Flood defence system with low environmental impact

A flood barrier (100) comprising:

• a wall (130);
• and
• a venturi effect pump (10) for drawing water from a second side (104) of the wall to a first side (102) of the wall, the wall configured to provide a barrier preventing movement of water from the first side of the wall to the second side of the wall,
• wherein the barrier further comprises a pipe (40) traversing the wall for transferring water between the first side of the wall and the second side of the wall, the pipe being terminated in the first side of the wall at the venturi effect pump, the venturi effect pump being feedable with water at the first side of the wall through a conduit inlet (22) so as to create suction in the pipe for drawing water through the pipe from the second side of the wall to drain water from the second side of the wall to the first side of the wall,
• wherein the wall is hollow and an internal area so present is configured to be filled with water to ballast the wall,
• wherein the internal area is configured to act as a portion of the pipe, and
• wherein the pipe is so configured by means of a valve or valves so as to allow the pipe to be closed from the internal area when a fill level of the internal area has been achieved.