Stretching across the River Thames at Woolwich Reach, the Thames Barrier is one of the world's largest movable flood barriers. Designed by Rendel, Palmer and Tritton and operational since 1982, its primary defense mechanism relies on ten massive steel gates. Four main gates span 61 meters each and weigh over 3,300 tonnes.
The engineering brilliance of these barriers lies in their rotating segmental radial gate design. Under normal conditions, the gates rest flat in concrete sills on the riverbed, allowing ships to pass freely over them. When a surge tide threatens London, hydraulic arms rotate these hollow D-section steel gates 90 degrees upward into a vertical position, creating a solid steel wall that blocks incoming sea water.
The curved geometry of the radial gates efficiently redirects the immense hydraulic pressure of the rising tide downward into the massive concrete piers anchored deep into the riverbed, rather than relying solely on the gate's shear strength. To return to the resting position, the gates are filled with water to sink back smoothly or rotated 180 degrees into an overhead maintenance position for inspection. This clever mechanism has protected Greater London from catastrophic flooding over 200 times since its construction.