Strengthening Unified Water Resource Management Through Legal Means**

Due to the large watershed area controlled by the Danjiangkou Reservoir, local governments and departments often focus on their own regional interests, making it difficult to consider the overall water resource protection of the entire watershed. Although in recent years, local governments have improved their understanding of water resource protection in the South-to-North Water Diversion water source area, when it comes to local interests, there is still a tendency to prioritize economic benefits over environmental protection, focusing on short-term gains at the expense of long-term interests. As water administrative authorities, basin institutions face significant constraints in exercising their responsibilities and authority in water resource protection and management.

China’s new Water Law has strengthened the unified management of water resources, clearly defining basin institutions as water administrative authorities and enhancing basin management. Since the state has already clarified the legal status, basin institutions must take on their responsibilities, strengthen the unified management and coordination of water resource protection departments, and incorporate management work into a more detailed, scientific, and unified track based on national interests. Therefore, given the characteristics of the Danjiangkou Reservoir, the urgent task now is to quickly formulate relevant regulations for protecting the water source area, such as the "Regulations on Water Resource Protection in the Water Source Area of the South-to-North Water Diversion Project." These regulations will constrain actions affecting the water environment through policy and administration. Formulating regulations ensures there is a legal basis, so basin institutions must adapt to the requirements of administrative rule of law and strengthen legal responsibilities to ensure the northward flow of clean water.

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