Floodbanks, stopbanks, flood protection schemes, river control... generally names like that.
There's some good pictures here
(which is where I nicked the above picture from). Click on the one of the Mataura (note spelling) River at Athol and it will take you through a slide-show of flood pictures (including one of an obviously concrete bridge labelled "the Iron Bridge". Yes, there is
a reason for that, but it involves a bridge that hasn't been there since some time last century...)
Floods are a fairly regular happening down here... we get a notable one every ten years or so. Ones I definitely remember are from 1978, 1984, 1987, 1999 and now this year's one (and minor floods are even more common - there was one less than a year ago).
The newspaper site linked above have just gone and put their 1984 flood 25th anniversary retrospective display back up... must still have had it archived somewhere from last January.