A barrage is a structure that is built across a river to control the level of the water. a hydro-electric tidal barrage. a wall of earth, stones etc built across a river to provide water for farming or to prevent flooding
the heavy fire of artillery to saturate an area rather than hit a specific target; "they laid down a barrage in front of the advancing troops"; "the shelling went on for hours without pausing"
{i} river dam; barrier of artillery fire to prevent enemy advance, bombardment; numerous questions
Specifically any of the five low weirs at the mouth of the River Murray constructed to exclude seawater from the Lower Lakes (eg: Lake Albert & Lake Alexandrina)