A Thames Barrier flood defence closure is triggered when a combination of high tides forecast in the North Sea and high river flows at the tidal limit at Teddington weir indicate that water levels would exceed in central London .
A Thames Barrier flood defence closure is triggered when high tides are forecast in the North Sea `` and '' river flows are high at the tidal limit at Teddington weir . If water levels might exceed 4.87 m in central London , that is the trigger .