Highlands Gate Golf Estate

The spillway at the dam, consisting of nine Armco culverts integrated into the dam wall, experienced a catastrophic failure of its downstream gabionerosion protection structure. Intense flooding displaced the structure, leaving an unprotected 4-meter-high vertical gravel face (C).

The intact butdisplaced gabion baskets were discovered approximately 10 meters downstream (D), partially buried under sand and stone.Following a detailed inspection by Civil Structural and Eco Engineers, the root cause of the failure was identified as the omission of a critical designelement for gabion structures exposed to flood conditions. Specifically, no gabion mattress was installed beneath the main structure or extended infront of its toe to prevent under-scouring.

Instead, the base of the main structure was reinforced with a solid slasto-paved area (A) approximately 2 meters wide. While this paved area mayhave provided temporary stability, it lacked the flexibility and adaptability of a gabion mattress to deform under pressure and distribute hydraulicforces effectively. As a result, the rigid slasto paving succumbed to the erosive power of floodwaters (B), exposing the toe of the main gabionstructure.

This exposure led to progressive undercutting, ultimately destabilizing the entire structure and causing its failure.This case underscores the importance of adhering to fundamental principles in gabion structure design, particularly in environments subject to highflood velocities.

Proper incorporation of gabion mattresses beneath and in front of the main structure provides essential protection against under-scouring, ensuring the long-term integrity and resilience of such systems.