Seaward side of the gates

These gates are now lowered into the water but still allow the incoming tide to flow under the tunnel and the raised gates on the other side, into the Eider River. On the outgoing tide, the gates on the landward side of the tunnel are lowered to the shut position until the water backs up to a certain height. Then the gates on both sides are opened and the rush of water flushes the silt and debris from the base of the floodgates. Good engineering!