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Sluice gate
A tidal sluice gate is a hydraulic structure installed across a canal at the point where the tidal salt front reaches an unacceptable concentration for the land uses it would affect. The gate operates on a simple principle: close when saltwater would enter from downstream, open when freshwater can flow freely or when floodwater needs to drain.
The Cái Lớn–Cái Bé Hydraulic Works Project, completed in stages between 2021 and 2022, is the most significant hydraulic infrastructure investment in VMD's history. The Cái Lớn gate spans 455 m across one of the delta's major tidal channels in Kiên Giang province; the Cái Bé gate spans 215 m on the adjacent channel. Together they form a hydraulic boundary protecting approximately 384,000 ha across Kiên Giang, Hậu Giang, Bạc Liêu, Cà Mau, and Sóc Trăng provinces — roughly one-fifth of VMD's total agricultural land.
The system has already demonstrated its value during the 2023 dry season, when it held the salinity front more than 40 km further inland than it would otherwise have reached under natural conditions. However, it has also generated the controversy alluded to earlier: fish mortality events and canal blackwater in enclosed zones during prolonged gate closure have been reported by fishing communities, and researchers at Cần Thơ University have documented dissolved oxygen collapses in isolated canal sections after 3–4 weeks of sustained gate closure.