The invention concerns a flood protection for protecting a back area against rising water level from a front area, the flood protection operating between a bottom and a water surface, including at least one barrier element with a longitudinal direction and a height direction, the longitudinal direction during operation extending substantially transversely of an area, e.g. a stream, a fjord, a river or an estuary, and the height direction during operation extending from the bottom of an area, e.g. a stream, a fjord, a river or an estuary, and up, where the at least one barrier element during operation interacts with a base arranged at the bottom of the actual area. The invention also concerns a method for operating such a flood protection. The new feature of the flood protection according to the invention is that it includes a movable and buoyancy balanced barrier element that includes an adjustable ballast system for regulating the buoyancy balance, the base of the flood protection including a bottom rail system, and the barrier elements including contact means arranged for contact with the bottom rail system.

To make it possible to raise a door body even if it is damaged by an impact of vehicle traffic or falling objects when it is in a lowered state, and to keep the door body in a raised state even if it is damaged by a water pressure of a tsunami or a high tide when it is in a raised state. A door body 2 of a floating flap gate 1 is disposed at an opening or at an access way. When water flows in, a forward end 2b of which swings upwards, in a direction in which the water flows in and within a plane in a height direction, around a base end 2a thereof which serves as a center of rotation, to block the opening or the access way. The door body 2 is formed from a hard polyurethane foam 4 in the form of a sheet.

A water-level control unit includes a housing with a flow channel. A valve element is positioned rotatable around a hinge axis inside the flow channel to close off a lower section of the flow channel while dividing it in a first upstream side and a second downstream side. The hinge axis is provided at a height above a bottom of the flow channel. The valve element includes a lower flap portion that in a closed position hangs down from the hinge axis. A floating body is provided at and connected to a side of the lower flap portion for moving the valve element from its closed towards an open position in dependence of a rising level of water at the first upstream side in the flow channel.

A water-level control unit includes a housing with a flow channel. A valve element is positioned rotatable around a hinge axis inside the flow channel to close off a lower section of the flow channel while dividing it in a first upstream side and a second downstream side. The hinge axis is provided at a height above a bottom of the flow channel. The valve element includes a lower flap portion that in a closed position hangs down from the hinge axis. A floating body is provided at and connected to a side of the lower flap portion for moving the valve element from its closed towards an open position in dependence of a rising level of water at the first upstream side in the flow channel.