Nation-building irrigation: 'Great canal' revives the Mekong Delta

Canal routes that "erased" millions of hectares of acid sulfate soils

Bài liên quan

Nation-building irrigation: Awakening the Red River Delta

After the liberation of the South, with a strategic vision for the Mekong Delta, the Party and the State devoted attention and resources to developing the irrigation system that channels freshwater and washes away salinity and acidity for this land.

Prof. Dao Xuan Hoc, former Deputy Minister of Agriculture and Rural Development (now the Ministry of Agriculture and Environment) and Chairman of the Vietnam Water Resources Development Association, shared that in the North, a closed dike system was built to prevent floods from entering, thereby utilizing alluvium and fostering biodiversity as well as other values of flooding. Meanwhile, the greatest achievement of the irrigation sector in the South has been using floods to rehabilitate acid sulfate soils, reducing affected areas from 1.8 million hectares before 1975 to just 130,000–150,000 hectares today.

As one of the experts and scientists who traveled from the North to the Mekong Delta in the 1980s to study acidity treatment and desalination, Mr. Nguyen Ty Nien, former Director General of the Department of Dyke Management and Flood and Strom Control, recalled, "Many solutions from the Netherlands, the U.S., etc., were proposed to rehabilitate the Dong Thap Muoi region, but they were all too costly. Thus, Vietnam had to take a different path, especially when the country was still poor."

At that time, General Secretary Le Duan personally worked many times with the entire irrigation system to find solutions for millions of hectares of acid sulfate soils, especially in the three sub-regions of Dong Thap Muoi, the Long Xuyen Quadrangle, and the Ca Mau Peninsula. These areas suffered from excess water and widespread flooding in the rainy season but severe water shortages, cracking soils, and acid sulfate soil oxidation in the dry season.

Believing that food security could not be guaranteed without solving irrigation, the irrigation sector devised the "great canal" to bring freshwater, suppress alum for rice farming, treat acidity, and desalinate.

Irrigation engineers and farmers worked together to suppress underground alum while washing away surface alum. Fields had to be kept under water at all times so that alum was pushed down into the deeper layers, preventing it from "seeping up" and raising concentrations on the surface. Meanwhile, surface alum was continuously washed away by regularly changing water.

Local governments and people also invested in building salinity-prevention sluices, helping to retain freshwater and "sweeten" salt-contaminated areas, thereby expanding the area for the second rice crop. Combined with the unique method of "underground sowing," the Mekong Delta has now become the nation's primary rice granary.

The Hong Ngu canal was the first irrigation structure to conquer this wild land, affectionately called the "Central Canal" by local people. Thanks to this project, the cultivated area of the Dong Thap Muoi region expanded significantly.

According to Prof. Dao Xuan Hoc, from the success of the Hong Ngu canal, Vietnam built eight major canals for acidity and alum washing in the Long Xuyen Quadrangle, including Chau Doc, Vinh Te, Cai San, Xeo Cha, Rach Gia–Ha Tien, Cai Trem, Ca Mau, and 30/4 canals.

The flood-based canal projects for alum washing were the second breakthrough in the South, marked by Prime Minister Vo Van Kiet's drastic directives and Prof. Nguyen Sinh Huy of Thuyloi University's scientific contributions. At the time, there were objections, but the results proved remarkably successful. From just 4 million tons when the country was reunified, rice output in the Mekong Delta now reaches about 25–27 million tons.

Outstanding projects across the Mekong Delta's three eco-regions

According to Mr. Vu Viet Hung, Deputy Director General of the Department of Water Works Management and Construction, over the past 20 years, through various sources, the Ministry of Agriculture and Rural Development (now the Ministry of Agriculture and Environment), together with localities, has invested in building numerous irrigation structures to regulate and manage water resources in the Mekong Delta.

Particularly, irrigation systems across ecoregions in the "land of nine dragons" have been thoroughly studied, planned, and invested in synchronously and methodically, tailored to local topography, hydrology, flow dynamics, agricultural ecosystems in each subregion, farming practices, and the livelihoods of local communities.

Specifically, the upper region (freshwater eco-zone), which is regularly affected by flooding but has abundant water resources, is basically free from saltwater intrusion. However, during years of weak flows, low water levels in rivers and canals make it difficult to secure gravity-fed irrigation and water transfer to several communes along the Tien and Hau rivers (in the former Long An and Kien Giang provinces), leading to water shortages. Agricultural production here mainly involves rice cultivation, vegetable farming, and freshwater aquaculture.

Irrigation projects in this region aim to proactively control extreme floods; prevent riverbank erosion to protect residential areas, infrastructure, and 2-crop rice fields; support aquaculture; improve flood drainage routes to the West Sea and Dong Thap Muoi; and reinforce the dike system while dredging canals to enhance water intake, storage, drainage, and flood regulation.

Key projects include the Tan Thanh–Lo Gach canal expansion (Phase 2); the Hong Ngu–Vinh Hung canal (in Dong Thap and former Long An provinces); the An Phong–My Hoa–Bac Binh Dong canal dredging; the Tra Su and Tha La canals; the construction of Tha La and Tra Su sluices; the Upper Mekong Region Management Project in An Giang and Dong Thap provinces; and livelihood models under WB9 Project.

In the middle region (transitional brackish–freshwater zone), water regimes are strongly influenced by tidal dynamics, with alternating saline and fresh water. Salinity intrusion is controlled through irrigation systems, ensuring freshwater remains the primary source. This region is a fruit-growing hub, highly vulnerable to drought, salinity intrusion, floods, and waterlogging.

In this region, irrigation projects have been invested in to complete the irrigation system for proactive water supply, upgrade dikes and embankments to protect urban areas and residential clusters, and enhance canals for fruit orchards and concentrated aquaculture zones. Key projects include the dredging of the Can Tho–Huyen Ham canal (Dong Thap–Vinh Long), the saline–freshwater boundary system in Soc Trang and Bac Lieu (former provinces), Component 3 under the WB9 project, the Southern Ben Tre irrigation project, and the Ninh Quoi lock sluice.

In the coastal zone (saline–brackish), which is completely unaffected by flooding and distant from Mekong freshwater sources but heavily influenced by tides and the sea, production focuses on saline and brackish aquaculture (intensive farming and shrimp–rice models). Projects aim to regulate water sources, provide domestic water supply, supply water for aquaculture and agricultural production, and limit the use of groundwater to prevent subsidence and erosion. They also apply technologies for water intake, storage, and treatment at the site for daily life during the periods of droughts, water shortages, and salinity intrusion, and wastewater management in aquaculture.

Notable projects include the Sub-region X–Southern Ca Mau irrigation system and livelihood model under WB6, Component 4 under the WB9 project, the Ca Mau sub-regions II, III, and V, and phase 1of the Cai Lon–Cai Be irrigation system project in the Kien Giang, Ca Mau, Hau Giang, and former Bac Lieu provinces.

According to Mr. Vu Viet Hung, the investment and construction of irrigation systems in the Mekong Delta have received special attention from the National Assembly and the Government, the consensus of ministries and agencies, and the support of local governments and people. These efforts have been further reinforced by the determination of the leadership of the Ministry of Agriculture and Rural Development, now the Ministry of Agriculture and Environment. Notably, there has been a marked shift in mindset and perception when investing in irrigation structures in the Mekong Delta.

Journey of transforming development mindsets

Mr. Hung further analyzed that, from a development perspective, this represents a shift in mindset from purely agricultural production, mainly rice cultivation, to diversified agricultural economic development that meets market demands, moving from quantity-driven growth to quality-oriented growth.

Respecting natural laws and aligning with actual conditions, the approach emphasizes adopting models that are environmentally friendly and sustainable, following the principle of proactively coexisting with floods, brackish water, and saltwater. It involves developing scenarios and effective response solutions for natural disasters such as storms, floods, droughts, and salinity intrusion under climate change, sea level rise, and upstream Mekong River development. Based on this, all investment activities must be coordinated in a unified manner, ensuring interregional and cross-sectoral integration, focusing on priority areas, and following a reasonable roadmap.

Regarding infrastructure solutions, the approach shifts from structures that prevent salinity and preserve freshwater for rice production to water control systems designed for sustainable production across different ecosystems (saline, freshwater, and brackish), supporting rice, fruit trees, and aquaculture simultaneously. Irrigation works are increasingly multi-functional, integrating waterway and road traffic, tourism, and domestic water supply.

Regarding structural solutions, Mr. Vu Viet Hung stated that there has been a transition from traditional sluices to mobile barge sluices and pillar dam sluices. Among these, the pillar dam sluice represents an important innovation, enhancing the capacity of design, construction, supervision, and management teams by significantly shortening construction time, reducing land clearance areas, allowing direct riverbed construction without the need for diversion channels as in traditional sluice technology, and increasing the wet cross-section of the sluice to nearly match that of the natural canal.

There has also been a transformation from automatic gates to forced gates, enabling proactive regulation and control of water sources. Among these structures, the Cai Lon sluice applies pillar dam technology, making it the largest water control sluice in the country and Southeast Asia.

These achievements demonstrate that irrigation projects approved for investment by the Ministry, together with a network of works funded by other resources from central to local levels, have contributed to the synchronization of the Mekong Delta's irrigation system. This integrated system supports irrigation and drainage, flood prevention and control, salinity management, riverbank erosion, and coastal erosion mitigation, thereby promoting socio-economic development in the region.

The Mekong Delta has become Vietnam's largest agricultural production hub, contributing 50% of the nation’s rice output, 65% of aquaculture production, and 70% of fruit production, as well as 95% of exported rice and 60% of exported fish. To achieve these outcomes, irrigation structures play a crucial role in proactively supporting cultivation and diversifying production models, fostering agricultural economic development at the local level.