Why do the gates not get jammed with built up silt?
The silt is allowed to drain out at regular intervals. This is called a “desilt”. The gates rest in concrete sills under the riverbed when not in use, the largest of which weigh 9,000 tonnes. There is a gap between each sill and gate (approximately 4 inches) to allow the natural tidal flow to keep the sills clean. The gap is narrower at each edge of the gate, preventing large debris getting into the slot.
