The complex changes in the Quang Hue River bed in recent years are one of the causes of salinity and water shortage in the downstream of the Vu Gia River. Photo: HOANG HIEP

Lesson 1: Climate change is increasingly extreme

In early 2025, a temporary dam to prevent saltwater intrusion on the Vinh Dien River was urgently built after saltwater from the Han River estuary penetrated deep into the Tu Cau pumping station. The water level of the Vu Gia River at the Ai Nghia hydrological station continued to fluctuate strongly due to the large flow through the Quang Hue River to the Thu Bon River as well as through the An Trach irrigation system.

12 years, 15 times of temporary damming the river

On March 10, 2025, the temporary dam of Vinh Dien River downstream of Tu Cau pumping station was completed to retain fresh water for irrigation of more than 1,855 hectares of rice and crops in Dien Ban town, part of Hoi An city (Quang Nam) and Hoa Quy ward, Ngu Hanh Son district (Da Nang); at the same time, ensuring domestic water supply for people in Dien Ban town and neighboring areas. This is the 15th time this temporary dam has been built in the past 12 years. However, the construction of this temporary dam not only obstructs the waterway from Han River to Thu Bon River, but also causes deep saltwater intrusion into Cam Le River and the raw water intake area of ​​Da Nang Water Plant.

Similarly, on the Quang Hue River (Dai Loc District, Quang Nam Province), over the past 12 years, Da Nang City and Quang Nam Province have coordinated to build temporary dams many times to reduce the rate of water diversion from the Vu Gia River to the Thu Bon River, especially when the water level of the Vu Gia River is low. However, in recent years, the Quang Hue River has undergone complex changes in its channel and there is still a potential risk that the Vu Gia River will open a new Quang Hue River mouth to join the Thu Bon River like the historic flood in 1999. Not only that, the situation of riverbank erosion and changes in the channel of the Quang Hue River is very complicated, causing many local water shortages in the two localities.

On the other hand, in recent years, due to the impact of hydroelectric projects in the upper reaches of the Vu Gia - Thu Bon River, especially the Dak Mi 4 hydroelectric plant, which almost completely transfers water from the Vu Gia River during the dry season to the Thu Bon River to generate electricity, the downstream of the Vu Gia River has been severely saline.

Along with that, due to the inadequate regulation of power sources in the national power system and the operating procedures of hydropower plants as well as the degradation of the An Trach irrigation system after more than 20 years of operation, the water level of Vu Gia River, Yen River, and La Tho River is often locally lowered, affecting domestic water supply and agricultural production. In particular, the water level of Vu Gia River in Ai Nghia has twice dropped historically in August 2023 and February 2024. In 2024, the salinity of Cam Le River and the raw water intake area of ​​Cau Do Water Plant has been extremely high and continuous for 3 months, affecting production in La Huong vegetable area and vegetable and rice areas along Yen River.

Not only that, the lowering of the Yen River's water level also causes the Tuy Loan River's water level to drop, threatening the reserve source of domestic water supply for Da Nang city, because the Tuy Loan pumping station was built with the intention of supplying additional water to the Cau Do water plant.

Vice Chairman of the People's Committee of Hoa Phong Commune (Hoa Vang District) Ngo Van Nhan said: "People who have been farming in the downstream of Yen River and Tuy Loan River for more than 40 years have never seen a year where the river water was as heavily and long-lastingly saline as in 2024. It can be said that this is historic salinity, with high salinity levels remaining for nearly 20 days at the beginning of the summer-autumn crop. Through research, one of the main reasons is that the freshwater source from upstream is low, so when the tide rises, the salinity intrudes and lies deep in Yen River."

Many challenges to water security

Deputy Director of the Department of Agriculture and Environment of Da Nang City Nguyen Hong An said that the downstream of Vu Gia - Thu Bon River is facing a series of serious problems affecting water security and sustainable development. The first challenge is the uneven distribution of water flow. Under the impact of climate change, rainfall is forecast to decrease sharply in the dry season, increasing the risk of prolonged drought, greatly affecting water resources for daily life, production and agriculture.

Changes in river flow and channel have caused the water level in the river to decrease, making it difficult for water exploitation projects along the river. The lowering of water levels has also reduced water intake capacity, especially in downstream areas during the dry season. The impact of climate change in recent years has caused prolonged heat waves, severe droughts and saltwater intrusion, disrupting the balance of the water resources system in the basin. This situation not only affects water resources but also causes great damage to people, property and the environment. In this context, the water resources of the Vu Gia - Thu Bon river basin at present and in the future depend largely on solving a series of inter-sectoral and basin-level issues.

Faced with the above challenges, there is a need for projects to prevent salinity, retain fresh water, regulate water resources and floods, and regulate rivers... in the coming time. Director of the Department of Management and Construction of Irrigation Works (Ministry of Agriculture and Environment) Nguyen Tung Phong acknowledged that the process of regulating the Vu Gia - Thu Bon river system has been going on for a long time, and the Ministry of Agriculture and Rural Development was also very interested in implementing it in the period from 1999-2013 and monitoring and evaluating the following years, because this is a very complex river system in terms of hydrology, hydraulics...

In recent times, socio-economic development, construction of hydroelectric reservoirs, climate change... have caused many changes in the terrain, channel, flow regime... of the Vu Gia - Thu Bon River. This poses an urgent problem of stabilizing water resources combined with river regulation to solve problems of the ratio of water diversion from the Vu Gia River to the Thu Bon River, flood drainage, sedimentation, landslides... At the same time, re-evaluate the situation, effectiveness, limitations... of the systems of works and solutions that have been deployed, as well as the above changes to have a comprehensive, interconnected, flexible solution to ensure water supply for daily life, agricultural production and flood drainage, natural disaster prevention, socio-economic development in Da Nang city and Quang Nam province.

HOANG HIEP

Source: https://baodanang.vn/kinhte/202504/dau-tu-cac-cong-trinh-thuy-hien-dai-da-muc-tieu-4004717/